Lysine Reverses the Inhibition of Flowering by Elastatinal, a Protease Inhibitor, in Lemna paucicostata 151

The flowering of Lemna paucicostata 151 that is normally inducedby nitrogen-free culture was suppressed by the application ofeither of two protease inhibitors, namely, elastatinal and bestatin,to the medium. These protease inhibitors prevented the flower-inductiveprocess(es) rather than the development of flower buds, suppressingof the degradation of some proteins. The amount of free lysinein plants increased during nitrogen-free culture and lysinehad a flower-inducing effect on the plant. However, levels ofendogenous lysine did not increase when elastatinal was presentin the medium. The suppressive effect of elastatinal on flowerinduction was almost completely reversed by simultaneous applicationof lysine to the medium while the suppressive effect of bestatinwas only partially reversed by lysine. These results suggestthat induction of flowering by nitrogen deficiency is due toendogenous free lysine and that elastatinal suppresses the proteolyticprocesses by which free lysine is generated from protein(s)during nitrogen-free culture. (Received August 7, 1992; Accepted February 9, 1993)