Application of melatonin in enhancing plant resistance to fluoride stress

Abstract

The present invention relates to the technical field of tea tree planting, and specifically relates to the application of melatonin in improving the resistance of plants to fluorine stress; the plant is a plant of the family Theaceae; the improvement of the resistance of plants to fluorine stress includes: reducing the fluorine absorption of plant roots under fluorine stress, reducing the fluorine accumulation in plant leaves, and increasing the SPAD value of plant leaves under fluorine stress. The beneficial effects of the present invention are: it can significantly reduce the fluorine accumulation and ensure the healthy growth of tea trees, which is beneficial to ensuring the nutritional quality of tea leaves and the safe utilization of tea leaves, and ensuring the health of drinkers.

Description

Technical Field

[0001] The present invention relates to the technical field of tea tree cultivation, and specifically relates to the application of melatonin in enhancing the resistance of plants to fluorine stress. Background Art

[0002] In recent years, with the increasing reports of fluorosis caused by excessive fluorine content in brick tea after people drink tea, tea trees and fluorine have become research hotspots. In the early stage, tea trees were one of the plants with the highest fluorine content in the plant kingdom. The fluorine content in tea trees was two orders of magnitude higher than that in general plants. Tea trees are a fluorine accumulator, with a high fluorine content in their leaves, accounting for more than 98% of the whole plant, followed by stems and roots.

[0003] However, fluorine is not an essential element for the growth of tea trees. Under high fluorine stress, fluorine can affect its normal growth by destroying the cell structure of tea trees and inhibiting enzyme activity. China has a long history of tea drinking. Exploring the relevant mechanisms of tea tree absorption, transport, and enrichment of fluorine and effective control measures is of great significance for formulating control plans to reduce the fluorine content in tea and ensuring the quality and safety of tea. According to the fluorine enrichment characteristics and related mechanisms of tea, many scholars have proposed measures for reducing fluorine in tea, mainly including:

[0004] 1. Screening of low-fluorine varieties

[0005] There are significant differences in the enrichment of fluorine elements among different tea tree varieties. Therefore, cultivating tea tree varieties with a low degree of fluorine enrichment is considered an effective measure to reduce the fluorine content in tea. Shu measured the fluorine content of several brick tea varieties and found that the fluorine content of the finished tea made from the fresh leaves of the Qianjuan series varieties was twice as high as that of other varieties. Chen Ruihong et al. analyzed 31 tea tree varieties using a fluoride electrode and found that there were significant differences in the fluorine content of mature leaves of different varieties. Among them, Wuniuzao was the highest, reaching 2163.2 mg / kg, while Zhenong 138 was only 805.7 mg / kg, with a difference of about twice. The results indicated that Zhenong 138 could be promoted as a low-fluorine variety. Although the screening of low-fluorine varieties has a positive effect on improving the safety of tea products and meeting the needs of specific regions, possible planting restrictions and cost factors also need to be considered during the promotion process.

[0006] 2. Improvement of cultivation environment and measures

[0007] External factors such as the soil environment, water environment, and atmospheric environment of tea plants can all affect the fluorine content in tea. If the fluorine content in the soil is high, the total fluorine and water-soluble fluorine contents of the produced tea will be significantly higher; if the fluorine content in the atmosphere exceeds the standard, the fluoride content of the produced tea will also be high. Research shows that whether the tea garden ecological environment is suitable is an external factor affecting tea quality, and there is a positive correlation between the fluorine content in tea and the total amount of fluoride in the tea garden. Selecting a tea garden microclimate environment with a low soil fluorine background value, good air environment, and no fluorine pollution is crucial for reducing fluorine in tea products. At the same time, reasonably controlling the soil and fertilizer environment of tea plants and matching the fertilization ratio according to the actual fluorine content in the soil can weaken the fluorine enrichment of tea plants. However, the implementation cost of this method is relatively high, and it takes a long time to see significant effects.

[0008] 3. Adding different exogenous substances to reduce fluorine accumulation

[0009] Ma Lifeng et al. analyzed the effect of calcium on fluorine absorption by tea plants using hydroponics and soil pot experiments. The results of the hydroponics experiment showed that adding calcium to the solution containing fluorine elements could significantly reduce the fluorine absorption by tea plants. Similar results were obtained in the soil pot experiment: adding Ca(NO3)2 significantly reduced the fluorine content in the mature leaves and new shoots of tea plants, and adding CaO also significantly reduced the fluorine absorption by tea plants. Ruan et al. studied the effect of calcium on fluorine absorption by this accumulative plant. The research suggested that calcium could reduce the fluorine enrichment of tea plants, but this reduction effect did not work by simply forming complexes to reduce the content of free fluorine in the soil so that it could not be absorbed by tea plants. Instead, calcium affected the properties of the cell wall or the membrane permeability of tea plant leaves, thereby changing the form and content of fluorine.

[0010] Tea plants have a high tolerance to aluminum. Aluminum can reduce the toxicity of fluorine by forming aluminum-fluoride complexes and decrease the fluorine content in tea. Pan et al. studied the alleviating effect of exogenous aluminum addition on fluorine stress in tea plants. The results showed that under fluorine treatment, adding exogenous aluminum increased the SOD activity and decreased the CAT activity, which was consistent with the research results of Li et al. This indicates that exogenous aluminum alleviates fluorine stress in tea by regulating the MDA content and antioxidant enzyme activities, and stimulates the synthesis and secretion of organic acids in roots under fluorine stress to protect cells from free radical damage. These results help us understand that aluminum alleviates fluorine stress and reduces the fluorine toxicity of tea plants by stimulating the production of organic acids in tea plants.

[0011] In summary, adding exogenous substances such as calcium and aluminum to reduce fluoride accumulation in tea plants has certain effects, but there are also some problems. First, excessive addition of calcium and aluminum may affect the soil pH value and the balance among various nutrient elements, thereby affecting the absorption of other minerals by tea plants; second, exogenous calcium and aluminum have obvious effects on the properties of tea plant leaves and the content of organic substances, etc. Therefore, the method of reducing fluoride accumulation by exogenous calcium and aluminum will seriously affect the quality and taste of tea. Therefore, in practical applications, these factors need to be comprehensively considered to ensure the effectiveness of the method for reducing fluoride accumulation in tea plants and the safety of tea products. Summary of the Invention

[0012] The object of the present invention is to overcome the deficiencies of the prior art and propose the application of melatonin in improving the resistance of plants to fluoride stress, which can significantly reduce the fluoride accumulation amount and ensure the healthy growth of tea plants, is beneficial to ensuring the nutritional quality of tea and the safe utilization of tea, and guarantees the health of drinkers; and provides a method for improving the resistance of plants to fluoride stress, which is applicable to the cultivation and management of tea plants under fluoride stress conditions.

[0013] The object of the present invention is achieved by the following technical solutions:

[0014] The present invention provides the application of melatonin in improving the resistance of plants to fluoride stress.

[0015] Furthermore, the plant is a plant of the family Theaceae. Theaceae is a family of dicotyledonous plants in the subclass Dilleniidae, mostly evergreen woody plants. There are about 30 genera and 750 species, mainly distributed in the subtropical and tropical regions of Asia. There are 15 genera and 500 species in China. Plants of the family Theaceae have important economic values and have various uses such as edible, drinkable, ornamental, wood utilization, skin care, beauty, and fertilizer production. For example, the young leaves of various teas in the tea section can be processed into tea leaves to prepare beverages.

[0016] More preferably, the plant of the family Theaceae is Zijuan and / or Longjing 43.

[0017] Furthermore, the improvement of the resistance of plants to fluoride stress includes: reducing the fluoride absorption of plant roots under fluoride stress and reducing the fluoride accumulation amount in plant leaves.

[0018] Even further, the improvement of the resistance of plants to fluoride stress further includes: increasing the SPAD value of plant leaves under fluoride stress and increasing the contents of total phenols, flavonoids and anthocyanins in plant leaves under fluoride stress.

[0019] The SPAD value, which is the chlorophyll content of leaves measured by a chlorophyll meter, is an important indicator for measuring the photosynthetic ability of plant leaves. In tea production, the SPAD value is used to evaluate the nitrogen nutrition status of tea leaves, and thus indirectly reflect the growth status and potential quality of tea leaves. Existing research shows that there is a certain positive correlation between the SPAD value of tea leaves and their yield and quality, which means that tea leaves with a higher SPAD value may have a better growth state and higher yield.

[0020] In a preferred embodiment of this solution, during application, an aqueous melatonin solution or a preparation containing melatonin is applied to plants suffering from fluorine stress poisoning, and the concentration of melatonin applied is 100 - 200 µmol / L.

[0021] The present disclosure also provides a method for improving the resistance of plants to fluorine stress, including: applying an aqueous melatonin solution or a preparation containing melatonin to plants suffering from fluorine stress poisoning; in the aqueous melatonin solution or the preparation containing melatonin, the concentration of melatonin is 100 - 200 µmol / L; the plants are plants of the Theaceae family.

[0022] In a preferred embodiment of this solution, the application method is foliar spraying.

[0023] In a preferred embodiment of this solution, the planting method of the plants is hydroponics, the spraying frequency is once a day, the spraying time is after sunset, and the spraying degree is based on the leaves dripping with water.

[0024] Further preferably, when the planting method is hydroponics, the concentration of melatonin sprayed is 100 µmol / L.

[0025] In a preferred embodiment of this solution, the planting method of the plants is field planting, the spraying frequency is once a week, the spraying time is after sunset, and the spraying degree is based on the leaves dripping with water.

[0026] Further preferably, when the planting method is field planting, the concentration of melatonin sprayed is 100 - 200 µmol / L.

[0027] It should be noted that the principle of using exogenous melatonin to reduce fluoride accumulation is significantly different from traditional physical or chemical strategies. Melatonin enhances the antioxidant capacity by regulating the physiological metabolism of tea plants, promotes the exclusion of fluoride by roots, reduces the transport and accumulation of fluoride in plants, and belongs to a physiological regulation mechanism. Traditional fluoride reduction techniques often rely on chemical additives or the physical adsorption and ion exchange effects of calcium and nitrogen fertilizers. According to existing experimental data, the fluoride accumulation in tea leaves significantly decreases after melatonin application. At the same time, key quality indicators in tea leaves (such as total phenols, flavonoids, etc.) are also improved, indicating that melatonin treatment can not only effectively reduce fluoride accumulation but also have a positive effect on the overall health and quality of tea plants. For Theaceae plants with leaves as products, both the reduction of fluoride content and the improvement of product quality are achieved.

[0028] Advantages of the present invention: The present disclosure provides the application of melatonin in improving the resistance of plants to fluoride stress; applying melatonin to Theaceae plants can not only reduce the fluoride absorption of plants under fluoride stress, decrease the fluoride content in leaves, but also increase the SPAD value of plant leaves under fluoride stress, improving the photosynthesis efficiency of tea plants;

[0029] Based on the above technical advantages, the present disclosure also provides a method for improving the resistance of plants to fluoride stress, applying an aqueous melatonin solution to plants poisoned by fluoride stress; experiments prove that applying melatonin can significantly reduce the fluoride accumulation and ensure the healthy growth of tea plants, which is beneficial to ensuring the nutritional quality and safe utilization of tea leaves and the health of drinkers;

[0030] The method for improving the resistance of plants to fluoride stress in the present disclosure can be foliar spraying of an aqueous melatonin solution or spraying an aqueous melatonin solution using a field watering system, which greatly facilitates its popularization and application in large-scale tea gardens, improves convenience, and is applicable to the cultivation and management of tea plants in tea gardens under fluoride stress conditions; the application amount of foliar spraying is preferably based on the melatonin solution sprayed onto the leaf surface until it reaches the dripping state. The concentration range of melatonin for foliar spraying in the field is preferably 100 - 200 μM, and the concentration range of melatonin for field spraying is preferably 200 μM. Description of the Drawings

[0031] Figure 1 It is a comparison diagram of the phenotypes of tea seedlings of hydroponic Longjing 43 before and after 10 days of treatment in Example 1 of the present invention;

[0032] Figure 2 It is a dot line graph of the relative content change of chlorophyll in mature leaves of hydroponic Zijuan in Example 1 of the present invention at 1, 4, 7, and 10 days of treatment;

[0033] Figure 3 It is a comparison diagram of the phenotypes of tea seedlings of hydroponic Zijuan before and after 10 days of treatment in Example 1 of the present invention;

[0034] Figure 4 It is a line graph of the relative content change of chlorophyll in the mature leaves of hydroponic Zijuan treated for 1, 4, 7, and 10 days in Example 1 of the present invention;

[0035] Figure 5 It is a schematic diagram of the water-soluble fluorine content of hydroponic Longjing 43 under different treatments in Example 1 of the present invention;

[0036] Figure 6 It is a schematic diagram of the total phenol content of hydroponic Longjing 43 under different treatments in Example 1 of the present invention;

[0037] Figure 7 It is a schematic diagram of the flavonoid content of hydroponic Longjing 43 under different treatments in Example 1 of the present invention;

[0038] Figure 8 It is a schematic diagram of the anthocyanin content of hydroponic Longjing 43 under different treatments in Example 1 of the present invention;

[0039] Figure 9 It is a schematic diagram of the water-soluble fluorine content of hydroponic Zijuan under different treatments in Example 1 of the present invention;

[0040] Figure 10 It is a schematic diagram of the total phenol content of hydroponic Zijuan under different treatments in Example 1 of the present invention;

[0041] Figure 11 It is a schematic diagram of the flavonoid content of hydroponic Zijuan under different treatments in Example 1 of the present invention;

[0042] Figure 12 It is a schematic diagram of the anthocyanin content of hydroponic Zijuan under different treatments in Example 1 of the present invention;

[0043] Figure 13 It is a bar graph of the water-soluble fluorine content in the mature leaves of LJ43 tea seedlings treated with CK2, M1, M2, and M3 in Example 2 of the present invention;

[0044] Figure 14 It is a bar graph of the water-soluble fluorine content in the mature leaves of LJ43 tea seedlings treated with CK2, M2, M4, and M5 in Example 2 of the present invention;

[0045] Figure 15 It is a bar graph of the water-soluble fluorine content in the mature leaves of ZJ tea seedlings treated with CK2, M1, M2, and M3 in Example 2 of the present invention;

[0046] Figure 16 It is a bar graph of the water-soluble fluorine content in the mature leaves of ZJ tea seedlings treated with CK2, M2, M4, and M5 in Example 2 of the present invention. Detailed implementation mode

[0047] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description. Example 1

[0048] Indoor hydroponic experiment

[0049] In this example, tea tree seedlings with uniform growth were selected for hydroponic experiments. During the hydroponic process, melatonin treatment and / or fluoride stress treatment were carried out. The fluoride stress treatment was used to simulate the excessive fluoride content in the environment to study the role of melatonin in fluoride accumulation in tea trees.

[0050] The specific technical scheme of this indoor hydroponic experiment is as follows:

[0051] 1. Select two tea tree varieties, Zijuan (ZJ) and Longjing 43 (LJ43), with uniform growth; for each tea tree variety, 4 treatments are set, and 7 tea seedlings are set for each treatment; the hydroponic experiment is carried out according to the set treatment groups.

[0052] 1.1 Design of experimental groups

[0053] The 4 treatment groups are: CK1: blank control group; F1: 100 µmol / L melatonin (100 MT); F2: 5 mmol / L F (5 F); F3: 5 mmol / L F + 100 µmol / L melatonin (5 F + 100 MT).

[0054] Among them, MT represents melatonin treatment; F represents fluoride stress treatment; F + MT represents fluoride stress treatment while melatonin treatment.

[0055] 1.2 Melatonin treatment

[0056] For treatments F1 and F3, melatonin was sprayed on the leaves. For treatment F1 and CK1, distilled water was sprayed on the leaves until the leaves dripped. The concentration of melatonin sprayed was 100 µmol / L, the application frequency of melatonin was once a day, and the spraying time was after sunset.

[0057] Preparation of melatonin stock solution (0.2 mol / L): Accurately weigh 2.3228 g of melatonin powder, dissolve it in absolute ethanol, and then make up the volume to 50 mL in a volumetric flask with distilled water. Preparation of 100 µmol / L melatonin: Pipette 0.5 mL of the stock solution and make up the volume to 1 L.

[0058] 1.3 Fluoride stress treatment

[0059] Twenty-four hours after the first foliar spraying of melatonin, treatments F2 and F3 were subjected to fluorine stress treatment. For the fluorine stress treatment, the hydroponic treatment solution was replaced with a 5 mmol / L sodium fluoride treatment solution (tea seedling culture solution with a sodium fluoride concentration of 5 mmol / L), while for treatments F1 and CK1, the hydroponic treatment solution was replaced with a tea seedling culture solution with a sodium fluoride concentration of 0.

[0060] Preparation of sodium fluoride stock solution (0.5 mol / L): Accurately weigh 21 g of sodium fluoride, dissolve it with the tea seedling culture solution, and make up the volume to 1 L.

[0061] 5 mmol / L sodium fluoride treatment solution: Directly take out 50 mL from 5 L of the tea seedling culture solution, and then add an equal volume of the sodium fluoride stock solution. During the preparation process, adjust the pH of the treatment solution with NaOH and HCl to make the pH of the treatment solution 5.00 ± 0.05.

[0062] The frequency of replacing the sodium fluoride treatment solution was once every three days, and the treatment time was 10 days, with a total of 4 times of replacing the treatment solution.

[0063] On the 1st, 4th, 7th, and 10th days of fluorine treatment, at 10 am, a SPAD-502PLUS handheld chlorophyll content measuring instrument was used to evaluate the relative chlorophyll content of the current fresh leaves. For each treatment, 3 mature leaves at the same leaf position were selected for measurement. After 10 days of sodium fluoride treatment, the 3rd and 4th mature leaves were collected from the top bud downwards, rinsed thoroughly with deionized water, and freeze-dried for determining the fluorine content.

[0064] 2. Experimental data and analysis

[0065] 2.1 Phenotypic indicators

[0066] The comparison diagram of the phenotypes of tea seedlings of hydroponic Longjing 43 (LJ43) before and after treatment is as Figure 1 shown; the line graph of the relative content change of chlorophyll in mature leaves of hydroponic Longjing 43 (LJ43) on the 1st, 4th, 7th, and 10th days of treatment is as Figure 2 shown.

[0067] The comparison diagram of the phenotypes of tea seedlings of hydroponic Zijuan (ZJ) before and after treatment is as Figure 3 shown; the line graph of the relative content change of chlorophyll in mature leaves of hydroponic Zijuan (ZJ) on the 1st, 4th, 7th, and 10th days of treatment is as Figure 4 shown.

[0068] By observing Figure 1 it can be concluded that melatonin treatment can significantly improve the phenotypic status of LJ43 tea tree leaves under fluorine stress, reducing leaf chlorosis and wilting. Secondly, as Figure 2As shown in the figure, the determination of the relative chlorophyll content (SPAD) of tea tree leaves shows that with the increase of the treatment time, melatonin can effectively restore the SPAD value of tea tree leaves, making it reach or exceed the level before fluoride treatment, thereby improving the photosynthesis efficiency. This result was also verified in the ZJ tea seedlings in Figure 3 and Figure 4 , showing the same trend. In summary, exogenous addition of melatonin can promote the healthy growth of tea trees, especially suitable for tea tree cultivation in fluorine-containing soils or fluorine-polluted environments.

[0069] 2.2 Quality indicators

[0070] Reference for the quality indicators of hydroponic Longjing 43 under different treatments Figures 5 - 8 As shown in the figure, Figure 5 is the bar chart of the water-soluble fluorine content in leaves; Figure 6 is the bar chart of the total phenol content in leaves; Figure 7 is the bar chart of the flavonoid content in leaves; Figure 8 is the bar chart of the total phenol content in leaves.

[0071] Reference for the quality indicators of hydroponic Zijuan under different treatments Figures 9 - 12 As shown in the figure, Figure 9 is the bar chart of the water-soluble fluorine content in leaves; Figure 10 is the bar chart of the total phenol content in leaves; Figure 11 is the bar chart of the flavonoid content in leaves; Figure 12 is the bar chart of the total phenol content in leaves.

[0072] As Figure 5 and Figure 9 shown, the water-soluble fluorine content of tea trees treated with melatonin is lower than that of tea trees not treated with melatonin. Therefore, the bar charts of the water-soluble fluorine content concentration in mature leaves under different treatments further show that after melatonin treatment, the fluorine accumulation in mature leaves of LJ43 and ZJ tea trees is significantly reduced. This result indicates that melatonin shows a significant effect in inhibiting leaf fluorine accumulation, thereby effectively reducing the toxicity of fluorine to tea trees.

[0073] In addition, the present disclosure also measured other key tea quality indicators, such as Figures 5 - 8 , and Figures 9 - 12 shown, after melatonin treatment, the contents of total phenols, flavonoids and anthocyanins in tea leaves increased significantly. Total phenols, flavonoids and anthocyanins are important secondary metabolites in tea leaves, which not only endow tea leaves with unique flavors and colors, but also have strong antioxidant properties, which can improve the nutritional value and market competitiveness of tea leaves. These results indicate that melatonin can not only protect tea trees by reducing fluorine accumulation, but also improve the quality of tea leaves.

[0074] In summary, the present disclosure has broad application prospects, especially in the cultivation of tea trees in fluorine-containing soil or fluorine-polluted environments. By exogenously adding melatonin, the fluorine content in tea leaves can be effectively reduced while improving its quality, which helps to increase the market value of tea leaves and ensure the health and safety of consumers. In addition, as a natural plant regulator, melatonin has the advantages of low toxicity and environmental friendliness, further enhancing its application potential in modern agriculture. Therefore, the present disclosure can not only meet the market demand for high-quality and low-fluorine tea leaves, but also provide an effective solution for the development of the tea industry in fluorine-polluted areas. Example 2

[0075] Field experiment

[0076] Based on the good results obtained in the indoor hydroponic experiment, the inventors of the present disclosure further carried out field experiments to verify and optimize its actual application effects.

[0077] The specific technical scheme of this field experiment is as follows:

[0078] 1. Select the Xiabao Tea Garden in Shaoxing, Zhejiang Province as the experimental site, and the tea trees are managed according to the same mode. Select two tea tree varieties, Zijuan (ZJ) and Longjing 43 (LJ43), with uniform growth, and set 5 treatments for each tea tree variety. Select two adjacent tea trees for each treatment.

[0079] 1.1 Experimental group design

[0080] The 5 treatment groups are: CK2: blank control group; M1: 100 µmol / L melatonin (100 MT); M2: 5 mmol / L F (5 F); M3: 5 mmol / L F + 100 µmol / L melatonin (5 F + 100 MT); M4: 5 mmol / L F + 200 µmol / L melatonin (5 F + 200 MT); M5: 200 µmol / L melatonin (200 MT);

[0081] Among them, MT represents melatonin treatment; F represents fluorine stress treatment; F + MT represents fluorine stress treatment while melatonin treatment.

[0082] 1.2 Melatonin treatment

[0083] The concentration of melatonin applied in the experimental group is 100 µmol / L or 200 µmol / L, the application frequency of melatonin is once a week, and the spraying time is after sunset. Treatments M1, M3, M4, and M5 are sprayed on the leaf surface with different concentrations of melatonin, and treatments M2 and CK2 are sprayed on the leaf surface with distilled water until the leaf surface drips.

[0084] Preparation of melatonin stock solution (0.2 mol / L): Weigh accurately 2.3228 g of melatonin powder, dissolve it in absolute ethanol, and then make up the volume to 50 mL in a volumetric flask with distilled water.

[0085] Preparation of 100 µmol / L melatonin solution: Pipette 0.5 mL of the stock solution and make up the volume to 1 L; Preparation of 200 µmol / L melatonin solution: Pipette 1 mL of the stock solution and make up the volume to 1 L.

[0086] 1.3 Fluoride stress treatment

[0087] Twenty-four hours after the first foliar spraying of melatonin, treatments M2, M3, and M4 were subjected to sodium fluoride treatment; for the fluoride stress treatment, the concentration used was 0 or 5 mmol / L (i.e., treatments M2, M3, and M4 used sodium fluoride at a concentration of 5 mmol / L, and treatments M1, M5, and CK2 used distilled water).

[0088] Preparation of sodium fluoride stock solution (0.5 mol / L): Weigh accurately 21 g of sodium fluoride and make up the volume to 1 L with pure water.

[0089] Preparation of 5 mmol / L sodium fluoride solution: Take 100 ml of the stock solution and make up the volume to 10 L.

[0090] For treatments M2, M3, and M4, 5 mmol / L sodium fluoride solution was used to irrigate the roots of tea plants, and for treatments M1, M5, and CK2, distilled water was used to irrigate the roots of tea plants. The degree of irrigation was such that the soil 20 cm below the ground surface of the tea plant roots was completely wet, and the irrigation frequency was once a week. The treatment time was two weeks (mainly based on the emergence of one bud and two leaves).

[0091] After the treatment was completed (after waiting for the emergence of one bud and two leaves), the top bud and the third and fourth mature leaves downwards were collected. After rinsing them thoroughly with deionized water, they were labeled and placed in a self-sealing bag and stored in a refrigerator. After being brought back to the laboratory, they were used for the determination of fluoride content.

[0092] 2. Experimental data and analysis

[0093] In this field experiment, a new treatment group with a melatonin concentration of 200 μM was added to further evaluate its effect on fluoride accumulation and growth status of tea plants. At the same time, considering the spraying cost, the spraying frequency of melatonin was appropriately reduced.

[0094] The experimental results are as Figures 13 - 16 shown. By adjusting the concentration and spraying frequency of melatonin, it is still possible to effectively control the fluoride accumulation in tea plant leaves, and while reducing the cost, good experimental results can still be maintained. This indicates that under field conditions, reasonably adjusting the application strategy of melatonin can achieve the expected fluoride reduction effect and has the feasibility of practical application.

[0095] Conclusion:

[0096] Through double verification of indoor and field experiments, the phenotypic improvement effect of exogenous melatonin on tea plants under fluoride stress and its role in reducing fluoride accumulation in tea leaves were determined. The results of the indoor experiment showed that the application of melatonin significantly reduced the yellowing and wilting of tea leaves, decreased the fluoride accumulation in the leaves, increased the SPAD value of tea leaves, and improved the photosynthesis efficiency of tea plants.

[0097] It was detected that whether from the phenotypic observation of the leaves or through the determination of the SPAD value, the application of melatonin not only had no negative impact on the cell membrane permeability, but may also promote the recovery of photosynthesis and cell metabolism to some extent. Therefore, this scheme will not affect the cell wall and membrane properties of tea leaves, showing obvious advantages in improving the growth status of tea plants and enhancing the tea quality.

[0098] To further verify the effect of melatonin, a treatment group with a melatonin concentration of 200 μM was added in the field experiment, and the spraying frequency was adjusted to optimize the application cost. The experimental results showed that even when the spraying frequency was reduced, the increased melatonin concentration could still effectively control the fluoride accumulation in tea leaves and maintain a good growth status.

[0099] Based on the results of the indoor and field experiments, the present disclosure provides an effective method for using melatonin, which is applicable to the cultivation and management of tea plants under fluoride stress. By reasonably adjusting the application concentration and frequency of melatonin, a significant reduction in fluoride accumulation can be achieved and the healthy growth of tea plants can be ensured, providing a scientific basis for tea garden management. The application amount of this method is set to spray the melatonin solution onto the leaf surface until it drips. The preferred range of the melatonin concentration for field application is 100 - 200 μM.

[0100] It should be particularly noted that after rainfall, the spraying frequency should be appropriately increased to ensure the effectiveness of melatonin.

[0101] In addition, it should be noted that melatonin can also be applied to the tea garden through irrigation water, but this method requires a high cost. On the one hand, the adsorption of melatonin in the soil and the complex interactions among other ions in the soil will reduce the effective absorption rate of melatonin by tea plants and affect its expected physiological regulation effect. On the other hand, the diffusion rate of melatonin in the soil is slow, which is not conducive to promptly alleviating the fluoride stress effect of tea plants. Therefore, foliar spraying of melatonin can directly act on tea leaves, not only accelerating the absorption speed, but also avoiding the problems of soil adsorption and ion interference, significantly improving the utilization efficiency of melatonin. In addition, foliar spraying is easy to operate, the dosage is controllable, and the cost is lower, which is suitable for large-scale application in tea gardens.

[0102] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in the relevant field. Any changes and variations made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. The use of melatonin in improving plant resistance to fluorine stress, characterized in that: The plant is a plant of the family Theaceae; When applied, a melatonin aqueous solution or a preparation containing melatonin is applied to plants poisoned by fluorine stress, and the concentration of the applied melatonin is 100-200 µmol / L.

2. The use according to claim 1, characterized in that: The Theaceae plant is Zijuan and / or Longjing 43.

3. The use according to claim 1, characterized in that: The method of improving the resistance of plants to fluorine stress also includes: improving the SPAD value of plant leaves under fluorine stress, and improving the content of total phenols, flavonoids and anthocyanins in plant leaves under fluorine stress.

4. A method for improving plant resistance to fluorine stress, characterized in that: include: applying a melatonin aqueous solution or a preparation containing melatonin to plants poisoned by fluorine stress; In the melatonin aqueous solution or the preparation containing melatonin, the concentration of melatonin is 100-200 µmol / L; The plant is a plant of the Theaceae family.

5. The method according to claim 4, characterized in that The application method is foliar spray.

6. The method according to claim 5, characterized in that: The plants are planted hydroponically, with a spraying frequency of once a day after sunset, and a spraying degree based on water dripping from the leaves.

7. The method according to claim 5, characterized in that: The plants are planted in the field, sprayed once a week after sunset, and sprayed to the extent of dripping on the leaves.

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