Hydrogen Sulfide and Redox Homeostasis for Alleviation of Heavy Metal Stress

Abstract

The industrial development has led to the release of heavy metals (HMs) in the environment beyond the safe limit. The effluents of industries carrying HMs like lead, mercury, cadmium, aluminium, zinc, copper, arsenic, etc. are admixed with the surrounding water bodies. Agricultural fields when irrigated with water from these polluted sources also get contaminated which ultimately has led to the toxicity in plants due to accumulation of metals in their tissues above the threshold limit. Metal toxicity reduces plant growth and affects crop yield. In addition, metal toxicity also induces the formation of reactive oxygen species (ROS) which disturb the redox homeostasis of the cells. ROS, when present above a threshold level in cells, damage the lipid membranes and other macromolecules. However, plants have some protective machinery such as osmolytes, and enzymatic and non-enzymatic antioxidants which protect them from metal stress and helps in the detoxification of ROS. As a potent endogenous gasotransmitter, hydrogen sulfide (H2S) can enhance the function of these protective machineries of plants when exogenously applied. H2S also protects proteins which are sensitive to damage by ROS through persulfidation of cysteine residues present in the protein. During metal stress, H2S can mediate the signalling pathways of calcium and nitric oxide (NO). This chapter mainly deals with the toxic effect of different HMs in plants, metabolism of H2S and its protective role during metal toxicity in plants.