Oxygen toxicity and antioxidative responses in arsenic stressed Helianthus annuus L. seedlings against UV-B

•The interactive effect of UV-B and As on the growth of Helianthus annuus•Pinpointed exact mode of action of damage on photosynthetic activity by using electron donors•Damaging effect by analysing damage and their indices•Arsenic posed more toxicity than UV-B and damage was enhanced under combined stressing.•Significant interactive effects on studied parameters suggest synergistic effect of twin stressors.

In order to know the impact of elevated level of UV-B on arsenic stressed Helianthus annuus L. var. DRSF-113 plants, certain physiological (growth - root and shoot lengths, their fresh masses and leaf area; photosynthetic competence and respiration) and biochemical parameters (pigments - Chl a and b, Car, anthocyanin and flavonoids; reactive oxygen species - superoxide radicals, H2O2; reactive carbonyl group, electrolyte leakage; antioxidants - superoxide dismutase, peroxidise, catalase, glutathione-S-transferase, proline) of their seedlings were analysed under the simultaneous exposures of two arsenic doses (6 mg kg− 1 soil, As1; and 12 mg kg− 1 soil, As2) and two UV-B doses (1.2 kJ m− 2d− 1, UV-B1; and 3.6 kJ m− 2d− 1, UV-B2). As1 and As2 alone declined all the studied growth parameters - along with photosynthetic pigments which were further aggravated after the simultaneous exposures of predefined levels of UV-B. Each As exposure was accompanied by significant accumulation of As in root, shoot and leaves and was substantiated by simultaneous exposures of UV-B doses which manifested into suppressed growth, decreased chlorophyll contents and photosynthesis. In similar conditions, other photo-shielding pigments, viz. carotenoids, anthocyanin and flavonoids along with respiration and oxidative stress markers such as O2•¯, H2O2; and indicators of cell membrane damage like MDA (malondialdehyde), RCG (reactive carbonyl group), electrolyte leakage were enhanced by As, and became more pronounced after the simultaneous exposures of UV-B doses. As doses stimulated the activities of SOD, POD, CAT, GST and Pro which got further accelerated after the simultaneous exposures of UV-B doses.

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