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Postharvest melatonin treatments have been reported to improve the quality and storability, especially to inhibit browning in many fruits, but the effect had not been systematically investigated on longan fruit. In this study, the effect of 0.4 mM melatonin (MLT) dipping on the quality and pericarp browning of longan fruits stored at low temperature was investigated. The MLT treatment did not influence the TSS content of longan fruits but lead to increased lightness and h° value while decreased a* value of pericarp. More importantly, the treatment significantly delayed the increase in electrolyte leakage and malonaldehyde accumulation, inhibited the activities of polyphenol oxidase and peroxidase, and thus retarded pericarp browning. In addition, the treatment significantly inhibited the production of O2•− and H2O2 while promoted the accumulation of glutathione, flavonoids, and phenolics at earlier storage stages in longan pericarp. Interestingly, the activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) were significantly upregulated but activities of catalase were downregulated in the MLT‐treated longan pericarp. MLT treatment effectively enhanced APX and SOD activities, increased flavonoid, phenolics, and glutathione content, protected cytomembrane integrity, inhibited the production of O2•− and H2O2 and browning‐related enzymes, and thus delayed the longan pericarp browning. Our results showed that 0.4 mM melatonin (MLT) dipping significantly increased the ROS scavenging ability by enhancing the activities of SOD and APX as well as increasing the content of GSH, phenolics, and flavonoids (especially at the earlier storage stages). This might result in the decreased level of O2•− and H2O2 and lower MDA (membrane lipid oxidation products) content, and thus, the treatment protected the cytomembrane integrity and prevented the pericarp from enzymatic browning by PPO and POD. In conclusion, postharvest melatonin treatment inhibited longan pericarp browning by increasing ROS scavenging ability and protecting cytomembrane integrity.

The WD40 transcription factor (TF) family is widespread in plants and plays important roles in plant growth and development, transcriptional regulation, and tolerance to abiotic stresses. WD40 TFs have been identified and characterized in a diverse series of plant species. However, little information is available on WD40 genes from D. longan. In this study, a total of 45 DlWD40 genes were identified from D. longan RNA-Seq data, and further analysed by bioinformatics tools. Also, the expression patterns of DlWD40 genes in roots and leaves, as well as responses to heat stress, were evaluated using quantitative real-time PCR (qRT-PCR). We found that the 45 DlWD40 proteins, together with 80 WD40 proteins from Arabidopsis and Zea mays, could be categorized into six groups. Of these, the DlWD40-4 protein was highly homologous to Arabidopsis WDR5a, a protein participating in tolerance to abiotic stresses. Moreover, a total of 25 cis-acting elements, such as abiotic stress and flavonoid biosynthesis elements, were found in the promoters of DlWD40 genes. The DlWD40-33 gene is targeted by miR3627, which has been proposed to be involved in flavonoid biosynthesis. Using qRT-PCR, ten of the 45 DlWD40 genes were demonstrated to have diverse expression patterns between roots and leaves, and these ten DlWD40 genes could also respond to varying durations of a 38 °C heat stress in roots and leaves. The results reported here will provide a basis for the further functional verification of DlWD40 genes in D. longan.

Gibberellic acids had been proven to improve the fruit quality and storability by delaying deterioration and maintaining the antioxidant system. In this study, the effect of GA3 spraying at different concentrations (10, 20, and 50 mg L−1) on the quality of on-tree preserved ‘Shixia’ longan was examined. Only 50 mg L−1 GA3 significantly delayed the decline of soluble solids (22.0% higher than the control) and resulted in higher total phenolics content (TPC), total flavonoid content (TFC), and phenylalanine ammonia-lyase activity in pulp at the later stages. The widely targeted metabolome analysis showed that the treatment reprogrammed secondary metabolites and up-regulated many tannins, phenolic acids, and lignans during the on-tree preservation. More importantly, the preharvest 50 mg L−1 GA3 spraying (at 85 and 95 days after flowering) led to significantly delayed pericarp browning and aril breakdown, as well as lower pericarp relative conductivity and mass loss at the later stages of room-temperature storage. The treatment also resulted in higher antioxidants in pulp (vitamin C, phenolics, and reduced glutathione) and pericarp (vitamin C, flavonoids, and phenolics). Therefore, preharvest 50 mg L−1 GA3 spraying is an effective method for maintaining the quality and up-regulating antioxidants of longan fruit during both on-tree preservation and room-temperature storage.

Reverse transcription quantitative PCR (RT-qPCR) as the accurate and sensitive method is use for gene expression analysis, but the veracity and reliability result depends on whether select appropriate reference gene or not. To date, several reliable reference gene validations have been reported in fruits trees, but none have been done on preharvest and postharvest longan fruits. In this study, 12 candidate reference genes, namely, CYP, RPL, GAPDH, TUA, TUB, Fe-SOD, Mn-SOD, Cu/Zn-SOD, 18SrRNA, Actin, Histone H3, and EF-1a, were selected. Expression stability of these genes in 150 longan samples was evaluated and analyzed using geNorm and NormFinder algorithms. Preharvest samples consisted of seven experimental sets, including different developmental stages, organs, hormone stimuli (NAA, 2,4-D, and ethephon) and abiotic stresses (bagging and girdling with defoliation). Postharvest samples consisted of different temperature treatments (4 and 22°C) and varieties. Our findings indicate that appropriate reference gene(s) should be picked for each experimental condition. Our data further showed that the commonly used reference gene Actin does not exhibit stable expression across experimental conditions in longan. Expression levels of the DlACO gene, which is a key gene involved in regulating fruit abscission under girdling with defoliation treatment, was evaluated to validate our findings. In conclusion, our data provide a useful framework for choice of suitable reference genes across different experimental conditions for RT-qPCR analysis of preharvest and postharvest longan fruits.

Longan was a characteristic fruit for both medicine and food in China, which was rich in primary and secondary metabolites. Comprehensive high‐throughput identification and comparison of metabolites in longan pulp among different varieties were still lacked. “Shixia” (SX) and “Chuliang” (CL) were the biggest major cultivars of longan in China. In this study, the content of total soluble solid, total flavonoid, and total phenolics indicated the difference of sweetness and bioactive compound content between the SX and CL pulp. Through a widely targeted metabolome, a total of 514 metabolites were identified and categorized into 23 groups mainly including flavonoids, amino acids & derivatives, lipids, phenolic acids, nucleotides & derivatives, alkaloids, organic acids and sugars & derivatives. A total of 89 metabolites with significantly differential accumulation (variable importance in projection (VIP) value ≧1, p‐value <.05) over 1.2 fold were found between SX and CL, which were mainly enriched into pathways including flavone and flavonol biosynthesis, glycolysis/gluconeogenesis, and arginine and proline metabolism. Higher leveled hexose and hexose‐phosphate (i.e., β‐D‐glucose, D(+)‐glucose, glucose‐1‐phosphate and glucose‐6‐phosphate), dominant organic acids (i.e., citric acid, succinic acid, D‐malic acid, and citramalate), and essential amino acids (L‐threonine, L‐valine, L‐isoleucine, L‐leucine, L‐phenylalanine and L‐lysine) in SX pulp might be contributed to the taste and flavor difference between SX and CL. Moreover, the greatly differential accumulated secondary metabolites especially flavonoids and phenolic acids might result in different medicinal and nutritional characteristic between SX and CL. In conclusion, this study provided a systemic metabolic basis for understanding the nutritional differences between SX and CL and would help deepen the molecular biology and pharmacology research on characteristic metabolites in longan pulp. A total of 514 metabolites were identified in SX and CL longan pulp and categorized into 23 groups by a widely targeted metabolome. A total of 89 significantly differential accumulated metabolites were found between SX and CL, which were mainly enriched into pathways including flavone and flavonol biosynthesis, glycolysis/gluconeogenesis, arginine, and proline metabolism. The greatly differential accumulated secondary metabolites especially flavonoids and phenolic acids might result in different medicinal and nutritional characteristic between SX and CL.

Precooling and sulfur dioxide fumigation were proved as effective methods for the preservation of longan (Dimocarpus longan Lour.) fruits. However, inadequate precooling and sulfur dioxide fumigation resulted in unexpected losses and short shelf life. A L9(34) orthogonal test was conducted to screen out ideal dosage of sodium metabisulfite (factor A), precooling method (factor B), and precooling duration (factor C) to improve the storability of longan fruit stored for 48 hr at room temperature (RT) (25℃). The overall qualities of all of the treated longan fruits after a 48‐hr storage (OQST) and during the 5‐day shelf at 25℃ (OQSF) were better than those of the control fruits. The treated fruits showed brighter fresh color (higher L*, b*, C*, and h° values but lower a* value), higher flavonoid, and chlorophyll contents. Moreover, the SO2 residue was concentrated in pericarp but little in aril for any of the 12 treatments. The multivariate variance analysis showed that factor A was dominant to determine both of the OQST and OQSF, while factor B affected the OQST, and factor C affected the OQSF. In total, “0.22% sodium metabisulfite + 4 hr precooling + uncovered precooling” was considered to be an ideal treatment. These results would contribute to improving longan postharvest preservation technology. The overall qualities of all of the treated longan fruits after a 48‐hr storage (OQST) and during the 5‐d shelf at 25℃ (OQSF) were better than those of the control fruits. The treated fruits showed brighter fresh color (higher L*, b*, C*, and h° values but lower a* value), higher flavonoid, and chlorophyll contents. Factor A (dosage of sodium metabisulfite) was the dominant factor, and “0.22% sodium metabisulfite + 4 hr precooling + uncovered precooling” was considered to be an ideal treatment.

Although the effects of phytohormones (mainly salicylic acid) on the storability of longan fruit have been reported, the relationship between postharvest hormone variation and signal transduction and storability remains unexplored. The basis of physiology, biochemistry, hormone content and signalling for the storability difference at room-temperature between ‘Shixia’ and ‘Luosanmu’ longan fruit were examined. ‘Luosanmu’ longan exhibited faster pericarp browning, aril breakdown and rotting during storage. ‘Luosanmu’ pericarp exhibited higher malondialdehyde but faster decreased total phenolics, flavonoid, glutathione, vitamin C, catalase activity and gene expression. Higher H2O2 and malondialdehyde but lower glutathione, glutathione-reductase and peroxidase activities, while higher activities and gene expressions of polygalacturonase, β-galactosidase and cellulose, lower covalent-soluble pectin, cellulose and hemicellulose but higher water-soluble pectin were observed in ‘Luosanmu’ aril. Lower abscisic acid and methyl jasmonate but higher expressions of LOX2, JAZ and NPR1 in pericarp, while higher abscisic acid, methyl jasmonate and salicylic acid together with higher expressions of ABF, JAZ, NPR1 and PR-1 in ‘Luosanmu’ aril were observed. In conclusion, the imbalance between the accumulation and scavenging of active oxygen in ‘Luosanmu’ longan might induce faster lipid peroxidation and senescence-related hormone signalling and further the polymerization of phenolics in pericarp and polysaccharide degradation in aril.

Metal nanoparticles, particularly silver nanoparticles (AgNPs), are developing more important roles as diagnostic and therapeutic agents for cancers with the improvement of eco-friendly synthesis methods. This study demonstrates the biosynthesis, antibacterial activity, and anticancer effects of silver nanoparticles using Dimocarpus Longan Lour. peel aqueous extract. The AgNPs were characterized by UV-vis absorption spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscope (FTIR). The bactericidal properties of the synthesized AgNPs were observed via the agar dilution method and the growth inhibition test. The cytotoxicity effect was explored on human prostate cancer PC-3 cells in vitro by trypan blue assay. The expressions of phosphorylated stat 3, bcl-2, survivin, and caspase-3 were examined by Western blot analysis. The longan peel extract acted as a strong reducing and stabilizing agent during the synthesis. Water-soluble AgNPs of size 9–32 nm was gathered with a face-centered cubic structure. The AgNPs had potent bactericidal activities against gram-positive and gram-negative bacteria with a dose-related effect. AgNPs also showed dose-dependent cytotoxicity against PC-3 cells through a decrease of stat 3, bcl-2, and survivin, as well as an increase in caspase-3. These findings confirm the bactericidal properties and explored a potential anticancer application of AgNPs for prostate cancer therapy. Further research should be focused on the comprehensive study of molecular mechanism and in vivo effects on the prostate cancer.

IntroductionNF-YB transcription factor is an important regulatory factor in plant embryonic development.ResultsIn this study, 15 longan NF-YB ( DlNF-YB ) family genes were systematically identified in the whole genome of longan, and a comprehensive bioinformatics analysis of DlNF-YB family was performed. Comparative transcriptome analysis of DlNF-YBs expression in different tissues, early somatic embryogenesis (SE), and under different light and temperature treatments revealed its specific expression profiles and potential biological functions in longan SE. The qRT-PCR results implied that the expression patterns of DlNF-YBs were different during SE and the zygotic embryo development of longan. Supplementary 2,4-D, NPA, and PP333 in longan EC notably inhibited the expression of DlNF-YBs ; ABA, IAA, and GA3 suppressed the expressions of DlNF-YB6 and DlNF-YB9 , but IAA and GA3 induced the other DlNF-YBs . Subcellular localization indicated that DlNF-YB6 and DlNF-YB9 were located in the nucleus. Furthermore, verification by the modified 5'RNA Ligase Mediated Rapid Amplification of cDNA Ends (5' RLM-RACE) method demonstrated that DlNF-YB6 was targeted by dlo-miR2118e, and dlo-miR2118e regulated longan somatic embryogenesis (SE) by targeting DlNF-YB6 . Compared with CaMV35S- actuated GUS expression, DlNF-YB6 and DlNF-YB9 promoters significantly drove GUS expression. Meanwhile, promoter activities were induced to the highest by GA3 but suppressed by IAA. ABA induced the activities of the promoter of DlNF-YB9 , whereas it inhibited the promoter of DlNF-YB6 .DiscussionHence, DlNF-YB might play a prominent role in longan somatic and zygotic embryo development, and it is involved in complex plant hormones signaling pathways.

The leaves of . are used unilaterally as Chinese herbal medicines to treat diabetes in Chongzuo and Hezhou, Guangxi, but the mechanism of its treatment of diabetes is not yet clear, and further research is needed. This study examined the effects of leaf ethanol extract of on metabolic pathways and gut microbiota in rats with type 2 diabetes mellitus (T2DM). The rats were randomly divided into four groups: HG + HFD (T2DM model, fed with high-sugar and high-fat diet), control (regular diet), MET (positive metformin), and LYY (leaf ethanol extract of ). Metabolite profiles and gut microbiota composition were analyzed using liquid chromatography_mass spectrometry and 16S rDNA sequencing. Metabolomics analysis revealed 61 distinct metabolites in the LYY group, such as Leu-Pro and taurolithocholic acid 3-sulfate, which influence valine, leucine, and isoleucine metabolism, unsaturated fatty acid biosynthesis, fatty acid metabolism, bile secretion, and pyruvate and propanoate metabolism. Additionally, 16S rDNA sequencing showed that LYY significantly altered the abundance of gut microbiota such as and (vs. HG + HFD group, < 0.05). LYY improved T2DM in rats may be associated with modulating metabolite levels and indirectly regulating glucose metabolism balance through changes in gut microbiota abundance. The efficacy of LYY in treating T2DM in rats may be related to the regulation of six metabolic pathways; it increased the abundance of and and decreased the abundance of , , and , thereby promoting impaired glucose tolerance and indirectly regulating the balance of glucose metabolism.