Labile phytochrome and photoperiodic flower induction in Pharbitis nil Chois. The irreversible phytochrome hypothesis

Abstract

Seedlings of <i>Pharbitis nil</i> cultivated under non-inductive conditions of white light were subjected to generative induction applying one 16-hour-long period of inductive night. During the eighth hour the night was interrupted with 1 min of red light pulse which completely inhibited the flowering. Treating the plants with KCN blocked the inhibiting effect of red light. Because KCN lowers considerably the rate of destruction of labile Pfd in some plant systems, it seems probable that red light night-break irradiation (without KCN), which blocked the flowering, leads also to the accumulation of unknown Pfd destruction products (irreversible phytochrome). It also suggests that it is not the labile PfrI itself but the products of its irreversible transformation that could be active in the photoperiodic control of flowering.