Sucrose, cell wall, and polyamine metabolisms involve in preserving postharvest quality of 'Zaosu' pear fruit by L-glutamate treatment.

'Zaosu' pear fruit is prone to yellowing of the surface and softening of the flesh after harvest. This work was performed to assess the influences of L-glutamate treatment on the quality of 'Zaosu' pears and elucidate the underlying mechanisms involved. Results demonstrated that L-glutamate immersion reduced ethylene release, respiratory intensity, weight loss, brightness (L*), redness (a*), yellowness (b*), and total coloration difference (ΔE); enhanced ascorbic acid, soluble solids, and soluble sugar contents; maintained chlorophyll content and flesh firmness of pears. L-glutamate also restrained the activities of neutral invertase and acid invertase, while enhancing sucrose phosphate synthetase and sucrose synthase activities to facilitate sucrose accumulation. The transcriptions of PbSGR1, PbSGR2, PbCHL, PbPPH, PbRCCR, and PbNYC were suppressed by L-glutamate, resulting in a deceleration of chlorophyll degradation. L-glutamate concurrently suppressed the transcription levels and enzymatic activities of polygalacturonases, pectin methylesterases, cellulase, and ß-glucosidase. It restrained polygalacturonic acid trans-eliminase and pectin methyl-trans-eliminase activities as well as inhibited the transcription levels of PbPL and Pbß-gal. Moreover, the gene transcriptions and enzymatic activities of arginine decarboxylase, ornithine decarboxylase, S-adenosine methionine decarboxylase, glutamate decarboxylase, γ-aminobutyric acid transaminase, glutamine synthetase along with the PbSPDS transcription was promoted by L-glutamate. L-glutamate also resulted in the down-regulation of PbPAO, PbDAO, PbSSADH, PbGDH, and PbGOGAT transcription levels, while enhancing γ-aminobutyric acid, glutamate, and pyruvate acid contents in pears. These findings suggest that L-glutamate immersion can effectively maintain the storage quality of 'Zaosu' pears via modulating key enzyme activities and gene transcriptions involved in sucrose, chlorophyll, cell wall, and polyamine metabolism.

Organic acids metabolism and GABA shunt involved in maintaining quality of Malus domestica by methyl jasmonate treatment.

Apples (cv. Golden Delicious) were used as the materials to investigate methyl jasmonate (MeJA) dipping on quality parameters, organic acids metabolism and GABA shunt during storage at 21 ± 1 °C and 75 ± 5 % relative humidity. Results demonstrated that MeJA treatment reduced mass loss, respiratory intensity and ethylene release, and maintained higher flesh firmness and soluble solid content of apples. MeJA also decreased malic acid content, increased succinic and tartaric acids contents, and inhibited cytoplasmic aconitase (Cyt-ACO), NADP-malate (NADP-ME), phosphoenolpyruvate dehydrogenase (PEPC), mitochondrial citrate synthase (Mit-CS), glutamate dehydrogenase (GAD), and GABA transferase (GABA-T) activities in apples. NADP-isocitrate dehydrogenase (NADP-IDH), mitochondrial cis-aconitase (Mit-ACO), and cytoplasmic NAD-malate dehydrogenase (CytNAD-MDH) activities in apples were also enhanced by MeJA dipping. Moreover, MeJA dipping enhanced MdCytNAD-MDH and MdNADP-IDH expressions, and down-regulated MdGAD, MdGABA-T, MdNADP-ME, MdPEPC, MdCyt-ACO and MdMit-CS expressions in apples. These results suggest that MeJA dipping can maintain storage quality of "Golden Delicious" apples by regulating organic acids metabolism and GABA shunt.

Effects of 1-MCP treatment on sprouting and preservation of ginger rhizomes during storage at room temperature.

The purpose of this study was to explore the effects of 1-MCP on the sprouting and preservation of ginger rhizomes during storage at room temperature. Ginger rhizomes were treated with 1 µL L-1 1-methylcyclopropene (1-MCP) and stored at 23 ± 0.2 °C. Our data showed that application of 1-MCP reduced the rate of sprouting during storage compared with the control rhizome. Respiration rate and the reducing sugar content were also reduced following 1-MCP treatment, while the starch content increased. 1-MCP treatment increased the total phenol content and inhibited polyphenol oxidase (PPO) activity. 1-MCP treatment was also associated with a higher ascorbic acid content but a reduced crude fiber content. The generation of superoxide anion free radicals (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) was lower following 1-MCP treatment, while the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) were higher compared with the controls. These results suggested that application of 1-MCP could reduce sprouting rates, decrease the accumulation of ROS, and maintain the quality of ginger rhizomes during storage at room temperature. It would be useful to further explore the role and mechanisms of action of ethylene in regulating the sprouting of ginger rhizomes.

Influences of postharvest ATP treatment on storage quality and enzyme activity in sucrose metabolism of Malus domestica.

The respiratory metabolism of apples remains vigorous after harvest, which can accelerate the consumption of sugar, organic acid, and other substances, thus leading to a decline in quality. The influence of postharvest ATP treatment on the changes of quality parameters and sucrose metabolism-related enzyme activity in apples was investigated in this study. The results showed that applying ATP effectively repressed the respiratory rate and weight loss and maintained higher levels of soluble solids content and flesh firmness in apples. In addition, ATP treatment enhanced succinate dehydrogenase, cytochrome oxidase, sucrose phosphate synthase, and sucrose synthase synthesis activities and reduced neutral invertase, acid invertase, and sucrose synthase cleavage activities in apples. These findings suggest that applying ATP after harvest could improve the internal quality of apples by suppressing the respiratory rate and modulating sucrose metabolism.

Postharvest acibenzolar-S-methyl treatment maintains storage quality and retards softening of apple fruit.

"Golden delicious" apples were dipped in 100 mg/L acibenzolar-S-methyl (ASM) to investigate the fruit quality and softening during 12 days of storage. Weight loss, flesh firmness, ethylene release, respiratory rate, content of total soluble solids and titratable acid, the activity of pectinase, cellulase, and ß-glucosidase, and water-insoluble pectin and water-soluble pectin contents were investigated. The results demonstrated that ASM treatment inhibited ethylene release and respiratory rate, reduced titratable acidity, and enhanced total soluble solids content in apples. Moreover, application of ASM suppressed the reduction of flesh firmness, activity of pectin methylesterase, and polygalacturonase. Cellulase, ß-glucosidase, and degradation of protopectin in apple fruit were also suppressed by ASM treatment during storage. In conclusion, ASM could maintain fruit quality by regulating cell wall-degrading enzymes during storage. PRACTICAL APPLICATIONS: Application of acibenzolar-S-methyl after harvest has the potential of delaying fruit softening by regulating cell wall-degrading enzymes, thus retain fruit quality.

Effects of trisodium phosphate treatment after harvest on storage quality and sucrose metabolism in jujube fruit.

BACKGROUND: Trisodium phosphate (TSP), generally recognized as safe (GRAS), could control postharvest diseases and maintain fruit quality. However, changes of fruit quality and sucrose metabolism in harvested jujube after TSP treatment remain largely unknown. In the current study, jujube fruit (cv. sanxing) was used to study the effects of TSP on storage quality and sucrose metabolism during storage at 20 ± 2 °C with 40-50% relative humidity (RH). RESULTS: The results showed that 0.5 g L-1 TSP treatment reduced weight loss and reduced sugar content, suppressed the reduction of fruit firmness, maintained ascorbic acid (AsA) content and inhibited respiratory rate of jujube fruit. In addition, TSP treatment also reduced acid invertase (AI) and neutral invertase (NI) activities in sucrose metabolism in jujube fruit. Sucrose synthase-cleavage (SS-c), sucrose synthase-synthesis (SS-s) and sucrose phosphate synthase (SPS) activities were also suppressed by TSP treatment. CONCLUSION: Treatment with TSP could effectively reduce enzymes activities in sucrose metabolism and maintain storage quality of jujube fruit during storage. © 2019 Society of Chemical Industry.

Effect of sodium nitroprusside treatment on shikimate and phenylpropanoid pathways of apple fruit.

Blue mould caused by Penicillium expansum is one of the important diseases of apple fruit during storage. Phenylpropanoid pathway is an important induction mechanism that can utilize downstream metabolites of shikimate pathway to synthesize a series of secondary metabolites. Apple fruit (cv. Fuji) were treated with sodium nitroprusside (SNP) to study its effect on blue mould, shikimate and phenylpropanoid pathways. The results showed that 1.0 mmol L-1 SNP significantly inhibited lesion development of apple fruit inoculated with P. expansum. The results also indicated that SNP enhanced MdDHQS, MdSKDH, MdSK and MdEPSPS genes expressions, increased shikimic acid, tryptophan, tyrosine and phenylalanine contents in apple fruit. The activities of phenylalanine ammonialyase, 4-coumarate: coenzyme A, ligase, cinnamate 4-hydroxylase, lignin, total phenolic compounds and flavonoids contents in apple fruit were also increased by SNP treatment. These results suggest that SNP might modulate shikimate and phenylpropanoid pathways to enhance disease resistance of apple fruit.

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

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. © 2018 Society of Chemical Industry.

Application of sodium silicate retards apple 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 ß-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. © 2018 Society of Chemical Industry.