Herbivore-induced changes in tomato (Solanum lycopersicum) primary metabolism: a whole plant perspective

Induced changes in primary metabolism are important plant responses to herbivory, providing energy and metabolic precursors for defense compounds. Metabolic shifts also can lead to reallocation of leaf resources to storage tissues, thus increasing a plant's tolerance. We characterized whole-plant metabolic responses of tomato (Solanum lycopersicum) 24 h after leaf herbivory by two caterpillars (the generalist Helicoverpa zea and the specialist Manduca sexta) by using GC-MS. We measured 56 primary metabolites across the leaves, stems, roots, and apex, comparing herbivore-attacked plants to undamaged plants and mechanically damaged plants. Induced metabolic change, in terms of magnitude and number of individual concentration changes, was stronger in the apex and root tissues than in undamaged leaflets of damaged leaves, indicating rapid and significant whole-plant responses to damage. Helicoverpa zea altered many more metabolites than M. sexta across most tissues, suggesting an enhanced plant response to H. zea herbivory. Helicoverpa zea herbivory strongly affected concentrations of defense-related metabolites (simple phenolics and precursor amino acids), while M. sexta altered metabolites associated with carbon and nitrogen transport. We conclude that herbivory induces many systemic primary metabolic changes in tomato, and that changes often are specific to a single tissue or type of herbivore. The potential implications of primary metabolic changes are discussed in relation to resistance and tolerance.