Effects of Gibberellins and Gibberellin-biosynthesis Inhibitors on Stem Elongation and Flowering of Raphanus sativus L.

Abstract

The effect of exogenous applications of several gibberellins (GAs) native to a cold-requiring plant Raphanus sativus L. was investigated to uncover the role of the GAs in cold-induced stem elongation and flowering of the plant. GA1 and GA4 promoted the stem elongation and flowering, whereas GA9 and GA20, which are thought to be precursors of GA4 and GA1, respectively, were less active. Prohexadione calcium, which inhibits hydroxylation of GAs including 2β- and 3β-hydroxylation, reduced the effects of GA9 and GA20 ; in contrast, it enhanced the effects of GA1 and GA4. These results strongly indicate that GA1 and GA4 are the endogenous biologically-active GAs in cold-induced stem elongation and flowering of R. sativus. We found no difference between GA1 and GA4 in their relative activity to stem elongation vs. flowering ; thus, we suggest that they have the same role in the promotion of stem elongation and flowering. Thus, it will be necessary to reduce GA1 and GA4 concentrations to control undesired stem elongation and flowering.