Traditional photosynthesis (known as C3) is present in the majority of plant species on earth. However it is very inefficient in conditions where carbon dioxide CO2 is low, water is scarce, and temperatures and salt levels are high. In these environments, side reactions in the cycle of photosynthesis lead to a loss of energy, CO2 and water. Nature solved this problem by evolving the C4 cycle which stops these side reactions occurring. The increased efficiency in C4 species also means that plant stomata (the tiny pores on leaves that control the exchange of gases) can stay open for a shorter time, reducing the amount of water these plants lose when their stomata are open.
This system evolved by recruiting enzymes from other processes in plants. Phosphoenolpyruvate carboxylase was the enzyme recruited for CO2 capture, and it functions differently in photosynthesis to how it functions when playing one of the other roles it performs in plants. Understanding these different functions is fundamental to discovering how to turn C3 crop species into plants that perform the more efficient C4 photosynthesis species. For example rice, which grows in warm environments with low CO2 levels, would benefit most, as it’s a crop that struggles in drought conditions while so much of the world’s population depends on it.
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