Cell wall and reactive oxygen metabolism responses of stored Shine Muscat grapes to combined melatonin and 24-epibrassinolide treatment

Abstract

Combined treatment with melatonin (MT) and 24-epibrassinolide (EBR) is a novel compound hormone preservation technology, but there are few studies on its effects in Shine Muscat grapes. This study used Shine Muscat grapes to investigate the effects of MT and EBR co-treatment on the regulation of cell wall metabolism and reactive oxygen species. After 56 days of storage, combined treatment with MT and EBR maintained the structural integrity of the cell wall and cellular organelles, delayed the decrease in cellulose content and original pectin and the increase in soluble pectin, and inhibited the activity of cellulase, polygalacturonase, pectin methylesterase, and β-galactosidase. The process of cell wall metabolism was slowed down and cell wall dissolution was inhibited during storage. At the same time, MT+EBR treatment group inhibited the increase of MDA content and production rate after harvest, and increased the contents of the total phenolic and flavonoid. At the end of storage, MDA content in fruit and fruit stalk of MT+EBR group was decreased by 19.03 %, 26.05 % compared with MT groups and decreased by 21.59 % and 31.39 % compared with EBR groups. MT+EBR treatment group could not only effectively improve the hydroxyl free radical clearance rate and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging rate of grape fruit and fruit stalk during storage, but also improve superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), phenylalanine ammonia-lyase (PAL), 4-coumaric acid-coenzyme A ligase (4CL) and cinnamic acid-4-hydroxylase enzyme activity(C4H). These results suggest that the combined MT/EBR treatment can maintain grape fruit firmness by regulating fruit cell wall metabolism, slowing down cellular microstructure damage, enhancing enzymatic antioxidant defense system, delaying post-harvest senescence, and prolonging the storage period.