Crassulacean Acid Metabolism or
CAM cycle
It is one
of the carbon pathways identified in succulent plants growing in semi-arid or
xerophytic condition. This was first observed in crassulaceae family plants
like Bryophyllum, Sedum, Kalanchoe and is
the reason behind the name of this
cycle. It is also noticed in plants from other families Examples: Agave, Opuntia, Pineapple and Orchids. The stomata are closed during day
and are open during night (Scotoactive). This reverse stomatal rhythm helps to
conserve water loss through transpiration and will stop the fixation of CO2
during the day time. At night time CAM plants fix CO2
Subsequently OAA is converted into malic acid like C4 cycle and gets accumulated in vacuole
increasing the acidity. During the day time stomata are closed and malic acid
is decarboxylated into pyruvic acid resulting in the decrease of acidity. CO2
thus formed enters into
Calvin Cycle and
produces carbohydrates (Figure13.21).
1. It is advantageous for succulent plants to obtain CO2 from malic acid when stomata are closed.
2. During day time stomata are closed and CO2 is not taken but continue
3. Stomata are closed during the day time and help the plants to avoid transpiration and water loss.
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