24-epibrassinolide alleviates postharvest yellowing of broccoli via improving its antioxidant capacity.

Postharvest crop yellowing is a major concern in the broccoli industry. The effect and underlying mechanisms of 24-epibrassinolide (EBR) treatment on yellowing in postharvest broccoli were investigated. Treatment with 2 µM EBR markedly inhibited the increase of the yellowing index and L* values, causing higher retention of the metric hue angle and chlorophyll content compared to the control. Treatment also alleviated oxidative damage by preventing the accumulation of malondialdehyde and superoxide anion (O2•-). The ascorbic acid content of broccoli reached its lowest value at the end of its shelf life, whereas that of the treated sample was obviously higher than the control. Moreover, treated broccoli exhibited higher superoxide dismutase, ascorbate peroxidase, and phenylalanine ammonia-lyase activities. Multivariate statistical analysis further demonstrated the effective enhancement of EBR treatment on antioxidant enzymes. These results indicate that exogenous application of EBR ameliorates postharvest yellowing by improving the antioxidant capacity of broccoli.

Glycine betaine treatment alleviates loss of aroma-related esters in cold-stored 'Nanguo' pears by regulating the lipoxygenase pathway.

Glycine betaine (GB) is known to alleviate chilling injury in many fruit species. Therefore, we studied how GB affects the biosynthesis of esters in 'Nanguo' pears. Based on the kinds of esters, total esters, and the quantity of the main esters, it was evident that aroma losses were alleviated by GB treatment. In addition, unsaturated fatty acids contents (linoleic and linolenic acid) and the activities of lipoxygenase (LOX) and alcohol acyltransferase (AAT) enzymes were also increased. Meanwhile, comparing with the control fruit, the genes directly involved in ester synthesis were up-regulated in the GB-treated fruit. In addition, an increase in the activities and gene expression of antioxidant enzymes was observed in the treated samples. Thus, GB treatment promotes the synthesis of esters by regulating the LOX pathway and increasing antioxidant capacity, thereby effectively improving the quality of esters in cold-stored fruit.

Exogenous glycine betaine treatment alleviates low temperature-induced pericarp browning of 'Nanguo' pears by regulating antioxidant enzymes and proline metabolism.

The effect of glycine betaine (GB) on chilling injury (CI)-induced pericarp browning in 'Nanguo' pears was investigated during shelf life at 20 °C after storage at 0 °C for 120 d. GB treatment alleviated the severity of browning in 'Nanguo' pears as represented by lower browning index (BI) and browning incidence. Membrane lipid peroxidation in GB-treated fruit was lower than that in the control, and membrane integrity was maintained in good condition. The activities and expression of ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) were higher in GB-treated fruit than in control fruit. Furthermore, significantly higher proline content, proline synthesis key enzyme activities, and gene expression were observed in the treated fruit, including ornithine d-aminotransferase (OAT) and Δ1-pyrroline-5-carbox-ylate synthetase (P5CS), which were consistent with the browning tendency. In a nutshell, GB treatment can effectively alleviate pericarp browning of cold-stored 'Nanguo' pears by regulating antioxidant enzymes and proline metabolism.

GABA application improves the mitochondrial antioxidant system and reduces peel browning in 'Nanguo' pears after removal from cold storage.

Although refrigeration is commonly used in the storage of 'Nanguo' pears (Pyrus ussuriensis Maxim.), long-term refrigeration can result in browning of the pericarp. In this study, we aimed to determine how γ-aminobutyrate (GABA) affects the mitochondrial oxidation defense system in 'Nanguo' pears and how it might be used to prevent post-refrigeration peel browning. We found that fruit treated with GABA browned slower, and had lower browning indices and reactive oxygen and malondialdehyde content; increased peroxidase, superoxide dismutase, alternating oxidase, and catalase enzyme activities; and heightened enzyme-related gene expression. The mitochondria of GABA-treated fruit also showed less damage following cold storage, and there were decreases in mitochondrial membrane permeability transition pore concentrations. Furthermore, we detected an increase in the endogenous GABA content of fruits following GABA treatment. These observations indicate that, by regulating the mitochondrial oxidative defense system and maintaining mitochondrial structure, GABA is effective in terms of reducing peel browning.

Low temperature conditioning alleviates loss of aroma-related esters of 'Nanguo' pears by regulation of ethylene signal transduction.

The optimum harvest time for 'Nanguo' pears lasts for only 20 days. Refrigeration is a common technique used to extend the fruit supply. However, with low-temperature storage, the proper aroma of the pear is lost when it matures during shelf-life at room temperature. In this study, we investigated the ability of low-temperature conditioning (LTC) to regulate aroma esters of 'Nanguo' pears, and identified the key genes in the ethylene signal transduction pathway based on RNA-seq analysis. LTC caused higher ethylene production and effectively alleviated the loss of aroma-related esters in 'Nanguo' pears during refrigeration and during the subsequent shelf-life at room temperature. Furthermore, the expression levels of PuERS1, PuEIN4, PuEIN2, and PuERF were increased under LTC treatment. Thus, we speculate that the alleviation effect of LTC on fruit aroma esters is closely related to ethylene signal transduction, including up-regulated expression of PuERS1, PuEIN4, PuEIN2, and PuERF.

Changes in energy metabolism accompanying pitting in blueberries stored at low temperature.

Low-temperature storage and transport of blueberries is widely practiced in commercial blueberry production. In this research, the storage life of blueberries was extended at low temperature, but fruit stored for 30 d at 0°C pitted after 2d at room-temperature. Fruit cellular structure and physiological parameters accompanying pitting in blueberries were changed. The objective of this research was to characterise properties of energy metabolism accompanying pitting in blueberries during storage, including adenosine phosphates and mitochondrial enzymes involved in stress responses. Physiological and metabolic disorders, changes in cell ultrastructure, energy content and ATPase enzyme activity were observed in pitting blueberries. Energy shortages and increased activity of phenylalanine ammonia lyase (PAL) and lipoxygenase (LOX) were observed in fruit kept at shelf life. The results suggested that sufficient available energy status and a stable enzymatic system in blueberries collectively contribute to improve chilling tolerance, thereby alleviating pitting and maintaining quality of blueberry fruit in long-term cold storage.