Effects of Ethylene and Gibberellins on the Elongation of Rice Seedlings (Oryza sativa L.)

Three-day-old rice seedlings treated with ethylene showed elongation of the 2nd and 3rd leaves. This ethylene-stimulated elongation was not observed in the presence of uniconazole-P or prohexadione, both gibberellin (GA) biosynthesis inhibitors, suggesting that GA was involved in the response. An analysis of endogenous GAs by GC-MS revealed that the GA1 level was reduced in the 3rd leaf in response to ethylene. Dose-response experiments showed that the responsiveness to GA1 was enhanced by ethylene. Feeding experiments of 14C-GA1 with ethylene-treated seedlings showed that ethylene may increase the conversion of GA1 to GA8. These results suggest that, in young seedlings of rice, ethylene stimulates leaf elongation by increasing the responsiveness to GA1 and the turnover of GA1.