Diethyldithiocarbamic Acid Inhibits the Octadecanoid Signaling Pathway for the Wound Induction of Proteinase Inhibitors in Tomato Leaves

The indudion of proteinase inhibitor I synthesis in tomato (Lycopersicon esculenfum) leaves in response to wounding is strongly inhibited by diethyldithiocarbamic acid (DIECA). DIECA also inhibits the induction of inhibitor I synthesis by the 18-amino acid polypeptide systemin, polygaladuronic acid (PGA), and linolenic acid, but not by jasmonic acid, suggesting that DIECA interferes with the octadecanoid signaling pathway. DIECA only weakly inhibited tomato lipoxygenase adivity, indicating that DIECA adion occurred at a step after the conversion of linolenic acid to 13(S)hydroperoxylinolenic acid (HPOTrE). DlECA was shown to efficiently reduce HPOTrE to 13-hydroxylinolenic acid (HOTrE), which is not a signaling intermediate. Therefore, in vivo, DIECA is likely inhibiting the signaling pathway by shunting HPOTrE to HOTrE, thereby severely reducing the precursor pool leading to cyclization and eventual synthesis of jasmonic acid. Phenidone, an inhibitor of lipoxygenase, inhibited proteinase inhibitor I accumulation in response to wounding, further supporting a role for its substrate, linolenic acid, and its product, HPOTrE, as components of the signal-transduction pathway that induces proteinase inhibitor synthesis in response to wounding, systemin, and PGA.