Ethylene: Indicator but Not Inducer of Phytoalexin Synthesis in Soybean

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Abstract
Cell wall preparations (elicitors) from Phytophthora megasperma var. sojae increase C2H4 formation, phenylalanine ammonia lyase activity and glyceollin accumulation in soybean cotyledons within about 1.5, 3 and 6 h after treatment, respectively. The immediate precursor of C2H4, 1-aminocyclopropane-1-carboxylic acid, stimulates C2H4 formation like the elicitor within 1.5 h after administration, whereas phenylalanine ammonia lyase activity and glyceollin concentration remain unchanged. Aminoethoxyvinylglycine, a specific inhibitor of C2H4 formation in higher plants, inhibits elicitor-induced C2H4 formation by about 95% but has no effects on phenylalanine ammonia lyase or glyceollin accumulation. C2H4 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.