and differentially respond to butachlor and UV-B stress.

Present study deals with responses of two cyanobacteria viz. and against butachlor [2-chloro-2,6-diethyl--(butoxymethyl) acetanilide] (low dose; 5 µg mL and high dose; 10 µg mL) and UV-B (7.2 kJ m) alone, and in combination. Butachlor and UV-B exposure, alone and in combination, suppressed growth of both the cyanobacteria. This was accompanied by inhibitory effect on whole cell oxygen evolution and photosynthetic electron transport activities. Both the stressors induced the oxidative stress as there was significant increase in superoxide radical (O ) and hydrogen peroxide (HO) contents resulting into increased lipid peroxidation and electrolyte leakage. In , low dose of butachlor and UV-B alone increased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), while activity of all these enzymatic antioxidants declined significantly at treatments with high dose of butachlor alone, and with low and high doses of butachlor and UV-B in combination. In enhanced activity of SOD, CAT and POD (except POD at high dose of butachlor and UV-B combination) was noticed. Ascorbate level in declined progressively with increasing intensity of stress while in varied response was noticed. Proline contents increased progressively under tested stress in both the organisms. Overall results suggest that was more sensitive than against butachlor and UV-B stresses. Hence, may be preferred in paddy field for sustainable agriculture.