Long- and short-term protective responses of rice seedling to combat Cr(VI) toxicity

In India, rice is the principal crop and is the staple diet of majority of the population. Widespread use of hexavalent chromium [Cr(VI)] in leather processing, wood preservatives, stainless-steel manufacture, and electroplating industries has resulted in contamination of paddy fields and poses a great challenge to the society be it crops, animals, or human beings. Cr(VI) toxicity results in growth inhibition and leading to changes in components of antioxidant systems as well as secondary metabolites. We evaluated the comparative short and long term effects of Cr(VI) stress on rice plants to explore the plant defense responses against Cr stress. Different assays including the phenolic and flavonoid content evaluation, malondialdehyde (MDA), proline, antioxidant enzyme analysis, and DPPH assay were performed to understand the plant response against the Cr(VI) stress. Total phenols and flavonoids were significantly higher in Cr stressed plants as compared to control groups. Under Cr(VI) exposure, significant higher accumulation of proline was observed. Similarly, high levels of MDA content were also observed after 7 days of Cr stress. In addition, the antioxidant activities such as GST, APX, and SOD including DPPH radical scavenging were also markedly increased during Cr(VI) stress. Further identification and quantification of phenols were done spectrophotometrically to view the whole spectrum of phenolics. HPLC analysis showed gallic acid as the main contributor to abiotic defense response. Our study showed that Cr stress imposes serious toxic effects and plant phenolics have a protective role against metal stress.