Original video: https://youtu.be/2wDph_9jSpI
This video explores the fascinating diversity of C4 photosynthesis. Learn how these subtypes evolved different strategies for concentrating CO2 and minimizing photorespiration. We'll examine the biochemical pathways, the roles of key enzymes, and how factors like climate and human intervention may have shaped their evolution. Discover the remarkable adaptability of plants and the ongoing story of C4 evolution!
Video Transcripts:
C3 vs C4 Photosynthesis
Um, yeah, you can see there is no distinction of the cells. Just, you got your stomata, CO2 gets in, and then all happening in one go for the C3 plant. For the C4 plant, mesophyll cells close to the atmosphere, CO2 gets in here. CO2 becomes the C4 compound. C4 compound gets into the bundle sheath, and then it gets decarboxylated, and then the regular cycle can happen. And then the C3 compound comes back to the mesophyll so that the C4 compound can be formed again, right? Oh, I'll put examples here. So, these are the three variants of, um, C4 subtypes, we call it, okay?
C4 Subtype Photosynthesis
Depending on what? Depending on the decarboxylating enzyme. So, you have type one, type two, type three. Most of the time, in all textbooks, you only learn this thing, but because this is a Cambridge-endorsed class, you get to learn the other two. So, the, the, the first one, the regular one, is this. It's very easy. You, you fix your carbon, CO2, using the HCO3. What is HCO3? Bicarbonate. To get oxaloacetate, then oxaloacetate will be converted to malate. Malate goes to the bundle sheath, and then gets decarboxylated. CO2 proceeds with the C3 cycle. The, the leftover is pyruvate. Pyruvate comes back to become phosphoenolpyruvate in the mesophyll.
For the second type, you see, there's a difference here. It's no longer malate, it's aspartate. Don't worry, it's still a four-carbon compound, it's, it's just a different arrangement of it. Now it becomes aspartic acid, still a type of amino acid, okay? Aspartate goes to the bundle sheath, but it will be converted to oxaloacetate again before it comes back to malate. So, this is a bit longer, right? It comes back to pyruvate, and then becomes alanine. Alanine changes back to pyruvate, then becomes the phosphoenolpyruvate.
For the third type, yeah, the third type is even longer, yeah. Why? Uh, this is the question. This is one of the proofs this thing is due to evolution, because some plants have a quicker way, some have the shorter way, some plants, kind of confused, have both ways. It looks uncertain, the biochemical pathway looks uncertain, even though the plants belong to the same family. So, evolution, as we know it, when it's still ongoing, nothing is fixed, anything is possible, right? So, this is the example to show you how evolution is still taking place.
Maybe this is the, the latest, the, the most, uh, advanced evolution of C4. Maybe this is the start of it. Maybe this is, uh, 100 million years ago, this has been around 150 million years ago, this has been around for, since 200 million years ago. So, this is the longest, so that's why it looks the simplest, right? Okay. Why, why it can become simpler, but this one, no.
If you think about it, compared to corn, guinea grass, and millet, who are more heavily used by humans? Corn. So, when humans interfere a lot, the, the speed of breeding becomes faster as well. When that happens, this evolution is cut short by so much time, right? The domestication of it. The domestication, not only to increase the yield, other things can happen as well, including biochemical improvement. This is biochemical improvement, right? So, in addition to the hot climate and so on, acting upon the plant, and the plant has to deal with it, the farmers can be blamed for the evolution as well, because they look for the plant that can withstand the, in Mexico, super, super hot, unpleasant situation, right?
So, this, plus nature, you get the most advanced of it. Maybe one day, don't be surprised, corn becomes this as well, no need for two cells, just one cell. But this, uh, for now, this is kind of difficult. This is actually for the much simpler plants, right? Actually, this is more, um, efficient because in here, there is no oxygen. In here, maybe oxygen, you still get oxygen here, right? And the oxygen can diffuse because this is still within the same cell, right? Okay. Oh, was that, was that all right?
Keywords: C4 photosynthesis, evolution, subtypes, biochemistry, photorespiration
Reference book: Plant Physiology and Development 7th Edition
by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger
Watch full video: https://youtu.be/0rBZkk8AYRg
Attribution 4.0 International — CC BY 4.0 - Creative Commons
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