Hongxia Qu

Energy status of ripening and postharvest senescent fruit of litchi (Litchi chinensis Sonn.)

BackgroundRecent studies have demonstrated that cellular energy is a key factor switching on ripening and senescence of fruit. However, the factors that influence fruit energy status remain largely unknown.ResultsHPLC profiling showed that ATP abundance increased significantly in developing preharvest litchi fruit and was strongly correlated with fruit fresh weight. In contrast, ATP levels declined significantly during postharvest fruit senescence and were correlated with the decrease in the proportion of edible fruit. The five gene transcripts isolated from the litchi fruit pericarp were highly expressed in vegetative tissues and peaked at 70 days after flowering (DAF) consistent with fruit ADP concentrations, except for uncoupling mitochondrial protein 1 (UCP1), which was predominantly expressed in the root, and ATP synthase beta subunit (AtpB), which was up-regulated significantly before harvest and peaked 2 days after storage. These results indicated that the color-breaker stage at 70 DAF and 2 days after storage may be key turning points in fruit energy metabolism. Transcript abundance of alternative oxidase 1 (AOX1) increased after 2 days of storage to significantly higher levels than those of LcAtpB, and was down-regulated significantly by exogenous ATP. ATP supplementation had no significant effect on transcript abundance of ADP/ATP carrier 1 (AAC1) and slowed the changes in sucrose non-fermenting-1-related kinase 2 (SnRK2) expression, but maintained ATP and energy charge levels, which were correlated with delayed senescence.ConclusionsOur results suggest that senescence of litchi fruit is closely related with energy. A surge of LcAtpB expression marked the beginning of fruit senescence. The findings may provide a new strategy to extend fruit shelf life by regulating its energy level.

Structure identification of a polysaccharide purified from Lycium barbarium fruit

The water-soluble bioactive polysaccharides can contribute to the health benefits of Lycium barbarium fruit. However, the structure characteristics of these polysaccharides remain unclear yet. An important polysaccharide (LBPA) was isolated and purified from L. barbarium in this work. It was identified by chemical and spectroscopic methods as arabinogalactan with β-d-(1→6)-galactan as backbone, which was different to any reported polysaccharides from this species before. This arabinogalactan was comprised of Araf, Galp, GlcpA and Rhap with a molar ratio of 9.2:6.6:1.0:0.9. The side chains, including α-l-Araf-(1→, α-l-Araf-(1→5)-α-l-Araf-(1→, β-l-Araf-(1→5)-α-l-Araf-(1→ and α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→, were linked to β-d-(1→6)-galactan at O-3. The putative structure was drawn as below. The molecular weight was determined to be 470,000g/mol by gel permeation chromatography.

Natural Occurrence, Analysis, and Prevention of Mycotoxins in Fruits and their Processed Products

Mycotoxins are small toxic chemical products formed as the secondary metabolites by fungi that readily contaminate foods with toxins in the field or after harvest. The presence of mycotoxins, such as aflatoxins, ochratoxin A, and patulin, in fruits and their processed products is of high concern for human health due to their properties to induce severe acute and chronic toxicity at low-dose levels. Currently, a broad range of detection techniques used for practical analysis and detection of a wide spectrum of mycotoxins are available. Many analytical methods have been developed for the determination of each group of these mycotoxins in different food matrices, but new methods are still required to achieve higher sensitivity and address other challenges that are posed by these mycotoxins. Effective technologies are needed to reduce or even eliminate the presence of the mycotoxins in fruits and their processed products. Preventive measures aimed at the inhibition of mycotoxin formation in fruits and their processed products are the most effective approach. Detoxification of mycotoxins by different physical, chemical, and biological methods are less effective and sometimes restricted because of concerns of safety, possible losses in nutritional quality of the treated commodities and cost implications. This article reviewed the available information on the major mycotoxins found in foods and feeds, with an emphasis of fruits and their processed products, and the analytical methods used for their determination. Based on the current knowledge, the major strategies to prevent or even eliminate the presence of the mycotoxins in fruits and their processed products were proposed.

Effects of anti-ethylene treatments on browning and energy metabolism of harvested litchi fruit

Litchi fruit were treated with 10 mL/L ethylene (C2H4), 0.1% cobalt chloride (CoCl2) and 1 mL/L 1-methylcyclopropene, respectively, packed individually in closed but vented containers, and then stored at ambient temperature (28–33°C). The effects of these treatments on the browning, energy metabolism and disease incidence of the fruit were investigated. Treatment with C2H4 enhanced the activities of polyphenol oxidase and phenylalanine ammonia-lyase. Ethylene also increased the accumulation of ADP and AMP, but decreased energy charge in fruit peel. Cobalt chloride treatment had an inhibitory effect on increases of peroxidase activity, ATP : ADP ratio, energy charge and ATP, ADP and AMP. Browning index was reduced by 8.4 and 10.4% and disease index was reduced by 10.7 and 12.7% in CoCl2 and 1-methylcyclopropene-treated fruit, respectively, suggesting a relationship between energy metabolism, browning and disease index.

Influence of the nitric oxide donor, sodium nitroprusside, on lipid peroxidation and anti-oxidant activity in pericarp tissue of longan fruit

Summary The effects of nitric oxide (NO) on lipid peroxidation and anti-oxidant activity in longan fruit were investigated during storage. Fruits were dipped for 5 min in a solution containing 1 mM sodium nitroprusside (SNP), an NO donor. They were then packed into polyethylene bags and stored for 6 d at 28°C. Changes in pericarp browning index, membrane permeability, malondialdehyde (MDA) content, the rate of superoxide production, the activities of lipoxygenase (LOX), superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT), α,αdiphenyl-βpicrylhydrazy (DPPH) radical scavenging activity, and reducing power were measured. Treatment with SNP inhibited pericarp browning and suppressed increases in membrane permeability and lipid peroxidation. These effects were associated with lower LOX activity, higher APX and CAT activities, better maintenance of DPPH radical scavenging activity and reducing power, and lower superoxide production rate. However, SOD activity was higher in control (non-SNP-treated) fruit than in SNP-treated fruit over the first 4 d of storage. Overall, these findings suggest that treatment with NO enhanced the anti-oxidant activity in pericarp tissue of longan fruit during storage, and contributed to reduced lipid peroxidation. Reduced lipid damage apparently maintained the compartmentation of enzymes and substrates and, thereby, lessened enzymatic browning.

Comparative transcriptome and metabolome provides new insights into the regulatory mechanisms of accelerated senescence in litchi fruit after cold storage

Litchi is a non-climacteric subtropical fruit of high commercial value. The shelf life of litchi fruit under ambient conditions (AC) is approximately 4–6 days. Post-harvest cold storage prolongs the life of litchi fruit for up to 30 days with few changes in pericarp browning and total soluble solids. However, the shelf life of litchi fruits at ambient temperatures after pre-cold storage (PCS) is only 1–2 days. To better understand the mechanisms involved in the rapid fruit senescence induced by pre-cold storage, a transcriptome of litchi pericarp was constructed to assemble the reference genes, followed by comparative transcriptomic and metabolomic analyses. Results suggested that the senescence of harvested litchi fruit was likely to be an oxidative process initiated by ABA, including oxidation of lipids, polyphenols and anthocyanins. After cold storage, PCS fruit exhibited energy deficiency, and respiratory burst was elicited through aerobic and anaerobic respiration, which was regulated specifically by an up-regulated calcium signal, G-protein-coupled receptor signalling pathway and small GTPase-mediated signal transduction. The respiratory burst was largely associated with increased production of reactive oxygen species, up-regulated peroxidase activity and initiation of the lipoxygenase pathway, which were closely related to the accelerated senescence of PCS fruit.

Comparative proteomic approaches to analysis of litchi pulp senescence after harvest

Litchi fruit (Litchi chinensis Sonn.) is highly perishable after harvest. The shelf life is only 4-6days under ambient temperature storage conditions, which has restricted the development of the litchi industry to a considerable extent. To investigate the molecular mechanisms of litchi fruit senescence, comparative proteomic analysis was carried out on litchi pulp. After two-dimensional gel electrophoresis (2-DE), 64 spots were significantly differentially expressed, 61 of which were successfully identified using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). All of the identified proteins were classified according to biological process, molecular function, and cellular component using Blast2GO. Results showed that those proteins were mainly involved in signal transduction, cell wall metabolism, primary and secondary metabolism, energy metabolism. Specifically, many up-regulated proteins were involved in auxin/ethylene regulation, which suggested that auxin and ethylene might cooperate to regulate litchi pulp senescence. Histone deacetylase and DNA methyltransferase might involve the down-regulation of proteins related to reactive oxygen species (ROS) scavenging, glycolysis, tricarboxylic acid cycle, and ATP synthesis in litchi senescence. A higher proportion of differentially expressed proteins were up-regulated and these were involved in a range of processes including cell wall organization or biogenesis, anaerobic respiration, protein degradation, lipid degradation. All of those proteins might accelerate fruit softening, deterioration and senescence. This study is the first to carry out proteomic analysis of the regulation of litchi fruit senescence.

Proteomic Analysis of Differentially Expressed Proteins Involved in Peel Senescence in Harvested Mandarin Fruit

Mandarin (Citrus reticulata), a non-climacteric fruit, is an economically important fruit worldwide. The mechanism underlying senescence of non-climacteric fruit is poorly understood. In this study, a gel-based proteomic study followed by LC-ESI-MS/MS analysis was carried out to investigate the proteomic changes involved in peel senescence in harvested mandarin “Shatangju” fruit stored for 18 days. Over the course of the storage period, the fruit gradually senesced, accompanied by a decreased respiration rate and increased chlorophyll degradation and disruption of membrane integrity. Sixty-three proteins spots that showed significant differences in abundance were identified. The up-regulated proteins were mainly associated with cell wall degradation, lipid degradation, protein degradation, senescence-related transcription factors, and transcription-related proteins. In contrast, most proteins associated with ATP synthesis and scavenging of reactive oxygen species were significantly down-regulated during peel senescence. Three thioredoxin proteins and three Ca2+ signaling-related proteins were significantly up-regulated during peel senescence. It is suggested that mandarin peel senescence is associated with energy supply efficiency, decreased antioxidant capability, and increased protein and lipid degradation. In addition, activation of Ca2+ signaling and transcription factors might be involved in cell wall degradation and primary or secondary metabolism.

Comparative Transcriptome Analysis of Penicillium citrinum Cultured with Different Carbon Sources Identifies Genes Involved in Citrinin Biosynthesis

Citrinin is a toxic secondary metabolite of Penicillium citrinum and its contamination in many food items has been widely reported. However, research on the citrinin biosynthesis pathway and its regulation mechanism in P. citrinum is rarely reported. In this study, we investigated the effect of different carbon sources on citrinin production by P. citrinum and used transcriptome analysis to study the underlying molecular mechanism. Our results indicated that glucose, used as the sole carbon source, could significantly promote citrinin production by P. citrinum in Czapek’s broth medium compared with sucrose. A total of 19,967 unigenes were annotated by BLAST in Nr, Nt, Swiss-Prot and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Transcriptome comparison between P. citrinum cultured with sucrose and glucose revealed 1085 differentially expressed unigenes. Among them, 610 were upregulated while 475 were downregulated under glucose as compared to sucrose. KEGG pathway and Gene ontology (GO) analysis indicated that many metabolic processes (e.g., carbohydrate, secondary metabolism, fatty acid and amino acid metabolism) were affected, and potentially interesting genes that encoded putative components of signal transduction, stress response and transcription factor were identified. These genes obviously had important impacts on their regulation in citrinin biosynthesis, which provides a better understanding of the molecular mechanism of citrinin biosynthesis by P. citrinum.

Litchi Fruit LcNAC1 is a Target of LcMYC2 and Regulator of Fruit Senescence Through its Interaction with LcWRKY1

Senescence is a key factor resulting in deterioration of non-climacteric fruit. NAC transcription factors are important regulators in plant development and abiotic stress responses, yet little information regarding the role of NACs in regulating non-climacteric fruit senescence is available. In this study, we cloned 13 NAC genes from litchi (Litchi chinensis) fruit, and analyzed subcellular localization and expression profiles of these genes during post-harvest natural and low-temperature-delayed senescence. Of the 13 NAC genes, expression of LcNAC1 was up-regulated in the pericarp and pulp as senescence progressed, and was significantly higher in senescence-delayed fruit than that in naturally senescent fruit. LcNAC1 was induced by exogenous ABA and hydrogen peroxide. Yeast one-hybrid analysis and transient dual-luciferase reporter assay showed that LcNAC1 was positively regulated by the LcMYC2 transcription factor. LcNAC1 activated the expression of LcAOX1a, a gene associated with reactive oxygen species regulation and energy metabolism, whereas LcWRKY1 repressed LcAOX1a expression. In addition, LcNAC1 interacted with LcWRKY1 in vitro and in vivo. These results indicated that LcNAC1 and LcWRKY1 form a complex to regulate the expression of LcAOX1a antagonistically. Taken together, the results reveal a hierarchical and co-ordinated regulatory network in senescence of harvested litchi fruit.