Effect of growth substances on flowering and sex expression in isolated apical buds of Spinacia oleracea

Abstract

Abstract Apical buds of Spinacia oleracea L. cv. Matador were isolated from 7‐day‐old vegetative seedlings and grown in sterile culture under inductive long, or non‐inductive short photoperiods. Flowering of isolated apices was inducible in long days in approximately 75% of the plants, and in short days by gibberellin treatment (about 40%) or by raising the temperature to 30–32°C (13%). In long days the percentage of flowering was further increased by gibberellin treatment (up to 90%), while it was unaffected by abscisic acid and was strongly decreased by Amo 1618 (55%). In long days the ratio of male to female plants was near 1. The percentage of female plants in long days was increased by gibberellins, and the percentage of male ones decreased by kinetin; as a consequence, the ratio of male to female plants was lowered to about 0.50 in both cases. Abscisic acid and Amo 1618 had the opposite effect, probably because they decreased the flowering in female plants, so that the sex ratio was shifted to 2.6 and 6.8, respectively. Simultaneous treatment with GA 3 reversed the effect of abscisic acid on the sex ratio, but the reversal of the shift to maleness induced by Amo 1618 was only partial. In short days, gibberellins also stimulated the flowering in female plants more than in male. However, when the flowering was induced by higher temperature, most flowering plants were male and kinetin increased their percentage further. The above results have been discussed in terms of different requirements for flowering in male and female plants.