THE INTERACTION IN PLANTA OF POLYGALACTURONASES FROM BOTRYTIS-CINEREAWITH A CELL WALL-BOUND POLYGALACTURONASE-INHIBITING PROTEIN (PGIP) INRASPBERRY FRUITS

The activities of four fungal polygalacturonases (endo-PGI, endo-PGII, exo-PGI, exo-PGII), detected when Botrytis cinerea was grown on immat ure fruits of red raspberry (Rubus idaeus), were fractionated into sol uble and wall-bound fractions. Western blots and plate-trapped antigen ELISA showed that endo-PGI and endo-PGII were most abundant in the ce ll wall-bound fractions of the host. Immuno-inhibition studies using a polyclonal antiserum against polygalacturonase-inhibiting protein (PG IP), purified from immature raspberry fruits, showed that the low leve l of fungal pc activity detected in fractions containing endo-PGI was due to the presence of PGIP. When a purified preparation of endo-PGI a nd endo-PGII from B. cinerea was allowed to react in vitro with either a crude host cell wall preparation, or one which had previously been treated to remove cell wall-bound proteins, both endo-PG isozymes had a greater binding capacity towards the former wall preparation. Endo-P GI and endo-PGII also had an affinity for fungal cell walls. Exo-PGI a nd exo-PGII bound to both fungal and host cell wails. Greater quantiti es of fungal endo-PGs were detected by ELISA in fruits previously froz en and thawed ('freeze-thawed') and inoculated, than in fresh inoculat ed fruit. This result paralleled the extent of fungal growth in these tissues as assessed by chitin assay and suggests that the resistance s hown by raspberries is dependent on continual replacement of inhibitor y substances or induced resistance mechanisms.