Phytotoxic Responses and Plant Tolerance Mechanisms to Cadmium Toxicity

Cadmium (Cd) is a non-essential highly toxic element that poses a potential health threat for plants, humans, and animals at considerably smaller concentrations. Plants can uptake Cd from soil and water due to its high mobility. In this review, the plant responses towards Cd phytotoxicity and the mechanism of Cd tolerance are summarized. Prevalent responses of Cd toxicity in plants are DNA damage, alteration in gene expression, cell division, and cell death which lead to metabolic, anatomic, and morphological modifications ranging from protein degradation to lower uptake of water and nutrients, chlorosis, inhibition of photosynthesis, and crop yield losses. Plants possess an array of mechanisms like cell wall binding, reduced transport, compartmentation in the vacuole, and chelation with metallothioneins, or phytochelatins in the detoxification and thus tolerance to Cd. Some plants develop structural and genetic adaption to achieve tolerance to Cd. Activation of plant antioxidative defense system and modulation of hormonal levels, alteration of secondary metabolites, and higher mineral nutrition triggers alleviation of Cd stress. The current state of knowledge on the effect of Cd stress and possible management strategies to avert damage and develop Cd-resistant crops have also been discussed.