Leaf is the main organ for photosynthesis of plants, and the change of LED plants grow light quality directly affects the growth of leaves.
The leaf area of birch seedlings grown under blue light was twice that under red light, and the leaf epidermal cell area, palisade tissue, spongy tissue and functional chloroplast area were larger than those under white light and red light.
The rice seedling test also had the same results. Compared with white light, the blue light of the plant growth lamp obviously promoted the widening and growth of rice seedling leaves, increased the angle between the leaves and the sheaths, and made the leaves flat; while the red light had the opposite effect, it inhibits leaf widening growth.
However, some people think that compound light is more conducive to the growth and development of leaves. The leaf area of lettuce is larger under the combination of red, blue and green light, followed by white light, and finally red and blue light.
The study also showed that increasing the proportion of LED red light in the composite light can promote the increase of tobacco leaf area to a certain extent, but the leaf weight of the leaves decreases and the leaves become thinner.
Stomata are channels for the entry and exit of water and oxygen, and are the portals of plant photosynthesis. Stomatal movement is regulated by many external environmental factors and internal factors, among which light is an important regulatory factor.
It was found in both monocot and dicotyledonous plants that LED blue light can promote the opening of stomata, while green light can reverse this effect. They believe that the reversible response of blue and green light to the opening and closing of air traps may be due to zeaxanthin two isomerizations.
That is, the physiologically active body that mainly absorbs green light and the inactive body that absorbs blue light. The principle that the blue light of the LED plant growth lamp promotes the opening of the stomata, that is, the blue light activates the plasma membrane ATPase to continuously pump out protons to form a transmembrane electrochemical gradient.
That is, K+ passes through the power of K+ channels, thereby promoting the absorption of K+ by guard cells, resulting in a decrease in intracellular osmotic force, guard cells absorb water and expand, and stomata open.
Under blue light, the malic acid in the guard cells increased to 173% of the original within 30 minutes, the sugar content increased to 215% of the original after 2 hours, and the starch hydrolysis products maltose and maltotriose also continued to increase;
However, under red light, the organic acid and maltose in the guard cells increased slightly, while the sucrose increased to 208% of the original within 2 hours.
Light of different wavelengths can regulate the growth of stems by affecting the level of endogenous hormones in plants. Blue-violet light can increase the activity of indole acetic acid oxidase and reduce the level of auxin (IAA), thereby inhibiting the growth of plants.
At the molecular level, red light promotes cell elongation, while blue light has the opposite effect. In general, long-wavelength LED red light promotes stem elongation. Whereas short-wavelength LED grow lights (blue light) inhibit stem elongation.