Differential response of oxidative stress and thiol metabolism in contrasting rice genotypes for arsenic tolerance

The mechanism of arsenic (As) tolerance was investigated on two contrasting rice (Oryza sativa L.) genotypes, selected for As tolerance and accumulation. One tolerant (Triguna) and one sensitive (IET-4786) variety were exposed to various arsenate (0–50 μM) levels for 7d for biochemical analyses. Arsenic induced oxidative stress was more pronounced in IET-4786 than Triguna especially in terms of reactive oxygen species, lipid peroxidation, EC and pro-oxidant enzymes (NADPH oxidase and ascorbate oxidase). However, Triguna tolerated As stress through the enhanced enzymes activities particularly pertaining to thiol metabolism such as serine acetyl transferase (SAT), cysteine synthase (CS), γ-glutamyl cysteine synthase (γ-ECS), γ-glutamyl transpeptidase (γ-GT), and glutathione-S-transferase (GST) as well as arsenate reductase (AR). Besides maintaining the ratio of redox couples GSH/GSSG and ASC/DHA, the level of phytochelatins (PCs) and phytochelatin synthase (PCS) activity were more pronounced in Triguna, in which harmonized responses of thiol metabolism was responsible for As tolerance in contrast to IET-4786 showing its susceptible nature towards As exposure.

► Rice varieties Triguna and IET-4786 showed differential phytotoxic responses and As accumulation.
► Arsenic induced oxidative stress and pro-oxidant enzymes activities were higher in IET-4786 than Triguna.
► Triguna tolerated stress through maintenance of thiol metabolic pathway & ASC/DHA & GSH/GSSG balance.
► PC species & PCS activity were more pronounced in Triguna than IET-4786.
► Contrastingly, IET-4786 is very sensitive to As exposure due to reduction of sulphate assimilation pathway.