| Alfalfa is a widely cultivated fine herbage,rich in protein and vitamins,and is known as"Queen of Forages".Studies have shown that environmental changes cause ultraviolet radiation to increase.In this study,5 alfalfa varieties,"Reindeer","Giant 201","3010","Giant"and"Vitoria"were used as experimental materials to study the morphological structure and physiological changes of ultraviolet radiation to screen out the alfalfa varieties with the strongest UV-B resistance.In this experiment,low dose UV-B was used to treat the most resistant alfalfa,and to explore the best radiation dose of its nutritional quality and secondary metabolites.1.The seedlings of Alfalfa for 30 days were irradiated with UV-B,the intensity of irradiation was 35±5 uW/cm~2,the irradiation time was 2 hours,and the UV resistance of different alfalfa varieties was compared for 7 days.The results were as follows:(1)After UV-B irradiation,different kinds of Alfalfa had apparent damage to different degrees,including leaf curling,yellow and wilting,among which,the phenotypic changes of"Giant"alfalfa were small.(2)Except the"Reindeer"alfalfa,the content of soluble sugar and soluble protein in the other four alfalfa was higher than the control.The soluble sugar of"Giant 201"was significantly higher than that of the control group.The soluble sugar content of"Giant"alfalfa increased by 23.44%,and the soluble protein of"Giant"alfalfa increased by the most.The increase of soluble sugar and soluble protein in"Reindeer"alfalfa was smallest.(3)UV-B radiation treatment resulted in the decrease of photosynthetic pigment content in alfalfa leaves,the smallest decrease in chlorophyll content of"Giant"alfalfa and the largest decrease in chlorophyll content of"3010"alfalfa.(4)UV-B radiation could increase the content of anthocyanin and total polyphenols,reduce the content of flavonoids.The content of anthocyanins in"Reindeer"and"Giant"alfalfa increase the most,and the content of total polyphenols in"Giant"alfalfa increased the most.And the reduction extent of flavonoid content,"Giant"alfalfa is leastt.(5)UV-B radiation increases the MDA content and relative conductivity of Alfalfa."Giant"alfalfa MDA and relative conductivity decreased the minimum."Giant 201"alfalfa MDA decrease most,and the relative conductivity of"3010"alfalfa decrease most.(6)UV-B radiation increase the activity of antioxidant enzymes-PAL,POD,SOD,CAT and APX,and there was a difference in the increase of enzyme activity among the different varieties.The activity of PAL,SOD and APX in"Giant"alfalfa increase most,and the the activity of POD in"Vitoria"and"Giant"increased greatly,and the biggest CAT activity is in"Reindeer".(7)The scanning electron microscopy(SEM)of alfalfa leaves showed that UV-B radiation resulted in cell shrinkage of leaf epidermal cells and reduced stomatal opening degree,and the stomatal opening degree of"Giant"alfalfa decreased slightly.2.The alfalfa with the strongest resistance to UV-B was irradiated with 24u W/cm~2 UV-B,and the treatment time was 0min,15min,30min,45min,60min,75min,and the 7d was treated continuously.The results showed that the total polyphenols and flavonoids were the highest in the 15min UV-B treatment group in alfalfa leaves.In 30min UV-B treatment group,the content of anthocyanins in alfalfa leaves was the highest,and there was no significant difference with 15min UV-B treatment group.In 45min UV-B treatment group,the PAL activity and soluble protein content of alfalfa leaves were the highest.The soluble sugar content in the 75minUV-B treatment group was the highest,while the soluble sugar content in the 45min UV-B treatment group was the second.In conclusion,"Giant"alfalfa has the strongest UV-B resistance.24 uW/cm~2UV-B treatment of 15min contributed to the improvement of the nutritional quality of"Giant"alfalfa,and the treatment of 45min UV-B was beneficial to the accumulation of secondary metabolites. |
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