Sodium Hydrosulfide Delays Postharvest Softening of Sand Pear Fruit in Association With Altered Ethylene Production and Cell Wall Metabolism.

Sodium hydrosulfide (NaHS), a hydrogen sulfide donor, has been reported to regulate postharvest senescence and quality maintenance in horticultural crops. However, its role in sand pear softening and the underlying physiological basis remain unclear. Mature fruits of the climacteric sand pear cultivar "Sucui No. 1" were treated with NaHS and stored at 20°C to evaluate its effects on postharvest quality, ethylene production, cell wall metabolism, and softening-related gene expression. Treatment with 1 mmol L-1 NaHS delayed firmness loss and reduced ethylene production, with limited effects on fruit color, weight loss, and total soluble solids during storage. NaHS-treated fruit retained significantly higher firmness than control fruit from Day 15 onward, with the largest difference between treatments being 3.25 N on Day 15. NaHS-treated fruit retained higher levels of cellulose, hemicellulose, covalently soluble pectin, and ionically soluble pectin, and accumulated less water-soluble pectin, indicating delayed cell wall polysaccharide disassembly. Consistently, NaHS suppressed the activities of several cell wall-modifying enzymes, including cellulase, β-glucosidase, xyloglucan endotransglucosylase/hydrolase, polygalacturonase, and pectin methylesterase. RNA sequencing and qRT-PCR analyzes showed that NaHS modulated the expression of genes associated with cell wall remodeling, ethylene biosynthesis, sulfur-related metabolism, and transcriptional regulation, particularly during the early-to-middle storage stage. Transient silencing assays further indicated that the XTH gene (gene11051) was associated with cellulose-hemicellulose remodeling, whereas the two PME genes (gene26382 and gene8920) were associated with pectin solubilization. These results suggest that the delay in postharvest softening following NaHS treatment was associated with coordinated changes in ethylene production and cell wall disassembly.