Growth Inhibition and Oxidative Stress Responses in Root and Shoot of Vigna radiata (L.) Wilczek under Nickel Toxicity

Abstract

An experiment was conducted to investigate the effects of nickel toxicity (100 µM Ni) on shoot and root growth, as well as the oxidative system in green gram (Vigna radiata L. Wilczek syn. Var. K-851) over a 16-day period. During this period the relationship between oxidative stress and Ni accumulation in shoot and root was studied. Depression in shoot and root growth was observed after 3d of Ni supply. Enhanced H₂O₂ concentration in roots only 24 hours after Ni supply indicated early induction of oxidative damage. Membrane lipid peroxidation was also observed early and was well related to Ni concentration. The ascorbate concentration in shoot and root showed an increase throughout the period of Ni supply, but dehydroascorbate concentration remained unaffected. The activity of the antioxidative enzymes SOD, APX and GR increased initially but decreased after 6 d of exposure to excess Ni supply. The activity of peroxidase increased up to 4 d but remained unaffected thereafter, and that of catalase decreased with the duration of excess Ni supply. Our findings suggest that oxidative damage, indicated by elevated H₂O₂ and malondialdehyde (MDA) levels, preceded the inhibition of shoot and root growth and was closely linked to the extent of Ni accumulation in the roots. Prolonged Ni exposure led to increased Ni accumulation, ultimately resulting in the breakdown of the antioxidative defense system in green gram.