Stress-induced factor involved in flower formation of Lemna is an alpha-ketol derivative of linolenic acid

A stress-induced substance(s) (factor C) incubated with norepinephrine (NE) has strong flower-inducing activity in Lemna paucicostata. We isolated an essential component (FIF) of factor C, and clarified its chemical structure as 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid, an alpha-ketol deriv ative of linolenic acid, which is formed via 9-hydroperoxy linolenic acid. Synthesized FIF showed flower-inducing activity after incubation with NE (f actor C activity) equivalent to that formed in the stressed Lemna. Jasmonic acid and 13-hydroxy-12-oxo-9(Z),15(Z)-octadecadienoic acid (12,13-alpha-ke tol linolenic acid), both of which are formed via 13-hydroperoxide of linol enic acid and all other derivatives of FIF synthesized by chemical and enzy matic processes failed to show the factor C activity. These results suggest that the molecular structure of FIF is very specific for the factor C acti vity.