Amelioration of toxic effects of lead (Pb) and chromium (Cr) in four black gram (Vigna mungo L.) Hepper] cultivars with the application of kinetin

To examine the effect of kinetin (Kin) in alleviating the toxic effects of lead (Pb) and chromium (Cr) on four black gram cultivars. This study was conducted in earthen pots lined with polyethylene bags and filled in with sterilized sand, at the University of Agriculture, Faisalabad, Pakistan during the spring season 2004. Thirty days after germination we imposed six treatments viz. control (T0), Pb @ 20 mg kg-1 (T1), Cr @ 30 mg kg-1 (T2), Kin @ 100 mug/g (T3), Pb @ 20 mg kg-1 & Kin & 100 mug/g (T4), Cr @ 30 mg kg- 1 & Kin @ 100 mug/g (T5). We observed significant reduction in the stomatal conductance, assimilation rate, transpiration rate, leaf area, and harvest index of black gram plants treated with Pb and Cr singly. The joint application of Kin and heavy metals (Pb and Cr) showed significant improvement in all the parameters under investigation but it could not fully ameliorate the toxic effects of heavy metals. As regards the heavy metal ion uptake by different plant organs, plants treated with Pb and Cr alone showed higher sequestering of both metals in their roots. However, plants receiving joint application of Kin and heavy metals (Pb and Cr) showed higher translocation of both heavy metals towards their shoot. Cr particularly showed more translocation towards roots than Pb. Despite both heavy metals significantly reduced all the parameters, Pb application either alone or in combination with Kin proved more toxic. All the parameters showed highly significant negative correlation with Pb content in both roots and shoot. The Cr content in the roots of black gram plants also showed strong negative correlation with all these parameters. Among the black gram cultivars Mash ES1 (V4) proved comparatively more sensitive, Mash 80 (V1) showed more resistance, while Mash 88 (V2) and Mash 97 (V3) exhibited optimum sensitivity to heavy metal treatments. This study has great implication for the selection of black gram cultivars suitable for cultivation in the riverine areas of Pakistan and resembling agro-ecosystems in the world threatened with the drainage of untreated industrial effluents.