Transcriptomic and metabolomic analyses insight into the synergistic effects of nitric oxide and hydrogen sulfide fumigation on enhancing postharvest antioxidant defense and phenylpropane metabolism in ‘crystal’ grape

Abstract

‘Crystal’ grapes are thin and juicy skin and brittle pericarp tissues, which are extremely perishable with a short shelf life after harvest, and in order to examine the influence of NO and H₂S fumigation on the physiological metabolism of ‘Crystal’ grape during postharvest storage. In this study, transcriptomic and metabolomic analyses revealed the impact of nitric oxide (NO) and hydrogen sulfide (H₂S) fumigation on the physiological metabolism, disease resistance in ‘Crystal’ grape. The results demonstrated that the combined treatment of NO and H₂S preserved the storage quality of ‘Crystal’ grape. This positive preservation effect was attributed to enhanced antioxidant capacity and the stimulation of phenolic secondary metabolite biosynthesis. The analysis were mainly enriched in phenylpropanoid and flavonoid biosynthesis pathways. NO + H₂S up-regulated the expression of key genes in phenylpropanoid metabolism, including VvPAL, Vv4CL, VvFLS, VvCCR, and VvPOD, and increased the enzymatic activities of phenylalamine ammonia lyase (PAL), cinnamate 4-Hydroxylase (C4H), peroxidase (POD), and beta-glucosidase (BGLU). Furthermore, with the positive regulation of the phenylpropanoid metabolic, NO + H₂S also activated the flavonoid biosynthesis, promoting the accumulation of secondary metabolites such as quercetin, kaempferol, myricetin, and (+) - catechin. These changes enhanced postharvest disease resistance and antioxidant capacity in ‘Crystal’ grape. Additionally, NO + H₂S treatment reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) accumulation by upregulating antioxidant enzymes, including ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD) and glutathione reductase (GR), thereby mitigating oxidative stress. This process helps maintain redox homeostasis, reduces membrane lipid peroxidation, and delays postharvest quality deterioration.