Introductory Crop Physiology (1+1)

Structural peculiarities of C4 plants

Structural Peculiarities of C₄ Plants

1. Presence of bundle sheath cells containing chloroplasts.
2. Bundle sheath cells are radially arranged around a vascular bundle.
3. Bundle sheath cells lack grana in their chloroplasts.
4. Bundle sheath cells are arranged in one or more layers consisting of large thick walled cylindrical cells, around vascular bundle, a characteristic feature of C₄ plants.
5. Bundle sheath cells remain surrounded by one or more wreath like layers of mesophyll cells. This anatomical arrangement is called as Kranz type (Kranz=wreath, a German term). (Kranz: Wreath of mesophyll cells around bundle sheath cells)
6. Mesophyll cells have well-developed grana. (Thus, C₄ pathway constitutes an example of dimorphism of chloroplasts) But, some C₄ plants (bermuda grass) have grana in chloroplasts of bundle sheath cells).
7. The ratio of PS I: PS II activity is three times higher than the bundle sheath cells.
8. The mesophyll cells are almost three times more active in non-cyclic electron transport system than that of bundle sheath cells.
9. For cyclic electron transport, both the cells are equally efficient.
10. Clear cut categorization of enzymes is found in C₄ cycle.


Most of the PEP carbocylase occurs in mesophyll cells. While most of ribulose- 1,5-diphosphate carboxylase and malic enzymes are found in bundle sheath cells. The C₄ cycle is also referred as the dicarboxylic acid cycle or the Carboxylation pathway or Hatch-Slack cycle or Co-operative Photosynthesis (Karpilov, 1970). In this Cycle, the characteristic point is the primary carboxylation reaction and the phosphoenolpyruvate (PEP) is found to be CO2 acceptor molecule.

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