Internode Elongation of Rice Plant : IV. Effects of gibberellic acid at different stages of growth on the elongation of internode.

Abstract

To see the changes in the internode growth with ageing, the rice plants (Oryza sativa L.) at different stages of growth were applied with the various concentrations of gibberellic acid (GA₃) at 0, 0.1, 10, and 1000 ppm by foliar spray. 1. During vegetative growth stage, the (n+2)-th internode was initially induced to elongate with the high level of GA₃ (1000 ppm) application to the plant of the (n)-th leaf stage, but after the young panicle formation the (n)-th interned initially elongated. 2. The low level of GA₃ (10 ppm) application to the plant of the (n)-th leaf stage elongated the (n)-th internode after the young panicle was initiated, but failed to stimulate the internode growth during vegetative growth stage. 3. when high concentration of GA₃ was applied to the plant before the 8.6th leaf stage, the 10th internode elongated very much being caused by high rate of cell division and cell elongation in the longitudinal direction of the internode. After the 8.6th leaf stage, however, GA₃ failed to stimulate the elongation of the 10th internode. These results may suggest that GA₃ acts as a trigger for the metabolic activity involved in the cell division and cell elongation or the internode which is ordinarily enhanced with panicle initiation, and the critical response of the internode to GA₃ depends on the specific status of the meristem of the internode at the time of GA₃ application.