DISTRIBUTION OF ENDOGENOUS GIBBERELLINS IN VEGETATIVE SHOOTS OF RICE

Levels of endogenous gibberellins in rice seedlings (Oryza sativa L., cv. Nipponbare) were compared between young and old leaves at the 4- and 5-leaf stages. The levels of GA(1), GA(19) and GA(53) were higher in the youngest leaf than in older leaves at the 5-leaf stage, but they did not differ significantly between the leaf sheath and the leaf blade. At the 4-leaf stage, the level of GA(1) was highest in the third leaf sheaths which contained young elongating tissues. These results indicate that gibberellins are synthesized in young vegetative tissues to promote their elongation growth. The levels of GA(1) in the youngest leaf sheaths of two cultivars of dwarf rice, Tan-ginbozu and Waito-C, were approximately 10% of that in the normal rice at the 5-leaf stage. This result could explain the retardation of shoot elongation in these dwarf cultivars.