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.

Graphical Abstract