Hydrogen peroxide generated by over-expression of cytosolic superoxide dismutase in transgenic plums enhances bacterial canker resistance and modulates plant defence responses.

HO generated during the oxidative burst, plays important roles in plant defenses responses against pathogens. In this study we examined the role of HO on bacterial canker resistance in transgenic plums over-expressing cytosolic superoxide dismutase. Three transgenic lines (C64, C66 and F12) with elevated levels of HO accumulation showed enhanced resistance against bacterial canker disease caused by Pseudomonas syringae pv. syringae, when compared to the non-transformed control. Analysis of the expression of several genes involved in the plant-pathogen interaction showed that the expression of those involved in SA pathway (pr1 and npr1) and JA (lox3) were activated earlier and transiently in transgenic lines C66 and F12 when compared to the wild type. However, the expression of genes involved in anthocyanin synthesis (chi, chs, f3h, dfr, atcs, myb10) and ethylene (acs) was induced at very low levels whereas it was activated by the pathogen at exaggerated levels in the non-transformed line. These results suggest that resistance observed in transgenic lines over-producing HO is correlated with an early and transient induction of defense genes associated with the SA and JA pathways and inhibition of gene expression associated with ethylene and anthocyanin biosynthesis.