2016 Volume 85 Issue 2 Pages 169-176
The effect of gibberellin (GA) on chilling-induced stem elongation and flowering in Lavandula × intermedia was investigated using several GAs and GA biosynthesis inhibitors related to chilling temperature and its period. Identification of GA1, GA19, GA20, and GA53 as endogenous GAs by GC/MS suggests the early C-13 hydroxylation pathway (→GA53→GA44→GA19→GA20→GA1→) is functioning, and GA1 is the biologically active GA in L. × intermedia. GA3 increased stem elongation with or without chilling treatment (CT), but did not induce flowering without CT. There was little difference in the effects on stem elongation and flowering among GA1, GA3, GA5, and dimethyl-GA4. GA biosynthesis inhibitor, especially uniconazole-P, inhibited stem elongation and flowering, but the inhibition was abolished by GA3. At least several weeks of CT were necessary for flowering, for example, in 8-week CT at 5°C, 9-week CT at 6°C and 12-week CT at 7°C. This period was defined as the minimum CT period. Under the minimum CT period, GA3 enhanced the flowering. However, the effect on flowering by GA3 was not found when the CT period became longer, for example, in 12-week CT at 5°C, 12-week CT at 6°C and 15-week CT at 7°C. This longer period was defined as the maximum CT period. These results suggest that the expression of endogenous GA is necessary for flowering in L. × intermedia, that the florigenic effect of GA3 on flowering varies with the period of CT, and that GA3 enhances the effect of CT on flowering in L. × intermedia, but cannot replace CT.