This document discusses C4 plants and their mechanism for carbon fixation. C4 plants have evolved a mechanism to fix carbon more efficiently than C3 plants in conditions like drought, heat, and low CO2/nitrogen levels. They concentrate CO2 around rubisco via a kranz anatomy structure to avoid photorespiration. The C4 mechanism involves converting phosphoenolpyruvate to oxaloacetate, then malate, transporting malate to bundle sheath cells where it is converted back to CO2 and pyruvate, regenerating phosphoenolpyruvate in a cyclic pathway. Major C4 plants include maize, sugarcane, millet, sorghum, and certain

1. Authors:
 Muhammad Hussaan (M.Phil. Botany + PhD Scholar)
 Arifa Feroz (MSc Botany + M. Phil Scholor)
 Aniqa Rasheed

2. C4 Plant:
 The plant whose first product of photosynthesis
is 4 carbon compound is called C4 plant.

3. Why plant use C4 mechanism ?
 Some plants which live in drought, at high
temperature and nitrogen and co2 limitation
environment. They use c4 mechanism.
 Because C4 plant fix more co2 as compare to
the C3 plant due to having kranz anatomy.
 C4 plant lose 277 molecules of water to fix per
molecules of co2 as compared to c3 use 833
molecules of water approximately at 30 c.
 They also avoid photorespiration process.

4. Why plant use C4 mechanism
?
 C4 enzyme fix carbon more efficiently as
compared to c3 plant who fix also oxygen
during carbon fixation process.
 Fixation of oxygen start the process of
photorespiration instead of carboxylation of
substrate, substrate oxidized and as a result
loss and start the process of
photorespiration.
 This process occur due to dual activity of
rubissco present in c3 plant such as
oxygenase and carboxylase activity.

5. Kranz anatomy:
 Their vascular bundles are surrounded by two
rings of cells
 Inner ring
contain bundle sheat cells (bundle sheat cells
contain starch rich chloroplast lacking grana.
 Outer ring contain
Mesophyll cells

6. Advantages of Kranz anatomy:
 Main function of kranz anatomy to provide a
site in which co2 concentrated around rubisco
and avoiding photorespiration mechanism.

7. Mechanism:
First step:
 Conversion of (PEP) into oxaloacetic acid
 In this step co2 react with phosphoenol pyruvic
acid to form oxaloacetic acid.
 This reaction take place in the presence of
enzyme phosphoenol pyruvate corboxylase.

8. Mechanism:
2ND Step:
Conversion of OAA into Malate:
 Oxaloacetic acid is converted into malate.
 This reaction is catalyzed by malate
dehydrogenase.

9. Mechanism:
3rd step:
 Conversion of malate into pyruvic acid:
 Malate is transported into bundle sheat cell. In
bundle sheat cell it is converted into pyruvic
acid by releasing Co2.

10. Mechanism:
4th step:
 Conversion of pyruvic acid into PEP:
 Pyruvic acid react with ATP and regenerate
phosphoenol pyruvate.
 This reaction take place in the presence of
pyruvate orthophosphate dikinase.

11. C4 mechanism

12. C4 mechanism:

13. C4 Plants
 Maize
 Sugarcane
 Millet
 Sorghum
 Grass species