Oxidative enzyme changes in sweet sorghum infested by stemborer (Chilo partellus Swinhoe)

Abstract

Induced response in plants is one of the important components of pest control in agriculture, and has been exploited for regulation of insect herbivore population. Plant phenols constitute one of the most common and widespread group of defensive compounds, which play a major role in HPR against herbivores. Oxidation of phenols catalyzed by polyphenol oxidase (PPO) and peroxidase (POD) is a potential defense mechanism in plants against herbivorous insects. Quinones formed by oxidation of phenols bind covalently to leaf proteins, and inhibit the protein digestion in herbivores. In addition, quinones also exhibit direct toxicity to insects. In the present study, we investigated the role of total phenols and oxidative enzymes in the defense response of sorghum, Sorghum bicolor (L.) Moench to the spotted stemborer, Chilo partellus Swinhoe. The changes of biochemical constituents such as leaf soluble protein, phenols, PPO and POD were assessed spectrophotometrically in 12 sorghum genotypes which included 10 sweet sorghum entries, a stemborer resistant and a susceptible check before and after stemborer infestation. After infestation of stemborer, phenols, peroxidase, polyphenol oxidase activity and TSP of sorghum genotypes were enhanced significantly. Resistant plants (IS 2205) exhibited higher levels of oxidative enzyme activities compared to susceptible plants (Swarna). Peroxidase and polyphenol oxidase activities and total protein content in all the infested genotypes were higher when compared to their control plants respectively. These findings suggest that resistant genotypes may be able to tolerate stemborer feeding by increasing their peroxidase and polyphenol oxidase activities and the elevated levels of enzymes may play a vital role in sorghum plants resistance to stemborer.