Hydrogen sulphide trapeze: Environmental stress amelioration and phytohormone crosstalk

Hydrogen sulphide (H₂S) is recognized as the third endogenous gasotransmitter in plants after nitric oxide (NO) and carbon monoxide (CO). Though initially visualized as a toxic gaseous molecule, recent studies have illustrated its diverse role in regulating plant growth and developmental physiology. H₂S is also a potent inducer of osmolytes and cellular antioxidants of enzymatic and non-enzymatic origins. It interacts with the Ca²⁺ and NO signaling pathways. Exogenous fumigation of H₂S or application of the H₂S donor, sodium hydrosulphide (NaHS) has been found to be beneficial in the amelioration of multiple abiotic stresses like salinity, drought, temperature, hypoxia and heavy metal toxicity. H₂S also protects stress-sensitive proteins via persulphidation of cysteine residues, prone to reactive oxygen species (ROS)-mediated oxidation. It is well established that plants are highly dependent on phytohormone signaling during any physiological process. By virtue of the diversity of the H₂S-mediated signaling network, interactions and crosstalks of this gasotransmitter with the plant hormones are evident. This article presents a detailed summary regarding the role of H₂S in oxidative and environmental stress tolerance; and furthermore illustrates the reported interactions with crucial hormones like abscisic acid, auxins, gibberellic acid, ethylene and salicylic acid under physiologically differing circumstances.