The light of nature comes from the sun, and the solar spectrum cocoa is roughly divided into three parts: ultraviolet light <400nm (UV-A315-400nm, UV-B280-315nm, UV-c100-280nm), far red light and infrared light >700nm ( Far red light 700-780nm, infrared light 780nm-1000μm), photosynthetically active radiation 400-700nm (blue-violet light 400-500nm, green light 500-575nm, yellow orange light 575-620nm, red light 620-700nm). Among them, the medium-ultraviolet UV-B and the far-ultraviolet UV-C are mostly absorbed by the ozone layer above the earth, and the ultraviolet light reaching the ground is mainly UV-A.
Light is the basic environmental factor for plant growth and development. Illumination not only supplies the energy needed for plant growth through photosynthesis, but is also an important regulator of plant growth and development.
Plant photoreceptor
A series of responses of plants to the external light environment are based on the absorption of light by photoreceptors. The main photoreceptors include photosynthetic pigments, phytochromes, cryptochromes, and photochromes. They perform their duties in plants, affecting the photosynthetic physiology, metabolic physiology, and morphogenesis of plants.
1.1 Photosynthetic pigments
Photosynthetic pigments are the basic building blocks of photosystems. Photosynthetic pigments include chlorophyll a, chlorophyll b and carotenoids. It mainly undertakes photosynthetic processes such as light energy reception, energy transfer and photoelectric conversion in photosynthesis. Experiments have shown that the main absorption wavelength of chlorophyll is 640-663 nm, and there is a secondary absorption peak at 430-450 nm. Carotenoids are more of a protective effect on the body. In photosynthesis, due to the presence of two optical systems Ps II and Ps I , the photosynthetic rate is much higher than that of monochromatic illumination when red and far red light are illuminated together.
Photosynthetic pigment absorption spectrum
1.2 phytochrome
The phytochrome is formed by covalently combining a chromophore group and an apoprotein, including two types, far red light absorption type (Pfr) and red light absorption type (Pr), mainly absorbing red light of 600-700 nm and 700- The far-red light of 760 nm regulates the physiological activities of plants by the reversible action of far red light and red light. In plants, phytochrome is mainly involved in the regulation of seed germination, seedling formation, establishment of photosynthetic systems, shading, flowering time and circadian rhythm response. In addition, it also regulates the stress resistance of plants.
Photosensitive pigment absorption spectrum
1.3 cryptochromes
The cryptochromes are blue-light receptors, which mainly absorb blue light of 320-500 nm and UV-A of near-ultraviolet light, and the absorption peaks are roughly at 375 nm, 420 nm, 450 nm and 480 nm. Cryptochrome is mainly involved in flowering regulation in plants. In addition, it is involved in regulating plant directional growth, stomatal opening, cell cycle, guard cell development, root development, abiotic stress, apical dominance, fruit and ovule development, programmed cell death, seed dormancy, pathogen response And magnetic field induction and other processes.
1.4 Directional light
The photoreceptor is a blue light receptor found after phytochrome and cryptochrome, which can be phosphorylated by binding to flavin mononucleotide. It can regulate the phototaxis of plants, chloroplast movement, stomatal opening, leaf extension and inhibition of hypocotyl elongation of yellowing seedlings.
2. The effect of light quality on plants
2.1 Red light
Red light generally exhibits inhibition of internode elongation, promotes tillering, and increases accumulation of chlorophyll, carotenoids, soluble sugars, and the like. Red light promoted the leaf area growth and β-carotene accumulation of pea seedlings; the lettuce seedlings pre-illuminated red light and applied near-ultraviolet light, and found that red light can enhance the activity of antioxidant enzymes and increase the content of near-ultraviolet absorbing pigments to reduce the near The damage of ultraviolet light on lettuce seedlings; the full light experiment of strawberry found that red light is beneficial to increase the content of organic acid and total phenol in strawberry.
2.2 Blu-ray
Blue light can significantly shorten the pitch of vegetables, promote the lateral extension of vegetables and reduce the leaf area. At the same time, blue light can also promote the accumulation of secondary metabolites in plants. In addition, it was found that blue light can alleviate the inhibition of photosynthetic system activity and photosynthetic electron transport ability of cucumber leaves by red light, so blue light is an important factor affecting photosynthetic system activity and photosynthetic electron transport ability. Plants have significant species differences in the need for blue light. After strawberry harvesting, it was found that the effect of 470nm on anthocyanin and total phenol content in different wavelengths of blue light was obvious.
2.3 Green light
Green light has always been a controversial light quality, and some scholars believe that it will inhibit the growth of plants, resulting in short plants and reduced yield of vegetables. However, there are also many studies on the positive effects of green light on vegetables. A low proportion of green light can promote the growth of lettuce; supplementing 24% of green light on the basis of red and blue light can promote the growth of lettuce.
2.4 Huang Guang
Yellow light is basically expressed as inhibition of plant growth, and since many researchers have incorporated yellow light into green light, there is very little literature on the effects of yellow light on plant growth and development.
2.5 ultraviolet light
Ultraviolet light is generally more manifested as a killing effect on organisms, reducing plant leaf area, inhibiting hypocotyl elongation, reducing photosynthesis and productivity, and making plants more susceptible to infection. However, proper supplementation of ultraviolet light can promote the synthesis of anthocyanins and flavonoids, and promote the synthesis of polyphenols by adding a small amount of UV-B to the harvested cabbage; post-harvest UV-c treatment can slow the red peppers. Glue dissolution, mass loss and softening process, which significantly reduces the rate of spoilage of red peppers and prolongs the shelf life, and promotes the accumulation of phenolic substances on the surface of red pepper. In addition, ultraviolet light and blue light affect the elongation and asymmetric growth of plant cells, thereby affecting the directional growth of plants. UV-B radiation results in a dwarf plant phenotype, small, thick leaves, short petiole, increased axillary branches, and root/crown ratio changes.
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2.6 far red light
The far red light is generally used in combination with red light. Due to the problem of absorbing the structure of the luminescent pigment of red light and far red light, the effects of red light and far red light on the plants can mutually cancel each other. When the white fluorescent lamp is the main light source in the growing chamber, the far-red radiation (the emission peak is 734 nm) is supplemented by LEDs, the anthocyanin, carotenoid and chlorophyll content are decreased, and the fresh weight, dry weight, stem length, leaf length and leaf width of the plant are increased. . The effect of supplemental FR on growth may be due to an increase in light absorption due to increased leaf area. Low R/FR treated Arabidopsis thaliana had larger and thicker leaves, increased biomass, and more soluble metabolite accumulation to improve cold resistance than high R/FR treatment.
3. Effect of light quality on plant tissue culture
Seedling morphogenesis and physiological and biochemical changes during plant tissue culture are regulated by many environmental factors (light, temperature, humidity, etc.). Among them, light plays an extremely important role in the growth and differentiation of plant cells, tissues and organs. The morphological stages of plant tissue culture from the callus induction to the formation of intact plants are affected by LED light quality, and the response of different tissue culture stages to light quality is different.
3.1 Effect of LED light quality on induction of callus induction, growth and differentiation
Callus culture is an important part of plant in vitro culture. The study found that 100% red light had the highest induction rate of orchid callus, and the callus had the best growth effect when the ratio of red to blue was 3:1. Monochrome red LEDs promote the formation of callus of Anthurium, but with the increase of the proportion of blue light, the callus induction rate of leaves is gradually reduced. Red and white light promoted the induction of pepper callus callus, while green and blue light showed inhibition. Yellow light is beneficial to the induction of radish hypocotyl callus, while blue light promotes the induction of cotyledon callus. Red light significantly promoted the induction and proliferation of garlic callus, while blue light had the strongest promoting effect on the differentiation of Chinese yam. Yellow light is most beneficial to grape callus proliferation, followed by green light. Yellow light is beneficial to the induction of radish hypocotyl callus, while blue light is beneficial to the induction of cotyledon callus, and red light is beneficial to callus proliferation. Red light is beneficial to the induction and proliferation of protocorm callus of Radix Paeoniae. The protocorm callus of the gladioli has the highest proliferation rate under red light. The callus induction rate of orchids under red light is the highest. Blue light and yellow light significantly promote the proliferation of white birch callus. It can be seen that the effects of different light qualities on callus induction vary depending on the type of plant or the type of explant.
The growth curve of callus under different light quality was “s” shape, but the effect of different light quality on callus growth was different due to different plant genotypes and matrix additives. Huangguang LED promotes the growth of Vietnamese ginseng callus, and red and blue LEDs inhibit callus growth. Among them, red LED has the strongest inhibitory effect, while green and white LED have no significant effect on callus growth. The effect of different light quality on the callus proliferation of broccoli was white light>red light, blue light>green light>yellow light, and the soluble protein content and water content of callus under different light quality were related to callus proliferation. Sex. The callus growth of radish was the highest under red light, while the yellow light had the lowest growth effect on callus. When no cinnamic acid is added, yellow light is most beneficial to the proliferation of callus of grape leaves. When cinnamic acid and light quality work together, green light is most suitable for the proliferation of callus, and the growth effect of yellow light on callus is obviously weakened. .
Light quality plays an important role in bud differentiation. Red light significantly promoted the differentiation of sugarcane callus into seedlings. The original bulb of Wenxinlan differentiates the number of adventitious buds under blue light. Both blue light and red blue light inhibited the differentiation of adventitious buds of lettuce explants. Under the red light irradiation, the callus of garlic was the highest, reaching 25%, followed by white light. The mixed light of blue light and red and blue inhibited the sprouting of callus. Among them, the blue light inhibition was the strongest, and the sprouting rate was only 3%. . Red light promoted the induction of adventitious buds from callus of Anthurium, while blue light was more conducive to the increase of the number of adventitious buds. The bud differentiation rate of the Chinese yam callus was the highest under blue light, followed by red light and white light, and low green light and yellow light. Maca callus has almost zero germination rate under blue light. Red blue light is beneficial to the differentiation of callus adventitious buds. Blue light promotes the increase of adventitious buds through cryptochromes. Red light regulates the apical dominance through phytochrome to promote the growth of adventitious buds.
3.2 Effect of LED light quality on the proliferation of tissue culture seedlings
The study found that red light in monochromatic light promoted the proliferation of tissue culture seedlings. The number of single buds of Phalaenopsis under pure red LEDs was significantly higher than that of the control fluorescent lamps, and the trials of chrysanthemum and tobacco also reached similar conclusions. However, single blue light is not conducive to the proliferation of tissue culture seedlings. The study on the growth of Eustoma and sugarcane tissue culture seedlings found that all the light quality treatments had the lowest proliferation rate of tissue culture seedlings under monochromatic blue light treatment. However, blue LED can effectively promote the formation of the original bulb of Phalaenopsis.
A large number of experiments have proved that compared with monochromatic LEDs, different LED combinations are more conducive to tissue culture seedling proliferation. LED red and blue combined light can promote the proliferation of sugarcane adventitious buds than monochromatic light, and is superior to fluorescent lamps and plant growth lamps. Under the combination of red and blue light, the regeneration of adventitious buds of Rhododendron chinense leaves was significantly better than 100% red and blue light. However, the demand for light quality ratios in different stages of tissue culture and proliferation of different plants or different species of the same species is not completely consistent. Alpine rhododendron had the best regeneration of adventitious buds under the treatment of red and blue light (3:1), while sugarcane had the highest number of adventitious buds under the treatment of red and blue light (4:1).
3.3 Effect of LED light quality on growth and development of tissue culture seedlings 3.3.1 Effect of LED light quality on growth of tissue culture seedlings
Studies have shown that the growth effect of LED monochromatic light on tissue culture seedlings is lower than that of different LED combinations. Red and blue LED combined light can enhance plant photosynthesis to promote plant growth and development. The white palm tissue culture seedlings treated with separate red or blue LEDs have poor growth, and the red-blue LED composite light with certain ratio is beneficial to promote plant growth. The net photosynthetic rate of the leaves of the chrysanthemums under the combination of red and blue LEDs was significantly higher than that of the monochromatic red and blue light, and the fresh weight and dry weight of the plants reached the maximum. Under the blue light, the dry weight of the aboveground part of the strawberry sugar-free tissue culture seedlings was the smallest. Dolly Phalaenopsis has the highest fresh weight and the highest dry weight under red and blue light.
The best red-blue LED ratio for tissue culture seedling growth, the conclusions of different plants are not consistent. Under the condition of 70% red light + 30% blue light, the double-butterfly and strawberry in Japan have the best growth of tissue culture seedlings. The growth index of anthurium tissue culture seedlings was significantly higher than that of the control under 50% red light + 50% blue light treatment. Red light (R) treatment of white and tissue culture seedlings, blue (B) treatment of white and tissue culture seedlings low, complex color light is conducive to white growth and morphogenesis; 1RB light source treatment of white and tissue culture seedlings soluble sugar The content is significantly higher than other treatments; red light and blue light (1:1) are most beneficial to the accumulation of soluble sugar in white and tissue culture seedlings.
Therefore, in tissue culture production applications, adjusting the optimal red-blue ratio is the key to producing good quality tissue culture seedlings.
3.4 Effect of LED light quality on roots and seedlings of tissue culture seedlings
The effect of light quality on root induction and growth of isolated plants varies with wavelength, and the effect of light quality depends on plant genotype and rooting substance concentration. Red light promoted the formation of adventitious roots of tissue cultured seedlings such as Anthurium, Phalaenopsis, Imperial flower and ground cover, which showed rapid rooting and denseness, and blue light showed obvious inhibition. Papaya tissue culture seedlings had the shortest root length under blue light; red-blue mixed light had a certain promoting effect on the growth of sweet potato tissue culture seedling roots. However, under the monochromatic red light, the root morphology of tissue culture seedlings is abnormal, and the survival rate of transplanting is low, while blue light is beneficial to improve the root activity in the later stage, which can promote dry matter accumulation, reduce water content and prevent plant vitrification. The root activity of chrysanthemums irradiated by monochromatic red light is low, and the survival rate of transplanting is only 75%, while the transplanting of tissue culture seedlings under red and blue light combination survives. The root length and root activity of the Phalaenopsis roots treated with the combination of far-red LEDs increased significantly compared to the control. Wenxinlan tissue culture seedlings have the longest root length under the combination of red and blue light, while the root length under fluorescent light is the shortest.
The LED light source used in the tissue culture stage affects the growth and survival of tissue culture seedlings after transplanting. The red-blue LED combined light source used in the indoor tissue culture stage can improve the survival rate of tissue culture seedlings of strawberry, white palm and chrysanthemum and promote the growth of seedlings after transplanting. Therefore, for plant tissue culture seedlings that are difficult to root, the rooting rate and rooting number can be increased by pre-treatment of red light, and then transferred to a certain ratio of red light, blue light and far red light to promote root growth and development. And improve root vigor, thereby improving the adaptability of tissue culture seedling transplanting.
4. Effect of light quality on vegetable seedlings
Light quality has a significant effect on the growth, development and photosynthesis of plant seedlings. Red light is conducive to the elongation of stems and dry matter accumulation of vegetable seedlings. Blue light is beneficial to the accumulation of protein and promotes the activity of antioxidant enzymes. The combined light is more conducive to the photosynthesis and growth of vegetable seedlings than single light. Ultraviolet radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, makes plants susceptible to pathogen attack, but induces flavonoid synthesis and defense mechanisms; it also significantly reduces soybean plant height and dryness. Heavy and moisture content, the damage to the photosynthetic pigments of seedlings is more serious. Blue light can inhibit the hypocotyl elongation and the elongation of tobacco stems and reduce the relative growth rate of red bean sprouts. It has an extremely important effect on the growth of plant leaves and roots, which can reduce the leaf area and reduce the number of leaves of lettuce seedlings. It is beneficial to promote the synthesis of nutrients related to flower bud differentiation and flower formation. Green light is not a high-efficiency absorption spectrum for photosynthesis, but supplementation with green light can synergize with red and blue light to synthesize pigments, which can significantly increase the plant height and stem diameter of tomato seedlings and promote the growth of pea sprouts. Red orange light is good for stem growth, and promotes plant flowering and chlorophyll formation, shortening growth cycle, increasing soluble sugar content and yield. Far red light can increase the dry weight, stem length, leaf length and leaf width of the plant; but in many cases it will offset the red light effect and reduce the content of anthocyanins, carotenoids and chlorophyll. In the morning, the cucumber seedlings were subjected to low-intensity blue light and red light for two hours, and it was found that the light supplement increased the fresh weight, leaf area and stem diameter of the seedlings. The use of red LEDs for nighttime light supplementation can promote the growth of cucumber seedlings in the early stage. The red and blue mixed light nighttime light supplement can promote the growth of cucumber seedlings and increase the seedling index. Using LED red and blue light as the light source, it can effectively promote the morphogenesis of cowpea, bitter gourd, lettuce and pepper seedlings. With the enhancement of LED red and blue light, the seedling morphological index is gradually increased, the chlorophyll synthesis is gradually increased, and the root activity is gradually enhanced. Different LED light quality has significant effects on the growth of different varieties of cucumber, pepper and tomato. The red or red-blue light can promote the growth of seedlings during seedling stage, which is conducive to the cultivation of strong seedlings. Filling light can increase the content of flavonoids and total phenols in tomato and pepper, enhance the activity of antioxidant enzyme system cAt and soD, and improve the plant’s resistance to stress and adaptability to the environment. After the light-filled greenhouse saplings were transplanted to the field, the growth stage and the agronomic traits at maturity were better than those in the greenhouse. The difference in leaf number and stem diameter reached a very significant level. The leaf length and width of flue-cured tobacco Ratio, single leaf weight, thickness, specific leaf weight, etc. are far superior to the control.
As an important characteristic of the light environment, light quality directly or indirectly affects the synthesis and transportation of plant hormones. Irradiation of red and blue light during seedling can significantly promote the growth of vegetable seedlings and increase the seedling index. Different bands of light can regulate the growth of internodes by affecting the hormone levels in plants. The phytochrome affects the growth of hypocotyls by affecting the level of endogenous GA in cowpea seedlings. Far red light promotes the significant elongation of the hypocotyls of tomato and lettuce seedlings, and the seedlings are severely long. Blue-violet light can increase the activity of auxin oxidase. By reducing the level of auxin in the plant, it can weaken the apical dominance and enhance the tillering ability, thereby inhibiting the internode elongation. The hypocotyl elongation of seedlings is related to the light quality of different wavelengths. White light and blue light can inhibit the elongation of stems, while green light significantly promotes the elongation of internodes. Exogenous application of IAA or GA can restore the hypocotyl of the lettuce seedlings inhibited by blue light to some extent, indicating that blue light may inhibit the elongation of hypocotyls by reducing the level of endogenous GAs in lettuce seedlings. The levels of various hormones in the plants under different complex light treatments were reduced, and the hypocotyls showed a lower growth rate. When the proportion of blue light is increased appropriately in the light treatment (R/B=7:3), the height of the seedling plants is significantly decreased, and the seedling index is significantly increased.
5. Influence of different light quality LED lamps on plant growth quality
Light quality has a great impact on plant growth and development, photosynthetic characteristics, yield and quality. Studies have shown that green light and red light can significantly promote the elongation of stems of colored sweet pepper seedlings, and blue light has a dwarf effect on seedlings. The effect of composite light is better than that of monochromatic light, and it is obviously long under green light. Red light is not conducive to the increase of chrysanthemum stems, red stem treatment stem length is 43.0% less than the control; also red light is conducive to the thickening of stems of chrysanthemum plants. Increasing the proportion of blue light can effectively reduce the plant height of cucumber seedlings, and the increase in the proportion of red light can make the photosynthesis products more transported to the leaves of the seedlings. The chlorophyll a, chlorophyll b and carotenoids of lettuce increased with the proportion of blue light. The blue light treatment or the increase of the blue light ratio significantly increased the chlorophyll content of the plant, so that the photosynthetic rate of the plant was significantly improved. It indicates that the high proportion of blue light intensity may be beneficial to the synthesis of photosynthetic pigments. The photosynthesis of 7% blue-light plants in the red-blue combined light can operate normally; as the proportion of blue light increases, the photosynthetic capacity of the leaves increases, but the photosynthetic capacity of the leaves decreases when the proportion of blue light exceeds 50%. Under the irradiation of single red light, the dry matter accumulates more, the internodes are longer, the stem diameter is smaller, the leaves are smaller, and the total sugar content is higher. Under the single blue light illumination, the dry matter accumulation is less. The internodes are shorter and the stems are thicker, which inhibits the elongation of the stems to some extent. The red sugar-treated cucumber seedlings had the highest soluble sugar content, and the blue-soluble soluble protein content was the highest, which was significantly different from the control. The chlorophyll content of tomato seedlings increased, the stomatal conductance and transpiration rate increased, and the photosynthetic rate was significantly higher than other treatments. The chlorophyll content of blue light treatment was slightly lower, but the photosynthetic rate was still significantly higher than that of the control. The reason may be blue light promotion. The open pores increase the intercellular CO2 concentration of the leaves. The increase in stomatal conductance of the leaves of plants is specifically induced by blue light.
For most plants, red light contributes to the increase in leaf area. Under the red light treatment, the leaves of radish seedlings, camphor seedlings, tomato, cucumber seedlings, tobacco, grass poison and lettuce were expanded faster and the leaves were larger. Similarly, blue light can increase the area of ??the blade, but blue light suppresses blade expansion of tobacco, poinsettia, and clover. The addition of blue light to red light can significantly increase the leaf area of ??lettuce. The leaf area of ??spinach under red, yellow and yellow light treatment was significantly larger than other treatments. Red light treatment is beneficial to the accumulation of dry matter in crops such as tomato, eggplant, cucumber and lettuce. The red-blue complex light promotes the growth of biomass such as pepper, phalaenopsis, vegetative and cucumber. The addition of green, yellow, violet and white light to the red and blue light combination has a significant effect on the biomass of lettuce, cherry tomatoes and non-heading Chinese cabbage.
Under red light, it is beneficial to the accumulation of carbohydrates in plants. Red light treatment can significantly improve the soluble sugar content of spinach, cucumber, pepper, tomato seedlings and radish sprouts. Red light can promote the accumulation of starch, which has been reported in crops such as soybean, cotton, oil sunflower sprouts and Brassica napus. Because the output of the photosynthetic product in the leaves can be inhibited by red light, the starch accumulates in the leaves. The change of soluble protein content in leaves is one of the reliable indicators reflecting the physiological function of leaves. Blue light is good for protein synthesis. Blue light promotes the soluble protein content of pea sprouts, lettuce, cucumber and sprouts. Blue light significantly promotes the total amount of amino acids and sugar content in chrysanthemum leaves. The current study found that blue light can significantly promote the dark breathing of mitochondria, and the organic acid produced during the breathing process can be used as a carbon skeleton for the synthesis of amino acids, thereby facilitating protein synthesis.
The composite spectrum also has different promoting effects on the photosynthetic products of plants. Yellow light is beneficial to the synthesis of soluble sugar and protein in lettuce, the formation of sucrose in tomato and the accumulation of free amino acids in rapeseed sprouts. Low dose UV-B combined with red light significantly increased the accumulation of sugar in tomato. Blue light and UV-A can promote the synthesis of protein in cucumber fruit. Blue-red combined light promotes the accumulation of soluble sputum and soluble proteins. Red, blue and white composite light promotes the synthesis of soluble sugar and nitrogen content. The total starch content of tomato seedlings treated with red, blue and green light combination was the worst. As a plant active oxygen scavenger, SOD maintains high activity in the environment to effectively remove active oxygen and keep it at a low level, thus reducing its damage to membrane structure and function. The study found that the activity of SOD in colored sweet pepper seedlings was the highest under green light, and the difference between blue light and red light was not significant. POD was an active oxygen scavenger, and its activity could reduce the damage of reactive oxygen species on the membrane, and the POD activity was the lowest under green light. CAT can scavenge free radicals and maintain the integrity of the membrane system to alleviate the harmful effects of harmful environment on plants. White light has the highest CAT activity, followed by blue light, higher CAT activity under green light, and the activity of yellow light and red light. similar. Violet and blue light can alleviate the senescence of plants by increasing the activity of antioxidant enzymes such as CAT and the gene expression of cucumber seedlings, delaying the degradation of chlorophyll and soluble proteins and membrane peroxidation.
Red light and blue light are the main light sources for plant absorption, and also the signal source for the main photoreceptors of plants. Under low light conditions, LED red and blue light source can effectively control the growth of cucumber seedlings, improve the quality of seedlings, and alleviate the physiological stress damage under low light. The red-blue complex light promoted the accumulation of biomass in pepper, rice five-leaf seedlings and lettuce plants. A red-blue combined light source with 60% blue light may be a relatively good source of cherry tomato fruit. The leaf area of ??tomato seedlings under red/blue (2:1) light filling conditions was the largest, but the leaf area values ??under red/blue (7:1) light-filling conditions were relatively small in red-blue composite light, indicating red light. The increase in proportion can only promote leaf growth within a certain range. Red light is beneficial to the radial growth of stems and leaves of oilseed rape. Appropriate increase of blue light ratio is beneficial to the lateral growth of stems and leaves, root development and photosynthetic pigment synthesis. The plants are not easy to fall, and can improve the photosynthesis, transpiration and fluorescence characteristics of leaves, thus promoting oil wheat. Vegetable growth increases biomass and nutrient content. Low light conditions can reduce the soluble protein content of cucumber seedlings. After red and blue light filling, the soluble protein has a significant increase. The soluble sugar content and soluble protein content in the leaves of tomato seedlings under red/blue (2:1) supplementation reached a maximum. The LED mixed red and blue light source processed the roots of the gourd and pumpkin seedlings, the dry matter content was high, the seedling index increased, and the seedling quality improved. The increase of blue light component in the red and blue mixed LED inhibited the elongation of the seedling stem and promoted the seedling stem. Thick increase. The cotyledon area, soluble sugar, starch, carbohydrate, sucrose and C/N of lettuce seedlings were the highest and significantly higher than red light, indicating that adding proper amount of blue light in red light is more conducive to the accumulation of carbohydrates in lettuce seedlings. The 25% and 50% blue light treatment is beneficial to the accumulation of lettuce biomass, the photosynthetic pigment content is large, the leaf area is large, the leaves are thick, which is beneficial to photosynthesis, and the root system is well developed and active, which is beneficial to nutrients. And moisture absorption, growth is better than other treatments. Chlorophyll content is greatly affected by the R/B ratio, and blue light significantly reduces the chlorophyll content in strawberry leaves. 660nm red light and 450nm blue light have a certain regulation effect on the chlorophyll content of lettuce. With the increase of blue light and red light, the content of chlorophyll a and b gradually decreases. The net photosynthetic rate and stomatal conductance of cucumber seedlings treated with red and blue light were the highest. The net photosynthetic rate, stomatal conductance and transpiration rate of single red and blue light were small, but the intercellular CO2 concentration was higher. Appropriate increase of blue light can increase the antioxidant enzyme activity of tomato seedlings. As the proportion of red light increases, the activities of antioxidant enzymes such as SOD and CAT increase first and then decrease, and R/B (2:1) fills light. The SOD activity decreased.
Mos studies have shown that blue light can reduce plant fresh weight and dry weight. With the increase of the proportion of blue light, the dry weight and fresh weight of lettuce showed a trend of increasing first and then decreasing. At different growth stages, the effect of blue light on the biomass of Phyllostachys pubescens was different. The increase of biomass in the early growth stage was inversely proportional to the red/blue value, and was proportional to the red/blue value in the late growth stage. Blue-violet light has an inhibitory effect on stem elongation. Compared to white light, blue-violet light significantly reduced the plant height of ginger plants and increased their stem diameter. In terms of the influence of light quality on roots, studies have shown that blue and purple-treated oat plants have more roots and developed roots.
The study found that red/blue (1:1) combined light energy significantly improved the growth and quality indicators of lettuce; red/blue (7:3) was the most suitable light quality condition for cucumber seedling growth, and the maximum photosynthetic rate could reach monochrome red. 4 times under the light. When the red/blue color is 8:1, the lettuce exhibits a distinct photosynthetic advantage. Adding yellow light on the basis of red and blue composite light is beneficial to the synthesis of spinach photosynthetic pigments, which significantly promotes the growth of spinach. Adding yellow and violet light can enhance the photosynthetic potential of cherry tomato seedlings and alleviate the red and blue weak light stress.
6. Effect of light quality on vegetable quality
Light quality affects many physiological processes of plants, especially in photosynthesis and plant morphogenesis. The rational use of specific light waves is beneficial to improve the nutritional quality of vegetables.
It is generally believed that red light is conducive to the accumulation of carbohydrates, promotes the synthesis of soluble sugars, but is not conducive to the accumulation of soluble proteins; and blue light can promote protein formation. Red blue light helps to reduce the amount of nitrate absorbed. The soluble sugar content of various varieties of lettuce was higher under blue or red-blue light treatment. Compared with white light, red and blue light treatment significantly reduced the amount of nitrate in the lettuce. Under the same light intensity and illumination time, the red, blue and white mixed LED illumination can reduce the hydroponic nitrate content compared with the red blue light. Under the white light condition, the treatment of supplementing blue or green light reduces the nitric acid in the lettuce. Salt content.
Different light qualities have different effects on the formation of secondary metabolites in plant organs. Red light, blue light, red and blue mixed light can promote the degradation rate of chlorophyll in colored sweet pepper fruits and increase the synthesis rate of carotenoids and anthocyanins, and slow down the synthesis speed of flavonoids. Blue light can induce the accumulation of flavonoids and anthocyanins, and increasing the proportion of blue light can promote the formation of lycopene and flavonoids in tomato fruit. Adding UV-B and blue light to lettuce at night can increase the content of quercetin in lettuce. The content of anthocyanins and carotenoids in leaves supplemented with ultraviolet light and blue light was significantly increased; blue light increased the content of chlorophyll in lettuce, and the treatment of blue light at night, the total phenol and flavonoid content of leaves and antioxidant capacity were the highest; Compared with red light treatment, the content of anthocyanin in the upper part of lettuce was significantly increased, and the content of anthocyanin in the upper part of lettuce was the lowest under blue light treatment. Red light: white light: The blue light increased the total anthocyanin content of Baisu under 8:1:1 treatment. The total phenolic content of red leaf, purple leaf and green leaf lettuce was the highest under red or blue combined light or white light, the content of flavonoids and anthocyanin was the lowest under red light, and the anthocyanin content was the largest under the combination of red and blue light. Under the condition of 100% blue light, the fresh weight of the raw menu can be significantly increased, and the vitamin C content is also 2.25 times of the control. The total phenolic content of basil under the light quality treatment of blue light 20%, green light 39%, red light 35%, far red light 5% and 1% ultraviolet light is significantly higher than other treatments; Significantly increase the chlorophyll and carotenoid content of lettuce.
A large number of studies have shown that the combination of red and blue light has a significantly higher effect on the nutritional quality of plants than monochromatic light. Compared with white light, the vitamin C content of lettuce and Komatsu treated under blue or red-blue light is significantly increased. Under controlled environmental conditions, red and blue light is the most suitable light treatment for increasing the content of perillaldehyde, limonene and anthocyanin in perilla. Compared with the absence of blue light, a certain proportion of blue light (59%, 47% and 35%) was added to red light, and the chlorophyll content, total phenolic content, total flavonoid content and antioxidant capacity of green leaf lettuce and red leaf lettuce were found. Significantly improved. Compared with white light treatment, red and blue composite light can promote the increase of soluble protein content of celery, and reduce the content of nitrate. The content of total phenol, red pigment, yellow pigment and total antioxidant capacity in soluble sugar and eggplant skin of eggplant are also improved. . Compared with white light, red and blue combined light (1:1) increased the soluble sugar and lycopene content of the fruit; red and blue combined light (3:1) significantly increased the free amino acid and soluble protein content. Compared with other treatments, 70% red light + 30% blue light treatment can significantly increase the fresh weight of the menu and the chlorophyll and carotenoid content.
Green light and yellow orange light, although there are not many reports and studies at present, it also has important physiological effects on vegetables. Different light qualities have different effects on photosynthetic pigments of lettuce, and the content of β-carotene is the highest under green light. Supplementation of orange light increased the total phenolic content of the oily wheat, and supplemented with green light increased its alpha-carotene and anthocyanin content. Supplementing green light can promote the accumulation of soluble sugar in lettuce and also reduce nitrate content.
Ultraviolet and infrared light also have a certain impact on the quality of vegetables. After adding UV-C (254nm) to pea seedlings, the vitamin C content did not change. After supplementing UV-A (365nm), the vitamin C content of pea seedlings was significantly reduced, but the content of flavonoids was increased. The UV-B-free source significantly reduced the amount of oxalic acid in the beet compared to the control. Supplementing UV light can increase the content of phenolic substances and α-carotene in rapeseed. The UV-B spinach with 6kJ·m-2 per day had the lowest ascorbic acid content, and the spinach with 4kJ·m-2 UV-B irradiation had higher anthocyanin content. After treatment with UV-A and UV-B, the content of anthocyanin was significantly increased in purple cabbage and green cabbage, and UV-B treatment was more effective than UV-A treatment in increasing anthocyanin content. The increase in the expression level of downstream structural genes in anthocyanin biosynthesis has a very close relationship. UV-A irradiation significantly increased the antioxidant enzyme activity of radish sprouts, and increased the ascorbic acid content in radish sprouts by increasing the expression of L-galactose pathway-related genes and GLDH enzyme activity. The anthocyanins, carotenoids and chlorophyll content of lettuce leaves supplemented by far infrared light treatment were significantly reduced. The addition of far-infrared light promotes the accumulation of vitamin C in lettuce and reduces biomass and pigment content. The addition of far-infrared light on the basis of red and blue light can significantly increase the content of total phenol, chlorogenic acid and caffeic acid in lettuce, and the antioxidant capacity is also significantly increased.
For sprouts, it is generally believed that blue-violet light can make seedlings robust and also promote the accumulation and synthesis of antioxidant substances. Supplementation of UV-A and blue light can increase the content of anthocyanins in lettuce sprouts, increase the content of carotenoids by blue light, increase the total phenolic content by adding red light, and supplement the far red light to make anthocyanins in the lettuce sprouts. Both carotene and total phenols are reduced. Red and blue light treatment can increase the content of vitamin C in pea seedling leaves, and the content of carotenoids in pea seedlings is higher under white light and red and blue light treatment, and the anthocyanin content is the highest under white light treatment. UV-B irradiation for 24 hours promoted the accumulation of kaempferol and quercetin in broccoli sprouts, and UV-B induced the synthesis of glucosinolate (GS). UV-B and blue light can increase the total phenolic content in radish sprouts and improve the antioxidant capacity of sprouts. The chlorophyll a and chlorophyll b and total
Light of different light quality or wavelength has distinct biological effects, including different effects on the morphological structure and chemical composition of plants, photosynthesis and organ growth and development.
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