Effects Of Spermidine And Nano Titanium Dioxide On Growth And Cadmium Accumulation Of Zea Mays Seedlings

The residual concentration of heavy metal cadmium（Cd）in some cultivated soil in the black soil area of northeast China exceeded the risk screening value of agricultural land soil pollution stipulated in Soil Environmental Quality Risk control standard for soil contamination of Agricultural Land（Trial）＿（GB15618-2018）,It poses a certain threat to the quality of cultivated land soil and the safety of agricultural products,so it is urgent to establish effective technical methods.In order to reduce the migration and accumulation of Cd in soil to crops,the goal of safe use of cultivated land was realized.In this study,Zea mays was used as the test plant,spermidine（Spd）and nano-titanium dioxide（Ti O₂-NPs）were selected as the soaking seed materials.The germination test was used to select the suitable seed concentration which could reduce Cd absorption of Zea mays.On this basis,the regulation rules of Spd and Ti O₂-NPs on the growth indexes,physiological characteristics and Cd accumulation of Zea mays seedlings under Cd stress were further investigated.In order to develop a method to alleviate the toxic effect of Cd accumulation on Zea mays.The study can provide a new method for the safe utilization of cultivated land contaminated by heavy metal Cd.The main findings are summarized as follows:（1）The results of germination test showed that:Compared with CK treatment,50 mg·L^-1 Cd could significantly inhibit Zea mays seed germination.Compared to Cd stress treatment,70 mg·L^-1Spd soaking treatment and 80 mg·L^-1 Ti O₂-NPs soaking treatment increased the germination potential,germination rate,germination index and vigor index of Zea mays seeds by 20.00%and31.44%,11.90%and 19.04%,18.84%and 28.42%,60.47%and 49.64%,respectively.It can effectively relieve the germination vigor of Zea mays seed under Cd stress.In addition,the above soaking seed treatment separately increasedα-amylase activity by 55.93%and 45.76%,which could provide more energy for seed germination.Compared with other concentrations of Spd and Ti O₂-NPs of the same substance,70 mg·L^-1 Spd and 80 mg·L^-1 Ti O₂-NPs had the best effect on alleviating Cd stress on Zea mays seed germination.（2）The results of hydroponics test show that:Compared with CK treatment,plant height,root length,dry weight and fresh weight of Zea mays seedlings under 50 mg·L^-1Cd stress were significantly reduced,while chlorophyll content synthesis was significantly inhibited and ROS level was increased,indicating that Cd treatment with this concentration had caused stress on Zea mays growth.Compared with Cd stress treatment,70 mg·L^-1 Spd and 80 mg·L^-1 Ti O₂-NPs single or composite soaking seed treatment could effectively alleviate the negative effects of Cd stress on the growth and typical physiological characteristics of Zea mays seedlings.In addition,in composite soaking seed treatment compared with Spd and Ti O₂-NPs single soaking seed treatment,the activities of superoxide dismutase,peroxidase and catalase of Zea mays seedling leaves respectively increased by 13.94%and 23.37%,21.25%and 38.15%,21.78%and 28.44%,all reached significant difference level.These results indicated that the composite soaking seed treatment could effectively activate the antioxidant enzyme system of Zea mays seedlings to alleviate the stress effect of Cd on Zea mays seedlings.（3）Soil culture test results show that:Under 50 mg·kg^-1 Cd stress,photosynthetic capacity and nutrient accumulation of Zea mays seedlings were significantly inhibited,and their normal physiological functions were disturbed.Compared with Cd stress treatment,Spd and Ti O₂-NPs single or composite soaking seed treatment.The photosynthetic characteristics（Pn,Tr,Gs,Gi）of Zea mays seedlings were alleviated to different degrees.The contents of total nitrogen,total phosphorus and total potassium in Zea mays seedling leaves were separately increased by 4.79%-7.11%,3.78%-8.25%and 8.59%-20.79%,among them,the composite soaking seed treatment significantly improved the above plant nutrient indexes.These results indicated that the composite soaking seed treatment could deal with Cd stress by alleviating nutrient accumulation.In addition,in composite soaking seed treatment compared with Spd and Ti O₂-NPs single soaking seed treatment,Cd accumulation in the shoots and roots of Zea mays seedlings were separately decreased by 11.26%and 18.64%,8.51%and 12.52%,reaching a significant difference level.It was further confirmed that the composite soaking seed treatment had the most obvious alleviating effect on Cd toxicity in Zea mays seedlings.