Pectolytic and cellulolytic activity in Rhizopus-infected rin and nor tomato mutants

Abstract

Polygalacturonase (PG) and polymethylgalacturonase (PMG) activity was recorded in the two non-ripening mutants of tomato devoid of these enzymes, rin and nor fruits, following Rhizopus stolonifer infection. Activity increased markedly with disease development.

C_x-cellulase activity, generally found in healthy rin and normal fruit, increased with maturity as well as with disease development. The effect of fungal infection on C_x-activity was particularly pronounced on the mature-green nor fruit, in which only traces of activity were recorded prior to inoculation.

At an advanced stage of disease development, infection brought pectolytic and cellulolytic activity in the standard and mutant fruits at all stages of maturity to a similar level, regardless of the differences in their initial enzyme levels. A correlation was drawn between the level of pectolytic activity and the rate of fruit softening in Rhizopus-infected mutant fruits. Tissue softening following infection was attributed to the activity of fungal polygalacturonases. The relatively high levels of C_x-cellulase found in infected mutants during the early stages of disease development, when only a slight or no softening was recorded, suggested a lack of relationship between cellulolytic activity and softening of tomato tissues.