THE POSSIBLE INVOLVEMENT OF PEROXIDASE IN RESISTANCE TO BOTRYTIS-CINEREA IN HEAT-TREATED TOMATO FRUIT

Mature green tomatoes immediately after harvest were resistant to infe ction by Botrytis cinerea, although if held for 2 days at 20 degrees C they lost this resistance. Heat treatment (38 degrees C for 3 days) a fter inoculation prevented B. cinerea development. If inoculated follo wing the heat treatment lesions developed but more slowly than on cont rol fruit. Only 60% of the heated fruit developed lesions if inoculate d inoculated after 3 days at 38 degrees C and the average size was 1.6 cm, while 100% of the control fruit developed decay and the average d ecay diameter was 3.5 cm. A highly anionic peroxidase (TAP) mRNA was a bundant in mature green tomatoes al harvest and decreased rapidly as t he fruits were held at 20 degrees C. Holding fruit at 38 degrees C pre vented the decrease in TAP mRNA, but once fruits were transferred to 2 0 degrees C the loss of mRNA was rapid. Soluble peroxidase activity de creased as harvested fruits were held at 20 degrees C, while during he at treatment activity was higher than at harvest. NaCl-extractable per oxidase activity was higher in fruits held at 20 degrees C or 38 degre es C than al harvest, bur a greater increase was seen in healed fruits . Activity gels showed the appearance of new isoforms in heated tomato es. We suggest that peroxidases may be involved in the resistance of h eated tomatoes to pathogen infection. (C) 1997 Academic Press Limited.