A common bean (Phaseolus vulgaris) mutant with constitutively low cysteine desulfhydrase activity exhibits growth inhibition but uniquely shows tolerance to arsenate stress

A mutant designated as pvcys exhibiting huge deficiency in foliar L-cysteine desulfhydrase and D-cysteine desulfhydrase activity were isolated from an ethylmethane sulfonate-mutagenized M2 population of a Phaseolus vulgaris L. genotype VL 63. The mutant showed growth inhibition and morpho-agronomic anomalies but exhibited high cysteine content and very low endogenous hydrogen sulfide concentration mainly due to crippling of cysteine degradation. Despite a normal glutathione and ascorbate redox pool, the mutant suffered oxidative stress due to over-accumulation of H2O2 and consequent membrane damage by lipid peroxidation. Uniquely, this oxidative load was relieved in the mutant upon imposition to 20 and 40 μM sodium arsenate through consumption of excess cysteine to meet the growing demand for glutathione and subsequently, to confer tolerance to arsenate-induced oxidative stress. Both L-cysteine desulfhydrase and D-cysteine desulfhydrase activity was constitutively low in the mutant, even in response to external stress. The pvcys mutation was monogenic recessive in inheritance.