Sex expression in cucumber (Cucumis sativus L.) and muskmelon (C. melo L.) was correlated with endogenous ethylene production. Plants of gynoecious (all female) sex types of the two species produced more ethylene than monoecius (male-female) plants. Sex expression in cucurbits is influenced by genetic, environmental, and hormonal factors. Monoecious strains of cucumber (Cucumis sativus L.) and muskmelon (C. melo L.) bear staminate (male) and pistillate (female) flowers. Gynoecious strains normally produce only pistillate flowers. Other cucumber and muskmelon strains produce staminate or pistillate and, in addition, perfect (hermaphroditic) flowers in various combinations. For example, andromonoecious strains are those that begin with staminate flowers and, eventually, also produce hermaphroditic flowers. Exogenous application of auxin (1, 2) and inhibitors of gibberellin biosynthesis (3) promote monoecious strains to form pistillate flowers, that is, increase femaleness. Application of gibberellin promotes formation of male flowers in monoecious and gynoecious phenotypes of cucumber (4, 5). Sex expression can be modified by daylength and temperature. Generally, short days and cool temperatures favor femaleness, while long days and high temperatures favor maleness, although there are exceptions (6). Determinations of endogenous growth substances indicate that strains with genetically strong female sex expression contain more auxin (7) and less gibberellin-like substances (8) than strains with strong male sex expression. There are certain differences between species; for example, gibberellin application does not cause male flower formation in gynoecious muskmelon (9). However, the results obtained with hormone applications and hormone determinations suggest the hypothesis that sex expression in cucurbits is controlled by an endogenous auxin-gibberellin balance (3, 7, 8, 10).Ethylene and 2-chloroethylphosphonic acid (ethephon), an ethylene-releasing compound, have recently been shown to promote femaleness in cucurbits (11, 12); thus, the effect of ethylene is similar to that of auxin. Exogenous application of auxin increases ethylene production by cucumber plants (13

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Gibberellins were extracted from seeds and green plants of different sex types of the closely related species Cucumis sativus L . (cucumber) and C. melo L. (muskmelon) . Both seeds and green plants of monoecious and andromonoecious lines of C. sativus contained significantly higher gibberellin levels at all growth stages tested than did a gynoecious line . Gibberellin activity in the monoecious and andromonoecious C. sativus line reached a maximum at the growth stage corresponding to flower differentiation at cotyledonary and first leaf axils . Vernalization of seeds of gynoecious plants resulted in increased male tendency correlated with increased gibberellin activity . In contrast, monoecious and andromonoecious lines of C. melo were gibberellin deficient relative to hermaphroditic and gynoecious lines .

Neutral and n-butanol fractions of a methanol extract of mature seeds of a monoecious line of Cucumis sativus (cucumber) were found to contain novel gibberellins. A β-D-glucoside was isolated from the n-butanol fraction and partially characterized by thin-layer chromatography as a derivative of gibberellin A1. The n-propyl ester of GA3 was isolated from the neutral fraction and the n-propyl ester of GA1 was tentatively identified as a second component of that fraction.