Physiological mechanisms and adaptation strategies of plants under heavy metal micronutrient deficiency/toxicity conditions

Abstract Among all micronutrients, metallic micronutrients are heavy metals by nature. These heavy metal micronutrients (HMmNs) are necessary for the proper functioning of plant cells, growth, and defense mechanisms but can be toxic to plants when taken up in higher concentrations. On the other hand, their deficiency can also cause physiological disturbance in plants and can also make them prone to various biotic and abiotic stresses. An adequate amount of these micronutrients, thus must be applied to plants for normal functioning. In the current scenarios, an excessive supply of these HMmNs through wastewater irrigation, industrial effluent application, and excessive use of agrochemicals is adding to their higher amounts, which is a major concern for sustainable agriculture. Excessive uptake of these metals can create oxidative stress in plants, thus disturbing plants biochemical machinery. The plant tends to avoid these disturbances via adopting tolerance and avoidance strategies which can further be amplified by exogenous suppression of metal concentrations (via application of amendments) as well as genetic engineering. This chapter is an effort to summarize all aspects of plant physiology associated with the normal functioning of plants under HMmNs deficiency and toxicity.