Increase in the Activities of Protein Kinases under a Flower-Inducing Condition in Lemna paucicostata

The activities of protein kinases and the phosphorylation ofsubstrate proteins were assayed in Lemna paucicostata 6746 culturedunder flower-inducing and non-inducing conditions. The activitiesof two protein kinases in the soluble fraction, one cAMP-activatedand the other cytokinin-inhibited, increased drastically underthe flower-inducing condition. However, no significant differencewas observed in the activities of another protein kinase inthe soluble fraction and a microsomal protein kinase, underflower-inducing and non-inducing conditions. The in vitro phosphorylation of cellular proteins was much greaterin the soluble fraction obtained from plants grown under theflower-inducing condition. Four polypeptides of mol wt 59,000,51,000, 16,000 and 14,000 were highly phosphorylated in thesample from flower-induced plants. No difference in cAMP levelwas observed between flower-inducing and non-inducing conditions.Cyclic AMP (Received April 27, 1987; Accepted October 19, 1987)