Magnesium-doped carbon dots, application thereof and method for promoting germination of tobacco seeds

Abstract

The invention provides a magnesium-doped carbon dot and application thereof and a method for promoting tobacco seed germination, and the preparation method of the magnesium-doped carbon dot comprises the following steps: 1) mixing tobacco powder and reduced glutathione according to a mass ratio of 1: (1.5-4), dissolving in formamide, and carrying out ultrasonic dispersion to obtain a reaction solution A; dissolving magnesium hydroxide with the mass being 1.2-1.4 times that of the tobacco powder in formamide, performing ultrasonic dispersion to obtain a reaction solution B, uniformly mixing the reaction solution B with the reaction solution A, and putting the mixture into a high-pressure reaction kettle for reaction; and 2) after the reaction is finished, cooling, carrying out suction filtration, transferring the obtained filtrate into a dialysis bag, and freeze-drying the dialyzed solution to obtain the magnesium-doped carbon dots. The invention belongs to the technical field of biological agriculture, and provides a magnesium-doped carbon dot which can effectively promote germination of tobacco seeds and is favorable for improving the cultivation level of strong seedlings.

Description

Technical Field

[0001] The invention belongs to the technical field of biological agriculture, and in particular relates to a magnesium-doped carbon dot and an application thereof and a method for promoting tobacco seed germination. Background Art

[0002] Tobacco is an important economic crop in my country, ranking first in the world in terms of planting area and output. Tobacco is a thermophilic crop that requires high light and water, but is afraid of waterlogging. Seeds are important agricultural production materials. The quality of seeds is mainly reflected by seed vitality, which is usually comprehensively evaluated based on indicators such as seed germination rate and germination index. Seed germination is the beginning of the plant growth cycle and a critical period in the life history of plants. At this stage, it is easily affected by moisture, temperature and light in the environment. Guizhou Province is located in a low-temperature and low-light area. There are many karst mountains in the province, which are prone to drought. The long-term low temperature, low light and dry climate in the early stage of seedling cultivation have become important constraints on tobacco seed germination and the cultivation of strong seedlings, resulting in low seed germination rate, weak tobacco seedlings, and difficulty in timely seedling formation.

[0003] Carbon dots (CDs) are a new type of nanocarbon material composed of dispersed spherical carbon particles. They are extremely small (below 10 nm), have fluorescent properties, and have the advantages of simple preparation, low toxicity, biocompatibility, and easy functionalization. Carbon dot nanomaterials have shown great application potential in fields such as agriculture and materials. Chinese patent application CN113115605 A discloses a method for promoting spinach seed germination using carbon dots. The carbon dots are prepared into a carbon dot aqueous solution with a concentration of 1-50 mg / L and then applied to spinach seeds for light-proof cultivation. The expression of aquaporin genes can be increased, which promotes spinach seed germination and improves the germination rate. Chinese patent application CN 113201330A discloses a magnesium-nitrogen-doped carbon dot and a preparation method thereof and use thereof in improving plant photosynthesis. The preparation steps of the magnesium-nitrogen-doped carbon dot include: dissolving citric acid, ethanolamine and magnesium hydroxide in ultrapure water, pouring the obtained mixed solution into a reactor after ultrasonic treatment and reacting at 200°C for 6 hours; cooling to room temperature after the reaction, filtering the product using a filter head with a pore size of 0.22μm, and then dialyzing it for 12 hours using a dialysis bag with a molecular weight cutoff of MW 100-500, and freeze-drying to obtain magnesium-nitrogen-doped carbon dots; discloses that rice seeds are cultured in the dark during the germination stage, and rice seedlings are treated with magnesium-nitrogen-doped carbon dots of different concentrations by foliar spraying, which can accelerate the metabolic rate of chlorophyll, improve activity and light absorption capacity, etc.

[0004] Tobacco seed germination has high requirements for light and temperature. Appropriate light conditions help promote tobacco seed germination, while too strong or too weak light may have a negative impact on seed germination. Tobacco seed germination is carried out at a certain temperature, with the optimum temperature being around 25-28°C and the lowest temperature being 7.5-10.0°C. The germination conditions of tobacco seeds are quite different from those of spinach seeds and rice seeds. In order to improve the seed germination and seedling cultivation level of tobacco, it is of great significance to provide a new type of magnesium-doped carbon dots and their application and a method for promoting tobacco seed germination. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention starts from three angles: weak light stress, PEG simulated drought stress and low temperature stress, studies the effects of carbon dot nanomaterials on naked MS Yunyan 87 seeds under different environmental stresses, and then provides a magnesium-doped carbon dot and its application and a method for promoting tobacco seed germination, which can effectively promote the germination of tobacco seeds and is beneficial to improving the level of strong seedling cultivation.

[0006] The purpose of the present invention will be further illustrated by the following detailed description.

[0007] In one aspect, the present invention provides a magnesium-doped carbon dot, the preparation method of which comprises the following steps:

[0008] 1) mixing tobacco powder and reduced glutathione at a mass ratio of 1:(1.5-4), dissolving the mixture in formamide, and dispersing the mixture by ultrasonic wave to obtain a reaction solution A; dissolving magnesium hydroxide in formamide at a mass of 1.2-1.4 times of the tobacco powder, and dispersing the mixture by ultrasonic wave to obtain a reaction solution B, mixing the mixture with the reaction solution A, and placing the mixture in a high-pressure reactor for reaction;

[0009] 2) After the reaction is completed, the mixture is cooled and filtered, and the obtained filtrate is transferred to a dialysis bag. The dialyzed solution is freeze-dried to obtain magnesium-doped carbon dots.

[0010] The magnesium-doped carbon dots (Mg@CDs) provided by the present invention are doped with magnesium and nitrogen atoms simultaneously in the carbon dots. Such dual doping can further regulate the electronic structure and chemical reaction activity of the carbon dots; the introduction of magnesium atoms may cause significant changes in the chemical properties on the surface or inside of the carbon dots, such as improving the photocatalytic activity. According to fluorescence spectrum detection, the optimal excitation wavelength of the magnesium-doped carbon dots provided by the present invention is 420nm, and the optimal emission wavelength is 650nm. Red light emission can be observed under the excitation of a handheld ultraviolet lamp, which is significantly different from the blue light emission of the magnesium-nitrogen-doped carbon dots disclosed in Chinese patent application CN 113201330 A.

[0011] Since magnesium hydroxide is difficult to dissolve, the present application first dissolves magnesium hydroxide alone in formamide and ultrasonically disperses it to obtain a reaction solution B, which is then reacted with a reaction solution A obtained by dissolving and dispersing tobacco powder and reduced glutathione, so that the materials are more fully dispersed and the quality of the magnesium-doped carbon dots obtained by the reaction is better.

[0012] Preferably, the reaction conditions include: pressure 0.2-3Mpa, temperature 160-190°C, time 7-9h. More preferably, the reaction conditions include: pressure 0.5-1.5Mpa, temperature 170-185°C, time 7.5-8.5h.

[0013] Preferably, the molecular weight cutoff of the dialysis bag is 3300-3700 Dalton. More preferably, the molecular weight cutoff of the dialysis bag is 3400-3600 Dalton.

[0014] Preferably, the dialysis time is 7-10 days. More preferably, the dialysis time is 7.5-9 days.

[0015] Preferably, the tobacco powder is obtained by removing stems, cutting, crushing and then sieving tobacco leaf samples.

[0016] In another aspect, the present invention provides the use of the magnesium-doped carbon dots in tobacco planting.

[0017] Preferably, the tobacco or tobacco seeds are in an abiotic stress environment, and the abiotic stress environment includes at least one of weak light, drought, and low temperature.

[0018] In addition, the present invention also provides a method for promoting tobacco seed germination, comprising the following steps: preparing the magnesium-doped carbon dots into an aqueous solution and applying it to tobacco seeds, wherein the concentration of the magnesium-doped carbon dots aqueous solution is 30-70 μg / mL. Appropriate light is required during the germination process, for example: 12 hours of light and 12 hours of darkness per day.

[0019] Preferably, the tobacco seeds are MS Yunyan 87 naked seeds.

[0020] Preferably, the concentration of the magnesium-doped carbon dots aqueous solution is 60 μg / mL.

[0021] Compared with the prior art, the beneficial effects of the present invention include:

[0022] (1) The present invention provides a novel magnesium-doped carbon dots (Mg@CDs). According to fluorescence spectrum detection, the optimal excitation wavelength of the magnesium-doped carbon dots provided by the present invention is 420 nm, and the optimal emission wavelength is 650 nm, which can increase the wavelength absorption range of tobacco seeds or tobacco plants for photosynthesis. Red light can be observed under the excitation of a handheld ultraviolet lamp, which is significantly different from the magnesium-nitrogen-doped carbon dots emitting blue light disclosed in Chinese patent application CN 113201330A.

[0023] (2) The present invention provides a novel application of magnesium-doped carbon dots in tobacco planting. Experiments have confirmed that the magnesium-doped carbon dots provided by the present invention can effectively alleviate the effects of abiotic stress environments such as weak light and drought, and promote tobacco seed germination. The effect is better than that of carbon dots not doped with magnesium, which is beneficial to improving the level of seedling cultivation. In relatively extreme environments, such as 10°C low temperature, 25% PEG simulated drought, and 1000 lux weak light, the magnesium-doped carbon dots provided by the present invention can also promote tobacco seed germination, with a faster germination speed and a higher germination index.

[0024] (3) The present invention also provides a method for promoting tobacco seed germination, wherein the concentration of the magnesium-doped carbon dot aqueous solution is low, which is beneficial for reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The X-ray photoelectron spectrum of the magnesium-doped carbon dots provided by the present invention; wherein 1-a is an analysis diagram of the magnesium-doped carbon dots as a whole, and 1-b is an analysis diagram of the elemental composition of C, N, etc.

[0026] Figure 2 A graph showing the fluorescence spectrum detection results of magnesium-doped carbon dots provided by the present invention.

[0027] Figure 3 An observation diagram of magnesium-doped carbon dots provided by the present invention under the excitation of a handheld ultraviolet lamp.

[0028] Figure 4 Germination index results of treatments with different concentrations of Mg@CDs.

[0029] Figure 5 Germination index results of treatments with different concentrations of CDs.

[0030] Figure 6 Effects of different light intensity treatments on naked seed germination rate of MS Yunyan 87.

[0031] Figure 7 Observation of germination under Mg@CDs treatment with different light intensities.

[0032] Figure 8 Effects of different drought stress treatments on naked seed germination rate of MS Yunyan 87.

[0033] Fig. 9 The effects of different temperature treatments on the naked seed germination rate of MS Yunyan 87.

[0034] Fig.10 Comparison of carbon dots accumulated in leaf tissues of tobacco plants after spraying.

[0035] Fig.11 Observation picture of MS Yunyan 87 tobacco plant 5 weeks after spraying. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0037] In the present invention, the experimental materials involved are conventional commercial products or can be obtained by conventional technical means in the art, and the detection methods used are carried out according to the general methods in the art or the instructions of the kit. % content, if not clearly stated, is understood according to the common practice in the art.

[0038] MS Yunyan 87 naked variety: MS Yunyan 87 was bred by the Yunnan Tobacco Science Research Institute and the China Tobacco Breeding Research (South) Center using Yunyan No. 2 as the female parent and K326 as the male parent. It was approved by the National Variety Approval Committee in December 2000.

[0039] The germination rate refers to the percentage of germinated seeds to the total number of seeds tested at the end of the specified germination test. The germination rate can approximately reflect the seedling rate, that is, the ratio of the number of seeds that have germinated to the total number of seeds tested. The germination index is an indicator of seed vitality. During the germination test, the number of germinated seeds is recorded every day and the germination index is calculated. The higher the germination index, the higher the seed vitality. The germination index reflects the germination rate. The higher the germination index, the stronger the seed vitality and the faster the seedlings emerge under natural conditions.

[0040] The germination test was conducted in accordance with the "Tobacco Industry Standard of the People's Republic of China YC / T 20-1994 - Tobacco Seed Inspection Procedure". The germination of tobacco seeds was observed and recorded at 4 pm every day. The specific records of different abiotic stress environmental factors are as follows:

[0041] The germination rate of tobacco seeds was counted on the 14th day of the weak light stress experiment; the germination rate of tobacco seeds was counted on the 20th day of the drought stress experiment; and the germination rate of tobacco seeds was counted on the 24th day of the low temperature stress experiment.

[0042] Germination rate = total number of seeds that can form radicles or plumules / number of seeds tested × 100%.

[0043] Germination index = GI = ΣGt / Dt (Dt is the number of days from the start of culture, Gt is the normal number of germinations on the corresponding day).

[0044] Data processing: Excel was used for preliminary data sorting and analysis, and DPS7.05 was used for variance analysis and multiple comparisons. When conducting hypothesis testing, a significance level of a=0.05 and a very significant level of a=0.01 were selected; Origin Pro 2018 was used to draw charts.

[0045] Example 1 Preparation of magnesium-doped carbon dots

[0046] The preparation method of magnesium-doped carbon dots (Mg@CDs) comprises the following steps:

[0047] 1) 0.4 g of tobacco powder and 1.2 g of reduced glutathione were mixed, dissolved in 35 mL of formamide, and ultrasonically dispersed for 30 min to obtain reaction solution A; 0.52 g of magnesium hydroxide was dissolved in 25 mL of formamide, and ultrasonically dispersed for 30 min to obtain reaction solution B, which was mixed with the reaction solution A and placed in a high-pressure reactor for reaction. The reaction conditions included: pressure 0.6-1 MPa, temperature 180°C, and time 8 h;

[0048] 2) After the reaction is completed, the mixture is cooled and filtered, and the obtained filtrate is transferred to a dialysis bag with a molecular weight cutoff of 3500 Dalton. The solution after 8 days of dialysis is treated by a vacuum freeze dryer to obtain magnesium-doped carbon dots.

[0049] Example 2 Characterization of Mg-doped C-dots

[0050] The magnesium-doped carbon dots prepared in Example 1 were subjected to X-ray photoelectron spectroscopy (XPS) analysis. The overall analysis of the magnesium-doped carbon dots is shown in FIG. Figure 1 -a, the analysis diagram of the elements such as C and N is as follows Figure 1 -b. Figure 1 It can be seen that the Mg element is successfully doped into the carbon dot nanomaterials.

[0051] The magnesium-doped carbon dots prepared in Example 1 were tested by fluorescence spectroscopy. Figure 2 As shown in Figure 2, the optimal excitation wavelength of magnesium-doped carbon dots is 420 nm, and the optimal emission wavelength is 650 nm. In addition, red light emission can be observed under handheld UV lamp excitation, such as Figure 3 shown.

[0052] Example 3 Investigation of the effect of magnesium-doped carbon dots on the germination of naked seeds of MS Yunyan 87

[0053] The preparation method of undoped magnesium carbon dots (CDs) for comparison comprises the following steps: 1) mixing 0.05 g of tobacco powder with 0.30 g of reduced glutathione, adding 10 mL of formamide, and ultrasonically dispersing for 20 min, and reacting in a muffle furnace at a temperature of 180° C. and a reaction time of 8 h; 2) after the reaction, cooling and centrifuging at a speed of 3500 r / min, filtering the supernatant through an organic filter membrane with a pore size of 0.22 μm, and transferring the obtained filtrate to a dialysis bag with a molecular weight cutoff of 3500 Dalton, and dialyzing for 7 days until no fluorescent substance can be detected in the solution outside the dialysis bag, filtering the dialyzed carbon dot solution through an aqueous filter membrane with a pore size of 0.22 μm, and freeze-drying the filtrate to obtain undoped magnesium carbon dots.

[0054] 1 Experimental design

[0055] An experimental group and a control group were designed. Each group selected the same conditions but different treatment combinations (magnesium-doped carbon dot concentration, different light intensity, different temperature, and different simulated drought degrees). The experiment was repeated 4 times, and one culture dish was used for each repetition. 100 seeds were sown in each culture dish.

[0056] 2 Investigation of the concentration of Mg-doped carbon dots

[0057] Tobacco seeds with uniform color and size were selected and evenly placed in a culture dish lined with cotton wool and filter paper. The culture dishes were divided into 4 groups and placed in a light incubator for culture, with a total of 3 experimental groups and a control group CK. The concentrations of A1 to A3 were set as 30.0 μg / mL, 60.0 μg / mL, and 90.0 μg / mL, respectively; each experimental group was treated with B1 to B3, and Mg@CDs, CDs, and MgSO were added to the B1 to B3 treatments, respectively. 4 The tobacco seeds in the culture dish were treated, and each treatment was repeated 4 times. The treatment settings of different concentrations of magnesium-doped carbon dots are shown in Table 1.

[0058] Table 1 Treatment settings of different concentrations of Mg-doped carbon dots

[0059]

[0060] Each group in the experiment was subjected to 12 hours of light and 12 hours of darkness every day. The light time periods were: first period: 8:00-20:00, temperature 25°C; second period (darkness): 20:00-8:00 the next day, temperature 25°C; relative humidity was maintained at 65%. The filter paper was always kept moist during the culture process, and seed germination was based on the radicle breaking through half the length of the seed. Starting from the second day after sowing, the number of seeds germinated and the growth of seedlings after germination in the experimental group and the control group were recorded at the same time every day. Continue to observe for a period of time and record relevant conditions until the seeds reach the maximum germination rate and the experiment is ended. The germination index results of treatments with different concentrations of Mg@CDs and CDs are shown below. Figure 4 , Figure 5 Lowercase letters in the figure indicate significant differences between different treatments at the P<0.05 level, and uppercase letters indicate significant differences between different treatments at the P<0.01 level.

[0061] from Figure 4 It can be seen that under the Mg@CDs treatment, there is no significant difference between 30.0μg / mL, 60.0μg / mL and 90.0μg / mL, and the difference between 0.0μg / mL and other treatments reaches an extremely significant level. Low concentrations of Mg@CDs can promote tobacco seed germination. As the concentration increases, the promotion effect weakens, but too high a concentration has a certain inhibitory effect on seed germination. At a concentration of 60.0μg / mL, the germination index of MS Yunyan 87 is the largest, reaching 34.59±1.47. Therefore, a concentration of 60.0μg / mL Mg@CDs was selected for subsequent experiments. Figure 5 It can be seen that although low concentrations of CDs can promote tobacco seed germination, there is no significant difference between 30.0μg / mL, 60.0μg / mL and 90.0μg / mL CDs and 0.0μg / mL.

[0062] 3. Lighting Experiment Investigation

[0063] Select tobacco seeds with the same color and size and place them evenly in a culture dish lined with cotton wool and filter paper. The culture dishes are divided into 4 groups (C1-C4) and placed in a light incubator for culture. The light intensity of C1-C4 is set to 1000Lux, 4000Lux, 7000Lux and 10000Lux; each experimental group is treated with 4 treatments from D1 to D4. Ultrapure water (control), 60.0μg / mL MgSO 4 , 60.0 μg / mL Mg@CDs and 60.0 μg / mL CDs were used to treat tobacco seeds in petri dishes, and each treatment was repeated 4 times. The treatment settings of different light experiments are shown in Table 2.

[0064] Table 2 Treatment settings for different lighting experiments

[0065]

[0066]

[0067] Each group in the experiment was subjected to 12 hours of light and 12 hours of darkness every day. The light time periods were: first period: 8:00-20:00, temperature 25°C; second period (darkness): 20:00-8:00 the next day, temperature 25°C; relative humidity was maintained at 65%. The filter paper was always kept moist during the culture process, and seed germination was determined when the radicle broke through half the length of the seed. Starting from the second day after sowing, the number of seeds germinated and the growth of seedlings after germination of the experimental group and the control were recorded at the same time every day. Continue to observe for a period of time and record relevant conditions until the seeds reach the maximum germination rate and the experiment is ended. The effects of different light intensity treatments on the naked seed germination rate and germination index of MS Yunyan 87 are shown as follows: Figure 6 , as shown in Table 3. The observation diagram of germination under different light intensities of Mg@CDs is shown in Figure 7 As shown, 1, 2, 3, and 4 in the figure represent 4 repeated serial numbers.

[0068] Table 3 Effects of different light intensity treatments on the germination index of naked seed MS Yunyan 87

[0069]

[0070]

[0071] Duncan test: The data in the table are mean ± standard error; different lowercase letters indicate significant differences (P<0.05), and different uppercase letters indicate extremely significant differences (P<0.01).

[0072] Depend on Figure 6 It can be seen that the seeds began to germinate on the second day, reached the maximum germination rate on the fourth day, and gradually tended to a stable level. On the second day after sowing, as the light intensity increased, the number of seeds that germinated gradually increased. In addition, the effect of Mg@CDs was better than that of CDs and MgSO 4 and ultrapure water, CDs is better than MgSO 4 As shown in Table 3, under the conditions of 10000Lux, 7000Lux, and 4000Lux light intensity, the two carbon dot materials Mg@CDs and CDs were treated with MgSO 4 , ultrapure water, and Mg@CDs and CDs. 4 There was no significant difference between the treatments of Mg@CDs and CDs and ultrapure water. Under 1000 Lux illumination, there was no significant difference between the treatments of Mg@CDs and CDs, but there was no significant difference between the treatments of MgSO 4, ultrapure water reached a very significant difference. Under the same light intensity of 1000-10000Lux, the percentage of the germination index of tobacco seeds treated with carbon dots and the control treatment was greater than 1, indicating that carbon dots can improve the germination index of seeds. At 4000-10000Lux, Mg@CDs treatment improved the germination index of seeds significantly better than CDs treatment. 4 The percentage of germination index of treated tobacco seeds with ultrapure water treatment was less than 1, which may be due to 60 μg / mL MgSO 4 If the concentration is too high, it will inhibit the germination of seeds.

[0073] 4PEG simulated drought stress experiment investigation

[0074] Tobacco seeds with uniform color and size were selected and evenly placed in a culture dish padded with cotton wool and filter paper. The culture dishes were divided into 5 groups (A1-A5) and placed in a light incubator for culture. Different drought degrees (A1-A5) were set for experiments. A1-A5 were respectively added with 30 mL of ultrapure water (normal), 15% PEG (mild drought), 20% PEG (moderate drought), 25% PEG (severe drought) and 30% PEG (extremely severe drought) in the culture dishes to simulate different degrees of drought conditions; each experimental group was subjected to 4 treatments from B1 to B4, and 60.0 μg / mL Mg@CDs, 60.0 μg / mL CDs, 60.0 μg / mL MgSO 4 and ultrapure water (control), and each treatment was repeated 4 times. The treatment settings of different drought stress experiments are shown in Table 4.

[0075] Table 4 Treatment settings for different drought stress experiments

[0076]

[0077] Each group in the experiment was subjected to 12 hours of light and 12 hours of darkness every day. The light time periods were as follows: the first period: 8:00-20:00, temperature 25°C; the second period (darkness): 20:00-8:00 the next day, light intensity of 10,000 Lux, temperature 25°C; relative humidity was maintained at 65%. The filter paper was always kept moist during the culture process, and seed germination was determined when the radicle broke through half the length of the seed. Recording began from the time the seeds germinated after sowing, and the number of seeds germinated and the growth of the seedlings after germination were recorded for the experimental group and the control group at the same time every day. Continue to observe for a period of time and record relevant conditions until the seeds reach the maximum germination rate and the experiment is ended. The effects of different drought stress treatments on the naked seed germination rate and germination index of MS Yunyan 87 are shown as follows: Figure 8 , as shown in Table 5. Since the seeds treated with 30% PEG did not germinate until they became moldy, Figure 8Results without 30% PEG treatment.

[0078] Table 5 Effects of different treatment combinations on the germination index of MS Yunyan 87

[0079]

[0080] Duncan test: The data in the table are mean ± standard error; different lowercase letters indicate significant differences (P<0.05), and different uppercase letters indicate extremely significant differences (P<0.01).

[0081] Depend on Figure 8 It can be seen that with the increase of drought stress, the lag period of seed germination was prolonged. When the mass fraction of PEG was 0%, 15%, 20%, and 25%, the seed skin breaking stage was reached, and the effect of Mg@CDs was better than that of CDs, ultrapure water, and MgSO 4 , the effect of CDs is better than that of ultrapure water and MgSO 4 As shown in Table 5, under the same mass fraction of PEG treatment, the percentage of germination index of Mg@CDs and CDs treated with ultrapure water is greater than 1, which is consistent with MgSO 4 , ultrapure water treatment reached a very significant difference, and there was a very significant difference between Mg@CDs and CDs, indicating that carbon dot materials can improve the germination index of seeds, and Mg@CDs treatment is significantly better than CDs treatment in improving the germination index of seeds. When the mass fraction of PEG is 15%, MgSO 4 The treatment was better than that of ultrapure water, and the difference was extremely significant. When the mass fraction of PEG was 20% and 25%, MgSO 4 There was no significant difference between the treatment and ultrapure water treatment.

[0082] 5 Temperature stress experimental investigation

[0083] Tobacco seeds with uniform color and size were selected and evenly placed in culture dishes padded with absorbent cotton and filter paper. The culture dishes were divided into 5 groups (A1-A5) and placed in a light incubator for culture. Different temperatures (A1-A5) were set for the experiment. A1-A5 were 25℃, 20℃, 15℃, 10℃ and 5℃, respectively. Four treatments (B1-B4) were carried out at each temperature, using 60.0μg / mLMg@CDs, 60.0μg / mL CDs, 60.0μg / mL MgSO 4 The tobacco seeds in the culture dish were treated with ultrapure water (control), and each treatment was repeated 4 times. The treatment settings of the different temperature experiments are shown in Table 6.

[0084] Table 6 Treatment settings for experiments at different temperatures

[0085]

[0086]

[0087] Each group was treated with 12 hours of light and 12 hours of darkness every day. The light time periods were as follows: the first period: 8:00-20:00, temperature 25°C; the second period (darkness): 20:00-8:00 the next day, relative humidity maintained at 65%, and light intensity of 10,000 Lux. The filter paper was always kept moist during the culture process, and seed germination was determined when the radicle broke through half the length of the seed. Recording began from the time the seeds germinated after sowing, and the number of seeds germinated and the growth of the seedlings after germination were recorded for the experimental group and the control group at the same time every day. Continue to observe for a period of time and record relevant conditions until the seeds reach the maximum germination rate and the experiment is ended. The effects of different temperature treatments on the naked seed germination rate and germination index of MS Yunyan 87 are shown as follows: Fig. 9 , as shown in Table 7. Since the seeds did not germinate until they became moldy due to the 5℃ treatment, Fig. 9 The results for the 5°C treatment are not included.

[0088] Table 7 Effects of different temperature treatments on the germination index of naked seed of MS Yunyan 87

[0089]

[0090]

[0091] Duncan test: The data in the table are mean ± standard error; different lowercase letters indicate significant differences (P<0.05), and uppercase letters indicate extremely significant differences (P<0.01).

[0092] Depend on Fig. 9 It can be seen that the seed germination time is different under different temperature conditions. As the temperature decreases, the seed germination lag period is prolonged. Under the temperature condition of 10-25℃, when the seeds are broken, the effect of Mg@CDs is better than CDs, ultrapure water and MgSO 4 ; The effect of CDs is better than that of ultrapure water. As shown in Table 7, under the same temperature treatment, the percentage of the germination index of the two carbon dot materials Mg@CDs and CDs to that of ultrapure water treatment is greater than 1, indicating that carbon dots can improve the germination index of seeds, and at 20℃ and 25℃, there is a very significant difference between Mg@CDs and CDs; while MgSO 4 The percentage of germination index of treated tobacco seeds with ultrapure water treatment was less than 1, which may be due to 60 μg / mL MgSO 4 If the concentration is too high, it will inhibit the germination of seeds.

[0093] Example 4 Investigation of the effect of magnesium-doped carbon dots on the growth of MS Yunyan 87 tobacco strain

[0094] This example further investigates the effect of spraying magnesium-doped carbon dot aqueous solution on the growth of MS Yunyan 87 tobacco plants. The comparison of carbon dots accumulated in the leaf tissues of tobacco plants after spraying is shown in the figure below. Fig.10 , where CK refers to spraying ultrapure water. The observation picture of MS Yunyan 87 tobacco strain after 5 weeks of spraying is shown in Fig.11 As shown. Fig.10 and Fig.11 It can be seen that spraying magnesium-doped carbon dots aqueous solution can promote the accumulation of nutrients and the growth of tobacco plants.

[0095] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A magnesium-doped carbon dot, characterized in that: The preparation method thereof comprises the following steps: 1) mixing tobacco powder and reduced glutathione at a mass ratio of 1:(1.5-4), dissolving the mixture in formamide, and dispersing the mixture by ultrasonic wave to obtain a reaction solution A; dissolving magnesium hydroxide in formamide at a mass of 1.2-1.4 times of the tobacco powder, and dispersing the mixture by ultrasonic wave to obtain a reaction solution B, mixing the mixture with the reaction solution A, and placing the mixture in a high-pressure reactor for reaction; 2) After the reaction is completed, the mixture is cooled and filtered, and the obtained filtrate is transferred to a dialysis bag. The dialyzed solution is freeze-dried to obtain magnesium-doped carbon dots.

2. The magnesium-doped carbon dots according to claim 1, characterized in that: The reaction conditions include: pressure 0.2-3 MPa, temperature 160-190° C., and time 7-9 h.

3. The magnesium-doped carbon dots according to claim 1 or 2, characterized in that: The molecular weight cut-off of the dialysis bag is 3300-3700 Dalton.

4. The magnesium-doped carbon dots according to claim 1 or 2, characterized in that: The dialysis time is 7-10 days.

5. The magnesium-doped carbon dots according to claim 1 or 2, characterized in that: The tobacco powder is obtained by removing stems, cutting into shreds, crushing and then sieving a tobacco leaf sample.

6. Use of the magnesium-doped carbon dots according to any one of claims 1 to 5 in tobacco planting.

7. The use of magnesium-doped carbon dots in tobacco planting according to claim 6, characterized in that: The tobacco or tobacco seeds are in an abiotic stress environment, and the abiotic stress environment includes at least one of weak light, drought, and low temperature.

8. A method for promoting tobacco seed germination, characterized in that: The method comprises the following steps: preparing the magnesium-doped carbon dots according to any one of claims 1 to 5 into an aqueous solution and applying the aqueous solution to tobacco seeds, wherein the concentration of the magnesium-doped carbon dots aqueous solution is 30-70 μg / mL.

9. The method for promoting tobacco seed germination according to claim 8, characterized in that: The tobacco seeds are MS Yunyan 87 naked seeds.

10. The method for promoting tobacco seed germination according to claim 8, characterized in that: The concentration of the magnesium-doped carbon dots aqueous solution is 60 μg / mL.

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