The inhibitory effect of ethephon on the flowering in Lemna perpusilla 6746 was shown to be related to sucrose concentrations and dilution factors of Hutner´s medium. When grown in 1/10-strength Hutner´s medium under 10(14) cycles, the plants have been completely inhibited in the floral induction by ethephon(>5ppm) in the presence of sucrose(>20 mM) in the medium. However, in a less diluted Hutner´s medium (1/2-strength), the inhibition of flowering by ethephon was observed to be partially diminished by sucrose at a high concentration(30 mM), while a low concentration of sucrose enhanced the inhibitory effect of ethephon in flowering. As inductive dark periods were extended, the effects of both compounds were partially nullified.
Since no significant amount of ethylene possibly released in ethephon decomposition in the medium was detected, the inhibitory effect of ethephon in flowering was postulated to be exerted only through ethylene production within the plants. Plants were incubated in 10 ppm ethephon-containing medium during either dark or light periods, singly or periodically. The most effective single treatment with ethephon was observed during the 4th dark period, when formation of floral stimulus was assumed to be completed beyond a critical level. This postulation can be partially supported by a fact that the plants should be exposed to at least more than four consecutive 10(14) cycles for flowering.
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