Diethyldithiocarbamic acid inhibits the octadecanoid signaling pathway for the wound induction of proteinase-inhibitors in tomato leaves

The induction of proteinase inhibitor I synthesis in tomato (Lycopersicon esculentum) 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, polygalacturonic acid (PCA), and linolenic acid, but not by jasmonic acid, suggesting that DIECA interferes with the octadecanoid signaling pathway. DIECA only weakly inhibited tomato lipoxygenase activity, indicating that DIECA action occurred at a step after the conversion of linolenic acid to 13(S)-hydroperoxylinolenic acid (HPOTrE). DIECA 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 PCA.

Biocontrol by phenazine-1-carboxamide-producing Pseudomonas chlororaphis PCL1391of tomato root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici

Seventy bacterial isolates from the rhizosphere of tomato were screened for antagonistic activity against the tomato foot and root rot-causing fungal pathogen Fusarium oxysporum f. sp. radicis-lycopersici. One isolate, strain PCL1391, appeared to be an efficient colonizer of tomato roots and an excellent biocontrol strain in an F. oxysporum/tomato test system. Strain PCL1391 was identified as Pseudomonas chlororaphis and further characterization showed that it produces a broad spectrum of antifungal factors (AFFs), including a hydrophobic compound, hydrogen cyanide, chitinase(s), and protease(s). Through mass spectrometry and nuclear magnetic resonance, the hydrophobic compound was identified as phenazine-1-carboxamide (PCN). We have studied the production and action of this AFF both in vitro and in vivo. Using a PCL1391 transposon mutant, with a lux reporter gene inserted in the phenazine biosynthetic operon (phz), we showed that this phenazine biosynthetic mutant was substantially decreased in both in vitro antifungal activity and biocontrol activity. Moreover, with the same mutant it was shown that the phz biosynthetic operon is expressed in the tomato rhizosphere. Comparison of the biocontrol activity of the PCN-producing strain PCL1391 with those of phenazine-1-carboxylic acid (PCA)-producing strains P. fluorescens 2-79 and P. aureofaciens 30-84 showed that the PCN-producing strain is able to suppress disease in the tomato/F. oxysporum system, whereas the PCA-producing strains are not. Comparison of in vitro antifungal activity of PCN and PCA showed that the antifungal activity of PCN was at least 10 times higher at neutral pH, suggesting that this may contribute to the superior biocontrol performance of strain PCL1391 in the tomato/F. oxysporum system.