The systemic accumulation of both
hydrogen peroxide (H(2)O(2)) and
proteinase inhibitor
proteins in tomato leaves in response to wounding was inhibited by the
NADPH oxidase inhibitors
diphenylene iodonium (DPI),
imidazole, and
pyridine. The expression of several defense genes in response to wounding,
systemin,
oligosaccharides, and
methyl jasmonate also was inhibited by DPI. These genes, including those of four
proteinase inhibitors and
polyphenol oxidase, are expressed within 4 to 12 hr after wounding. However, DPI did not inhibit the
wound-inducible expression of genes encoding prosystemin,
lipoxygenase, and
allene oxide synthase, which are associated with the octadecanoid signaling pathway and are expressed 0.5 to 2 hr after wounding. Accordingly, treatment of plants with the H(2)O(2)-generating
enzyme glucose oxidase plus
glucose resulted in the induction of only the later-expressed defensive genes and not the early-expressed signaling-related genes. H(2)O(2) was cytochemically detected in the cell walls of vascular parenchyma cells and spongy mesophyll cells within 4 hr after wounding of wild-type tomato leaves, but not earlier. The cumulative results suggest that
active oxygen species are generated near cell walls of vascular bundle cells by oligogalacturonide fragments produced by
wound-inducible
polygalacturonase and that the resulting H(2)O(2) acts as a second messenger for the activation of defense genes in mesophyll cells. These data provide a rationale for the sequential, coordinated, and functional roles of
systemin,
jasmonic acid, oligogalacturonides, and H(2)O(2) signals for systemic signaling in tomato plants in response to wounding.