ROS generation, oxidative burst and dynamic expression profiles of ROS-scavenging enzymes of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) in response to Erwinia amylovora in pear (Pyrus communis L)

Here, the intensity and ratio of superoxide anion (O-2(center dot)), hydrogen peroxide (H2O2) and hydroxyl anion (OH center dot-) formation along the in vitro shootlets of four pear (Pyrus communis L.) rootstocks (i.e., Pyrodwarf, OH x F40, OH x F69 and OH x F333) were scrutinized under E. amylovora inoculation, over 144 hpi. Furthermore, following identifying the most tolerant and susceptible pear rootstocks (i.e., OH x F69 and OH x F40, respectively), the dynamic expression profiles of three ROS-scavenging enzymatic genes including superoxide dismutase (SOD), Catalase (CAT) and ascorbate peroxidase (APX) were elucidated in response to E. amylovora, over 96 hpi. The highest disease tolerance was observed in OH x F69, and OH x F333, Pyrodwarf and OH x F40 occupied the next descending positions, respectively. Furthermore, the O-2(center dot-) generation rates were almost similar in all the pears studied, though the accumulation of H2O2 and OH center dot- and intensities thereof were considerably distinctive and significantly followed up the levels of disease resistance. Comparing to the controls (0 hpi), in both susceptible and tolerant pear rootstocks, transcription activity of SOD, CAT, and APX genes were overall stimulated with relatively high abundance over 24, 48, 72 and 96 hpi, though some fluctuations were also recorded. Our ROS results, altogether, indicated that E. amylovora is capable enough to stimulate ROS formation in pear, though its progress is extremely dependent upon the susceptibility ratio of the plant. Lastly, the particular expression patterns and different response time of three genes designated that pear rootstocks differentially activates genes encoding antioxidant enzymes to mitigate the possible damage of ROS during E. amylovora invasion.