Plant light is the key signal and important energy for plant growth. According to the intensity of light, the wavelength of light, the length of light, plants judge the climate and season, so that their own state changes, to determine whether germination, growth, flowering, fruiting so that can better adapt to the environment. At the same time, plants also use plant light for light cooperation to provide energy for their own growth. Research on the relationship between plants and light can promote the development of cultivation techniques.
Direct Effects of Plant Light on Plants
Plant light works as an external signal. In addition to controlling photosynthesis as an energy source, plant light also acts as a signal to affect many aspects of plant growth and development, from seed germination and de-etiolation to nutritional morphology, circadian rhythm, gene expression, geotropism, and phototropism, The development of plants induced and regulated by light is called photomorphogenesis. The effects on plant morphology include
- Effects of plant light on the formation of gibberellin GA in some plant seeds.
- Promote apical dominance: plant light can promote the expansion of stem tips and young leaves, and inhibit the growth of lateral buds and stem elongation.
- Cause tropism: for example, there is a big difference in the shape between the seedlings growing in the dark and the seedlings growing in the plant light.
- Effects of photoperiod on plants: light affects the growth process of plants, such as seed germination and dormancy, bud germination and growth, yellow flower phenomenon, plant growth slowing down and stopping in winter, etc.
- Generally speaking, the photomorphogenesis of plants is a process of growth, development, and differentiation induced and regulated by light. The leaves of seedlings growing in the dark are smaller, but those growing in the light are much larger. As far as the shape of leaves is concerned, the growth and division of cells change the shape of leaves, both of which are the processes of light morphogenesis.
There are two types of light morphogenetic reactions in plants: red light reaction and blue light reaction. The leaf enlargement was mainly caused by a red light reaction; However, stomatal opening, chloroplast differentiation, and movement were blue light responses. The photoreceptor of the red light reaction is phytochrome, which exists in almost all parts of higher plants. Phytochrome is composed of chromophores and deproteinization. It has been confirmed that there are two forms of phytochrome in plants, namely pr (red light absorption type & physiological inactivation type) and PFR (far-red light absorption type & physiological activation type). PR is blue-green and PFR is light green. As long as the conditions are satisfied, they can transform into each other. The photoreceptor of the blue light reaction is called a blue/near ultraviolet photoreceptor.
Under red light irradiation, PR changes to PFR, and under far-red light irradiation, PFR changes to pr. In many plants, PFR can slowly reverse to PR in the dark. Unlike the red light reaction which can be reversed by far-red light, the blue light reaction can not be reversed by the longer wavelength light. Red light is the most effective in inducing flowering, germination of some seeds, growth of stems and leaves, leaf abscission, formation of rhizomes and bulbs, dormancy of buds, and chlorosis; Blue light is the most effective in the stomatal opening, delaying senescence, increasing protein content, phototropism, chlorophyll synthesis, chloroplast differentiation, and movement, and stem elongation inhibition.
Effects of Light Morphogenesis on Plants
- Effect of plant light on plant seed germination
When the seeds are imbibed, their germination is often affected by light. Many seeds need light to germinate well. Small seeds are often affected. There are also a few horticultural crops with large seeds. In addition, the germination of many seeds is not affected by light, some are inhibited by light, and even some are promoted by short-term light, but inhibited by continuous light. Light quality also affected seed germination. The germination of seeds was also affected by light quality. Under the red light and green light, the germination of cucumber seeds is inhibited, and it is difficult to germinate. But under white light, yellow light, blue light, or even under dark light, the seeds can germinate. Some kinds of seeds soaked in GA3 can replace light demand, and even for seeds not affected by light, these hormones sometimes have stimulating effects. The formation of Gibberellin acid can affect the germination of seeds. Far-red light can reduce the gibberellin content of soaking pea seeds, while red light can increase the gibberellin content. The light wave can reverse each other, indicating that the photosensitizer PR and PFR of seeds can affect the formation of Gibberellin acid after being stimulated by red light.
- Effect of plant light on the growth of plant leaves
The vast majority of plants in the absence of light are very difficult to grow, although sometimes the leaves of plants (in a period of time) in the dark species can also grow rapidly, this time is very short, and the vast majority of the time, the plants need light for growth, and the leaves of double wild boar plants in the absence of light can not develop normally. Light promoted leaf enlargement was mainly due to enhanced cell division, and there was no significant difference of the final cell size between those under the light and those kept in the dark. In intact leaves, the differentiation rate of cell division and elongation of leaves grown under bright light was faster than that under low light intensity. Light plays a key role in the growth and development of plant leaves, especially in bilobate plants.
- Effect of plant light on plant stem growth
The stem elongation rate of many plants in the daytime is lower than that at night, which is the inhibition of light on growth to a large extent. At low energy, the inhibition of blue light is less than that of red light. If the light intensity is increased, the inhibition of blue light will be enhanced. For a plant sprouting in the dark, photosensitive element does not work in such an environment, the green light has almost no effect, and blue light is relatively weak, which indicates that light has different effects on green seedlings and yellow seedlings. When plants germinate in the sun, high-intensity red light can promote stem elongation, while blue light with the same intensity has the greatest inhibition on stem elongation. Long-wavelength light (red light) promoted stem elongation, while short-wavelength light (blue light) inhibited stem elongation. Blue light can inhibit cell growth, while red light can promote cell growth. Blue light can increase leaf area, but it can prevent petiole growth. Red light is very important and blue light is also very important for the growth of plants. It is the result of both sides. Blue light is one of the necessary conditions for the strong growth of plants.
- Effect of plant light on chlorophyll synthesis in plants is inseparable from the participation of light.
The ratio of chlorophyll a to chlorophyll b is 3:1. The total carotenoid content of cells grown in the dark is very small, but it can increase 10 times during the process of turning green. In addition, chlorophyll synthesis is also related to light quality. The chlorophyll content was the highest under blue light, followed by white and red light, and the lowest under dark and green light. The ratio of chlorophyll a: b was different under different light quality. The ratio of chlorophyll a: b was the highest under yellow light and blue light, and the red light was more conducive to the formation of chlorophyll a. Compared with white light and blue light, the chlorophyll a: b ratio of leaves under red light treatment was lower, while the chlorophyll content of leaves under blue light was lower than that under white light and red light, but its chlorophyll a: b ratio was the highest, that is to say, the plants under blue light culture generally had the characteristics of sunny plants, while the plants under red light culture were similar to those under shade plants.
- Effect of plant light on anthocyanin formation
Many plants form colored anthocyanins in some organs. The formation of this pigment requires sufficient soluble sugar supply directly from photosynthesis. In addition, light can also affect anthocyanin synthesis in other ways. In general, blue light promotes anthocyanin synthesis. A high-intensity light is also needed for anthocyanin synthesis. If high-intensity blue light is used to irradiate sorghum seedlings for several hours, and then maintained in the dark, the anthocyanin content will gradually increase. However, if the plants are irradiated with blue light, that is, with low-level far-red light for a short time, only about half of the pigment is formed. The inhibition effect of far-red light can be reversed repeatedly by red light irradiation. Anthocyanins are synthesized by two plant photoreceptors: one is considered cryptochrome, which absorbs Blue / near ultraviolet light, and the other is a phytochrome which absorbs red (PR) and far red (PFR).
- Effect of plant light on plant flowering
Photoperiod is the mutual length between day and night in a day. The length of day and night is not invariable. It changes with the change of longitude and latitude and season. Although their total length is invariable, the relative length is changing all the time. Photoperiod is a very reliable signal of seasonal variation. Plants in different regions of the earth gradually adapt to the environment in the process of long-term evolution. Their growth, including rooting, germination, growth, flowering, and fruiting, changes periodically with seasons. Each process of plant growth is basically affected by photoperiod, and the effect on flowering is more significant. When flowering plants regulated by photoperiod reach flowering maturity state, flowering can be induced under suitable photoperiod conditions. The earlier the plant blooms in certain continuous sunshine, and the longer the sunshine, the earlier it blooms. Short-day plants can bloom only when their photoperiod is shorter than the critical day length. The number of days of photoperiod induction is related to plant age. In many plants, the number of days of photoperiod induction decreases with the increase of age. The sensitivity of leaves to photoperiod changes with growth, from weak to strong, and from strong to weak. The sensitivity of young leaves to light is relatively poor. With the growth, the sensitivity to photoperiod gradually becomes stronger. The sensitivity of growing leaves to light will gradually become worse, and the sensitivity of old leaves to light is relatively poor. The light intensity needed to induce flowering is not high, about 50-100lx, so the light intensity is not an absolute factor to induce flowering. The transition from vegetative growth to reproductive growth is regulated by red far-red and blue near-ultraviolet receptors. The sunshine is received by the photosensitizers in the leaves, which can receive red and far-red signals. Red light and far-red light can reverse the flowering reaction repeatedly. It is the last light irradiation that determines the flowering of plants. If the last light irradiation is red light, the short-day plants will not bloom; if the last one is far-red light, the plants will bloom.
Indirect Effects of Plant Light on Plants
Light as energy. Light is the basis of photosynthesis, which affects the formation of assimilation, enzyme activation, stomatal opening, and so on. Insufficient light will affect photosynthetic capacity, thus limiting carbon assimilation, and ultimately affecting the formation of plant photosynthetic products. The growth of plants is inseparable from light, water, temperature, gas, and other environmental factors. Many of these factors can regulate the growth trend of plants, and light is no exception. Light can not only provide different environmental signals for the development and growth of plants but also provide energy for the photosynthesis of plants. Light energy affects all stages of plant growth and development.
Light is the energy source of photosynthesis. The whole photosynthesis can be divided into two classes: light reaction and dark reaction. In the light reaction stage, plants use light energy to produce ATP and NADPH; In the dark stage, chloroplasts assimilate CO2 to synthesize carbohydrates using NADPH and ATP produced by the light reaction. Photosynthesis is a photochemical reaction. Within a certain range of light intensity, the photosynthetic rate increases with the increase of light intensity. When the light intensity exceeds or falls below a certain critical value (light saturation point and compensation point), the photosynthetic intensity does not increase. The higher the light intensity is, the higher the photosynthetic rate is. The development of light regulation almost includes the whole stage of plant development, including seed germination, leaf and root development, branching, flowering, and fruiting.
Control of Light to Affect Plant Growth
- Reduce plant lighting cost
Not all wavelengths of light plants can carry out photosynthesis. Studies show that the wavelengths of light plants can carry out photosynthesis are 400nm-700nm. When planting, we use this band of light to reduce our energy waste, increase the absorption of light, accelerate the growth of crops, and reduce our costs.
- Improvement of product quality
Through research, we found that light has a significant impact on plant growth, through the control of light, we can control the growth of plants. With more control of the light, flowers will boost long flowering time and less fruiting time, so the growth of flowers is certainly high quality. For fruit, we should make them bear more fruits, and make them produce more sugars to increase their taste. In this way, the fruit produced must be of high quality. Through the control of light, let the crops grow in the direction we want, and improve the quality of products.
- Off-season planting
Generally vegetables and fruits can only grow in a specific period of time a year. By controlling light and other conditions, we can make them not affected by external factors, so that they can grow in the time we need. In this way, we can plant the products we want in any season. In the cold winter, we can still eat fresh vegetables and fruits.
Advantages of LED Plant Light
Compared with other light sources, LED has the advantages of high safety and reliability, small size, lightweight, long life, low energy consumption, and high luminous efficiency. Moreover, the length of lightwave emitted by LED is mostly in the range of 400nm-700nm, which is suitable for plant photosynthesis. Because of these advantages, LED is especially suitable for indoor or greenhouse cultivation and is widely used in plant tissue culture, protected horticulture, factory seedling, and aerospace ecological protection system, which is an important research direction of modern agricultural development.
Prospects of MOKOlight
The development of any industry can’t be promoted by one or two people. We need to work together to promote it. With the rapid development of society, people’s demand is higher and higher, and the demand for farming and other planting industries is getting higher and higher. Although the LED grow light has made considerable progress, there is still much room for improvement. MOKOLight is fortunate to be born in this era. It will continue to increase investment and contribute to modern planting technology while achieving certain led research results.
