Mechanisms Of Light Quality On Substance Metabolism And Nutritional Quality Of Radish Sprouts

In recent years, with the industrial production of sprouts and consumers’ strict requirements for food safety, it has become the new research focus in protected cultivation that light-emitting diodes were utilized as a source of plant lighting to improve the growth and quality of sprouts in vegetable cultivation. In this study, ’Qingtou’ and ’Yanghua’ radishes were tested to investigate the effects of light quality on growth, nutritional quality, phenolic, antioxidant activity and anthocyanin of radish sprouts. Research results will make positive contribution for application of light quality in radish sprouts industrial production and improve nutritional value of radish sprouts. The main results were as follows:1. The effects of light quality on ’Yanghua’ and’Qingtou’ radish sprouts cultivated for 7 days have been investigated. The results showed that light treatments dramatically inhibited hypocotyl elongation of radish sprouts, especially UV-B, as compared with dark treatment. Also, UV-B treatment significantly decreased the fresh shoot weight of radish sprouts. The soluble sugar content of’Yanghua’radish sprouts was significantly increased under white light treatment, and significantly decreased under yellow light treatment. While, the soluble sugar content of ’Qingtou’radish sprouts was significantly decreased under yellow, blue and UV-B light treatment. The contents of soluble protein, free amino acid and vitamin C in ’Yanghua’radish sprouts were obviously increased under UV-B treatment. In addition, blue light treatment dramatically increased the free amino acid content in ’Yanghua’radish sprouts, but not in’Qingtou’ radish sprouts. The vitamin C content of’Qingtou’radish sprouts was obviously increased under UV-B treatment, but dramatically decreased under yellow light treatment. These results suggest that light treatments, especially UV-B, are effective in promoting nutritional quality of radish sprouts.2. The effects of light quality on growth, total phenolic contents, antioxidant and phenylalanine ammonia-lyase (PAL) activity of radish sprouts have been studyed. The results showed that the growth, total phenolic contents, antioxidant and PAL activity of radish sprouts that treated with different light spectrum qualities varied with light quality and treatment time. The hypocotyl length and growth of radish sprouts rapidly increased from 3 to 7 d, and then they increased slowly. Accumulated phenolic in sprouts also showed the general trend distribution of early stage of culture> late stage of culture. Compared to dark treatment, radish sprouts grown in UV-B treatment were found to have much higher concentrations of phenolic. Accordingly, the antioxidant activity and PAL activity were highest in the UV-B treatment. In addition, the blue light treatment also induced the PAL activity and increased the phenolic content in ’Yanghua’ radish sprouts. These results suggest that light treatments of radish sprouts, especially UV-B and blue light, are effective in promoting dietary phenolic antioxidants.3. Light induced the anthocyanin accumulation of ’Yanghua’ radish sprouts controlled with dark treatment, while the ’Qingtou’ radish sprouts have little anthocyanin accumulation. The anthocyanin content of ’Yanghua’ radish sprouts that treated with different light qualities varied with light quality. The anthocyanin content was highest under UV-B treatment. The anthocyanin content in ’Yanghua’ radish sprout hypocotyl was increased progressively with time and significantly higher than control after 24 h treatment. Consistently, PAL activity increased with time. The relationship between anthocyanin content and PAL activity was 0.804 under UV-B treatment, while it was 0.248 under dark treatment. Furthermore, the expression of anthocyanin biosynthetic genes CHI, CHS, F3H, DFR and ANS were significantly increased under UV-B treatment. These results indicated that UV-B induced anthocyanin accumulation in hypocotyl of ’Yanghua’ radish sprouts by up-regulating anthocyanin biosynthetic genes and increasing activity of PAL. In addition, anthocyanin content of hypocotyl was increased continuously after 6 or 12 h from UV-B to dark, and the related gene expression was continuously increased after UV-B to dark. These suggesting that the high expression of anthocyanin biosynthesis gene induced by UV-B was sustainable in the dark, which contributed to the increasing of anthocyanin content. This approach can be used to enhance the anthocyanin content and improve economic efficiency.