Kranz anatomy is a specialized structural adaptation in C4 plants where mesophyll cells are arranged in a ring-like fashion around bundle sheath cells.
Understanding Kranz Anatomy
The term "Kranz" means "wreath" in German, aptly describing this ring-like arrangement. This unique anatomical structure is crucial for the C4 photosynthetic pathway, enabling these plants to thrive in hot and arid environments. The main features of Kranz anatomy include:
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Mesophyll Cells: These cells are arranged in a circle around the bundle sheath cells. They primarily fix CO2 initially using PEP carboxylase, which has a higher affinity for CO2 than RuBisCO (the enzyme used in the C3 pathway).
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Bundle Sheath Cells: These cells surround the vascular bundles (xylem and phloem) and are densely packed with chloroplasts. These chloroplasts are often larger and have reduced grana compared to those in mesophyll cells. The CO2 fixed in the mesophyll cells is then released into the bundle sheath cells, where it is refixed by RuBisCO in the Calvin cycle.
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Dimorphic Chloroplasts: In many C4 plants, the chloroplasts in the bundle sheath cells are different from those in the mesophyll cells. Bundle sheath chloroplasts often have reduced grana (thylakoid stacks) and are primarily involved in the Calvin cycle.
Significance of Kranz Anatomy
Kranz anatomy facilitates the C4 photosynthetic pathway, offering several advantages:
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Increased CO2 Concentration: By concentrating CO2 in the bundle sheath cells, Kranz anatomy minimizes photorespiration, a wasteful process that occurs when RuBisCO binds to oxygen instead of carbon dioxide.
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Enhanced Photosynthetic Efficiency: This allows C4 plants to maintain high photosynthetic rates even when stomata are partially closed to conserve water in hot, dry environments.
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Adaptation to Harsh Environments: C4 plants with Kranz anatomy are well-adapted to environments with high temperatures, low water availability, and limited CO2.
Examples of C4 Plants
Many important agricultural crops and grasses exhibit Kranz anatomy and utilize the C4 photosynthetic pathway, including:
- Corn (Maize)
- Sugarcane
- Sorghum
- Various grasses (e.g., Bermuda grass)
