Spodoptera litura-mediated chemical defense is differentially modulated in older and younger systemic leaves of Solanum lycopersicum

Abstract

Main conclusion: Metabolite profling, biochemical assays, and transcript analysis revealed diferential modulation of specifc induced defense responses in local, older, and younger systemic leaves in Solanum lycopersicum upon Spodoptera litura herbivory. Plants reconfgure their metabolome upon herbivory to induce production of defense metabolites involved in both direct and indirect defenses against insect herbivores. Herbivory mediated leaf-to-leaf systemic induction pattern of primary and nonvolatile secondary metabolites is not well studied in tomato. Here, we show that, in cultivated tomato Solanum lycopersicum herbivory by generalist insect, Spodoptera litura results in diferential alteration of primary metabolites, majorly sugars and amino acids and specifc secondary metabolites in local, younger, and older systemic leaves. Cluster analysis of 55 metabolites identifed by GC–MS showed correlation between local and younger systemic leaves. Re-allocation of primary metabolites like glucose and amino acids from the local to systemic leaf was observed. Secondary metabolites chlorogenic acid, cafeic acid, and catechin were signifcantly induced during herbivory in systemic leaves. Among specifc secondary metabolites, chlorogenic acid and catechin signifcantly inhibits S. litura larval growth in all stages. Local leaf exhibited increased lignin accumulation upon herbivory. Diferential alteration of induced defense responses like reactive oxygen species, polyphenol oxidase activity, proteinase inhibitor, cell wall metabolites, and lignin accumulation was observed in systemic leaves. The metabolite alteration also resulted in increased defense in systemic leaves. Thus, comparative analysis of metabolites in local and systemic leaves of tomato revealed a constant re-allocation of primary metabolites to systemic leaves and diferential induction of secondary metabolites and induced defenses upon herbivory.