CHARACTERIZATION OF CELERY HYDROLYTIC ENZYMES INDUCED IN RESPONSE TO INFECTION BY FUSARIUM-OXYSPORUM

The induction of celery (Apium graveolens) chitinases and β-1,3-glucanases by infection with Fusarium oxysporum f. sp. apii was characterized to evaluate the potential role of these enzymes as defence mechanisms in the celery-Fusarium system. Celery root chitinase activity was strongly induced (19- to 30-fold) following inoculation with compatible and incompatible races of F. oxysporum f. sp. apii . Six isoforms were observed, five of which were localized extracellularly. In contrast, β-1,3-glucanase increased at most two-fold, and there was only a single, intracellular isoform. Chitosan treatment of susceptible plants prior to infection with F. oxysporum f. sp. apii race 2 resulted in an induction of these enzymes comparable to what was observed by fungal infection, and a significant delay of disease symptoms. Isolated cell walls of the pathogen were hydrolysed by crude celery root extracts, but chitinase activity on fungal substrate appeared to be dependent on β-1,3-glucanase activity. © 1993 Academic Press, Inc.