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, diisopropylfluorophosphate, elastatinal and p-toluenesulfonyl-L-lysinechloromethyl ketone hydrochloride, were examined for their effectson flowering of a short-day plant Lemna paucicostata 6746 anda long-day plant Lemna gibba G3. Each of the inhibitors greatlyinhibited the flowering of Lemna paucicostata 6746 that is normallyinduced by nitrogen deficiency. Bestatin or elastatinal givenonly during the first half of the culture period inhibited theflowering more clearly than when each was given during the latterhalf, 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 Lemnapaucicostata 6746 induced by photoperiodic stimulus, ferricyanideand continuous far-red light. Simultaneous application of thesetwo inhibitors was more effective in the inhibition of photoperiodicallyinduced and ferricyanide-induced flowering than was each inhibitoralone. They also completely inhibited the photoperiodic floweringof Lemna gibba G3. These results suggest that the inductionor activation of some proteases, probably followed by the degradationof some protein(s), is necessary for the induction of floweringin both these plants. (Received November 21, 1989; Accepted February 19, 1990)