How to grow plants

Abstract

To provide a plant growth method for obtaining a plant with a low content of harmful substances in hydroponics.SOLUTION: The present invention relates to a method for growing a plant in hydroponics, the method including the step of supplying the plant with a culture medium containing glutathione, thereby reducing the content of nitrate nitrogen in the plant.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for growing plants hydroponically and to plants grown hydroponically. [Background technology]

[0002] Some of the cultivation of mainly commercial plants such as vegetables and flowers is carried out indoors where they are less susceptible to the effects of the natural environment. Generally, indoor cultivation is carried out at high density, and hydroponic cultivation using a liquid medium (culture solution) without using solid media such as soil is widely practiced. Hydroponic cultivation has the advantages of being easy to prevent plant diseases and pollution, easy to control growth, and allows year-round production.

[0003] Glutathione is a peptide composed of three amino acids, L-cysteine, L-glutamic acid, and glycine, and is present not only in the human body but also in many other living organisms, including other animals, plants, and microorganisms.It is an important compound for the body, playing a role in eliminating reactive oxygen species, detoxifying, and metabolizing amino acids.

[0004] Glutathione exists in the body in one of two forms: reduced glutathione (N-(N-γ-L-glutamyl-L-cysteinyl)glycine, hereafter also referred to as "GSH"), in which the thiol group of the L-cysteine ​​residue is reduced to form SH, and oxidized glutathione (hereafter also referred to as "GSSG"), in which the thiol group of the L-cysteine ​​residue of two molecules of GSH is oxidized to form a disulfide bond between the two glutathione molecules.

[0005] Glutathione is known to be useful in the fields of fertilizers, pharmaceuticals, cosmetics, etc. Patent Document 1 discloses that glutathione (particularly GSSG) is useful as a plant growth regulator that improves the harvest index of plants, such as by increasing the number of seeds and flowers of plants.

[0006] Patent Document 2 discloses a method for producing leafy vegetables in which the leafy vegetables are hydroponically cultivated under LED irradiation by simultaneously irradiating the vegetables with green light and purple light to reduce nitrate ions and increase ascorbic acid. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2008 / 072602 [Patent Document 2] Patent Publication No. 2018-113934 [Non-patent literature]

[0008] [Non-Patent Document 1] Tamura, Y. et al., Metabolomic evaluation of the quality of leaf lettuce grown in practical plant factory to capture metabolite signature LEDs, Frontiers in plant science, 9: 665, (2018) Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, hydroponic cultivation has advantages not found in conventional soil cultivation. On the other hand, in soil cultivation, which has been widely practiced since ancient times, much knowledge has been obtained about the conditions for growing plants of desired quality. Non-Patent Document 1 reports that when the same type of plant (vegetable) is grown in soil and hydroponic cultivation, its appearance, taste, concentration of functional substances, etc. are different. Therefore, when growing plants in hydroponic cultivation, even if the fertilizer composition, cultivation temperature, etc. are set to the same conditions as the optimal conditions for soil cultivation, the problem remains that plants of the desired quality are not necessarily obtained.

[0010] Edible vegetables such as leafy vegetables are desired to be rich in functional ingredients such as vitamins, minerals, polyphenols, and amino acids. On the other hand, it is desired to have a lower content of harmful substances such as nitrate nitrogen. However, when obtaining such useful plants, the wealth of knowledge gained from soil cultivation cannot be directly applied to hydroponic cultivation. Therefore, it is desired to clarify suitable cultivation conditions for obtaining useful plants in hydroponic cultivation.

[0011] The present invention aims to provide a method for growing plants in hydroponic cultivation to obtain plants with low harmful substance content. It also aims to provide a hydroponic cultivation device, a hydroponic cultivation system, and a harmful substance reduction promoter to obtain plants with high harmful substance content. [Means for solving the problem]

[0012] As a result of extensive research, the inventors discovered that supplying a culture solution containing glutathione to plants in hydroponic cultivation reduces the content of nitrate nitrogen, a harmful substance, and thus completed the present invention. That is, according to the present specification, the following invention is provided.

[0013] (1) A method for hydroponically cultivating a plant, comprising a step of supplying a culture solution containing glutathione to the plant, thereby reducing the nitrate nitrogen content of the plant. (2) The method of (1), further comprising the step of irradiating the plant with violet light. (3) The method according to (2), wherein the purple light has a wavelength of 405 nm. (4) The method according to (2) or (3), wherein the purple light is irradiated by artificial light. (5) The method according to (2) or (3), wherein the purple light is irradiated as sunlight. (6) Any of the methods (1) to (5), wherein the glutathione is oxidized glutathione. (7) The method according to any one of (1) to (6), wherein the culture medium has a glutathione content of 1 to 300 ppm. (8) Any of the methods (1) to (7), wherein a culture solution containing glutathione is supplied during the period from after planting of the plant until harvest. (9) The method according to any one of (1) to (8), wherein a culture solution containing glutathione is supplied multiple times. (10) The method according to any one of (1) to (9), wherein the plant is a leafy vegetable. (11) A plant produced by cultivating it using any of the methods described in (1) to (10). (12) Plant nitrates, including glutathione condition Promotes reduction of nitrogen content. (13) The agent according to (12) for addition to a culture solution composition for hydroponic culture. (14) The agent according to (12) for addition to a culture solution composition for hydroponic cultivation under irradiation with purple light. Effect of the Invention

[0014] According to the present invention, it is possible to provide a method for growing plants in hydroponic cultivation to obtain plants with a low content of harmful substances. Also, according to the present invention, it is possible to provide a hydroponic cultivation device, a hydroponic cultivation system, and a harmful substance reduction promoter for obtaining plants with a low content of harmful substances. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [1] How to grow plants hydroponically The method of the present invention is a method for growing a plant hydroponically, which comprises a step of supplying a culture solution containing glutathione to the plant, thereby reducing the nitrate nitrogen content of the plant.

[0016] [1-1] Configuration of the method of the present invention In the present specification, the term "plant" is not particularly limited and includes any plant that can be artificially cultivated. The method of the present invention is particularly suitable for hydroponic cultivation of commercial plants, particularly edible plants such as vegetables, fruits, and seaweed. Furthermore, the method of the present invention is more suitable for cultivation of leafy vegetables.

[0017] As used herein, "leafy vegetables" refers to vegetables whose leaves and stems are primarily edible, and examples include, but are not limited to, lettuce, mizuna, spinach, chrysanthemum, komatsuna, bok choy, cabbage, Chinese cabbage, leeks, mitsuba, shiso, mustard greens, kale, and herbs (lucol, basil, etc.).

[0018] In this specification, "nitrate nitrogen" refers to nitrogen that exists in the form of nitrates and nitrate ions. Nitrate nitrogen is said to cause the bitterness and astringency of vegetables, and if contained in large amounts, it impairs the taste of vegetables. In addition, if humans ingest a large amount of nitrate nitrogen, it is reduced to nitrite nitrogen by intestinal bacteria in the body, and if this is absorbed into the body, it may cause oxygen deficiency such as methemoglobinemia.

[0019] The plant obtained by the method of the present invention preferably has a lower nitrate nitrogen content than a plant obtained without the method of the present invention. For example, when the method of the present invention is applied to lettuce, the nitrate nitrogen content of the obtained lettuce is preferably 300 mg or less, particularly 200 mg or less per 100 g fresh weight. When the method of the present invention is applied to komatsuna, the nitrate nitrogen content of the obtained komatsuna is preferably 700 mg or less, particularly 600 mg or less.

[0020] The nitrate nitrogen content of the plant obtained by the method of the present invention is reduced compared to the plant grown without the method of the present invention. Specifically, the nitrate nitrogen content of the plant of the present invention is, for example, preferably 0.9 times (90%) or less, more preferably 0.7 times (70%) or less, and even more preferably 0.5 times (50%) or less, compared to the plant grown without the method of the present invention.

[0021] Leafy vegetables, seaweed, etc. are known to contain folic acid. In the narrow sense, folic acid refers to putenoylmonoglutamic acid, which rarely occurs in nature. In this specification, "folic acid" is defined to include not only folic acid in the narrow sense, but also multiple derivatives of putenoylmonoglutamic acid that are generally present in foods. Folic acid is a type of vitamin B group, and is a water-soluble vitamin that is also called vitamin M, vitamin B9, and buteroylglutamic acid. Folic acid is a vitamin B 12 Folic acid is an ingredient that plays an important role in the development of the human body, promoting the production of red blood cells together with folic acid, promoting the biosynthesis of nucleic acids and proteins to assist in the production and regeneration of cells, etc. Folic acid is an ingredient that is particularly important for fetuses, and its intake is recommended for pregnant women. According to the Ministry of Health, Labor and Welfare's "Dietary Reference Intakes for Japanese" (2020 edition), the recommended daily intake of folic acid is 240 μg for adults, and an additional 240 μg is recommended for pregnant women. Meanwhile, folic acid is a water-soluble vitamin, and while the health damage caused by excessive intake is very limited, it is recommended that the daily intake be 1000 μg or less.

[0022] The plant obtained by the method of the present invention preferably has a higher folic acid content than the plant obtained by other methods. For example, when the method of the present invention is applied to lettuce as a plant, the folic acid content of the obtained lettuce is preferably 35 μg or more, particularly 40 μg or more, and 500 μg or less, particularly 250 μg or less per 100 g of fresh weight. When the method of the present invention is applied to komatsuna, the folic acid content of the obtained komatsuna is preferably 90 μg or more, particularly 95 μg or more, and 500 μg or less, particularly 250 μg or less per 100 g of fresh weight.

[0023] The plant obtained by the method of the present invention preferably has an improved folic acid content compared to a plant grown without the method of the present invention. Specifically, the folic acid content in the plant of the present invention is, for example, preferably 1.05 times (5% increase) or more, more preferably 1.1 times (10% increase) or more, more preferably 1.2 times (20% increase) or more, more preferably 1.25 times (25% increase) or more, and even more preferably 1.5 times (50% increase) or more, compared to a plant grown without the method of the present invention.

[0024] In this specification, "polyphenol" refers to a component having a structure containing two or more phenolic hydroxyl groups. Polyphenols contained in edible plants such as vegetables include apiin, anthocyanin, chlorogenic acid, lactucopycoclin, quercetin, rutin, isoflavone, etc. It has been reported that polyphenols have a strong antioxidant effect, and have carcinogenesis suppression effects, anti-aging effects, capillary protection effects, anti-allergic effects, etc.

[0025] The plant obtained by the method of the present invention preferably has a higher polyphenol content than a plant obtained without the method of the present invention. For example, when the method of the present invention is applied to lettuce, the polyphenol content of the obtained lettuce is preferably 40 mg or more, particularly 50 mg or more. Among lettuces, lettuce varieties having red to reddish brown leaves, particularly red lettuce, are known to have a high polyphenol content. When the method of the present invention is applied to red lettuce, the polyphenol content of the obtained red lettuce is preferably 50 mg or more, particularly 80 mg or more per 100 g fresh weight. When the method of the present invention is applied to Japanese radish, the polyphenol content of the obtained Japanese radish is preferably 60 mg or more, particularly 70 mg or more per 100 g fresh weight.

[0026] The plant obtained by the method of the present invention preferably has an improved polyphenol content compared to a plant grown without the method of the present invention. Specifically, the polyphenol content in the plant of the present invention is, for example, more preferably 1.1 times (10% increase) or more, more preferably 1.2 times (20% increase) or more, more preferably 1.25 times (25% increase) or more, and even more preferably 1.5 times (50% increase) or more compared to a plant grown without the method of the present invention.

[0027] In the present specification, glutathione may be oxidized glutathione (GSSG), reduced glutathione (GSH), or a mixture of GSSG and GSH. Each form of glutathione can be produced, for example, by the method described in International Publication No. 2016 / 017631. GSSG is a substance formed by binding two molecules of GSH (N-(N-γ-L-glutamyl-L-cysteinyl)glycine) via a disulfide bond, and the free form is represented by the following formula. [ka]

[0028] In the present specification, GSSG may include various forms of GSSG, such as a free form that is not bound to other substances and is not ionized, a salt formed between GSSG and an acid or base, a hydrate thereof, a mixture thereof, etc. GSSG has a characteristic structure in which two oligopeptide chains with n being 3 and consisting of the same amino acid sequence are linked by a disulfide bond via the side chain of each cysteine ​​residue.

[0029] The salt of GSSG is not particularly limited as long as it is one or more salts acceptable for the purpose, such as ammonium salt, calcium salt, magnesium salt, sodium salt, lithium salt, etc.

[0030] GSH is also referred to as N-(N-γ-L-glutamyl-L-cysteinyl)glycine. In this specification, GSH may include various forms of GSH, such as a free form that is not bound to other substances and is not ionized, a salt formed with GSH and an acid or base, a hydrate thereof, and a mixture thereof.

[0031] The salt of GSH is not particularly limited as long as it is one or more salts acceptable for the purpose, such as ammonium salt, calcium salt, magnesium salt, sodium salt, lithium salt, etc.

[0032] In the method of the present invention, glutathione preferably contains GSSG. The mass ratio of GSSG to glutathione is preferably 70% or more, 80% or more, 90% or more, 95% or more, 98% or more, or 100%.

[0033] In this specification, the term "culture solution" refers to a liquid used in hydroponic cultivation and supplied to the roots of plants. Specifically, it refers to a commercially available liquid fertilizer (e.g., Hyponica (registered trademark) liquid fertilizer (Kyowa Co., Ltd.)) containing nutrients essential for plant growth such as nitrogen, phosphorus, and potassium, diluted with water. The culture solution used in the method of the present invention further contains glutathione. The lower limit of the amount of glutathione contained in the culture solution is preferably 0.5 ppm or more in total for all forms, and more preferably 1 ppm or more. The upper limit of the amount of glutathione is preferably 300 ppm or less in total for all forms, and more preferably 100 ppm or less, and even more preferably 20 ppm or less. The amount of glutathione referred to here refers to the amount converted into free GSSG.

[0034] In this specification, "purple light" refers to light having a wavelength of 405 nm. In the present invention, the light irradiated to the plant may be either artificial light or natural light (sunlight) as long as it contains purple light. "Artificial light" here refers to light other than natural light in general, and incandescent lamps, fluorescent lamps, LEDs, etc. can all be used as light sources. The light irradiated to the plant is light having a photosynthetic photon flux density (PPFD) of 100 μmol / m 2 s or more, especially 150 μmol / m2 s or more. The embodiment in which artificial light is used will be described below.

[0035] In indoor cultivation of plants, artificial light such as fluorescent lamps and LEDs is usually used. In outdoor greenhouse cultivation, artificial light may be used to supplement sunlight. As the LED, one adjusted to a broad wavelength spectrum suitable for plant cultivation, or an RGB independent dimming LED light source capable of controlling red, blue, and green light can be suitably used. In the method of the present invention, in addition to these lights, it is preferable to use a purple LED light source that emits purple light having a wavelength of about 380 to 420 nm (peak wavelength: about 405 nm) in combination. This purple light of 405 nm is a light source for inducing photomorphogenic stress. Such an LED light source is arranged so that light is irradiated to the plants in each cultivation tank. Here, photomorphogenesis will be briefly explained. Photomorphogenesis is a type of photoresponse of plants, and refers to the control of the morphology of plants, such as growth differentiation, by light. In higher plants, a type mediated by phytochrome, a type of photoreceptor, and a type mediated by (ultraviolet-) blue receptor are known. In general, photomorphogenesis in blue light responses (blue light response, ultraviolet-blue light response, ultraviolet-blue light response) is known to involve inhibition of hypocotyl elongation, cotyledon expansion, cotyledon opening and closing, and pigment biosynthesis.

[0036] Hydroponic cultivation methods are broadly divided into two types: the deep flow technique (DFT) and the nutrient film technique (NFT). In the DFT method, the cultivation tank is kept horizontal, a relatively large amount of nutrient solution is stored, seedlings are planted with a floating planting panel, and the nutrient solution is circulated to cultivate the plants. The DFT method is characterized by maintaining the whole or part of the plant's roots immersed in the nutrient solution. Since the whole roots are immersed in a large amount of nutrient solution, it is necessary to pump air into the nutrient solution using an air pump or the like to prevent root rot due to lack of oxygen. In the NFT method, the cultivation tank is fixed with a gentle slope and the nutrient solution is allowed to flow down in small amounts. Since the nutrient solution is circulated in a thin layer, it has the advantage that the oxygen in the air dissolves in the nutrient solution in large amounts, making it easier for the roots of the plants to take up a lot of oxygen, but it also has issues such as the need to keep the nutrient solution flowing constantly and the nutrient solution's concentration and composition being prone to change. The method of the present invention may be carried out by either the DFT method or the NFT method.

[0037] [1-2] Each step of the method of the present invention The method of the present invention includes a step of supplying a culture solution containing glutathione to a plant, and is not particularly limited in detail in other steps as long as the method can reduce the nitrate nitrogen content, but preferred embodiments of each step of the method of the present invention are shown below. As a preferred embodiment of the method of the present invention, an embodiment in which the "plant" is a vegetable will be described below, but it is not intended that the method of the present invention be limited to a method for growing vegetables.

[0038] One embodiment of the method of the present invention may include (a) a seedling raising step of growing vegetable seeds or the like into seedlings, (b) a planting step of transplanting the raised seedlings into a hydroponic cultivation device, (c) a step of supplying a culture solution to the roots of the planted vegetables, and (d) a step of irradiating purple light to the leaves of the planted vegetables.

[0039] (a) Seedling raising process The method of the present invention may include a seedling raising step. In this specification, "seeding raising" refers to a step of raising a plant seed or bulb until it becomes a seedling. Hereinafter, as a preferred embodiment of the present invention, a step of raising and raising a plant seed is shown, but the present invention is not limited to seed raising. Usually, seeds are not raised in a main cultivation environment from the beginning, but are raised in a different environment until they germinate and become seedlings. Seeding may be performed in soil, or may be performed in a porous and water-absorbent substrate such as urethane foam, sponge, or sea sponge that has been moistened.

[0040] In the seedling raising process, the means for supplying water include bottom irrigation, spraying, etc., but bottom irrigation is more preferable. The water to be supplied may contain glutathione, nitrogen, phosphorus, potassium, etc.

[0041] (b) Planting process The seedlings obtained in the seedling raising step are transplanted (planted) into a hydroponic cultivation system, specifically, into a planting panel on a cultivation tank. When a substrate is used for raising the seedlings, the seedlings may be planted with the substrate attached to their roots. In either case, the seedlings need to be planted so that their roots are kept in contact with the culture solution.

[0042] (c) Culture solution supply process The plant is grown until it can be harvested. During the growing period, the roots of the plant are kept in contact with the culture solution, but the culture solution is preferably circulated or periodically replaced to prevent the proliferation of bacteria and the like. The culture solution may always contain glutathione, or may alternate between one containing glutathione and one not. Alternatively, a method of adding glutathione to a culture solution tank or a concentrated stock solution tank once or multiple times in a system in which a normal culture solution not containing glutathione is perfused may be used. The time when glutathione is supplied to the plant is not particularly limited, and as described above, glutathione may be supplied during the seedling raising process, but it is particularly preferable to supply glutathione during the period from planting to harvest. Although it depends on the cultivation period, it is preferable that glutathione is added to the culture solution multiple times, once every 3 days to 2 weeks, preferably once every 7 to 10 days, after planting. In this case, the amount of glutathione added to the culture solution is preferably such that the glutathione concentration in the culture solution supplied to the plant is 0.5 to 300 ppm, particularly 1 to 100 ppm, and further preferably 1 to 20 ppm. The number of times that glutathione is added to the culture solution is preferably multiple times, particularly 2 to 20 times. The form of glutathione added to the culture solution is not particularly limited, and it may be in a liquid form such as an aqueous solution, or in a solid form such as powder or granules.

[0043] (d) Violet light irradiation process The method of the present invention comprises a step of irradiating the leaves of a plant with violet light, particularly light with a wavelength of 405 nm. The time of irradiating the leaves of the plant with violet light is not particularly limited, and may be throughout the entire growing period from the seedling period to the main cultivation period, but it is preferable that the violet light is irradiated during the period from planting to harvesting, particularly during the period during which a culture solution containing glutathione is supplied. The light irradiated to the plant may be artificial light or natural light, as long as it contains violet light.

[0044] In indoor cultivation of plants, artificial light such as fluorescent lamps and LEDs is used. In the method of the present invention, it is preferable to use a purple LED light source in addition to conventionally used artificial light such as fluorescent lamps and LEDs. The light irradiation time per day is not particularly limited, and may be all day, but may be repeatedly turned on and off according to the outdoor sunlight hours. In particular, irradiation from the purple LED light source may be all day.

[0045] [2] Plants grown by the method of the present invention The plant of the present invention is characterized in that it is grown by the method described in the above item [1] Method for growing a plant by hydroponic cultivation. Specifically, the plant is grown by hydroponic cultivation while being supplied with a culture solution containing glutathione.

[0046] The plant of the present invention has a lower nitrate nitrogen content than plants grown without the method of the present invention.When the plant of the present invention is lettuce, the nitrate nitrogen content of the obtained lettuce is preferably 300mg or less, particularly 200mg or less per 100g fresh weight.When the plant of the present invention is Komatsuna, the nitrate nitrogen content is preferably 700mg or less, particularly 600mg or less.

[0047] The plant of the present invention has a reduced nitrate nitrogen content compared to a plant grown without the method of the present invention. Specifically, the nitrate nitrogen content in the plant of the present invention is, for example, preferably 0.9 times (90%) or less, more preferably 0.7 times (70%) or less, and even more preferably 0.5 times (50%) or less, compared to a plant grown without the method of the present invention.

[0048] The plant of the present invention preferably has a high folic acid content compared to plants grown without the method of the present invention. When the plant of the present invention is lettuce, the folic acid content is preferably 35 μg or more, particularly 40 μg or more, and 500 μg or less, particularly 250 μg or less per 100 g of fresh weight. When the plant of the present invention is "Komatsuna", the folic acid content is preferably 90 μg or more, particularly 95 μg or more, and 500 μg or less, particularly 250 μg or less per 100 g of fresh weight.

[0049] The plant of the present invention preferably has an improved folic acid content compared to a plant grown without the method of the present invention. Specifically, the folic acid content in the plant of the present invention is, for example, preferably 1.05 times (5% increase) or more, more preferably 1.1 times (10% increase) or more, more preferably 1.2 times (20% increase) or more, more preferably 1.25 times (25% increase) or more, and more preferably 1.5 times (50% increase) or more compared to a plant grown without the method of the present invention. On It is even more preferable that there is.

[0050] The plant of the present invention preferably has a high polyphenol content compared to plants grown without the method of the present invention.When the plant of the present invention is lettuce, the polyphenol content is 40mg or more, preferably 50mg or more.In particular, when the plant of the present invention is red lettuce, the polyphenol content is preferably 50mg or more, particularly 80mg or more per 100g fresh weight.When the plant of the present invention is komatsuna, the polyphenol content is preferably 60mg or more, particularly 70mg or more per 100g fresh weight.

[0051] The plant of the present invention preferably has an improved polyphenol content compared to a plant grown without the method of the present invention. Specifically, the polyphenol content in the plant of the present invention is, for example, more preferably 1.1 times (10% increase) or more, more preferably 1.2 times (20% increase) or more, more preferably 1.25 times (25% increase) or more, and even more preferably 1.5 times (50% increase) or more compared to a plant grown without the method of the present invention.

[0052] Unless otherwise specified above, the cultivation method and other detailed conditions for the plant of the present invention are the same as those described in the section [1] Method for growing a plant by hydroponic cultivation.

[0053] [3] Agents for reducing the nitrate nitrogen content in plants The present invention relates to a method for promoting the reduction of nitrate nitrogen content in plants, the method comprising the steps of:

[0054] The reduction promoter of the present invention may be glutathione itself or may be in the form of a glutathione-containing composition combined with other components, so long as it contains glutathione and is used to supply glutathione to a plant to reduce the nitrate nitrogen content of the plant.

[0055] The reduction promoter of the present invention is preferably used to make the culture solution for hydroponic cultivation contain glutathione. The reduction promoter of the present invention may be the culture solution itself containing glutathione. When the reduction promoter of the present invention is the culture solution itself containing glutathione, the concentration of glutathione in the culture solution is preferably 0.5 to 300 ppm, particularly 1 to 100 ppm, and further preferably 1 to 20 ppm.

[0056] The decline promoter of the present invention may be an additive added to a culture solution for hydroponic culture. The decline promoter as an additive may be in the form of an aqueous solution or a solid (granules, powder, etc.). When the additive is an aqueous solution, it may contain components such as a surfactant (linear alkylbenzene sulfonate, etc.), a dispersion stabilizer (carboxymethylcellulose, its salt, etc.), a thickener, and an antioxidant, in addition to glutathione and water. The glutathione concentration in the liquid is not particularly limited, but when added to a culture solution, the final concentration of glutathione is preferably 0.5 to 300 ppm, particularly 1 to 100 ppm, and further preferably 1 to 20 ppm. When the additive is a solid, it may contain components such as a surfactant (linear alkylbenzene sulfonate, alkylnaphthalene sulfonate, lauryl sulfate, castor oil potassium soap, etc.), a dispersion stabilizer (carboxymethylcellulose, its salt, etc.), an excipient (lactose, etc.), a disintegrant, a thickener, and an antioxidant. The glutathione concentration in the solid is not particularly limited, but when added to a culture medium, the final concentration of glutathione is preferably 0.5 to 300 ppm, particularly preferably 1 to 100 ppm, and further preferably 1 to 20 ppm.

[0057] When the agent for promoting plant growth of the present invention is an additive and is a glutathione-containing composition, it may further contain other components beneficial to plants in addition to glutathione, such as one or more fertilizer components selected from nitrogen, phosphoric acid, and potassium.

[0058] When the reduction promoter of the present invention is an additive and a glutathione-containing composition, the method for producing it is not particularly limited, and it can be produced by mixing the respective components, or if it is a solid composition, by carrying out operations such as grinding, granulation, drying, etc. as necessary, and if it is a liquid composition, by carrying out operations such as stirring, emulsification dispersion, etc. as necessary.

[0059] The reduction promoter of the present invention is preferably used in the method of the present invention. Specifically, it is preferably a reduction promoter for supplying a culture solution containing glutathione to a plant when the plant is grown in hydroponics. The reduction promoter of the present invention may further be a reduction promoter for supplying a culture solution containing glutathione to a plant when the plant is grown in hydroponics by irradiating the plant with purple light.

[0060] Unless otherwise specified above, the type of plant to be cultivated, the composition of the culture solution used, and other detailed conditions for the decline promoter of the present invention are the same as those described in the section [1] Method for cultivating plants hydroponically. EXAMPLES

[0061] The present invention will now be described with reference to specific examples, which, however, are not intended to limit the scope of the present invention.

[0062] <Test Example 1: Lettuce cultivation under sunlight I> The test was conducted using an NFT-type hydroponic cultivation facility in a solar-powered vinyl greenhouse. Seeds of leaf lettuce "Viva Verdi" were sown on a urethane mat that had absorbed sufficient water, and the seedlings were raised for three weeks. Seedlings with uniform growth were selected and planted in the cultivation facility. The culture solution was made using a commercially available hydroponic fertilizer (containing nitrogen, phosphorus, potassium, etc.), and the pH and electrical conductivity (EC) were monitored and adjusted once a week. Oxidized glutathione was added to the culture solution tank immediately after planting, 10 days after planting, and 20 days after planting to adjust the GSSG concentration of the culture solution in the treatment area (T area) to 15 ppm (free GSSG equivalent concentration is 13.4 ppm). 24 days after planting, the test plants were harvested, and the contents of folic acid, total polyphenols, and nitrate nitrogen per 100 g of fresh weight were measured. The contents of folic acid, total polyphenols, and nitrate nitrogen were measured by microbiological quantification, total polyphenols by the Folin-Ciocalteu method, and nitrate nitrogen by high performance liquid chromatography, referring to the "Analysis Manual for the 2015 Edition (7th Revised) of the Standard Tables of Food Composition in Japan" published by the Ministry of Education, Culture, Sports, Science and Technology. The polyphenol content was calculated as the (+)-catechin content.

[0063] Table 1 shows the contents of folic acid, total polyphenols, and nitrate nitrogen per 100g fresh weight of harvested lettuce in the treatment area (T area) where GSSG was supplied after planting, and the control area (C area) where GSSG was not supplied. Compared to the lettuce in the C area, the lettuce in the T area had a higher folic acid content and a lower nitrate nitrogen content.

[0064] [Table 1]

[0065] Table 1 shows that by adding glutathione to the culture solution during hydroponic cultivation under sunlight, the folic acid content of lettuce can be improved and the nitrate nitrogen content can be reduced.

[0066] <Test Example 2: Lettuce cultivation under sunlight II> Leaf lettuce "Frill Ice" was cultivated under the same cultivation conditions as those described in Test Example 1. In the treatment area (T1 area), a culture solution with a GSSG concentration of 10 ppm (free GSSG equivalent concentration 9.3 ppm) was bottom-watered on the 3rd and 12th days after sowing during seedling raising. In the treatment area (T2 area), oxidized glutathione was added to the culture solution tank immediately after planting, 7 days, 14 days, 21 days, 28 days, and 35 days after planting to adjust the GSSG concentration of the culture solution to 10 ppm (free GSSG equivalent concentration 9.3 ppm). 42 days after planting, the test plants were harvested and the contents of folic acid, total polyphenols, and nitrate nitrogen per 100 g of fresh weight were measured.

[0067] Table 2 shows the contents of folic acid, total polyphenols, and nitrate nitrogen per 100 g fresh weight of harvested lettuce in the treatment group where GSSG was supplied during seedling raising (T1 group) and the treatment group where GSSG was supplied after planting (T2 group). The contents of folic acid, total polyphenols, and nitrate nitrogen were measured in the same manner as in Test Example 1. Compared to the lettuce in the T1 group, the lettuce in the T2 group had higher folic acid and polyphenol contents and lower nitrate nitrogen contents.

[0068] [Table 2]

[0069] As shown in Table 2, adding glutathione to the culture solution after planting in hydroponic cultivation under sunlight improves the folic acid and polyphenol content of lettuce and reduces the nitrate nitrogen content compared to when it is added during seedling cultivation.

[0070] <Test Example 3: Cultivation of red leaf lettuce under artificial light I> The cultivation conditions under artificial light irradiation were as follows. The test was conducted using a hydroponic DFT-type hydroponic cultivation facility equipped with red / green / blue LED light sources (red light was 660 nm, green light was 525 nm, and blue light was 460 nm). In a closed environment, seeds were sown on a urethane mat that had absorbed sufficient water, and seedlings were raised for three weeks at an air temperature of 21-22°C, with a light period of 16 hours and a dark period of 8 hours. Seedlings with uniform growth were selected and planted in the cultivation facility. The culture solution was made using commercially available hydroponic fertilizer (containing nitrogen, phosphorus, potassium, etc.), and the pH and EC were monitored and adjusted once a week. 22 days after planting, the test plants were harvested and the contents of folic acid, total polyphenols, and nitrate nitrogen per 100 g of fresh weight were measured. The contents of folic acid, total polyphenols, and nitrate nitrogen were measured under the same conditions as in Test Example 1, except that the nitrate nitrogen content was measured using ion chromatography (see the Ministry of Education, Culture, Sports, Science and Technology's "Analysis Manual for the 2015 Edition (7th Edition) of the Standard Tables of Food Composition in Japan"). In this Test Example, the polyphenol content was calculated as the amount of gallic acid.

[0071] In addition to the above cultivation conditions, the area supplied with GSSG (without exposure to purple light) was designated as T1, the area supplied with GSSG and exposed to purple light was designated as T2, the area exposed to purple light (without supply of GSSG) was designated as C2, and the area neither supplied with GSSG nor exposed to purple light was designated as C1.

[0072] Red leaf lettuce "Black Rose" was grown under the above cultivation conditions. The light conditions were red, blue, and green LED light sources with a total PPFD of 150 μmol / m 2s, and a section was also set up where it was irradiated with 405 nm purple light at the same time. The GSSG concentration in the culture solution in the treatment section was adjusted to 300 ppm (free GSSG equivalent concentration: 279 ppm) by adding oxidized glutathione to the culture solution tank immediately after planting, one week after planting, and two weeks after planting.

[0073] The folic acid, total polyphenol, and nitrate nitrogen contents per 100g of fresh weight of the harvested lettuce in each group are shown in Table 3. Compared to the C1 and C2 groups, the lettuce in the T1 and T2 groups had higher folic acid and polyphenol contents and lower nitrate nitrogen contents.

[0074] [Table 3]

[0075] Table 3 shows that, in hydroponic cultivation under artificial light, just as under sunlight irradiation, adding and supplying glutathione to the culture solution can improve the folic acid content of lettuce and reduce the nitrate nitrogen content. Furthermore, by adding glutathione to the culture solution and irradiating it with purple light, the folic acid content was significantly improved and the nitrate nitrogen was significantly reduced. This shows that purple light plays an important role in improving the folic acid content and reducing nitrate nitrogen in lettuce. Furthermore, the polyphenol content was improved under artificial light irradiation.

[0076] <Test Example 4: Cultivation of red leaf lettuce under artificial light II> Red leaf lettuce "Black Rose" was cultivated under the same cultivation conditions as those described in Test Example 3. The light conditions were red, blue, and green LED light sources with a total PPFD of 200 μmol / m 2 s, and a section was also set up where it was irradiated with 405 nm purple light at the same time. The GSSG concentration in the culture solution in the treatment section was adjusted to 1 ppm (free GSSG equivalent concentration: 0.9 ppm) by adding oxidized glutathione to the culture solution tank immediately after planting, one week after planting, and two weeks after planting.

[0077] Table 4 shows the contents of folic acid, total polyphenols, and nitrate nitrogen per 100g fresh weight of harvested lettuce in each group. The contents of folic acid, total polyphenols, and nitrate nitrogen were measured in the same manner as in Test Example 3. The lettuce in the T1 and T2 groups had higher folic acid and polyphenol contents and lower nitrate nitrogen contents than the lettuce in the C1 and C2 groups.

[0078] [Table 4]

[0079] From Table 4, it was found that adding glutathione to the culture solution during hydroponic cultivation under artificial light irradiation can improve the folic acid content and polyphenol content of lettuce and reduce the nitrate nitrogen content. Comparison with Test Example 3 revealed that the effect can be obtained when the glutathione concentration in the culture solution is 0.9 ppm or more and 279 ppm or less.

[0080] <Test Example 5: Cultivation of Komatsuna under artificial light I> Komatsuna "Yokata-na" was cultivated under the same cultivation conditions as those described in Test Example 3. The light conditions were red, blue, and green LED light sources with a total PPFD of 200 μmol / m 2 s, and a section was also set up where it was irradiated simultaneously with 405 nm purple light. The GSSG concentration in the culture solution in the treatment section was adjusted to 10 ppm (free GSSG equivalent concentration 9.3 ppm) by adding oxidized glutathione to the culture solution tank immediately after planting, one week after planting, and two weeks after planting.

[0081] Table 5 shows the contents of folic acid, total polyphenols, and nitrate nitrogen per 100g fresh weight of the harvested komatsuna in each group. The contents of folic acid, total polyphenols, and nitrate nitrogen were measured in the same manner as in Test Example 3. The komatsuna in the T2 group had higher folic acid and polyphenol contents and lower nitrate nitrogen contents than the komatsuna in the C1 and C2 groups. The komatsuna in the T1 group had higher folic acid contents and lower nitrate nitrogen contents than the komatsuna in the C1 and C2 groups.

[0082] [Table 5]

[0083] From Table 5, it was found that adding glutathione to the culture solution during hydroponic cultivation under artificial light irradiation can improve the folic acid content and polyphenol content of komatsuna and reduce the nitrate nitrogen content. Comparison with Test Examples 1, 2, 3, and 4 revealed that the effect was obtained for normal lettuce, red lettuce, komatsuna, and other leafy vegetables in general.

[0084] <Test Example 6: Cultivation of Komatsuna under artificial light II> Komatsuna "Yokata-na" was cultivated under the same cultivation conditions as those described in Test Example 3. The light conditions were red, blue, and green LED light sources with a total PPFD of 200 μmol / m 2 s, and a section was also set up where it was irradiated with 405 nm purple light at the same time. The GSSG concentration in the culture solution in the treatment section was adjusted to 1 ppm (free GSSG equivalent concentration: 0.9 ppm) by adding oxidized glutathione to the culture solution tank immediately after planting, one week after planting, and two weeks after planting.

[0085] Table 6 shows the contents of folic acid, total polyphenols, and nitrate nitrogen per 100g fresh weight of the harvested komatsuna in each group. The contents of folic acid, total polyphenols, and nitrate nitrogen were measured in the same manner as in Test Example 3. The komatsuna in the T1 and T2 groups had higher folic acid and polyphenol contents and lower nitrate nitrogen contents than the komatsuna in the C1 and C2 groups.

[0086] [Table 6]

[0087] From Table 6, it was found that by adding glutathione to the culture solution during hydroponic cultivation under artificial light irradiation, the folic acid content and polyphenol content of komatsuna can be improved and the nitrate nitrogen content can be reduced. A comparison with Test Example 5 revealed that the effect can also be obtained for komatsuna when the glutathione concentration in the culture solution is 0.9 ppm or more.

Claims

1. 1. A method for growing plants hydroponically, comprising: The method includes a step of supplying a culture solution containing oxidized glutathione at a content of 1 to 300 ppm to the plant, A method for reducing the nitrate nitrogen content of the plant.

2. The method of claim 1 , further comprising the step of irradiating the plant with violet light.

3. The method of claim 2 , wherein the violet light has a wavelength of 405 nm.

4. 4. The method according to claim 2 or 3, wherein the violet light is artificial light.

5. The method according to claim 2 or 3, wherein the purple light is irradiated as sunlight.

6. A method according to any one of claims 1 to 5, wherein a culture solution containing oxidized glutathione is supplied during the period from planting of the plant until harvest.

7. A method according to any one of claims 1 to 6, wherein a culture medium containing oxidized glutathione is supplied multiple times.

8. The method according to any one of claims 1 to 7, wherein the plant is a leafy vegetable.

9. An agent for promoting the reduction of nitrate nitrogen content in plants, comprising oxidized glutathione.

10. The agent according to claim 9, for addition to a culture solution composition for hydroponic cultivation.

11. The agent according to claim 9, which is to be added to a culture solution composition for hydroponic cultivation under irradiation with purple light.

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