The Role Of NO In UV-A-induced Ascorbic Acid Biosynthesis In Radish Sprouts

In recent years,as the development of sprouts idustry and the strict requirements of people for food safety,it has become a research hot point in protected cultivation that light environment was regulated to improve the growth and quality of sprouts in vegetable industry.In this study,’Yanghua’ radish was used as research metarial to investigate the effects of NO and UV-A on the AsA content,antioxidant activity and the synthesis of AsA in radish sprouts.The research will make positive contribution to the application of light in sprouts industry and provide scientific evidence for the improvement of nutritive value of radish sprouts.The main studies were as follows:1.After 3 d dark cultivation,the radish sprouts were transferred into white light and UV-A for 48 h.Compared with control,white light and UV-A radiation significantly decreased the hypocotyl length of radish sprouts,while the fresh weight,dry weight and the moisture content were affected slightly.The contents of ascorbic acid under UV-A were significant higher than those under dark in every time point,and compared with white light,over 24 h UV-A irradiation significantly increased the AsA content.The activities of APX,POD and SOD were significantly enhanced by 36 and 48 h UV-A treatment,and the activity of CAT was significantly increased by 24 and 48 h UV-A treatment.In addition,the expression of most genes in the L-Galactose pathway and the activity of GLDH could be increased by UV-A irradiation.All these results promote us to hypothesize that UV-A radiation promotes the biosynthesis of AsA in radish sprouts.2.The effects of NO and UV-A on AsA content,endogenous NO concentration,activities of NR and NOS and the expression of synthesis genes of AsA were studyed.The results showed that NO played an important role in the increase of AsA under the UV-A radiation.Compared with white light,addition of SNP(NO donor)under UV-A can further improve the content of ascorbic acid.However,the increase can be suppressed by addition of PTIO(the NO scavenger)or the inhibitors of nitrate reductase(NR)and the nitric oxide synthase(NOS),which was consistent with the content of endogenous NO.Moreover,the results showed that the NR pathway might play a major role in the involvement of NO in UV-A-induced AsA accumulation.Through the quantitative PCR analysis,we observed that NO increased the As A content by up-regulating the expression of GP1,PMM,VTC2 and GLDH in L-Galactose pathway in radish sprouts.