What is Kranz Anatomy?
The word Kranz means “burden” or “ring”. Kranz anatomy is a peculiar structure in C4 Plants where the mesophyll cells are arranged in a ring-like pattern around the cells of the group mantle The number of chloroplasts in the cells of the group mantle is higher than in the mesophyll cells. This is seen in C4 grasses such as maize and in some dicots.
Kranz Anatomy in C4 Plants
Light-dependent cycles and the Calvin cycle are distinguished in C4 plants. The Calvin cycle occurs in bundle sheath cells and light-dependent structures occur in mesophyll cells.
Atmospheric oxygen is first metabolized to form the 4-carbon compound oxaloacetate in mesophyll cells, which is catalyzed by PEP carboxylase.
Oxaloacetate is converted to malate which is transported in bundle sheath cells. Malate is broken down in the bundle sheath cells, releasing carbon dioxide.
Rubisco fixes carbon dioxide into sugar. The mesophyll cells constantly push carbon dioxide into the cells of the cluster cortex, and the amount of carbon dioxide around Rubisco is always high. This reduces light absorption.
In most plants, carbon dioxide is fixed as a 3-carbon compound by the action of ribulose bisphosphate carboxylase oxygenase (Rubisco).
Rubisco can also catalyze a reaction with oxygen resulting in a wasteful process known as photorespiration. To eliminate this, the C4 pathway fixes atmospheric carbon dioxide by an enzyme called phosphoenolpyruvate carboxylase. Carbon dioxide is then released to recombine Rubisco.
In C4 grasses such as maize, the mesophyll cells surround the bundle cortex cells, and the bundle cortex cells surround the vein.
