Characteristic Features of C4 plants :
- C4 plants are usually found in tropical regions where the temperature is between 30-35ºC and light intensity is very high.
- Photorespiration does not take place in C4 plants or the rate of photorespiration is very low.
- C4 plants have a high photosynthetic rate (40-80 mg CO2 per hour) whereas the rate of photosynthesis in C3 plants is 10-15 mg CO2 per hour.
- The leaves of C4 plants exhibit specific histological structures. The vascular bundle (V.B.) of leaves of C4 plants is bounded by bundle sheath cells. The cells of the bundle sheath are bounded by mesophyll cells. Bundle sheath cells have different types of chloroplasts. This type of anatomical structure is known as Kranz’s anatomy.
- Leaves of C4 plants contain two types (of dimorphic) chloroplast :
(i) Mesophyll Chloroplast: It is smaller grana is present there and starch grains are absent
(ii) Bundle sheath Chloroplast: It is larger lacking grana and possessing starch grains.
Malic acid and aspartic acid are formed from pyruvic acid within mesophyll
(i) Ribulose diphosphate carboxylase or Rubisc: This enzyme is found within the chloroplast of bundle sheath cells. It catalyzes the oxidative decarboxylation of malic acid to produce pyruvic acid and reduces the CO2 to the C3 cycle.
(ii) Phosphoenol pyruvic carboxylase (PEP-C): This enzyme is found in the chloroplast of mesophyll cells and it reduces atmospheric CO2 by the C4 cycle.
- There are two pathways of CO2 fixation in C4 plants.
(i) C4-cycle ( takes place in mesophyll cells) and
(ii) C3-cycle ( takes place in bundle sheath cells)
