Nitrate nutrition enhances nickel accumulation and toxicity in Arabidopsis plants

Nickel (Ni) has become a major heavy metal contaminant. The form of nitrogen nutrition remarkably affects IRT1 expression in roots. IRT1 has an activity of transporting Ni2+ into root cells. Therefore, nitrogen-form may affect Ni accumulation and toxicity in plants. The assumption was investigated in this study. The Arabidopsis plants were treated in Ni-contained growth solutions with either nitrate (NO3 (-)) or ammonium (NH4 (+)) as the sole N source. After 7-day treatments, Ni concentration, IRT1 expression, Ni-induced toxic symptoms and oxidative stress in plants were analyzed. The NO3 (-)-fed plants contained a higher Ni concentration, had a greater IRT1 expression in roots, and developed more severe toxic symptoms in the youngest fully expanded leaves, compared with the NH4 (+)-fed plants. The Ni-induced growth inhibition was also more significant in NO3 (-)-fed plants. Interestingly, Ni exposure resulted in greater hydrogen peroxide (H2O2) and superoxide radical (O-2 (. -)) accumulations, more severe lipid peroxidation and more cell death in NO3 (-)-fed plants, whereas the opposite was true for NH4 (+)-fed plants. Furthermore, the Ni-enhanced peroxidase (POD) and superoxide dismutase (SOD) activities were greater in NO3 (-)-fed plants NO3 (-) nutrition promotes Ni uptake, and enhances Ni-induced growth inhibition and oxidative stress in plants compared with NH4 (+) nutrition.