| Medicago sativa L,Leguminosae,is one of the most widely cultivated,most important and resourceful perennial grasses in the world,with the reputation of "King of Pasture".In this experiment,alfalfa was cultured for three weeks under incandescent lamp as control(CK),and treated with different doses of UV-B radiation for 7 days(0.5 h·d-1、1 h·d-1、1.5 h·d-1、2 h·d-1、2.5 h·d-1、3 h·d-1)to study the effects of UV-B radiation on the morphological structure,photosynthetic characteristics,photosynthetic pigments and UV-absorbing compounds of alfalfa of a different degree.The results showed that the UV-B radiation inhibited the root length,internode length and plant height of alfalfa,and the appearance of the plant treated with 1.5 h was yellow and short,and the stem and root became thinner,leaves began to yellow,showing rust;the plant leaves surface treated with 2 h·d-1 was curl and shrivel,the surface area was reduced,and it was too unsmooth to the dead.Through the paraffin section technique we can see that the chlorophyll was significantly reduced,the edge of stalk cells were distorted,the cortical cells were loose and the cells were disintegrated due to the loss of water;with the method of scanning electron microscopy,the leaves treated for more than 1.5 h the surface stoma of the leaves was closed and the epidermal cells were depressed and the depression was serious at 2.5 h and 3 h.With prolongation of the irradiation time,the photosynthetic rate(Pn),stomatal conductance(Cond)and transpiration rate(Trmmol)was decreased compared with CK,the photosynthetic rate decreased by 87.638% and the stomatal conductance decreased by 94.536%,the transpiration rate decreased by 97.483% of the leaves treated 2 h·d-1,and the intercellular CO2 concentration increased by 6.733%,and the difference was very significant(p <0.01),the photosynthetic characteristics indicators of leaves under the 3 h treatment was not able to measure;UV-B radiation of different doses had inhibition effect on the contents of chlorophyll a(Chla),chlorophyll b(Chlb),chlorophyll a + b(Chla + b)and carotenoid(Car)in alfalfa,and the difference was very significant(p <0.01).The UV-B radiation can significantly promote the UV-absorbing compounds of alfalfa,the content of total phenol and flavonoids were highest in 2.5 h compared with CK,rise 109.951% and 18.165% respectively.The anthocyanin content was the highest at 2 h,which is increased by 58.741%,reached extremely significant difference(p <0.01).UV-B,RL-UV-B and RL-DRL-UV-B radiation treatment were used to study the response mechanism of Phy to UV-B radiation stress.The results showed that compared with CK,the photosynthetic characteristics,photosynthetic pigments and other nutritional quality have a certain inhibitory effect in the short-term(2 h)UV-B radiation.If with the 10 min red light pre-radiation,the indicators have enhanced.If join the far red light,the protective effect of red light disappeared;the short-term(2 h)UV-B radiation enhanced the uv-absorbing compounds,H2O2,POD,SOD as well as CAT activity of alfalfa.The 10 min red light pre-radiation will reduced the damage.If join the far red light,the protective effect of red light disappeared.The activity of APX both reduced.In order to further study the effect of UV-B on the molecular level of alfalfa and the interaction between UV-B receptor proteins UVR8 and the red light receptor proteins Phy,the core fragment of UVR8 gene was cloned in this laboratory with 1194 bp. |
