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

K12 Standards

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High School

Environmental Science

Earth’s Systems

HS-ESS2-6

C4 Pathway and CAM

- [Instructor] Algunas
plantas, como el maíz,

han desarrollado por adaptación
formas alternativas de fijar

el carbono más eficientes
en ambientes cálidos.

En una, la vía C4,

durante el primer paso
de fijación del carbono,

el dióxido de carbono, CO2,

entra en las células del mesófilo

y, por medio de la enzima PEP carboxilasa,

se combina con el compuesto
de carbono libre, PEP,

para formar un compuesto de
cuatro carbonos, oxalacetato,

que se convierte después
en un ácido organometálico.

En este caso, malato.

El malato se transporta a
las células del haz vascular

en lo profundo de la hoja,
donde el oxígeno es limitado,

y se rompe, liberando CO2,

el cual ahora puede
ingresar al ciclo de Calvin

e interactuar con la RuBisCO

para eventualmente producir azúcares.

Otras plantas como las piñas

usan el metabolismo ácido
de las crasuláceas o vía CAM

para fijar el carbono.

Las plantas CAM sólo abren
sus estomas en la noche

para evitar la pérdida
de agua durante el día.

Al igual que la vía C4, el CO2 primero

es fijado por la PEP
carboxilasa en oxalacetato

que luego se convierte en malato.

En lugar de transferir el
malato a otra parte de la hoja,

las plantas CAM almacenan este
compuesto en las vacuolas de

las células del mesófilo,
liberándolo durante el día

para que el ciclo de Calvin pueda proceder

junto con las reacciones
luminosas de la fotosíntesis.

<ol>
	<li>Edwards, E.J. Trayectorias evolutivas, accesibilidad y otras metáforas: el caso de la fotosíntesis C4 y CAM. Nuevo Fitólogo. 223 (4), 1742-1755 (2019).</li>
</ol>

vía c4 y cam

La mayoría de las plantas utilizan la vía C3 para la fijación de carbono. Sin embargo, algunas plantas, como la caña de azúcar, el maíz y los cactus que crecen en condiciones de calor, utilizan vías alternativas para fijar carbono y conservar la pérdida de energía debido a la fotorrespiración. La fotorrespiración es el proceso que ocurre cuando la concentración de oxígeno es alta. En tales condiciones, la enzima rubisco del ciclo de Calvin se une a O2 en lugar de CO2, lo que detiene la fotosíntesis y consume energía. Vía C4 La vía C4 es utilizada por plantas como el maíz y la caña de azúcar. En el primer paso, el CO2 ingresa a las células del mesófilo y la enzima fosfoenolpiruvato carboxilasa (PEP carboxilasa) lo agrega al compuesto de 3 carbonos PEP para formar el compuesto de 4 carbonos oxaloacetato. Luego el oxalacetato se convierte en ácidos orgánicos, predominantemente malato. Luego, el malato se transporta a las células de la vaina del haz en lo profundo de la hoja, donde la concentración de oxígeno es baja. Es aquí donde el malato se descompone para liberar una molécula de CO2. Luego, el CO2 ingresa al ciclo de Calvin y se convierte en azúcar con la ayuda de la enzima RuBisCo. En condiciones cálidas y áridas, la separación física de la fijación de carbono y el ciclo de Calvin son ventajosos, ya que las plantas pueden cerrar sus estomas para conservar agua. Como resultado, pueden mantener baja la concentración de oxígeno y, por lo tanto, favorecen la unión de CO2 a RuBisCo en lugar de O2. Vía CAM Otras plantas, como los cactus y la piña, utilizan la vía del metabolismo del ácido crasuláceo (CAM) para fijar carbono. Las plantas CAM abren sus estomas por la noche para evitar la pérdida de agua durante los días calurosos. Una vez que el CO2 ingresa a las células del mesófilo, se combina con la PEP para formar oxaloacetato y eventualmente malato. Luego, el malato se almacena en vacuolas hasta el día siguiente, cuando se libera para ingresar al ciclo de Calvin. Así, la fijación del carbono se produce durante la noche y el ciclo de Calvin, impulsado por reacciones dependientes de la luz, continúa durante el día. De esta manera, las plantas CAM separan la fijación de carbono y la síntesis de azúcar en diferentes momentos del día.

Vía C4 y CAM

La mayoría de las plantas utilizan la vía C3 para la fijación de carbono. Sin embargo, algunas plantas, como la caña de azúcar, el maíz y los cactus que crecen en condiciones cálidas, utilizan alternativas ...

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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 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.

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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...

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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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