Metal Toxicity and Nitrogen Metabolism in Plants: An Overview

Heavy metal pollution has emerged as a severe threat to the environment as well as global food security. Exposure of plants to the heavy metals could cause perturbations in various physiological, biochemical, and metabolic processes including nitrogen (N) uptake and assimilation. Here, we discussed the effects of metal toxicity on N uptake, N forms, mechanism of metal toxicity, and nitrogen assimilation in plants. We provided a detailed description on the behavior of various enzymes including nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) under metal toxicity. We highlighted the response of various nitrogenous compounds and their special role under metal toxicity. In addition, we discussed the effects of excess metals on N fixation in plants and provided the guidelines for further studies.