Plants C3 and C4, differences and examples

Plants C3 and C4, differences and examples

Examples of C3 and C4 plants, differences and notions of plant physiology. From photorespiration to the Calvin cycle.

Proposing a page that summarizes the differences between C3 and C4 plants is not at all easy. We are faced with complex mechanisms of plant physiology which, if we do not go into molecular detail, are not easy to understand. On this page I will try to explain the main differences between C3 and C4 plants assuming that you know what photosynthesis is and what the products of plant metabolism are.

The differences between C3 and C4 plants reside both at the tissue level and in the type of organized autotrophic cycle.

Plants C3

C3 plants are all those plants characterized by the Calvin cycle alternating with Photorespiration.

The Calvin cycle allows the growth of the plant (the biosynthesis of those macromolecular complexes that allow the plant to grow).

Photorespiration, on the other hand, limits the growth of the plant and consumes the oxygen present in the plant cell and which has been partially released by the same photosynthesis (with the photolysis of water associated with the PSII complex).

They are called C3 plants because the fruit of carbon organization is given by two molecules of triose phosphate (3phosphoglycerate), therefore two molecules athree carbon atoms.

C3 plants live in temperate climate zones, which allows the leaves to fully open the stomata at certain times of the day. With the complete opening of the stomata, the carbon dioxide necessary for the activation of the carboxylic reactions operated by Rubisco can enter.

I steal

Rubisco is an enzyme found in all plants:C3, C4isCAM. The problem is that theI stealmanages to tie bothoxygenmolecular, is carbon dioxide. In fact, both molecules (O2 and CO2) have a planar geometry with negative sigma exposed on both sides.

Under conditions of equal amounts of CO2 and O2 in the plant cell, Rubisco tends to bind carbon dioxide for carbon fixation. Stress conditions, however, do not always allow a complete opening of the stomata and oxygen levels could be much higher than those of CO2. In addition, PSII constantly releases molecular oxygen for the recovery of the electron missing from the phaeophytin which is the first electronics donor of photosynthesis.

So for plants that live in atemperate weather, metabolismC3is possible because, under optimal conditions, theI stealmanages to make carbon fixation prevail over photorespiration. Theplants C3therefore, they have not evolved strategies to accumulate CO2 because the climatic conditions in which they thrive are compatible with the operating mechanisms implemented.

Plants C4

C4 plants live in areas with a tropical climate and therefore during the day they have mostly closed stomata. CO2 does not enter.

These plants, to prevent theI stealcould constantly react with oxygen and implement thephotorespiration, have evolved a CO2 accumulation system near the rubisco.

The photosynthetic tissues of C4 plants are organized differently. In C4 plants, in fact, there are canonical chloroplasts but devoid of rubiscus (in the cells of the leaf mesophyll) and chloroplasts that present the rubiscus but are devoid of PSII (in the cells of the collar sheath).

In practice, in theplants C4a first fixation of the carbon takes place by an enzyme called "PEP-Carboxylase" (fosphenopyruvate carboxylase). This first organization occurs in the cytosol, where the first molecule a is formedfour carbon atoms(C4), oxaloacetate.

The oxaloacetate is then transformed to malate by a dehydrogenase that exploits the reducing power. This occurs in the chloroplasts of mesophyll cells (devoid of rubiscus). The patient reaches the chloroplasts of the cells of the collar sheath (which instead have the steal).

It is here that the malic enzyme releases CO2 and pyruvate from the patient, producing reducing power. This mechanism occurs continuously, so much so that in these chloroplasts the CO2 levels are such as to allow the rubisk to avoid photorespiration and to favor carbon fixation. From here, the C4 plants implement the Calvin cycle.

Examples of C4 plants

Plants with C4 metabolism are usually tropical species, especially herbaceous plants that are able to conclude their vegetative cycle in a short time. Among the most important examples, from an agronomic point of view, we remember corn (zea mays), sugar cane and sorghum.

Examples of C3 plants

C3 plants are both arboreal and herbaceous. Examples of C3 plants include sunflower, cotton, tobacco, wheat, bean, oak, maple ...

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