Tag: cam plants

Certain plants which have Crassulacean Acid metabolism (CAM) are known as CAM plants. They have scotoactive stomata. Their stomata remain open during night. It is characteristic feature of CAM plants. These plants fix carbon dioxide during night but form sugars only during day when RuBisCO is active. Sedum, Kalanchoe, Pineapple, Opuntia are the examples of CAM plants. These plants also perform double carbon dioxide fixation. The carbon dioxide acceptor in CAM plants is Phosphoenol pyruvic acid (PEP) during night and Ribulose bisphosphate is carbon dioxide acceptor during day time. The first stable product in case of CAM plants is Oxalo acetic acid (OAA).

CAM plants are usually the succulents (eg : cacti, agave) as they are efficient at storing water due to the climates they live in i.e., dry and arid. The leaves of succulent plants are thick, contains moisture and have a coat of wax to reduce evaporation. During the day, the plants close their stoma to prevent the loss of water and open it at night to absorb the carbon dioxide from the surrounding atmosphere. The carbon dioxide is later converted into malate, which is used in the process of photosynthesis (via the calvin cycle) when the daylight returns.

In CAM plants, photophosphorylation occurs in bundle sheath cell during night. Hence, stomata is open during night in order to fix the carbon dioxide. During night, a four carbon acid is produced when stomata are open. RuBisCo enzyme fixes carbon during the day time during the light reactions. Examples of plants that show CAM photosynthesis are cactus and pineapple.

CAM (Crassulacean Acid Metabolism) photosynthesis is found in most desert plants, particularly the succulents (plants that store water in thick, fleshy leaves). CAM plants keep their stomata closed during the day to conserve water. At night, the stomata open to allow CO$ _{2}$ to enter. CO$ _{2}$ is incorporated into organic acids which are then stored within the mesophyll cells. During the day, CO$ _{2}$ is released from the organic acids to supply the Calvin Cycle. Thus, CAM photosynthesis occurs in fleshy green leaves and not in thin green leaves with reticulated venation or Thin green leaves with parallel or thin colored leaves. Thus, option C is correct and other options are incorrect.

Phosphoenol pyruvate is formed from the decarboxylation of oxloacetate and hydrolysis of one guanosine triphosphate molecule. This reaction is catalyzed by the enzyme phosphoenolpyruvate carboxylase. This reaction is a rate limiting step in gluconeogenesis.

GTP + Oxaloacetate -----> GDP + Phosphoenolpyruvate + $CO _2$.

Certain plants especially succulents which grow under extremely xerophytic conditions, fix atmospheric carbon dioxide in the dark. Since the process was first observed in the plants belonging to family Crassulaceae such as Bryophyllum, Kalanchoe, Sedum etc., it was termed crassulacean acid metabolism (CAM). Such plants are known as CAM plants. The most characteristic feature of these plants is that their stomata remain open at night but closed during the day. Thus, CAM is a kind of adaptation in succulents to carry out photosynthesis without much loss of water. This helps in conserving water in these plants. 

CAM plants are mainly succulent xerophytes. Besides C3 and C4 cycles, Crassulacean acid metabolism is a third mechanism for fixing carbon dioxide. It is found not only in members of the family Crassulaceae eg., Kalanchoe, Sedum, Crassula, but also in the members of family Cactaceae example Opuntia. Besides it also occurs in some members of Liliaceae, Orchidaceae, Bromeliaceae, Euphorbia sp and pteridophytes like Isoetes. In CAM plants the stomata are open at night and during day time the stomata remain close.

CAM photosynthesis is a carbon fixation pathway present in some plants, such as desert plants. These plants fix carbon dioxide during night, storing it as the four carbon acid malate. The malate is then reduced to a three carbon compound oxaloacetate and the carbon dioxide. This carbon dioxide is released during the day, where it is concentrated around the enzyme RuBP carboxylase and increases the efficiency of photosynthesis. The carboxylating enzyme used during day is RuBP carboxylase and during the night its PEP carboxylase.

Answer is option C.

In CAM plants there is temporal separation between initial carbon dioxide fixation and Calvin cycle. In these plants, during night time the stomata are open and atmospheric carbon dioxide is fixed into organic acids like malic acid. The organic acids are stored in cell vacuoles during night time. During day time the stomata are closed and organic acids are decarboxylated to release carbon dioxide. The released carbon dioxide is fixed by the RuBisCO and usual reactions of the Calvin cycle.

• Kranz anatomy is a special structure of leaves in C4 PLANTS e.g. maize, sugarcane, sorghum, and millets.
  
• Mustard and Spinach belongs to C3 plants.
  
• Tulip is an example of a CAM plant.