Name: plant carbon fixation in hot climates
Uploaded: 2019-03-11T09:21:13.000Z
Duration: 1 min 27 s
Channel: JoVE

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HS-ESS2-6

C4 Pathway and CAM

像玉米这样的植物 已经采用了替代方法， 在炎热，干燥的环境中更有效地固定碳。
 在一个方面，C4路径 ，在第一个碳固定步骤中， 二氧化碳，C02， 进入叶肉细胞， 并通过酶PEP羧化酶， 与游离碳化合物，PEP结合， 形成四碳化合物，草酰乙酸， 然后将其转化为金属有机酸。
 在这种情况下，苹果酸。
 苹果酸被运输到叶片深处的 成束的薄层细胞中，氧气被限制并分解， 释放出二氧化碳， 然后二氧化碳可以通过卡尔文循环， 然后用RuBisCO 直接生成糖。
 其他植物如菠萝 使用Crassulacean酸代谢或CAM途径 来固定碳。
 CAM植物仅在夜间打开气孔 以防止白天失水。
 与C4途径类似， 首先通过PEP羧化酶将CO2固定在草酰乙酸中， 然后将其转化为苹果酸。
 CAM植物不是将苹果酸转移到叶子的另一部分， 而是将这种化合物储存在叶肉细胞液泡中， 在白天释放它， 使得卡尔文循环 可以与光合作用中的光反应一起进行。

<ol>
	<li>Edwards， EJ 进化轨迹、可访问性和其他隐喻:C4 和 CAM 光合作用的案例。 新植物学家。223 （4）， 1742-1755 （2019）。</li>
</ol>

c4通路和cam

一些植物，如甘蔗和玉米，生长在炎热的条件下，使用一种称为C4通路的替代过程来固定碳。这个循环从大气中的CO2进入叶肉细胞开始，在叶肉细胞中，CO2被用来从磷酸烯醇丙酮酸（PEP）生成草酸酯（一种四碳分子）。然后草酰乙酸转化为苹果酸盐，转运到氧浓度较低的束鞘细胞。在那里，CO2从苹果酸盐中释放，进入卡尔文循环被转化为糖。景天酸代谢（CAM）通路是在仙人掌等植物中进行的，这些植物在白天也需要保存水分。CAM植物在夜间让CO2进入叶片，并产生苹果酸盐，苹果酸盐储存在液泡中，直到第二天。然后苹果酸盐从液泡中释放出来，在卡尔文循环中进行处理。C4通路在局部分离不同的进程，而CAM通路按时间顺序分离它们。

<h4>C4的途径</h4>
 
一些植物，如玉米和甘蔗，已经进化出另一种固定碳的方法，有助于避免在炎热干燥的环境中水分流失。其中一种方法是C4途径。第一步，CO2进入叶肉细胞，磷酸烯醇丙酮酸（PEP）羧化酶将其加入3-碳化合物PEP中，形成4-碳化合物草酰乙酸。草酰乙酸被转化成一种叫做苹果酸的有机酸。
 
随后，苹果酸被输送到叶片深处氧浓度较低的维管束鞘细胞中。苹果酸被分解，释放出一个CO2分子，然后进入卡尔文循环，核酮糖二磷酸缩化酶（rubisco）将其转化为糖。C4途径在炎热、干旱的条件下具有优势，因为植物会关闭气孔以保存水分。因此，它们可以保持较低的氧浓度，从而有利于CO2与二磷酸核酮糖羧化酶的结合，而不是O2。当氧浓度较高时，二磷酸核酮糖羧化酶与O2>结合，而不是与CO2结合，这一过程称为光呼吸，它会停止光合作用并消耗能量。
 
<h4>CAM的途径</h4>
 
其它植物，如仙人掌和菠萝，利用景天酸代谢（CAM）途径来固定碳。CAM植物主要在夜间打开气孔，以防止在炎热的白天水分流失。夜间CO2进入叶肉细胞，与PEP结合形成草酰乙酸，最终形成苹果酸。苹果酸则储存在液泡中，直到第二天从液泡中释放出来，进入卡尔文循环。光合作用的第一阶段在白天进行，因为它们依赖于光，而卡尔文周期的光独立反应则在夜间进行。以这种方式，CAM植物利用一天中不同的时间分离CO2固定和糖合成。

C4通路和CAM

大多数植物采用C3途径进行碳固定。然而，一些在高温环境下生长的植物，如甘蔗、玉米和仙人掌，则利用替代的……

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plant carbon fixation in hot climates

Plant carbon fixation in hot climates can follow the C4 pathway or the CAM pathway. These alternative pathways help some plants reduce energy loss from photorespiration. Photorespiration happens when oxygen levels are high and rubisco, the enzyme in the Calvin cycle, binds O2 instead of CO2. When that happens, photosynthesis slows and energy is used up.

The C4 pathway is used by plants such as corn and sugarcane. In mesophyll cells, CO2 first joins with PEP, or phosphoenolpyruvate, through the action of PEP carboxylase. This forms the 4-carbon compound oxaloacetate, which is then changed into organic acids, mostly malate.

Malate moves into the bundle sheath cells deep in the leaf, where oxygen levels are low. There, malate is broken down and releases CO2. That CO2 enters the Calvin cycle and is turned into sugar with the help of RuBisCo. In hot, dry conditions, this separation of carbon fixing and sugar production helps the plant close its stomata and save water while keeping oxygen low.

Other plants, such as cacti and pineapple, use the CAM pathway, or crassulacean acid metabolism. CAM plants open their stomata at night to limit water loss during the day. CO2 enters the mesophyll cells at night and combines with PEP to form oxaloacetate and then malate.

The malate is stored in vacuoles until the next day. During the day, it is released so the Calvin cycle can begin. In CAM plants, carbon fixation happens at night, while sugar synthesis follows during the day with energy from the light-dependent reactions. This time-based separation helps these plants survive hot, dry environments.

Plant Carbon Fixation in Hot Climates

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Photosynthesis in Chloroplasts and Leaves

Photosynthesis happens in plants and in some bacteria. It is the process that captures carbon dioxide and solar energy to make glucose. Glucose stores chemical energy as carbohydrates. The overall biochemical equation is 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. Photosynthesis also releases oxygen into the atmosphere and helps maintain Earth’s atmospheric oxygen content. Photosynthetic reactions take place in chloroplasts, which are specialized membrane-enclosed parts of the plant cell.

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Chloroplasts are the organelles where photosynthesis takes place in green algae and plants. They are also found in green stems and unripe fruit. In plants, mesophyll cells in the leaf contain the highest density of chloroplasts. Each chloroplast has a double membrane. The outer membrane faces the plant cell cytoplasm on one side and the chloroplast intermembrane space on the other. The inner membrane separates that narrow space from the stroma, which is the watery interior of the chloroplast.

photosystem ii

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Photosystem II is a multi-protein complex that captures light energy and begins the flow of electrons in photosynthesis. It uses bound pigments to harvest photons and send that energy to its reaction center. From there, the energy continues through the electron transport chain and on to photosystem I. The pigments in photosystem II include chlorophyll a, chlorophyll b, and carotenoids. They are arranged in two parts of the photosystem: the antenna complex and the reaction center. The antenna...

photosystem i

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Photosystem I helps convert light energy into NADPH during photosynthesis. It works with photosystem II in the thylakoid membrane of the chloroplast, but it uses a different electron supplier and a different electron acceptor. Electrons excited in photosystem II move to photosystem I through an electron transport chain. That chain includes plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As the electrons travel between the two photosystems, they lose energy and must be...

the calvin cycle

Carbon Fixation in Photosynthesis

Photosynthesis uses light energy to turn carbon dioxide into carbohydrates. It also releases oxygen as a by-product. These products help support most food webs and make aerobic life possible. Photosynthesis has two main stages, and they happen in different parts of the chloroplast. The light-dependent reactions take place in the thylakoid membranes. Chlorophyll absorbs light energy there and helps split water molecules. This releases O2 and makes ATP and NADPH. The light-independent reactions...

c4 pathway and cam

Plant carbon fixation in hot climates can follow the C4 pathway or the CAM pathway. These alternative pathways help some plants reduce energy loss from photorespiration. Photorespiration happens when oxygen levels are high and rubisco, the enzyme in the Calvin cycle, binds O2 instead of CO2. When that happens, photosynthesis slows and energy is used up. The C4 pathway is used by plants such as corn and sugarcane. In mesophyll cells, CO2 first joins with PEP, or phosphoenolpyruvate, through the...

key terms and concepts

Learn how C4 and CAM pathways help plants like corn, sugarcane, cacti, and pineapple reduce photorespiration and save water in hot climates.

Plant Carbon Fixation in Hot Climates | JoVE K12

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Plant Carbon Fixation in Hot Climates

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