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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Environmental Science

Earth’s Systems

HS-ESS2-6

C4 Pathway and CAM

- [Anlatıcı] Mısır gibi bazı bitkiler sıcak kuru ortamlarda daha verimli karbon bağlamak için alternatif yollar geliştirmiştir.
 Biri C4 yoludur.
 İlk karbon bağlama adımında karbondioksit CO2 mezofil hücrelerine girer ve PEP karboksilaz enzimi sayesinde dört karbonlu bileşik oksaloasetatı oluşturmak için üç karbonlu bileşik PEP ile birleşir, daha sonra genellikle başka bir organik aside çevrilir, bu örnekte bu asit malik asittir.
Malik asit, oksijenin sınırlı olduğu, parçalanıp CO2 salınan yaprak derinlerindeki demet kını hücrelerine taşınır, bu CO2 Calvin döngüsüne girerek RuBisCo ile buluşur ve şeker üretir.
 Ananas gibi bazı bitkiler krassulasean asit metabolizmasını yani CAM yolunu kullanarak karbon bağlar.
 CAM bitkileri gündüz su kaybını önlemek için stomalarını sadece gece açarlar.
C4 yoluna benzer olarak CO2 öncelikle PEP karbosiklaz tarafından oksaloasetata bağlanır, sonra malik aside çevrilir.
 Malik asidi yaprağın başka bir kısmına taşımak yerine CAM bitkileri bu bileşiği mezofil hücresi kofullarında depolar ve gündüz salarlar, böylece Calvin döngüsü fotosentezdeki ışık reaksiyonlarıyla birlikte sürdürülebilir.

<ol>
	<li>Edwards, E.J. Evrimsel yörüngeler, erişilebilirlik ve diğer metaforlar: C4 ve CAM fotosentezi örneği. Yeni Fitolog. 223 (4), 1742-1755 (2019).</li>
</ol>

c4 yolağı ve cam

<h4>Genel Bakış</h4>

Sıcak koşullarda yetişen şeker kamışı ve mısır gibi bazı bitkiler, karbonu düzeltmek için C4 yolu adı verilen alternatif bir işlem kullanır. Döngü, fosfoenolpiruvattan (PEP) oksaloasetat-dört karbonlu bir molekül-üretmek için kullanılan mezofil hücrelerine giren atmosferden CO2 ile başlar. Oksaloasetat daha sonra malat haline dönüştürülür ve oksijen konsantrasyonunun düşük olduğu kılıf hücrelerine taşınır. Orada, CO2 malattan salınır ve şekerlere dönüştürüldüğü Calvin döngüsüne girer. CAM yolu, gün boyunca su tasarrufu yapması gereken kaktüsler gibi bitkilerde gerçekleştirilir. CAM bitkileri, CO2 ‘i gece yapraklara bırakır ve ertesi güne kadar vakuollerde saklanan malat üretir. Malat daha sonra vakuollerden salınır ve Calvin döngüsünde işlenir. C4 yolu farklı süreçleri yerel olarak ayırırken, CAM yolu bunları kronolojik olarak ayırır.

<h4>C4 Yolağı</h4>

Mısır ve şeker kamışı gibi bazı bitkiler, sıcak ve kuru ortamlarda su kaybını önlemeye yardımcı olan karbonu düzeltmek için alternatif yollar geliştirmiştir. Böyle bir yöntem C4 yolağıdır. İlk aşamada, CO2 mezofil hücrelerine girer ve enzim fosfoenolpiruvat (PEP) karboksilaz, 4-karbon bileşiği oksaloasetatı oluşturmak için 3-karbon bileşiği PEP’e ekler. Oksaloasetat daha sonra malat adı verilen organik bir aside dönüştürülür.

Daha sonra, malat, oksijen konsantrasyonunun düşük olduğu yaprağın derinliklerinde demet kılıf hücrelerine taşınır. Malat, daha sonra rubisco enziminin şekere dönüştürdüğü Calvin döngüsüne giren bir CO2 molekülünü serbest bırakarak parçalanır. C4 yolu, bitkiler su tasarrufu için stomalarını kapatacakları için sıcak, kurak koşullarda bir avantaj sağlar. Sonuç olarak, oksijen konsantrasyonunu düşük tutabilirler ve bu nedenle CO2 ' un O2 yerine rubisco'ya bağlanmasını tercih edebilirler. Oksijen konsantrasyonu  daha yüksek olduğunda, rubisco bağlar O2 yerine CO2— bir süreç denilen fotorespiration— hangi fotosentez durdurmak ve enerji tüketir.

<h4>CAM Yolağı</h4>

Kaktüsler ve ananas gibi diğer bitkiler, karbonu sabitlemek için crassulacean asit metabolizması (CAM) yolağını kullanır. CAM bitkileri öncelikle sıcak bir günde su kaybını önlemek için geceleri stomalarını açar. Geceleri CO2 mezofil hücrelerine girer, burada oksaloasetat ve sonunda malat oluşturmak için PEP ile birleşir. Malat daha sonra vakuollerden salındığı ve Calvin döngüsüne girdiği ertesi güne kadar vakuollerde saklanır. Fotosentezin ilk aşamaları, ışığa bağımlı oldukları için gün boyunca ilerlerken, Calvin döngüsünün ışıktan bağımsız reaksiyonları gece boyunca gerçekleşir. Bu şekilde, CAM bitkileri günün farklı zamanlarını kullanarak CO2 fiksasyonunu ve şeker sentezini ayırır.

C4 Yolağı ve CAM

Çoğu bitki, karbon fiksasyonu için C3 yolunu kullanır. Bununla birlikte, sıcak koşullarda yetişen şeker kamışı, mısır ve kaktüsler gibi bazı bitkiler alternatif kullanır ...

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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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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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