POLYGALACTURONASE PRODUCED BY BOTRYTIS FABAE AS ELICITOR OF TWO FURANOACETYLENIC PHYTOALEXINS IN VICIA FABA PODS
A. Buzi, G. Chilosi, A.M. Timperio, L. Zolla, S. Rossall, P. Magro
Polygalacturonase, produced by Botrytis fabae in infected faba bean pods, was separated by isoelectric focusing and tested as possible elicitor of the phytoalexins wyerone acid and wyerone. The isoenzyme profile was characterised by multiple forms within a restricted range of isoelectric points (pI). These were indicated as very acidic, acidic and basic. Using liquid isoelectric focusing, polygalacturonase isoenzymes were separated into four different isoenzyme pools. These pools, tested at a range of concentrations, acted as an elicitor of wyerone acid and wyerone in endocarp pod tissues, the former being more prevalent. The level of phytoalexin accumulation varied depending on the enzymatic pool tested. Time course analysis revealed that phytoalexins accumulated at higher levels when lower enzyme doses were used. Each pool of isoenzymes was found to produce dark-brownish lesions similar to those observed from tissues inoculated with the pathogen. The possible dual role of polygalacturonase isoenzymes from B. fabae as putative pathogenicity determinants or defence responses elicitors during broad bean colonisation is discussed.