Inhibitory role of gibberellins in theobroxide-induced flowering of Pharbitis nil

Theobroxide, a novel active compound isolated from a fungus, has been reported previously to induce potato tuberization and flower bud formation in Pharbitis nil under non-inductive long-day conditions. Up to date, the action mechanism of theobroxide on flower-bud induction of P. nil, however, is still unknown. In the present study, we observed a reduction of the stem length, along with the induction of flower buds, in theobroxide-treated and short-day-grown P. nil plants. Also, the results showed that flower bud formation was delayed markedly in P. nil seedlings with removal of cotyledons or exposure to night break. The suppression effect of night-break and cotyledon-removal, however, was abolished completely by spraying theobroxide. Endogenous gibberellin1/3 contents in P. nil plants treated with theobroxide or grown under short-day conditions were relatively lower, suggesting that gibberellins probably are negatively involved in theobroxide- and short-day-induced flower-bud formation of P. nil.