Impact of low and high fluence rates of UV-B radiation on growth and oxidative stress in Phormidium foveolarum and Nostoc muscorum under copper toxicity: differential display of antioxidants system

摘要

In the present study, impact of low (UV-BL) and high (UV-BH) fluence rates of UV-B on growth, oxidative stress and antioxidant system was studied in two cyanobacteria i.e. Phormidium foveolarum and Nostoc muscorum under Cu (2 and 5 μM) toxicity after 24 and 72 h of experiments. UV-BH and Cu treatment decreased growth of both the cyanobacteria and Cu induced decrease in growth was accompanied by a significant increase in Cu accumulation. Levels of reactive oxygen species (ROS), i.e. superoxide radicals (SOR; $ text O_{2}^{cdot,-} $ ) and hydrogen peroxide (H2O2) were significantly increased by Cu and UV-BH exposure which in turn accelerated lipid peroxidation (malondialdehyde: MDA) and protein oxidation (reactive carbonyl groups: RCG). Activities of enzymatic antioxidants, such as superoxide dismutase (SOD), peroxidase (POD) and glutathione-S-transferase (GST) were increased by both doses of Cu as well as UV-B. Conversely, Cu and UV-BH drastically decreased catalase (CAT) activity. After the commencement of 24 h of treatment with Cu alone and together with UV-BH, non-protein thiols (NP-SH) contents were decreased while after 72 h, a reverse trend was noticed. Unlike NP-SH, cysteine content decreased appreciably during the treatments. In contrast to this, low dose (UV-BL) of UV-B did not influence growth, SOR, H2O2, MDA and RCG contents. An improvement in CAT activity and NP-SH content was observed under Cu and UV-BL treatment; hence, UV-BL treatment resulted into certain degree of protection against Cu toxicity in both the organisms. Thus, the results showed that UV-BH and UV-BL exerted differential effects on both the organisms under Cu toxicity, and compared to N. muscorum, P. foveolarum was less affected by Cu and UV-BH.