Do chloroplasts in C4 plant mesophyll cells perform photosynthetic dark reactions?

C4 plant photosynthesis is very special, there are chloroplasts in the rosette-shaped structure, in which there are microgranules, but only photoreactions, while vascular sheath cell chloroplasts have no microgranules and can only carry out dark reactions, and these two coordinate to complete photosynthesis, that is, organic matter is actually generated in vascular sheath cells.

This is because the chloroplasts here have a different structure and only react with light, while the dark reaction takes place in the vascular bundle sheath cells (cells in the inner ring of the "rosette-shaped structure"). Why not, because of this division of labor, the efficiency is relatively high.

The vascular bundles of C4 plant leaves are surrounded by vascular sheaths that are chloroplasts, but there are no basal grains or stunted development in them. Here, the Calvin cycle is mainly carried out.

Its mesophyll cells contain a unique enzyme, phosphoenolpyruvate carbonidase, which causes carbon dioxide to be assimilated by a three-carbon compound, phosphoenolpyruvate, to form a four-carbon compound oxaloacetate, which is also the origin of the name of this dark reaction type. After this oxaloacetate is converted to malate, it enters the vascular sheath and decomposes to release carbon dioxide and a molecule of glycerol. Carbon dioxide enters the Calvin cycle, followed by the same process as C3.

Glycerol, on the other hand, is resynthesized from phosphoenolpyruvate, a process that consumes ATP.

Chloroplast. Leaving the cell, photosynthesis can still take place under suitable conditions.

Some plants can still photosynthesize below 0, such as lichens in the polar regions.

But the temperature changes, regardless of whether it is a light reaction or a dark reaction.

are affected, but mainly affect the dark reaction, because the dark reaction is more than the light reaction in terms of both the type of enzyme and the number of enzymes.

The effect of temperature on photosynthesis is actually achieved by affecting the activity of enzymes related to photosynthesis. Therefore, repentance does not only affect the dark reaction, but affects the whole process. For example, when winter comes, the temperature drops, and the intensity of photosynthesis is still low despite the abundance of sunlight.

C4 plants. The Calvin cycle (C3 cycle) is performed only in the parenchyma cells of the vascular sheath.

Starch is formed only in the parenchyma cells of the vascular sheath.

Mesophyll cells only play a role in fixing CO2.

The reason: chloroplasts inside the mesophyll cells of C4 plants.

The number is smaller. The individual is small.

There are basal grains. Whereas, the parenchyma cells of the vascular sheath are larger.

It contains many larger chloroplasts.

However, chloroplasts do not have a bactogranula or are underdeveloped.

As a result, there is a large number of plasmodesmata between the parenchyma cells of the vascular sheath and their adjacent mesophyll cells.

The second congratulatory connection is: in the mesophyll cytoplasm.

Initially CO2 with phosphoenol-pyruvate.

Catalyzed by phosphoenolpyruvate carboxylase.

Fixed HCO3-

Oxaloacetate is generated.

And then after a series of reactions.

At last. as a donor of CO2.

That is, tetracarbon dicarboxylic acid is decarboxylated in the vascular sheath of the first target to release CO2, which is assimilated by the C3 pathway in the vascular sheath cells).

To be clear, the C4 plant photosynthesis pathway is the result of plant photosynthetic carbon assimilation to the tropical environment.

Olympiad or University Bio Content.

Although the mesophyll cells of C4 plants have normal chloroplasts, they lack enzymes related to dark reactions, so they cannot carry out dark reactions, but can only undergo light reactions.

In this figure, A is a photosynthetic light reaction because there is light, B is a dark reaction, glucose is changed to pyruvate after D, so it is aerobic respiration phase 1, and C is aerobic phase 2 and 3.

So 1 oxygen.

2. Photosynthesis light reaction reduces hydrogen ATP

3 Mitochondria. 4. Oxygen content c

a. The light reaction must be carried out on the chloroplast matrix, and the dark reaction must be carried out in the chloroplast matrix, a is correct;

b. The light reaction needs the ADP and PI provided by the dark reaction, the dark reaction needs the ATP and [H] of the jujube should be provided with the light reaction, and the dark reaction cannot generate [H], B error;

c. Both light reaction and dark reaction require enzyme catalysis, and c is wrong;

d. Both the light reaction and the dark reaction have carried out material metabolism and energy metabolism, so there are material changes and energy changes, D is wrong

Therefore, a

a. In the summer, when the light is strongest at noon on a sunny day, the stomata are closed, and the carbon dioxide in the eggplant before entering the mesophyll cells is reduced, which affects the fixation reaction of carbon dioxide, resulting in a weakened reaction, and the content of three-carbon compounds in the chloroplast will decrease in the short term, a is correct;

B. The site of ATP production at the root tip is the cytoplasmic matrix and mitochondria, B is wrong;

c. Under low oxygen concentration, the intensity of anaerobic respiration and aerobic respiration is relatively weak, which is conducive to storage, and c. error;

d. Lutein has no conversion of light energy, and D is wrong

Therefore, a

At this time, the rate of photosynthesis is equal to the rate of respiration, that is, there are only two processes C and D in the figure above.