The effect of light on plants.
Light has a particularly important position in the growth and development of plants, and it affects almost all growth stages of plants.
The effects of light on plants are mainly manifested in two aspects:
One is to provide radiant energy for plant photosynthesis.
The second is as a signal to regulate many physiological processes throughout the life cycle of plants.
The effect of light on plant growth-photosynthesis and phytochrome Generally, the growth and development of plants rely on sunlight, but the factory production of vegetables, flowers and other economic crops, tissue culture, and the propagation of test-tube seedlings also require supplementary light from artificial light sources to promote photosynthesis.
Photosynthesis refers to the process by which green plants use light energy through chloroplasts to convert carbon dioxide and water into organic matter that stores energy and release oxygen. The key participant in this process is the chloroplast inside the plant cell. Under the action of sunlight, the chloroplast converts the carbon dioxide that enters the leaves through the stomata and the water absorbed by the roots into glucose and releases oxygen at the same time. The photosystem in which the photoreaction occurs is composed of a variety of pigments, such as chlorophyll a, chlorophyll b, and carotenoids. The main absorption spectra of chlorophyll a, chlorophyll b and carotenoids are concentrated at 450nm and 660nm, so in order to promote photosynthesis, 450nm deep blue LED and 660nm super red LED are mainly used, and some white LEDs are combined to achieve this. High-efficiency LED plant lighting, as shown in Figure 1:
In order to be able to sense the light intensity, light quality, light direction and photoperiod of the surrounding environment and respond to its changes, plants have evolved a photoreceptive system (photoreceptor). Photoreceptors are the key for plants to experience changes in the external environment. In the light response of plants, the most important photoreceptors are photosensitizers that absorb red light/far-red light.
Phytochrome is a type of pigment protein that has a reversal effect on the absorption of red light and far-red light, participates in photomorphogenesis, and regulates plant development. It is extremely sensitive to red light and far-red light, and is used throughout the growth and development of plants from germination to maturity. Both play an important regulatory role in the process.
Phytochromes in plants exist in two relatively stable states: red light absorbing type (Pr, lmax=660nm) and far-red light absorbing type (Pfr, lmax=730nm). The two light absorption types can reverse each other under red light and far-red light.
Studies on phytochromes show that the effects of phytochromes on plant morphology include seed germination
Hair, de-yellowing, stem elongation, leaf expansion, shade avoidance and flowering induction.
Therefore, a complete LED plant lighting solution requires not only 450nm blue light and 660nm red light, but also 730nm far-red light. Deep blue (450nm) and super red (660nm) can provide the spectrum required for photosynthesis, and far-red light (730nm) can control the whole process of plants from germination to vegetative growth to flowering.