The Mechanisms Of UV-A-Mediated Content Increased Of Ascorbic Acid In Soybean Sprouts And The Key Roles Of H₂ During This Process

In recent years,with the industrialization of sprouts technology and the more and more strict requirements for sprouts safety,it has become the new research focus to improve the growth and quality of sprouts by regulating the light environment which is precise controlled by light-emitting diode.In this study,used the seedling of 'Dongnong690'soybeans as the experimental material to investigate the effects of various light qualities on growth and metabolism of ascorbic acid,to clarify the regulating effects of UV-A radiation on AsA-GSH cycle,to illuminate the key roles of H₂ during the UV-A-mediate up-regulation of the ascorbic acid content.Our research results will provide scientific basis for sprouts industrial production about screening suitable light quality.What's more,it is also an environment-friendly strategy to increase the nutritional value of soybean sprouts.1.The effects of various light qualities on 'Dongnong690' soybean sprouts which were cultivated for 4 days have been investigated.The results indicated that,compared with dark treatment,light qualities,especially UV-A and UV-B dramatically inhibited hypocotyl elongation,decreased fresh weight and edible fresh weight of soybean sprouts,but there was no significantly influence on edible rate have been observed in different light quality treatments.Different effects on ascorbic acid content were observed under different light quality treatment,Different effects of diverse light quality treatments on accumulation of ascorbic acid were observed,compared with dark,light treatments could significantly increased the ascorbic acid content both in hypocotyls and cotyledon of soybean sprouts.Among all light treatments,UV-A irradiation has the most significant effects on promoting ascorbic acid metabolism which reached a maximum of 64.92?g·g-1 FW and 77.23 ?g·g-1 FW respectively in hypocotyls and cotyledon of soybean sprouts after 36 h treatment.However,In totally,light treatments,especially UV-A irradiation,could effectivly promoting the accumulation of ascorbic acid in soybean sprouts.2.The effects of UV-A on the accumulation of ascorbic acid and glutathione,the key enzyme activities and the expression of critical genes during the AsA-GSH cycle have been studied.Results showed that though UV-A treatment inhibited hypocotyl elongation,but markedly increased ascorbic acid accumulation both in hypocotyls and cotyledon of soybean sprouts,especially after 36 h treatment,compared with dark treatment.The contents of glutathione,the enzyme activities and the expression of key genes during AsA-GSH cycle indicated that,after 36 h treatment,contents of glutathione notably increased in cotyledon of soybean sprouts,the enzyme activities of DHAR and GR and the expressions of their genes in hypocotyl and cotyledon were notably improved in contrast to the control.To sum up,we guess that light is conducive to the accumulation of ascorbic acid in soybean sprouts and this probably results from the enhancement of the enzyme activity of DHAR and GR and up-regulated expressions of their genes.3.UV-A irradiation could significantly increased the content of ascorbic acid in hypocotyls of soybean sprouts after 36 h treatment when compared with dark and white radiation.,content of ascorbic acid could be further promoted by co-treatment with exogenous hydrogen rich water?HRW?,and this increasing function depended on the HRW concentration.We further detected the hydrogen release amount of each experimental group in hypocotyl of soybean sprouts with the usage of gas chromatography.Results showed that,after 36 h UV-A irradiation,with the increase of HRW concentration,hydrogen release amount increased gradually and the content of ascorbic acid had a similar tendency with the hydrogen release..Furthermore,the expressions of critical genes which involved in process of biosynthesis,cycle and degradation of ascorbic acid have been tested,results shows that AsA biosynthetic genes?GMP1?VTC2?VTC4?GalDH?,cycle genes?MDHAR?DHAR?and degradation genes?APX1?APX2?were notably increased under UV-A company with HRW treatment,while the expressions of other genes were unaltered.In sum,co-treatment with hydrogen rich water and UV-A was further improved the content of ascorbic acid in hypocotyls of soybean sprouts when compared with UV-A treatment alone.We speculated that hydrogen rich water treatment may increase the hydrogen release amount and which then up-regulate the expressions of key genes which involved in AsA biosynthesis?GMP1?VTC2?VTC4?GalDH?,AsA cycle?MDHAR,DHAR?and degradation?APX1?APX2?.