Kranz Anatomy

Kranz Anatomy - Definition 

Kranz anatomy refers to a specialized anatomical structure found in the leaves of certain plants, particularly in C4 plants. The term "kranz" is derived from the German word for "wreath" or "garland," which describes the arrangement of cells in a circular or concentric pattern.

• In plants with kranz anatomy, the leaf structure is characterized by two distinct types of photosynthetic cells: bundle sheath cells and mesophyll cells. The bundle sheath cells are arranged in a ring or concentric layers surrounding the veins, while the mesophyll cells are located between the bundle sheath cells and the leaf surface.

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Primary Functions of Kranz Anatomy 

The primary functions of kranz anatomy in plants are as follows:

Increased Photosynthetic Efficiency

Kranz anatomy enhances photosynthesis in C4 plants by spatially separating carbon fixation and the Calvin cycle, leading to more efficient carbon dioxide utilization.

Minimization of Photorespiration

Kranz anatomy reduces photorespiration by segregating carbon dioxide-rich bundle sheath cells from oxygen-rich mesophyll cells, optimizing carbon assimilation.

Concentration of Carbon Dioxide

The arrangement of bundle sheath cells creates a carbon dioxide-rich microenvironment, facilitating efficient carbon fixation by Rubisco.

Water Use Efficiency

Kranz anatomy reduces water loss through transpiration by spatially separating photosynthetic cells and minimizing exposure to the atmosphere.

Adaptation to High Light and Temperature

Kranz anatomy enables C4 plants to thrive in high light and temperature conditions by optimizing photosynthesis and minimizing the detrimental effects of photorespiration.

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Kranz Anatomy Diagram

The Kranz anatomy is characteristic of C₄ plants. In these plants, the leaves exhibit vascular bundles that are surrounded by both bundle sheath cells and mesophyll cells. The bundle sheath cells are tubular in shape and have thick cell walls. Within the bundle sheath cells, the chloroplasts are larger in size and do not possess grana, whereas the chloroplasts in the mesophyll cells are fewer and contain grana.

Stages of Kranz Anatomy 

The following are the stages of kranz anatomy in plants:

1. Leaf Differentiation: Specialized leaf tissues develop with distinct regions of bundle sheath cells and mesophyll cells.
2. Spatial Arrangement: Bundle sheath cells form concentric layers around leaf veins, while mesophyll cells are located between bundle sheath cells and leaf surface.
3. Carbon Fixation: Carbon dioxide is first fixed into a four-carbon compound in mesophyll cells using the C4 pathway and PEP carboxylase.
4. Bundle Sheath Barrier: Bundle sheath cells limit carbon dioxide diffusion, creating a concentrated CO2 environment for subsequent Calvin cycle reactions.
5. Calvin Cycle: Four-carbon compounds are decarboxylated in bundle sheath cells, releasing carbon dioxide for the Calvin cycle and sugar production.
6. Water Conservation: Spatial separation of cells reduces water loss through transpiration.

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Advantages of Kranz Anatomy 

Kranz anatomy provides a significant advantage as it enhances a plant's ability to efficiently produce its own food. It involves specialized cells surrounding the veins in leaves, optimizing light absorption and enabling increased production of sugar and oxygen for the plant's use.

Characteristics of Kranz Anamotmy

The following are the characteristics of kranz anatomy in plants:

• Circular Arrangement: Bundle sheath cells are arranged in a circular pattern around leaf veins.
• Spatial Separation: Bundle sheath cells create a barrier, separating them from mesophyll cells and optimizing carbon dioxide concentration.
• Enhanced Efficiency: Kranz anatomy minimizes photorespiration and increases photosynthetic efficiency in high light and temperature conditions.

C3 Plants

C3 plants are photosynthetic plants that fix carbon through the C3 pathway. The first product of carbon dioxide fixation in C3 plants is a three-carbon compound known as 3-phosphoglycerate (3-PGA). C3 plants include the vast majority of plant species, including most crops and many trees.

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C4 Plants 

C4 plants are photosynthetic plants that fix carbon via the C4 pathway. The first product of carbon dioxide fixation in C4 plants is a four-carbon compound known as oxaloacetate or malate. This pathway enables C4 plants to capture and concentrate carbon dioxide more efficiently, reducing photorespiration and increasing their ability to thrive in high light and temperature conditions. Examples of C4 plants include maize, sugarcane, and certain grasses.

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Difference between C3 & C4 Plants 

The following table summarizes the differences between C3 and C4 plants: