Different oxidative burst patterns occur during host and nonhost resistance responses triggered by Xanthomonas campestris in pepper

Abstract

The hypersensitive reaction (HR) is the most common plant defense reaction against pathogens. HR is produced during both host- and nonhost-incompatible in- teractions. Several reports suggest that similarities exist between host and nonhost resistances. We assayed the pattern of generation of reactive oxygen species (ROS) and scav- enging enzyme activities during nonhost pathogen-plant interactions (Xanthomonas campestris pv. campestris/Capsicum annuum L.) and incompatible host pathogen-plant interactions (Xanthomonas campestris pv. vesicatoria race1/Capsicum annuum L.). Both O2 - and H2O2 accumulated much faster during nonhost resistance when compared to the host resistance. The scavenging enzyme activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) were also different during the host- and nonhost-incompatible interactions. CAT activity was much higher during nonhost resistance, and several new isozymes of SOD and POX were detected during nonhost resistance when compared to the host resistance. Lipoxygenase (LOX) activity was higher in host resistance than nonhost resistance during the early stages of infection. Interestingly, the nitric oxide (NO) radical accumulated equal amounts during both host and nonhost resistance at early stages of infection. Further studies are needed to determine the specific pathways underlying these differences between host and nonhost resistance responses.