Changes in cell wall pectin and pectinase activity in apple and tomato fruits during Penicillium expansum infection

Cell wall pectin degradation in apple and tomato fruit during infection by Penicillium expansum was investigated. In infected apple fruit, a significant decrease in the average molecular mass was observed in pectins extracted with CDTA and also in pectins extracted with Na2CO3. In tomato fruits, depolymerisation was also observed in both pectic fractions during infection, the major change being in the pectins extracted with Na2CO3. This pectin depolymerisation associated with P. expansum infection can be attributed to the action of pectinases; in apple fruit, a significant increase in polygalacturonase and pectin methylesterase was observed in infected fruits, although in tomato fruit the only increase in enzymatic activity significantly related to the infection was in polygalacturonase. These differences between apple and tomato fruit during fungus infection could be related to differences in cell wall structure and composition and also to the specificity of P. expansum's infection spectrum in each case. In both cases, pectin depolymerisation might increase the porosity of the wall and allow increased access of fungus colonisation and facilitate the progress of the fungal infection.