Effect Of Melatonin And Its Compound Application With Silicon On The Growth And Cadmium Resistance In Maize

Heavy metal cadmium（Cd）is an industrial and environmental pollutant.In recent years,crop cadmium exceeds the standard frequently across the country.Maize is an important food crop and feed crop.Reducing the toxic effect of cadmium stress on maize and reducing the absorption and transhipment of cadmium by maize are crucial for high-yield,efficient,green and safe grain production.Melatonin has the ability to regulate plant growth and development as well as to enhance plant stress tolerance,and it has attracted increasing attention as a potential plant growth regulator.The common production methods of melatonin are foliar-spraying,root-irrigation,seed-soaking,seed-dressing and other methods.In this study,the maize variety "Yudan 9953" was used as the experimental material,and the effects of different melatonin application methods（foliar-spraying,seed-soaking and seed-dressing）and concentrations on maize morphology,physiology and physiology were investigated under greenhouse and field conditions.or yield,and further explored the effect of melatonin and silicon combined use on cadmium tolerance and cadmium transport in maize.（1）Under indoor conditions,according to the effect of promoting the growth of maize shoots and roots,it was concluded that the relatively suitable foliar-spraying concentration was 100 μmol/L,the seed-soaking concentration was 50 μmol/L,and the root-irrigation concentration was 20-50 μmol/L;Under the conditions,according to the effect of promoting the growth and yield of maize shoots,the appropriate foliar spray concentration was 100 μmol/L.（2）The suitable concentration of melatonin（50 μmol/L）was immersed in maize seeds and mixed with corn seeds,respectively,and cultured in nutrient solution containing silicon and cadmium.The results showed that the compound application of melatonin and silicon increased the plant height and root parameters such as total root length of maize under cadmium treatment,and decreased the cadmium content in roots and shoots as well as the health risk index of cadmium.A suitable concentration（100 μmol/L）of melatonin was sprayed on maize seedlings grown in soil supplemented with silicon and cadmium.The results showed that the compound application of melatonin and silicon significantly improved the plant height,stem diameter,root characteristic parameters and bioaccumulation of various parts of the maize seedlings,and relieved the inhibition of cadmium stress on the growth of maize seedlings.The oxidative damage caused by cadmium stress was alleviated by enhancing the activity of antioxidant enzymes（SOD,POD）in maize leaves,increasing soluble protein content,reducing MDA content and relative electrical conductivity of maize leaves.The accumulation of cadmium in different parts of maize seedling was reduced and the health risk index of cadmium was reduced.The compound application of melatonin and silicon can not only promote the growth and development of maize under normal environment,but also alleviate the inhibition effect of cadmium stress on the growth of maize seedlings and reduce the cadmium content in plants.In the test,the mitigation effect of appropriate concentration of melatonin seed-soaking,seed-dressing or foliar-spraying and silicon composite application was greater than that of cadmium toxicity alone,indicating that the two have synergistic effect.Since the seed-soaking process of melatonin is easily affected by indoor environment and human factors,foliar-spraying and seed-dressing methods are more convenient and stable,and more suitable for field production.