The light in nature comes from the sun, and the solar spectrum can be 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 mid-ultraviolet UV-B and far-ultraviolet UV-C are mostly absorbed by the ozone layer above the earth, and the ultraviolet light reaching the ground is mainly near-ultraviolet UV-A. The existence of II and Ps I shows that when red light and far-red light are irradiated together, the synthesizing rate is much higher than that of monochromatic light.
Phytochromes are formed by covalent bonding of chromophores and apoproteins, including far-red light absorption type (Pfr) and red light absorption type (Pr). They mainly absorb red light at 600-700nm and 700- The far-red light at 760nm regulates the physiological activities of plants through the reversible effects of far-red light and red light. In plants, phytochromes are mainly involved in the regulation of seed germination, seedling formation, establishment of photosynthetic system, shade avoidance, flowering time and circadian rhythm response. In addition, it also plays a regulatory role in the stress resistance of plants.
Cryptochrome is a blue light receptor, which mainly absorbs blue light and near-ultraviolet light UV-A at 320-500nm, with absorption peaks approximately at 375nm, 420nm, 450nm and 480nm. Cryptochromes are mainly involved in the regulation of flowering in plants. In addition, it is also involved in the regulation of plant tropism, stomata 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.
luciferin is a blue light receptor discovered after phytochrome and cryptochrome. It can be phosphorylated after binding to flavin mononucleotide. It can regulate the phototaxis of plants, chloroplast movement, stomata opening, leaf extension and hypocotyl elongation of chloroplast seedlings.
2. The effect of light quality on plants
Different light qualities or wavelengths of light have significantly different biological effects, including different effects on the morphological structure and chemical composition of plants, photosynthesis, and organ growth and development.
2.1 Red light
Red light generally inhibits internode elongation of plants, promotes tillering, and increases the accumulation of chlorophyll, carotenoids, soluble sugars and other substances. Red light can promote the growth of leaf area and β-carotene accumulation of pea seedlings; lettuce seedlings are pre-red light and then applied with near-ultraviolet light. It is found that red light can enhance the activity of antioxidant enzymes and increase the content of near-ultraviolet absorbing pigments, thereby reducing near-ultraviolet Light damages lettuce seedlings; a full-light experiment on strawberries found that red light is beneficial to increase the content of organic acids and total phenols in strawberries.
Blue light can significantly shorten the pitch of vegetables, promote the horizontal expansion of vegetables and reduce leaf area. At the same time, blue light can also promote the accumulation of plant secondary metabolites. In addition, experiments have found that blue light can reduce the inhibition of red light on the photosynthetic system activity and photosynthetic electron transport capacity of cucumber leaves. Therefore, blue light is an important factor affecting the photosynthetic system activity and photosynthetic electron transport capacity. There are significant species differences in the blue light needs of plants. Strawberry was supplemented with postharvest light and found that 470nm in blue light of different wavelengths had a significant effect on the content of anthocyanins and total phenols.
2.3 Green light
Green light has always been a controversial light quality. Some scholars believe that it can inhibit the growth of plants, cause short plants and reduce vegetable yields. 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; adding 24% of green light on the basis of red and blue light can promote the growth of lettuce.
2.4 yellow light
Yellow light basically inhibits plant growth, and because many researchers incorporate yellow light into green light, there is very little literature on the effect of yellow light on plant growth.
2.5 UV light
Ultraviolet light generally shows more damage to organisms, reducing plant leaf area, suppressing 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. By adding a small amount of UV-B to the postharvest cabbage to promote the synthesis of polyphenols; postharvest UV-c treatment can slow down the fruit of red pepper Glue dissolution, quality loss and softening process, thereby significantly reducing the spoilage rate of red pepper, extending the shelf life, and promoting 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 leads to dwarf plant phenotypes, small and thick leaves, short petioles, increased axillary branches, and changes in the root/shoot ratio.
2.6 Far red light
Far-red light is generally used in proportion to red light. Due to the structure of the photosensitive pigment that absorbs red light and far-red light, the effects of red light and far-red light on plants can be mutually converted and mutually offset. When the white fluorescent lamp is the main light source in the growth room, LEDs are used to supplement far-red radiation (emission peak 734nm), the content of anthocyanin, carotenoid and chlorophyll is reduced, while the fresh weight, dry weight, stem length, leaf length and leaf width of the plant increase . The effect of supplementing FR on growth may be due to the increase in light absorption caused by the increase in leaf area. Arabidopsis thaliana treated with low R/FR has larger and thicker leaves, increased biomass, and accumulation of more soluble metabolites, which improves cold resistance.
3. The effect of light quality on plant tissue culture
In the process of plant tissue culture, seedling morphogenesis and physiological and biochemical changes 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. In the process of plant tissue culture, each morphological stage from explant callus induction to formation of complete plants is affected by LED light quality, and different tissue culture stages of different plants have different responses to light quality.
3.1 The effect of LED light quality on callus induction, growth and differentiation
3.1.1 Effect on callus induction
callus culture is an important part of plant in vitro culture. The study found that 100% red light has the highest induction rate for orchid callus, and the growth effect of callus is the best when the ratio of red to blue light is 3:1. Monochromatic red LED promoted the formation of callus of Anthurium andraeanum, but with the increase of the proportion of blue light, the induction rate of leaf callus gradually decreased. Red light and white light promoted the induction of callus from pepper cotyledons, while green light and blue light showed inhibition. Yellow light is beneficial to the induction of callus from radish hypocotyls, while blue light promotes the induction of cotyledon callus. Red light significantly promotes the induction and proliferation of garlic callus, while blue light has the strongest effect on promoting the differentiation of callus of Chinese yam. Yellow light is most conducive to the proliferation of grape callus, followed by green light. Yellow light is beneficial to the induction of callus from the hypocotyls of radish, while blue light is beneficial to the induction of cotyledon callus, and red light is beneficial to the proliferation of callus. Red light is beneficial to the induction and proliferation of oncidium protocorm callus. Gladiolus protocorm callus had the highest proliferation rate under red light. The callus induction rate of orchids was the highest under red light. Blue light and yellow light can promote the proliferation and growth of callus of white birch. It can be seen that the effect of different light quality on callus induction varies with plant species or explant types.More about:led grow light Manufacturers