The possible involvement of peroxidase in resistance to Botrytis cinerea in heat treated tomato fruit

Mature green tomatoes immediately after harvest were resistant to infection 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) after inoculation prevented B. cinerea development. If inoculated following the heat treatment lesions developed but more slowly than on control fruit. Only 60% of the heated fruit developed lesions if inoculated 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 decay diameter was 3.5 cm. A highly anionic peroxidase (TAP) mRNA was abundant in mature green tomatoes al harvest and decreased rapidly as the fruits were held at 20 degrees C. Holding fruit at 38 degrees C prevented the decrease in TAP mRNA, but once fruits were transferred to 20 degrees C the loss of mRNA was rapid. Soluble peroxidase activity decreased as harvested fruits were held at 20 degrees C, while during heat treatment activity was higher than at harvest. NaCl-extractable peroxidase activity was higher in fruits held at 20 degrees C or 38 degrees C than al harvest, bur a greater increase was seen in healed fruits. Activity gels showed the appearance of new isoforms in heated tomatoes. We suggest that peroxidases may be involved in the resistance of heated tomatoes to pathogen infection. (C) 1997 Academic Press Limited.