Roles of reactive oxygen species and anti-oxidant systems in the resistance response of chayote fruit (Sechium edule) to melon fly [Bactrocera cucurbitae (Coquillett)

Abstract

SummaryThe purpose of this study was to determine the roles of reactive oxygen species (ROS), cellular anti-oxidants, and anti-oxidative enzyme activities in the responses to infestation by melon fly (Bactrocera cucurbitae) in resistant fruit of chayote (Sechium edule) and in susceptible fruit of bitter gourd (Momordica charantia). The patterns of change in ROS following infestation of fruit showed that there was a significantly higher rate of hydroxyl radical (OH•) production in susceptible bitter gourd compared to chayote. The activities of four free radical-scavenging enzymes, catalase (CAT), peroxidase (POX), polyphenol oxidase (PPO), and superoxide dismutase (SOD), as well as the levels of cellular anti-oxidants, changed rapidly following infestation in both chayote and bitter gourd fruit, with distinct differences in the magnitude and timing of the responses. Data analysis indicated that the rapid production of excess hydrogen peroxide (H2O2) in chayote fruit immediately following infestation, and the effective neutralisation of H2O2 by the concerted action of anti-oxidative enzymes and cellular anti-oxidants, prevented melon fly infestation and overcame the damaging effects of free radicals. In contrast, the imbalance created between free radical production, especially the highly destructive OH• and superoxide radicals (O2•–), and their incomplete removal by anti-oxidative enzymes and cellular anti-oxidants, caused substantial damage to plant tissues that facilitated and predisposed melon fly maggots to feed on bitter gourd fruit making it more susceptible to infestation by melon fly. The rapid generation of H2O2, coupled with the timely action of H2O2-scavenging enzymes and cellular anti-oxidants, appeared to be the major contributing factor for resistance against melon fly in chayote. Analysis of the results showed that anti-biosis, targeting larval development might play a crucial role in the resistance of chayote fruit to infestation by melon fly.