Ethylene: Indicator but Not Inducer of Phytoalexin Synthesis in Soybean

Cell wall preparations (elicitors) from Phytophthora megasperma var. sojae increase C(2)H(4) formation, phenylalanine ammonia lyase activity, and glyceollin accumulation in soybean cotyledons within about 1.5, 3, and 6 hours after treatment, respectively. The immediate precursor of C(2)H(4), 1-aminocyclopropane-1-carboxylic acid, stimulates C(2)H(4) formation like the elicitor within 1.5 hours after administration, whereas phenylalanine ammonia lyase activity and glyceollin concentration remain unchanged. Aminoethoxyvinylglycine, a specific inhibitor of C(2)H(4) formation in higher plants, inhibits elicitor-induced C(2)H(4) formation by about 95% but has no effects on phenylalanine ammonia lyase or glyceollin accumulation. It was concluded that C(2)H(4) is a signal accompanying the specific recognition process which finally leads to the induction of phytoalexin formation, but it is not functioning as a link or messenger in the induction sequence of glyceollin accumulation.