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Tests of a Mechanistic Model of One Hormone Regulating Both Sexes in Cucumis sativus (Cucurbitaceae)
Tongjia Yin and James A. Quinn
American Journal of Botany
Vol. 82, No. 12 (Dec., 1995), pp. 1537-1546
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2446182
Page Count: 10
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A mechanistic model of sex determination in flowering plants, which assumes that one hormone has male and female cell receptors to inhibit one sex and induce the other independently, was tested in cucumbers (Cucumis sativus) by applications of hormones and their inhibitors. Applications of gibberellic acid (GA) and an inhibitor of its synthesis (paclobutrazol) showed that GA had dual effects on sex expression of promoting maleness and inhibiting femaleness. Conversely, applications of Ethrel (an ethylene release agent) and AgNO3 (an ethylene action inhibitor) indicated that ethylene induced femaleness and inhibited maleness. Results of various combined applications of the two hormones and their inhibitors suggested that ethylene had overriding effects on GA and acted more directly on sex expression in cucumber. These experiments indicated that there is only one hormone, not two, regulating sex expression in cucumber, and that the sex hormone is likely to be ethylene. Results thus supported the assumption of the model that one hormone can regulate both sexes by inducing one and inhibiting the other independently. Model predictions were confirmed that from a monoecious line, female plants could be induced by increasing the ethylene level, and male plants induced by decreasing the ethylene level. On the other hand, as the model predicts, applications of ethylene or its inhibitor induced gynomonoecious, female, and trimonoecious plants from a hermaphroditic line. In conclusion, all assumptions and predictions of the one-hormone model were confirmed in the experiments.
American Journal of Botany © 1995 Botanical Society of America, Inc.