Evaluation Of Drought Rsistance Of Maize Seedlings Based On Resonance Optical Properties Of Nano-Gold SPR Plasma

Due to the special optical properties,gold nanoparticles(GNPs)has a characteristic plasmon resonance(SPR)absorption peak in UV-visible-near infrared region,and the position and intensity of the absorption peak mainly depend on their size and shape of GNPs.Antioxidants in maize have a reducing effect and can mediate the synthesis of GNPs,thus their antioxidant activity can be detected by the GNPs synthesis.Antioxidant activity could be used as one of the indicators for evaluating maize resistance,because the expression of antioxidant enzymes and the accumulation of antioxidants are positively correlated with their resistance to drought stress.This study aimes to establish an accurate and rapid method for evaluating the drought resistance of maize seedlings based on the optical properties of nanogold SPR,to provide a theoretical basis for further study on the effects of drought on the physiological and biochemical characteristics of maize seedlings and the screening of drought-resistant maize varieties.The main results are as follows:1.The four maize varieties,Zhengdan958,Xundan20,Denghai662 and Yuyu22,were selected for drought resistance test.The antioxidant capacity of maize seedling leaves of different varieties before and after drought stress were detected by the synthesis of GNPs.The results showed that the drought resistance of four varieties of maize seedlings from strong to weak was Zhengdan958>Xundan20>Deghai662>Yuyu22;the SOD drought resistance coefficients of Zhengdan958,Xundan20,Denghai662,Yuyu 22 were 1.43,1.23,1.23,1.19,respectively;the MDA drought resistance coefficients were 0.89,0.82,0.82,and 0.57,respectively;the TAC of four varieties of maize seedlings before and after drought stress was measured by the synthesis of GNPs.The antioxidant capacity from strong to weak was:Zhengdan958>Xundan20>Denghai662>Yuyu22,which was consistent with its drought resistance.2.The antioxidant capacity of the four maize varieties before and after drought stress was detected by free radical scavenging DPPH method,ferric ion reduction FRAP method and Folin phenol FC method,combined the results of drought resistance physiological indicators,the correlation and principal component analysis between different methods were performed.The results showed that the DPPH free radical scavenging rates of Zhengdan958,Xundan20,Denghai662 and Yuyu22 were 44.29%,43.50%,42.05%and 39.67%,respectively;the FRAP values were 0.84,0.80,0.80 and 0.72 mmol/L,respectively;total phenolic content were 3.92,3.44,3.40,2.77 mg GAE/g,respectively.In addition,the detection values were higher after drought;linear analysis showed that the correlation between GNPs method and FC,FRAP and DPPH were 0.57,0.81,0.89 respectively;The results of principal component analysis showed that the contribution rate of the GNPs method in the interpretation of the total variation was 0.647,while the contribution rate of the FC method was 0.210.Indicating the GNPs method for detecting the antioxidant activity of maize seedlings to evaluate its drought resistance has good reliability.3.The conditions of the established GNPs method were optimized and the method was confirmed.The GNPs were characterized by X-ray photoelectron spectroscopy XPS and transmission electron microscopy TEM,and the drought resistance of four varieties of maize seedlings was evaluated by the developed GNPs method.The results showed that the optimal condition of GNPs method was that the water extract concentration of maize leaves was 6.26g/L,using a phosphate buffer of pH=8 in a constant temperature water bath at 35℃ for 10 minutes;The linear correlation coefficient R2 of the water extract and the absorbance of GNPS was 0.997,the RSD of the 6 replicate samples was 1.19%,and the RSD value of the sample stored at 4℃ in 9 hours was 1.2%,indicating the GNPs method has good accuracy and stability.EDX had a large amount of Au,and the 4f characteristic peak of gold element was found in XPS spectrum.The SEAD diagram had the characteristic crystal plane index of Au,and the TEM morphology shows the average diameter of synthetic GNPs was 42.01 nm,which fully confirmed the formation of GNPs in the reaction.The evaluation results of drought resistance of four maize varieties were consistent with the results of previous drought resistance tests.4.Antioxidant secondary metabolites in maize seedling leaves were detected by infrared IR and high performance liquid chromatography HPLC.The results showed that the infrared spectrum of maize leaf aqueous extract had characteristic peaks of functional groups in phenols at 3384.69 cm-1,1515.47 cm-1.The C18 column(4.6 min×250 mm,5 μm)was used for chromatographic separation with mobile phases consisted of acetonitrile-0.5%acetic acid solution with gradient elution at a flow rate of 1.0 mL/min.The detection wavelength was set at 280 nm and column temperature was 30℃.The content of four phenolic compounds in the leaves of maize seedlings was as follows:coumalic acid>chlorogenic acid>caffeic acid>gallic acid;the content of coumaric acid,chlorogenic acid and gallic acid after drought stress decreased,the content of caffeic acid increased;the content of four phenolic compounds in different varieties of maize seedlings changed differently under drought,which was related to its sensitivity to drought.