Responses of growth and antioxidative enzymes to various concentrations of nickel in Zea mays leaves and roots

To assess nickel-induced toxicity in plants, Zea mays seeds were germinated and cultured on nutrient solution with nickel concentrations of 50-200 ?M for a period of two weeks. Observed biological makers included biomass, soluble and total protein contents, and the activities of guaiacol peroxidase (GPX), ascorbate peroxidase (APX), catalase (CAT), and phenylalanine ammonia-lyase (PAL) in the leaves and roots of maize. The fresh and dry weight of leaves and roots increased in 50 ?M nickel but decreased in 100 and 200 ?M. Soluble and total protein contents were significantly increased by increasing nickel concentrations up to 200 ?M nickel in both roots and leaves of maize. Significant increases of ascorbate peroxidase (the highest activity at 200 ?M nickel), catalase (the highest activity at 50 ?M nickel), and phenylalanine ammonia-lyase (the highest activity at 100 ?M nickel) were observed in the leaves and roots of Zea mays seedlings at all tested nickel concentrations. Guiacol peroxidase activity was decreased in the leaves and roots of Zea mays seedlings exposed to different levels of nickel. The present results suggested that treatment with different levels of nickel may enhance the antioxidant activities in the leaves and roots of Zea mays seedlings, thus alleviate Ni-induced oxidative damage and enhance Ni tolerance.