Inhibition of Flower Induction by Some Inhibitors of Protease in the Short-day Plant Lemna paucicostata 6746 and the Long-day Plant Lemna gibba G3

Four inhibitors of proteases, namely, bestatin, diisopropyl fluorophosphate, elastatinal and p-toluenesulfonyl-L-lysine chloromethyl ketone hydrochloride, were examined for their effects on flowering of a short-day plant Lemna paucicostata 6746 and a long-day plant Lemna gibba G3. Each of the inhibitors greatly inhibited the flowering of Lemna paucicostata 6746 that is normally induced by nitrogen deficiency. Bestatin or elastatinal given only during the first half of the culture period inhibited the flowering more clearly than when each was given during the latter half, suggesting that they inhibited the inductive process(es) involved in flowering rather than development of flower buds. Bestatin or elastatinal greatly inhibited the flowering of Lemna paucicostata 6746 induced by photoperiodic stimulus, ferricyanide and continuous far-red light. Simultaneous application of these two inhibitors was more effective in the inhibition of photoperiodically induced and ferricyanide-induced flowering than was each inhibitor alone. They also completely inhibited the photoperiodic flowering of Lemna gibba G3. These results suggest that the induction or activation of some proteases, probably followed by the degradation of some protein(s), is necessary for the induction of flowering in both these plants.