Role of Sulfur in Protection Against Major Environmental Stress in Plants

Sulfur, an essential macronutrient for plant growth, is a crucial component of several primary and secondary metabolites. Plants are frequently subjected to various environmental stresses, comprising of abiotic stress like salinity, heavy metal, drought, cold or biotic stress like pathogenic invasions. These are marked by the induction of oxidative stress by the generation of reactive oxygen species (ROS), to combat this plethora of sulfur-containing compounds are produced. “Master antioxidant” glutathione (GSH) acts as a redox sensor maintaining cellular homeostasis and preventing oxidative denaturation of proteins by protecting their thiol groups. Null mutation of GSH gene was lethal for plants. Downregulation of GSH1 , GSH2 gene, involved in GSH synthesis, led to hypersensitivity towards stress. Overexpression of glutathione reductase ( GR1 and GR2 ) glutathione transferase ( GST ) and GSH peroxidase ( GPX ) genes imparted better stress tolerance. GSH also serves as a substrate for detoxifying enzyme glyoxalase-1 during salt stress. Phytochelatins (PCs), oligomers of GSH, play key role during heavy metal stress by chelating, compartmentalizing metal ions and phytochelatin synthase ( PCS ) gene overexpression was beneficial for both 474 metal and salt stress tolerance. Drought exposure induces the production of osmoprotectants such as choline- O -sulfate and polyamines. Elemental sulfur has antifungal activity along with several secondary metabolites like glucosinolates (GSLs), camalexin, etc. Knocking out transcription factors (TFs) MYB28 and MYB29 involved in glucosinolate synthesis pathway made plants 1.8 times more susceptible to pathogen attacks than the single mutants. Benzylated thiosulfinates exhibit broad spectrum antimicrobial properties. We briefly review here the protective role of these sulfur compounds in imparting tolerance against the major abiotic and biotic stress in plants.