NUCLEOLYTIC ACTIVITIES IN PEPPER LEAVES REACTING HYPERSENSITIVELY TO XANTHOMONAS CAMPESTRIS PV VESICATORIA
R. Buonaurio, A. Polverari, G. Tarparelli, S. Guiderdone
A substrate-based gel assay was used to determine RNase and DNase activities in the incompatible interaction between pepper leaves (cv. ‘Early Calwonder 10R’) and the avirulent race 2 of Xanthomonas campestris pv. vesicatoria from 0 to 24 hours after inoculation, and for comparison in leaves inoculated with the virulent race 1 of the same bacterium (compatible interaction). Two major bands of RNase activity, with apparent molecular mass of 18 and 27 kDa were detected in pepper leaf extracts. Both activities were markedly inhibited by Mg2+ and Zn2+; activity of the 18 kDa RNase was stimulated by Ca2+. Activity banding at 25 kDa activity, degrading both RNA and DNA as substrate (nuclease activity) and inhibited by EDTA and Zn2+, was detected in bacterial cell extracts and in culture fluids of both races 1 and 2 of X. campestris pv. vesicatoria. No significant changes in plant nucleolytic activity were detected in hypersensitively reacting leaves, whereas an increase in the bacterial 25 kDa activity band was observed in both compatible and incompatible interactions.