Induction of phytoalexin synthesis in Soybean: Elicitor-induced increase in enzyme activities of flavonoid biosynthesis and incorporation of mevalonate into glyceollin

Abstract

Soybean (Glycine max) cotyledons removed from 6-to 8-day-old seedlings were treated with mycelial walls of Phytophthora megasperma var. sojae (elicitor) and the activity changes of the enzymes phenylalanine ammonia-lyase and flavanone synthase were determined. Large increases and subsequent decreases in the activities of both enzymes were found in the elicitor-induced cotyledons. No changes in enzyme activities, occurred in control cut cotyledons with elicitor omitted. Concomitant with the elicitor-stimulated changes in enzyme activities there was accumulation of the soybean phytoalexin, glyceollin. [2-14C] Mevalonic acid was incorporated into glyceollin in elicitor-treated but not in untreated cotyledons. The results prove that stimulation of the enzymes of flavonoid biosynthesis and probably glyceollin biosynthesis are caused by the effect of the P. megasperma elicitor and not merely by wounding the plant material. The induced enzyme levels could control glyceollin biosynthesis.