Phytoalexin Production by Isolated Soybean Protoplasts

Protoplasts, Soybean Cell Suspension Cultures, Phytoalexin Production, Phytophthora megasperm a f. sp. glycinea, Glucan Elicitor Protoplasts isolated enzymatically from suspension-cultured cells of soybean (Glycine max L. Merr., cv. Harosoy 63) were used to study the production of the isoflavonoid-derived phytoale­ xin, glyceollin. A large enhancement in the in vivo rates of synthesis and catalytic activities of two of the enzymes associated with glyceollin biosynthesis, phenylalanine ammonia-lyase and chalcone synthase, preceded phytoalexin accumulation during early stages of culture of isolated protoplasts while cell wall regeneration occurred. A glucan elicitor from cell walls of the fungus Phytophthora megasperma f. sp. glycinea, an effective inducer of the phytoalexin response in cultured cells, was not capable of enhancing phytoalexin formation in protoplasts. Lack of respon­ siveness of the protoplasts to the glucan elicitor could either be associated with their stressed metabolic state in which the response system is already saturated or with the removal from cultured cells of an essential factor of the glucan elicitor-mediated phytoalexin induction during protoplast isolation. At least two components of the protoplast isolation medium, the osmoticum and the fungal endopolygalacturonase, have the potential to initiate the observed phytoalexin synthesis during protoplast isolation. Our results indicate that under the methods employed isolated soybean protoplasts display a stress response which other types of soybean cells show following microbial attack or treatment with elicitor.