Oxidative stress mitigation and initiation of antioxidant and osmoprotectant responses mediated by ascorbic acid in Brassica juncea L. subjected to copper (II) stress

Abstract

Copper (Cu) is an essential yet toxic metal, which holds the ability to induce production of reactive oxygen species (ROS) in living cells resulting in severe abiotic stress. Therefore, the aim of our current study was to investigate the effects of extrinsically added ascorbic acid (AA) on oxidative stress indicators and redox homoeostasis remediators in 7-day-old seedlings and 60-day-old plants of Brassica juncea L. (hyper-accumulator species) subjected to Cu (II) stress. Our findings showed that seed germination ballooned by 55.4% in Cu (II) stressed seedlings upon addition of 50 mg l−1 AA. Copper content accelerated in stressed seedlings and plants; however, a negative interaction was seen upon addition of AA. Both seedlings and plants exposed to Cu (II) accumulated free radicals such as H2O2 and superoxide anion, however, the addition of AA in the growth media decreased H2O2 and superoxide anion generation indicating ROS detoxification. Confocal microscopy also revealed improved cell viability and reduced H2O2 content because of enhanced antioxidant activity upon addition of AA as a protective chelate. Antioxidants such as ascorbate, flavonoids and glutathione rose significantly in Cu (II) stressed seedlings and plants in the presence of AA. Protein content increased by 51.3% and 47.5% in seedlings and plants growing in a binary combination of 100 mg l−1 Cu and AA (75 mg l−1 and 25 mg l−1), respectively. Sharp peaks for stress indicator amino acids such as cysteine and proline were seen in spectral analysis of B. juncea seedlings exposed to Cu (II). Protein thiols increased in plants grown in various binary doses Cu (II) and AA. This study provides sufficient evidence regarding the protective role of ascorbic acid (AA) against ROS and its suggested use as a soil amendment against Cu (II) toxicity in B. juncea.