EFFECTS OF GIBBERELLINS AND GIBBERELLIN-BIOSYNTHESIS INHIBITORS ON STEM ELONGATION AND FLOWERING OF RAPHANUS-SATIVUS L

The effect of exogenous applications of several gibberellins (GAs) nat ive to a cold-requiring plant Raphanus sativus L. was investigated to uncover the role of the GAs in cold-induced stem elongation and flower ing of the plant. GA(1) and GA(4) promoted the stem elongation and flo wering, whereas GA(9) and GA(20), which are thought to be precursors o f GA(4) and GA(1), respectively, were less active. Prohexadione calciu m, which inhibits hydroxylation of GAs including 2 beta(-) and 3 beta- hydroxylation, reduced the effects of GA(9) and GA(20); in contrast, i t enhanced the effects of GA(1) and GA(4). These results strongly indi cate that GA(1) and GA(4) are the endogenous biologically-active GAs i n cold-induced stem elongation and flowering of R. sativus. We found n o difference between GA(1) and GA(4) in their relative activity to ste m elongation vs. flowering; thus, we suggest that they have the same r ole in the promotion of stem elongation and flowering. Thus, it will b e necessary to reduce GA(1) and GA(4) concentrations to control undesi red stem elongation and flowering.