Comportement des fractions peroxydasique et catalasique solubles au cours d'interactions entre le piment et le virus de la mosaïque du tabac ou le Phytophthora capsici

Abstract

Soluble peroxidase (EC 1.11.1.7) and catalase (EC 1.11.1.6) activities were evaluated in leaves of pepper (Capsicum annuum) infected with Phytophthora capsici (causal agent of mildew) and by the tobacco mosaic virus (TMV). Necrotic infections induced large increases in peroxidase activities. However, the extent of the variations was larger in cv. Phyo 636, resistant, than in cv. Yolo Wonder, after contamination with P. capsici. Systemic infection with TMV didn't significantly modify this activity. Infection with P. capsici induced an increased catalase activity, whereas a systemic infection with TMV reduced this activity. Fractions responsible for peroxidase activities were separated by electrofocusing on agarose gel. Necrotic fungal or viral interactions strongly affected the activity of the anodic and neutral fractions of total soluble extracts. A race–cultivar response was observed during the interactions with P. capsici. One of the fractions was strongly inducible. Studies conducted in the perinecrotic areas, following infection by P. capsici, showed inversely proportional gradients in peroxidase and catalase activities. Contamination with P. capsici stimulated soluble peroxidase activities located in the intercellular compartment where all fractions were represented. One of the fractions was strongly stimulated. On the opposite, catalase activity was reduced in this compartment. Differences observed in the activity patterns of the isoperoxidases suggest a specific role for each of them. Data on intra- and extra-cellular compartments suggest the existence of a selective molecular movement. The activity pattern of catalase and of peroxidase indicate a regulation of hydrogene peroxyde rate acting, at low concentrations, as a secondary messenger and contributing, at high concentrations, to the destruction of pathogenic organisms in the intercellular spaces. Key words: Capsicum, Phytophthora, tobacco mosaic virus (TMV), electrofocusing, peroxidase, catalase.