Induction of systemic resistance in potato by rhizobacterium Rhizobium etli strain G12 is not associated with accumulation of pathogenesis-related proteins and enhanced lignin biosynthesis

Whereas pathogen- and chemically induced systemic resistance in plants is c haracterized by enhanced accumulation of pathogenesis-related (PR) proteins ; increased peroxidase activity and cell wall modifications such as lignifi cation, the signal transduction pathways fdr; rhizobacteria-induced systemi c resistance are poorly understood. The rhizobacterium Rhizobium etli strai n G12 has been shown to induce systemic resistance in potato towards the po tato cyst nematode Globodera pallida. The results presented here clearly de monstrated that the resistance reaction triggered by Rhizobium etli G12 was not accompanied by enhanced accumulation of PR proteins such as chitinase and beta -1,3-glucanase. This was demonstrated in the presence as well as i n the absence of the nematode. Peroxidase activity was only enhanced after challenge inoculation with the nematode. The highest levels, of peroxidase activity were achieved in non-bacterized roots, indicating a general stress response of the plant to nematode attack. In contrast to other plant defen se reactions where enhanced peroxidase activity is associated with an incre ased lignification of root cells as mechanical barrier against pathogen att ack, lignin content was not affected in bacteria-treated roots. It is concl uded that rhizobacteria-induced systemic resistance triggers a signal trans duction pathway different from common pathogen or chemical induced pathways .