Endogenous gibberellins and their effects on flowering and stem elongation in cabbage (Brassica oleracea var. capitata)

Abstract

SummaryEndogenous gibberellins were extracted from cabbage shoots and were analysed using gas chromatography and mass spectrometry. Nine gibberellins (GA1, GA19, GA20, GA44, GA12, GA4, GA15, GA24 and GA25) were identified. Two gibberellin biosynthesis pathways were suggested, an early-13-hydroxlyated pathway and a non-13-hydroxylated pathway, to operate in cabbage shoots. GA1, GA4 and prohexadione calcium, a gibberellin biosynthesis inhibitor, were applied to the shoot tip of cabbage ‘Sousyu’ and ‘Kinkei No.201’ with or without cold treatment. Without cold treatment, stem elongation was increased by gibberellins and was suppressed by prohexadione calcium in both cultivars. But prohexadione calcium treatment, followed by gibberellin, promoted stem elongation more than gibberellin alone. Flowering was not induced by gibberellin or prohexadione calcium without cold treatment. When gibberellin and prohexadione calcium were applied during a cold treatment, stem elongation after the cold treatment was increased by gibberellins and was suppressed by prohexadione calcium in both cultivars. Flower bud appearance was promoted by GA1 and GA4 in ‘Sousyu’, but in ‘Kinkei No. 201’ only GA4 was markedly effective. Inhibition of stem elongation and delay of flower bud appearance by prohexadione calcium were overcome by applying GA1 or GA4. Neither gibberellin nor prohexadione calcium treatment changed the number of leaf nodes at anthesis. These results indicated that stem elongation and flower bud development are regulated by gibberellins, but gibberellins might have little effect on flower induction.