Roles of Hydrogen Gas in Plants under Abiotic Stress: Current Knowledge and Perspectives.

Hydrogen gas (H) is a unique molecular messenger, which is known to be involved in diverse physiological processes in plants, from seed germination to seedling growth to regulation of environmental stresses. In this review, we focus on the role of H in plant responses to abiotic stresses, such as temperature, osmotic stress, light, paraquat (PQ)-induced oxidative stresses, and metal stresses. In general, H can alleviate environmental stresses by improving the antioxidant defense system, photosynthetic capacity, re-establishing ion homeostasis and glutathione homeostasis, maintaining nutrient element homeostasis, mediating glucose metabolism and flavonoid pathways, regulating heme oxygenase-1 (HO-1) signaling, and interaction between H and nitric oxide (NO), carbonic oxide (CO), or plant hormones. In addition, some genes modulated by H under abiotic stresses are also discussed. Detailed evidence of molecular mechanisms for H-mediated particular pathways under abiotic stress, however, is scarce. Further studies regarding the regulatory roles of H in modulating abiotic stresses research should focus on the molecular details of the particular pathways that are activated in plants. More research work will improve knowledge concerning possible applications of hydrogen-rich water (HRW) to respond to abiotic stresses with the aim of enhancing crop quality and economic value.