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Photosynthesis: Light regulates the activity of the key C4 enzyme

Writer's picture: PlantHouse EnterprisePlantHouse Enterprise

This video explores the fascinating interplay between light and enzyme activity in C4 photosynthesis. Discover how light activates key enzymes like NADP-malate dehydrogenase through the ferredoxin system, enabling efficient CO2 capture during the day. We'll also uncover how these enzymes are regulated during darkness to conserve resources and allow for plant growth. Learn how C4 plants optimise their metabolism for maximum efficiency!


Video Transcript:

So is light important? Yes, light is important because light is actually responsible for activating many of the enzymes that you saw on this table here, Table B. Here, for example, NADP-malate dehydrogenase is dependent on ferredoxin. Ah, you see this guy again? Remember you saw this thing before? You saw this thing before when you were learning about Rubisco activation. You see this again.


Who else is dependent on this? NADP-malate dehydrogenase, which is in reaction number three, I think, should be number three. Yep, number three. Meaning that without light, the dehydrogenation of malate is not activated. If it's not activated, how on Earth is it going to capture CO2? It's not going to happen.


And some of the, uh, unusual things also happen because at night, some of these enzymes need to be downregulated. Uh, which enzyme? Let me see. Yeah, this, this phosphorylation, this, in the darkness, it needs to be, uh, activated because in the, in the, in the darkness, well, there's no photosynthesis, right? So, why waste the metabolic resources? So, plants rely on the activation of all of these compounds to upregulate or downregulate these enzymes so that they are doing the job in the right manner, right?


If they are active during the night, when there is no ATP produced, because, remember, these two cells, they kind of are not having photosystem II in both of them, only one of them has it, right? So, they need to have some kind of communication to tell, "We are ready because we have been activated by the sunlight, so now you can enter." The other side needs to tell, "We can't do much now because the darkness has, some of our guys have been deactivated, so no more resources for you, so stop doing stuff." Right? So, this communication is happening on a regular basis.


For, for the purpose of what? Easy. If the plant is active all the time, when is it going to grow? Plus, it's, it's not sleeping, but it needs the darkness to do elongation, to relax the cell wall so that the expansion can take place, yeah? Not to say that in the day expansion is not happening, but when it's darkness, the starch can break down, it can break down, then this can be used as energy for the growth and expansion until the light comes back in, yeah?


So, if you think about it, that is smart. It means the plant knows how to utilize the time at the best of its capacity. During the day when the energy is available, stop enlarging, stop growing, but acquire all the energy that is possible. At night, when there is no light, there is no energy, break down the energy, do the expansion, do the elongation, efficient. If it's growing during the daytime, who's going to do all this biochemical pathway, right? So, but that's, that's, that's the, the smart thing about, about this, this, this whole thing, okay? Right. Um, so, this is pretty much, yeah.


Keywords: C4 photosynthesis, light regulation, enzyme, activation, ferredoxin, NADP, malate, dehydrogenase, plant metabolism, biochemistry


Reference book: Plant Physiology and Development 7th Edition

by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger



Attribution 4.0 International — CC BY 4.0 - Creative Commons

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