Star-shaped cationic nano-carrier, preparation method thereof, prepared nano-pesticide and application of nano-pesticide in freezing prevention of young pears

Abstract

The invention belongs to the technical field of pear young fruit freezing prevention, and particularly relates to a star-shaped cationic nano-carrier and a preparation method thereof, a prepared nano-pesticide and application of the nano-pesticide in pear freezing prevention. The star-shaped cationic nano-carrier is obtained by carrying out amidation reaction on branched polyethyleneimine and tung oil at high temperature, the nano-carrier and jasmonic acid methyl ester can spontaneously form a stable nano-structure in a water phase, namely the star-shaped cationic jasmonic acid methyl ester nano-pesticide, and the nano-pesticide can overcome the technical bottlenecks that jasmonic acid methyl ester is easy to volatilize and easy to photodecompose; the long-term stable storage of the active ingredients is realized, the good adhesiveness is realized, and meanwhile, the anti-freezing capability of the young pears can be improved.

Description

Technical Field

[0001] This invention belongs to the field of antifreeze technology for young pears, specifically relating to a star-shaped cationic nanocarrier and its preparation method, the prepared nano-pesticide, and its application in antifreeze for young pears. Technical Background

[0002] Pear trees are important economic fruit trees, but young pears and their flowering period are extremely vulnerable to late frost damage in early spring. When faced with low temperatures, the cell membrane system of young fruits is damaged, and physiological metabolism is disrupted, leading to stunted fruit development, rust spots on the fruit surface, and even massive fruit drop. This has a devastating impact on the yield and quality of pears, causing huge economic losses to fruit farmers.

[0003] Traditional orchard frost protection measures mainly include fumigation, irrigation, and spraying antifreeze. However, these methods all have significant limitations: fumigation pollutes the environment and is severely dependent on weather conditions; irrigation requires large amounts of water and may exacerbate orchard pests and diseases; while conventional chemical antifreeze agents are often unstable in effect, have a short duration of action, and large-scale use may cause phytotoxicity or environmental residue problems. Therefore, developing efficient, safe, and convenient frost protection technology for young pears has become an urgent need for the healthy development of the pear industry.

[0004] In recent years, the plant endogenous hormone methyl jasmonate (MeJA), as a highly efficient "signaling molecule," has shown great potential in inducing systemic stress resistance in plants. Studies have shown that exogenous application of MeJA can effectively activate the plant's defense system, induce the expression of cold-resistance-related genes (such as COR and LEA), promote the accumulation of osmotic regulatory substances such as soluble sugars and proline, and stabilize cell membrane structure, thereby significantly improving the plant's tolerance to low-temperature freezing damage. This provides a novel approach for developing new bio-based antifreeze agents.

[0005] However, the direct application of methyl jasmonate in field production still faces many technical bottlenecks: (1) Poor stability: Methyl jasmonate is volatile and photodegradable. After being sprayed in the field, the active ingredients remaining on the leaves and fruit will degrade rapidly, resulting in a short window of actual action and making it difficult to continue to play a role before the critical frost.

[0006] (2) Low absorption efficiency: The hydrophobic cuticle on the surface of plant leaves and the waxy layer on the surface of fruit skin form a natural physical barrier, making it difficult for lipophilic MeJA molecules to be absorbed and transported by plant tissues efficiently and quickly.

[0007] (3) Lack of targeting: Conventional preparations cannot preferentially deliver the active ingredients to key parts such as young fruits that are most susceptible to frost damage, resulting in waste of active ingredients and low utilization rate.

[0008] This invention provides a drug delivery system that can improve the stability of methyl jasmonate, promote its absorption, and precisely target young fruit. This system is of great theoretical and practical significance for overcoming the bottleneck of methyl jasmonate in agricultural stress resistance applications and upgrading the antifreeze technology for young pears. It is a technical problem that urgently needs to be solved. Summary of the Invention

[0009] To address the problems in the prior art, one objective of this invention is to provide a star-shaped cation nanocarrier, the general structural formula of which is shown in Formula I: I.

[0010] The second objective of this invention is to provide a method for preparing a star-shaped cation nanocarrier as described above, comprising the following steps: S1. Add polyethyleneimine and tung oil to N,N-dimethylformamide in a molar ratio of 12:1, stir until homogeneous, and obtain a mixed solution; S2. The mixed solution is refluxed at 80~100℃ for 12 h, and the mixed solution after reaction is dialyzed to retain products with a molecular weight greater than 7000~7500 Da, so as to obtain star-shaped cation nanocarriers.

[0011] Preferably, the polyethyleneimine has a weight-average molecular weight of 35-60, wherein the ratio of primary amine, secondary amine, and tertiary amine is approximately 1:2:1; and the N,N-dimethylformamide has a purity greater than 99.9%.

[0012] More preferably, the weight-average molecular weight of the polyethyleneimine is 43.07.

[0013] The third objective of this invention is to provide the application of the star-shaped cationic nanocarriers described above in increasing the adhesion of nanopesticides.

[0014] The fourth objective of this invention is to provide a star-shaped cationic methyl jasmonate nanopesticide, which includes the star-shaped cationic nanocarrier as described above and an effective dose of methyl jasmonate loaded on the star-shaped cationic nanocarrier.

[0015] Preferably, the preparation method of the nanopesticide is as follows: the star-shaped cationic nanocarrier, methyl jasmonate and deionized water are added to deionized water according to a set mass ratio, and stirred. The star-shaped cationic nanocarrier and methyl jasmonate self-assemble to obtain the desired nanopesticide.

[0016] Preferably, in the nanopesticide, the concentration of the star-shaped cationic nanocarrier is 0.1 ~ 2.0 mg / mL, and the mass ratio of the star-shaped cationic nanocarrier to methyl jasmonate is 1: (0.1 ~ 0.5).

[0017] The fourth objective of this invention is to provide the application of the star-shaped cationic methyl jasmonate nanopesticide described above in improving the frost resistance of young pear fruits.

[0018] Preferably, the method for improving the frost resistance of young pear fruit is as follows: on the 7th to 15th day after the pear tree is in full bloom, the nano-pesticide is sprayed three times at a set interval of 12 hours, and the amount of each spray is 0.5 to 1.5 L / tree.

[0019] The beneficial effects of this invention are as follows: 1) Star-shaped polymer polyethyleneimine (PEI), due to its unique three-dimensional branched structure, possesses more terminal functional groups, lower solution viscosity, and stronger loading capacity compared to traditional linear polymers, making it a highly promising candidate for drug delivery. This application utilizes the abundant amino groups in branched polyethyleneimine (PEI) and the unsaturated fatty acid chains in tung oil to construct a star-shaped amphiphilic nanocarrier with both a hydrophilic core (PEI) and a hydrophobic shell (tung oil derivative) through a high-temperature catalytic amidation reaction. Multiple amino groups of PEI act as "growth points," reacting with multiple tung oil molecules to form a three-dimensional star structure with PEI as the hydrophilic core and long tung oil chains as hydrophobic arms. The hydrophobic cavity of this structure exhibits excellent compatibility with methyl jasmonate (MJ), enabling efficient encapsulation and nanoscale dispersion of MeJA in ethanol solutions through hydrophobic interactions and van der Waals forces, forming a stable nanostructure and significantly improving the encapsulation efficiency and drug loading of MeJA. In this structure, the hydrophilic PEI core faces the external aqueous phase, ensuring the stability of the nanocarrier; while the interior consists of a hydrophobic core composed of tung oil chains, achieving nanoscale encapsulation of methyl jasmonate. The long tung oil chains effectively block light, heat, and oxygen, overcoming the technical bottlenecks of methyl jasmonate's volatility and photodegradation, and achieving long-term stable storage of the active ingredient.

[0020] 2) Tung oil, as a natural oil, possesses excellent adhesive properties. Through hydrogen bonding, it can react with the carboxyl groups on the surface of young pears, thereby increasing the adhesion of nano-pesticides to the pear surface and enhancing the resistance of methyl jasmonic acid (MJ) to rain erosion, ensuring its long-term retention. Simultaneously, the large number of hydroxyl groups in tung oil also provides antifreeze properties, further improving the frost resistance of young pears. Furthermore, as a natural and renewable plant oil, tung oil is widely available, lower in cost, and exhibits good biodegradability compared to some synthetic polymers, making the technology in this application compliant with the requirements of green agriculture and sustainable development.

[0021] 3) This application is specific in its choice of tung oil. The inventors' previous research revealed that not all oils containing unsaturated fatty acid chains and hydroxyl groups can be used to prepare the nanocarriers required for this application. For example, although castor oil has a large number of hydroxyl groups, the double bonds of ricinoleic acid are non-conjugated, resulting in a very slow oxidative polymerization rate and almost no drying to form a film. When applied to the surface of fruit, it remains viscous and oily; because it cannot form a film, its actual antifreeze effect is poor and may even cause side effects. Other drying oils (such as linseed oil and perilla seed oil) also primarily have non-conjugated double bonds, resulting in a much slower drying rate than tung oil, and they lack a high hydroxyl content, thus failing to replace tung oil in achieving rapid film formation and antifreeze effects.

[0022] 4) The star-shaped cationic methyl jasmonate nanopesticide prepared in this application can protect young pears from freezing. The PEI skeleton in the nanocarrier provides a high density of positive charge (cationic characteristics). When the nano-formulation is sprayed on the plant surface, it can firmly adhere to the generally negatively charged cuticle of leaves and young fruits through strong electrostatic adsorption, resisting rain erosion and extending the window of action. Furthermore, the nanoscale particles can more easily penetrate through the gaps in the waxy layer of the young pear epidermis, thereby promoting the absorption and internal transport of methyl jasmonate by the young pear tissue and improving bioavailability. Attached Figure Description

[0023] Figure 1 The image shows the 1H NMR spectrum of the star-shaped cation nanocarrier prepared in Example 1.

[0024] Figure 2 The Fourier transform infrared spectrum of the star-shaped cation nanocarrier prepared in Example 1.

[0025] Figure 3 The potential dynamic light scattering curve of the star-shaped cation nanocarrier solution prepared in Example 1 is shown.

[0026] Figure 4 The dynamic light scattering curve of the star-shaped cation nanocarrier solution prepared in Example 1 is shown.

[0027] Figure 5 Transmission electron microscopy image of the star-shaped cation nanocarrier solution prepared in Example 1.

[0028] Figure 6 The image shows the adhesion of star-shaped cationic methyl jasmonate nanopesticides to the surface of young fruits under a fluorescence microscope. The red fluorescence in the image represents the nanopesticides. In the image, a is the control (CK), b is the test result at 12 h, c is the test result at 24 h, and d is the test result at 36 h.

[0029] Figure 7The images show the morphological observation results of young fruits in different treatment groups after the frost damage test. The three test objects in each treatment group correspond to the results observed at 12 h, 24 h and 36 h from left to right.

[0030] Figure 8 The figures show the results of protective enzyme activity, membrane lipid peroxidation products, and reactive oxygen species content in young fruits from different treatment groups after a frost damage experiment. Figure a shows POD peroxidase activity, b shows SOD superoxide dismutase activity, c shows CAT catalase activity, d shows H2O2 hydrogen peroxide content, e shows MDA malondialdehyde content, and f shows O2 content. - Results of superoxide anion production rate. Detailed Implementation

[0031] To facilitate understanding, the technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0032] Example 1

[0033] A star-shaped cation nanocarrier, prepared by the following method: S1. Dissolve 116.1 mmol of polyethyleneimine (PEI, 5 g) and 9.28 mmol of tung oil (8.13 g) in 120 mL of N,N-dimethylformamide (DMF) and mix well to obtain a mixed solution; S2. The mixed solution was refluxed at 100℃ for 12 h. After the reaction solution was removed, it was dialyzed. The molecular weight cutoff of the dialysis bag was 7000~7500 Da. The dialysis time was 28 h. The water was changed at least five times during the dialysis process. The retained substances were purified to obtain star-shaped cation nanocarriers.

[0034] The product prepared in Example 1 was characterized by NMR, and the 1H NMR spectrum is shown below. Figure 1 As shown; further Fourier transform infrared spectroscopy and dynamic light scattering analysis were performed, and the Fourier transform infrared spectrum is shown below. Figure 2 As shown, it can be seen that 1550cm -1 and 1650 cm -1 Characteristic peaks of amide II and amide I bands appear at 3290 cm⁻¹. -1 The NH peak at that point weakens. The dynamic light scattering curves of the product potential and particle size are shown below. Figure 3 and Figure 4 As shown, the potential of the prepared product is +67, and the average particle size of the product is 250 nm, which proves that the star-shaped cation nanocarrier TO-PEI (TP) was successfully synthesized.

[0035] The general structural formula of the prepared star-shaped cation nanocarrier is as follows:

[0036] The preparation process can be represented as follows:

[0037] The prepared star-shaped cation nanocarriers were observed using transmission electron microscopy, and the results are as follows: Figure 5 As shown, the star-shaped cation nanocarrier forms the morphology of nanospheres.

[0038] Example 2

[0039] A star-shaped cation nanocarrier, prepared by the following method: S1. Dissolve 23.2 mmol of polyethyleneimine (PEI, 1 g) and 2.28 mmol of tung oil (2 g) in 25 mL of N,N-dimethylformamide (DMF) and mix well to obtain a mixed solution; S2. The mixed solution was refluxed at 100℃ for 12 h. After the reaction solution was removed, it was dialyzed. The molecular weight cutoff of the dialysis bag was 7000~7500 Da. The dialysis time was 24 h. The water was changed at least five times during the dialysis process. The retained substance was purified to obtain star-shaped cation nanocarriers.

[0040] Example 3

[0041] A star-shaped cation nanocarrier, prepared by the following method: S1. Dissolve 11.6 mmol of polyethyleneimine (PEI, 0.5 g) and 1.14 mmol of tung oil (TO, 1 g) in 20 mL of N,N-dimethylformamide (DMF) and mix well to obtain a mixed solution; S2. The mixed solution was refluxed at 100℃ for 12 h. After the reaction solution was removed, it was dialyzed. The molecular weight cutoff of the dialysis bag was 7000~7500 Da. The dialysis time was 24 h. The water was changed at least five times during the dialysis process. The retained substance was purified to obtain star-shaped cation nanocarriers.

[0042] Example 4

[0043] A star-shaped cationic jasmine methyl ester nanopesticide, prepared by the following method: The star-shaped cationic nanocarrier TO-PEI and methyl jasmonate were dissolved together in ethanol at a set mass ratio, and deionized water was slowly added dropwise. In the aqueous phase, the star-shaped cationic nanocarrier and methyl jasmonate self-assembled to obtain the desired nano-pesticide.

[0044] In this embodiment, the star-shaped cation nanocarrier was prepared according to Example 1, and the amounts of star-shaped cation nanocarrier, methyl jasmonate, ethanol and deionized water were 20.0 mg, 5.0 mg, 10.0 mg and 50 mL, respectively.

[0045] To facilitate subsequent experiments, fluorescent labeling was added to the prepared star-shaped cationic jasmine methyl ester nanopesticide. The method was as follows: 0.23 mmol of TO-PEI (0.3 g), 0.012 mmol of 2-iminothiacyclopentane hydrochloride (1.6 mg) and 0.0044 mmol of rhodamine B (2.1 mg) were dissolved in N,N-dimethylformamide (DMF) and reacted at room temperature for 12 hours to obtain the nanopesticide.

[0046] experiment

[0047] Star-shaped cationic methyl jasmonate nanopesticides enhance the frost resistance and pesticide adhesion of young pear fruits.

[0048] Using 'Cuiguan' pear seedlings 15 days after full bloom as test material, the following treatment groups were set up: no treatment at room temperature (control group RT), spraying with water (CK), methyl jasmonate (MeJA, 100 μM), star-shaped cationic nanocarrier (blank TP, Example 1, 0.12 mg / mL), and fluorescently labeled star-shaped cationic methyl jasmonate nanopesticide (MeJA-TP, where the effective concentration of methyl jasmonate was 100 μM and the corresponding background concentration of nanocarrier TP was 0.12 mg / mL).

[0049] Use a handheld sprayer to evenly spray the young fruit and surrounding leaves on both sides, applying enough to completely wet the surface without dripping (approximately 5 mL per fruit). Repeat all treatments three times, with each application spaced 12 hours apart.

[0050] After the third spraying, branches with young fruit treated as described above were cut and subjected to low-temperature treatment at -4℃. Specifically, after the sprayed branches were dried at room temperature to remove surface droplets, they were inserted into conical flasks filled with water to prevent water loss during treatment. The branches were then placed in a low-temperature incubator, maintaining a relative humidity of 75% ± 5%. This high humidity environment prevented excessive water loss due to excessive transpiration during low-temperature treatment, ensuring that frost damage symptoms were primarily caused by low temperature rather than drought stress. The temperature was initially set at 25℃ for 2 hours to ensure all samples were at the same physiological starting point. Subsequently, the temperature was programmed to decrease from 25℃ to -4℃ at a rate of 2℃ / hour to simulate a natural frost process. Then, the treatment was continued at -4℃ for 4 hours. After treatment, the temperature was slowly increased to 4℃ at a rate of 2℃ / hour and maintained at 4℃ for 2 hours. Finally, the samples were moved back to room temperature for further observation to avoid secondary damage to the tissues caused by rapid temperature increases.

[0051] 1. At 12 h, 24 h, and 36 h, pear fruits treated with fluorescent star-shaped cationic methyl jasmonate nanopesticides were observed under a fluorescence microscope. The surface of the fruits was assessed using fluorescence signals to determine pesticide adhesion and the uniformity of adhesion. Results are as follows: Figure 6 As shown in the figure, compared with the control group (water CK), the star-shaped cationic methyl jasmonate nanopesticide still exhibited strong adhesion after 36 h of treatment.

[0052] 2. The frost resistance of the young fruits in the control group and experimental group was observed at 12 h, 24 h, and 36 h, respectively. The results are as follows: Figure 7 As shown.

[0053] Figure 7 The results, from left to right, represent 12 h, 24 h, and 36 h. Figure 7 As can be seen, the RT group exhibited plump and healthy morphology, serving as a baseline for fruits unaffected by low-temperature stress. The MeJA-TP group showed plump and full fruits, maintaining normal turgor pressure and spherical structure. The fruit surface was smooth, without obvious wrinkling or depressions, and the peel retained a relatively healthy green or yellowish-green color, indicating the least chlorophyll degradation and cell necrosis. The CK control group showed obvious wrinkling and wilting; the fruits became shriveled due to water loss, exhibiting more pronounced depressions and increased brown areas, indicating tissue necrosis. Compared to the MeJA-TP group, the MeJA group showed slight wilting. The plump and smooth phenotype of the MeJA-TP group clearly demonstrates that the cell membrane system of the young fruit in this treatment group suffered the least damage at low temperatures, with minimal water loss, and the cells were still able to maintain normal structure and function. This indicates that the star-shaped cationic methyl jasmonate nanopesticide provided in this application can significantly improve the frost resistance of young pear fruits.

[0054] 3. At 12 h, 24 h, and 36 h, the activities of CAT (catalase), POD (peroxidase), SOD (superoxide dismutase), MDA (malondialdehyde), H2O2 (hydrogen peroxide), and O2 in the young pear fruits of each treatment group were measured. - The rate of production of (superoxide anion).

[0055] The procedure for determining the activity of the protective enzyme is as follows: Weigh 0.5 g of frozen young fruit tissue and grind it into a homogenate with 5 mL of pre-cooled phosphate buffer (50 mM, pH 7.8) in a pre-cooled mortar. Centrifuge the homogenate at 4℃ and 12000 ×g for 20 minutes and collect the supernatant as the crude enzyme extract, which is used to determine the activities of CAT, POD and SOD. All operations are performed in an ice bath. (1) CAT activity determination: Add 50 μL of crude enzyme extract and 950 μL of freshly prepared H2O2 phosphate buffer (50 mM, pH 7.0, containing 15 mM H2O2) to a 1 mL reaction system, and immediately measure the initial absorbance at 240 nm and the absorbance after 1 minute of reaction under a UV spectrophotometer. (2) POD activity assay: In a 3 mL reaction system containing 50 mM phosphate buffer (pH 7.0), 10 mM guaiacol, 5 mM H2O2 and 50 μL crude enzyme extract, the initial absorbance at 470 nm and the absorbance after 1 minute of reaction were immediately measured using a spectrophotometer. (3) SOD activity assay: In a 3 mL reaction system containing 50 mM phosphate buffer (pH 7.8), 13 mM methionine, 63 μM NBT, 1.3 μM riboflavin, 0.05 mM EDTA-Na2 and 50 μL crude enzyme extract, one test tube was placed in the dark as a blank control, and the remaining test tubes were placed under 4000 Lux light for 20 minutes.

[0056] Determination of membrane lipid peroxidation products and reactive oxygen species content: (1) MDA content determination: Weigh 0.5 g of tissue, add 5 mL of 10% trichloroacetic acid (TCA) for grinding and extraction, centrifuge and collect the supernatant. Take 2 mL of supernatant, add 2 mL of 0.6% TBA solution, mix well and react in a boiling water bath for 15 minutes, cool rapidly and centrifuge again. Measure the absorbance of the supernatant at 532 nm, 600 nm and 450 nm.

[0057] (2) H2O2 content determination: Weigh 0.5 g of tissue, grind and extract with pre-cooled acetone, and collect the supernatant after centrifugation. Add 0.1 mL of 20% titanium sulfate and 0.2 mL of concentrated ammonia to 1 mL of supernatant to form a precipitate. Centrifuge and discard the supernatant. Wash the precipitate several times with acetone and then dissolve the precipitate with 3 mL of 2 M sulfuric acid.

[0058] (3) O2 -Production rate determination: Weigh 0.5 g of tissue, add 3 mL of pre-cooled 50 mM phosphate buffer (pH 7.8), grind, centrifuge, and collect the supernatant; take 1 mL of the supernatant, mix with 1 mL of 50 mM phosphate buffer (pH 7.8) and 0.5 mL of 10 mM hydroxylamine hydrochloride, and react in a 25°C water bath for 1 hour. Then add 1 mL of 17 mM p-aminobenzenesulfonic acid (soluble in glacial acetic acid) and 1 mL of 7 mM... - Naphthylamine (soluble in glacial acetic acid), mix well and keep warm at 25°C for 20 minutes.

[0059] Under normal circumstances, the content of reactive oxygen species (ROS) in plants is in dynamic equilibrium and does not harm the plants. However, under low-temperature stress, the cell membrane system is damaged, disrupting the balance between ROS production and scavenging. Excessive free radical content can affect the normal life activities of cellular components, including superoxide anions (O2). - Reactive oxygen species (ROS) include hydrogen peroxide (H2O2). To maintain redox homeostasis in plants, plants activate protective enzymes to cope with low-temperature stress. These enzyme systems actively remove excess ROS, but as stress intensifies, exceeding the scavenging capacity of the enzyme system, plants suffer damage and die. Protective enzyme systems play a crucial role in scavenging ROS and maintaining the integrity of protective membranes. For example, peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) are important protective enzymes in plants that can remove the accumulation of ROS, mitigate the harmful effects of low-temperature stress, stabilize plant membrane systems, and reduce the content of malondialdehyde (MDA) produced by membrane lipid peroxidation.

[0060] The test results at 36 hours are as follows Figure 8 As shown in the figure, after 36 h of growth, compared with the control group, the contents of CAT, POD, and SOD in the treatment with star-shaped cationic methyl jasmonate nanopesticide were significantly increased, and the contents of MDA, H2O2, and O2 were also increased. - The content of [agent] was significantly reduced. These results further demonstrate that spraying star-shaped cationic methyl jasmonate nanopesticides significantly improves the frost resistance of young pear fruits.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A star-shaped cation nanocarrier, characterized in that, The general structural formula of the nanocarrier is shown in formula (Ⅰ): （Ⅰ）。 2. A method for preparing a star-shaped cation nanocarrier as described in claim 1, characterized in that, Includes the following steps: S1. Add polyethyleneimine and tung oil to N,N-dimethylformamide in a molar ratio of 12:1, stir until homogeneous, and obtain a mixed solution; S2. The mixed solution is refluxed at 80~100℃ for 12 h, and the mixed solution after reaction is dialyzed to retain products with a molecular weight greater than 7000~7500 Da, so as to obtain star-shaped cation nanocarriers.

3. The preparation method according to claim 2, characterized in that, The weight-average molecular weight of the polyethyleneimine is 35-60, and the purity of the N,N-dimethylformamide is greater than 99.9%.

4. The preparation method according to claim 3, characterized in that, The weight-average molecular weight of the polyethyleneimine is 43.

07.

5. The application of the star-shaped cationic nanocarrier as described in claim 1 in increasing the adhesion of nanopesticides.

6. A star-shaped cationic methyl jasmonate nanopesticide, characterized in that, It includes the star-shaped cation nanocarrier as described in claim 1 and an effective dose of methyl jasmonate loaded on the star-shaped cation nanocarrier.

7. The star-shaped cationic methyl jasmonate nanopesticide as described in claim 6, characterized in that, The preparation method of the nanopesticide is as follows: the star-shaped cationic nanocarrier, methyl jasmonate and deionized water are added to deionized water according to a set mass ratio, and stirred. The star-shaped cationic nanocarrier and methyl jasmonate self-assemble to obtain the desired nanopesticide.

8. A star-shaped cationic methyl jasmonate nanopesticide as described in claim 6 or 7, characterized in that, In the nanopesticide, the concentration of the star-shaped cationic nanocarrier is 0.1 ~ 2.0 mg / mL, and the mass ratio of the star-shaped cationic nanocarrier to methyl jasmonate is 1: (0.1 ~ 0.5).

9. The application of the star-shaped cationic methyl jasmonate nanopesticide as described in any one of claims 6-8 in improving the frost resistance of young pear fruits.

10. The application as described in claim 9, characterized in that, Seven to fifteen days after the pear trees have fully blossomed, the nano-pesticide is sprayed three times at a set interval of 12 hours, with a single application rate of 0.5 to 1.5 L per tree.

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