In the process of plant senescence, chlorophyll degradation, rapid loss of protein and RNA hydrolysis are mainly manifested in leaf senescence. Chloroplast is very sensitive to the change of light environment, especially affected by light quality. Red light, blue light and red blue combination light are beneficial to chloroplast morphogenesis, blue light is beneficial to starch accumulation in chloroplast, red light and far red light have negative effects on chloroplast development. The combination of blue light and red blue light can promote the synthesis of chlorophyll in cucumber seedling leaves, while the combination of red and blue light can delay the decline of chlorophyll content in the later stage, which is more obvious with the decrease of red light ratio and the increase of blue light ratio. The chlorophyll content of cucumber seedling leaves treated with red and blue light of LED plant illumination lamp beads was significantly higher than that of fluorescent lamp control and monochromatic red and blue light treatment; led3030 lamp beads blue light could significantly improve the chlorophyll a / b value of the plants.
The changes of cytokinin (CTK), auxin (IAA), abscisic acid (ABA) and many enzyme activities were observed during leaf senescence. The content of phytohormone is easily affected by light environment. Different light quality of the light supply lamp has different regulatory effects on phytohormone, and the initial step of the light signal transduction pathway involves cytokinin.
The effect of different light quality on the activity of antioxidant enzymes was significant. The APX activity of rape seedling increased significantly and the POD activity decreased after 9 days of red light treatment; the POD activity of tomato was 20.9% and 11.7% higher than that of white light after 15 days of red light and blue light treatment, respectively. The POD activity of green light treatment was the lowest after 20 days of white light treatment, only 55.4% of that of white light; the soluble leaf of cucumber seedling was significantly increased after 4 hours of blue light treatment. Protein content, pod, SOD, APX, CAT activity. In addition, the activity of SOD and APX decreased with the increase of light duration. The activity of SOD and APX decreased slowly but was higher than that of white light. The activities of peroxidase, IAA peroxidase and IAA peroxidase in tomato leaves and eggplant leaves were significantly decreased by red light irradiation, but the activities of peroxidase in eggplant leaves were significantly increased. Therefore, the reasonable light supplement strategy of led3030 can effectively delay the senescence of Protected Horticultural Crops and improve the yield and quality.