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, so have evolved to reduce the loss of carbon dioxide (CO2) during photosynthesissince this is an essential gas during the process of transforming the Sun’s energy into food for plants.
Photosynthesis characteristics of C4 plants
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. Is consists of the absorption of solar energy and carbon dioxide through the chloroplasts of the cells found in the green or photosynthetic parts of plants, and water from the roots, to transform it into food through a series of chemical reactions.
At first, this light energy changes to chemical energy, being the molecules NADPH (nicotin adenine dinucleotide phosphate) and ATP (adenosine triphosphate, the first to store it. But later, these molecules they synthesize carbohydrates as carbon dioxide is reduced.
The last stage in this process is when plants use the energy they have gained during the day to fix carbon from carbon dioxide in the form of glucose. This is part of the Calvin cycle.
However 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 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). In them, CO2 will be released, 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 CO2which 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:
- Generally, grow faster than C3 plants.
- They make better use of carboneither to produce more roots and / or more leaves.
- Lose less water during photosynthesis (according to this article, it is estimated that they lose 277 water molecules for each CO2 molecule, while C3 plants lose 833 water molecules for each one of CO2 they fix).
- Boost glucose productionwhich 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?
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.
Therefore, knowing them can be very useful to know what to grow in areas where there is little water availability.