JP2023174451A - Plant cultivation method and plant cultivation device - Google Patents

Abstract

To provide a plant cultivation method for performing light control of distribution of glucose produced by photosynthesis to a primary metabolism route and a secondary metabolism route, and realizing control of metabolite production in each metabolic reaction.SOLUTION: In at least a part of a cultivation period from sowing to harvest, irradiation is performed with main light for photosynthesis and additional light for promoting photosynthesis of a plant via the main light. The additional light includes additional signal light whose light intensity varies periodically and additional moderation light whose light intensity changes more gently than the additional light. The wavelength of the additional signal light includes a light absorption wavelength band of a red light receptor in the plant.SELECTED DRAWING: Figure 1

Description

The present invention relates to, for example, a plant cultivation method that promotes production of useful components in plants, and a plant cultivation device.

Plants convert glucose produced through photosynthesis into other substances through primary and secondary metabolic cycles. Primary metabolism is common to all plants and produces the chemical energy necessary for plant survival and growth, as well as the chemicals necessary for the formation of organs such as roots, stems, and leaves. Secondary metabolism differs from plant to plant, but it produces chemicals that help protect against and repair damage from foreign invaders and damage.
Chemical substances produced by plants through metabolism are useful for humans as detoxifying, analgesic, antipyretic, and antioxidant medicines. For this reason, genetic recombination technology and genome editing technology are being applied with the aim of efficiently producing plant metabolites.

International Publication No. 2019/031559

The method described in Patent Document 1 irradiates light with a relatively small duty ratio in a light environment where plants are not photosynthesizing. Experiments conducted by the inventors have shown that plants are damaged by relatively strong stimuli and undergo deterioration. Furthermore, there is also the problem that the production of products of primary metabolism and secondary metabolism cannot be independently controlled.

The present invention provides a plant cultivation method and a plant cultivation device that can optically control the distribution of glucose produced by photosynthesis to the primary metabolic pathway and the secondary metabolic pathway, and further control the production of metabolites within each metabolic reaction. The task is to do so.

The present invention provides a plant cultivation method and a plant cultivation device having the following configurations.

(1) During at least a part of the cultivation period from sowing to harvest, main light for photosynthesis and additional light for promoting photosynthesis of plants by the main light are irradiated, and the additional light has a light intensity of The wavelength of the additional signal light includes additional signal light that changes periodically and additional relaxed light whose light intensity changes more slowly than the additional light, and the wavelength of the additional signal light falls within the light absorption wavelength band of red photoreceptors in the plant. Plant cultivation methods including.
(2) Separating the leaves or buds of the plant from the roots, branches, or stems, irradiating only the leaves or buds with the main light for a certain period of time, and then keeping them in a dark place for a certain period of time (1) ) The plant cultivation method described in .
(3) A plant cultivation device that is irradiated with main light for photosynthesis of plants,
an additional light source that irradiates additional light that promotes photosynthesis of plants by the main light;
and an irradiation light control unit capable of driving and controlling the additional light source,
The additional light source is
an additional signal light source that emits additional signal light whose light intensity periodically fluctuates;
an additional relaxation light source that emits additional relaxation light whose light intensity changes more slowly than the additional light;
irradiating the additional relaxation light together with the additional signal light;
A plant cultivation device in which the wavelength of the additional signal light includes a light absorption wavelength band of a red photoreceptor within the plant.

According to the present invention, there is provided a plant cultivation method and a plant cultivation apparatus in which the distribution of glucose produced by photosynthesis to the primary metabolic pathway and the secondary metabolic pathway is optically controlled, and further, the production of metabolites within each metabolic reaction can be controlled. can be provided.

FIG. 2 is an explanatory diagram showing light absorption wavelength bands of photosynthetic pigments and photoreceptors. FIG. 2 is an explanatory diagram showing the flow of glucose, which is a photosynthetic product, being distributed to a translocation pathway and a secondary metabolic pathway. FIG. 2 is an explanatory diagram showing a light absorption spectrum of phytochrome. FIG. 3 is an explanatory diagram showing a state change of phytochrome due to light absorption. It is an explanatory view showing additional light of an embodiment. It is an explanatory view showing a light irradiation profile after harvest of an embodiment. FIG. 1 is a schematic configuration diagram of a plant cultivation device. (a) to (d) are explanatory diagrams showing the conditions of Example 1. (a) to (d) are explanatory diagrams showing the conditions of Example 2. (a) to (d) are explanatory diagrams showing the conditions of Example 3.

Embodiments of the present invention will be described in detail below.

<Plant cultivation method>
<<Technology to increase metabolites using stress>>

In this embodiment, first, a plant cultivation method using stress caused by phytochrome will be described. Next, a method of cultivating plants that utilizes stress caused by trauma to plants will be explained.

<<Stress caused by phytochrome>>
Plants use photoreceptors to utilize light and the light environment for growth. Photoreceptors include chlorophyll and carotenoids that collect the light energy necessary for photosynthesis, and phytochromes, cryptochromes, and photololopins that collect information about the light environment. Figure 1 shows photoreceptors in plants and their respective light absorption wavelengths.

Plants use light energy captured by chlorophyll and carotenoids to produce the carbohydrate glucose (C ₆ H ₁₂ O ₆ ) from water (H ₂ 0) and carbon dioxide (CO ₂ ). Glucose is distributed between primary and secondary metabolic pathways.

Among the above-mentioned three types of photoreceptors (phytochrome, cryptochrome, and photorolopin) that sense the light environment, phytochrome controls flower bud formation, germination, promotes growth from bud to leaf, and controls metabolism. When phytochromes sense light, genes involved in flower bud formation and germination are expressed. Expression refers to the activation of genes that perform individual functions when proteins called gene transcription factors bind to genes. Phytochromes control expressed genes by moving into the cell nucleus.

Phytochrome is a tissue in which many proteins are assembled. Phytochromes are classified into Pfr type and Pr type depending on their aggregation state. Pfr-type phytochromes bind to specific gene transcription factors in the cell nucleus and promote their degradation. As a result, the expression levels of multiple genes controlled by this gene transcription factor increase or decrease, and the properties of the cell change. Pr-type phytochromes are located far away from genes, so they do not interact with genes. Therefore, cell properties do not change depending on Pr-type phytochrome.

FIG. 2 shows the optical absorption spectrum of phytochrome in the red to far infrared region. Pr-type phytochrome absorbs red light between 600 nm and 710 nm. Pfr-type phytochrome absorbs light in the long wavelength range from 600 nm, including red light. The vertical axis in FIG. 2 is absorbance. In FIG. 2, absorbance and optical density (O.D., also referred to as "optical density") are the same.

The texture of phytochrome changes when it absorbs light. Figure 3 shows the reversible change between Pr type and Pfr type due to red light and far-red light. When Pr-type phytochrome absorbs red light, it changes to Pfr-type. Conversely, when Pfr-type phytochrome absorbs far-red light, it changes to Pr-type.

When red light and far-red light, which are sufficient for photosynthesis to occur, are simultaneously irradiated, phytochrome cycles between the Pr type and the Pfr type, and each distribution reaches a certain light equilibrium state. In the absence of light, phytochrome gradually undergoes thermal relaxation from the Pfr form to the Pr form. Irradiation with light with a wavelength longer than 700 nm promotes the conversion from Pfr type to Pr type. On the other hand, light with a wavelength of 600 nm to 710 nm is absorbed by both Pr type and Pfr type. In this case, since the Pr type absorbs more light, conversion from the Pr type to the Pfr type is predominant in phytochrome.

When phytochrome becomes Pfr type, it moves to the cell nucleus, but when it becomes Pr type, it localizes to the cytoplasm and becomes a foreign substance. For cells, foreign phytochrome becomes a stress factor. Therefore, if the cellular stress induced by phytochrome is S, the Pr type stress is S (Pr type), and the Pfr type stress is S (Pfr type), then the relationship between these is S(Pr type)>S( Pfr type).

Plants are exposed to environmental stresses such as strong light, high temperature, low temperature, and dryness. When cells are damaged by these environmental stresses, plants produce a variety of antioxidants through metabolic reactions to protect, alleviate, and repair the damage. Ascorbic acid and polyphenols are typical antioxidants, but they are secondary metabolites.

FIG. 4 shows the process by which glucose flows into the primary metabolic pathway and the secondary metabolic pathway. From glucose synthesized through photosynthesis, starch, sucrose, fructose, etc. are synthesized in the primary metabolic pathway. A part of these enters the secondary metabolic pathway, and many types of secondary metabolites are synthesized. When plants sense stress conditions, they activate secondary metabolic reactions and increase the production of antioxidants such as vitamin C (ascorbic acid), polyphenols, and s-allylcysteine.

By controlling the stress that plants receive through the state of phytochrome assembly (Pr type or Prf type), we can change (control) the distribution ratio and amount of glucose, a photosynthetic product, to the primary and secondary metabolic pathways. be able to.

The plant cultivation method according to the present embodiment is an environment in which plants are grown using sunlight (natural light) or artificial light such as LED (main light described later), by adding light whose light intensity changes periodically. irradiate. Since the additional light changes the amino acid organization of the phytochromes, the stress conditions caused by them also change. This makes it possible to control metabolite production. The additional light will also be referred to as "additional light" below. Additional light will be described later.

<<Plant growth using main light>>
In this embodiment, sunlight (natural light) and artificial supplementary light are referred to as "main light" for photosynthesis. This main light is light for directly causing or increasing photosynthesis. Principal light is light emitted from sunlight, LEDs, etc., and is the light that is primarily responsible for photosynthesis. With respect to photosynthesis, the "main light" is light that has a photosynthetically effective quantum flux density that is greater than or equal to the optical compensation point, and the "additional light" is light that has a photosynthetically effective quantum flux density that is less than the optical compensation point. The difference between the carbon dioxide absorption rate during photosynthesis (μmolCO ₂ m ^-2 s ^-1 ) and the carbon dioxide release rate during respiration (μmolCO ₂ m ^-2 s ^-1 ) is the photosynthetic rate (μmolCO ₂ m ^-2 s ^-1 ). It is. The light compensation point is PPFD (Photosynthetically Effective Quantum Flux Density), where the photosynthetic rate becomes zero, but this value differs depending on the plant. The light of PPFD that exceeds the light compensation point can be said to be light for photosynthesis, and the principal light of PPFD that exceeds the light compensation point can be said to be the principal light for photosynthesis.

<<Additional light promotes metabolism and growth>>
In this embodiment, auxiliary light different from the main light is artificially created and irradiated onto the plants. This auxiliary light is referred to as "additional light." This additional light irradiation is performed at a predetermined time or period, although the details will be described later. Additional light is light for indirectly promoting photosynthesis.

Additional light can indirectly increase photosynthesis by stimulating the viability of a plant's DNA. Plants are known to have a light accumulation function, and they accumulate the intensity and duration of sunlight on a daily basis. When the integration function detects a decrease in PPFD (PPDF decrease) in the main light, the DNA in the plant's chloroplasts issues a command to increase the production of chlorophyll in the light antenna. This increases the amount of light absorption and promotes photosynthesis.

In this embodiment, a differential function for detecting the rate of change in light intensity, which plants have latently, is utilized. Pulsed light (signal light) that repeatedly turns on and off at regular intervals is the most efficient way to stimulate the differential functions of plants. This pulsed light (signal light) is hereinafter referred to as "additional signal light". The additional signal light is light included in the additional light. In this embodiment, the plant is irradiated with this additional signal light alone or together with the additional relaxation light.

The additional signal light is insufficient compared to the main light to cause photosynthesis. For this reason, plants perceive that they are temporarily starved for photosynthesis. When DNA detects photosynthetic starvation, it issues a command to produce more chlorophyll to absorb more of the light needed for photosynthesis. Furthermore, the additional signal light causes the DNA to issue commands to control the opening and closing of the stomata, which are the entrances and exits for outside air, so that the amount of carbon dioxide absorbed increases. As a result, the additional pulsed light irradiation increases the light energy required for photosynthesis and the amount of carbon dioxide absorbed. That is, the additional signal light in this embodiment functions as a trigger signal for causing DNA to issue a command to increase chlorophyll production and a command to open and close stomata. The effect of additional signal light in this way of thinking is defined as the DNA triggering effect of additional signal light.

The DNA trigger effect increases proportionally to the number of triggers per time, but is independent of the strength of the trigger signal. If the time interval of the trigger signals becomes too short, the DNA triggering effect will decrease. Further, the photosynthesis promoting effect of the additional light including the additional signal light can be obtained regardless of the value of the PPFD of the main light.

In addition to this, in this embodiment, light whose light intensity changes more slowly than the additional signal light (additional relaxation light) is combined with the additional signal light in accordance with the desired photosynthesis promoting effect. The additional relaxation light has a sinusoidal waveform, and the fundamental period is 1 ms or more. The period of the additional signal light is 8 μs<T<200 μs, and the fundamental period of the additional relaxation light is 125 to 2 times or more the period T of the additional signal light.

In this way, by irradiating plants with the additional light obtained by combining the additional signal light with the additional relaxation light, the photo stress felt by the plants is further alleviated than when the additional signal light is applied alone. can. That is, the additional light of this embodiment is light that can improve the optical stress reduction effect of the additional light as much as possible by combining the additional signal light and the additional relaxation light.

The additional signal light is a light that repeats turning on and off at an arbitrary period. The additional relaxation light is light whose intensity is approximately constant. In this embodiment, the additional relaxation light may slightly include ripples at a frequency of about 60 Hz.

It is thought that the additional signal light of this embodiment can alleviate the light stress on plants compared to the pulsed light of the prior art. However, by adding not only the additional signal light of this embodiment but also another type of light (here, additional relaxation light), it is possible to more effectively reduce the optical stress that the additional light gives to the plants.

In order to alleviate the optical stress caused by the additional signal light as much as possible, it is desirable that the PPFD of the additional relaxation light be equal to or higher than that of the additional signal light. The wavelength ranges (wavelength bands) of the additional signal light and the additional relaxation light may be the same or different. In either case, there is a photosynthesis promoting effect. However, it is desirable that the wavelength band of the additional signal light and the wavelength band of the additional relaxation light have a common part (overlapping part) with each other (at least some wavelength bands are common).

Plants are sensitive to temporal changes in light intensity. Therefore, when a plant is irradiated with additional signal light and additional relaxed light at the same time, the plant preferentially detects the additional signal light. We define this plant response as the cocktail party effect in plant light sensing. The cocktail party effect for additional light is effective even when the main light is illuminated.

When photosynthesis that is weaker than that produced by the main light occurs periodically, the plant recognizes that it is in a state of photosynthetic starvation, and its DNA issues a command to synthesize chlorophyll in the light antenna. As a result, the efficiency of light use for photosynthesis improves, and the rate of photosynthesis increases even if the PPFD of the primary light from sunlight or artificial light remains constant. An increase in photosynthetic rate is observed even when only the additional signal light is irradiated.

A photosynthesis promoting effect and a more stable growth promoting effect can be obtained by superimposing additional relaxing light that changes more slowly than the additional signal light. Since the additional signal light is light that gives a trigger signal to DNA, there are no restrictions on PPFD. On the other hand, it is desirable that the PPFD of the additional relaxation light is equal to or higher than that of the additional signal light.

For example, in the plant cultivation method of this embodiment, during the process of irradiating sunlight or artificial light as main light for photosynthesis, additional light is irradiated during any cultivation period from sowing to harvest. The additional light is at least one of light whose light intensity changes periodically (additional signal light) and light whose light intensity changes gradually (additional relaxation light). In some cases, only the additional signal light is irradiated as additional light.

The additional light is light that can excite phytochromes, which are protein photoreceptors. The plant cultivation method of the present embodiment is a plant cultivation method in which the additional light is additionally irradiated at any time of the day, and the fluctuation of the light intensity (PPFD) of the additional signal light is periodic. The fluctuation period is 8 μs or more and 200 μs or less, the wavelength of the periodically fluctuating light is 500 nm or more and 2000 nm or less, and the duty ratio of the periodically fluctuating light is, for example, 0.1 or more. This point will be discussed later.

Pr-type phytochromes are localized in the cytoplasm. When Pr-type phytochrome is converted to Pfr-type, it moves closer to the cell nucleus. Conversely, when Pfr-type phytochrome changes to Pr-type, it moves away from the cell nucleus and localizes within the cytoplasm. Therefore, when Pfr-type phytochrome that was close to the cell nucleus converts to Pr-type, it moves away from the cell nucleus. Conversely, when Pr-type phytochrome converts to Pfr-type, it moves closer to the cell nucleus.

We explain the mechanism by which additional light with periodically varying light intensity (PPFD) promotes phytochrome conversion. As mentioned above, phytochrome is a tissue in which many proteins are assembled. When amino acids absorb light, the phytochrome texture changes locally. In order to efficiently convert the entire amino acid assembly, it is effective to continue to excite the amino acids intermittently.

In other words, when one amino acid molecule absorbs light, a vacancy (a positively charged hole created by the escape of a negatively charged electron) is created in the HOMO orbital (highest occupied orbital) and becomes the LUMO orbital (lowest unoccupied orbital). produces an electron. As a result, the local electrically neutral state within the amino acid is disrupted, and the atomic arrangement of the amino acid molecule is distorted. When this distortion occurs throughout the amino acid texture, distortion occurs throughout the amino acid texture.

At this time, the deformation of the entire structure of the amino acid assembly can be promoted by irradiating light whose intensity changes sharply (FIG. 5) rather than by irradiating light whose intensity is approximately constant over time. By repeating the cycle of momentarily deforming the amino acid texture and then waiting for a certain amount of time, it becomes possible to exert a large deformation force on the entire amino acid texture. Therefore, in order to efficiently convert the entire amino acid assembly, it is effective to continue to excite the amino acids intermittently.

In the absence of light (in the dark), Pfr-type phytochrome slowly returns to the Pr-type due to thermal relaxation. Therefore, in order to permanently obtain Pfr-type phytochrome, it is necessary to excite Pr-type phytochrome during a time period when there is no main light for photosynthesis.

The rate of conversion between the Pr and Pfr forms of phytochrome, and the rate of movement of the Pfr form into and out of the cell nucleus, increase in proportion to the number of photoexcitations per hour. If the time interval of photoexcitation of phytochrome becomes too short, it approaches continuous light irradiation, and the effect of promoting approach and detachment decreases. Therefore, there is a period of light intensity change that is suitable for moving phytochrome most efficiently.

FIG. 5 is a diagram showing additional light in this embodiment. The graph in FIG. 5 shows the temporal change in the number of photons (representing photosynthetic effective quantum flux density (PPFD)) incident on the leaf surface.

In this embodiment, the pulse shape of the additional light is trapezoidal. The period (basic period) of the additional light is T, the rise time of one pulse is ΔT ₁ , the peak time is ΔT ₂ , and the fall time is ΔT ₃ . Among these, the light intensity of ΔT ₁ and ΔT ₃ changes with time. The gradients of time changes in ΔT ₁ and ΔT ₃ may be the same or different for ΔT ₁ and ΔT ₃ . Furthermore, the gradient at ΔT ₁ or ΔT ₃ may be changed in the middle of ΔT ₁ or ΔT ₃ . The waveforms at ΔT ₁ and ΔT ₃ can be made to have a curved shape (bow shape, circular arc shape, wave shape, _etc. ) or step shape (step shape, staircase shape, etc.) to make the slopes at ΔT ₁ and ΔT 3 different in the middle. For example,

According to experiments conducted by the inventors, the photosynthesis promoting effect of additional light can be favorably obtained when the period T of additional light is 8 μs<T<200 μs. Further, ΔT1 and ΔT3 before and after the peak time ΔT ₂ can be obtained satisfactorily when either one is 5 μs or less.

In this embodiment, in addition to this, light whose light intensity changes more gently than the additional light (on the left side in FIG. 2) (additional relaxation light) is combined with the additional light in accordance with the desired photosynthesis promoting effect. The basic period of the additional relaxation light is 1 ms or more. The period of the additional light is 8 μs<T<200 μs, and the fundamental period of the additional relaxation light is 125 to 2 times or more the period T of the additional light.

In this way, by irradiating plants with additional light obtained by combining additional light with additional relaxing light, the light stress felt by plants can be further alleviated than when the additional light is applied alone. That is, the additional light of this embodiment is light that can improve the optical stress reduction effect of the additional light as much as possible by combining the additional light and the additional relaxation light.

The additional light is light that repeats turning on and off at an arbitrary period. The additional relaxation light is light whose intensity is approximately constant. In this embodiment, the additional relaxation light may slightly include ripples at a frequency of about 60 Hz.

It is believed that the additional light of this embodiment can alleviate light stress on plants compared to the pulsed light of the prior art. However, by adding not only the additional light of this embodiment but also another type of light (here, additional relaxation light), it is possible to more effectively reduce the optical stress that the additional light gives to the plants.

In order to alleviate the optical stress caused by the additional light as much as possible, it is desirable that the PPFD of the additional relaxing light be equal to or higher than that of the additional light. The wavelength ranges (wavelength bands) of the additional light and the additional relaxed light may be the same or different. In either case, there is a photosynthesis promoting effect. However, it is desirable that the wavelength band of the additional light and the wavelength band of the additional relaxation light have a common part (overlapping part) with each other (at least some wavelength bands are common).

The additional light may be applied at any time within 24 hours in a day, or may be applied at a predetermined time. The wavelength of the additional light ranges from 500 nm to 2000 nm.

<<Stress caused by trauma>>

Immediately after germination, plant shoots synthesize secondary metabolic substances such as vitamins and polyphenols that are not contained in dried seeds.

The inventors considered using stress caused by trauma to rapidly increase the amount of metabolites contained in shoots and leaves.
In order to take advantage of the stress caused by trauma, shoots that perform photosynthesis are cut off from the base and kept in an environment where water cannot escape. In this state, photosynthesis is allowed to occur for a certain period of time under the same light environment as before harvesting, and after that, it is maintained for a certain period of time under an environment without light. When shoots and leaves are cut, they sense traumatic stress. In this way, shoots and leaves limit the translocation of photosynthetic products, while activating secondary metabolism and increasing the production of antioxidants that have stress protection, mitigation, and cell repair effects.

FIG. 6 shows a light irradiation profile (post-harvest light irradiation profile) in this embodiment. The light irradiation according to this embodiment is also referred to as "post-harvest light irradiation" or the like. Starting from the top, the light irradiation profile when left in a dark place after harvest (no light irradiation), the light irradiation profile when irradiated with a white LED for 12 hours, and the light irradiation profile when irradiated with a white LED for 24 hours. It shows. Post-harvest light irradiation to plants is performed by appropriately using these modes of light irradiation.
By using the method described above, secondary metabolites contained in shoots and leaves can be significantly increased within about 12 hours after cutting. Secondary metabolism promotion technology that utilizes traumatic stress is effective for all kinds of plants, including sprouts of barley, broccoli, and garlic, as well as olive, tea, red perilla, and perilla leaves.

The above-mentioned plant cultivation method (plant cultivation method using stress caused by trauma) may be performed alone, or may be performed following plant cultivation using stress caused by phytochrome.

The plant cultivation method according to this embodiment is effective for photosynthesis of all types of plants. Therefore, it can be applied to promoting the growth of leafy vegetables, flowers, fruit trees, seaweed, algae, and microalgae. Furthermore, it is effective for plant cultivation in fields, greenhouses, plant factories, terrestrial aquaculture, on the sea surface, under the sea, and in mountainous areas.

<Plant cultivation device 10>
FIG. 7 shows a schematic configuration of the plant cultivation device 10 of this embodiment. The plant cultivation device 10 includes a cultivation bed 12 for hydroponic or soil cultivation, a light irradiation unit 14 that irradiates light toward the cultivation bed 12, and an irradiation light control unit 16 that drives the light irradiation unit 14 to turn on. ing. The plant cultivation device 10 includes a protection member 18 that covers the cultivation bed 12 to form a cultivation chamber. It is also possible to omit the protective member 18.

The light irradiation unit 14 includes a main light source 20 that irradiates main light, and an additional light source 22 that irradiates additional light. The main light source 20 and the additional light source 22 are individually driven and controlled by the irradiation light control unit 16 (here, current control). In FIG. 5, the main light source 20 and the additional light source 22 are shown side by side, but the light from the main light source 20 and the light from the additional light source 22 are transmitted through a diffusion plate (not shown) ), and the cultivation bed 12 is irradiated via the same route. The light from the additional light source 22 may be directed toward the cultivation bed 12 via an optical fiber (not shown). As the optical fiber, an edge-emitting or side-emitting type can be used as appropriate.

The main light source 20 lights up continuously within a predetermined period of time and continuously emits main light (also referred to as "continuous irradiation light"). As the main light source 20, for example, an artificial light source such as an LED, a fluorescent lamp, a plasma lamp, a mercury lamp, an incandescent lamp, a metal halide lamp, a sodium lamp, or an electrodeless lamp is used.

It is also possible to use sunlight as other main light. When using sunlight, it is possible not to use the main light source 20 or to omit the main light source 20. It is also possible to use sunlight and the light from the main light source 20 in combination. In this case, sunlight and light from the main light source 20 may be used depending on conditions such as time of day. Furthermore, sunlight and the light from the main light source 20 may be emitted simultaneously.

The additional light source 22 includes an additional signal light source 24 and an additional relaxation light source 26. The additional signal light source 24 emits additional signal light, and the additional relaxation light source 26 emits additional relaxation light. The additional signal light and additional relaxation light constitute additional light (FIG. 4).

In FIG. 5, the additional signal light source 24 and the additional relaxation light source 26 are shown side by side, but the additional signal light and the additional relaxation light are transmitted through a diffuser plate (not shown) (even if it is a diffuser lens). irradiation to the cultivation bed 12 via a similar route. The additional light source 22 may be one in which the additional signal light source 24 and the additional relaxation light source 26 are integrated and integrated.

The additional signal light source 22 is capable of emitting light within a wavelength range of 500 nm to 2000 nm. The additional signal light source 24 may include various light sources such as LED, EL (electroluminescence), laser, ultraviolet light, and infrared light, as long as they can emit light with a wavelength suitable for growing the plants to be cultivated. Can be adopted. Further, it is desirable to use a light source that can easily control pulse lighting as the additional signal light source 24. As the additional relaxation light source 26, various light sources such as a cold cathode fluorescent lamp, an LED monochromatic lamp, and an LED fluorescent lamp driven by a power line (50 Hz or 60 Hz) can be employed, for example.

Although not shown, the additional light source 22 may include a light source that continuously emits light and a shutter placed in the middle of the optical path. In this case, the optical path is intermittently interrupted by a shutter to form signal light. It is also possible to attach a wavelength limiting filter to the white light source to form light of a required wavelength. A shutter or a filter may be provided for each of the additional signal light source 24 and the additional relaxation light source 26.

The light irradiation unit 14 is installed above the ceiling surface or side wall of the protection member 18, or above the pillars installed on the cultivation bed 12, or the like. The light irradiation unit 14 illuminates the cultivation bed 12 in accordance with a command from the irradiation light control unit 16.

The light irradiation unit 14 may include a plurality of main light sources 20 and a plurality of additional light sources 22. In this case, it is possible to arrange the plurality of main light sources 20 and the plurality of additional light sources 22 at different positions and with different irradiation angles. For example, it is also possible to alternately arrange a plurality of main light sources 20 and a plurality of additional light sources 22. It is also possible to include a plurality of main light sources 20 and a single additional light source 22 (or a single main light source 20 and a plurality of additional light sources 22). It is also possible to install additional light sources 22 so that the cultivation bed 12 is irradiated with light from a plurality of directions. In this way, a more stable growth promoting effect can be obtained.

In this way, by providing a plurality of main light sources 20 and/or a plurality of additional light sources 22, it becomes possible to perform more precise light irradiation. By varying the arrangement and irradiation angle of the plurality of light sources, the plants on the cultivation bed 12 can be uniformly irradiated with light, and uneven growth depending on location can be suppressed.

The irradiation light control unit 16 drives the light irradiation unit 14 to turn on based on the plant cultivation method of this embodiment. The irradiation light control unit 16 can drive only the main light source 20 to turn on, drive only the additional light source 22, or drive both the main light source 20 and the additional light source 22 to turn on at the same time. It is possible.

When the light irradiation section 14 includes a plurality of main light sources 20 and/or a plurality of additional light sources 22, the irradiation light control section 16 can synchronize and turn on the same type of light sources. Furthermore, when dividing the cultivation bed 12 into a plurality of blocks (test plots), the irradiation light control unit 16 can individually control the main light source 20 and the additional light source 22 in each block. .

The irradiation light control unit 16 may synchronize the main light source 20 and the additional light source 22 on a block-by-block basis, or may synchronize the main light source 20 and the additional light source 22 in a plurality of blocks or all blocks. By synchronizing the additional signal light in the additional light source 22, the duty ratio of the additional signal light irradiated to the plants can be maintained accurately.

Such a plant cultivation device 10 can be widely applied to small-sized cultivation kits for easy indoor cultivation in general households, agricultural greenhouses, large-sized ones such as plant factories having built cultivation rooms, etc. is possible.

Here, agricultural greenhouses include agricultural vinyl greenhouses in which a translucent film is spread over the entire surface of the greenhouse, as well as agricultural glass houses in which film is stretched over the entire inside of the glass windows. can. In agricultural glass houses, air containing moisture in the cultivation space inside the house passes through the film and exits the house through the gap between the glass windows and the framework of the glass windows. Therefore, even in agricultural glass houses, it is possible to prevent the inside of the house from becoming hot and humid. Note that the above-mentioned "translucent property" means that light necessary for growing plants passes through during the day.

When a light source for additional light (in this case, additional light source 22) is installed inside an agricultural greenhouse, a portion of the additional light is reflected and diffused (reflection and diffusion) by glass plates, resin plates, resin films, etc. This has the advantage of increasing the irradiation efficiency of additional light. A similar effect of improving irradiation efficiency can be obtained with small-scale cultivation kits and plant factories.

Furthermore, it is possible to consider the effective direction of irradiation of additional light (additional signal light and/or additional relaxation light). The growth promoting effect can be obtained whether the additional light is irradiated from the same direction as the main light or from a direction different from the main light. Furthermore, if additional light is applied to areas where the main light does not reach sufficiently (for example, the front and back surfaces of leaves in the shade, or the underside of leaves in sunny areas), the growth promotion effect will be even greater. is obtained.

Specifically, additional light is irradiated upward from the ground (including diagonally upward) to a plant, such as a grape, whose branches extend horizontally. In this case, more light hits the underside of the leaf (the side facing the ground) in the shade. Photosynthesis takes place more actively than when no additional light is irradiated, and the sweetness of the grapes increases. In this way, by setting the irradiation direction of the additional light according to the environment in which the plants are cultivated, the characteristics of the plants, etc., the growth of the plants can be promoted even more effectively.

<Comparison of additional light in the prior art and this embodiment>
Table 1 below shows a comparison between the prior art (technical matters disclosed in Patent Document 1 mentioned above) and the basic technical matters of the plant cultivation method (additional light irradiation) according to the present embodiment. .

As shown in Table 1, the main light is sunlight and artificial light (LED etc.) in both the prior art and the present embodiment. The period of the additional light is 8 μs to 500 μs in the prior art and 8 μs to 200 μs in the present embodiment. The duty ratio of the additional light is limited to 20% or less in the prior art, but is not limited in this embodiment.

The photosynthetic photon density (μmol·m ^-2 ·s ^-1 ) of the additional light is limited to 0.001 to 4.0 in the prior art, but there is no such limit in this embodiment. In the prior art, there is only one type of light added to the main light, and in this embodiment, there are two types: additional light and additional relaxation light. The wavelength band is 400 nm to 500 nm in the prior art and 500 nm to 2000 nm in this embodiment.

In the prior art, the irradiation period is the growing period after planting, and in the present embodiment, it is any period from sowing to the seedling-raising period and the growing period (including the entire period). The period from sowing to planting is defined as the seedling-raising period, and the period from planting to harvesting is defined as the growing period.

The irradiation time period of one day is the night time period in the prior art, and the irradiation time period in the present embodiment is any time period within 24 hours of the day. The technical effect is that the prior art allows for promotion of growth and increase of useful components, and this embodiment allows for individual control of growth and production of useful components.

Although not listed in Table 1, in the prior art, relatively strong stimulation is given to plants by pulsed light. Furthermore, since the wavelength band of the pulsed light is limited to the blue wavelength band, in situations where leaves overlap, it is difficult for the light to reach hidden leaves. Furthermore, individual control of growth and secondary metabolism (independent control of growth rate and production of useful substances) is difficult.

On the other hand, in the present embodiment, the stimulation given to plants is less than that of the prior art due to the superposition of flashing light (additional light) and slowly changing light (additional relaxation light). The plant cultivation method and plant cultivation apparatus 10 of this embodiment are capable of individually controlling growth and secondary metabolism. Individual control of growth and secondary metabolism is possible by changing the wavelength and light intensity of additional light and additional relaxation light.

Note that this embodiment is merely an example of the implementation of the present invention, and the technical scope of the present invention should not be interpreted to be limited thereby. That is, the present invention can be implemented in various forms without departing from its gist or main features.

Hereinafter, embodiments of the present invention will be described in detail with reference to Examples. By irradiating additional light under the conditions described in each example, the distribution of glucose produced through photosynthesis promoted by the additional signal light to the primary metabolic pathway and secondary metabolic pathway can be optically controlled, and each metabolic It becomes possible to control metabolite production within a reaction. More specifically, the stress caused by the additional signal light controls the distribution of glucose produced through photosynthesis promoted by the additional signal light and additional relaxed light between the primary metabolic reaction pathway and the secondary metabolic reaction pathway, and further, The production ratio of metabolites within each metabolic reaction pathway can be controlled by stress induced by additional signal light. However, the present invention is not limited to the following description.

<Example 1>
In Example 1, the effect of additional light irradiation on the growth of lettuce was investigated. FIG. 8 shows the conditions according to Example 1 by a diagram of four regions separated by broken lines. The upper left diagram (region) in FIG. 8 shows the irradiation periods of various types of light, etc., and the upper right diagram (region) shows the irradiation time periods of various types of light in one day. The lower left diagram (region) shows the characteristics of various types of light, and the lower right diagram (region) shows changes in the number of photons of the additional signal light, the period of the additional relaxed light, etc.

First, lettuce seeds were scattered on a sponge containing water, kept in a dark place for 3 days, and then exposed to main light for 7 days (first prescribed period) to grow seedlings. The numerical value "3" shown at the left end of the arrow related to "principal light" in the upper left diagram of FIG. 8 means storage for three days (second predetermined period) in a dark place. Similarly, the value "7" on the horizontal axis in the upper left diagram of Figure 8 indicates that another 7 days (10 days in total (second predetermined period)) have passed after the storage in the dark for the past 3 days. It means that. Next, the seedlings were planted in a hydroponic cultivation kit and cultivated for 28 days. During cultivation, the temperature was maintained at 22°C and the humidity was maintained at 40-50%. Hyponex (registered trademark: liquid fertilizer manufactured by Hyponex Japan Co., Ltd.) was diluted 1000 times and used as the liquid fertilizer.

The lettuce was irradiated with the main light and two types of additional light (upper left diagram and upper right diagram in FIG. 8). The additional light is a combination of additional signal light and additional relaxation light.
As shown in the upper right diagram in FIG. 8, the main light was irradiated from 0:00 to 12:00 during the 24 hours of the day, and the additional light was irradiated from 6:00 to 18:00. The PPFD (μmol・m ^-2・s ^-1 ) of each light is 220 for the main light, 0.05 for the additional signal light, and 0.05 for the additional relaxed light, as shown in the lower left diagram in Figure 8. there were.
As shown in the upper left diagram in FIG. 8, the main light was applied from the 3rd day to the 35th day after sowing, and the additional light was applied from the 7th day after planting to the 35th day.

Hereinafter, a test in which cultivation was performed using only main light will be referred to as a control (hereinafter sometimes abbreviated as "CNT"), and a test in which additional light was irradiated will be referred to as a comparative test.

In Example 1, the following two types of comparative tests "1." to "2." were conducted (bottom left diagram in FIG. 8).
1. Comparative test 1 Irradiation with additional light in the wavelength range from 620 nm to 640 nm 2. Comparison test 2 Irradiation of additional light with wavelength range from 710nm to 1000nm

In Comparative Test 1 to Comparative Test 2 above, the parameters of additional signal light 1 and additional signal light 2 were fixed to the following values (lower right diagram in FIG. 8).
T=25μs, ΔT ₁ =2μs, ΔT ₂ =2μs, ΔT ₃ =4μs
Here, T, ΔT _{1 ,} ΔT _{2 ,} and ΔT ₃ have the same meanings _as explained in connection with FIG. 5 .
The period of additional signal light 1 and additional signal light 2 was 16.7 ms.

The plants were harvested on the 35th day after sowing, the harvested wet weight of the portion excluding roots was measured, and the wet weight ratio was calculated using the following formula (1). Wet weight was determined from the average value of 10 plants.

[Harvest wet weight ratio] = Harvested wet weight of test plot/harvested wet weight of control (CNT) (1)

The weight of ascorbic acid (vitamin C) and glutamic acid contained in 1 g of harvested wet weight of lettuce was quantitatively analyzed using a high performance liquid chromatography device (hereinafter referred to as HPLC device). The ascorbic acid ratio (weight ratio) was calculated using equation (2).

[Ascorbic acid weight ratio] = Ascorbic acid weight of test plot/wet ascorbic acid weight of control (CNT) (2)
The total weight ratio of ascorbic acid contained in lettuce was calculated using the following equation (3).

[Ascorbic acid total weight ratio] = [Harvest wet weight ratio] x [Ascorbic acid weight ratio] (3)

The glutamic acid ratio (weight ratio) was calculated using equation (4).

[Glutamic acid weight ratio] = Glutamic acid weight of test plot/Wet glutamic acid weight of control (CNT) (4)
The total weight ratio of glutamic acid contained in lettuce was calculated using the following formula (5).

[Glutamic acid total weight ratio] = [Harvest wet weight ratio] x [Glutamic acid weight ratio] (5)

Table 2 shows the calculation results of the harvest wet weight ratio, ascorbic acid weight ratio, and total ascorbic acid weight ratio in each comparative test.

According to Example 1, additional light irradiation (additional light irradiation ) has the effect of increasing the harvested wet weight of lettuce. Furthermore, it has the effect of promoting the production of ascorbic acid, which is synthesized through secondary metabolism, and glutamic acid, which is synthesized through primary metabolism. Furthermore, from the results of Comparative Test 1 and Comparative Test 2, additional light has the effect of promoting the synthesis of ascorbic acid and glutamic acid. Furthermore, from the results of Comparative Test 1 and Comparative Test 2, additional light irradiation with a wavelength of 620 nm to 640 nm is highly effective in promoting the synthesis of glutamic acid, and additional light irradiation with a wavelength of 710 nm to 1000 nm promotes the synthesis of ascorbic acid. is highly effective.

<Example 2>
The effect of additional light irradiation on the growth of garlic shoots and the synthesis of the secondary metabolite allylcysteine (indicated as "s-allylcysteine" in Figure 4) was investigated. FIG. 9 shows the conditions according to the second embodiment by a diagram of four regions separated by broken lines. The upper left diagram (region) in FIG. 9 shows the irradiation periods of various types of light, etc., and the upper right diagram (region) shows the irradiation time periods of various lights in one day. The lower left diagram (region) shows the characteristics of various types of light, and the lower right diagram (region) shows changes in the number of photons of the additional signal light, the period of the additional relaxed light, etc.

First, the garlic bulbs were stored at a temperature of 4°C for 1 day, and then at a temperature of 20°C for 24 hours. Next, the garlic bulbs were placed on top of the moist rock wool with an interval the length of one garlic bulb apart.

Garlic bulbs were irradiated with main light 1, additional light 1, and main light 2 (upper left diagram and upper right diagram in FIG. 9). The additional light is a combination of additional signal light and additional relaxation light.
As shown in the upper right diagram in FIG. 9, during the 24 hours of the day, main light 1 is from 0:00 to 12:00, additional light 1 and additional light 2 are from 6:00 to 20:00, and main light 2 is from 12:00. It was irradiated from 1:00 to 24:00. The PPFD (μmol·m ^-2 ·s ^-1 ) of each light is 160 for principal light 1, 0.1 for additional signal light, and 3.0 for additional relaxed light, as shown in the lower left diagram in Figure 9. , the main light 2 was 160.
As shown in the upper left diagram in FIG. 9, main light 1 was applied from the first day to the sixth day of cultivation, and additional light was applied from the first day to the sixth day of cultivation. Main light 2 was applied for 12 hours immediately after main light 1 was turned off on the 6th day of cultivation.

Hereinafter, a test in which cultivation was performed using only main light 1 will be referred to as a control (hereinafter sometimes abbreviated as "CNT"), and a test in which cultivation was performed using additional light and main light 2 will be referred to as a comparative test.
The wavelength range of principal light 1 and principal light 2 is from 400 nm to 750 nm.

In Example 2, the following two types of comparative tests "1." to "2." were conducted (bottom left diagram in FIG. 9).
1. Comparative test 1 Irradiation of additional light 1 with a wavelength range of 600 nm to 660 nm 2. Comparison test 2 Irradiation with additional light and main light 2

In Comparative Test 1 and Comparative Test 2 described above, the parameters of the additional signal light were fixed to the following values (lower right diagram in FIG. 9).
T=30μs, ΔT ₁ =2μs, ΔT ₂ =10μs, ΔT ₃ =4μs
Here, T, ΔT _1, ΔT _2, and ΔT ₃ have the same meanings _as explained in connection with FIG. 5.

In Comparative Test 1 and Comparative Test 2 described above, the basic cycle of the intensity change of the additional relaxation light was 16.7 ms.

In control and comparative test 1, only the new shoots were cut (harvested) from the bulbs at 2:00 pm on the 6th day of cultivation. In Comparative Test 2, only the new shoots were cut (harvested) from the bulbs at 14:00 on the 6th day of cultivation, placed in a transparent container maintained at a humidity of 65%, and irradiated with Principal Light 2.

The harvested wet weight of only the new shoots cut from the garlic bulb was measured, and the wet weight ratio was calculated using the following equation (6). Wet weight was determined from the average value of 20 plants.

[Harvest wet weight ratio] = Harvested wet weight of test plot/harvested wet weight of control (CNT) (6)

The weight of allylcysteine contained in garlic sprouts was quantitatively analyzed using a high performance liquid chromatography device (hereinafter referred to as an HPLC device). The allylcysteine ratio was calculated using equation (7).

[Ascorbic acid weight ratio] = Ascorbic acid weight of test plot/wet ascorbic acid weight of control (CNT) (7)

The total weight ratio of allylcysteine contained in garlic sprouts was calculated using the following formula (8).

[Allylcysteine total weight ratio] = [Harvested wet weight ratio] x [allylcysteine weight ratio] (8)

Table 3 shows the calculation results of the harvest wet weight ratio, allyl cysteic acid weight ratio, and allyl cysteine total weight ratio in each comparative test.

According to this Example 2, from the results of "harvest wet weight ratio" and "allylcysteine weight ratio" which represent the ratio with control (CNT), additional light irradiation (additional light irradiation) requires harvesting of garlic sprouts. It has the effect of increasing wet weight and allylcysteine, a secondary metabolic component. Furthermore, from the results of Comparative Test 1 and Comparative Test 2, the light irradiation of Principal Light 2 does not have the effect of increasing harvested wet weight compared to Comparative Test 1, but has the effect of increasing allylcysteine.

<Example 3>
In Example 3, the influence of post-harvest light irradiation on polyphenols contained in fresh olive leaves was investigated. FIG. 10 shows the conditions according to the third embodiment by a diagram of two regions separated by a broken line. The upper diagram (region) in FIG. 10 shows the type of principal light, and the lower diagram (region) shows the test method.

Olives were grown in the field. Principal light 1 is sunlight. The olive leaves were cut (harvested) at noon (afterwards) on a sunny day. The following test was conducted using 200 g of fresh olive leaves.

As shown in the lower diagram of Figure 10, below, the polyphenol quantitative test of fresh olive leaves immediately after cutting (harvesting) is referred to as control (hereinafter sometimes abbreviated as "CNT"), A test in which fresh olive leaves (harvested) are irradiated with main light to quantify polyphenols after 24 hours is called a comparative test.

In Example 3, three types of comparative tests (Comparative Tests 1 to 3) were conducted: "1." to "3." below.
1. Comparative test 1: Leave in the dark for 24 hours 2. Comparison test 2 Irradiated with main light 2 with wavelength range from 380 nm to 770 nm and PPFD (μmol・m ^-2・s ^-1 ) of 230 for 12 hours (first predetermined period), 12 hours in a dark place (second predetermined period) )Stand still 3. Comparative test 3 Main light 2 with wavelength range from 380 nm to 770 nm and PPFD (μmol・m ^-2・s ^-1 ) of 230 is irradiated for 24 hours

For Comparative Tests 2 and 3, the cut (harvested) olive leaves were placed in a container with a humidity of 65%. Thereafter, it was irradiated with light (principal light) from a white LED (wavelength range from 380 nm to 770 nm) and stored in a dark place (12 hours in Comparative Test 2 and 24 hours in Comparative Test 3).

The total amount of polyphenols contained in fresh olive leaves was quantified by absorbance measurement. The total polyphenol weight ratio was calculated using the following formula (1).

[Total polyphenol weight ratio] = total polyphenol weight of test plot/total polyphenol weight of control (CNT) (1)

Table 4 shows the calculation results of the total polyphenol weight ratio in each comparative test.

According to Example 3, from the results of the "total polyphenol weight ratio" representing the ratio with the control (CNT), irradiation with main light immediately after harvest has the effect of increasing the total polyphenol weight contained in fresh olive leaves. be. From the results of Comparative Test 2, the effect of increasing the total polyphenol weight is large when the sample is left standing in a dark place after the irradiation with Main Light 2 is completed.

<Light compensation point of each plant>
The value of the light compensation point of lettuce is 20 to 30 (μmol·m ⁻² ·s ⁻¹ ). Although we have not obtained specific data on the light compensation point of barley, it is 7 ^to 15 (μmol·m -2·s -1 ) for rice, so barley is also 7 to 15 (μmol·m ^-2 ·s ^-1 ). s ^-1 ). Regarding olives, we have not obtained specific data, but the light compensation point for tea is based on the literature (Plant Environmental Engineering (J.SHITA) 24(1):16-24. 2012. ``Light under low light conditions''). The effect of differences in quality on the photosynthesis and nitrogen absorption and assimilation abilities of young tea plants (Toshikazu Suzuki et al.) shows that the light compensation point is 30 to 50 (μmol・m ^-2・s ^-1 ), and the light saturation point is 500. ~850 (μmol·m ⁻² ·s ⁻¹ ). Therefore, it can be inferred that the optical compensation point of the olive is also in the range of 30 to 50 (μmol·m ⁻² ·s ⁻¹ ).

<Inventions that can be extracted from the embodiments and examples>
(1) During at least part of the cultivation period from sowing to harvest, irradiation of main light for photosynthesis (sunlight, artificial light, etc.) and additional light to promote photosynthesis of plants by the main light, The additional light includes additional signal light whose light intensity changes periodically and additional relaxed light whose light intensity changes more slowly than the additional light, and the wavelength of the additional signal light (such as 500 to 2000 nm) is , a plant cultivation method that includes the light absorption wavelength band (wavelength band of 600 nm or more, etc.) of red photoreceptors (Pr-type phytochrome, Pfr-type phytochrome, etc.) in plants.
(2) Separate the leaves or buds of the plant from the roots, branches, or stems, irradiate only the leaves or buds with the main light for a certain period of time (such as a first predetermined period), and then keep the leaves or buds in a dark place for a certain period of time. The method for cultivating plants according to (1) above, wherein the plant cultivation method is maintained for a period of time (such as a second predetermined period).
(3) A plant cultivation device (plant cultivation device 10, etc.) that is irradiated with main light (sunlight, artificial light, etc.) for photosynthesis of plants,
an additional light source (such as the additional light source 22) that irradiates additional light that promotes photosynthesis of plants by the main light;
comprising an irradiation light control unit (e.g. irradiation light control unit 16) capable of driving and controlling the additional light source,
The additional light source is
an additional signal light source (such as the additional signal light source 24) that emits additional signal light whose light intensity periodically fluctuates;
an additional relaxation light source (such as the additional relaxation light source 26) that irradiates additional relaxation light whose light intensity changes more slowly than the additional light;
irradiating the additional relaxation light together with the additional signal light;
A plant cultivation device in which the wavelength of the additional signal light (500 to 2000 nm, etc.) includes a light absorption wavelength band (600 nm or more wavelength band, etc.) of red photoreceptors (Pr type phytochrome, Pfr type phytochrome, etc.) in the plant.

The plant cultivation method of the present invention is effective for outdoor cultivation, greenhouse cultivation, and plant factory cultivation. It has a growth-promoting effect on all plants that perform photosynthesis, so lettuce, leaves such as perilla and basil, fruit trees such as strawberries, grains such as rice and wheat, seaweed such as wakame, human extract and euglena. It can be used to improve production efficiency and reduce production costs of green algae, etc.

10: Plant cultivation device 12: Cultivation bed 14: Light irradiation unit 16: Irradiation light control unit 18: Protective member 20: Main light source 22: Additional light source 24: Additional light source 26: Additional relaxing light source

Claims (3)

During at least part of the cultivation period from sowing to harvest, main light for photosynthesis and additional light for promoting photosynthesis of the plants by the main light are irradiated, and the additional light has a light intensity that is periodically Plant cultivation comprising additional signal light that fluctuates and additional relaxation light whose light intensity changes more slowly than the additional light, and the wavelength of the additional signal light includes a light absorption wavelength band of red photoreceptors in the plant. Method. 2. The method according to claim 1, wherein leaves or buds of the plant are separated from roots, branches, or stems, only the leaves or buds are irradiated with the main light for a certain period of time, and then kept in a dark place for a certain period of time. Plant cultivation methods. A plant cultivation device that is irradiated with main light for photosynthesis of plants,
an additional light source that irradiates additional light that promotes photosynthesis of plants by the main light;
and an irradiation light control unit capable of driving and controlling the additional light source,
The additional light source is
an additional signal light source that emits additional signal light whose light intensity periodically fluctuates;
an additional relaxation light source that emits additional relaxation light whose light intensity changes more slowly than the additional light;
irradiating the additional relaxation light together with the additional signal light;
A plant cultivation device in which the wavelength of the additional signal light includes a light absorption wavelength band of a red photoreceptor within the plant.