Yunfen Liu

Low-temperature (LT) storage effectively mitigates postharvest deterioration in longan fruit. To investigate the changes in sucrose metabolism underlying this effect, we compared the dynamic changes in sugar metabolism indicators under LT and room-temperature (RT) conditions. This sugar conversion was associated with the increased activities of acid invertase (AI), neutral invertase (NI), sucrose synthase (SS), fructokinase (FRK) and hexokinase (HXK) and the inhibited activity of sucrose phosphate synthase (SPS). Consistently, the transcription levels of DlAI, DlNI, DlSS, DlFRK and DlHXK were upregulated, while the transcriptional level of DlSPS was suppressed. In contrast, LT storage maintained higher sucrose levels with gradual declines in glucose and fructose. Meanwhile, the activities of AI, NI, SS, FRK and HXK were inhibited while SPS activity was promoted, accompanied by transcriptional downregulation of DlAI, DlNI, DlSS, DlSPS, and DlFRK. Pearson correlation and principal component analyses further revealed distinct sugar-metabolite networks between the two storage regimes. Collectively, LT storage preserves sucrose, coinciding with the transcriptional repression of catabolic pathways while maintaining biosynthetic capacity, which may contribute to restraining sugar depletion. These findings advance our understanding of LT-regulated sugar metabolism and offer theoretical support for optimizing postharvest cold-storage strategies.

Blue mold caused by Penicillium italicum triggers severe tissue decay and limits postharvest shelf life, representing the primary constraint to the commercial supply chain of Shatangju mandarins (Citrus reticulata cv. Shatangju). In this study, the biocontrol efficacy of an antagonistic yeast, Meyerozyma guilliermondii SR1, against postharvest blue mold in Shatangju mandarins was evaluated. The results showed that SR1 significantly inhibited the in vitro growth of P. italicum, delayed disease progression and restricted pathogen sporulation in inoculated fruits during storage. Furthermore, SR1 rapidly colonized fruit wounds to establish a population advantage and enhanced the antioxidant defense capacity of the host fruits. Meanwhile, SR1 treatment significantly reduced postharvest weight loss, with no significant differences in total soluble solids (TSS) and titratable acidity (TA) compared with the control. In conclusion, M. guilliermondii SR1 showed significant biocontrol efficacy against postharvest blue mold in Shatangju mandarins, which provides an experimental basis for the research and development of green citrus postharvest preservatives.

As a typical sucrose-accumulating fruit, longan commonly experiences sugar receding during on-tree preservation, leading to quality deterioration. To investigate the mechanism of sucrose degradation in longan fruit, we conducted genome-wide identification and analysis of key genes involved in sucrose synthesis and catabolism based on the ‘Shixia’ (SX) genome. The results revealed that longan contained 8 sucrose synthases (SUSs), 4 sucrose phosphate synthases (SPSs), and 26 invertases (INVs). Notably, members of the longan SUS, SPS, and cell wall invertase (CWINV) families all contained the motif 10 sequence, while cytoplasmic invertase (CINV) members exhibited diverse motif combinations. Similarity analysis revealed that sequence similarity was reliable only when the sequence lengths of the compared genes were comparable. Cis-acting elements and miRNA prediction showed that these genes were enriched in MYB elements and regulated by miR156/827/171. Additionally, the expansion of SUS, SPS, and INV genes was driven by segmental duplication events under purifying selection. Furthermore, the ‘Chuliang’ (CL) cultivar exhibited slower on-tree sucrose degradation than SX, with sucrose accounting for 72.2% of total sugars at maturity, which is 33.4% higher than SX. Enzyme activity assay during the sucrose decline stage revealed that SUS, SPS, and INV activities were generally higher in SX pulp than in CL. Furthermore, correlation analysis showed that the activities of AINV and A/N-INV were both significantly negatively correlated with TSS and sucrose content, respectively. Additionally, the expression of DlCWINV10 exhibited a negative correlation with TSS (p < 0.05) and sucrose content (r = −0.6, p = 0.07), suggesting that DlCWINV10 may play an important role in the sucrose degradation process. In summary, this study elucidates the characteristics of SUS, SPS, and INV gene families in longan and their potential roles in sucrose metabolism, providing a theoretical foundation for understanding the on-tree sucrose degradation mechanism.

Sulfur fumigation (SF), acid dipping (HCl treatment, HAT), and their combination (SF+HAT) are common methods for long-term preservation and color protection of litchi. However, their effects on the metabolic profile of the litchi pericarp have not been investigated. SF resulted in a yellowish-green pericarp by up-regulating lightness (L*), b*, C*, and h° but down-regulating total anthocyanin content (TAC) and a*, while HAT resulted in a reddish coloration by up-regulating a*, b*, and C* but down-regulating L*, h°, and TAC. SF+HAT recovered reddish color with similar L*, C* to SF but a*, b*, h°, and TAC between SF and HAT. Differential accumulated metabolites (DAMs) detected in HAT (vs. control) were more than those in SF (vs. control), but similar to those in SF+HAT (vs. control). SF specifically down-regulated the content of cyanidin-3-O-rutinoside, sinapinaldehyde, salicylic acid, and tyrosol, but up-regulated 6 flavonoids (luteolin, kaempferol-3-O-(6″-malonyl)galactoside, hesperetin-7-O-glucoside, etc.). Five pathways (biosynthesis of phenylpropanoids, flavonoid biosynthesis, biosynthesis of secondary metabolites, glutathione metabolism, and cysteine and methionine metabolism) were commonly enriched among the three treatments, which significantly up-regulated sulfur-containing metabolites (mainly glutathione, methionine, and homocystine) and down-regulated substrates for browning (mainly procyanidin B2, C1, and coniferyl alcohol). These results provide metabolic evidence for the effect of three treatments on coloration and storability of litchi.

Colletotrichum capsici is an important pathogen causing anthracnose in postharvest peppers in parts of Asia, seriously compromising quality and storage life. Unveiling the pathogenic mechanism can better prevent postharvest disease in pepper. This study investigated the impacts of C. capsici infection on cell wall and phenylpropanoid metabolism in postharvest pepper. Compared to the non-inoculated peppers, C. capsici infection notably increased the disease index, damaged visual quality, and reduced the firmness. Morphological observations showed that C. capsici infection contributed to the collapse of epidermal cell structure. During the early stage, C. capsici triggered pepper’s defensive responses, including lignin deposition around the wounds, increased cellulose and hemicellulose content, and boosted disease-resistance enzymes, including phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), laccase (LAC), β-1,3-glucanase (β-1,3-Glu), and chitinase (CHI), alongside elevated total phenolics and flavonoids. However, as storage time progressed, the activities of carboxymethy cellulase (Cx), polygalacturonase (PG), pectin methylesterase (PME), and β-glucosidase (β-Glu) remained at a high level, leading to a reduction in cell wall components, a decline in the activities of disease-resistance enzymes, and a decrease in phenylpropanoid metabolite, resulting from disease progression in pepper. These insights highlight the need for early intervention strategies to mitigate postharvest losses by targeting pathogen-induced stress responses and cell wall integrity preservation.

The failure to promptly eliminate excessive reactive oxygen species (ROS) leads to the oxidation of biological macromolecules such as proteins, which is a key factor in chilling injury (CI) in harvested fruits and vegetables. Methionine sulfoxide reductase (Msr) is a class of redox proteins that reduce methionine sulfoxide (MetSO) in oxidized proteins back to methionine (Met), thereby restoring protein function. In recent years, the role of Msr in protecting fruits and vegetables from CI has attracted increasing research interest. This review summarizes the classification, distribution, and subcellular localization of Msr in plants and examines its roles and regulatory mechanisms in mitigating CI. The discussion focuses on postharvest CI, ROS dynamics, and Msr-related regulatory pathways. This review provides insights into improving plant quality and enhancing cold resistance through genetic engineering.

This study aims to investigate the impacts of the peach gum (PG) edible coating film on pericarp browning of ‘Guiwei’ litchi stored at ambient temperature. Factor analysis was applied to comprehensively evaluate the effect of different concentrations (0, 1%, 2%, 4%) of PG treatments. Compared to the control, 4% PG treatment could effectively suppress the rising of relative electric conductivity, delay the degradation of anthocyanin, maintain the a* and c*value and higher TSS content, and inhibit the browning index. Moreover, 4% PG treatment reduced the accumulation of total phenols and flavonoids, including gallic catechin (GC), epigallocatechin (EGC), epigallocatechin gallate (EGCG), epicatechin (EC), epicatechin gallate (ECG), and catechin gallate (CG), restrain the peroxidase activity. 4% PG treatment also contributes to higher organic acid content (oxalic acid, ascorbic acid, malic acid, and succinic acid), maintaining good litchi flavor. In conclusion, the 4% PG treatment provides good performance, and these findings will provide a promising approach for litchi preservation.

Chilling injury is the dominant factor for quality deterioration and marketability suffers of cucumber fruit during low-temperature storage. Nitric oxide (NO) is a kind of endogenous signaling molecule that significantly regulates the abiotic stress response. In the current investigation, the membrane lipid and energy metabolism were investigated after cucumber fruit was exposed to a sodium nitropruside (SNP) solution that acts as a NO donor before being kept at 4°C for 12 days. The results illustrated that SNP treatment reduced chilling injury and lightened the increase in membrane permeability under cold stress, maintaining a better quality. Subsequently, SNP regulated lipid metabolism by reducing the expression of genes encoding PLA, PLD, lipase, and LOX and decreasing the activities. Compared to the control, the SNP-treated fruit exhibited higher ATP and EC (energy charge) levels. Moreover, SNP-treated suppressed the decrease of H⁺-ATPase, Ca²⁺-ATPase, SDH, and CCO activity, which is involved in energy metabolism. The above results showed that exogenous nitric oxide might be an effective method to alleviate the chilling damage in postharvest cucumber fruit by modifying membrane lipids and energy metabolism.

Okra pod is sensitive to low temperature, which results in chilling injury under improper low‐temperature storage. This study aimed to evaluate the effect of different concentrations of methyl jasmonate (MeJA) treatment on okra pod stored at 4 ± 1°C for 12 days and illuminate the mechanism of MeJA alleviating chilling injury. Compared to the control, MeJA treatments maintained lower relative electric conductivity (REC), chilling injury (CI) degree, and lignin content, as well as higher total soluble solids, total soluble sugar, pectin content, and chlorophyll content. The factor analysis was applied to comprehensively evaluate the effects of MeJA so that 1 μmol/L MeJA was screened as the optimum concentration to maintain the okra quality throughout the storage time. In contrast with control, MeJA not only accelerated the generation of antioxidant substances (phenolics and flavonoids) but also increased the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activity, inhibited malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content accumulation, and the polyphenol oxidase (PPO) activity. This work confirmed that MeJA could effectively alleviate chilling injury and maintain the quality during cold‐stored by regulating reactive oxygen species (ROS) metabolism. These results provide theoretical guidance for the application of MeJA in okra storage and preservation.

The aim of this study was to investigate the effect of 20 mg/L 2,4-D on the quality during ripening of on-tree longan fruits. We investigated external and internal properties of the on-tree longan fruits. The results showed that 2,4-D treatment promotes the growth based on the fruit size and weight. The respiration rate, contents of TSS, total soluble sugar, sucrose, glucose, fructose, and hexose revealed an increasing tendency with advancing the maturity and reached the high status during 110-126DPA. By contrast, the relative electric conductivity and TA content displayed a declining trend during the ripening stage, increase with the senescence. All these pieces of information indicated that 2,4-D treatment could effectively promote the sensory quality of on-tree longan fruit, prolong the harvest time to 118DPA, while CK should harvest before 110DPA.