A method for enhancing plant resistance to heavy metal chromium using silicon layer-by-layer self-assembly

Abstract

The present invention discloses a method for enhancing plant resistance to heavy metal chromium by utilizing layer-by-layer self-assembly of silicon. Specifically, the method comprises the following steps: before transplanting the plant, the root system of the plant is alternately immersed in a cationic silicon polymerization inducer solution and a silicic acid solution, and one or more layers of silicon are formed on the surface of the plant root system by layer-by-layer self-assembly, and then the plant is transplanted into a chromium-containing environment. Using the method of the present invention, a silicon layer can be formed on the surface of the plant root system, so that the silicon content of the root system can be increased to a maximum of 1733 μg / g in a short period of time, and the chromium content in the aboveground part is reduced by 68%-75.2% compared with ordinary culture. In addition, the present invention is superior to directly adding silicon to the nutrient solution in terms of rice growth conditions, increasing the silicon content of the root system, and limiting the chromium content in the aboveground part.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural environmental protection, and more specifically, relates to a method for enhancing the ability of plants to resist heavy metal chromium stress by utilizing silicon layer-by-layer self-assembly. Background Art

[0002] As industrial activities progress, some farmlands are contaminated with heavy metals, which can damage plant growth and development and cause a significant reduction in grain production. In addition, heavy metals accumulate in plants and are enriched in the food chain, threatening animal and human health. Chromium (Cr) is an important mineral resource and a highly toxic teratogenic and mutagenic heavy metal pollutant in the environment. The simplest strategy to deal with heavy metal pollution in farmland is to prevent it from being absorbed by plants from the soil to prevent the metals from entering the aboveground parts. How to maintain safe agricultural production in contaminated soil is an urgent problem to be solved.

[0003] Silicon is a beneficial element for plants. Since silicon, after being deposited in the cell wall, can block metal ions from entering cells and inhibit the transport of metals from roots to the aboveground parts, its role in helping plants resist metal stress has been widely reported. However, silicon polymerizes slowly in the roots. In addition, due to a possible lack of transport proteins or certain specific components of the cell wall, the silicon content of most dicotyledons is significantly lower than that of monocotyledons. Therefore, even if silicon is applied exogenously, the increase in silicon content in the plants is limited, and the effect on resistance to adverse stress is not obvious. How to regulate the rate of silicon polymerization in plants and how to enable non-silicon-loving plants to use silicon to increase their ability to resist adverse stress have become bottlenecks in plant silicon nutrition. Summary of the Invention

[0004] The purpose of the present invention is to quickly increase the silicon content in plant roots, enhance their resistance to heavy metal stress, and provide a safe, economical and practical operation scheme.

[0005] To achieve the above objectives, the specific technical solutions adopted by the present invention are as follows:

[0006] A method for enhancing plant resistance to heavy metal chromium by utilizing layer-by-layer self-assembly of silicon. The method comprises the following steps: before transplanting the plants, the plant roots are alternately immersed in a cationic silicon polymerization inducer solution and a silicic acid solution, and one or more layers of silicon are formed on the surface of the plant roots by layer-by-layer self-assembly. The plants are then transplanted into a chromium-containing environment.

[0007] Preferably, the plant is a monocotyledonous plant or a dicotyledonous plant; the monocotyledonous plant is preferably rice; the dicotyledonous plant is preferably pakchoy.

[0008] Preferably, the cationic silicon polymerization inducer in the cationic silicon polymerization inducer solution is one or more of polyquaternium-10, cationic guar gum, gelatin, chitosan, poly-L-lysine, aqueous polyurethane, polyacrylamine hydrochloride, cationic polyacrylamide, polydimethyldiallylammonium chloride, and polyethyleneimine.

[0009] Preferably, the cationic silicon polymerization inducer in the cationic silicon polymerization inducer solution is cationic guar gum.

[0010] Preferably, the plant roots are alternately immersed in a cationic silicon polymerization inducer solution and a silicic acid solution for two rounds, forming two silicon layers on the surface of the plant roots.

[0011] Preferably, the root system of the plant is immersed in the cationic silicon polymerization inducer solution and the silicic acid solution for 10 minutes to 1 hour respectively.

[0012] Preferably, the roots of the plants are immersed in the cationic silicon polymerization inducer solution and the silicic acid solution for 20 minutes respectively.

[0013] Preferably, the concentration of the cationic silicon polymerization inducer solution is 0.5% by mass.

[0014] Preferably, the concentration of the silicic acid solution is 100 mM.

[0015] Preferably, the chromium-containing environment is chromium-containing soil or nutrient solution.

[0016] Compared with the prior art, the present invention has the following beneficial effects: in a heavily chromium-polluted environment (chromium concentration in the nutrient solution is 500 μM), under ordinary culture conditions, the chromium content in the aboveground part of rice increases significantly after 3 days of stress, growth is significantly inhibited, and a large number of rice die. However, when the roots are immersed in silicic acid for a short time, silicon polymerization on the root surface is slow, silicon deposition is less, and the ability to alleviate chromium stress is weak. Using the layer-by-layer self-assembly method of the present invention, a silicon layer can be formed on the surface of the plant root system, and the silicon content of the root system can be increased to a maximum of 1733 μg / g in a short period of time. Compared with ordinary culture, the chromium content in the aboveground part is reduced by 68%-75.2%. In addition, the present invention is superior to directly adding silicon to the nutrient solution in terms of rice growth conditions, increasing the silicon content of the root system, and limiting the chromium content of the aboveground part. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1Surface morphology of rice roots after different material pretreatments. Ck represents a 40-minute soak in water alone, P0si represents a 20-minute soak in water followed by a 20-minute soak in a silicic acid solution, and P1-P10 represent a 20-minute soak in ten polymer solutions followed by a 20-minute soak in silicic acid. At a 500 nm scale, the Ck root surface is smooth, the P0si treatment exhibits fine particles, and the P1-P10 treatments exhibit deposits of various morphologies.

[0018] Figure 2 Effects of ten materials on the silicon content and chromium content of rice under chromium stress. A represents the silicon content, the bar graph in B represents the chromium content, and the dotted line graph represents the chromium transport coefficient. P1-P10 represents soaking in ten polymer material solutions for 20 minutes and then soaking in silicic acid for 20 minutes, and then placing in 1 / 4 Hoagland nutrient solution containing 500μM chromium. P0si represents soaking in water for 20 minutes and then soaking in silicic acid solution for 20 minutes, and then placing in chromium-containing nutrient solution. Cr represents soaking in water for 40 minutes and then placing in chromium-containing nutrient solution. Ck represents soaking in water only for 40 minutes and then placing in nutrient solution without chromium stress. The data represent the mean and standard error of three replicates. Data with different letters are significantly different at p<0.05.

[0019] Figure 3 Effects of different treatments on silicon and chromium content in rice under chromium stress. Five soaking times (10 min, 20 min, 30 min, 40 min, and 1 h) and five numbers of self-assembly layers (1, 2, 3, 4, and 5) were set. A represents silicon content, the bar graph in B represents chromium content, and the dotted line graph represents the chromium transport coefficient. Data represent the mean and standard error of three replicates. Data with different letters are significantly different at p < 0.05.

[0020] Figure 4 Correlation analysis of root silicon content with root and aboveground chromium content in the method optimization experiment. A represents the relationship between root silicon and root chromium content, and B represents the relationship between root silicon and aboveground chromium content. 95% confidence intervals are also shown.

[0021] Figure 5 Effects of optimal materials and methods on silicon content and chromium content in pakchoi under chromium stress. A represents silicon content, the bar graph in B represents chromium content, and the dotted line graph represents the chromium transport coefficient. G represents the use of the method of the present invention under 500 μM chromium stress, Si represents the direct addition of silicon to the chromium nutrient solution, and Ck represents 500 μM chromium stress. The data represent the mean and standard error of three replicates, and data with different letters are significantly different when p < 0.05. This method significantly increases the silicon content in the roots, reduces the chromium content in the aboveground parts, and reduces the transport coefficient, and its effect is better than directly adding silicon to the nutrient solution. DETAILED DESCRIPTION

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0023] Therefore, the present invention provides a method for enhancing plant resistance to heavy metal chromium by utilizing layer-by-layer self-assembly of silicon. This method can quickly increase the silicon content in plant roots and improve their resistance to heavy metal chromium stress. The specific method is to alternately soak the plant roots in a cationic silicon polymerization inducer solution and a silicic acid solution before transplanting the plants, and form one or more layers of silicon on the surface of the plant roots through a layer-by-layer self-assembly method, and then transplant the plants into a chromium-containing environment.

[0024] The present invention can be applied to monocotyledons (such as rice) or dicotyledons (such as pakchoi). Taking rice as an example, since the surface of the cell wall of rice roots is negatively charged, in the above-mentioned layer-by-layer self-assembly method, a layer of silicon can be formed on the surface of the rice roots by alternating between soaking in a cationic silicon polymerization inducer solution and a silicic acid solution. The cationic silicon polymerization inducer solution is a solution prepared from cationic polymers. During this alternating soaking process, the rice roots are immersed in the cationic silicon polymerization inducer solution to form a cationic polymer layer on the root surface. The roots are then placed in a silicic acid solution. Since the positive charge of the cationic polymer promotes the polymerization of silicic acid, a layer of silicon can be formed on the root surface. If a second layer of silicon is required, the roots are again immersed in the cationic polymer solution and then transferred to the silicic acid solution, whereupon a second layer of silicon is formed on the surface of the first layer of silicon. Thus, by controlling the number of cycles in which the rice roots are alternately soaked in the cationic silicon polymerization inducer solution and the silicic acid solution, the number of silicon layers on the root surface can be adjusted. This method can rapidly increase silicon content in rice roots, reduce chromium content in aboveground parts, lower the chromium transport coefficient, and improve rice growth under chromium stress. Similarly, the layer-by-layer self-assembly method of the present invention can also be applied to dicotyledonous plants, such as pakchoy, to increase silicon content in pakchoy roots and significantly reduce chromium content in aboveground parts.

[0025] The cationic silicon polymerization inducer in the cationic silicon polymerization inducer solution of the present invention can be a cationic polymer material. The cationic polymer material can be a natural cationic polymer or a synthetic organic polymer. Suitable natural cationic polymers include: 1. Polyquaternium-10 (cationic cellulose), 2. Cationic guar gum, 3. Gelatin, 4. Chitosan, 5. Poly-L-lysine. Suitable synthetic organic polymers include: 6. Waterborne polyurethane, 7. Polyacrylamine hydrochloride, 8. Cationic polyacrylamide, 9. Polydimethyldiallylammonium chloride, and 10. Polyethyleneimine. Considering safety, price, and efficacy, cationic guar gum is recommended as a cationic polymer for inducing rapid silicon polymerization. It is non-toxic, widely available, and inexpensive. It effectively promotes silicon polymerization and significantly improves rice's resistance to chromium.

[0026] In addition, the anti-chromium stress effects of different immersion times and numbers of silicon self-assembly layers were screened. The recommended immersion time was 20 minutes, and two rounds of immersion were the best options. The silicon content in the rice roots increased rapidly, the chromium content in the aboveground parts was significantly reduced, and the growth condition was good.

[0027] In addition, since plants absorb silicon in the form of monosilicic acid, it is recommended to use 100mM silicic acid, which can be prepared by acidification of sodium silicate or by using a hydrogen-type cation exchange resin. It is recommended that the cationic polymer be dissolved in deionized water before use to prepare a 0.5% solution by weight.

[0028] The plants processed by the layer-by-layer self-assembly of the present invention can be transplanted into a chromium-containing environment such as chromium-containing soil or nutrient solution to alleviate chromium stress.

[0029] The specific implementation and technical effects of the present invention are described in detail below through several embodiments.

[0030] Example 1

[0031] In this embodiment, the method of enhancing plant resistance to heavy metal chromium by using silicon layer-by-layer self-assembly includes the following steps:

[0032] (1) Preparation of cationic silicon polymerization inducer solution and silicic acid solution

[0033] In this example, ten cationic polymer materials were selected as cationic silicon polymerization inducers: 1. Polyquaternium-10 (cationic cellulose), 2. Cationic guar gum, 3. Gelatin, 4. Chitosan, 5. Poly-L-lysine, 6. Water-based polyurethane, 7. Polyacrylamine hydrochloride, 8. Cationic polyacrylamide, 9. Polydimethyldiallylammonium chloride, and 10. Polyethyleneimine. These ten cationic polymer materials were dissolved in deionized water to prepare 0.5% by weight solutions for later use.

[0034] Separately, prepare 100 mM silicic acid solution for later use.

[0035] (2) Experiments in different treatment groups

[0036] Rice seedlings (variety Nipponbare) with consistent growth conditions 21 days after germination were selected for the experiment. The specific method is: soak the roots in a cationic silicon polymerization inducer solution for 20 minutes to form a polymer layer on the surface, and shake it continuously during the period. Then soak the roots in a 100mM silicic acid solution for 20 minutes. Since the positive charge of cationic polymers can promote the polymerization of silicic acid, a silicon layer can be formed. Ten cationic silicon polymerization inducer solutions are each set up as a treatment group, recorded as P1-P10. The rice seedlings with different treatments were placed in a 1 / 4 Hoagland nutrient solution containing 500μM Cr(Ⅲ) (prepared by chromium chloride) and cultured for 3 days.

[0037] In addition, four control treatments were set up: CK, P0si, Si, and Cr. In the CK group, rice seedlings were immersed in pure water for 40 minutes, then placed in a chromium-free 1 / 4 Hoagland nutrient solution for 3 days. In the P0si group, rice seedlings were immersed in pure water for 20 minutes, then in a silicic acid solution for 20 minutes, then placed in a 1 / 4 Hoagland nutrient solution containing 500 μM Cr(III) (prepared with chromium chloride) for 3 days. In the Si group, rice seedlings were immersed in a 1 / 4 Hoagland nutrient solution supplemented with 1 mM silicic acid for 40 minutes, then placed in a 1 / 4 Hoagland nutrient solution containing 500 μM Cr(III) (prepared with chromium chloride) for 3 days. In the Cr group, rice seedlings were immersed in pure water for 40 minutes, then placed in a 1 / 4 Hoagland nutrient solution containing 500 μM Cr(III) (prepared with chromium chloride).

[0038] In this example, the pH of the nutrient solution in different treatment groups was adjusted to 5.6 to maintain consistency among treatments.

[0039] For the 12 treatment groups P1-P10, CK, and P0si, the silicon deposition on the surface of rice roots after the rice seedlings were immersed but not yet transferred to the nutrient solution was as follows: Figure 1 As shown in the figure, the root surface of the Ck group is smooth, the P0si group has fine particles, and the P1-P10 treatment groups have deposits of various forms.

[0040] The silicon and chromium contents of the shoots and roots were measured after 3 days of cultivation. Figure 2 As can be seen from the figure, the P2 (cationic guar gum) treatment group had the best effect. The silicon content in the roots was 2.49 times that of the silicic acid soaking treatment group, the chromium content in the aboveground part was reduced by 75.2% compared with the Cr treatment group, and the chromium transport coefficient was reduced to 0.06.

[0041] Example 2

[0042] In this example, experiments were conducted by adjusting various parameters to determine the optimal immersion time and number of layers for enhancing plant resistance to heavy metal chromium through layer-by-layer self-assembly of silicon. The thickness of the silicon layer on the root cell wall can be controlled by adjusting the immersion time and the number of alternating adsorption cycles of cationic polymers and silicic acid.

[0043] A 0.5% cationic silicon polymerization inducer solution was prepared with cationic guar gum. Rice seedlings (21 days after germination, Nipponbare variety) were alternately immersed in the cationic silicon polymerization inducer solution and a 100 mM silicic acid solution. To compare the effects of different immersion times on the final results, this example set five immersion times of 10 min, 20 min, 30 min, 40 min, and 1 h, respectively designated as T10, T20, T30, T40, and T60. The immersion time here refers to the time spent in each of the two solutions. For example, a 10-min immersion time refers to 10 min in the cationic silicon polymerization inducer solution followed by a 10-min immersion in the 100 mM silicic acid solution. Furthermore, to compare the effect of the number of silicon layers on the final results during the layer-by-layer self-assembly process, this example maintained a constant immersion time of 20 minutes and alternately immersed the seedlings in a cationic silicon polymerization inducer solution and a 100mM silicic acid solution for 1, 2, 3, 4, and 5 cycles, designated as Group 1, Group 2, Group 3, Group 4, and Group 5, respectively. The rice seedlings with these different treatments were then placed in a 1 / 4 Hoagland nutrient solution containing 500μM Cr(III) (prepared with chromium chloride) and cultured for 3 days. The silicon and chromium contents of the shoots and roots were then measured. This example also employed the same CK and Cr groups as in Example 1.

[0044] The results of this example are as follows Figure 3 Finally, it was determined that 20 minutes of soaking and two alternating times were the optimal parameters for the layer-by-layer self-assembly process of the present invention. In addition, a linear fitting analysis was performed on the silicon content in the roots and the chromium content in the aboveground parts in the experiment of this embodiment. Figure 4 The results show that there is a significant negative correlation between the silicon content in the roots and the chromium content in the aboveground parts in the experiment of this example.

[0045] Example 3

[0046] In this example, the method of enhancing plant resistance to heavy metal chromium using layer-by-layer self-assembly of silicon was applied to a dicotyledonous plant (Brachia chinensis). The optimal materials, soaking time, and number of layers (cationic guar gum, 20 minutes, 2 rounds) determined in the above-mentioned example were used to treat the roots of Brassica chinensis. During the treatment process, a cationic silicon polymerization inducer solution with a mass fraction of 0.5% was prepared with cationic guar gum. The roots of Brassica chinensis were alternately soaked twice in the cationic silicon polymerization inducer solution and a 100mM silicic acid solution, with the soaking time in each solution being 20 minutes. The roots of Brassica chinensis were then placed in a 1 / 4 Hoagland nutrient solution containing 500μM Cr(III) (prepared with chromium chloride) and cultured for 3 days.

[0047] This example also included a deionized water soaking group (CK) for the same duration, and a nutrient solution treatment group (Si) supplemented with 1 mM silicic acid. In the CK group, the pakchoi roots were soaked in pure water for 40 minutes, then placed in a 1 / 4 Hoagland nutrient solution containing 500 μM Cr(III) (prepared from chromium chloride) and cultured for 3 days. In the Si group, the pakchoi roots were soaked in a 1 / 4 Hoagland nutrient solution supplemented with 1 mM silicic acid for 40 minutes, then placed in a 1 / 4 Hoagland nutrient solution containing 500 μM Cr(III) (prepared from chromium chloride) and cultured for 3 days.

[0048] The results of silicon and chromium contents in the shoots and roots of the three treatment groups after 3 days of cultivation are as follows: Figure 5 Results showed that the method significantly increased silicon content in cabbage roots, exceeding that of the silicon-added nutrient solution, reaching 1502 μg / g and approaching the silicon content achieved with rice. However, the increase in silicon content in the aboveground part was less pronounced than in the silicon-added nutrient solution. Furthermore, the method significantly reduced chromium content in the aboveground part, from 75.8 μg / g to 19.0 μg / g, and the transfer coefficient decreased from 0.027 to 0.009.

[0049] Through the above description, relevant staff can make various changes and modifications without departing from the technical idea of ​​this invention. The technical scope of this invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims. The embodiment described above is only a preferred solution of the present invention, but it is not intended to limit the present invention. Ordinary technicians in the relevant technical field can also make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly, characterized in that: Before transplanting the plants, the plant roots are alternately immersed in a cationic silicon polymerization inducer solution and a silicic acid solution, so that one or more layers of silicon are formed on the surface of the plant roots through a layer-by-layer self-assembly method, and then the plants are transplanted into a chromium-containing environment; The plant is rice or pakchoy; The cationic silicon polymerization inducer in the cationic silicon polymerization inducer solution is one or more of polyquaternium-10, cationic guar gum, gelatin, chitosan, poly-L-lysine, aqueous polyurethane, cationic polyacrylamide, and polydimethyldiallylammonium chloride; The root system of the plant is immersed in the cationic silicon polymerization inducer solution and the silicic acid solution for 10 minutes to 1 hour respectively.

2. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The cationic silicon polymerization inducer in the cationic silicon polymerization inducer solution is cationic guar gum.

3. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The root system of the plant is alternately immersed in a cationic silicon polymerization inducer solution and a silicic acid solution for two rounds, so that two silicon layers are formed on the surface of the plant root system.

4. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The root system of the plant is immersed in the cationic silicon polymerization inducer solution and the silicic acid solution for 20 minutes respectively.

5. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The concentration of the cationic silicon polymerization inducer solution is 0.5% by mass.

6. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The concentration of the silicic acid solution is 100 mM.

7. The method for enhancing plant resistance to heavy metal chromium by utilizing silicon layer-by-layer self-assembly as claimed in claim 1, characterized in that: The chromium-containing environment is chromium-containing soil or nutrient solution.

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