Regulation of stem elongation in chinese cabbage by inflorescence removal and application of growth regulators

The effect of inflorescence removal on stem elongation in Chinese cabbage cv. Spring A was studied. Removal of the inflorescence before its visibility, or upon its appearance but before the beginning of bolting (stages 1–3), markedly reduced the stem length. Removal after the beginning of bolting (stage 5) had no effect on stem length.Application of GA₃ to the treated plants partially or fully restored the elongation of the flowering stem, whereas paclobutrazol inhibited the elongation of the treated, as well as the control stems. Indole-3-acetic acid (IAA) or kinetin was ineffective in restoring stem elongation of the plants from which the inflorescence had been removed. Inflorescences at stages 1–2 were found to secrete about 10 times more gibberellic acid (GA)-like activity compared with control apices or inflorescences at stage 5.It is suggested that the developing inflorescence is the major source of GAs which control stem elongation. However, shortly after the appearance of the inflorescence at the onset of bolting, stem elongation is no longer dependent on GAs derived from the apical inflorescence but require GAs from other sources.Contribution from the Agricultural Research Organization, The Volcani Center Bet Dagan, Israel No. 2218-E, 1987 series.