Heavy Metals Stress and Plants Defense Responses

Abstract

Heavy metals bioaccumulation and bio amplification in the environment are serious constraints for plants and all living organisms. Heavy metals have a serious impact on crop production, and, additionally, their intake in foodstuffs has devastating impacts on human health and causes severe diseases, including Alzheimer’s, cancer, and Parkinson’s disease. Heavy metals reduce seed germination, root and shoot growth, biomass accumulation, and yield, and cause chlorosis and necrosis and inhibit various physiological processes like photosynthesis, transpiration and cause oxidative damage in plants. The heavy metals interact with vital organs such as DNA and protein, and lead to the production of reactive species (ROS). The production of ROS brings severe metabolic, morphological as well as physiological abnormalities in plants which include the degradation of proteins and lipid peroxidation. In such circumstances, plants have adopted a range of defense mechanisms to overcome the toxic effects of metals. One of the key defense mechanisms of plants’ response to heavy metals is the use of chelating molecules through the production of Phyto-chelations, at both intra- and intercellular levels, which then act to remove ions of HMs from sensitive sites of the cell and, secondly, metallothioneins which protect plants by scavenging ROS. Many compounds, such as proline, which are not enzymatically synthesized, are able to boost the capacity of metals detoxification of intracellular enzymes. Plants’ symbiotic relationships with arbuscular mycorrhizal is another way to counter HMs as it has the capability to immobilize HMs and minimize their uptake via plant roots through the process of binding of ions of HMs. The use of miRNA, organic acids, amino acid and salicylic acid and transgenic species can effectively enhance plants’ defense response against HMs’ stress.

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