Effects of Nickel Toxicity on the Indices of Germination and Ca2+ ATPase Activity in Cowpea Plant ( Vigna unguiculata  )

Despite the essential role in plants, toxicologists have considered Nickel (Ni) toxicity as an environmental threat to biological systems upon over-exposure. The study examined the phytotoxicity of Ni at 0, 50 and 100 ppm concentrations on fresh weight, length and growth rate of plant as well as leaf Ca²⁺ ATPase activity using Cowpea seedlings grown in contaminated soil for seven (7) days of exposure. The study revealed no significant alterations (p > 0.05) in the fresh weight (1.97±0.16 g and 1.42±0.22 g) of cowpea seedlings exposed to 50 and 100 ppm Nicontaminated soil relative to the control vehicle (2.05±0.12 g). In each case, the mean length (9.12±0.88 cm), growth rate (53.75±0.45 %) and leaf Ca²⁺ ATPase activity (55.90±1.49 units/mg protein) of cowpea seedlings grown in soil samples treated with 100 ppm Ni showed marked significant decrease (p < 0.05) in relation to their controls, but these parameters measured in cowpea seedlings of soil samples treated with 50 ppm Ni showed no significant difference (p > 0.05) as compared with the control vehicles. Therefore, the phytotoxicity of Ni on the measured parameters was observed to occur significantly at 100 ppm with adverse effects on plant length, plant growth rate and leaf Ca²⁺ ATPase activity.