Nitric oxide and hydrogen sulfide: two intimate collaborators regulating plant defense against abiotic stress

In the era of climate change, plants are continuously exposed to various abiotic stresses like extreme temperature, water scarcity, flooding, salinity, toxic metals/metalloids, and atmospheric pollutants. Physiological disorders, enzymes inactivation as well as altering the cellular redox homeostasis are attributed to these stressors, limiting plant survival, as well as crop yield loss. Considering the potential threat from these adverse situations, plant biologists are searching for new aids to combat crop loss and plant survival. Contrary, plants also have developed many adaptive features, and defense mechanisms, among which the synthesis of signaling molecules such as gasotransmitters—nitric oxide (NO) and hydrogen sulfide (H2S), are very important. These signaling molecules play vital roles in enhancing antioxidant defense and synergistic interactions with phytohormones and other protective molecules, are considered as the most promising and effective against abiotic stresses. In recent years, numerous pieces of evidence showed the endogenous concentration of both of these gasotransmitters can regulate each other as well as specific defense-related entities, especially within the antioxidative mechanisms. Moreover, NO and H2S donors have also been tested exogenously on different plant species, and both of them showed promising protection against adverse conditions. Although a significant advancement in exploring the molecular basis of such protections has been made recently, still a lot is to find out. Therefore, in this review, we have illustrated a panorama of the intimate relationship between these two signaling molecules, conferring abiotic stress tolerance in plants based on available literature. Moreover, we will try to give an indication of the research gaps and future research prospects in this specific ground.