Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, additional steps to fix carbon in the C4 path require additional energy costs in the form of ATP.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

If we assume that in the Calvin cycle in C4 plants, as well as in C3 plants, 3 ATP molecules and 2 NADPH molecules are used to fix one CO2 molecule, then to regenerate the carbon acceptor in the cycle Hatch-Slack, that is, the conversion of pyruvate to FEP, requires an additional 2 ATP molecules.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a result, 5 ATP molecules and 2 NADPH molecules are consumed per CO2 molecule in the C4 path [1].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For this reason, C4 plants need a higher level of insolation for optimal growth.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Discovery history


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The first mention that sugar cane may have dicarboxylic tetracarbonic acid as the first product of photosynthesis appeared in 1954 as a short note without reference and was published in the annual report of the Hawaiian Sugar Planters Association Experimental Station.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In more detail, this work appeared in the form of a short message authored by H.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

P. Korchak, K. E.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Hartt and G. O. Burra.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A full article by this group of researchers was published only in 1965 [2].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This long delay is due to the discrepancy between the results obtained and data obtained at Melvin Calvin's laboratory, with which the Hawaiian group had close contact at the time [3].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Soviet scientists obtained similar results at about the same time.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the works of L. A. Nezgovorova (1956—1957), it was found that with short exposures of corn leaves in light, 14C out of 14CO2 is found in aspartic acid [4].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Around the same time, in 1960, the Russian scientist Yu.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

S. Karpilov published data demonstrating that malic and aspartic acids are the first to form in corn during radioactive labeling [5].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In 1963, Yu.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

S. Karpilov together with his colleague I. A. Tarchevsky published a second article, which considered the effect of the procedure for killing leaves on radioactive labeling of photosynthesis products.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Karpilov published his next article on this topic only in 1969.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Needless to say, neither Soviet nor Hawaiian scientists knew about each other's achievements until 1969 [3].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Scientists Marshal Davidson Hatch and Charles Roger Slack, who worked at the Australian company's laboratory in Brisbane at the time, knew about the results of the Hawaiian group since the 1960s.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

So in 1965, when a full-fledged article was published, they decided to double-check this data.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

After repeating the results of the Hawaiian group on the radioactive labeling of sugarcane photosynthesis products, they identified oxaloacetate as the first carbon acceptor, using a special killing technique [3] .


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Based on their data, they compiled a simple working model and in 1966 published an article in which they first described this biochemical pathway as a new type of photosynthesis, fundamentally different from Calvin cycle [6] [3].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Over the next four years, Hatch and Slack did a lot of work to decipher the C4 path: they postulated and confirmed the role of FEP carboxylase in the primary fixation of CO2, they discovered vegetable pyruvate phosphate dikinase, somewhat previously found in bacteria, as well as previously unknown NADP-dependent malate dehydrogenase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, they studied the localization of these, as well as many other enzymes, in mesophyll cells and the bundle lining.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At that time, it was assumed that quadricarbon dicarboxylic acids should transfer one carbon atom to a precursor to form triosophosphate in the recarboxylation reaction.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, later, when it was discovered that the decarboxylating NADP-malik enzyme was localized in large quantities in the lining cells, it became clear that CO2 would enter the Calvin cycle as a result of repeated fixation, and this hypothesis fell away.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In 1970, Hatch and Slack at an international meeting in Canberra presented a detailed scheme of C4 photosynthesis of the NADP-malate dehydrogenase type, where the audience suggested that this path serves for the concentration of CO2 in the cells of the conductive beam lining, which was soon confirmed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The importance of this injection mechanism for suppressing Rubisco's oxygenase activity and photorespiration became clear only over the next few years [3]


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Initially, Hatch and Slack named the type of photosynthesis they described the C4 photosynthetic pathway of dicarboxylic acids [3], a name that was later abbreviated to C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Subsequently, in the literature, this process was also called the cycle, or the path of Hatch-Slack.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In Russian literature, there is sometimes a designation of the path of Hatch — Slack — Karpilov, emphasizing the contribution of a Soviet researcher.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Leaf anatomy


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 plants are characterized by a special leaf structure, the so-called fender anatomy (German: Kranz - crown, crown).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For the first time, this type of leaf structure was described in 1884 by the German botanist Gottlieb Gaberlandt [7].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The conductive bundles in such plants are surrounded by two layers of green cells of the assimilation parenchyma.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The outer layer is formed by mesophyll cells that are not differentiated into spongy and palisade parenchyma, and the inner layer is formed by cells of the vascular bundle lining.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The lining cells are connected to mesophyll cells by a variety of plasmodesms, due to which an active exchange of metabolites is possible between them.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A feature of the leaf structure of C4 plants is the presence of no more than 2-3 layers of mesophyll cells, which makes it easy to exchange photosynthesis products through plasmodesms.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Mesophyll cells and conductive bundle lining cells differ structurally and functionally.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Mesophyll cells are small, loose, chloroplasts always have grains in them and they rarely contain starch.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase is located in these cells, which attaches CO2 to phosphoenolpyruvate to form oxaloacetate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The lining cells are larger, with a thickened, often suberinized, cell wall, fit snugly against the vessels of the leaf, chloroplasts in them may not have grain and often contain starch grains.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Here the Rubisco enzyme is localized and the normal Calvin cycle takes place [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Some C4 plants are also characterized by chloroplast dimorphism, when chloroplasts of mesophyll cells have numerous grains, and in the lining cells, the faces are rudimentary and almost completely are missing [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, such dimorphism is not necessary for C4 photosynthesis and is found only among plants with a certain biochemical type [9].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Not all C4 plant species have a suberine layer, but all of them strive to prevent the diffusion of CO2 from the lining cells, so the position of chloroplasts in these cells becomes especially important.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In species with a suberin layer, chloroplasts are located centrifugally, that is, at the maximum distance from the conducting beam and closer to the mesophyll.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In species without a suberine layer, chloroplasts are located centripetally, close to the cell wall, as close as possible to the conducting beam and away from the mesophyll.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This distribution of chloroplasts lengthens the diffusion path of CO2 and reduces leakage into mesophyll cells [10].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Biochemistry


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In C3 plants, dark photosynthesis reactions begin with the fixation of CO2 by the Rubisco enzyme on the ribulose-1,5-bisphosphate acceptor to form two molecules of 3-phosphoglycerate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, due to the double (carboxylase and oxygenase) activity of Rubisco, part of the substrate for fixing CO2 reacts with oxygen and oxidizes, which leads to a loss of substrate and energy, as well as entails additional costs for the disposal of the resulting dicarbon compound, 2-phosphoglycolate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The sum of these processes is called photorespiration and makes a significant contribution to reducing the overall efficiency of photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

To overcome the limitations associated with Rubisco's adverse reaction in conditions of low CO2 and high O2 in the modern atmosphere, C4 plants have developed an effective mechanism for concentrating CO2 at the site of Rubisco localization, creating favorable conditions for the work of this enzyme.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Instead of directly fixing Rubisco in the Calvin cycle, CO2 is assimilated into mesophyll cells in the form of tetracarbonic organic acid, which is then transported to the cells of the lining of the vascular bundles, where it is decarboxylated to release CO2.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The anatomical prerequisite for CO2 injection is a larger number of mesophyll cells (approximately 5-7 per cell of the lining).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, CO2, previously recorded in five cells, falls into one [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the cells of the lining, CO2 enters the normal Calvin cycle, where Rubisco is fixed a second time and is used for the synthesis of carbohydrates.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Due to the constant gradient of metabolites, as well as the CO2-impermeable cell wall of the lining, the CO2 concentration in the Rubisco carboxylation site, even with closed stomata, increases 14 times compared to the equilibrium concentration of CO2 in water (from 5 μmol/L to 70 μmol/L, respectively) [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At such high concentrations of CO2 in the carboxylation site, the oxygenase reaction is largely suppressed, the efficiency of photosynthesis increases, and energy losses for photorespiration decrease.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The primary fixation of CO2 in C4 plants is carried out by the enzyme phosphoenolpyruvate carboxylase or FEP carboxylase located in mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Unlike Rubisco, it fixes carbon dioxide in the form of a bicarbonate ion HCO3−, and not CO2.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since a charged molecule is used as a substrate, an adverse reaction with an uncharged molecule like O2, which also differs from bicarbonate in terms of spatial structure.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The effectiveness of the mechanism for pre-fixing CO2 with FEP carboxylase does not lie in the high affinity of the enzyme to the substrate (Km (HCO3−) = 0.2—0.4 mmol/L for FEP carboxylase [11] versus Km (CO2) = 10-15 μmol/l for Rubisco [11]), and in the fact that in the cytosol at normal temperature and pH 8, the ratio of HCO3−:CO2 is approximately 50:1.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, FEP carboxylase, unlike Rubisco, can attach the dominant form of carbon dioxide in this equilibrium reaction and effectively fix CO2, even if semi-closed in stomata, the concentration of CO2 dissolved in water will fall below the level acceptable for Rubisco [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The formation of HCO3− from CO2 occurs with the participation of the zinc-containing carbonic anhydrase enzyme, which is also localized in the cytosol of mesophyll cells and accelerates the establishment of balance between the two forms carbon dioxide:


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

O


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

H


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

O


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

H


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

O


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

H


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

{\ displaystyle\ mathrm {CO_ {2} +H_ {2} O\ rightleftharpoons HCO_ {3} ^ {-} +H^ {+}}


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase catalyzes the irreversible condensation of FEP and HCO3− molecules to form oxaloacetate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase has a very high affinity for FEP.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Oxaloacetate is converted to malate or aspartate and in this form is transported to the lining cells, where it again becomes malate and undergoes oxidative decarboxylation:


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

HCO3− Fn


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEPCPhosphoenol pyruvate (FEP) Oxaloacetate


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a result of oxidative decarboxylation, CO2 and pyruvate are formed from malate, which in one form or another returns to mesophyll cells, where it is again converted to FEP using enzyme chloroplasts.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The enzyme-catalyzed reaction is quite unusual, the name “dikinase” refers to an enzyme that catalyzes double phosphorylation.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the first, reversible stage of the reaction, one phosphate residue is transferred from ATP to inorganic phosphate to form pyrophosphate, and the second (Fβ) is attached to pyruvate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Chloroplasts localized in the stroma instantly hydrolyzes the resulting pyrophosphate, which makes the reaction irreversible [12].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, the carbon dioxide acceptor is regenerated and the cycle is closed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

ATP+FN AMP+FFN


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

PFDCpyruvatPhosphoenolpyruvate


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

An effective carbon dioxide concentration mechanism allows C4 plants to create such a diffuse current to ensure sufficient carbon dioxide supply even with increased stomatal resistance.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is this effect that makes it possible to spend almost half as much water on fixing one CO2 molecule as C3 plants, because with a decrease in the width of the stomatal gap, water losses also decrease proportionally [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Three types of C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

According to the type of C4 acid that carries carbon dioxide to the lining cells (malate or aspartate), a C3 product that returns to mesophyll cells for regeneration (pyruvate or alanine), as well as with the nature of decarboxylating reactions in the lining cells, three variants of the C4 photosynthesis pathway are distinguished [1]:


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NADP+-malate dehydrogenase type: Malate undergoes oxidative decarboxylation in chloroplasts under the action of NADP-dependent decarboxylating malate dehydrogenase (NADP-dependent malik enzyme) with formation of NADPH and CO2 molecules.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NAD+-malate dehydrogenase type: Malate is decarboxylated in mitochondria using NAD-dependent decarboxylating malate dehydrogenase (NAD-dependent malik enzyme) to form one NADH molecule.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The released carbon dioxide diffuses into chloroplasts.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP-carboxykinase type: Malate is decarboxylated in mitochondria according to the NAD-malate dehydrogenase type, but in addition, there is direct decarboxylation of oxaloacetate in the cytoplasm with FEP carboxykinase with the consumption of one ATP molecule and the formation of FEP.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxykinase (FEPCA) has been found in corn, a typical NADP-MDH plant, which allows it to transport carbon dioxide in the form of aspartate (about 25%); many dicotyledonous C4 plants also contain FEPCA in addition to the main decarboxylating enzyme.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The coexistence of different types of C4 photosynthesis, for example, NADP-MDH and FEPKK or NAD-MDH and FEPKK, provides the plant with additional flexibility and the ability to transport other types of C4 acids and products, which return to mesophyll cells for regeneration.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Moreover, some plants without FEPKK activity are still able to transport several metabolites, such as aspartate and malate, as is the case with grain sorghum.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Each of the mixed types of C4 photosynthesis, as well as the “pure” NADP- and NAD-malate decarboxylase pathways, has its own specific environmental advantages.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this sense, the division into three independent biochemical types should be considered relatively conditional [13].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The FEP-carboxykinase type is never found in its pure form, and even in plants traditionally classified as this type, FEP carboxykinase provides, albeit more, but never all decarboxylating activity.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Among other things, FEP carboxykinase is widely used as an auxiliary decarboxylase by plants with NADP- and NAD-MDH types.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For this reason, it was proposed to divide C4 photosynthesis only into NADP- and NAD-malate dehydrogenase types, which clearly differ in decarboxylating enzyme and structural plan, and FEP carboxylase the type is considered as an auxiliary, which is used to varying degrees by different plants [13].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NADP-malate dehydrogenase type (NADP-MDH)


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NADP-malate dehydrogenase type (NADP-MDH) [11] or NADP-malicenzyme type (NADP-ME) [14] has historically been the first biochemical type of C4 photosynthesis studied.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Important crops such as corn, sorghum, dewdrop and sugar cane are photosynthesized along this path [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Malate and pyruvate are used as transport products.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Oxaloacetate, which is formed as a result of carboxylation of FEP, is transported by means of a specific carrier to chloroplasts, where it is reduced by NADP-malate dehydrogenase to malate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The resulting malate is carried into the cytosol and diffuses from mesophyll cells into the lining cells through plasmodesms.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The malik enzyme, which is localized in the chloroplasts of the lining cells, catalyzes the conversion of malate to pyruvate with the release of CO2, which is fixed by Rubisco.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The resulting pyruvate with the participation of a specific carrier is exported from chloroplasts of the lining cells and diffuses through plasmodesms into mesophyll cells, where it enters the mesophyll cells with the help of another carrier chloroplasts, where the pyruvate phosphate dikinase enzyme converts it back to FEP [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since chloroplasts of the lining cells, unlike chloroplasts of mesophyll cells, do not contain carbonic anhydrase, the diffusion of CO2 in the stroma of the lining cells is slower than in mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The suberine layer between the lining and mesophyll cells in some plants probably also makes it difficult for CO2 to leak through cell walls, so that only the possibility of leakage through plasmodesms remains.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The proportion of CO2, which was concentrated in the lining cells, but diffused back into mesophyll cells due to leakage, is estimated as 10—30% for different species [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Plants with this type of C4 photosynthesis are characterized by the presence of chloroplast dimorphism.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Chloroplasts of mesophyll cells have many grains, while chloroplasts of lining cells contain mainly stromal lamellas and a small number of granal stacks with low photosystem activity II, which makes it possible to reduce the oxygen content in the Rubisco activity site.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There is a gradation in the number of chloroplast grains of the lining cells, from rudimentary grains in corn and dewdrop to their complete absence in sorghum and sugar cane [15].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Agricultural chloroplasts of the lining cells perform cyclic phosphorylation with the participation of photosystem I and synthesize only ATP.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

All the recovery equivalents necessary for the Calvin cycle are provided by mesophyll cells due to non-cyclic electron transport.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Oxidation in the cells of the malate lining provides no more than a third of the NADPH necessary for the operation of the Calvin cycle.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The remaining part of the required NADPH together with ATP is supplied from chloroplasts of mesophyll cells to chloroplasts of the lining cells using the triosophosphate-3-phosphoglycerate shuttle mechanism, through triosophosphate carrier of the inner membrane of the corresponding chloroplasts [16].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NAD-malate dehydrogenase type (NAD-MDH)


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NAD-malate dehydrogenase type (NAD-MDH) [11] or NAD-malate enzyme type (NAD-ME) [14] has been found in most species, including millet, amaranth, purslane [1], willow tea and marsh [7].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Chloroplasts of both mesophyll cells and lining cells have facets and an active photosystem II [17].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The lining cells contain many large mitochondria with well-developed crista [18].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Aspartate and alanine are used as transport products.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this case, oxaloacetate, which is formed in the FEP carboxylase reaction, is converted to aspartate by reamination, which catalyzes glutamate-aspartate aminotransferase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since the concentration of glutamate in the cell is high, it is convenient for maintaining the diffusion current between the cells of the mesophyll and the lining.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a result of transamination, the concentration of aspartate becomes 5 times higher than the concentration of oxaloacetate, which creates a strong diffusion current.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

After diffusion into the lining cells, aspartate is transported to the mitochondria.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The mitochondrial isoenzyme form of glutamate-aspartate aminotransferase catalyzes the conversion of aspartate to oxaloacetate, which is then reduced by NAD-malate dehydrogenase to malate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Malate is decarboxylated by NAD-Malik enzyme to form pyruvate, and NAD+ formed in the oxaloacetate reduction reaction is again reduced to NADH.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The CO2 formed during the reaction diffuses into chloroplasts, where it is assimilated with the participation of Rubisco.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Pyruvate leaves the mitochondria and in the cytosol is converted to alanine with the participation of alanine-glutamate aminotransferase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since this reaction is equilibrium and the concentration of alanine is much higher than pyruvate, an intense diffusion flow of alanine into mesophyll cells occurs.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In mesophyll cells, alanine is converted to pyruvate involving the same aminotransferase mentioned above.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Pyruvate is transported to chloroplasts, where it is converted to FEP with the participation of pyruvate phosphate dikinase in the same way as in the case of NADP-MDH type [17].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxykinase type (FEPCC)


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP-carboxykinase type (FEPKK or FEP-KK) [11] has been found in several fast-growing tropical cereals that are used as fodder crops.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This pathway of photosynthesis is used by some members of the genus millet (), [8] and eggplant [7].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Aspartate, alanine, malate and phosphoenol pyruvate are used as transport products.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As in the NAD-MDH type C4 metabolism, oxaloacetate is converted to aspartate in mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Aspartate diffuses into the cells of the lining, where oxaloacetate is regenerated with the participation of aminotransferase localized in the cytosol.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In cytosol, under the action of the FEP carboxykinase enzyme, oxaloacetate is converted to FEP with ATP consumption.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The CO2 released in the reaction diffuses into chloroplasts, and FEP diffuses back into mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In plants of this type, ATP costs for pumping CO2 into the lining cells are mainly associated with the consumption of ATP by FEP carboxykinase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Mitochondria provide this reaction with the necessary amount of ATP by oxidizing malate with the participation of the NAD-malik enzyme.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The source of malate, as in the case of NADP-malate dehydrogenase type, is mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, in C4-FEP-carboxykinase metabolism, only a small part of CO2 is released in mitochondria, and most of it is released in the cytosol [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Regulation


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 photosynthesis is regulated by three main enzymes, each of which is activated by light, so that the C4 pathway is active only during daylight hours.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase is regulated in two ways: through phosphorylation and allosterically.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The main allosteric inhibitors of FEP carboxylase are carboxylic acids, such as malate and aspartate [19] [20].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since malate is formed at the next step of the CAM and C4 cycles, immediately after FEP carboxylase catalyzes the condensation of CO2 and FEP into oxaloacetate, feedback is formed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Both aspartate and oxaloacetate are easily converted into each other by the transamination mechanism; thus, high concentrations of aspartate inhibit FEP carboxylase by feedback.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The main allosteric activators of FEP carboxylase in plants are triosophosphates [21] and fructose-1,6-bisphosphate [22].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Both molecules are indicators of active glycolysis and signal the need to produce oxaloacetate in order to increase the flow of the substance through the tricarboxylic acid cycle.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, an increase in glycolysis means an increased supply of FEP and, therefore, a larger acceptor to fix CO2 and transport it to the Calvin cycle.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

When the leaf is in the dark, the activity of FEP carboxylase is low.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this case, the enzyme's affinity for the substrate, FEP, is very low; the process is also inhibited by low malate concentrations.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Therefore, in the dark, the enzyme in the leaf is practically inactive.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

When the leaf is illuminated in an unknown way, the FEP carboxylase kinase is activated, which phosphorylates the hydroxyl group of the serine residue in the FEP carboxylase protein.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase kinase breaks down rapidly, so the amount of enzyme in the cell is determined by the intensity of gene transcription.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

FEP carboxylase can be inactivated again if the phosphate group is removed by a specific phosphatase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The activated (phosphorylated) enzyme is also inhibited by malate, but in this case, higher concentrations of malate are required to achieve the effect.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Both kinase and phosphatase are regulated at the transcription level.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is also believed that malate provides feedback in this process, reducing the level of kinase expression and increasing the expression of phosphatase [20].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Pyruvate phosphate dikinase (PFDC) is also a light-dependent enzyme.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is inactivated in the dark due to phosphorylation on the threonine residue.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This reaction is carried out by an unusual bifunctional PFDK-regulating protein (PFDK-RP or PDRP).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It has both kinase and phosphatase activity.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Phosphorylation is quite unusual, since ADP rather than ATP is used as a donor of the phosphate group.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The dephosphorylation reaction is also unusual: instead of a water molecule, PFRP transfers the cleavage phosphate group to free inorganic phosphate (Fn) to form pyrophosphate (FFN).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The activity of PDRP depends on the level of ADP in the chloroplast stroma.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

ADP is a substrate for kinase activity and at the same time a strong competitive phosphatase inhibitor.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the dark, the level of ADP increases significantly, as a result of which phosphatase activity is suppressed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the light, due to photophosphorylation, the concentration of ADP decreases sharply, there is no substrate left for the kinase reaction, and phosphatase ceases to be suppressed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a result, PDRP cleaves phosphate from pyruvate phosphate dikinase and activates it [23].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

NADP-malate depadrogenase is activated by light due to the operation of the ferredoxin-thioredoxin system.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

During photosynthesis light reactions, light energy feeds the transport of electrons from water to ferredoxin.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Ferredoxin-thioredoxin reductase enzyme uses reduced ferredoxin to reduce the thioredoxin disulfide bond from disulfide to dithiol.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Reduced thioredoxin restores the cysteine-cysteine disulfide bond in NADP-malate depadrogenase, which converts the enzyme into its active form [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Isotope discrimination


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A convenient method for identifying C4 plants is based on determining the ratio of carbon isotopes 13C/12C.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The method is based on the fact that plants absorb natural carbon isotopes in different amounts during photosynthesis (atmospheric CO2 contains 98.89% 12C and 1.11% 13C).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In general, plants prefer 12CO2, absorb 13CO2 to a lesser extent and even less 14CO2.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Fractionation of 13CO2 is more pronounced when Rubisco works, since the reaction catalyzed by this enzyme is slower, and the lighter isotope 12CO2 is fixed by the enzyme much more willingly than slowly diffusing 13CO2.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Faster FEP carboxidase does not distinguish between isotopes, and since Rubisco sells almost all CO2 previously fixed by FEP carboxylase in C4 plants, the percentage of 13C in C4- the plant corresponds to the product of the FEP-carboxylase reaction, while in the C3 plant it is determined by the isotope ratio characteristic of Rubisco.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Accordingly, C4 plants contain a relatively higher percentage of 13C, carbohydrates isolated from C4 plants are heavier than sugars from C3 plants [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The ratio of 13C/12C is determined by mass spectrometric methods and is expressed by the value Δ13c, which is the deviation of the isotopic composition of the test sample (13C/12C) from the isotopic the composition of the standard (13C/12C) art.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The standard (PDB or Chicago Standard) is the ratio of isotopes in the calcite of the Belemnitella americana fossil of the Cretaceous period; Δ13c in the test sample is usually expressed in ppm as follows way [14]:


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

δ


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

specimen


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

standard


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

standard


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

{\ displaystyle\ delta ^ {13} C\\ lbrack {} ^ {0\!


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

_ {00}\ rbrack= {\ frac {\ frac {{} ^ {13} C} {{} ^ {12} C}}\ {\ text {sample}} - {\ frac {{} ^ {13} C} {{} ^ {12} C}}\ {\ text {standard}}} {{\ frac {{} ^ {13} C} {{} ^ {12} C}}\ {\ text {standard}}}\ cdot 1000}


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The more negative the Δ13c value is, the lower the content of the 13C isotope.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In C4 plants, the Δ13c value is about -14 ‰, in C3 plants - about -28 ‰ Since sugar cane is a C4 plant, and sugar beet is a C3 plant, the content of the isotope 13C can be mass- spectrometrically determine the origin of sucrose.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this way, it is possible, for example, to distinguish real rum (made from sugar cane) from blended rum (with the addition of sugar made from beets) [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Special forms of C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 photosynthesis without fender anatomy


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Although most C4 plants have fender anatomy, there are several species that perform the C4 cycle without dividing into lining and mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

These four plants belong to the subfamily haze: Bienertia cycloptera, Bienertia sinuspersici and Bienertia kavirense.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

They grow in desert, saline areas of the Middle East: B. sinuspersici in various countries of the Persian Gulf, B. cycloptera in Turkey, Afghanistan and Iran, B. kavirense in the Iranian salt desert (Dashte - Kavir), and S. aralocaspica near salt plants in Central Asia.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

They are characterized by a unique C4 mechanism for injecting CO2 within a single cell [24] [25] [26] [27].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

All of the above plants belong to the NAD-MDH biochemical type [28].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Although the cytological structure of the two genera differs, the basic principle in both cases is to use large vacuoles to separate the cell into two compartments.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

S. aralocaspica has very long cells of the palisade parenchyma, divided into two compartments by a large vacuole that occupies almost the entire cell space.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The parenchyma is located in one layer and is more densely packed on the outside of the leaf, but is looser on the inside.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the region close to the epidermis of the leaf (distal), chloroplasts with a low grain content and without Rubisco are located, here FEP is synthesized from pyruvate using the enzyme pyruvate phosphate dikinase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the inner (proximal) section there are ordinary granal chloroplasts and mitochondria, there is Rubisco and the Calvin cycle operates [28].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The genus members have a different structure.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The leaf parenchyma is located in two to three layers.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Most of the cell is filled with vacuoles and broken into a thin cytosolic strip on the periphery and an unusual central compartment with a large number of chloroplasts in the middle.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A certain analogue of fender anatomy is observed here, large chloroplasts with a reduced amount of grain and an incomplete set of enzymes of the Calvin cycle are located on the periphery, where FEP regenerates, and the center is a cluster of half the size of chloroplasts with normal faces and active Rubisco, where the Calvin cycle takes place.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Together with these chloroplasts, mitochondria and peroxisomes are located in the center [28].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In both cases, the actin and microtubular cytoskeleton are responsible for the distribution of two types of chloroplasts throughout the cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Also, with unicellular C4 photosynthesis, FEP carboxylase is not isolated, it is evenly distributed throughout the cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this regard, the question arises about the possible mechanism of its inhibition at Rubisco's place of work in order to avoid re-fixation of the released CO2 [28].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Another example of C4 photosynthesis without fender anatomy is the marine green macroalgae Udotea flabellum [29] and unicellular diatom [30].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Optional C4 photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Hydrilla verticillata is a freshwater immersed flowering plant that gathers in large mats below the surface of the water in summer.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Under conditions of high temperature, low CO2 content and high O2, the plant changes from C3- to C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since Hydrilla verticillata does not have fender anatomy, the whole process takes place within a single cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Photosynthesis follows the NADP-MDH biochemical pathway, and the cytoplasm induces the synthesis of FEP-carboxylase, as well as a number of other proteins: malik enzyme, PFDC and aminotransferases.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The main decarboxylating enzyme, NADP-malik enzyme, is located in chloroplasts, and pyruvate phosphate dikinase acts there, which regenerates FEP [31].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Another example of switching between C3- and C4 metabolism is the leafless sedge, which can grow both submerged and on land.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The leaves of this plant are completely reduced and the stems take over the photosynthesis function.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

When growing underwater, it photosynthesizes along the C3 pathway, but on land it passes to C4 metabolism along with the formation of fender anatomy - this process is controlled by abscisic acid.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the same time, even simply shoots that are above the water surface can pass to C4 [31].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Combining C4 and CAM


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Metabolism by type of fat (CAM photosynthesis) includes some enzymes of C4 photosynthesis necessary for injection and concentration of CO2.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, in the case of CAM plants, the preliminary and final fixation of CO2 is not separated in space, but in time.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Nevertheless, during the day, the CAM pathway and classical C3 photosynthesis can work in parallel in obligate CAM plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There were even species of optional CAM plants (C3-CAM) that switched from C3- to CAM metabolism only in drought or salinization conditions.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this case, C3 and CAM photosynthesis can occur within one cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There are very few examples of CAM and C4 metabolism occurring in the same plant.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Most C4 plants are represented by cereals in which CAM photosynthesis is never detected, just as typical CAM plants, such as orchids and bromeliads, do not have pure C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Only a few plant species from the genus purslane can use both routes, including Portulaca mundula [32].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In these plants, CAM photosynthesis takes place in the sap filled internal cells of the stem and leaves, where water is stored, while C4 photosynthesis takes place in the outer cells of the leaf.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, even in these plants, both pathways do not work in the same cell, which means that CAM and C4 photosynthesis are incompatible [33].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Several reasons are given as an explanation.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For example, it would be difficult to precisely regulate both pathways due to their biochemical similarity.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, each of them is based on a different anatomical structure and transport mechanisms that are important for the corresponding function, but cannot be combined in one cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Finally, two simultaneous paths of CO2 concentration do not provide an environmental advantage.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C3-C4 transitional forms


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A number of C3 plants have typical morphological features of C4 plants, such as the anatomical organization of leaves with the separation of the parenchyma into mesophyll and the lining of the conductive bundle, where they can concentrate carbon dioxide.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, the value of their carbon dioxide compensation point is between those for C3- and C4 plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the same time, the mechanism they use for concentrating CO2 is completely uncharacteristic of C4 plants [34].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Due to their anatomical similarity, such plants were mistakenly called C3-C4 transitional forms or “C3-C4 hybrids”, although this name is basically not true due to the different biochemistry of the mechanism of CO2 concentration [35].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The concentrating mechanism of these plants is based on the so-called C2 photosynthesis, which uses photorespiration enzymes.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

If Rubisco uses oxygen as a substrate instead of carbon dioxide, 2-phosphoglycolate is formed, which is processed during photorespiration.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In peroxisomes, glycolate is converted to glycine, two glycine molecules are condensed to form serine and CO2 using the glycine decarboxylase complex (GDK).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In C3-C4 transition plants, active GDK is localized only in the cells of the bundle lining, so that glycine transported from mesophyll is decarboxylated there and enriches CO2 cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Mesophyll cells also express GDK proteins, but it is not active here, since one or more expressed subunits contain mutations.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Due to the glycine-serine shuttle and the transport of C2 compounds, this form of metabolism is sometimes called “C2 photosynthesis”.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The advantage of this shuttle mechanism is that CO2 is not released in each cell separately, but is concentrated inside the lining cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a result, the chance for re-capture of carbon dioxide is significantly increased, Rubisco's working conditions improve, which means that photorespiration and associated energy costs are reduced.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A similar mechanism aimed at reducing photorespiration has been found in at least the following eight families of higher plants: Aizoaceae, Poaceae, Boraginaceae, Brassicaceae, Asteraceae, Amaranthaceae, Chenopodiaceae and Cleomaceae [36].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In some plants from the genus (Asteraceae), the glycine shuttle functions along with conventional C4 photosynthesis [37].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Ecology


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

According to the latest data, C4 photosynthesis has independently occurred at least 65 times in 19 different families, and is an unrivaled example of convergent evolution [38] [39].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In many genera, both C3- and C4 species are found.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 plants account for 5% of total plant biomass and 3% of the total number of plant species [40] [41].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

They occupy only 17% of the Earth's surface, but they carry out about 30% of terrestrial photosynthesis [42].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In total, about 8,100 species [43] are known that use the C4 carbon fixation pathway, all of them belong to flowering plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Among dicotyledonous plants, only 4.5% of all plants use this route, and 40% among monocotyledonous plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Despite this, in the treasure trove of monocotyledonous C4 plants are found only in three families, while in dicotyledonous ones - in 16 families.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The largest group of C4 plants among monocotyledonous plants is undoubtedly herbs; 46% of all herbs use C4 photosynthesis, which corresponds to 60% of all C4 plant species.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This group includes crops such as corn, sugar cane, millet and sorghum [44] [45].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In the dicotyledonous treasure, the maximum number of C4 species falls on the order of Caryophyllales.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Of all the Caryophyllales families, the richest family in this respect is the Chenopodiaceae family, in which 550 out of 1400 species use C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

About 250 out of 1,000 closely related Amaranthaceae species also use C4 photosynthesis [40] [46].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Most C4 plants grow in the tropics and subtropics below 45° latitude in conditions of high temperatures, lack of water and plenty of sunlight.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is in such climatic conditions that they can successfully compete with C3 plants due to the lack of photorespiration.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

However, this does not mean the dominance of C4 metabolism in dry and warm conditions.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Thus, only four species of C4 plants were found in the southeastern Karakum [14].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Speaking about arid and warm places, it should be noted that C4 species grow in moderately arid conditions, when there is water, but it is not always enough.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

CAM plants predominate in extra-arid conditions [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Analysis of the flora of North America showed that in California, C4 plants account for 4.38% of all species, and among cereals - 82%, while in the Great Lakes region and Quebec - only 0.17% of all species and 12% among cereals.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There are practically no C4 species in tropical rain forests [14].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In California's Death Valley, 70% of all growing species are C4 plants [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

They also predominate in the southern steppes and savannas.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 species account for more than two-thirds of all grass species below 30° latitude, while above 50° latitude C3 grasses predominate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At a latitude of 35—38°, the flora is equally rich in C3- and C4 species [47].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In temperate climates, C4 species are mostly active in late spring and summer.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In contrast, C3 species are active throughout the year.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In habitats with harsh winters, C3 species usually begin to grow several weeks earlier than C4 species.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As a rule, C4 grasses are rarely found in cold regions, such as in the boreal zone between 50 and 65 degrees latitude or at high altitude.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The exception is the treeless alpine tundra zone with its dry climate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, the Orinus thoroldii C4 herb has been discovered in Tibet, growing at an altitude of 5,200 meters.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In general, they do not enter the polar and circumpolar regions (beyond the latitude of 65°) [48].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Many C4 plants are resistant to cold, hundreds of C4 perennials are able to survive frost down to -20°C at rest.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

They thrive even in temperate and cool climates, such as the southern coast of New Zealand or the coastal swamps on the Atlantic coast of Canada and the United Kingdom.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In cold and dry conditions, shrubs with C4 photosynthesis grow, for example, species of the genus Atriplex, which can grow as early as April, in the presence of snow and freezing temperatures.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Such plants are especially abundant in the alpine tundra, where they are found in abundance at an altitude of more than 3,500 or even 4,800 meters, as is the case in the Andes.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

When growing at an altitude of more than 3,500 meters, mountain C4 species are able to tolerate night frosts with freezing temperatures and occasional snowfalls, which can occur here even in the middle of summer [47].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The analysis shows that such mountain C4 species grow in certain microsites, often on the southeastern slopes between rocks, where there is no wind, and intense sunlight during the day can heat the leaf is 10—25°C higher than the air temperature, so that photosynthesis takes place at a temperature of 25—35°C.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

An increase in leaf temperature during the day is a prerequisite for the successful competition of such high-mountain plants with C3 species [47].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Abiotic factors


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Photosynthesis depends on a number of abiotic factors that influence each other.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

One of these factors is the concentration of CO2, which is recorded during photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

If we assume that the amount of light in excess is not a limiting factor in itself, we can see that there will be an increase in the rate of photosynthesis with an increase in the concentration of CO2 in the environment.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This process is limited — the rate of photosynthesis reaches saturation, and at sufficiently high concentrations it can even decrease.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

On the other hand, when the concentration of carbon dioxide is too low, its fixation during photosynthesis is balanced by photorespiration and respiration processes.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The point at which both processes are in equilibrium is called the CO2 compensation point.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 plants have an effective mechanism for assimilating CO2 through the enzyme FEP carboxylase and weak photorespiration, so their CO2 compensation point tends to almost zero (< 0.001 volume percent CO2 [49]).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As can be seen from the graph, the photosynthesis rate in C4 plants with a low CO2 content increases much faster than that of C3, so at low concentrations of carbon dioxide, C4 plants always have competitive advantage.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For most higher C3 plants, the CO2 compensation point is at fairly high concentrations and amounts to 0.005—0.015% CO2 [1] in the ambient air.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

On the other hand, the rate of photosynthesis of C4 plants reaches a plateau and stops growing at a CO2 content slightly above its usual concentration in the air, which is due to the complete saturation of the enzyme FEP - carboxylases.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In C3 plants, the rate of photosynthesis continues to increase even after a twofold increase in CO2 content compared to normal.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Their photosynthesis saturation is achieved at approximately 0.05-0.10% CO2 [49].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In this regard, the opinion has been repeatedly expressed that an increase in anthropogenic CO2 emissions shifts the ecological balance in favor of C3 plants [43].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As already mentioned, due to the injection of carbon dioxide C4, plants can keep the stomata in a more closed position and significantly save water.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Water loss for transpiration in C4 plants is 250—350 g of H2O with an increase in the dry weight of the plant by 1 g, and in C3 — 450—950 g [7].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In C4 plants, the compensation light point is much higher than that of C3 plants, they need much more light to fully exist and grow.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Nevertheless, in high light conditions, they are much higher than C3 plants in terms of photosynthesis intensity and growth rate [50].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Under natural conditions, C4 plants do not achieve light saturation, and on clear days they use light completely even at noon, but the high point of light compensation imposes restrictions on their growth in low light conditions, that is, their growth is limited by light, and only when a severe lack of water causes them to close their stomata, and therefore reduce their carbon dioxide consumption gas, their growth is limited by the CO2 concentration [8].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is known that the work of the concentrating mechanism of C4 plants requires additional energy costs in the form of ATP and NADPH: 3 ATP molecules and 2 NADPH molecules per CO2 molecule for the C3 pathway and 5 ATP molecules and 2 NADPH molecules in the case of the C4 pathway.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Be that as it may, the costs pay off, as at high CO2 concentrations at the caboxylation site, the oxygenase reaction is significantly suppressed, and energy losses in photorespiration are significantly reduced.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Therefore, C4 metabolism does not necessarily require large energy consumption; in fact, at elevated temperatures, C4 photosynthesis is energetically more profitable than C3 photosynthesis, as evidenced by the graph temperature dependence of photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The reason for this is that since the oxygen content in the atmosphere is much higher than the carbon dioxide content, Rubisco's oxygenase activity increases more with increasing temperature than carboxylase.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Therefore, in a warm climate, C4 plants, which not only have a reduced need for water supply, but also suppressed photorespiration, have a significant advantage compared to C3 plants [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For most C3 plants in the temperate climatic zone, the temperature optimum of photosynthesis falls on 25—30°C.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In plants with C4- and CAM metabolism, the temperature optimum is 30—35°C [1].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, C4 metabolism provides plants with more efficient use of nitrogen.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Due to the presence of a concentrating mechanism, they need significantly less Rubisco than C3 plants, which compensate for the low concentration of CO2 in the carboxylation site with a high content Rubisco in chloroplasts.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is estimated that a C4 plant needs about 13-20% of the amount of Rubisco C3 plant in order to achieve the same photosynthesis rate.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Free nitrogen, which is not consumed by Rubisco, is used to synthesize lumen proteins and water-soluble proteins [51].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is calculated that the efficiency of nitrogen use per leaf area in C4 plants is higher than that of C3.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This, however, does not mean that they contain less nitrogen or that they are associated with nitrogen-poor soils.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For example, C4 grasses used for sowing lawns are very demanding on the presence of nutrients in the soil, as they have evolved in conditions in which nutrients were abundant [52].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Limited life forms


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

With a few exceptions, all C4 plants are represented by herbs and shrubs - there are no trees among them.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In places where C4 plants predominate, forests are not formed and a completely different landscape is formed.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The exception is members of the genus Euphorbia endemic to Hawaii, reaching a height of 6 to 10 meters.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

is a shade-tolerant tree from Oahu that grows in the shade of other trees; Euphorbia olowaluena grows in dry forests on the island of Hawaii.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Two other species that grow in Hawaii, and can also become small trees up to 4 meters high.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Another exception to the paradigm of the absence of trees among C4 plants is the Haloxylon ammodendron saxaul growing in Kazakhstan, whose old individuals can grow up to 10-12 meters and form dominant, central trunk.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Haloxylon ammodendron forms dense plantations along rivers in Central Asia, sometimes referred to as forests in the broad sense of the word; however, these “forests” are more like tall thickets shrubs and are not typical forests, as in areas with moderate humidity, where trees can grow more than 20 meters in height [53]


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The absence, with a few exceptions, in trees of the C4 path, as well as the low representation of C4 plants in the undergrowth, has long been the subject of discussion.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is often hypothesized that due to increased energy requirements, C4 photosynthesis is ineffective in low light conditions.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Although recent data show that C4 plants are indeed slightly less adapted to shading compared to C3 species, this difference is not so significant and does not explain why C4 trees do not were able to form in more open spaces.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Various explanations are put forward from the standpoint of evolution, physiology and ecology, but so far there is no clear answer to this question [53].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Comparison of characteristics of C3-, C4- and CAM plants


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Economic importance


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Among cultivated plants, C4 species (corn, sorghum, some types of millet, sugar cane) are more important than among wild plants, their productivity ranges from 33% (taking into account residues, not used for their intended purpose, such as cereal straw, stems and leaves of root crops) up to 38% of the total productivity of major crops [14].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

These plants also have higher growth rates.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Under optimal irrigation and fertilization conditions, corn and sugar cane crops are the most productive of the known agrocenoses [56].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 plants also include the most resistant weeds, including 8 of the 10 most malicious weeds, such as pig finger and chicken millet [11].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

C4 plants can also be used to produce biofuels, such as corn in the US or sugar cane in Brazil.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Alternatively, the option of growing cold-resistant C4 cereals, such as millet, for the production of cellulosic ethanol is also being considered.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For example, the yield of cold-resistant cereals from the genus Miscanthus is 15—29 tons of dry matter per hectare per year [57].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

One of the problems associated with the growth of the world's population is the depletion of food supplies, especially since the amount of arable land available for cultivation is steadily decreasing.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

One of the ways to increase yields is to use C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The simplest possible approach is to change wild, uncultivated C4 species in order to create a new crop on their basis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For example, breeding methods could be used to breed a rice-like cultivated plant from chicken millet [58].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

An alternative approach is to introduce the C4 path into existing cultivated C3 plants using genetic engineering methods.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Rice, which serves as a grain crop for half of the world, and soybeans, capable of symbiotic nitrogen fixation, are considered as the main candidates for such a transformation.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

To work in this direction, a large international project was assembled, organized on the basis in the Philippines, called “Project C4-Ris”, which includes 12 laboratories from eight countries.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In December 2015, the project announced the creation of a rice cultivar with a rudimentary form of C4 photosynthesis.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

All the main enzymes of the C4 pathway were built into the cells of this variety, although the created plants still rely on C3 photosynthesis for the most part.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Nevertheless, this result showed the fundamental possibility of the C4 cycle in rice [59].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

As of today, all attempts to start a C4 cycle within one cell by simply introducing the appropriate enzymes have either failed or have been extremely ineffective.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The reason for many early failures was the absence in transformable plants of the proteins described above, regulators of the main enzymes of C4 metabolism, which would ensure their adjustment in accordance with the level of illumination and energy state of the cell, as well as regulatory genetic sequences necessary for the correct expression of key proteins.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Another serious obstacle is the absence of any barriers in this scheme against the leakage of CO2 from the cell.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The most obvious solution would be to create a full-fledged fender anatomy, but at the moment the genes responsible for the development of such a structure remain unknown, and their search remains a priority direction [60].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Evolution


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

According to modern geological data, C4 photosynthesis arose in the Oligocene about 30 million years BC [38].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This period is characterized by a drop in temperature and carbon dioxide concentration (from 1000 ppm (parts per million) to about 300 ppm).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, the atmospheric concentration of O2 increased from 18% to 21%.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There were extremely unfavorable conditions for C3 photosynthesis, which contributed to the high intensity of photorespiration.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is assumed that it was the low availability of CO2 that was the reason for the beginning of the selection of plants with injection mechanisms, which ultimately led to the emergence of C4- and CAM paths of the modern type.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In addition, the climate of that time became more arid, and open spaces with high light appeared (steppes, empty, prairies, pampas, savannahs).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The seasonality of the climate and the frequency of fires also increased, which also probably played a significant role in the selection of signs of C4- and CAM species [61].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

A decrease in CO2 concentration is considered an important evolutionary trigger and a common prerequisite for the formation of C4 plants, but not necessarily the main one.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Since C4 photosynthesis has evolved over 30 million years since its first appearance, local factors undoubtedly played an important role.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There are six global centers that are considered as the nucleus for many C4 Eudicots and some cereals: North America, South America, South Africa, East Africa and Arabia, Central Asia and Australia.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

These are warm and dry regions with a moderately arid climate and regular rainfall during the summer.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Salty, sandy or dry soils contributed to the emergence and spread of C4 plants, another favorable factor was the high level of insolation.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

About 23 million years ago, C4 plants were already widely distributed in Africa, America and South Asia.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The distribution took place gradually, especially in the low and middle latitudes [39].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This type of photosynthesis gained global, ecological significance only after the widespread spread of C4 cereals and the expansion of the influence of C4 plants in meadow ecosystems and savannas.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

This happened at the end of the Miocene and the beginning of the Pliocene about 2 to 8 million years ago.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It remains controversial whether the decrease in the concentration of CO2 in the atmosphere was a global common factor for this spread (at least it is an important prerequisite for this).


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Other reasons could well be climate change, the emergence of large herbivores and an increase in the frequency of forest fires [62].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Stages of C4 metabolism formation


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

From an evolutionary point of view, the conversion of C3 plants to C4 is a fairly simple process: all the necessary structural elements and enzymes are already present in C3 plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

For example, FEP carboxylase enzymes and chloroplast NADP-malate dehydrogenase are normally present in the closing cells of C3 plants, where they provide the synthesis of malate ions necessary for the opening of stomatal crevices.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Similarly, all plants have malik-enzyme isoforms that are located in the cytosol, chloroplasts or mitochondria and normally provide anaplerotic metabolic pathways.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Strong clustering of C4 species within certain groups, for example, the PACMAD treasure, within which C4 photosynthesis occurred about 18 times [39], indicates that not all C3 plants are equally good are suitable for the occurrence of C4 photosynthesis, and that this requires favorable preadaptations.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

To date, the process of formation of C4 metabolism is as follows: at the first stage, there was an accumulation of favorable preadaptations, such as a high number of veins in the leaf, as well as genome-wide doubling, which resulted in copies of the genes necessary for the C4 pathway.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Subsequently, these copies underwent appropriate specialization.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the second stage, protocrantz anatomy was consistently formed: the lining cells increased in size, the number of organelles increased in them, mitochondria shifted and clustering occurred, and chloroplasts.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

It is assumed that such transformations could be beneficial to the plant, as they led to the appearance of a unicellular glycine shuttle, which allowed the plant to release CO2 from photorespiration metabolites in close proximity to chloroplasts.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Such plants are found in nature and their CO2 compensation point is 5— 15% lower than that of typical C3 plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the third stage, full-fledged C2 photosynthesis occurred: the number of mesophyll cells decreased in relation to the cells of the bundle lining, and GDK was inactivated in mesophyll cells.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

At the fourth stage, full-fledged C4 photosynthesis emerged on the basis of these plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

The assumption about the emergence of C4 species from C3-C4 transition forms arose, in particular, on the basis that in some of the latter, the activity of FEP-carboxylase, PFDC and NADP-ME was 2—5 times higher than in C3 species.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

During the final, fifth stage, the new concentrating mechanism was optimized and fine-tuned for the most effective action, which ultimately led to the emergence of full-fledged C4 plants.


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

There should have been an increase in the expression of key enzymes and the emergence of the necessary regulatory mechanisms, an improvement in the kinetic qualities of FEP carboxylase, and a decrease in Rubisco expression in cells mesophyll and change of stomata operating mode [63].


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

See also


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

ABC flower development model


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

CAM photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Photorespiration


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Photosynthesis


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Notes


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Literature


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In Russian


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

In English


Question: When was the Hatch Slack cycle opened?

C4 photosynthesis

Category:Photosynthesis


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Blockade of the Ukrainian fleet in Donuzlav

The blockade of the Ukrainian fleet in Donuzlav lasted from March 3 to March 26, 2014.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

It began with the blocking of the exit from Donuzlav by the missile cruiser “Moscow”, and then was associated with the sinking by the Russian side of the large anti-submarine ship “Ochakov” in order to prevent the exit Ukrainian fleet to Odessa.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

As a result, 13 Ukrainian ships were blocked in Donuzlav.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The blockade ended with the establishment of control over the last ship under the Ukrainian flag in Crimea, the Cherkassy.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

As a result of this operation, the Ukrainian fleet lost control over a number of its ships.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Military base


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

260px|mini|left|berth of the Southern Naval Base of Ukraine


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

260px|mini|right|landing ship Konstantin Olshansky during exercises in Donuzlav in 2009


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

In 1961, a 200-meter canal was dug, which turned Lake Donuzlav into a bay.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Since then, the development of this region has been associated with the Crimean Naval Base.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

After the division of the Black Sea Fleet, the base came under the control of Ukraine.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The Southern Naval Base of Ukraine was established.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On the territory of Donuzlav, joint exercises of NATO and Ukraine “Sea Breeze” were repeatedly held [1] [2], which caused disapproval from Russia [3] [4].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

At the time of the beginning of the blockade, the following military facilities and formations of the Ukrainian Navy were located in the village of Novoozernoye: 257 combined weapons and property depot (military unit A4290), naval reconnaissance point (military unit A3343), the Southern Naval Base of Ukraine (military unit A2506) and 21 areas of the coastal surveillance system (military unit A4249) [5].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Also in the Donuzlav area in the village of Mirny, there is an abandoned anti-submarine air base [6] [7].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

As of March 2014, ships of the 5th brigade of surface ships of the Ukrainian Navy were based in Novoozernoye [5] [8]:


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

corvette Vinnitsa (U206);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Chernigov sea minesweeper (U310);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Cherkasy sea minesweeper (U311);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Genichesk raid minesweeper (U360);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Kirovograd medium landing ship (U401);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Konstantin Olshansky large amphibious assault ship (U402);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Gorlovka transport (U753);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

anti-sabotage boat “Feodosia” (U240);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Kherson torpedo boat (U891);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Dobropole boat (U854).


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The 8th separate division of support vessels included [5] [9]:


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

“Evpatoria” fire-fighting boat (U728);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

sea tug Kovel (U831);


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Novoozernoye tow boat (U942).


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Background


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

From February 23 to February 27, the executive authorities of Sevastopol and the Autonomous Republic of Crimea were changed [10] [11].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The new Crimean government declared the illegitimacy of the Ukrainian authorities and appealed for assistance and assistance to the leadership of Russia, which supported the Crimean authorities [12] [13].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On March 1, after receiving appeals from the Crimean government and Viktor Yanukovych, Russian President Vladimir Putin submitted an appeal to the Federation Council on the use of Russian troops on the territory of Ukraine [14].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On the same day, the Federation Council, meeting for an extraordinary meeting, agreed to the use of Russian troops in Ukraine [15].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Also, on March 1, 2014, by decree of Acting President of Ukraine Oleksandr Turchinov, Denis Berezovsky was appointed commander of the Naval Forces of Ukraine.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The next day, the Rear Admiral took the oath to the new leadership of the Crimea and was appointed commander of the Crimean Navy [16].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On the same day, he was removed from his post by the decision of Acting Minister of Defense of Ukraine Igor Tenyukh and by decree of the Acting President of Ukraine.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Sergei Haiduk was appointed commander instead of Berezovsky [17] [18] [19].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The course of events


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

According to the Minister of Defense of Ukraine Igor Tenyukh, the fleet at that time had only four ships conditionally combat-ready, including the large amphibious assault ship Konstantin based in Donuzlav Olshansky” [20].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

Answering the question why the Ukrainian ships were not withdrawn from the Crimea at the end of February 2014, Tenyukh accused the Commander-in-Chief of the Armed Forces of Ukraine Yuri Ilyin, who, according to him, did not give corresponding order [21].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

However, Ilyin himself accused Tenyukh of the absence of such an order [22].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The commander of the Cherkasy minesweeper Yuriy Fedash claims that on February 27, an order was issued to bring military units to combat readiness, but on the same day it was canceled.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On February 28, by oral order, Fedash claims, the ships went to Odessa, but by order of Denis Berezovsky they returned back [23].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On March 2, 2014, four KAMAZ trucks with armed men arrived in the village of Novoozernoye [24].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

They settled in the building of an abandoned barracks and installed the flag of Russia over it [25] [26].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On March 3, 2014, information appeared about the blocking of the Southern Naval Base of Ukraine by military personnel of the Russian Federation [27].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The 200-meter exit from Donuzlav Bay was blocked by the flagship of the Russian Black Sea Fleet, the Moskva missile cruiser, accompanied by four support ships [28] [29].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On land, the Ukrainian unit was blocked by about 100 servicemen of Russia.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

At the same time, the ships of the Ukrainian Navy received an order to withdraw from the pier and disperse along Donuzlav [30].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

260px|mini|right|Chernigov minesweeper in Donuzlav in 2008


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The commander of the Black Sea Fleet of the Russian Federation Alexander Vitko personally came to negotiations with the command of the unit with a request to surrender and take the oath to the Crimean people, but he was refused [31].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

It was also refused to execute Denis Berezovsky's order — the ships to go to the pier and hand over their weapons to warehouses [30].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On the morning of March 4, Crimean Prime Minister Sergei Aksyonov said that the personnel of Ukrainian military units are ready to obey the new government of Crimea and that with regard to commanders who refuse to comply his orders, criminal proceedings will be initiated [32].


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

On March 4, unmarked armed men began digging trenches near the pier.


Question: How was the crew of the ship Konstantin Olshansky honored after returning to Ukraine?

The next day, March 5, the exit from Donuzlav began to be blocked by the ships SFP-183, Moskva, Shtil and Molniya [24].