Abstract
We examined the changes of the endogenous ethylene levels in the leaf sheaths and the panicle in the life cycle of rice plants. The ethylene concentrations in the gas air squeezed from the leaf sheaths ranged from 12 nl/l to 22 nl/l in the active-tillering stage. Then, the ethylene was decreased to the concentrations of 6 nl/l-8nl/l in the early panicle formation stage. A peak of ethylene concentration in the leaf sheath was observed at the heading and anthesis stage. At this stage the ethylene concentrations were 16 nl/l to 18 nl/l. Ethylene was hardly detected in the leaf sheaths 14 days after heading. The tendencies mentioned above were observed in the fluctuation profiles of the ethylene contents per leaf sheath and also in the fluctuations of the ethylene content per 1g fresh weight of leaf sheath. During vegetative growth stage, ethylene concentration was higher in the older leaf sheath (the fourth leaf sheath from the uppermost leaf unfolded) than in the younger one, although this tendency was not observed during the reproductive growth stage. In the panicle, ethylene level was remarkably higher than that in the leaf sheaths. The ethylene concentration in the squeezed gas air from the panicle was 97 nl/l at the heading and anthesis stage. The concentration increased rapidly after anthesis and reached 220 nl/l fourteen days after heading. As the gas air content in a panicle gradually decreased after anthesis, the ethylene contents per panicle and 1g fresh weight of panicle showed a peak at around the heading and anthesis stage.
