Light is one of the important environmental factors in plant growth. Due to its small size, light weight, long lifespan, and adjustable light intensity, LED has become one of the important light sources for the regulation of the light environment of plants and has obvious advantages in energy saving and promotion of plant growth. At present, LED has been used in plant tissue culture research to a certain extent, and some great progress has been made. This article introduces the main characteristics of grow LED light and its application in plant tissue culture.
The unique advantages of LED make it one of the important light sources for plant tissue culture research. Since the 1980s, some countries in the world have successively begun research on the application of LEDs in plant tissue culture. Some colleges and universities and scientific research institutions in China have also started research in this area and have made some gratifying progress. This article briefly summarizes the work that LED has done in-plant facility cultivation from the following aspects and makes an assessment of its application prospects in this field.
The role of grow LED light
Light and plants
Light is one of the most important environmental factors in plant growth. It not only provides radiation energy for plant photosynthesis but also provides signal transduction for plants and regulates their development process. Plants are always in a constantly changing light environment throughout their life cycle. In the long-term evolution, plants not only adapt to changes in the light environment but also influence each other to change the surrounding light environment.
Light and pigment
The wavelength of sunlight reaching the ground is approximately from 300 to 2600 nm, of which the effective wavelength for photosynthesis is between 400 and 700 nm, of which blue light at 425 to 490 nm and red light at 610 to 700 nm contribute to photosynthesis. The maximum absorption of light by plants is 520~610 nm (green), which is very low. From this, we can see that not all light contributes to the photosynthesis of plants. Pigments can absorb light energy to produce a series of biochemical reactions, and different pigments absorb different wavelengths. There are many pigments in plants that play different roles.
However, two types of pigments, phytochrome, and cryptochrome, play a key role in regulating the response of plants to light. There are two tautomers of phytochromes-red phytochrome (Pr) and far-red phytochrome (Pfr). Pr absorbs red light with a wavelength of about 660 nm, and Pfr absorbs far-red light with a wavelength of about 730 nm. Phytochrome regulates the response of many different plants to light, including photoperiod, seed germination, leaf development, hypocotyl elongation, and de-yellowing. Cryptochromes absorb light waves in the range of blue and ultraviolet light, and other pigments are related to the development of plants. It can be seen that the blue light around 460 nm and the red light around 660 nm are the light waves most needed by plants, and they play a key role in the growth and development of plants.
Introduction and advantages of LED
Introduction to LED
LED (light-emitting diodes), that is, light-emitting diodes, is a device that can effectively convert electrical energy into electromagnetic radiation. In 1962, the joint laboratories of GE, Monsanto, and IBM developed the red-emitting semiconductor compound GaAsP. In 1965, the world’s first commercially available LED that emits infrared light made of germanium was born. With the continuous advancement of technology, the development of white light LEDs has been quite rapid in recent years. The luminous efficiency of white light LEDs has reached 30 lm/W, and laboratory research results can reach 60 lm/W, greatly surpassing incandescent lamps and approaching fluorescent lamps. The growth efficiency of MOKOLight LED grow light is very high, and its effect on plant growth is very obvious.
Analysis of LED advantages
LED has the advantages of long life, high light conversion rate, energy saving, not easy color fading, stability, environmental protection, small size, and so on. The half-width range of the light emitted by LED is tens of nanometers to several nanometers, and the wavelength range is consistent with the wavelength required for plant growth. The luminous flux of red LED is relatively large, and the luminous efficiency is high.
Application of grow LED light source in plant tissue culture
The application of LED in plant tissue culture is developed based on the development of LED technology and the environmental regulation of plant tissue culture. As early as 1982, there was a test report on the use of a red LED light source with a wavelength of 650 nm to supplement light in greenhouse tomatoes. Later, LEDs were also applied to environmental regulation in plant tissue culture, and the role of LEDs in energy-saving was discussed.
At present, the research on the role of LED in plant tissue is more inclined to the effect of light intensity and light quality on the growth of tissue culture seedlings. On the one hand, the research on the two pairs of photoperiods is less. As far as the world is concerned, the application research of LED in plant tissue culture is mainly concentrated in Japan and the United States. Japan’s research is in a leading position in the world. It has not only developed an LED light-emitting system specifically applied to plant tissue culture, but also obtained some important basic data in combination with other environmental control factors. Some scientific research institutions in China have also started research in this area and independently developed some LED light source systems for plant tissue culture research.
The selection on light quality
When LEDs were first developed, people discovered red light around 660nm, using red light as the main light source and fluorescence as a supplement. With the in-depth research on plant photosynthesis and the breakthrough of new LED materials, various wavelengths of LEDs are used in plant tissue culture, and research has found that the best effect is red light at around 660nm and blue light at around 460nm.
Different light quality has a great influence on the growth of plants. Scientists use LED grow lights to cultivate orchids and found that red light is very beneficial to the growth of seedlings and can promote the growth of seedling leaves, but red light will inhibit the accumulation of chlorophyll, and blue light will promote plants to produce chlorophyll. The best ratio of red light to blue light for orchid seedling growth is 8:2.
After many comparison experiments, scientists have found that when the ratio of red light and blue light is 3:1, the growth effect of tissue-cultured seedlings is the best, and red light irradiation has the best induction efficiency for tissue-cultured seedlings. In the group culture of grapes, we found that blue light inhibits the elongation of grape seedlings, but can promote the formation of leaves and chlorophyll, and promote the development of leaf stomata. Far-red light has a certain effect on stem growth and chlorophyll accumulation. The red light helps with the growth and rooting of the grapes.
Although the red light in the grow LED light can inhibit the growth of chlorophyll to a certain extent, the blue light in the grow LED light can promote the growth of chlorophyll. Red light is conducive to the accumulation of plant sugars and starches, and blue light promotes the synthesis of chlorophyll and protein. Red light and blue light have a huge impact on plant growth, and their effects on plant growth are different. A reasonable ratio of blue light and red light is the best way to improve light quality. To obtain suitable light quality, first understand people’s needs for target crops, and perform grow LED light ratios according to needs to obtain the optimal tissue light source.
The selection on light intensity
Light intensity refers to the number of photons emitted per unit area per unit time, the unit is μmol/(m2·s). Light intensity is an important factor affecting plant photosynthesis. For plants, light intensity is the photosynthetic quantum flux (PPF). Plants with different light intensities have different effects on tissue culture. Strawberry grows best when the PPF is 60μmol/(m2·s); when the PPF is 60~70μmol/(m2·s), the fresh weight of Taro tissue culture seedlings is Relatively high. Through further research, we found that light intensity still has different effects at different growth stages of plant tissue culture. In the beginning, the plant tissue wounds did not heal. If the light intensity is too high, it is easy to burn the plant. The cause of plant leaf expansion should increase the light intensity. , Promote plant photosynthesis.
The selection on photoperiod
The research of Chen Yusong et al. showed that the most suitable grow LED light environment for gentian out of the bottle index is 50% of blue light, PPF of 120μmol/(m2·s), and photoperiod of 16 h. The best light environment for gentian research using fluorescent lamps in Taiwan Sugar Research Institute is PPF 80μmol/(m2·s), and the photoperiod is 12Hr. Research by RCJao et al. showed that when the photoperiod is 16 h, the cultivation effect of potato tissue cultured plantlets under simultaneous irradiation of red and blue light is better than that of alternative irradiation of red and blue light. In addition, long-term irradiation of low PPF is better than long-term irradiation of high PPF. The effect is good.
The selection on power supply mode
Research by Lai Jianzhou et al. has shown that with direct current to drive LEDs, the 40 Hz power supply frequency provided by the driver can be more power-efficient than 60 Hz. However, to further reduce the cost, we can directly use the AC power supply for driving, which can avoid the production cost of the AC-DC conversion circuit. Studies have shown that it is feasible to use AC-powered all-red LEDs to produce color alocasia tissue culture seedlings. Jao Ruey-Chi et al. claimed in the research on potatoes that if we only consider the growth rate, the plant grows best when the LED is at 720 Hz (1.4 ms), the working ratio is 50%, and the photoperiod is 16 h. Considering the issue of energy consumption, the LED is the most energy-efficient when the working ratio is 50% at 180 Hz (5.5 ms), and the light period is 16 h.
Application prospects of grow LED light source in plant tissue culture
Restrictive factors and countermeasures
Some shortcomings of LED itself, such as low brightness, difficult heat dissipation of PN junction, poor spot brightness and chromaticity uniformity, and high price limit the promotion and application of LED in plant tissue culture, which is not conducive to the industrialization of LED in plant tissue culture Large-scale application in production. Solve this problem requires the development and improvement of optoelectronic technology, as well as the introduction of relevant policies and regulations. With the development of optoelectronic technology, the technical problems of LED itself will be solved, and the price of LED will also be reduced, which will help the wide application of LED in tissue culture.
Development Trend
LED is a new type of high-efficiency and energy-saving light source. Using LED as a light source in plant tissue culture can reduce the cost of tissue culture. At the same time, due to the characteristics of LED light quality, adjustable light intensity, and narrow waveband, the research on plant photophysiology will be more in-depth. In the future, the application of LED in plant tissue culture should strictly control the lighting device, select the appropriate LED, consider the performance and reliability and the special use conditions of plant lighting; combine the characteristics of the LED, use the LED rationally, and consider the rated working conditions of the LED.
The design of the drive circuit and the selection of the power supply should be combined with other factors of environmental regulation, such as CO2 fertilization, temperature regulation, and so on. In addition, it is necessary to combine the use of plant growth regulators to make the application research of LED in plant tissue culture more in-depth and systematic.
