Different Responses Of Maize And Northern Teosinte Upon UV-B Radiation

Maize(Zea mays L.)is an important food crop in the world,and its wild relative species teosinte are natural germplasm resources for maize improvement.Understanding the responses of maize and its wild relatives to stresses is of great significance to the effective use of wild resources.At the present study,maize(B73)and its wild relative(northern teosinte)were used as materials,and the same dose of UV-B was used for radiation treatment.their responses to UV-B were investigated.The main results are as follows:1.UV-B radiation decreased the plant height,leaf area and relative water content of both maize and northern teosinte where the plant height of maize was reduced by 22.7%,and it was 42% for teosinte.For leaf area,it was decreased by 27.7% in maize and 25.5% in northern teosinte.The relative water content of maize was lessened by 3.3% and 1.2%,respectively.2.UV-B treatment reduced the chlorophyll content of maize and northern teosinte.Compared with the control,the chlorophyll content of maize decreased by 20.7% and it was.25.6% for maize;The ratio of chlorophyll a/b increased under UV-B in both of maize and northern teosinte which was 10.2% and 10.6%,respectively;UV-B radiation changed the values of the chlorophyll fluorescence parameters in both maize and northern teosinte.For maize,NPQ was significantly reduced(P<0.05)and no difference presented for the maximum photochemical quantum yield(qP)and photochemical quenching(Fv/Fm)of photosystem II(P>0.05);they all significantly lowered in northern teosinte(P<0.05).The Fv/Fm,qP,and NPQ in maize were reduced by 5%,12.3%,and 7%,respectively,while those of northern teosinte were 7%,35.6% and 46.9%,respectively.After UV-B radiation,the stomata of maize and northern teosinte were all decreased,and the wax content was increased.We also found that the stomata of northern teosinte are originally bigger than that of maize which is one of the inherent differences between them.3.UV-B treatment significantly reduced the soluble sugar content of maize and northern teosinte(P<0.05).Within them,the soluble sugar content of maize was reduced by 13.8% and it was 14.3% in northern teosinte.SDS-PAGE was performed to analyze the total proteins from four groups.The results exhibited that there were bands missing with UV-B irradiation,indicating that UV-B radiation inhibited the expression of certain proteins.4.DAB and NBT staining showed that ROS content increased in both maize and northern teosinte upon UV-B radiation.The content of ROS in maize was lower than that of northern teosinte by color observation.We measured the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)and found them all enhanced upon UV-B radiation.In maize the activities of SOD,POD and CAT increased by 52.5%,59.9% and 16.9%,respectively,while they were 30.1%,20.05% and 12.8%,respectively.The current results suggest that the antioxidant enzymes in maize can effectively scavenge free radicals under UV-B radiation,which is consistent with the lower content of ROS in maize under UV-B.ROS can oxidize lipids and produce MDA.The study found that the UV-B radiation higher MDA content in both maize and teosinte,in which it was higher in northern teosinte than in maize which is consistent with the ROS content.5.UV-B treatment promoted the synthesis of flavonoids in both maize and northern teosinte where it increased by 17.8% and 11.3%,respectively.The expressio n of key genes in the synthetic pathway of flavonoids were determined by real-time PCR.The results showed that CHS and CHI genes were significantly higher expressed upon UV-B radiation in both maize and teosinte where the CHS genes of maize were double higher expressed compared with that of northern teosinte.We also tested the content of other flavonoids like quercetin and kaempferol with TCL technique.The results showed that with UV-B radiation,the bands color of quercetin and kaempferol were obviously brightened,which means the contents of both substances increased.UV-B radiation had different degrees of influence on maize and its wild relative northern teosinte.Relatively speaking,maize had stronger tolerance to the experimental conditions than northern.