Remobilization of Nitrogen in Senescing Leaves

Although the contribution of remobilized nitrogen to the formation of new tissues might differ depending on the type of organs, nutritional status of nitrogen, plant species etc., reutilization of the remobilized nitrogen can be seen all the time throughout the life span of the plant. In field-grown rice, about 80% of the ear nitrogen is derived from the remobilized nitrogen from vegetative organs (Mae, 1997), and about 60% of the remobilized nitrogen is originated from the leaf blades (Mae and Ohira, 1981). The reutilization of remobilized nitrogen by the plant includes several steps: (1) degradation of the macromolecules into small molecules in source cells; (2) interconversion of the small molecules to transportable forms; (3) transport from source cells to sink cells mainly via phloem; (4) conversion of the transported compounds to available forms and their utilization in sink tissues. Here, interconversion of nitrogenous compounds during senescence, especially in preparation for transport or storage in leaf tissues, is described.

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