Determination of Relative Auxin Content in Hermaphrodite and Andromonoecious Cucumis sativus L.

A causal relationship between growth substances and sex expression probably exists in Cucuntis sativus L. (cucumber). This assumption is based on a number of publications which documented a shift towards femaleness in monoecious cucumbers treated with auxins (8), or with growth retardants (16). An even more remarkable shift, but towards maleness, was caused by gibberellins (24). The experimental modification of sex expression of C. sativus and other plant species by growth substances was reviewed by Heslop-Harrison (11). According to this review and more recent information (13, 18, 23), the cucumber may be regarded as an example, rather than an exception, in respect to ithe relationship between growth substances and sex expression. Nevertheless, the effect of applied auxin does not necessarily prove that this substance is the natural regulator of sex differentiation in plants. Only 2 studies of other authors, who tested the relationship between sex expression and natural auxin content, came to our attention (12, 4). The Heslop-Harrisons (12) found that CO treatment induced a shift to femaleness in male Cannabis plants and tested auxin content of CO treated and nontreated plants. The results obtained -indicated the probability that CO has increased the free auxin, though, due to variability of the results, the authors did not accept them as conclusive. A very large difference in auxin content between male and female Cannabis plants was found by Conrad and Mothes (4). Female planits contained 30 times more auxin than male plants. In Cannabis, as in Cucumis, auxin application to the plants caused a shift toward femaleness (10). In a previous study (5) the amount of growth substances in stem itips and leaves of monoecious (M/M, st+/st+) and heterozygous-gynoecious (M/M, st+/st) cucumber plants was tested. But due, probably, to the low sensitivity of the bioassay used, only differences in inhibitors, but not in auxin, were found. In that study, leaves of equal size of the 2 sex types were compared. Later studies showed that such a comparison is inaccurate. It was found that in st/st plants floral buds develop in axils of