Canying Li

The Role of Reactive Oxygen Species in ASM-Induced Disease Resistance in Apple Fruit

Blue mould caused by Penicillium expansum is one of the most important postharvest diseases of apple fruit. The present study was to evaluate how disease resistance in apple fruit (cv. Fuji) was affected by the dipping of acibenzolar-S-methyl (ASM) and diphenylene iodonium (DPI), a NADPH oxidase specific inhibitor. Lesion diameter on the fruit inoculated with P. expansum was significantly (P ≤ 0.05) decreased by dipping with 0.1 g/L ASM. Decreased lesion development was associated with the accumulation of hydrogen peroxide (H2O2), release of superoxide anion (O2 −), enhancement activities of NADPH oxidase (NOX), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR). Antioxidants content including ascorbic acid (AsA) and reduce glutathione (GSH) was also induced by ASM treatment. While catalase (CAT) activity was inhibited by ASM dipping. Compared with ASM treated fruit, fruit treated with DPI prior to ASM treatment exhibited bigger lesion diameter. Moreover, DPI treatment inhibited ASM-induced H2O2 and O2 − accumulation, the increase of the activities of NOX, SOD, APX, GR and content of AsA and GSH. These results suggest that pretreatment with DPI prevented accumulation of ROS induced by ASM and showed serious disease symptoms, which showed the important role of ROS in ASM-induced resistance in apple fruit.

Effect of trisodium phosphate dipping treatment on the quality and energy metabolism of apples

The effects of postharvest trisodium phosphate (TSP) dipping (0.5 mg/mL) on the quality and mitochondrial energy metabolism of apple fruit (cv. Golden delicious) were studied. The results indicated that TSP treatment inhibited the respiration intensity, delayed the increase of weight loss, and inhibited the decrease of flesh firmness, ascorbic acid (AsA), titratable acid (TA) and soluble solids content (SSC) of apple fruit. The results also indicated that TSP treatment delayed the decline of the content of ATP, ADP and energy charge of apple fruit, and enhanced the activity of H+-ATPase, Ca2+-ATPase, succinate dehydrogenase and cytochrome C oxidase. These results suggested that TSP could maintain the quality of apple fruit by mediating respiration and mitochondrial energy metabolism.

Application of sodium silicate retards the apples softening by suppressing the activity of enzymes related to cell wall degradation: Application of sodium silicate retards the apples softening by suppressing the activity of enzymes related to cell wall degradation

BACKGROUND During the storage of apples, apple softening is one of the main problems. Sodium silicate has been used to enhance disease resistance and maintain quality of fruits. In the present study, apple fruit (cv. Golden delicious) were treated with 100 mmol L-1 sodium silicate for 10 min and stored at 20 °C to investigate its effects on weight loss, flesh firmness, and the activity of cell wall-degrading enzymes. RESULTS The results indicated that 100 mmol L-1 of sodium silicate treatment delayed the increase of weight loss and decrease of the flesh firmness in apples. Sodium silicate treatment also suppressed the activity of polygalacturonic acid transeliminase and pectin methyltranseliminase, pectin methylgalacturonase, polygalacturonase, cellulase and β-galactosidase in the fruit. CONCLUSIONS Delaying apple softening by sodium silicate treatment is closely related to the inhibition of the activity of cell wall-degrading enzymes and weight loss.

Reactive oxygen species metabolism and phenylpropanoid pathway involved in disease resistance against Penicillium expansum in apple fruit induced by ϵ-poly-l-lysine: Disease resistance against Penicillium expansum in apple fruit induced by ϵ-poly-l-lysine

BACKGROUND Blue mould caused by Penicillium expansum comprises a notable disease of apple fruit during storage. ϵ-Poly-l-lysine (PL) consists of ϵ-amino and α-hydroxyl and has been used in food preservation. In the present study, apple fruits (cv. Fuji) were used to investigate the effects of PL dipping treatment, at different concentrations of PL, on the lesion diameter of fruit inoculated with P. expansum, aiming to screen the optimal concentration for controlling blue mould. The effects of PL at the optimal concentration on reactive oxygen species (ROS) metabolism and the phenylpropanoid pathway were also investigated. RESULTS The results indicated that 25, 50, 100 and 200 µL L-1 PL treatment significantly decreased the lesion diameter in apple fruit inoculated with P. expansum and the smallest lesion diameter was determined for 50 µL L-1 PL-treated fruits. The results also indicated that 50 µL L-1 PL treatment increased the hydrogen peroxide content and the activities of enzymes involved in ROS metabolism, including superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and peroxidase in apple fruit. The activity of phenylalanine ammonia-lyase and the contents of lignin, total phenolic compounds and flavonoids were also enhanced by PL treatment. CONCLUSION The disease resistance to P. expansum in apple fruits enhanced by PL treatment is related to activating ROS metabolism and the phenylpropanoid pathway and the accumulation of antifungal compounds.

Changes in the sucrose metabolism in apple fruit following postharvest acibenzolar-S-methyl treatment: Changes in the sucrose metabolism in apple fruit following postharvest

BACKGROUND Apple (cv. Ralls) fruit were treated with 0.1 g L-1 acibenzolar-S-methyl (ASM) for 10 min to evaluate the changes in enzyme activity and gene expression in the sucrose metabolism during storage at 20 °C with 30%-40% relative humidity. RESULTS The results showed that sucrose phosphate synthase (SPS) and sucrose synthase synthesis (SS-s) activity was enhanced by ASM in apple fruit during the entire storage period. Sucrose synthase-cleavage (SS-c) and neutral invertase (NI) activity was suppressed by ASM treatment but acid invertase (AI) activity was increased in the middle period after ASM treatment. Acibenzolar-S-methyl treatment also significantly inhibited SPS and NI gene expression in apple fruit during storage. However, SS gene expression increased in the ASM-treated apple fruit. High levels of expression of the fructokinase (FK) and hexokinase (HK) genes were observed during the middle storage period in the ASM-treated fruit. CONCLUSION Taken together, these results suggest that ASM delays the senescence of apple fruit by regulating the sugar metabolism.