Gibberellin-Induced Suppression of Chloroplast Starch Formation from Exogenous Sucrose in Isolated Epidermis of Light-Grown Cucumber Hypocotyls |
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Authors: | Katsumi, Masayuki Kazama, Haruko Yamada, Junko Matsumura, Michiko |
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Affiliation: | Biology Department, International Christian University Osawa, Mitaka, Tokyo 181, Japan |
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Abstract: | The effects of gibberellin A3(GA3) on chloroplast starch formationfrom exogenous sucrose in epidermal strips of light-grown cucumber(Cucumis sativus L. cv. Aonagajibai) hypocotyls were studied.Chloroplast starch formation was measured by counting microscopicallythe number of I2KI stained chloroplasts. In the presence ofsucrose (150 mM) and in light, chloroplast starch formationoccurred rapidly for 5 hr and then the rate declined. GA3 (100µM) simultaneously supplied with sucrose clearly suppressedboth the rate and the degree of starch formation. When the epidermiswas preincubated in the dark with sucrose in the presence orabsence of GA3 and then post-incubated in light with bufferonly in the presence or absence of GA3, starch formation wassuppressed to the same degree by GA3 given either in the pre-or post-incubation period. When the epidermis was preincubatedin the dark with GA3 alone and then transferred to light forpost-incubation with sucrose alone, GA3 suppressed the initialrate of starch formation during the post-incubation period.The degradation of chloroplast starch formed in advance fromexogenous sucrose in light was not significantly affected byGA3 These results are discussed in relation to the mechanismof the GA3 action and also to the GA3-induced decrease in theosmotic potential of the cell. (Received February 2, 1982; Accepted May 31, 1982) |
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