In C4 plants, Calvin cycle operates ina)stroma of bundle sheath chlor...
The C4 plants have a characteristic leaf anatomy called kranz anatomy. Here two types of chloroplasts are present - bundle sheath chloroplasts and mesophyll chloroplasts. In C4 plants, there are two carboxylation reactions which occur first in mesophyll chloroplasts and then in bundle sheath chloroplasts. CO2 acceptor molecule in mesophyll chloroplasts is PEP (Phospho-enol pyruvate) and not Ribulose 1 , 5-biphosphate. Further it has enzyme PEPcarboxylase for initial CO2 fixation. RuBP carboxylase is absent in mesophyll chloroplasts but is present in bundle sheath chloroplasts. The first product formed is oxaloacetic acid and hence it is known as C4 cycle. Bundle sheath cells fix CO2 through C3 cycle.
In C4 plants, Calvin cycle operates ina)stroma of bundle sheath chlor...
Understanding C4 Plants and the Calvin Cycle
C4 plants have a specialized mechanism for photosynthesis that allows them to efficiently capture carbon dioxide and minimize water loss.
Location of the Calvin Cycle
- The Calvin cycle in C4 plants occurs in the stroma of bundle sheath chloroplasts.
- This unique location is crucial because the bundle sheath cells are protected from oxygen, which can inhibit the Calvin cycle due to photorespiration.
Structure of Chloroplasts
- Bundle Sheath Chloroplasts: These contain the enzymes necessary for the Calvin cycle.
- Mesophyll Chloroplasts: While the initial fixation of CO2 occurs here, the subsequent steps of the Calvin cycle take place in the bundle sheath cells.
Advantages of C4 Pathway
- C4 plants, such as maize and sugarcane, have evolved to thrive in hot and dry environments.
- The C4 pathway minimizes photorespiration, allowing for higher efficiency in photosynthesis compared to C3 plants.
Process Overview
- CO2 is initially fixed into a 4-carbon compound in the mesophyll cells.
- This compound is then transported to the bundle sheath cells, where it is converted back into CO2, subsequently entering the Calvin cycle in the stroma.
Conclusion
- Understanding the location of the Calvin cycle in C4 plants is essential for appreciating their adaptation to specific environments.
- The stroma of bundle sheath chloroplasts is integral for reducing photorespiration and enhancing photosynthetic efficiency.