Characteristic Features of CAM plants
- The stomata remain closed during the day (light) and open at night (dark).
- CO2 fixation takes place in chlorophyll-containing cells of leaves and stems during night
(dark) and malic acid synthesis takes place.
- Malic acid formed during the dark (night) is stored in large vacuoles.
- During the day time, decarboxylation of malic acid takes place and CO2 gas is released.
This CO2 is converted into sucrose and storage glucans (e.g. Starch) by C3-cycle.
Thus, CAM plants show the diurnal cycle of organic acid formation i.e. they fix atmospheric CO2 during the night by CAM and fix internally borne CO2 by C3-cycle during day time.
It is completed in the following two parts:
1 Acidification and 2. Deacidification
- Acidification: Acidification takes place during the following steps:
(i) The stored carbohydrates are converted into phosphoenol pyruvic acid (PEP) through glycolysis. As the stomata open during nthe ight, the CO2 diffuses freely into the leaf through open stomata at night.
(ii) The CO2 combines with PEP in the presence of phosphoenol–carboxylase (PEP-C) enzyme to produce oxaloacetic acid (OAA).
(iii) The oxaloacetic acid (OAA) is not reduced into MALIC ACID in the presence of malic dehydrogenase enzymes.This reaction is facilitated by the n presence of reduced NADP+ ( =NADPH + H+) formed during glycolysis. This malic acid, thus produced in the dark as a result of acidification is stored in the vacuoles. The oxaloacetic acid (OAA) may also be interconverted into aspartic acid
2. Deacidification: The decarboxylation of malic acid into pyruvic acid and CO2 in the presence of light is called deacidification.
CO2 liberated is fixed by the C3 cycle on coming next night this starch is converted into PEP, and is thus ready to accept atmospheric.
