Phytochrome Regulation of Biochemical and Enzymatic Changes During Senescence of Excised Rice Leaves

Abstract

The effect of brief irradiation with red and/or far-red light in regulating the senescence of excised rice ( Oryza sativa L. cv. Ratna) leaves was studied. Red light was effective in arresting the loss of chlorophyll and protein and the gain of α-amino nitrogen. Total soluble sugar and non-reducing sugar content decreased during the senescence of leaves kept in continuous darkness (control) whereas reducing sugar content initially increased and subsequently decreased. Red light was also effective in arresting the loss of decreasing total soluble sugar and non-reducing sugar levels and rise in the reducing sugar levels. Decrease in the catalase and alkaline PPase activities and increase in the peroxidase and acid PPase activities was arrested by red light irradiation during excised leaf senescence. On the other hand, a brief irradiation with far-red light accelerated the senescence process by exhibiting the reverse effect as compared to red light irradiation. The effect of red light was almost nullified by a consecutive brief irradiation with far-red light. The results suggest that the enhanced biochemical and enzymatic changes during rice leaf senescence by far-red light and their retardation by red light is presumably mediated by the phytochrome system.