Salicylic acid alleviates methyl viologen induced oxidative stress through transcriptional modulation of antioxidant genes in Zea mays L

Salicylic acid (SA) is an important growth regulator that participates in both biotic as well as abiotic stress re- sponse in plants. Both-biotic and abiotic stresses are characterized by elevated cellular reactive oxygen species (ROS). We examined the biochemical and molecular effects of SA on the ROS scavenging system in maize. Pre- treatment of maize plants with SA prior to stress, reduced electrolyte leakage, enhanced protein accumulation, improved root biomass and grain yield. SA application also led to a general enhancement in the biochemical activities of three major ROS scavenging antioxidant enzymes, viz. superoxide dismutase (SOD), catalase (CAT) and peroxidases (POX). However, corresponding transcripts of various antioxidant isozymes depicted a dynamic response for different SA doses. Under stress, pre-treatment with 0.5 mM SA led to enhanced expression of all the Sod genes analyzed while higher SA concentration repressed many Sod genes. Cat 1 showed clear dose- dependent repression in response to graded concentrations of SA, while Cat 3 showed inverse dose-dependent activation in response to graded concentrations of SA. Apx 1 was found to be up-regulated at 0.5 mM SA, while higher doses of SA, i.e. 1.0 and 1.5 mM led to its repression. All the three concentrations of SA repressed Apx 2 gene. Taken together, our results indicate that SA has the potential to alleviate oxidative stress in maize through biochemical and transcriptional modulation of ROS scavenging pathway. Also, the concentration of SA has a great bearing in its alleviating role, with lower concentrations (viz 0.5 mM) being more desirable