Induction of enzymes of phytoalexin synthesis in cultured soybean cells by an elicitor from Phytophthora megasperma f. sp. glycinea

The glucan elicitor from cell walls of the fungal pathogen, Phytophthora megasperma f. sp. glycinea, induced rapid but transient increases in enzyme activities of general phenylpropanoid metabolism (phenylalanine ammonia-lyase and 4-coumarate: CoA ligase) and of the flavonoid pathway (chalcone synthase) in cell suspension cultures of soybean (Glycine max). After transferring cells into fresh medium, two peaks of inducibility for the enzymes by elicitor were observed, one shortly after transfer (stage I), and one at the end of the linear growth phase (stage II). Only one of the two isoenzymes of 4-coumarate: CoA ligase (isoenzyme 2), for which a specific involvement in flavonoid biosynthesis has been postulated, was affected by the elicitor. For two of the induced enzymes, phenylalanine ammonia-lyase and chalcone synthase, the changes in activity at stage I were shown to be preceded by large changes in their rates of synthesis, as determined by in vivo labelling with [³⁵S] methionine and immunoprecipitation.Abbreviations Pmg Phytophthora megasperma f. sp. glycinea - glyceollin is a term used to designate the 3 isomers which accumulate in challenged soybean tissue (Moesta and Grisebach 1981b)