Insecticides are used worldwide in agriculture in vast amount every year. Use of pyrethroid insecticides has increased during past two decades due to their high knock down action and considerably low mammalian toxicity. Residual toxicity of the insecticides has also gone up due to their extensive use making it necessary to develop strategies for their rapid detoxification in the environment. The present study was undertaken to study the response of normal and cypermethrin pre-exposed Anabaena sp. PCC 7119 strains against the pyrethroid insecticide. Assay for 5 days showed enhanced growth performance of the tolerant strain up to 40 μM cypermethrin compared to that of normal strain. The stress indicating fluorescence parameters, viz., relative variable fluorescence at J level (Vj), net rate of PSII closure (M0) and effective dissipation of active RC (DI0/RC) were low in the strain having tolerance than of a normal one. Similarly, there was enhancement of the photosynthetic efficiency measured through the estimation of variable fluorescence (Fv) and fluorescence yield. The plant efficiency measured through derived fluorescence parameters, viz., maximum trapping rate of active PSII (TR0/ RC), trapping probability (TR0/Abs), electron transport probability (ET0/TR0), and electron transport in active RC (ET0/RC) showed higher values in the tolerant strain than in the normal one.
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