Application of medium molecular weight gamma-polyglutamic acid in reduction of crop heavy metal accumulation and promotion of crop growth

Abstract

The invention discloses application of medium-molecular-weight gamma-polyglutamic acid in reduction of heavy metal accumulation of crops and promotion of crop growth, the relative weight-average molecular weight range of the medium-molecular-weight gamma-polyglutamic acid is 200-300 kDa, and meanwhile, the invention provides a preparation method of the medium-molecular-weight gamma-polyglutamic acid. By adding the medium-molecular-weight gamma-polyglutamic acid into the soil, heavy metals Cr and Cu in the soil absorbed by the cucumbers can be remarkably reduced, the content of proline is remarkably increased, the total oxidation resistance is improved, the content of malondialdehyde is remarkably reduced, and the growth of the cucumbers is promoted. According to the method disclosed by the invention, the polyglutamic acid is degraded by adopting a one-step method (gamma-PGA) to obtain the medium-molecular-weight polyglutamic acid (gamma-PGA), so that absorption and enrichment of cucumbers on heavy metals Cr and Cu in soil can be reduced, the growth and development of the cucumbers can be remarkably promoted, and the fresh weight of fruits can be increased.

Description

Technical Field

[0001] The invention belongs to the technical field of crop cultivation, and particularly relates to a method for preparing medium molecular weight polyglutamic acid (γ-PGA), and a method for reducing the accumulation of heavy metal chromium and copper in cucumbers and promoting the growth of cucumbers by using the same. Background Art

[0002] In recent years, the problem of heavy metal pollution has become increasingly serious worldwide. Excessive heavy metal content in the soil will not only change the physical and chemical properties of the soil, threaten biodiversity, and reduce food production, but will also accumulate in the human body through the food chain, posing a serious threat to human health.

[0003] There are many problems in the practical application of existing heavy metal remediation technologies. Physical methods have high investment costs and high energy consumption; chemical methods may increase secondary pollution and cause soil degradation; plant remediation has low costs and high benefits, but the absorption capacity of plants is limited and the growth cycle is relatively slow. Therefore, it is urgent to develop soil heavy metal remediation strategies that are less invasive, cost-effective, and green and pollution-free.

[0004] γ-Polyglutamic acid (γ-PGA) is a water-soluble high molecular amino acid polymer synthesized by microorganisms. γ-PGA can complex heavy metals in aqueous solution and form γ-PGA and heavy metal precipitation, which reduces the bioavailability of heavy metals and the content of heavy metals in crops. It also has good biocompatibility and biodegradability, and its degradation products are harmless to the environment and will not cause secondary pollution. However, the effect of γ-PGA on the chromium and copper content of plants in heavy metal contaminated soil has not been reported.

[0005] Conventional γ-PGA on the market has a large molecular weight (>600kDa) and strong adhesiveness and metal ion chelating properties, but studies have shown that high molecular weight γ-PGA can inhibit seed germination. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide the application of medium molecular weight (200-300kDa) γ-PGA in reducing the accumulation of heavy metals in crops and promoting crop growth, while achieving the purpose of reducing the chromium and copper content of crops and promoting crop growth.

[0007] In order to solve the above technical problems, the present invention discloses an application of medium molecular weight γ-polyglutamic acid in reducing heavy metal accumulation in crops and promoting crop growth, wherein the relative weight average molecular weight of the medium molecular weight γ-polyglutamic acid is in the range of 200 to 300 kDa.

[0008] Specifically, the medium molecular weight γ-polyglutamic acid is prepared by the following steps: using a γ-polyglutamic acid (γ-PGA, molecular weight) aqueous solution with a mass concentration of 2% to 3% and a weight average molecular weight of 700 to 750 kDa as a reaction substrate for degradation, adjusting the pH of the aqueous solution to 2 to 3, preferably, using hydrochloric acid or sulfuric acid to adjust the pH, reacting at 115 to 121° C. for 1 to 2 hours to obtain a degradation product, adding 3 to 4 times the volume of ethanol, preferably ethanol with a mass fraction of 95%, to the degradation product to generate a precipitate, collecting the precipitate, and freeze-drying the obtained powder using a vacuum freeze dryer, namely the medium molecular weight polyglutamic acid.

[0009] Wherein, the crops are food crops, vegetable crops or melon and fruit crops.

[0010] Furthermore, the crop is cucumber.

[0011] The heavy metal is any one or both of chromium and copper.

[0012] The promoting crop growth is to increase the fresh weight of seedlings.

[0013] Specifically, when applied, the medium molecular weight γ-polyglutamic acid powder is added to the soil for planting crops, and the added amount is 2.25-3.75g of the medium molecular weight γ-polyglutamic acid powder per kilogram of soil.

[0014] When in use, medium molecular weight γ-polyglutamic acid powder is dissolved in water to obtain a polyglutamic acid aqueous solution with a mass concentration of 4-5%, which is then added to the soil and stirred evenly to fully disperse the polyglutamic acid aqueous solution in the soil.

[0015] The present application further proposes a method for planting cucumbers, comprising dissolving medium molecular weight γ-polyglutamic acid in water and mixing the mixture with soil and stirring the mixture to obtain soil mixed with γ-PGA, and then sowing sterilized cucumber seeds in the soil mixed with γ-PGA, wherein the relative number average molecular weight of the medium molecular weight γ-polyglutamic acid is in the range of 200 to 300 kDa.

[0016] Specifically, the cucumber seeds were sterilized by surface sterilizing with 0.1% HgCl2 for 10-15 min and then rinsing with sterile distilled water several times.

[0017] Beneficial effects: The present invention prepares a medium molecular weight polyglutamic acid (γ-PGA, 200-300 kDa), and adds it to the soil, which can significantly reduce the absorption of heavy metals Cr and Cu in the soil by cucumbers, significantly increase the proline content, improve the total antioxidant capacity, and significantly reduce the content of malondialdehyde, thereby promoting the growth of cucumbers. The present invention uses a one-step method (γ-PGA) to degrade polyglutamic acid to obtain medium molecular weight polyglutamic acid (γ-PGA), which can reduce the absorption and enrichment of heavy metals Cr and Cu in the soil by cucumbers, while significantly promoting the growth and development of cucumbers and increasing the fresh weight of fruits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0019] Figure 1 The effects of γ-PGA on cucumber growth and heavy metal content under Cr and Cu stress in a greenhouse experiment are shown;

[0020] Figure 2 The effect of γ-PGA on cucumber growth and heavy metal content under Cr and Cu stress in a plot experiment is shown;

[0021] Figure 3 The effects of γ-PGA on proline, malondialdehyde content and total antioxidant capacity under Cr and Cu stress are shown;

[0022] Figure 4 The stability and characterization of γ-PGA metal chelates are shown. DETAILED DESCRIPTION

[0023] Example 1 Preparation of a medium molecular weight polyglutamic acid (γ-PGA).

[0024] With a concentration of 2% to 3% polyglutamic acid (γ-PGA, Na + The aqueous solution of (type, Mw 700kDa, provided by Nanjing Xuankai Biotechnology Co., Ltd.) was used as a reaction substrate for degradation, the pH of the aqueous solution was adjusted to 2-3, and the temperature was kept at 115-121°C for 1h to obtain a degradation product, and an ethanol reagent with a volume of 3 times was added to the degradation product to generate a precipitate, which was collected and freeze-dried using a vacuum freeze dryer to obtain a medium molecular weight polyglutamic acid (γ-PGA) with a relative average molecular weight range of 200-300kDa.

[0025] Molecular weight detection method and steps: Na2SO4 is used as the mobile phase, narrow distribution standard is used to obtain the instrument constant, and broad distribution standard is used to verify the instrument constant. The weight average molecular weight of the purified γ-PGA sample is determined by GPC by detecting the peak time of the γ-PGA sample under the differential refractive index detector.

[0026] (1) Preparation of broad standard, narrow standard and mobile phase: Use 0.3 mol / L Na2SO4 aqueous solution as mobile phase, adjust pH to 4.0, filter through 0.22 μm microporous membrane, and ultrasonically degas for 15 min. Take 24.16 mg of 24 kDa narrow distribution standard PEO and 23.92 mg of 67 kDa broad distribution standard, dissolve them in mobile phase and make up to 10 ml, respectively, to prepare broad standard and narrow standard solutions, and filter the prepared solutions through 0.22 μm microporous membrane.

[0027] (2) Chromatographic conditions: A Waters Ultrahydrogel Linear (7.8 mm × 300 mm) gel chromatography column was used for determination using a differential refractive index detector (RI) configured in the OMNISE system. The detection column temperature was 30°C, the flow rate was 0.5 ml / min, and the injection volume was 100 μL.

[0028] (3) Preparation and determination of sample solution 0.1 g of γ-PGA sample was accurately weighed, dissolved in mobile phase and fixed to 100 ml to prepare a 1 mg / mL γ-PGA sample solution. The prepared solution was filtered through a 0.22 μm microporous filter membrane. The γ-PGA sample solution was tested in the same manner as above, the peak time was recorded, and the weight average molecular weight of the γ-PGA sample was calculated.

[0029] The medium molecular weight γ-PGA used in the following examples is the medium molecular weight polyglutamic acid prepared in Example 1.

[0030] Example 2 Effects of γ-PGA on cucumber growth and heavy metal content under Cr and Cu stress under greenhouse conditions.

[0031] Cucumber seeds ("Jinyou No. 1" provided by Tianjin Academy of Agricultural Sciences) were surface sterilized with 0.1% HgCl2 for 15 min, then rinsed 3 times with sterile distilled water, and the surface sterilized seeds were sown in a flower pot containing 1 kg of soil. The soil was collected from a cucumber field in Pukou, Nanjing, China. The soil was air-dried, sieved through a 2 mm sieve, and mixed evenly. The soil in the area was yellow-brown soil (Argosol, Udiqi), with a pH of 6.81, an available potassium of 265.70 mg / kg, an available phosphorus of 41.49 mg / kg, a nitrate nitrogen of 9.18 mg / kg, a nitrate nitrogen of 6.73 mg / kg, a nitrate nitrogen of 1.02 mg / kg, an organic matter content of 12.83 g / kg, a chromium content of 79.12 mg / kg, and a copper content of 30.82 mg / kg. According to different treatments, Cr, Cu, glutamic acid (Glu), high molecular weight (commercially available Mw 700 kDa) and medium molecular weight γ-PGA (prepared in Example 1) were added to the initial soil. The amount of Cr and Cu added was based on the "Standard for Risk Control of Soil Environmental Quality of Agricultural Land Soil Contamination" (GB15618-2018).

[0032] Set up 7 processes:

[0033] control group, untreated soil;

[0034] Cr group, soil contained 750 mg / kg Cr (CrCl3·6H2O);

[0035] Cr+Glu group, soil contained 750 mg / kg Cr and 3.75 g / kg Glu;

[0036] Cr+PGA-1 group, soil contained 750 mg / kg Cr and 3.75 g / kg high molecular weight γ-PGA;

[0037] Cr+PGA-2 group, soil contained 750 mg / kg Cr and 3.75 g / kg medium molecular weight γ-PGA;

[0038] Cu group, soil contained 250 mg / kg Cu ​​(CuSO4);

[0039] Cu+Glu group, soil contained 250 mg / kg Cu ​​and 2.25 g / kg Glu;

[0040] Cu+PGA-1 group, soil contained 250 mg / kg Cu ​​and 2.25 g / kg high molecular weight γ-PGA;

[0041] Cu+PGA-2 group, soil contained 250 mg / kg Cu ​​and 2.25 g / kg medium molecular weight γ-PGA;

[0042] Each treatment had three replicate pots. All pots were randomly placed in a greenhouse at a temperature of 23-27°C and an air humidity of 65%-70%. All cucumber seedlings were harvested after 30 days of cultivation.

[0043] Accurately weigh 5g of cucumber seedling sample to be tested, dry it in an oven at 105℃ to constant weight; grind it into powder in a mortar; add 20ml HNO3 and 4ml HClO4 in sequence, and burn on an electric furnace until the solution is clear and white smoke is completely eliminated; place it in a crucible and burn it at 500℃ in a muffle furnace for 6h; transfer the cooled sample to a volumetric flask, make up to volume with deionized water, and mix it by inversion; use an inductively coupled plasma spectrometer (ICP-AES) to determine the concentrations of Cr and Cu in each treatment.

[0044] The effect of γ-PGA on the fresh weight of cucumber seedlings in high Cr and high Cu soils was studied in a greenhouse experiment. Figure 1 As shown in AB: Compared with the control, Cr and Cu treatments significantly reduced the fresh weight of cucumber stems and roots. Compared with Cr and Cu treatments, the addition of Glu and high molecular weight γ-PGA significantly increased the fresh weight of cucumber seedlings. Cr+PGA-2 and Cu+PGA-2 treatments significantly increased the fresh weight of cucumber seedlings by 15.23% to 41.82% (15.23% for stems; 41.82% for roots), 76.27% to 153.63% (153.63% for stems; 76.27% for roots); Cr+PGA-2 and Cu+PGA-2 treatments significantly increased the fresh weight of cucumber seedlings by 48.14% to 76.70% (48.14% for stems; 76.70% for roots), 258.84% to 298.27% (258.84% for stems; 298.27% for roots). It can be seen that under Cr and Cu stress, medium molecular weight γ-PGA has a better effect on promoting the growth of cucumber seedlings than glutamate monomer and high molecular weight γ-PGA.

[0045] Effects of γ-PGA on heavy metal content in cucumber seedlings grown in high Cr and high Cu soils. Figure 1CD shows: Compared with the control, Cr and Cu treatments significantly increased the Cr and Cu contents in the stems and roots of cucumber. Compared with the Cr and Cu treatments, Glu and high molecular weight γ-PGA significantly reduced the Cr and Cu contents in the stems and roots, indicating that glutamic acid monomers and high molecular weight γ-PGA also reduced the absorption rate of Cr and Cu in cucumber seedlings. Importantly, compared with the Cr and Cu treatments, Cr+PGA-2 and Cu+PGA-2 treatments significantly reduced the Cr content of cucumber seedlings by 67.45-86.77% (67.45% in the stems; 86.77% in the roots) and the Cu content by 94.67-98.21% (94.67% in the stems; 98.21% in the roots). The Cr and Cu contents in the stems and roots of cucumber seedlings treated with medium molecular weight γ-PGA were lower than those treated with glutamic acid monomers and high molecular weight γ-PGA.

[0046] From the above results, it can be seen that under Cr and Cu stress, medium molecular weight γ-PGA can better reduce the absorption of Cr and Cu by cucumber seedlings than glutamate monomer and high molecular weight γ-PGA.

[0047] Example 3: Fresh weight of cucumber plants and fruits and heavy metal content in fruits in a plot experiment.

[0048] The plot experiment has five treatments:

[0049] control group, untreated soil;

[0050] Cr group, soil contained 750 mg / kg Cr (CrCl3·6H2O);

[0051] Cu group, soil contained 250 mg / kg Cu ​​(CuSO4);

[0052] Cr+PGA group, soil contained 750 mg / kg Cr and 3.75 g / kg medium molecular weight γ-PGA;

[0053] In the Cu+PGA group, the soil contained 250 mg / kg Cu ​​and 2.25 g / kg medium molecular weight γ-PGA.

[0054] A pre-prepared cement pool (3m long, 3m wide, 1m deep) was selected for each plot. 6750kg of untreated soil was added to each area. The soil physical and chemical properties and treatment methods were the same as those in the greenhouse experiment. Each treatment was repeated 3 times, for a total of 15 plots. After the cucumber fruits matured, the cucumber plants and fruits were collected.

[0055] The heavy metal content in the fruit was determined in the same manner as in Example 1.

[0056] The effects of medium molecular weight γ-PGA on cucumber fruit growth and Cr and Cu contents were studied in a small plot experiment. Figure 3As shown in AB: Compared with the control, Cr or Cu treatment significantly reduced the fresh weight of cucumber plants and fruits; compared with Cr and Cu treatments, Cr+PGA and Cu+PGA treatments significantly increased the fresh weight by 13.47-13.50% (plant fresh weight 13.47%; fruit fresh weight 13.50%) and 23.50-25.30% (plant fresh weight 25.30%; fruit fresh weight 23.50%); compared with the control, Cr and Cu treatments significantly increased the Cr and Cu contents in cucumber fruits; in addition, compared with Cr and Cu treatments, Cr+PGA and Cu+PGA treatments significantly reduced the Cr and Cu contents in cucumber fruits, and the Cr and Cu contents in the fruits were almost undetectable.

[0057] Example 4 Effect of γ-PGA on proline (Pro) content, malondialdehyde (MDA) content and total antioxidant capacity (T-AOC) under Cr or Cu stress.

[0058] Under adverse conditions, the proline (Pro) content in plants increases significantly. Therefore, the increase in proline can be used as one of the physiological indicators of stress-resistant breeding; malondialdehyde (MDA) is the final decomposition product of membrane lipid peroxidation, and its content can reflect the degree of damage to plants caused by adverse conditions; oxidative stress is a state in which the free radicals produced in the body exceed the body's antioxidant clearance capacity, causing oxidative damage to cells and tissues. Therefore, the above values ​​reflect the ability of plants to resist stress. The present application further investigates the effects of medium molecular weight γ-PGA on proline (Pro) content, malondialdehyde (MDA) content and total antioxidant capacity (T-AOC) under Cr or Cu stress.

[0059] Cucumber and soil treatments were the same as in the greenhouse experiment. Cucumber seedlings were destructively collected 7 days after sowing. The method for determining proline content was based on the method of Bates et al. (1973). Plant samples were cut into pieces, 5 ml of 3% sulfosalicylic acid was added, and then 2 ml of supernatant was mixed with 2 ml of acetic acid and 3 ml of 2.5% ninhydrin. The mixture was water-bathed in boiling water for 40 min, and the reaction mixture was extracted with 4 mL of toluene. Proline content was determined by spectrophotometry at 520 nm, and proline content was calculated based on the proline standard curve. Malondialdehyde content was determined by the thiobarbituric acid method of Liu et al. (2012). Cucumber samples were ground, homogenized with 5% (w / v) trichloroacetic acid, and centrifuged at 8000 g for 15 min. The supernatant was mixed with 5 mL of 0.5% thiobarbituric acid (prepared with 20% trichloroacetic acid) and water-bathed in boiling water for 25 min. The concentration of supernatant was determined spectrophotometrically at 450, 532, and 600 nm, and the MDA content was calculated. T-AOC was determined using a kit (Nanjing Bioengineering Institute, China) and the spectrophotometer was measured at 520 nm.

[0060] We investigated the effect of molecular weight γ-PGA on oxidative stress in cucumber seedlings under Cr and Cu stress by measuring Pro content, MDA content and T-AOC. Figure 3 As shown in the figure: Compared with the control, Cr or Cu treatment significantly increased the Pro content, MDA content and T-AOC content of cucumber seedlings, indicating that cucumber seedlings will produce oxidative stress under Cr and Cu stress. Compared with Cr and Cu treatments, the proline content of Cr+PGA-2 and Cu+PGA-2 treatments increased significantly by 32.56% and 38.17%, respectively ( Figure 3 A-3B). Compared with the Cr and Cu treatments, the MDA content in the Cr+PGA and Cu+PGA treatments was significantly reduced by 38.95% and 32.64%, respectively ( Figure 3 C-3D). Compared with the Cr and Cu treatments, the Cr+PGA and Cu+PGA treatments significantly increased T-AOC by 58.32% and 80.95%, respectively ( Figure 3 E-3F). In addition, the effects of glutamic acid monomer and high molecular weight γ-PGA on Pro content, MDA content and T-AOC in cucumber seedlings were weaker than those of medium molecular weight γ-PGA.

[0061] Example 5 Stability determination and characterization of the molecular weight γ-PGA metal chelate.

[0062] Preparation of medium molecular weight γ-PGA metal chelate Two groups were set up: Cr group, added with 750 mg / kg Cr and 3.75 g / kg γ-PGA; Cu group, added with 250 mg / kg Cu ​​and 2.25 g / kg γ-PGA. The suspension was centrifuged at 4000 g for 30 min, and the precipitate was kept at -20 °C. The Cr content in the supernatant and precipitate was determined by ICP method. 3+ and Cu 2+ The residual amount of γ-PGA in the supernatant was determined by high performance liquid chromatography: a Shimadzu LC-20A column (Shimadzu, Kyoto, Japan) and two OHpakSB-806M HQ columns (8.0 mm × 300 mm, Shodex, Japan) were used; the solvent system consisted of Na2SO4 and acetic acid (pH 4.0); the UV-visible photodiode detector had a detection wavelength of 210 nm, and 1 g / L γ-PGA was used as the standard.

[0063] Soil extract was prepared by mixing 50 g of soil (the same soil as in the greenhouse experiment) with 1 L of sterile deionized water. After removing soil particles by filtration, the resulting supernatant containing soil microorganisms and nutrients was defined as soil extract. Then 10 g of γ-PGA-Cr or γ-PGA-Cu was added to 1 L of soil extract, and 5 mL of soil extract supernatant was collected every 14 days until the 20th week. The total volume of soil extract was maintained at 1 L during the entire experiment. The contents of Cr and Cu in the supernatant were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and 10 replicates were set for γ-PGA-Cr and γ-PGA-Cu treatments.

[0064] The surface structures of γ-PGA, γ-PGA-Cr and γ-PGA-Cu were observed using a scanning electron microscope (SEM, Apreo2, Thermo Fisher Scientific, USA). The freeze-dried powder samples were mixed with dry KBr, ground evenly, and pressed into transparent sheets. Fourier transform infrared spectroscopy (FITR, iS50, Thermo Fisher Scientific, USA) was used to detect the peak changes of functional groups between γ-PGA, γ-PGA-Cr and γ-PGA-Cu in the wave number range of 400 to 4000 cm -1 .

[0065] The relationship between γ-PGA and Cr 3+ and Cu 2+ The chelation effect of chelate was investigated and the stability of the chelate in soil extract was tested. Figure 4 AC shows: free Cr 3+ % of total Cr 3+ 60.70% of Cr 3+ 39.30%; free Cu 2+ Cu 2+ 57.34% of Cu 2+ 42.66%( Figure 4 A). On the other hand, 3.75 g / L γ-PGA at 750 mg / L Cr 3+ In the presence of 250 mg / L Cu 2+ There is still 67% of γ-PGA (initial concentration is 2.25g / L) free ( Figure 4 B). The degradation rates of γ-PGA-Cr and γ-PGA-Cu in soil extracts were fast in the first 5 weeks and then entered a stable period. After 28 weeks, the degradation rates of γ-PGA-Cr and γ-PGA-Cu were 20.89% and 26.13%, respectively. Figure 4 C). Therefore, it can be seen that γ-PGA-Cr and γ-PGA-Cu can remain relatively stable for a long time.

[0066] The structures of γ-PGA, γ-PGA-Cr and γ-PGA-Cu were characterized by SEM and FTIR. Figure 4 DE shows:γ-PGA in the presence of Cr 3+ and Cu 2+ After chelation, the surface morphology changed significantly. The surface structure of γ-PGA was porous. 3+ and Cu 2+ The adsorption of Cr 3+ and Cu 2+ Afterwards, the surface of γ-PGA becomes rougher and a large number of small particles ( Figure 4 D) With Cr 3+ After chelation, the peak of γ-PGA shifted from 3293.21 cm-1 to 3250.92 cm-1. -1 , moving from 1591.44cm-1 to 1616.84cm -1 , from 1402.43cm -1 Move to 1427.01cm -1 . With Cu 2+ After chelation, the peak of γ-PGA changed from 3293.21 cm -1 Move to 3309.22cm -1 , from 1591.44cm -1 Move to 1613.10cm -1 , from 1402.43cm -1 Move to 1413.26cm -1 γ-PGA at 3293.21cm -1 The NH absorption peak is at 1591.44 cm -1 The NH absorption peak of amide II is at 1402.43 cm -1 The COO- absorption peak is at ( Figure 4 E) The results showed that the carboxyl, amino and amide bonds of γ-PGA participated in the Cr 3+ and Cu 2+ Chelation.

[0067] The present invention provides a method for reducing the accumulation of heavy metal chromium and copper in cucumber and promoting the growth of cucumber by using medium molecular weight polyglutamic acid (γ-PGA). There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. Application of medium molecular weight γ-polyglutamic acid in reducing heavy metal accumulation in crops and promoting crop growth, including: The relative weight average molecular weight of the medium molecular weight γ-polyglutamic acid is in the range of 200-300 kDa.

2. The use according to claim 1, characterized in that: The medium molecular weight γ-polyglutamic acid is prepared by the following steps: using a γ-polyglutamic acid aqueous solution with a mass concentration of 2% to 3% and a weight average molecular weight of 700 to 750 kDa as a reaction substrate for degradation, adjusting the pH of the aqueous solution to 2 to 3, reacting at 115 to 121° C. for 1 to 2 h to obtain a degradation product, adding ethanol to the degradation product to generate a precipitate, collecting the precipitate, and freeze-drying the resulting powder, which is the medium molecular weight polyglutamic acid.

3. The use according to claim 1, characterized in that: The crops are food crops, vegetable crops or melon and fruit crops.

4. The use according to claim 3, characterized in that: The crop is cucumber.

5. The use according to claim 1, characterized in that: The heavy metal is any one or both of chromium and copper.

6. The use according to claim 1, characterized in that: The promoting crop growth is to increase the fresh weight of seedlings.

7. The use according to claim 1, characterized in that: When used, the medium molecular weight γ-polyglutamic acid powder is added to the soil used for growing crops, and the added amount is 2.25-3.75 g of the medium molecular weight γ-polyglutamic acid powder per kilogram of soil.

8. The use according to claim 5, characterized in that: When in use, medium molecular weight γ-polyglutamic acid powder is dissolved in water to obtain a polyglutamic acid aqueous solution with a mass concentration of 4-5%, which is added to the soil and stirred evenly to fully disperse the polyglutamic acid aqueous solution in the soil.

9. A method for growing cucumbers, characterized in that: The medium molecular weight γ-polyglutamic acid is dissolved in water and mixed with soil and stirred evenly to obtain soil mixed with γ-PGA, and then the sterilized cucumber seeds are sown in the soil mixed with γ-PGA, wherein the relative number average molecular weight of the medium molecular weight γ-polyglutamic acid is in the range of 200 to 300 kDa.

10. The method according to claim 6, characterized in that The method for disinfecting cucumber seeds is: surface disinfection with 0.1% HgCl2 for 10-15 minutes, and then rinse several times with sterile distilled water.

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