Effects of Nickel Toxicity on Seedling Growth, Photosynthetic Pigments, Carotenoids and Phenols Contents of Cowpea Vigna unguiculata (L.)

Nickle pollution is worldwide problem due to industrial and anthropogenic activities. Seedlings of cowpea (Vigna unguiculata) were treated to different (NiSO4.6H2O) concentrations as 0.0 mM, 0.6 mM, 1.2 mM, 1.8mM and 2.4 mM salt into distilled water. The seedlings of V. unguiculta became less tolerable to nickel at higher concentration 2.4 mM as compared to control treatment. Nickel in trace amount is required for plant growth. In present study, the high level of nickel concentration 1.8 and 2.4 mM significantly (p<0.05) affected seedling growth performance and physiological, biochemical parameters of V. unguiculata. The nickel treatments at 1.2 mM concentrations significantly (p<0.05) affected the number of leaves, shoot, seedling length, fresh weight and dry weight of seedling and root / shoot ratio of V. unguiculata. The treatment of Ni+2 at 1.20 mM also significantly affected shoot root and seedling fresh and dry weight of cowpea. The leaf area, leaf weight ratio and root fresh and dry weight of V. unguiculata showed less affect at 0.6 to 2.4 mM treatment of nickel. Nickel treatment at 0.6 mM, 1.2 mM, 1.8 mM and 2.4 mM concentrations showed considerable effects on relative water content, chlorophyll ‘a', chlorophyll ‘b' total chlorophyll, carotenoids and phenols of Vigna unguiculata.