Involvement of Epicatechin in the Regulation of Natural Resistance of Avocado Fruit against Postharvest Pathogens

Abstract

In this project it was found that the activation of the mechanism of resistance in avocado fruits to Colletotrichum gloeosporioides depends on the increase of the level of the preformed antifungal diene. This increase is regulated by the synthesis of the flavonoid epicatechin present in the fruit peel. Epicatechin is an inhibitor of the enzyme lipoxygenase whose activity catalyze the breakdown of the antifungal diene. Increase in epicatechin concentration inhibits the breakdown of the antifungal compound and since the compound is continuously synthesized, both combined processes result in the increase of the antifungal level. Biotic and abiotic elicitors affecting the mechanism of resistance, all activate the synthesis of epicatechin. As abiotic elicitors were tested wounding, ethylene and CO2 treatments. As biotic elicitors were tested challenge inoculation with C. gloeosporioides, Colletotrichum magna (a non pathogen of avocado) and also non pathogenic strain of C. magna. In all the cases activation of the key enzymes of the phenylpropanoic pathway is followed by an enhance in the level of epicatechin and the antifungal diene. In order to determine the level of regulation by the different elicitors of the mechanism, the genes encoding for key enzymes of the phenylpropanoic pathway were cloned and it was found that the different elicitors regulate the expression of those genes at a translational level. Modulation of the mechanism of resistance could also be done by activation of lipoxygenase gene expression. For this purpose lipoxygenase from avocado was cloned and its over-expression, under the effect of methyl jasmonate, determined.