Extensive industrial activities resulted in an increase in chromium (Cr) contamination in the environment. The toxicity of Cr severely affects plant growth and development. Cr is also recognized as a human carcinogen that enters the human body via inhalation or by consuming Cr-contaminated food products. Taking consideration of Cr enrichment in the environment and its toxic effects, US Environmental Protection Agency and Agency for Toxic Substances and Disease Registry listed Cr as a priority pollutant. In nature, Cr exists in various valence states, including Cr(III) and Cr(VI). Cr(VI) is the most toxic and persistent form in soil. Plants uptake Cr through various transporters such as phosphate and sulfate transporters. Cr exerts its effect by generating reactive oxygen species (ROS) and hampering various metabolic and physiological pathways. Studies on genetic and transcriptional regulation of plants have shown the various detoxification genes get up-regulated and confer tolerance in plants under Cr stress. In recent years, the ability of the plant to withstand Cr toxicity by accumulating Cr inside the plant has been recognized as one of the promising bioremediation methods for the Cr contaminated region. This review summarized the Cr occurrence and toxicity in plants, role of detoxification genes in Cr stress response, and various plants utilized for phytoremediation in Cr-contaminated regions.

Abiotic stresses adversely affect cellular homeostasis, impairing overall growth and development of plants. These initial stress signals activate downstream signalling processes, which, subsequently, activate stress-responsive mechanisms to re-establish homeostasis. Dehydrins (DHNs) play an important role in combating dehydration stress. Rice (Oryza sativa L.), which is a paddy crop, is susceptible to drought stress. As drought survival in rice might be viewed as a trait with strong evolutionary selection pressure, we observed DHNs in the light of domestication during the course of evolution. Overall, 65 DHNs were identified by a genome-wide survey of 11 rice species, and 3 DHNs were found to be highly conserved. The correlation of a conserved pattern of DHNs with domestication and diversification of wild to cultivated rice was validated by synonymous substitution rates, indicating that Oryza rufipogon and Oryza sativa ssp. japonica follow an adaptive evolutionary pattern; whereas Oryza nivara and Oryza sativa ssp. indica demonstrate a conserved evolutionary pattern. A comprehensive analysis of tissue-specific expression of DHN genes in japonica and their expression profiles in normal and PEG (poly ethylene glycol)-induced dehydration stress exhibited a spatiotemporal expression pattern. Their interaction network reflects the cross-talk between gene expression and the physiological processes mediating adaptation to dehydration stress. The results obtained strongly indicated the importance of DHNs, as they are conserved during the course of domestication.

OsGSTU30 increases the abiotic stress tolerance in plants either by its catalytic activity or by modulating the expression of stress responsive genes.

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Extensive use of hexavalent chromium [Cr(VI)] in leather tanning, stainless-steel production, wood preservatives and electroplating industries has resulted in widespread environmental pollution and poses a serious threat to human health. A plant's response to Cr(VI) stress results in growth inhibition and toxicity leading to changes in components of antioxidant systems. In a previous study, we observed that a large number of glutathione S-transferase (GST) genes were up-regulated under Cr(VI) stress in rice. In this study, two rice root-specific Tau class GST genes (OsGSTU30 and OsGSTU41) were introduced into yeast (Schizosaccharomyces pombe). Transformed yeast cells overexpressing OsGSTU30 and OsGSTU41 had normal growth, but had much higher levels of GST activities and showed enhanced resistance to Cr(VI) as compared to control cells (transformed with empty vector). Also, a higher accumulation of chromium was found in the transformed yeast cells as compared to the control cells. Manipulation of glutathione biosynthesis by exogenous application of buthionine sulfoximine abolishes the protective effect of OsGSTs against Cr(VI) stress. These results suggest that Tau class OsGSTs play a significant role in detoxification of Cr(VI), probably by chelating and sequestrating glutathione-Cr(VI) complexes into vacuoles.