Cuticle properties, wax composition, and crystal morphology of Hami melon cultivars (Cucumis melo L.) with differential resistance to fruit softening.

Cuticle wax chemicals are cultivar-dependent and contribute to storage quality. Few research reported on wax analysis between melting flesh-type (MF; 'Jinhuami 25') and nonmelting flesh-type (NMF; 'Xizhoumi 17' and 'Chougua') Hami melons. Chemicals and crystal structures of Hami melon cuticular wax, cell wall metabolism related to fruit melting, and fruit physiology were analyzed to observe wax functions. Results showed that Hami melon cuticle wax predominantly consists of esters, alkanes, alcohols, aldehydes, and terpenoids. MF-type has a lower alkane/terpenoid ratio, concomitant to its higher weight loss and cuticle permeability. Micromorphology of wax crystals appears as numerous platelets with irregular crystals, and the transformation of wax structure in NMF Hami melon is delayed. Waxy components affect cell wall metabolism and physiological quality, which results in the pulp texture difference between MF-type and NMF-type during storage. Results provide a reference for the regulation of wax synthesis in both types of melons.

Exogenous melatonin activates the antioxidant system and maintains postharvest organoleptic quality in Hami melon (Cucumis. melo var. inodorus Jacq.).

Hami melon is prone to postharvest perishing. Melatonin is a signaling molecule involved in a variety of physiological processes in fruit, and it improves fruit quality. We hypothesized that melatonin treatment would improve the storage quality of Hami melon by altering its respiration and reactive oxygen species (Graphical abstract). Our results indicated that optimal melatonin treatment (0.5 mmol L-1) effectively slowed the softening, weight loss, and respiratory rate of the Hami melon fruit. Furthermore, melatonin markedly improved the antioxidant capacity of the fruit and protected it from oxidative damage by decreasing its contents of superoxide anions, hydrogen peroxide, and malondialdehyde. Melatonin significantly enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase. The total phenol, total flavonoids, and ascorbic acid contents were maintained by melatonin treatment. This treatment also repressed the activities of lipase, lipoxygenase, and phospholipase D, which are related to lipid metabolism. Thus, exogenous melatonin can maintain postharvest organoleptic quality of Hami melon fruit by increasing its antioxidant activity and inhibiting reactive oxygen species production.

Isolation in the control of epidemic.

Among many epidemic prevention measures, isolation is an important method to control the spread of infectious disease. Scholars rarely study the impact of isolation on disease dissemination from a quantitative perspective. In this paper, we introduce an isolation ratio and establish the corresponding model. The basic reproductive number and its biological explanation are given. The stability conditions of the disease-free and endemic equilibria are obtained by analyzing its distribution of characteristic values. It is shown that the isolation ratio has an important influence on the basic reproductive number and the stability conditions. Taking the COVID-19 in Wuhan as an example, isolating more than 68% of the population can control the spread of the epidemic. This method can provide precise epidemic prevention strategies for government departments. Numerical simulations verify the effectiveness of the results.

Incorporation of 1-methylcyclopropene and salicylic acid improves quality and shelf life of winter jujube (Zizyphus jujuba Mill. cv. Dongzao) through regulating reactive oxygen species metabolism.

Winter jujube fruit is susceptible to aging, peel reddening, dehydration, shrinkage, and tissue softening during shelf life after it is removed from the cold storage conditions. In this study, the effects of 1-methylcyclopropene (1-MCP) and salicylic acid (SA) on the quality of winter jujube fruit during shelf life were investigated by measuring physiological indexes and the activities of antioxidant enzymes and enzymes related to reactive oxygen species (ROS) metabolism of winter jujube fruit. The results showed that 1-MCP treatment and SA treatment suppressed weight loss, respiratory rate, malondialdehyde (MDA) content, H2O2 content, and O 2 - · production rate, but improved firmness, color difference (ΔE), soluble solid content (SSC), titratable acidity (TA), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia-lyase (PAL) activities, ascorbic acid content, glutathione content, total phenolic content, and total flavonoid content in comparison with the control. Particularly, the combined treatment of 1-MCP and SA (1-MCP+SA treatment) showed the maximum efficacy compared to the 1-MCP treatment and SA treatment alone. 1-MCP+SA treatment exhibited the best preservation effect, followed by SA treatment and 1-MCP treatment. Thus, the combined treatment of 1-MCP and SA is an effective approach to maintain the postharvest quality of winter jujube fruit and extend the shelf life.

Effect of salicylic acid treatment on antioxidant capacity and endogenous hormones in winter jujube during shelf life.

This study investigated the effects of exogenous salicylic acid (SA) treatment (0, control; 3 mmol L-1) on the antioxidant and hormone levels of winter jujube during shelf life (20 d) at 4 °C. The results showed that 3 mmol L-1 SA treatment preferably maintained firmness, color, titratable acidity, and total soluble solids, and effectively reduced the respiratory intensity and TSS/TA value (13.08%) of the fruit. Compared with the control group, the SA group had a higher content of sucrose (14.03%) and malic acid (29.13%). Meanwhile, SA reduced the accumulation of H2O2 (27.73%) and O2- (45.44%) by enhancing the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and the content of antioxidant substances (ascorbic acid, total phenols, total flavonoids, and glutathione) in the fruit. In addition, 3 mmol L-1 SA treatment led to higher levels of endogenous abscisic acid (18.49%) and SA (20.47%) in fruit, and lower concentration of jasmonic acid (42.68%), but had a weak effect on indole acetic acid levels.

Dissecting the Chloroplast Proteome of the Potato (Solanum Tuberosum L.) and Its Comparison with the Tuber Amyloplast Proteome.

The chloroplast, the energy organelle unique to plants and green algae, performs many functions, including photosynthesis and biosynthesis of metabolites. However, as the most critical tuber crop worldwide, the chloroplast proteome of potato (Solanum tuberosum) has not been explored. Here, we use Percoll density gradient centrifugation to isolate intact chloroplasts from leaves of potato cultivar E3 and establish a reference proteome map of potato chloroplast by bottom-up proteomics. A total of 1834 non-redundant proteins were identified in the chloroplast proteome, including 51 proteins encoded by the chloroplast genome. Extensive sequence-based localization prediction revealed over 62% of proteins to be chloroplast resident by at least one algorithm. Sixteen proteins were selected to evaluate the prediction result by transient fluorescence assay, which confirmed that 14 were distributed in distinct internal compartments of the chloroplast. In addition, we identified 136 phosphorylation sites in 61 proteins encoded by chloroplast proteome. Furthermore, we reconstruct the snapshots along starch metabolic pathways in the two different types of plastids by a comparative analysis between chloroplast and previously reported amyloplast proteomes. Altogether, our results establish a comprehensive proteome map with post-translationally modified sites of potato chloroplast, which would provide the theoretical principle for the research of the photosynthesis pathway and starch metabolism.

Comparative elucidation of bioactive and volatile components in dry mature jujube fruit (Ziziphus jujuba Mill.) subjected to different drying methods.

This study investigated the effects of convective drying(CD) and freeze drying(FD) on bioactive and volatile components in jujube. No significant difference in total phenolic, total flavonoids and antioxidant capacity among CD60, CD70, CD80 and FD samples (P > 0.05). LC-MS/MS analysis showed that this trend mainly originated from the dynamic equilibrium relationships between caffeic acid, chlorogenic acid, p-hydroxybenzoic acid, rutin, epicatechin, and quercetin. HS-SPME-GC-MS identified 31 volatile organic compounds (VOCs) comprising more than 80% aldehydes and acids. Principal component analysis distinguished the VOC characteristics of samples subjected to different drying methods. Six VOCs had an odor activity value (OAV) >1, most of which were fatty acid oxidation or Maillard reaction products. Combined with the precursor components, these reactions were speculated to be the major VOC-producing pathways in dried jujube. Considering the bioactive components and flavor retention, CD at 60 °C was an effective drying method with potential to replace FD.

The Role of Cell Wall Polysaccharides Disassembly and Enzyme Activity Changes in the Softening Process of Hami Melon (Cucumis melo L.).

To investigate the physiological and molecular properties relating to cell wall carbohydrate metabolism in fruit, the ultrastructure and polysaccharides compositions of the cell wall, as well as the fruit quality and activities of enzymes relating to fruit softening, were studied for three Hami melon varieties ('Xizhoumi 17', 'Jinhuami 25', and 'Chougua') representing three different storability levels. The results showed that 'Chougua' maintained a higher firmness on day 18, with the lowest decay incidence (0%). 'Chougua' showed a better storage quality and intact cell wall structure. The molecular weight and monosaccharide composition of cell wall polysaccharides for Hami melons underwent great changes during storage, and the degradation of pectin polysaccharides was obvious, involving the depolymerization of macromolecular polymers accompanied by the production of new macromolecular polymers and composition changes in pectin monosaccharides (glucose, galactose, and arabinose) during the softening process of the Hami melons. Polygalacturonase, pectin methylesterase, xyloglucan endo-transglycosylase/hydrolase, α-arabinofuranosidase, ß-galactosidase, and cellulase were associated with fruit softening at different stages of storage. There were similar softening mechanisms in the three Hami melons. This study will provide reference for further study on the fruit softening mechanisms of Hami melons.

Optimising nutrients in the culture medium of Rhodosporidium toruloides enhances lipids production.

Rhodosporidium toruloides is a useful oleaginous yeast, but lipids production is affected by various factors including nutrients in the culture medium. Herein, the R-ZL2 high-yield mutant strain was used to investigate the effects of different carbon sources (sucrose, glucose, xylose), nitrogen sources (ammonium sulphate, ammonium nitrate), and C/N ratio on lipids production capacity, get the following conclusion (1) Compared with glucose and xylose, sucrose was a superior carbon source for lipids production; (2) When using ammonium sulphate as the nitrogen source, a C/N ratio of 200:1 achieved the highest biomass, lipids production and lipids content (10.7 g/L, 6.32 g/L and 59%, respectively), and lipids produced under different C/N conditions have potential for biodiesel production (except for C/N = 40 and C/N = 80); (3) When using ammonium nitrate as the nitrogen source, a C/N ratio of 200:1 achieved the highest biomass, lipids production and lipids content (12.1 g/L, 8.25 g/L and 65%, respectively), and lipids produced under different C/N ratio conditions have potential for biodiesel production. Thus, a combination of sucrose and ammonium nitrate was optimal for the lipid accumulation in R-ZL2. The findings will lay a foundation for further improving lipids yields.

Physicochemical, Structural, and Biological Properties of Polysaccharides from Dandelion.

The edible and medicinal perennial herb dandelion is known to have antitumor, antioxidant, and anticomplement properties. However, the structural characterization and biological effects of its polysaccharides are not well understood. Here, we aimed to extract and investigate a novel polysaccharide from dandelion. A water-soluble polysaccharide, PD1-1, was successfully obtained from dandelion through ultrasonic-assisted extraction and purification using diethylaminoethyl (DEAE)-Sepharose fast flow and Sephadex G-75 columns. The results showed that PD1-1 is an inulin-type polysaccharide with a molecular weight of 2.6 kDa and is composed of glucose (52.39%), and mannose (45.41%). Glycosidic linkage analysis demonstrated that PD1-1 contains terminal α-d-Man/Glcp-(1→ and →1)-ß-d-Man/Glcf-(2→ glycosidic linkage conformations. A physicochemical analysis indicated that PD1-1 has a triple helix structure and exhibits important properties, including good swelling, water-holding, and oil-holding capacities. Furthermore, PD1-1 showed good antioxidant activities in DPPH and hydroxyl free radical scavenging abilities, with IC50 values of 0.23 mg/mL and 0.25 mg/mL, respectively, and good hypoglycemic activities in α-amylase and α-glucosidase inhibition, with IC50 values of 0.53 mg/mL and 0.40 mg/mL, respectively, in a concentration-dependent manner. Results suggest that PD1-1 possesses efficacious antioxidant and hypoglycemic properties and has potential applications as a functional food ingredient.

Improvement of lipid production in oleaginous yeast Rhodosporidium toruloides by ultraviolet mutagenesis.

The oleaginous yeast Rhodosporidium toruloides AS 2.1389 is viewed as desirable industrial microorganisms that can accumulate a high content of lipids for biodiesel production. In this study, we attempted to improve lipid accumulation in the yeast Rhodosporidium toruloides by UV irradiation mutagenesis and selection based on lithium chloride tolerance or ethanol-H2O2 tolerance. The biomass concentration, lipid yield and glucose consumption of mutant R. toruloides were determined. The transcription levels of lipid accumulation-related genes in the wild-type and mutant strains were also determined. The lithium chloride-tolerant strain R-ZL2 and the ethanol-H2O2-resistant strain R-ZY13 were generated by UV mutagenesis. The two mutant strains showed greater lipid productivity and lipid yield compared to the wild type. Transcriptional analysis revealed that IDP1, GPD1 and GND were expressed at significantly higher levels in the two high-lipid-producing mutants. In conclusion, lipid productivity and lipid yield in R. toruloides were successfully improved via UV mutagenesis and selection. We also identified some lipid accumulation-related genes for improving lipid productivity through genetic engineering.