Gibberellin Inhibits Floral Initiation in the Perennial Woody Plant Jatropha curcas

Gibberellin (GA) is an important phytohormone and has been reported to promote flowering in annual and biennial plants, but may play an opposite role in woody perennial plants. In this study, the promoting or inhibiting effect of GA on floral initiation was investigated in Jatropha curcas L., a perennial woody plant, which has great potential as renewable energy plant due to the high oil content in the seed. We found that exogenous application of gibberellic acid (GA3) inhibited flowering, whereas GA biosynthesis inhibitors promoted flowering. The promotive effect of the GA biosynthesis inhibitor paclobutrazol on floral initiation could be diminished by GA3 treatment. The expression levels of GA biosynthesis genes Jatropha GA 3-oxidase 3 (JcGA3ox3) and the GA receptor genes, Jatropha GA-INSENSITIVE DWARF 1C (JcGID1C) were decreased, whereas a GA catabolism gene, Jatropha GA 2-oxidase 8 (JcGA2ox8), was elevated during floral transition. These results suggest that GA inhibits floral initiation in J. curcas.