Mechanisms Of UV-B-Induced Synthesis Of Phenolics In Soybean Sprouts

Because of rich nutrition,unique flavor,soft quality and pollution-free,sproutsare commonly consumed.Therefore,sprout has become a kind of promising emerging vegetable industry.Light emitting diode(LED)was applied to accurately modulate light spectral energy distribution.The effects of light on the growth and phenolics synthesis of soybean(Glycine max)sprouts were studied.The results will make positive contribution tothe lightapplication inthe industrial production of soybean sprouts.The main results were as follows:1.Light emitting diode(LED)was applied to accurately modulate light spectral energy distribution.The effects of light quality and photoperiod on the growth,total phenolics content and DPPH scavenging activity in soybean(Glycine max)sprouts were studied.The results of light quality test indicated that hypocotyl length and edible rate were significantly decreased by UV-B,which was favorable for water accumulation in plant.Every light treatment significantly increased the content of total phenolics in hypocotyls.The total phenolics content reached the max under UV-B treatment,and was much higher than that under the darkness and other light treatments.Under UV-B treatment,the DPPH scavenging activity in hypocotyls and cotyledon of soybean sprouts reached the max,and was significantly higher than that under the darkness.The photoperiod test showed that the root length reached the max and the hypocotyl length reached the min when the photoperiod was 8 h·d-1 under UV-B.The total phenolics content and DPPH scavenging activity were significantly decreased by 8 h·d-1 and 12 h·d-1 UV-B treatment,and were much higher than that under the darkness and other light treatments.Overall,8 h·d-1 UV-B treatment was more beneficial for the total phenolics content and the DPPH scavenging activity in soybean sprouts.2.Darkness(D),LED(light emitting diode)white light(W)and UV-B were applied to cultivate soybean sprouts.The effects of UV-B on phenolics content,PAL activity and the genes of the key enzymes in hypocotyls of soybean sprouts were studied.The results showed that,comparing with D and W treatment,the total phenolics content in hypocotyls was significantly increased under UV-B.What's more,the total phenolic acids content under UV-B was significantly promoted comparing with D.So were the content of syringic acid,p-coumaric acid and ferulic acid.Comparing with D and W,UV-B also significantly promoted the PAL activity.Different gene expressions of 6 key enzymesinvolved in phenolicsynthesis were investigated using RT-qPCR,in which Actin was used as reference gene.The results indicated that the relative expression of PAL2,CHS8,FLS and ANSwere increased graduallyunder UV-B duringcultural time.PAL2was significantly higher than D and Wat4d and 5 d under UV-B.CHS8,FLS and ANSwere significantly higher than D and W only at 4 dunder UV-B,This work founded the basis for further study on the connection between UV-B and phenolics accumulation in soybean sprouts.3.Darkness(D),LED(light emitting diode)white light(W)and UV-B were applied to cultivate soybean sprouts.The effects of UV-B on the signals to UV-B responses in hypocotyls of soybean sprouts were studied.The results showed that,comparing with D and W,the total phenolics content in hypocotyls was significantly increased under UV-B.So were the content of MDA and H2O2;but the activity of SOD,POD and CAT decreased significantly.Comparing with W,the relative expression ofPR-2,PR-4 and PR-6 stayed low under UV-B treatment.What's more,after 3 d cultivation,the relative expression ofUVR8 and COP1 were significantlyhigher under UV-B than D and W.As above,UV-B had effecteson UVR8 signal pathway.And,H2O2 might be the form of signaling molecule involved in signal transduction to stimulate the downstream phenolicssynthesis.