Involvement of Ethylene in Gravity-Regulated Peg Developlnent in Cucumber Seedling

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Peg development on the lower side of the transition (TR) zone of the hypocotyl and the root in cucumber seedlings was inhibited by two inhibitors of ethylene biosynthesis, aminoethoxyvinyl glycine and aminooxyacetic acid, and by an inhibitor of ethylene action, Ag-thiosulfate. These ethylene inhibitors also inhibited plumular hook formation of the cucumber hypocotyl. When cucumber seeds were germinated in a vertical position or on a horizontal clinostat, the seedlings exhibited straight growth without formation of a plumular hook and failed to develop a protuberant peg. In the seedlings germinated in a vertical position, exogenous IAA induced a distinct peg-like protuberance, whereas ACC and ethylene stimulated overall swelling around the TR zone, which obviously differed from the normal peg. In horizontally placed seedlings, however, peg development was more pronounced due to treatment with 5μl/liter of ethylene. These results indicate that a high ethylene level in the hook region plays some role in peg development. TIBA, an inhibitor of auxin transport, at 10^<-4>_M inhibited peg development, as reported previously by Witztum and Gersani (1975), but a somewhat lower concentration of TIBA induced two distinct pegs, on both the lower and upper sides of horizontally grown seedlings.
日本植物生理学会の論文