Protection of phenylpropanoid metabolism by prior heat treatment in Lycopersicon esculentum exposed to Ralstonia solanacearum

Heat shock inhibits pathogen-induced resistance mechanisms in incompatible plant hosts, leaving them vulnerable to pathogen attack. Prior exposure of organisms to non-lethal heat induces heat shock proteins and acquired therm otolerance to otherwise lethal high temperatures. The phenylpropanoid pathw ay is a target of heat-related inhibition but it is unknown whether thermot olerance protects this pathway or its key regulator, phenylalanine ammonia- lyase (EC 4.3.1.5, PAL). It was hypothesised that prior exposure to a heat shock pulse to induce the accumulation of heat shock proteins, specifically the 70-kDa heat shock protein (Hsp70 - inducible/Hsc70 - constitutive), wo uld protect phenylpropanoid metabolism from heat-induced inhibition. The to mato, Lycopersicon esculentum L. cv. UC82B, transformed with PAL2-GUS, and Ralstonia solanacearum, biovar II, were used as incompatible host-pathogen model. A prior heat shock pulse induced significant accumulation of Hsp70/H sc70 and enhanced cell viability. This protected the pathogen-activated phe nylpropanoid pathway (PAL2-GUS activity, PAL enzyme activity, lignin deposi tion) from heat-induced inhibition and promoted cell survival after a subse quent prolonged heat shock. This study suggests phenylpropanoid metabolism as a target of Hsp70/Hsc70-related protection of the resistance response ac tivated in tomato against avirulent strains of Ralstonia solanacearum from heat-induced inhibition during a concomitant heat shock. (C) 2001 Editions scientifiques et medicales Elsevier SAS.