In this study, ultraviolet (UV) spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking were utilized to systematically elucidate the binding mechanism between aptamers and ochratoxin A (OTA) at different solution conditions (pH, metal ions, and Ca²⁺ concentrations). The results indicated that the optimal pH for aptamer binding to OTA was 6–7. In the presence of Ca²⁺, the primary binding mode between aptamers and OTA was intercalation. Compared with monovalent metal ions, Ca²⁺ significantly enhances the stability of aptamer-OTA complexes. In addition, the CD spectra showed that Ca²⁺ and Mg²⁺ induced the formation of a hybrid G-quadruplex structure between aptamers and OTA. Molecular docking demonstrated that hydrogen bonds were formed between the aptamer bases DG-5 and DG-27 and OTA, with a dissociation constant (K_d) of 725 nmol/L. In summary, this study provides a systematic analysis of how solution conditions influence the interaction between aptamers and OTA, offering a theoretical basis for advancing the application of aptamers in biosensors.

To investigate the role of Rho4, a small GTPase, in host resistance during fruit-pathogen interactions, we inoculated apple fruits separately with a wild-type (WT) strain, a Rho4-deleted mutant (ΔPeRho4) and a complemented strain (ΔPeRho4-C) of Penicillium expansum. The lesion size was assessed, and transcriptomic analysis of tissues at the disease-health interface was performed to identify differentially expressed genes (DEGs). The expression and activity of key enzymes involved in phenylpropanoid metabolism were measured and changes in related metabolites were examined. Our results showed that fruits inoculated with ΔPeRho4 exhibited significantly smaller lesions compared with those inoculated with the WT strain, and the lesion size of ΔPeRho4-C was similar to the WT level. Transcriptomic profiling identified 216 DEGs, among which four were associated with the phenylpropanoid pathway and up-regulated in ΔPeRho4 inoculated tissues. Moreover, ΔPeRho4 inoculation significantly increased the expression and activities of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumaroyl-coenzyme A ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD). It also promoted the accumulation of phenolic acids, lignin monomers, total phenolics, flavonoids, and lignin. These results suggest that the deletion of Rho4 attenuated the pathogenicity of P. expansum, which may indirectly trigger the activation of phenylpropanoid metabolism at the disease-health interface and enhance defense responses in apple fruits. This study provides new insights into the molecular mechanisms by which fungal small GTPases influence host resistance and offers potential strategies for postharvest disease control.

Pink mold rot is one of the major diseases of tomatoes, which can occur before and after harvest, causing great losses in tomato production, storage and transportation. This study investigated the in vitro inhibitory effect of cuminal against Trichothecium roseum Pers. Link, the fungal pathogen causing pink mold rot of tomatoes. The inhibitory effect of a composite coating consisting of cuminal and oleaster gum on disease incidence in tomatoes artificially wounded and inoculated with T. roseum and the effect of the composite coating on disease resistance in tomato fruit were evaluated. The results showed that cuminal effectively inhibited the spore germination and mycelial growth of T. roseum under in vitro conditions, cuminal at a concentration of 0.1 μL/mL inhibited colony growth by more than 80%. Under in vivo conditions, the composite coating significantly inhibited the growth of T. roseum on tomato fruit, delayed lesion expansion and reduced decay incidence. After 9 days of storage, the lesion diameter and the decay incidence of the fruit treated with the composite coating containing 30 mg/mL oleaster gum and 0.2% (V/V) cuminal were 36.7% and 69.2% of those in the control group, respectively. The composite coating effectively increased the H₂O₂ content of tomato fruit during the early stage of storage, increased enzyme activities such as peroxidase (POD), phenylalanine ammonia-lyase (PAL) and 4-coumarate-CoA ligase (4CL), and enhanced the accumulation of total phenols and flavonoids in tomato fruit. These results suggest that the composite coating containing oleaster gum and cuminal can effectively inhibit the occurrence and development of postharvest pink mold rot of tomatoes, and its mechanism is not only related to the inhibition of pathogen growth by cuminal, but also to enhanced disease resistance in tomato fruit.

To study the effect of linolenic acid (LA) on wound healing in postharvest apple fruit and to explore the underlying biochemical mechanisms, artificially wounded apple fruit (cv. Fuji) were treated with 1 mmol/L LA or sterile water containing a small amount of ethanol as a control. The wound healing effect of LA was evaluated by measuring disease index and mass loss rate of apple. The key enzyme activities related to phenylpropane metabolism and its metabolite contents, H₂O₂ content and peroxidase (POD) activity at the wounds were measured. Compared to the control group, LA treatment decreased significantly the mass loss of wounded fruit and the disease index of inoculated fruit during wound healing. LA treatment increased the activities of four key enzymes involved in phenylpropane metabolism (phenylalanine ammonia lyase (PAL), cinnamic acid-4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4CL) and cinnamyl alcohol dehydrogenase (CAD)), and elevated the levels of four phenolic acids (erucic acid, ferulic acid, cinnamic acid and caffeic acid) and three lignin alcohol monomers (coniferyl alcohol, cinnamyl alcohol and sinapyl alcohol), as well as total phenols, flavonoids, and lignin at the wounds. LA treatment also enhanced H₂O₂ content and POD activity. In summary, LA could promote wound healing of apple fruit by activating phenylpropanoid metabolism, and increasing H₂O₂ content and POD activity.

We aimed to study the effects of multiple sprays with amino oligosaccharide (AOS) during fruit development on wound healing in harvested muskmelons. The muskmelon plants and fruits (cv. Manao) were sprayed with AOS at 2 mL/L for four times at the four stages (young fruit stage, early stage of enlargement, late stage of enlargement and mature stage) of fruit development. The effect of AOS sprays on the mass loss and disease index of harvested fruits during wound healing was evaluated. The formation of closing layer was observed on the wounds. Related metabolic enzyme activities were determined. AOS sprays effectively reduced the mass loss and disease index of wounded fruits inoculated with Trichothecium roseum during wound healing. On day 7, the mass loss and disease index of the treated group were 28.64% and 32.00% lower than those of the control group, respectively. The sprays promoted the deposition of suberin polyphenolics and lignin at wound sites, and the cell layer of suberin polyphenolics and lignin deposited was 22.70% and 25.07% thicker than those in the control group on the 5th day of healing. The sprays also increased phenylalanine ammonia lyase activity, and enhanced the contents of total phenols, flavonoids and lignin. In addition, the sprays significantly raised H₂O₂ content and peroxidase activity at wound sites. Taken together, preharvest multiple sprays with AOS could promote wound healing in harvested muskmelons by activating phenylpropane metabolism, and increasing H₂O₂ content and peroxidase activity.

Chlorine dioxide (ClO₂) is a safe and effective disinfectant that is widely used for preserving fruits and vegetables as well as controlling microorganisms. However, the mechanism by which ClO₂ treatment affects wound healing in potato tubers remains unclear. The half cut potato tubers ‘cv. Atlantic’ were soaked with 25 mg/L ClO₂ for 10 min, which were stored for 0, 3, 5, 7, 14, and 21 d at room temperature in dark for wound healing. The mass loss rate and the disease index of wounded tubers inoculated with Fusarium sulphureum were determined, the deposition of suberin poly phenolic (SPP) and lignin at wound sites were observed, and the activities of the key enzymes of phenylpropanoid metabolism and peroxidase (POD) as well as the content of phenylpropanoid metabolism products and H₂O₂ at wound sites were measured. This result showed that ClO₂ at 25 mg/L accelerated SPP and lignin deposition and increased cell layer thickness at wounds. Furthermore, the mass loss rate and disease index (after inoculated with F. sulphureum) of potato tubers significantly was reduced by 20.8% and 45.3%, respectively, on day 14 after ClO₂ treatment. Additionally, ClO₂ enhanced the contents of five phenolic acids (cinnamic, p-coumaric, caffeic, ferulic, and sinapic acids) and three lignin monomers (p-coumaryl, sinapyl, and coniferyl alcohols) by increasing phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and cinnamyl alcohol dehydrogenase (CAD) activities. Moreover, ClO₂ treatment significantly promoted the synthesis of total phenolics, flavonoids and lignin and elevated H₂O₂ content and peroxidase activity. In conclusion, ClO₂ treatment accelerated the deposition of SPP and lignin at wound sites, decreased the mass loss rate and disease index of damaged potato tubers during healing, triggered the phenylpropanoid metabolism pathway, and increased H₂O₂ content and POD activity. These findings provide evidence that ClO₂ treatment can accelerate wound healing in potato tubers.

In this study, artificially wounded potato tubers were treated with 2 mmol/L salicylic acid (SA) for 10 min. Reactive oxygen species (ROS) production and ROS scavenging enzyme activities were determined, and in vitro antioxidant capacity and cell membrane integrity in the wounds were analyzed during the early wound healing (within 12 h after wounding) period. The results showed that SA increased the activities of NADPH oxidase and superoxide dismutase, and promoted the accumulation of superoxide anion radical and H₂O₂ in tuber wounds during the early wound healing period. SA increased the activity of peroxidase, but decreased the activity of catalase. SA also increased the activities of ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase and glutathione reductase, and increased the levels of ascorbic acid and reduced glutathione. In addition, SA treatment improved the capacity to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and ferric reducing antioxidant power (FRAP) and reduced cell membrane permeability and malondialdehyde (MDA) content. In conclusion, SA could maintain cell membrane integrity and consequently ensure the smooth progress of normal metabolism during early wound healing by regulating ROS homeostasis and improving in vitro antioxidant activity in potato tuber wounds.