Florigenic Effect of Gibberellin on Flowering According to Period of Chilling Treatment in Lavandula × intermedia

抄録

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.