Impaired Growth with declined pigment content and biochemical toxicity induced by Nickel (Ni<sup>+2</sup>) in sixty days exposed <i>Sesbania sesban</i> seedlings

Heavy metal contamination, driven by both natural and human activities, poses significant environmental risks. Nickel, a key heavy metal, harms plants and animals when its concentration exceeds safe levels. This study investigates the phytotoxic effects of various nickel concentrations on the biochemical parameters such as chlorophyll, carotenoid, proline, protein and catalase activity of Sesbania species. A pot experiment was conducted with nickel concentrations of 50, 100, 200, and 300 ppm alongside a control group (0 ppm), using NiCl2 as the source of nickel and the observations were made over 60 days. Results showed a significant decline in shoot length, from 63.4 cm to 12.2 cm, with growth inhibition observed at 200 ppm to 300 ppm. Chlorophyll and carotenoid concentrations decreased 6-7 times in plants exposed to 300 ppm nickel treatments compared to control. Proline accumulation was doubled with 100 ppm nickel treatments, which gradually declined to nearly 70% in plants with 300 ppm Ni treatment due to retarded growth. The protein concentration was decreased from 10.1 mg/gm fr. wt. to 7.9 mg/gm fr. wt. with increased Ni treatment from 100 ppm to 200 ppm whereas catalase activity was decreased from 6.4 nKat/mg protein to 2.2 nKat/mg protein with increased Ni treatment of 50 ppm to 100 ppm. Common sesban seedlings' protein and proline content showed a strong positive correlation (r=0.895). Overall, the study highlights the harmful effects of elevated nickel concentrations on Sesbania sesban, demonstrating its negative impact on plant growth and biochemical parameters.