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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C4 Pathway and CAM

Niektóre rośliny, które rosną w bardzo gorącym środowisku, wyewoluowały strategie radzenia sobie z utratą wody i skutecznego wiązania węgla.
Dwa przykłady to rośliny kukurydzy, które wykorzystują szlakC4 i kaktusy, które wykorzystują metabolizm kwasu gruboszowego lub szlak CAM.
W roślinach C4 wiązanie węgla zachodzi w komórkach mezofilu. Enzym karboksylaza PEP łączy dwutlenek węgla z fosfoenolopirogronianem, tworząc szczawiooctan. 
Szczawiooctan jest następnie enzymatycznie przekształcany w jabłczan lub inny kwas organiczny. Następnie te kwasy organiczne są transportowane do komórek osłonki pęczka Hisa w celu rozbicia na CO2 i pirogronian. CO2 wchodzi w cykl Calvina, a pirogronian uzupełnia PEP.
W przeciwieństwie do elektrowniC4, w których wiązanie CO2 i cykl Calvina są oddzielone w przestrzeni, instalacje CAM rozdzielają te dwa etapy w czasie. Rośliny CAM otwierają aparaty szparkowe do poboru CO2 tylko w nocy, aby zapobiec utracie wody.
Węgiel jest wiązany w cząsteczce jabłczanu i przechowywany w wakuolach komórek mezofilu do światła dziennego. CO2 jest uwalniany w ciągu dnia, a cykl Calvina przebiega wraz z reakcjami świetlnymi.

<ol>
	<li>Edwards, E.J. Trajektorie ewolucyjne, dostępność i inne metafory: przypadek fotosyntezy C4 i CAM. Nowy fitolog. 223 (4), 1742-1755 (2019).</li>
</ol>

Ścieżka c4 i cam

Większość roślin wykorzystuje szlak C3 do wiązania węgla. Jednak niektóre rośliny, takie jak trzcina cukrowa, kukurydza i kaktusy, które rosną w gorących warunkach, wykorzystują alternatywne ścieżki wiązania węgla i oszczędzania strat energii w wyniku fotooddychania. Fotooddychanie to proces zachodzący przy wysokim stężeniu tlenu. W takich warunkach enzym rubisco w cyklu Calvina wiąże O2 zamiast CO2, co wstrzymuje fotosyntezę i zużywa energię.

Ścieżka C4

Szlak C4 jest wykorzystywany przez rośliny takie jak kukurydza i trzcina cukrowa. W pierwszym etapie CO2 dostaje się do komórek mezofilu, a enzym karboksylaza fosfoenolopirogronianowa (karboksylaza PEP) dodaje go do 3-węglowego związku PEP, tworząc 4-węglowy szczawiooctan. Szczawiooctan przekształca się następnie w kwasy organiczne, głównie jabłczan. Jabłczan jest następnie transportowany do komórek pochewki pęczka w głąb liścia, gdzie stężenie tlenu jest niskie. To tutaj jabłczan ulega rozkładowi z uwolnieniem cząsteczki CO2. Następnie CO2 wchodzi w cykl Calvina i przekształca się w cukier za pomocą enzymu RuBisCo.

W gorących i suchych warunkach fizyczne oddzielenie wiązania węgla od cyklu Calvina jest korzystne, ponieważ rośliny mogą zamykać aparaty szparkowe, aby oszczędzać wodę. W rezultacie mogą utrzymywać niskie stężenie tlenu i dlatego sprzyjają wiązaniu CO2 z RuBisCo, a nie z O2.

Ścieżka CAM

Inne rośliny, takie jak kaktusy i ananasy, wykorzystują szlak metabolizmu kwasu gruboszowego (CAM) do wiązania węgla. Rośliny CAM otwierają swoje aparaty szparkowe w nocy, aby zapobiec utracie wody w upalne dni. Gdy CO2 dostanie się do komórek mezofilu, łączy się z PEP, tworząc szczawiooctan i ostatecznie jabłczan.

Jabłczan jest następnie przechowywany w wakuolach do następnego dnia, kiedy to zostaje uwolniony i wchodzi w cykl Calvina. Zatem wiązanie węgla następuje w nocy, a cykl Calvina, napędzany reakcjami zależnymi od światła, przebiega w ciągu dnia. W ten sposób rośliny CAM oddzielają wiązanie węgla i syntezę cukru w różnych porach dnia.

Ścieżka C4 i CAM

Większość roślin wykorzystuje szlak C3 do wiązania węgla. Jednak niektóre rośliny, takie jak trzcina cukrowa, kukurydza i kaktusy, które rosną w gorących warunkach, używają alternatywnych ...

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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

what is photosynthesis?

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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anatomy of chloroplasts

Chloroplasts and Photosynthesis in Plant Cells

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

Photosystem I and NADPH Formation

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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