Regulation of gibberellin biosynthesis and stem elongation by low temperature in Eustoma grandiflorum

摘要

Heat-induced resetted Eustoma grandiflorum requires low temperature for induction of stem elongation and flowering. Although heat-induced resetting is associated with a reduction of gibberellin A_1 (GA_1) content, how thermo-induction affects GA biosy nthesis is unclear. Thus, we examined levels of GA, precursors including that of ent-kaurene which is the first committed step in GA biosynthesis. We used uniconazole, an ent-kaurene oxidase inhibitor to estimate the ent-kaurene biosynthesis activity. Th e accumulation level of ent-kaurene in stems of the cold-treated seedlings was approximately 1,8 times that of the non-cold-treated seedlings, whereas no difference was observed in the leaves. No change was observed in endogenous levels of GAt and GA_(20 ) in stems of the heat-induced resetted plants during the cold treatment, whereas their levels increased with stem elongation after transfer to warm conditions. In contrast to the levels of GA_1 and GA_(20), endogenous levels of ent-kaurene, ent-kaurenoi c acid, GA_(53), GA_(44) and GA_(19) in the stems markedly increased at the end of cold treatment. These results indicate that ent-kaurene biosynthesis and its metabolism early in the GA biosynthetic pathway are stimulated by low temperature and, later, the stimulation leads to an increment of endogenous levels of GA_1 which is essential for stem elongation of the heat-induced resetted E. grandiflorum.