Isolation and characterization of polygalacturanase inhibitor protein from chillies (Capsicum annuum L.)

Abstract

The experimental study undertaken for “Isolation and characterization of polygalacturonase-inhibiting protein from chillies affected by anthracnose fruit rot” is described in this thesis. Chilli fruit PGIp was purified by ammonium sulfate fractionation, gel-filtration on Sephadex G-150 column and ion-exchange chromatography on DEAE cellulose. The degree of purification achieved was 24.08 –fold in resistant variety and 20.96 in susceptible variety. The PGIP preparation was homogenous with one major band as revealed by native PAGE. The molecular weight of chilli PGIP of both resistant and susceptible variety determined by SDS-PAGE suggested that chilli PGIP is a single polypeptide chain of 37kDa molecular weight. The chilli PGIP was found to be stable in the pH range of 3.0-9.0. The chilli PGIP was maximally active at 60 ºC although the activity was retained up to 90 ºC. By using increasing doses of the purified chilli PGIP, it was possible to inhibit up to 90% of Colletotrichum capsiciii polygalacturonase activity. Chilli PGIP demonstrated high level of specificity for polygalacturonase from Colletotrichum capsicii when assayed against the polygalacturonases from other five fungi. The chilli PGIP from both resistant and susceptible varieties were found to be similar in their physic-chemical characteristics. The high specificity and the degree of inhibition obtained with chilli GPIP are pointers to the effectiveness of PGIP in avoiding pathogen ingress.