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. The presence of II and Ps I shows that the photosynthetic rate is much higher than that of monochromatic illumination when the red and far red light are illuminated together.
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.
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.
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
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.
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.
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.
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.