Heavy Metal-induced Germination and Early Growth Impairment in Amaranthus lividus L.: Implications of Oxidative Membrane Damage

摘要

Seeds of a tropical leaf crop Amaranthus lividus L. were treated with different concentrations of PbCl_2 and CdCl-2 till 168 h of germination. Their effects on the levels of reactive oxygen species and activities of several antioxidative enzymes, oxidative damage to membrane lipids, proteins, overall membrane integrity and ethylene evolution were estimated. Treatment with both the heavy metals caused significant reduction in germination and early growth performances depending on the concentrations oftreatment. Decline in post-germinative early growth performances under Pb~(2+) and Cd~(2+) exposure was documented through root length, shoot length, biomass accumulation and summative relative growth index values. Treatment with 10~(-3) M lead and 10~(-4) M cadmium salts significantly raised the levels of O_2~. and H_2O_2 with concomitant reduction in activities of antioxidative enzymes like catalase, peroxidase and superoxide dismu-tase in 168-h-old seedlings with increasing concentrations of heavy metals. Seedlings under treatment manifested significant enhancement of lipoxygenase mediated membrane lipid peroxidation and reduction in membrane protein thiol level compared to untreated seedlings. Significant impairment of membrane integrity or destabilization of newly assembled membrane system of juvenile tissues of lead and cadmium-supplemented seedlings could be evidenced from the data of UV-absorbance spectra of tissue leachate, membrane permeability status, membrane injury index and relative leakage ratio. Ethylene evolution in lead and cadmium-treated seedlings exhibited a prominent decline, supporting the view of loss of membrane integrity in Amaranthus seedlings. A possible role of reactive oxygen species-mediated membrane damage could be suggested as a plausible mechanism for heavy metal-induced toxicity and post-germinative growth impairment or seedling establishment.