| Pak-choi(Brassica campestris L.ssp.chinensis(L.)Makino var.communis Tsen et Lee)is an important cruciferous vegetable crop in East and Southeast Asia and is widely consumed in China and Japan.Pakchoi is a crisp vegetable and represents an excellent source of vitamins,minerals,and carotenoids.Pakchoi has been receiving greater commercial interest due to its attractive appearance and high nutritional value.Leaves of harvested pakchoi,however,are susceptible to yellowing,wilting,and decay during storage at ambient temperatures,which results in a rapid deterioration in overall quality.Several studies of methods to extend the shelf life of harvested produce have been conducted,including low temperature storage,dimethyl dicarbonate treatment,exogenous nitric oxide treatment,citrus peel essential oil treatment,and controlled atmosphere storage.Light plays a vital role in plant growth and development,as well as regulating the levels of phytochemicals.Light-emitting diode(LED)technology can be uses to control spectral composition and light intensity.LED lighting offers novel possibilities in regulating the postharvest quality of produce due its advantages of small size,durability,efficiency,and relatively cold emitting surfaces,white,red,and green LED lighting treatments enhanced the storage life of leaf lettuce and white-blue LED irradiation maintained or improved the quality of Brussels sprouts during storage and transport.Thus,the use of LED lighting may also have a beneficial effect on preserving or increasing the nutritional and health-promoting compounds in harvested fruits and vegetables.In this study,the effect of LED irradiation on quality in pak-choi.The effect of LED irradiation on senescence,antioxidant enzyme and chlorophyll-related enzyme activity,as well as their corresponding gene expression was evaluated in pakchoi.Results indicated that LED irradiation significantly delayed the senescence of harvested pakchoi when stored at 20 °C for 7 d,and the maintenance of the postharvest quality of pakchoi was associated with a reduction in the rate of respiration.The LED treatment also induced higher levels of gene expression and enzyme activity of several antioxidant enzymes,relative to the untreated control group.The LED treatment also suppressed the expression and activity of several chlorophyll-degrading genes(Br Chlase1,Br Chlase2,and Br PPH)and enzymes,and increased the expression of the chlorophyll synthetase gene,Br HEMA1.Metabolomic datas show that,a total of 633 different metabolites were identified among the three groups of samples,that were associated with 24 different metabolic pathways.Four of the pathways with significant differences in response to LED irradiation were carbon pool by folate,folate biosynthesis,thiamine metabolism,and glutathione metabolism.Porphyrin and chlorophyll metabolism,as well as glucosinolate biosynthesis,were also significantly affected by LED irradiation.Relative to the untreated control,LED-treated pak-choi maintained a higher level of metabolites in six metabolic pathways,including a higher level of folic acid,glutathione,and total glucosinolate after 5 d of storage.The transcriptome results indicated that LED irradiation significantly delayed the senescence of postharvest pak-choi.Moreover,7761 differentially expressed genes by LED irradiation during the postharvest storage were identified by transcriptomic analysis.Several pathways were markedly affected by LED irradiation,and two of which with the most conspicuous variation were photosynthesis and glucosinolate biosynthesis,notably,porphyrin and chlorophyll metabolism were also significantly affected by LED irradiation.Further metabolome analysis revealed that LED irradiation maintained a higher level of metabolites in above three metabolic pathways,and following by a high content of chlorophyll and total glucosinolate at 5 d of storage.These results indicate that postharvest LED illumination represents a potential tool for modifying the metabolic profile of pa-choi to maintain quality and nutraceutical levels during storage. |
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