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

Heat-induced rosetted Eustoma grandiflorum requires low temperature for induction of stem elongation and flowering. Although heat-induced rosetting is associated with a reduction of gibberellin A1 (GA1) content, how thermo-induction affects GA biosynthesis 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.The 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 GA1 and GA20 in stems of the heat-induced rosetted plants during the cold treatment, whereas their levels increased with stem elongation after transfer to warm conditions. In contrast to the levels of GA1 and GA20, endogenous levels of ent-kaurene, ent-kaurenoic acid, GA53, GA44 and GA19 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 GA1 which is essential for stem elongation of the heat-induced rosetted E. grandiflorum

Methodology for the synthesis of 11,13-dihydroxy gibberellins

A general procedure has been established for the synthesis of 11,13-dihydroxy gibberellins. The key steps involve the isomerization of the 19,10 lactone functionality to the 19,2-isomer, bromination at C-1 and C-11, then selective nucleophilic displacement of the 11-bromo substituent by acetate with silver(1) acetate. Reconstitution of the 19,10 lactone functionality was effected by bromolactonization of a Δ9-ene 19-carboxylic acid to give a 9β-bromo 19,10-lactone followed by stereoselective hydrogenolysis of the bromo substituent

Dynamics of Abscisic Acid Levels during Grain-Filling in Rice : Comparisons between Superior and Inferior Spikelets

In a rice panicle, the superior spikelets display higher growth rates than the inferior spikelets during the initial phase of grain-filling. To better understand the regulatory mechanism of this phenomenon, we examined the dynamics of endogenous abscisic-acid (ABA) levels and the effects of shading on the dynamics during the grain-filling period in superior and inferior spikelets. While ABA content in the superior spikelets increased rapidly after flowering, that in the inferior spikelets increased slowly and reached the maximum later than in the superior spikelets. Shading significantly exaggerated the inherently different ABA dynamics between the superior and inferior spikelets. We concluded that ABA levels are correlated with the dry matter accumulation patterns of spikelets. These results support our hypothesis that ABA is involved in assimilate partitioning among spikelets in a panicle during the initial phase of grain-filling of rice