Host-Pathogen Interactions XXX. Characterization of Elicitors of Phytoalexin Accumulation in Soybean Released from Soybean Cell Walls by Endopolygalacturonic Acid Lyase*

Endopolygalacturonic acid lyase, purified from the phytopathogenic bacterium, Erwinia carotovora , induces phytoalexin accumulation in soybean ( Glycine max L .) cotyledons. This pectin-degrading enzyme releases heat-stable elicitors of phytoalexin accumulation from soybean cell walls, citrus pectin, and citrus sodium polypectate. The most elicitor-active m olecules ob­ tained by treating soybean cell walls with endopolygalacturonic acid lyase have been purified and characterized. The cell-wall-derived elicitors are a-l,4-linked oligogalacturonides with degrees of polymerization o f eight to twelve residues. The molecules with the highest specific elicitor activity were identified as a -l,4 -lin ked decaand undecagalacturonides that contained 4,5-unsaturated galactosyluronic acid at the nonreducing termini.