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

K12 Standards

Louisiana Student Standards for Science

High School

Environmental Science

Earth’s Systems

HS-ESS2-6

C4 Pathway and CAM

- [Instructeur] Sommige planten zoals maïs hebben alternatieve manieren om koolstof efficiënter te produceren in warme, droge omgevingen. In één, de C4-route, tijdens de eerste koolstoffixatiestap, komt kooldioxide, CO2, de mesofylcellen binnen en via het enzym PEP carboxylase, combineert met de drie koolstofverbinding, PEP, om de vier koolstofverbinding, oxaloacetaat, te vormen, die vervolgens wordt omgezet in een ander organisch zuur. In dit geval, malaat.

Malaat wordt getransporteerd naar de bundel sheeth cellen diep in het blad, waar zuurstof wordt beperkt en afgebroken, waardoor CO2 vrijkomt, die vervolgens door de Calvin cyclus kan gaan en vervolgens met RuBisCO kan interageren om uiteindelijk suikers te produceren. Andere planten zoals ananassen gebruiken de Crassulacean zuurstofwisseling of CAM-route om koolstof te fixeren. CAM-planten openen hun huidmondjes alleen 's nachts om waterverlies overdag te voorkomen.

Net als bij de C4-route wordt CO2 eerst door PEP-carboxylase gefixeerd in oxaloacetaat, dat vervolgens wordt omgezet in malaat. In plaats van malaat over te brengen naar een ander deel van het blad, slaan CAM-planten deze verbinding op in mesofylcelvacuolen, waardoor het overdag vrijkomt, zodat de Calvijncyclus samen met de lichtreacties in de fotosynthese kan doorgaan.

c4-traject en cam

De meeste planten gebruiken de C3-route voor koolstoffixatie. Sommige planten, zoals suikerriet, maïs en cactussen die in warme omstandigheden groeien, gebruiken echter alternatieve routes om koolstof vast te leggen en energieverlies als gevolg van fotorespiratie te beperken. Fotorespiratie is het proces dat plaatsvindt wanneer de zuurstofconcentratie hoog is. Onder dergelijke omstandigheden bindt het rubisco-enzym in de Calvin-cyclus O2 in plaats van CO2, waardoor de fotosynthese stopt en energie wordt verbruikt.

C4-pad

De C4-route wordt gebruikt door planten zoals maïs en suikerriet. In de eerste stap komt CO2 de mesofylcellen binnen en het enzym fosfoenolpyruvaatcarboxylase (PEP-carboxylase) voegt het toe aan de 3-koolstofverbinding PEP om de 4-koolstofverbinding oxaalacetaat te vormen. Oxaalacetaat wordt vervolgens omgezet in organische zuren, voornamelijk malaat. Malaat wordt vervolgens naar de bundelschedecellen diep in het blad getransporteerd, waar de zuurstofconcentratie laag is. Hier wordt malaat afgebroken, waarbij een molecuul CO2 vrijkomt. CO2 komt vervolgens in de Calvin-cyclus terecht en wordt, met behulp van het enzym RuBisCo, omgezet in suiker.

In warme, droge omstandigheden is de fysieke scheiding tussen koolstoffixatie en de Calvin-cyclus voordelig, omdat de planten hun huidmondjes kunnen sluiten om water te conserveren. Hierdoor kunnen ze de zuurstofconcentratie laag houden en de binding van CO2 aan RuBisCo bevorderen in plaats van O2.

CAM-pad

Andere planten, zoals cactussen en ananas, gebruiken het crassulaceanzuurmetabolisme (CAM) om koolstof vast te leggen. CAM-planten openen hun huidmondjes 's nachts om waterverlies tijdens warme dagen te voorkomen. Zodra CO2 de mesofylcellen binnendringt, combineert het met PEP om oxaalacetaat en uiteindelijk malaat te vormen.

Malaat wordt vervolgens in vacuolen opgeslagen tot de volgende dag, wanneer het wordt vrijgegeven om de Calvin-cyclus in te gaan. De koolstoffixatie vindt dus 's nachts plaats, en de Calvin-cyclus, gevoed door de lichtafhankelijke reacties, gaat overdag door. Op deze manier scheiden CAM-planten koolstoffixatie en suikersynthese op verschillende tijdstippen van de dag.

C4-traject en CAM

Most plants use the C3 pathway for carbon fixation. However, some plants, such as sugar cane, corn, and cacti that grow in hot conditions, use alternative ...

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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 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.

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Plant Carbon Fixation in Hot Climates

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