MODIFICATION OF COMPETENCE FOR IN-VITRO RESPONSE TO FUSARIUM-OXYSPORUM IN TOMATO CELLS .1. SELECTION FROM A SUSCEPTIBLE CULTIVAR FOR HIGH AND LOW POLYSACCHARIDE CONTENT

Plant cell walls play a major role in the outcome of host-parasite int eractions. Wall fragments released from the plant, and/or the fungal p athogen, can act respectively as endogenous and exogenous elicitors of the defence response, and other wall components, such as callose, lig nin, or hydroxyproline-rich glycoproteins, can inhibit pathogen penetr ation and/or spreading. We have previously demonstrated that calli fro m tomato cultivars resistant in vivo to Fusarium oxysporum f.sp. lycop ersici show a high amount of polysaccharides in vitro. The aim of the present work was to assess the possible role of polysaccharide content and/or synthetic capacity in determining the competence of plant cell s for active defence. For this purpose, tomato cell clones with increa sed and decreased polysaccharide (FL(+), FL(-)) and callose (A(+), A(- )) content have been selected by means of specific stains as visual ma rkers and tested for the effect of these changes on the extent of resp onse to Fusarium. The analysis of several parameters known to be indic ative of active defence (cell browning after elicitor treatment, perox idase and beta-glucanase induction and inhibition of fungal growth in dual culture) clearly shows that FL(+) and A(+) clones have acquired a n increased competence for the activation of defence response. The res ults are thoroughly discussed in terms of an evaluation of the relativ e importance of constitutive and/or inducible polysaccharide synthetic capacity for plant response to pathogens, and their possible regulati on by plant physiological backgrounds.