Evidence for chewing insect-specific molecular events distinct from a general wound response in leaves

The timing of transcript accumulation of several wound-induced genes is different in insect-damaged and mechanically damaged leaves. Transcripts for the proteinase inhibitor II and 3-hydroxy-3-methylglutaryl-coenzyme A reductase genes accumulate more rapidly in potato (Solanum tuberosum L.) leaves chewed on by caterpillars than in leaves damaged mechanically. The timing of maximum transcript accumulation was not affected by the degree of damage inflicted by the insect larvae. When applied to a mechanical wound site, regurgitant isolated from Manduca sexta larvae causes transcript accumulation profiles to shift to parallel those in insect-damaged tissue. Whether obtained from larvae fed either potato leaves or a nonplant diet, insect regurgitant fed through the petiole of detached leaves also induces accumulation of these transcripts. The transcript accumulation-inducing activity of regurgitant is enhanced by heating at 100 degrees C. Our data suggest that a heat-stable, insect-derived elicitor functions to induce the rapid accumulation of transcripts that may be involved in plant defense against herbivores. Distinct signal transduction pathways that can distinguish between insect damage and abiotic damage might therefore exist in plants.