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Effects of LED Light Quality on Crop Growth, Leaf Photosynthetic Pigment and Bud Differentiation

The light quality of LED plant grow lights has influence on the flowering of crops. It has been found that there are 5 different gene-coded phytochromes (PhyA~PhyE) in Arabidopsis. PhyA and PhyB are not necessary for flowering induction, but they are involved in the regulation of the flowering time. PhyA is overexpressed in plants to bloom earlier, and PhyB delays plant blooming. PhyA participates in the "extremely low radiation response" and the far red light "high radiation response", while PhyB participates in the "low radiation response" and the red light "high radiation response".

Therefore, the far red and blue light of the good LED grow lights promote flowering, while the red light plays an inhibitory role. In addition, some people have studied the effect of light quality on flower bud differentiation from the aspects of nutrient supply and other aspects. The higher amino acid content and energy substances under the blue light of the LED grow lights provide cell structure components and energy for the flower bud differentiation and flower development of the chrysanthemum, and the number of buds and the number of flowers per plant of the chrysanthemum are both higher than the control under this treatment.

1. The effect of LED plant grow lights on the formation of photosynthetic pigments in leaves

Photosynthetic pigments can absorb, transmit and convert light energy, and are the material basis for photosynthesis of plants. Their content and composition directly affect the photosynthetic rate of leaves. The blue light of LED plant grow lights can promote the formation of chlorophyll in hyacinth callus, while the red light reduces its total chlorophyll content.

Compared with pure red light, when red light is mixed with blue light, yellow light and orange light respectively, the promotion of chlorophyll synthesis in sorghum, cucumber and sorghum leaves is weaker; when the blue light is mixed with other lights, the chlorophyll synthesis in these three plants is greatly promoted.

This effect of mixed light is due to the fact that when pure red light or pure blue light is mixed with light of other wavelengths, the content of activated phytochrome changes, and the activation of cryptochrome is also different, which causes various biological effects. Chlorophyll a is an important photosynthetic pigment, it can transfer the absorbed light energy to the photosynthetic chemical reaction center. Blue light can increase the chlorophyll a content of a variety of algae plants, so plants cultivated with LED grow lights generally have higher chlorophyll a/b values, while plants cultivated with red light have lower chlorophyll a/b.

Carotenoids are auxiliary pigments for chloroplast photosynthesis, which can help chlorophyll receive light energy. Studies have shown that the light quality of types of LED grow lights can affect the carotenoid content of coffee leaves, especially the synthesis of different types of carotenoids. Compared with white light, yellow light, red light, and blue light all reduce the carotenoid content of lettuce.

2. The effect of light quality of LED plant grow lights on crop bud differentiation

Different wavelengths of light have different effects on crops in inducing bud formation. The formation of bulbs and protocorms of lily and tiger head orchid as underground buds does not depend on light quality conditions, while the adventitious buds of African violets and Begonia variegated as ground buds and above-ground buds are promoted by the red light of LED plant grow lights. In contrast, blue light and darkness have an inhibitory effect; blue light in tobacco is beneficial to the formation of adventitious buds, and red light and darkness have an inhibitory effect. Short-wave light can promote the growth of tobacco buds at a lower intensity, while long-wave light needs to be at a higher light intensity to promote buds.

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