Light is the basic environmental factor of plant growth and development. Light not only provides energy for plant growth through photosynthesis, but also is an important regulatory factor for plant growth and development.
1. Photoreceptors in plants
A series of plant responses to the external light environment are based on the absorption of light by photoreceptors. The main photoreceptors include photosynthetic pigments, photosensitive pigments, cryptochrome and phototropin. They play their respective roles in the plant body, affecting plant photosynthetic physiology, metabolic physiology, morphogenesis and other aspects.
1. 1 photosynthetic pigment
Photosynthetic pigments, which include chlorophyll a, chlorophyll b and carotenoids, are the basic building blocks of the optical system. It is mainly responsible for light energy reception, energy transfer, photoelectric conversion and other photosynthetic processes in photosynthesis.
1. 2. Photosensitive pigment
Photosensitive pigments are formed by covalent combination of chromogenic groups and deauxyl proteins. In plants, photosensitive pigments are mainly involved in the regulation of seed germination, seedling formation, establishment of photosensitive system, shade avoidance, flowering time and circadian rhythm response. In addition, still have adjusting control effect to the resistance physiology of plant.
1. 3 cryptochrome
Cryptochrome is a blue light receptor, which is mainly involved in the regulation of flowering in plants. In addition, it is involved in the regulation of 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 induction.
1. 4 to the light
Phototropin is a blue light receptor discovered after photosensitive pigment and cryptochrome. It can phosphorylate with flavin mononucleic acid. It can regulate phototaxis, chloroplast movement, stomatal opening, leaf extension and hypocotyl elongation of xanthate seedlings.
2. Effects of light quality on plants
Different light quality or wavelength has different biological effects, including different effects on plant morphological structure and chemical composition, photosynthesis and organ growth and development.
2. A red light
Red light generally inhibits internode elongation of plants, promotes tillers and increases the accumulation of chlorophyll, carotenoids and soluble sugars.
2. 2 blu-ray
Blue light can significantly shorten the internode spacing of vegetables, promote the lateral extension of vegetables and reduce leaf area. Meanwhile, blue light can also promote the accumulation of secondary metabolites in plants.
2. 3 green
Green light has long been a controversial source of light, and some researchers believe it inhibits plant growth, stunts plants and reduces vegetable production. However, a number of studies have been published on the positive effects of green light on vegetables. Adding 24 percent green light to red and blue improves lettuce growth.
2. 4 yellow light
Yellow light basically inhibits plant growth, and because many researchers incorporate yellow light into green light, there is little literature on the effect of yellow light on plant growth and development.
2. 5 ultraviolet
Ultraviolet light is generally more of a biological killing effect, reducing plant leaf area, inhibiting hypocotyl elongation, reducing photosynthesis and productivity, and making plants more susceptible to infection.
2. 6 far red
Far red light is generally used in the ratio of red light to red light. Due to the structure problem of photosensitive pigments absorbing red light and far red light, the effects of red light and far red light on plants can be transformed and offset each other.
3. Effects of light quality on plant tissue culture
Morphological and biochemical changes of seedlings in 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. In the process of plant tissue culture, various morphogenesis stages from the callus induction of explants to the formation of complete plants are affected by LED light quality, and the response to light quality is different in different tissue culture stages of different plants.
3. 1. 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.
3. 1. 2. Effects on callus growth
The growth curves of callus under different light quality were "s" shaped, but the effects of different light quality on callus growth were different due to different plant genotypes and matrix additives. Yellow LED promoted callus growth of Vietnamese ginseng, red and blue LED inhibited callus growth, among which red LED had the strongest inhibitory effect, while green and white LED had no significant effect on callus growth.
3. 1. Effect on bud differentiation of callus
Light quality plays an important role in bud differentiation.
3. 2. Effect of LED light quality on tissue culture seedling proliferation
It was found that red light in monochromatic light promoted the proliferation of tissue culture seedlings. The single bud number of phalaenopsis under pure red LED increased significantly than that of the control fluorescent lamp, and similar results were obtained in the experiments of chrysanthemum and tobacco.
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
White palm tissue culture seedlings treated with red or blue LED alone showed poor growth, while red and blue LED composite light with a certain ratio was beneficial to promote plant growth. Under the combination of red and blue LED light, the net photosynthetic rate of chrysanthemum tissue culture seedling leaves was significantly higher than that of monochrome red and blue light, and the fresh weight and dry weight reached the maximum value. The dry fresh weight of strawberry seedling was the least under blue light. The fresh and dry weight of polygonum is the highest under red and blue light.
3. 4. Effect of LED light quality on rooting of tissue culture seedlings
The effects of light quality on root induction and growth of isolated plants varied with different wavelength, and the effects of light quality depended on plant genotype and rooting substance concentration.
4. Effects of light quality on vegetable seedlings
Light quality, as an important characteristic of light environment, directly or indirectly affects the synthesis and transport of plant kinin. Irradiation of red and blue light at seedling stage can significantly promote the growth of vegetable seedlings and improve the robust seedling index.