Application of tryptophan nitrate in reducing content of cadmium and arsenic in plants

Abstract

The invention provides application of tryptophan nitrate to reduction of cadmium and arsenic contents in plants, and belongs to the technical field of application of tryptophan nitrate. According to the method, nitric acid and tryptophan are adopted as raw materials, the tryptophan nitrate solid is prepared, the tryptophan nitrate solid serves as a foreign aid substance to be applied to the rice, accumulation of Cd and As in the rice can be remarkably reduced, and the content of essential elements in the rice is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of application of tryptophan nitrate, and in particular relates to application of tryptophan nitrate in reducing the cadmium and arsenic contents in plants. Background Art

[0002] The increase in heavy metal pollution in rice paddies has attracted great attention from governments around the world because it seriously threatens ecological and food security. The main factors leading to cadmium (Cd) and arsenic (As) pollution are sewage irrigation, atmospheric precipitation, excessive use of fertilizers, industrial leaching, and the use of agricultural inputs. Cd and As pollution are characterized by high pollution, large pollution areas, and easy absorption by crops. With the development of modern industry in the 20th century, human activities are the main cause of these metal pollution. The increased accumulation of cadmium and arsenic in rice cultivation has led to serious food losses and endangered human health. Therefore, it is necessary to adopt different methods to reduce the absorption of pollutants by rice, one of which is to add or spray exogenous substances. Summary of the Invention

[0003] In light of this, the present invention aims to provide a method for using tryptophan nitrate to reduce cadmium and arsenic content in plants. This method uses nitric acid and tryptophan as raw materials to prepare solid tryptophan nitrate. Applying the solid tryptophan nitrate as an external aid to rice significantly reduces the accumulation of Cd and As in rice and increases the content of essential elements in the rice.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The invention provides an application of tryptophan nitrate in reducing the cadmium and arsenic contents in plants.

[0006] Preferably, the tryptophan nitrate consists of nitric acid and tryptophan in a molar ratio of 1:0.5-1.5.

[0007] Preferably, the tryptophan is L-tryptophan.

[0008] Preferably, the preparation method of tryptophan nitrate is: mixing tryptophan with dilute nitric acid, reacting for 1 to 3 hours, and then rotary evaporating to obtain tryptophan nitrate solid.

[0009] Preferably, the concentration of the dilute nitric acid is 0.5 to 1.5 mol / L.

[0010] Preferably, the reaction temperature is 25-70°C.

[0011] Preferably, the plant is rice.

[0012] The present invention also provides an application of tryptophan nitrate in increasing the content of essential elements in plants.

[0013] Preferably, the plant is rice.

[0014] Preferably, the essential elements include Mg, Ca, Fe, Mn and Zn.

[0015] Compared with existing technologies, the present invention has the following beneficial effects: It uses nitric acid and tryptophan as raw materials to prepare solid tryptophan nitrate. Applying the solid tryptophan nitrate as an external aid to rice significantly reduces the accumulation of Cd and As in rice and increases the content of essential elements in rice. The present invention primarily utilizes hydroponic, potted, and field trials to provide data support for the use of tryptophan nitrate in rice foliar fertilizers to reduce Cd and As levels, providing a theoretical basis for addressing the problem of excessive Cd and As levels in rice in southern China. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Effects of tryptophan nitrate on Cd and As contents in roots and shoots of X24 and Z35 rice seedlings, where a and b represent Cd contents, and c and d represent As contents;

[0017] Figure 2 The effect of tryptophan nitrate on the content of sulfhydryl compounds in X24 and Z35 rice seedlings, where a is the root system of X24 rice seedlings, b is the aboveground part of X24 rice seedlings, c is the root system of Z35 rice seedlings, and d is the aboveground part of Z35 rice seedlings;

[0018] Figure 3 Effects of tryptophan nitrate on O2 in roots and shoots of rice seedlings ·- and H2O2 content, where a and b are O2 ·- content, c and d are H2O2 contents;

[0019] Figure 4 Effects of tryptophan nitrate on Cd and As contents in rice grains of X24 and Z35, where a and c represent Cd contents, and b and d represent As contents;

[0020] Figure 5 The effect of tryptophan nitrate on the essential element contents in rice grains of X24 and Z35, where a represents the contents of K, Ca, and Mg, and b represents the contents of Fe, Mn, and Zn;

[0021] Figure 6 The effect of tryptophan nitrate on the amino acid content of X24 and Z35 rice grains, where a is X24 rice grains and b is Z35 rice grains;

[0022] Figure 7 The effects of tryptophan nitrate on the Cd and As contents in early and late rice grains, where a and c are Cd contents, and b and d are As contents;

[0023] Figure 8 is the effect of tryptophan nitrate on the essential element contents of early and late rice grains, where a is the content of K, Ca, and Mg, and b is the content of Fe, Mn, and Zn;

[0024] Figure 9 The figure shows the effect of tryptophan nitrate on the amino acid content of early rice and late rice grains, where a represents early rice grains and b represents late rice grains. DETAILED DESCRIPTION

[0025] The invention provides an application of tryptophan nitrate in reducing the cadmium and arsenic contents in plants.

[0026] In the present invention, the tryptophan nitrate is composed of nitric acid and tryptophan in a molar ratio of 1:0.5-1.5, preferably 1:0.7-1.3, and more preferably 1:1; and the tryptophan is L-tryptophan.

[0027] In the present invention, the preparation method of tryptophan nitrate is as follows: tryptophan is mixed with dilute nitric acid, reacted for 1 to 3 hours, and then rotary evaporated to obtain tryptophan nitrate solid; the concentration of the dilute nitric acid is 0.5 to 1.5 mol / L, preferably 0.8 to 1.2 mol / L, and more preferably 1 mol / L; the reaction time is preferably 1.5 to 2.5 hours, more preferably 2 hours, and the reaction temperature is 25 to 70° C., preferably 50 to 65° C., and more preferably 60° C.; the rotary evaporation is performed using a rotary evaporator to distill to obtain tryptophan nitrate solid, and the rotary evaporation temperature is 20 to 30° C., preferably 23 to 27° C., and more preferably 25° C.

[0028] In the present invention, the use concentration of the tryptophan nitrate is 0.20-1.50 mmol / L, the use amount of the tryptophan nitrate is 20-150 L / mu; and the plant is rice.

[0029] The present invention also provides an application of tryptophan nitrate in increasing the content of essential elements in plants.

[0030] In the present invention, the use concentration of the tryptophan nitrate is 0.20-1.50 mmol / L, and the use amount of the tryptophan nitrate is 20-150 L / mu; the increasing the content of essential elements in plants is to increase the content of essential elements in rice grains; the essential elements include Mg, Ca, Fe, Mn and Zn.

[0031] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1 Preparation of tryptophan nitrate

[0033] Tryptophan (CAS: 73-22-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 mol / L dilute nitric acid (MOS grade, purchased from Tianjin Fengchuan Chemical Reagent Technology Co., Ltd.) were mixed in a 1:1 molar ratio, reacted at 60°C for 2 h, and then distilled using a rotary evaporator at room temperature to obtain solid tryptophan nitrate.

[0034] Example 2 Preparation of tryptophan nitrate

[0035] Tryptophan (CAS: 73-22-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 mol / L dilute nitric acid (MOS grade, purchased from Tianjin Fengchuan Chemical Reagent Technology Co., Ltd.) were mixed in a molar ratio of 1:0.5, reacted at 60°C for 2 hours, and then distilled using a rotary evaporator at room temperature to obtain solid tryptophan nitrate.

[0036] Example 3 Preparation of tryptophan nitrate

[0037] Tryptophan (CAS: 73-22-3, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 mol / L dilute nitric acid (MOS grade, purchased from Tianjin Fengchuan Chemical Reagent Technology Co., Ltd.) were mixed in a molar ratio of 1:1.5, reacted at 60°C for 2 hours, and then distilled using a rotary evaporator at room temperature to obtain tryptophan nitrate solid.

[0038] Experimental Example 1

[0039] 1. Experimental Design

[0040] A hydroponic experiment was conducted using the indica rice varieties Xiangzaoxian No. 24 (X24) and Zhongzao No. 35 (Z35) as test materials. Healthy, plump, and uniformly sized seeds were selected and soaked in a 5% H2O2 solution for disinfection for 30 minutes, and then washed with ultrapure water. The seeds were evenly distributed in the seedling tray using a quantitative distribution method, and a 1 cm ultrapure water cover layer was maintained. The seedling tray was placed in a 28°C constant temperature incubator for germination, and after the radicle broke through the seed coat, it was transferred to an artificial climate chamber for further cultivation. When the seedlings developed to the two-leaf stage, strong seedlings with uniform plant height were selected and transplanted to a hydroponic box with a volume of 8L for further cultivation. Hoagland nutrient solution was used to supply nutrients during the cultivation process. Environmental parameters of the artificial climate chamber: photoperiod 16h / 8h (day / night), light intensity 105μmol·m -2 ·s -1 The temperature during the light period is 28°C, the dark period is 25°C, and the relative humidity is 70%±5%. The environmental control system uses a PLC module to achieve precise control of multiple parameters.

[0041] After the rice seedlings grew to four leaves, they were treated with root immersion for 7 days: T0 (control group), T1 (0.20mmol·L -1Tryptophan nitrate), T2 (0.50mmol·L -1 Tryptophan nitrate), T3 (0.80mmol·L -1 Tryptophan nitrate), T4 (1.20mmol·L -1 Tryptophan nitrate) and T5 (1.50mmol·L -1 Both the control group and the treatment group maintained Cd (2.70 μmol·L -1 ) and As(15.00μmol·L -1 ) constant concentration exposure treatment, and the treatment solution was replaced every two days to ensure the stability of the ion concentration. The tryptophan nitrate was obtained according to the method of Example 1 and diluted with water to different treatment group concentrations.

[0042] After the treatment, the rice seedlings were immersed in 5.00mmol·L -1 Rice seedling roots were placed in a CaCl₂ solution for 30 minutes, then washed with ultrapure water. Rice seedling samples were collected and separated into root and aerial parts for measurement of various parameters. Fresh samples were stored in a -80°C freezer, while dried samples were placed in a 75°C oven to a constant weight.

[0043] 2. Determination of Cd and As Content in Rice

[0044] An accurately weighed 0.25 g dry sample was placed in a digestion tube, 7.00 mL of MOS HNO₃ was added, and the sample was allowed to stand for at least 5 hours. A DigiBlock ED54 electrothermal digester (LabTech, Beijing, China) was used for sample digestion, initially at 110°C for 2.5 hours. After cooling, 1.0 mL of H₂O₂ was added and digestion continued for 1.5 hours. Deacidification was then performed at 170°C. Deionized water was then added to bring the volume to 25.0 mL. After filtration, the sample was analyzed, and Cd concentration was determined using an inductively coupled plasma mass spectrometer (iCAP QICP-MS, Thermo Scientific, Waltham, MA, USA). The method for determining As was similar to that for Cd, except that the digestion temperature was maintained at 110°C, the digestion time was 4 hours, and no H₂O₂ was added. As content was determined using an atomic fluorescence spectrometer (AFS-8520, Haiguang, Beijing, China). Quality assurance and quality control were ensured by using rice flour component analysis standard material (rice flour standard material GBW(E)100350) and blank digestion samples. The recovery rate was between 90% and 110%, verifying the accuracy and reliability of the data. Figure 1 .

[0045] like Figure 1As shown in Figure 2, the Cd and As contents in the roots of X24 and Z35 rice seedlings were much higher than those in the aboveground parts. Under the T0 treatment, the Cd contents in the roots of X24 and Z35 rice seedlings reached 676.19 mg·kg -1 and 751.76 mg·kg -1 , and the As content reached 774.96 mg·kg -1 and 837.63 mg·kg -1 The Cd contents in the aboveground parts of X24 and Z35 seedlings were 10.27 mg·kg -1 and 13.58 mg·kg -1 , and the As content was 20.19 mg·kg -1 and 22.75 mg·kg -1 Compared with T0, with the increase of tryptophan nitrate treatment concentration, the Cd and As contents in rice seedlings gradually decreased. -1 When treated with tryptophan nitrate, Cd and As concentrations in seedlings X24 and Z35 decreased most significantly. Cd concentrations in the roots of seedlings X24 and Z35 decreased by 59.42% and 61.50%, respectively, and in the aboveground parts by 57.06% and 60.82%, respectively. As concentrations in the roots of seedlings X24 and Z35 decreased by 64.94% and 67.07%, respectively, and in the aboveground parts by 61.27% and 64.62%, respectively.

[0046] 3. Determination of sulfhydryl compound content in rice

[0047] The sulfhydryl compounds in fresh rice seedling samples were extracted using 0.1% trifluoroacetic acid buffer (TFA). The supernatant was collected by centrifugation at 12000 rpm for 10 min at 4°C and 650.0 μL of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (HEPES, 200.0 mmol·L -1 , pH = 9) and 25.0 μL tris(2-carboxyethyl)phosphoric acid solution (TCEP, 20.0 mmol·L -1 After standing at room temperature for 5 min, 20.0 μL of monobromomanganese solution (mBBr, 50.0 mmol·L -1 ), and then reacted in the dark for 30 min to perform the derivatization reaction. Then 100.0 μL of MSA solution (methanesulfonic acid, 1.0 mol·L -1) to stop the reaction. The resulting sample was filtered through a 0.22 μm membrane filter and quantitatively analyzed using a high-performance liquid chromatography (HPLC) equipped with an Agilent Zorbax Eclipse XDB-C18 (4.6 nm × 30 mm, 1.8 μm, Agilent Technologies Inc, Princeton, MN, USA). Results are shown in 2.

[0048] like Figure 2 As shown in Figure 2, the GSH content in the roots of rice seedlings was high, while the PCs content was low, especially PC2 and PC4. In addition, the Cys and PCs content in the roots of rice seedlings was higher than that in the aboveground parts, while the GSH content was higher in the aboveground parts. Compared with T0, the application of tryptophan nitrate significantly increased the Cys and GSH content in rice seedlings. When the tryptophan nitrate concentration was 1.50 mmol·L -1 The Cys and GSH contents in the roots of X24 rice seedlings increased from 24.28 μmol·kg -1 and 28.79 μmol·kg -1 Increased to 38.62 μmol·kg -1 and 67.45 μmol·kg -1 , with increases of 59.06% and 134.28% respectively; the Cys and GSH contents in the aboveground part of X24 rice seedlings increased from 20.74 μmol·kg -1 and 67.43 μmol·kg -1 Increased to 28.94 μmol·kg -1 and 103.64 μmol·kg -1 The Cys and GSH contents in the roots of Z35 rice seedlings increased from 28.49 μmol·kg -1 and 32.59 μmol·kg -1 Increased to 45.82 μmol·kg -1 and 73.52 μmol·kg -1 , with increases of 60.83% and 125.59% respectively; the Cys and GSH contents in the aboveground part of Z35 rice seedlings increased from 25.74 μmol·kg -1 and 73.81 μmol·kg -1 Increased to 32.65 μmol·kg -1 and 105.42 μmol·kg -1 The increases were 26.85% and 42.83% respectively. On the contrary, the contents of PC2, PC3 and PC4 decreased with the addition of glutamic acid chloride. -1After the addition of tryptophan nitrate, the contents of PC2, PC3 and PC4 in the roots of X24 rice seedlings increased from 8.51, 29.75 and 9.49 μmol·kg -1 decreased to 4.37, 13.33, and 4.83 μmol·kg -1 , with decreases of 48.65%, 55.19% and 49.10% respectively; the contents of PC2, PC3 and PC4 in the aboveground part of X24 rice seedlings decreased from 7.58, 22.52 and 7.35 μmol·kg -1 decreased to 4.24, 11.43, and 4.82 μmol·kg -1 The PC2, PC3 and PC4 contents in the roots of Z35 rice seedlings decreased from 9.32, 32.43 and 9.42 μmol·kg -1 decreased to 4.57, 15.34, and 5.03 μmol·kg -1 , with decreases of 50.97%, 52.70% and 46.60% respectively; the contents of PC2, PC3 and PC4 in the aboveground part of Z35 rice seedlings decreased from 8.23, 26.38 and 8.85 μmol·kg -1 decreased to 4.97, 13.86, and 5.01 μmol·kg -1 , with decreases of 39.61%, 47.46% and 43.39% respectively.

[0049] 4. Determination of ROS Activity

[0050] In order to determine the activity of the enzyme, the aerial part and root part of the fresh rice sample were ground with liquid nitrogen. The present invention uses a standardized kit detection system to detect the active oxygen components (H2O2, O2 ·- ) content was detected using ELISA kits (Cat. No. BC3590 / BC1295 / BC0220) produced by Solebeau Technology Co., Ltd. All testing procedures strictly followed the standard operating procedures provided by the manufacturer to ensure data comparability and reproducibility. Figure 3 .

[0051] Figure 3 The results showed that tryptophan nitrate has an effect on O2 ·- and H2O2 content. Cd-As stress can cause oxidative stress in rice seedlings, producing excessive O2 ·- and H2O2, and O2 in the roots of rice seedlings ·- The contents of O2 in rice seedlings are lower than those in the aboveground parts. ·- The content of H2O2 decreased with the increase of tryptophan nitrate concentration. -1After tryptophan nitrate, O2 ·- The contents of O2 in the aboveground part decreased by 30.77% and 34.21% respectively. ·- The H2O2 content in the roots of X24 and Z35 rice seedlings decreased by 36.78% and 35.16% respectively, and the H2O2 content in the aboveground parts decreased by 32.01% and 31.97% respectively.

[0052] Experimental Example 2

[0053] 1. Experimental Design

[0054] The indica rice varieties Xiangzaoxian 24 (X24) and Zhongzao 35 (Z35) were selected as experimental materials. The experimental soil was collected from the cultivated layer (0-20 cm depth) of a typical Cd-As complex-contaminated agricultural area in Hunan Province.

[0055] Healthy, plump, and uniformly sized seeds were selected and sterilized by soaking them in a 5% H2O2 solution for 30 minutes, followed by washing with ultrapure water. The seeds were evenly distributed in seedling trays using a quantitative distribution method, maintaining a 1cm layer of ultrapure water over the seed surface. After germination at 30°C in the dark for two days, the seeds were transferred to vermiculite trays and continuously supplied with Hoagland nutrient solution. After one month of incubation, seedlings of uniform growth were selected and transplanted into soil pots containing 5kg of experimental soil. The pots were then kept submerged in water until the rice reached maturity.

[0056] Spraying treatment during rice flowering period: T0(0mmol·L -1 Tryptophan nitrate), T1 (0.20mmol·L -1 Tryptophan nitrate), T2 (0.50mmol·L -1 Tryptophan nitrate), T3 (0.80mmol·L -1 Tryptophan nitrate), T4 (1.20mmol·L -1 Tryptophan nitrate) and T5 (1.50mmol·L -1 Tryptophan nitrate). Each pot was sprayed with 30 mL of the corresponding treatment solution each time. The spraying treatment was performed twice, with one day between the two treatments. Each treatment group contained 5 replicates. After the rice was fully mature, the complete rice plants and root soil samples were collected. The plant samples were cleaned with ultrapure water and dried in the sun. The sample grains were then measured and analyzed for indicators. The tryptophan nitrate was obtained according to the method of Example 1 and diluted with water to the concentrations of different treatment groups.

[0057] 2. Determination of Cd, As and Essential Elements in Rice Grains

[0058] An accurately weighed 0.25 g dry sample was placed in a digestion tube, 7.00 mL of MOS HNO₃ was added, and the sample was allowed to stand for at least 5 hours. A DigiBlock ED54 electrothermal digester (LabTech, Beijing, China) was used for sample digestion, initially at 110°C for 2.5 hours. After cooling, 1.0 mL of H₂O₂ was added and digestion continued for 1.5 hours. Deacidification was then performed at 170°C. Deionized water was then added to bring the volume to 25.0 mL. After filtration, the sample was analyzed. Cd, K, Ca, Mg, Fe, Mn, and Zn concentrations were determined using an inductively coupled plasma mass spectrometer (iCAP Q ICP-MS, Thermo Scientific, Waltham, MA, USA). The method for determining arsenic (As) was similar to that for Cd, except that the digestion temperature was maintained at 110°C, the digestion time was 4 hours, and no H₂O₂ was added. As content was determined using an atomic fluorescence spectrometer (AFS-8520, Haiguang, Beijing, China). Quality assurance and quality control were ensured by using rice flour component analysis standard material (rice flour standard material GBW(E)100350) and blank digestion samples. The recovery rate was between 90% and 110%, verifying the accuracy and reliability of the data. Figures 4-5 .

[0059] like Figure 4 As shown in Figure 2, foliar spraying of tryptophan nitrate can significantly reduce the accumulation of Cd and As in rice grains, and the higher the concentration, the more significant the effect. -1 Tryptophan nitrate had the best inhibitory effect. The Cd content in X24 rice grains ranged from 0.32 mg·kg -1 Down to 0.18 mg kg -1 , a decrease of 43.75%; As content from 0.68 mg·kg -1 Dropped to 0.43 mg kg -1 The Cd content in Z35 rice grains decreased from 0.37 mg·kg -1 to 0.19 mg kg -1 , a decrease of 48.65%; As content from 0.83 mg·kg -1 Down to 0.49 mg kg -1 , a decrease of 40.96%.

[0060] Figure 5 Figure 2 shows changes in the essential element content of rice grains after foliar application of tryptophan nitrate. Rice genotype influences the essential element content of its grains, with Z35 rice grains containing higher levels of essential elements than X24 rice grains. K is the most abundant of the six essential elements, reaching 4.36 g·kg in X24 and Z35 rice grains, respectively. -1~4.83g·kg -1 and 5.64 g·kg -1 ~5.93g·kg -1 Mg content ranked second, with the content in X24 and Z35 rice grains ranging from 1.06 g·kg -1 ~1.13g·kg -1 and 1.31 g·kg -1 ~1.36g·kg -1 The second is Ca, which is 0.27 g·kg in X24 and Z35 rice grains. -1 ~0.36g·kg -1 and 0.34 g·kg -1 ~0.43g·kg -1 The contents of Fe, Mn and Zn are much lower than the above three, and their contents in rice grains range from 0.02 g·kg -1 ~0.07g·kg -1 Compared with the control group, foliar application of tryptophan nitrate significantly increased the calcium content in rice grains, with increases of 7.4% to 33.3% and 2.9% to 26.5% in X24 and Z35 rice grains, respectively. However, the iron, manganese, and zinc contents in X24 and Z35 rice grains decreased slightly, while the changes in potassium and magnesium contents were not significant.

[0061] 3. Determination of amino acid content in rice grains

[0062] The amino acid content was determined according to the Chinese National Food Safety Standard (GB5009.124-2016). First, the rice sample was ground into a fine powder, then 0.25 g of the sample was accurately weighed into a test tube and 15.0 mL of HCl (6 mol·L -1 ). After the sample tube was placed in ice water to cool for 5 minutes, it was filled with high-purity nitrogen and sealed for storage. The sample was placed in a constant temperature oven and completely digested at 110°C for 22 hours. After complete digestion, the test tube was removed, and after cooling to room temperature, the sample was filtered and diluted to 50 mL. Take 1.0 mL of digestion solution in a glass sample, blow dry with high-purity nitrogen in a 50°C water bath, and then add 1.0 mL of ultrapure water to the injection bottle for secondary drying. Finally, 2.0 mL of sodium citrate buffer (pH = 2.2) was added to dissolve the precipitate and filtered with a 0.22 μm filter membrane. The final sample solution was mixed with 50.0 μL of borate buffer (0.4 mol·L -1 , pH = 10.2) and mixed thoroughly for 1 min to initiate the derivatization reaction, and then 10.0 μL of OPA reagent was added and reacted for 3 min. Figure 6 .

[0063] Figure 6 The chart shows the changes in the total amino acid content of rice grains. Glutamic acid is the most abundant amino acid in rice grains, and its content in X24 rice grains ranges from 11.47 to 13.94 g·kg. -1 The content of Z35 rice grains is 12.05-14.25 g·kg -1 . Spraying tryptophan nitrate on the leaves promoted the synthesis of amino acids in rice grains, and the higher the concentration of tryptophan nitrate, the more obvious the effect. In the X24 rice grains, the increases in glutamic acid, serine, histidine, glycine and lysine were large, with the highest increases being 21.53%, 35.33%, 33.06%, 24.45% and 35.98%, respectively. In the Z35 rice grains, the increases in aspartic acid, glutamic acid, serine, histidine, glycine, alanine, tyrosine and lysine were large, with the highest increases being 17.79%, 18.26%, 20.82%, 35.27%, 25.69%, 16.21%, 18.69% and 20.98%, respectively.

[0064] Experimental Example 3

[0065] 1. Experimental Design

[0066] Field experiments were conducted in cadmium-arsenic contaminated rice paddies in Xiangtan City, Hunan Province (N:28°41′, E:112°52′). Early rice varieties included Zhongzao 35, sown in late April, sprayed in mid-June, and harvested in mid-to-late July. Late rice varieties included Huazhan, sown in late July, sprayed in mid-to-late September, and harvested in November.

[0067] The field experiment adopted a randomized complete block design, which included 6 treatments and a plot area of ​​5m 2 During the flowering period of rice, different concentrations of tryptophan nitrate were sprayed on the leaves: T0 (0mmol·L -1 Tryptophan nitrate), T1 (0.20mmol·L -1 Tryptophan nitrate), T2 (0.50mmol·L -1 Tryptophan nitrate), T3 (0.80mmol·L -1 Tryptophan nitrate), T4 (1.20mmol·L -1 Tryptophan nitrate) and T5 (1.50mmol·L -1 Tryptophan nitrate), each treatment group was set up with four replicates, the treatment solution volume for each treatment was 300 mL / time, sprayed once a day, and sprayed continuously for 2 days. The tryptophan nitrate was obtained according to the method of Example 1 and diluted with water to the concentrations of different treatment groups.

[0068] 2. Determination of Cd, As and Essential Elements in Early / Late Rice Grains

[0069] For specific determination methods, see "2. Determination of Cd, As and Essential Elements in Rice Grains" in Experimental Example 2, and the results are shown in Figures 7 and 8 .

[0070] To verify the effect of spraying tryptophan nitrate on the accumulation of Cd and As in rice grains, the Cd and As contents of early and late rice were measured. Figure 7 As shown in Figure 2, the content of Cd and As in rice grains decreased significantly after application of tryptophan nitrate. -1 Under tryptophan nitrate treatment, the Cd and As contents in early rice grains increased from 0.28 mg·kg -1 and 0.41 mg·kg -1 Reduced to 0.19 mg kg -1 and 0.29 mg·kg -1 , the decrease range was 10.71% to 32.14% and 9.76% to 29.27%. -1 Under tryptophan nitrate treatment, the Cd and As contents of late rice increased from 0.31 mg·kg -1 and 0.43 mg·kg -1 Reduced to 0.19 mg kg -1 and 0.30 mg·kg -1 The decrease ranges were 9.68% to 38.71% and 6.98% to 30.23%. This shows that spraying tryptophan nitrate in the field can effectively slow down the accumulation of Cd and As in rice grains.

[0071] like Figure 8 As shown in the results, foliar spraying of tryptophan nitrate has a significant effect on the content of essential elements in rice grains. The content of essential elements in rice grains varies with rice varieties and seasons. The content of these elements in late rice grains is significantly higher than that in early rice grains. The order of their content in rice grains is K, Mg, Ca, Mn, Fe, and Zn. Compared with the control group, foliar spraying of tryptophan nitrate increased the content of K, Ca, and Mg in rice grains, while reducing the content of Fe, Mn, and Zn. Spraying 1.5mmol·L -1 After tryptophan nitrate supplementation, the K, Ca, and Mg contents in early rice grains increased by 4.7%, 34.8%, and 7.4%, respectively, while the Fe, Mn, and Zn contents decreased by 15.6%, 16.4%, and 22.2%, respectively. In late rice grains, the K, Ca, and Mg contents increased by 1.9%, 28.6%, and 5.1%, respectively, while the Fe, Mn, and Zn contents decreased by 14.9%, 14.0%, and 19.0%, respectively.

[0072] 3. Determination of amino acid content in rice grains

[0073] For specific determination methods, see "3. Determination of amino acid content in rice grains" in Experimental Example 2, and the results are shown in Figure 9 .

[0074] Depend on Figure 9 It can be seen that spraying tryptophan nitrate in the field has an impact on the amino acid content of rice grains. The amino acid content in rice grains is one of the important parameters for evaluating rice quality. Among the non-essential amino acids, glutamic acid, aspartic acid, and cysteine ​​are high, while among the essential amino acids, valine and leucine are high. After spraying tryptophan nitrate in the field, the amino acid content in rice grains increased. When the spraying concentration of tryptophan nitrate was 1.5mmol·L -1 When the temperature was adjusted for 24 h, the content of glutamic acid, histidine, glycine, isoleucine and lysine in early rice grains increased significantly, which were 32.44%, 19.58%, 14.29%, 18.94% and 11.28% respectively; the content of glutamic acid, histidine, glycine, isoleucine and lysine in late rice grains increased significantly, which were 29.70%, 21.32%, 14.23%, 16.67% and 14.74% respectively.

[0075] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Application of tryptophan nitrate in reducing cadmium and arsenic content in plants.

2. The use according to claim 1, characterized in that The tryptophan nitrate is composed of nitric acid and tryptophan in a molar ratio of 1:0.5-1.

5.

3. The use according to claim 2, characterized in that The tryptophan is L-tryptophan.

4. The use according to claim 3, characterized in that The preparation method of tryptophan nitrate comprises the following steps: mixing tryptophan with dilute nitric acid, reacting for 1 to 3 hours, and then performing rotary evaporation to obtain tryptophan nitrate solid.

5. The use according to claim 4, characterized in that The concentration of the dilute nitric acid is 0.5-1.5 mol / L.

6. The use according to claim 5, characterized in that The reaction temperature is 25-70°C.

7. The use according to any one of claims 1 to 6, characterized in that The plant is rice.

8. Use of tryptophan nitrate in increasing the content of essential elements in plants.

9. The use according to claim 8, characterized in that The plant is rice.

10. The use according to claim 9, characterized in that The essential elements include Mg, Ca, Fe, Mn and Zn.

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