Characteristics of C4 plants

The plant kingdom has developed different strategies to survive. Some are visible, such as cactus spines for example, which are nothing more than modified leaves that have replaced the ability to photosynthesize with that of protecting the body of these plants. But there are others that are not so, such as the so-called C4 plants.

They are plants that generally live in arid or semi-arid regions, which is why they have evolved to reduce the loss of carbon dioxide (CO2) during photosynthesis since this is an essential gas during the energy transformation process of the Sun in food for plants.

Photosynthesis characteristics of C4 plants

C4 plants live in dry regions

Image – Wikimedia / Ninghui Shi

To better understand C4 plants, we are going to first explain the photosynthesis that we know best, mainly because it is the one studied at school, C3. This consists of the absorption of solar energy and carbon dioxide through the chloroplasts of the cells that are found in the green or photosynthetic parts of the plants, and water by the roots, for, through a series of chemical reactions , transform it into food.The chloroplasts are organelles responsible for photosynthesis.

At first, this light energy changes to chemical energy, being the molecules NADPH (nicotine adenine dinucleotide phosphate) and ATP (adenosine triphosphate, the first to store it. But later, these molecules synthesize the carbohydrates as the dioxide carbon is reduced.

The last stage of this process is when the plants use the energy they have obtained during the day to fix the carbon of the carbon dioxide in the form of glucose. This is part of the Calvin cycle.

But photosynthesis in C4 plants is different. They have two types of chloroplasts . Some are next to the conducting vessels (we could say that they are the equivalent to the veins of animals), and others that are found in the cells of the peripheral chlorophyll parenchyma, which are those that are closer to the margins of the leaves. The latter are also called mesophilic cells, and they are those that have chloroplasts that will fix carbon dioxide with the help of the PEPA (phosphoenolpyruvic acid) molecule and the enzyme phosphoenolpyruvate carboxylase.

From these molecules, oxaloacetic acid will be generated, which is composed of 4 carbons (which is why they are known as C4 plants). This is then transformed into malic acid, and that is when it passes to the chloroplasts that contain the internal cells of the conducting vessels through the plasmodesmata (these are structures that the wall that surrounds the cell nucleus, the cytoplasm, has). The CO2 will be released in them, and the Calvin cycle can continue.

Climate and plants C4

Plants that live in hot and dry areas have much more difficulty than the rest to avoid the loss of water. But to live you have to breathe, and in doing so it is inevitable to lose water. Therefore, when temperatures are high, the stomata (pores) of the leaves close, and by doing so the oxygen generated during photosynthesis increases its concentration.

In normal situations, when the amount of oxygen and carbon dioxide is balanced, the enzyme that is responsible for fixing carbon (RuBisCO) can fulfill its function without problem. But when the concentration of CO2 is lower than that of oxygen, this enzyme catalyzes the latter gas and not CO2 , which is what happens in C4 plants.

These are very special, because in addition to having two types of chloroplasts (see upper section), the enzyme phosphoenolpyruvate carboxylase, which is one of those involved in carbon fixation, supports high concentrations of oxygen.

What are the advantages of C4 plants?

There are several important advantages that these plants have:

  • They generally grow faster than C3 plants.
  • They make better use of carbon , either to produce more roots and / or more leaves.
  • They lose less water during photosynthesis. it is estimated that they lose 277 water molecules for every CO2 molecule, while C3 plants lose 833 water molecules for every one of CO2 they fix).
  • They drive the production of glucose , which is the end result of photosynthesis.
  • They can live on land where there is little water.

For all these reasons, they are becoming more and more interesting, especially for growing in dry climates.

What are C4 plants?

Amaranth s a C4 plant

There are many plants that carry out C4 photosynthesis. For example, corn, grass, amaranth, sugar cane, sorghum, or rye . They are those that have less dense tissues than those that originate from temperate climates, such as maples or camellias, for example.

Therefore, knowing them can be very useful to know what to grow in areas where there is little water availability.

Characteristics of C4 plants

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