Role of Gibberellin in the Growth Response of Submerged Deep Water Rice

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Abstract
Ethylene, which accumlates in the air spaces of submerged stem sections of rice is involved in regulating the growth response caused by submergence. The role of GA in the submergence response was studied using tetcylacis (TCY), a new plant growth retardant, which inhibits GA biosynthesis. Stem sections excised from plants that were watered with a solution of 1 .mu.M TCY for 7-10 days did not elongate when submerged in the same solution or when exposed to 1 .mu.M/l ethylene in air. GA3 at 0.3 .mu.M overcame the effect of TCY and restored the rapid internodal elongation in submerged and ethylene-treated sections to the levels observed in control sections that were not treated with TCY. The effect of 0.01-0.2 .mu.M GA3 on internodal elongation was enhanced 2- to 8-fold when 1 .mu.l/l ethylene was added to the air passing through the chamber in which the sections were incubated, GA3 and ethylene caused a similar increase in cell division and cell elongation in rice internodes. Ethylene may cause internodal elongation in rice by increasing the activity of endogenous GA. In internodes from which the leaf sheath was peeled off, growth in response to submergence, ethylene and GA3 was severely inhibited by light.