Ethylene and Gibberellin: Regulation of Internodal Elongation and Nodal Root Development in Floating Rice

Ethylene and GA3 stimulated internodal elongation in the excised stem sections of floating rice. The combined application of ethylene and GA3 exerted a cooperative effect on internodal elongation, although the effect was variety dependent. Stimulative effect of ethylene on internodal growth in intact floating rice plants was virtually absent when the plants were pre-treated with Ancymidol, α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidine methanol, an inhibitor of gibberellin biosynthesis. Submergence of intact plants, which also induced internodal elongation, had no stimulative effect when the plants were pre-treated with Ancymidol. Submergence of intact plants increased the endogenous gibberellin level. The internode of young, intact 9 day old seedlings responded neither to submergence nor ethylene, but when seedlings were pre-treated with GA3 they responded to either one. Nodal root development was also enhanced by either ethylene or GA3. Combined application of ethylene and GA3 exerted a co-operative effect on nodal root development. Ancymidol-treated plants did not produce nodal roots even though they were subjected to submergence, whereas nontreated control plants produced nodal roots normally.