Sodium silicate treatment accelerates biosynthesis and polymerization of suberin polyaliphatics monomers at wounds of muskmelon.

Suberin polyaliphatics (SPA) is an important component of healing closing layer at fruit wounds. However, few study is available on the effect of sodium silicon treatment on SPA monomers biosynthesis and polymerization at muskmelon wounds. In this study, sodium silicate enhanced PLA2 (Phospholipase A2, PLA2) expression and enzyme activity, increased oleic acid, linoleic acid, and linolenic acid contents, and degree of fatty acids unsaturation at wounds. Sodium silicate upregulated the expressions of LACS4 (Long chain acyl CoA synthetase, LACS), KCS10 (ß-ketoacyl CoA synthase, KCS), CYP86B1 (Cytochrome P450 oxygenase, CYP), FAR3 (Fatty acyl CoA reductase, FAR), GPAT1 (Glycerol-3-phosphate acyltransferase, GPAT) and ABCG6 (ATP-binding cassette transporter), as well as their enzymes activities and ABC content. It is suggested that sodium silicate accelerates the deposition of SPA at muskmelon wounds by increasing the degree of fatty acids unsaturation, and promoting SPA monomers biosynthesis.

BTH-induced joint regulation of wound healing at the wounds of apple fruit by JA and its downstream transcription factors.

Jasmonic acids (JAs) are important injury signaling molecules, which participate in the process of wound healing in plants. However, how JA and its downstream transcription factors involve in wound healing in apple fruit mediated by BTH has not been reported yet. In the present study, BTH treatment up-regulated gene expression of MdLOX3.1, MdAOS1, MdAOC, and MdOPR3, promoting JA synthesis at fruit wounds. Moreover, BTH up-regulated the gene expression of MdMYC2, MdGAIPB, and MdMYB108 transcription factors and increased MdPAL1, Md4CL2, MdCOMT1, and MdCAD6 expression. In addition, BTH facilitated the synthesis of phenylpropanoid metabolism products and accelerated suberin polyphenolics deposition at the wounds, which effectively reduced fruit weight loss and lesion diameter of apple fruit inoculated with Penicillium expansum during healing. It is suggested that BTH induced wound healing in apple fruit by the stimulating JA and its downstream transcription factors, and phenylpropanoid metabolism.

Post-harvest chitosan treatment suppresses oxidative stress by regulating reactive oxygen species metabolism in wounded apples.

Mechanical wound on fruit triggers the formation of reactive oxygen species (ROS) that weaken cell walls, resulting in post-harvest losses. This mechanism can be controlled by using fruit preservatives to stimulate fruit antioxidant enzyme activities for the detoxification of ROS. Chitosan is a safe and environmentally friendly preservative that modulates ROS in whole fruits and plant cells, but the effects of chitosan on the ROS metabolism of mechanically wounded apples during storage are unknown. Our study focused on exploring the effects of post-harvest chitosan treatment on ROS production, cell membrane integrity, and enzymatic and non-enzymatic antioxidant systems at fruit wounds during storage. Apple fruits (cv. Fuji) were artificially wounded, treated with 2.5% (w/v) chitosan, and stored at room temperature (21-25°C, RH = 81-85%) for 7 days. Non-wounded apples were used as healthy controls. The results showed that chitosan treatment stimulated the activities of NADPH oxidase and superoxide dismutase and increased the formation of superoxide anions and hydrogen peroxide in fruit wounds. However, malondialdehyde, lipoxygenase, and membrane permeability, which are direct biomarkers to evaluate lipid peroxidation and membrane integrity, were significantly decreased in the wounded fruits after chitosan treatment compared to the wounded control fruits. Antioxidant enzymes, such as peroxidase and catalase activities, were induced by chitosan at fruit wounds. In addition, ascorbate-glutathione cycle-related enzymes; ascorbate peroxide, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and the content of substrates, mainly ascorbic acid, dehydroascorbate, reduced glutathione, and glutathione, were increased at fruit wounds by chitosan compared to the wounded control fruits. Our results show that wounding stimulated the production of ROS or oxidative stress. However, treatment with chitosan triggered antioxidant systems to scavenge ROS and prevent loss of fruit membrane integrity. Therefore, chitosan promises to be a favorable preservative in inducing tolerance to stress and maintaining fruit quality.

Preharvest multiple sprays with chitosan promotes the synthesis and deposition of lignin at wounds of harvested muskmelons.

As an important elicitor, chitosan could activate the synthesis of lignin in many plants. However, no report is available on whether preharvest chitosan sprays affects the synthesis and deposition of lignin at wounds of harvested muskmelons. In the present study, the plants and fruit of muskmelons were multiple sprayed with 0.1% chitosan during fruit development. Here, we found that chitosan sprays increased the activities of 4-coumaric acid-coenzyme A ligase, cinnamyl-CoA reductase and cinnamyl alcohol dehydrogenase, and elevated the levels of p-coumaryl alcohol, coniferyl alcohol, sinapyl alcohol and lignin at wounds. Chitosan sprays enhanced H2O2 level and peroxidase activity, and accelerated the deposition of lignin at wounds. Moreover, chitosan sprays resulted in a higher hardness and lower resilience, springiness and cohesiveness of the healing tissues. Taken together, preharvest chitosan sprays accelerated the deposition of lignin at wounds of muskmelons by activating lignin metabolism, and increasing H2O2 content and peroxidase activity.

Chitosan Treatment Promotes Wound Healing of Apple by Eliciting Phenylpropanoid Pathway and Enzymatic Browning of Wounds.

Chitosan is an elicitor that induces resistance in fruits against postharvest diseases, but there is little knowledge about the wound healing ability of chitosan on apple fruits. Our study aimed at revealing the effect of chitosan on the phenylpropanoid pathway by determining some enzyme activities, products metabolites, polyphenol oxidase activity, color (L*, b*, a*), weight loss, and disease index during healing. Apple (cv. Fuji) fruits wounded artificially were treated with 2.5% chitosan and healed at 21-25°C, relative humidity = 81-85% for 7 days, and non-wounded fruits (coated and non-coated) were used as control. The result shows that chitosan treatment significantly decreased weight loss of wounded fruits and disease index of Penicillium expansum inoculated fruits. The activities of phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4CL), cinnamoyl-CoA reductase (CCR), and cinnamyl alcohol dehydrogenase (CAD) were elicited throughout the healing period by chitosan, which increased the biosynthesis of cinnamic acid, caffeic acid, ferulic acid, sinapic acid, p-coumaric acid, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Also, total phenol, flavonoid, and lignin contents were significantly increased at the fruits wounds. In addition, chitosan's ability to enhance polyphenol oxidase activity stimulated enzymatic browning of wounds. Although wounding increased phenylpropanoid enzymes activities before healing, chitosan caused higher enzyme activities for a significant healing effect compared with the control. These findings imply that chitosan accelerates apple wound healing by activating the phenylpropanoid pathway and stimulating enzymatic browning of wounds.

Effects of nitric oxide treatment on lignin biosynthesis and texture properties at wound sites of muskmelons.

Lignin is an important component of the healing tissue in fruits. In this study, we treated muskmelon (Cucumis melo L. cv. "Manao") fruit with exogenous nitric oxide (NO) donor sodium nitroprusside (SNP) to observe and analyze its effect on lignin synthesis and accumulation during healing. Results showed that SNP treatment enhanced the contents of endogenous NO and H2O2, increased the activities of phenylalanine ammonia lyase, cinnamate 4 hydroxylase, cinnamyl alcohol dehydrogenase, and peroxidase, and raised the contents of sinapyl alcohol, coniferyl alcohol, coumaryl alcohol, and lignin. SNP augmented the hardness of the healing tissue and decreased its resilience, springiness, and cohesiveness. In addition, SNP treatment effectively reduced the weight loss and disease index of wounded muskmelons. All these results suggest that lignin metabolism mediated by NO play a crucial role in wound healing of muskmelons.

Modification performance and electrochemical characteristics of different groups of modified aptamers applied for label-free electrochemical impedimetric sensors.

Amino and thiolated aptamers are the main aptamers used to construct label-free electrochemical impedimetric aptasensors. In this study, the modification performance and electrochemical properties of amino aptamers and thiolated aptamers were studied in the construction of label-free impedimetric sensors. The results showed that the initial modification density of amino aptamers was higher than that of thiol aptamers. Aptamers can recognize and bind OTA to generate electrical signals. The higher the density of aptamer modification was, the better the electric signals were. If only considering the initial modification density, amino aptamers were more suitable for the preparation of aptasensors than thiolated aptamers. However, the modification density of the amino aptamer decreased with the prolonged immersion time in 1 mM HCl solution, which suggests that the stability of this sensor was poor. However, the thiolated aptamer maintained relatively constant density and could be reused. Thus, the thiolated aptasensor had a wide range and good reproducibility and stability for the determination of ochratoxin A (OTA). In addition, this study proved that gold nanoparticles play an important role in signal amplification by increasing the effective gold surface to fix more aptamers in the process of sensor preparation.

Rapid Determination of Ochratoxin A in Grape and Its Commodities Based on a Label-Free Impedimetric Aptasensor Constructed by Layer-by-Layer Self-Assembly.

A simple and sensitive label-free impedimetric aptasensor for rapid determination of ochratoxin A (OTA) has been developed, which was based on the combination between thiolated aptamer and gold nanoparticles by layer-by-layer self-assembly. Because of the interaction between aptamer and OTA, the relative normalized electron-transfer resistance (ΔRct) values obtained by electrochemical impedance spectroscopy (EIS) was proportional to the concentration of OTA and showed a good linear relationship from 0.1 to 10.0 ng/mL, with a lower detection limit (0.030 ng/mL) than one-step thiolated DNA aptasensor. The established method was successfully applied to detect and analyze OTA in table wine and grape juice, and the recovery was 90.56%⁻104.21% when PVP effective removed of phenolic substances. The label-free impedimetric aptasensor was used for rapid detection and quantitation of OTA in the inoculated grapes with the Aspergillus Nigri (H1), and the production of OTA (62.4 µg/kg, 20 µg/kg) far exceeded the maximum levels of 2 µg/kg after inoculation for three days. The developed method exhibited a good specificity, high sensitivity, time-efficient, and it could be applied to detect the OTA concentration in grape and its commodities.