The elicitation of the hypersensitive response of potato tuber tissue by a component of the culture filtrate of Phytophthora infestans

Abstract Filtrates from 5-week-old cultures of race 4 of Phytophthora infestans contained an elicitor of the hypersensitive reaction in tuber discs of the potato cultivar Kennebec which caused both browning of discs and accumulation of the sesquiterpenoid phytoalexins rishitin and lubimin. Elicitor activity was associated with a fraction of molecular weight of more than 10 000; the most active fractions obtained by preparative isoelectric focussing contained bands which stained for both protein and carbohydrate on analytical gels. Neither polygalacturonase present in the active fractions, nor any of the other polysaccharide-depolymerizing enzymes present in the crude culture filtrate, was involved in elicitation, since treatments which inactivated polygalacturonase (heat and pronase) did not reduce elicitor activity. Furthermore, these experiments indicated that the protein moiety of the elicitor was not important for its eliciting activity; the importance of the carbohydrate moiety was indicated by the loss of activity after periodate oxidation. The culture filtrate elicitor did not contain any fatty acids and did not interact synergistically with arachidonic acid.