Characterization of two Sclerotinia sclerotiorum polygalacturonases with different abilities to elicit glyceollin in soybean

Two endo-polygalacturonase isoenzymes (PG-II and PG-IV), with masses of 34 and 30 kDa respectively, were purified from soybean hypocotyls infected by Sclerotinia sclerotiorum. The pH optimum for both isoenzymes was about 4.6, but PG-IV exhibited a broader range of pH activity. PG-IV showed a much higher affinity for pectin than did PG-II. PG-II hydrolyzed polygalacturonic acid in a more random fashion than PG-IV. Oligouronides produced by PG-II showed a higher phytoalexin elicitor activity. PG-IV produced a large degree of maceration of soybean hypocotyls releasing a significant amount of uronides. The properties of PG-II and PG-IV are discussed in relation to the different ability of the two isoenzymes to elicit glyceollin in soybean.