Application and regulation of hydrogen sulfide in storage of fruits and vegetables

Abstract: In recent years, hydrogen sulfide (H2S), as an emerging endogenous gas signal molecule after nitric oxide (NO) and carbon monoxide (CO), has attracted more and more attention of researchers. In people’s traditional concept, H2S is a colorless, highly corrosive gas with the smell of rotten eggs. How-ever, researchers found that low concentrations of H2S have a positive effect in cells, studies have shown that H2S has the functions of inducing seed germination, promoting the growth and development of roots, stems, leaves and other organs, and enhancing resistance to biotic and abiotic stresses. In re-cent years, there have been many researches on the preservation and disease resistance of fruits and veg-etables, which started with Hu’s research on strawberries in 2012, and then applied to various fruits and vegetables, and attracted wide attention from scholars in postharvest physiology of fruits and vegeta-bles. As a signal molecule, the application concentration of exogenous H2S is very low, so the treated fruit and vegetable products are safe. Some studies have shown that the exogenous H2S treatment plays a positive role in the preservation of postharvest fruits and vegetables like kiwifruit, mulberry, banana, sweet cherry, hawthorn fruit, strawberry, litchi, broccoli, daylily flower, pak choy, sweet potato, pear, lo-tus root, apple and so on. During postharvest storage, fruits and vegetables will be affected by fruit softening, decay, and pathogen infection, which will lead to the decline of fruit quality and shortening of shelf life. The latest research showed that H2S treatment could significantly delay fruit ripening and se-nescence. The quality of postharvest fruits and vegetables is reflected by color, firmness, soluble solid content (SSC), titratable acid (TA) and vitamin C (Vc) content. Some studies have shown that exoge-nous H2S treatment could maintain the SSC, Vc and chlorophyll content, and inhibit the decrease of firmness. From the perspective of postharvest physiology, the researchers elaborated the role of H2S in the process of fruits and vegetables metabolism, and discussed the regulation mechanisms of H2S on postharvest fruits and vegetables preservation from the aspects of respiration, energy metabolism, plant hormones, active oxygen system. At the same time, exogenous H2S treatment could also regulate the postharvest physiology of fruits and vegetables by affecting gene expression, signal transduction and protein modification. The main enzymes related to energy metabolism are ATPase, succinate dehydroge-nase (SDH) and cytochrome c oxidase (CCO). Through the regulation of these enzymes’activities, H2S treatment could affect the energy metabolism of cells and delay fruit senescence. Ethylene as an impor-tant plant endogenous hormone plays important roles in a multitude of physiologic processes, including growth, development, maturation, and senescence. Studies have shown that H2S treatment could inhibit ethylene biosynthesis by suppressing the gene expression of key enzymes including ACC synthase(ACS) and ACC oxidase (ACO) thus slow down the ripening and senescence of postharvest fruits and vegetables. Antioxidant system in plants could keep a delicate balance between reactive oxygen species (ROS) production and scavenging, thereby maintain ROS at a non-toxic level. Exogenous H2S treat-ment could delay senescence of postharvest fruits and vegetables by regulating the activities of antioxi-dant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbic acid peroxidase (APX) and glutathione reductase (GR). Reduced glutathione (GSH) and ascorbic acid (AsA)are important non-enzymatic substances for scavenging ROS, which directly or indirectly quench high-ly active oxygen free radicals through a variety of ways. Exogenous H2S treatment reduced the loss of non-enzymatic antioxidants and the damage of reactive oxygen species to postharvest fruits and vegeta-bles. Softening is a typical characteristic of fruit ripening and senescence, so maintaining high firmness or reducing softening degree is one of the main goals to prolong the storage life of postharvest fruits and vegetables. The degradation of cell wall has a great influence on fruit ripening and softening. H2S not only participates in the endogenous sulfur metabolism of plants, but also interacts with other signal molecules like Ca 2 +, nitric oxide (NO), carbon monoxide (CO), salicylic acid (SA) and jasmonic acid (JA). It is also related to protein sulfhydrylation modification, but the related mechanism is not clear and needs further study. In this paper, the effects of H2S on the preservation and disease resistance of fruits and vegetables, as well as its regulation mechanism on the ripening and senescence of fruits and vegetables were summarized. Combined with the latest research progress at home and abroad and our own research work, the mechanism of H2S regulation on the ripening and senescence of postharvest fruits and vegetables was summarized, to provide reference for further study of H2S. In the future, we suggest to focus on the interaction of endogenous H2S with other signal molecules on the postharvest preservation and disease prevention mechanisms of fruits and vegetables. As a relatively new field of plant metabolism, protein disulfide (Cys-SSH) needs further exploration in the metabolic pathway of postharvest fruits and vegetables.