Physiological Mechanisms Of Oxytetracycline And Ciprofloxacin Regulating Maize Seed Germination And Seedling Growth

Antibiotic pollution has become one of the main sources of soil pollution.Maize is the world’s largest crop with edible,forage and industrial value.Harbin,Heilongjiang Province is a city with developed animal husbandry and pharmaceutical industry.The antibiotic pollution caused by enterprise sewage discharge to urban rivers and agricultural soil in Harbin can not be ignored.In order to explore the effects of typical antibiotics in soil on physiological and biochemical reactions of maize,Longken 10 was used as material and selection of tetracycline antibiotics oxytetracycline（oxytetracycline,OTC）and quinolones antibiotics ciprofloxacin（ciprofloxacin,CIP）widely used in production,with setting different concentration gradient(0,3,5,30,60,120 mg·L^-1)and using nutrient solution hydroponic method.And then,the effects of maize seed germination and growth,seed germination-related enzymes,seedling biomass,photosynthetic enzymes,nitrogen metabolism and endogenous hormone content were investigated.On the one hand,this study aims to analyze the germination and seedling growth of maize under different antibiotic pollution conditions.On the other hand,it provides theoretical support for rational use or avoidance of antibiotics in the field to ensure the safety of crop growth.The results are as follows:The seed germination experiment showed that compared with CK,3-5 mg·L^-1 treatment group could promote the growth of maize seed roots and buds.And 30-120 mg·L^-1 treatment group inhibited the growth of maize seed roots and buds,and when OTC concentration was 3 mg·L^-1 and CIP concentration was 5 mg·L^-1,the growth of seed roots and buds was the best.In contrast,OTC had stronger inhibitory effect,and maize seed roots were more sensitive to OTC and CIP than maize seed buds.After OTC and CIP treatments,the key enzymes affecting maize grain growth were promoted at low concentration and inhibited at high concentration.Except for the 120 mg·L^-1treatment group,OTC and CIP showed promotion effects on the activities of phosphofructose kinase,α-amylase andβ-amylase and inhibited the activities of hexokinase and COX.The seed hydroponic experiment showed that compared with CK,when CIP concentration was5 mg·L^-1 and OTC concentration was 3 mg·L^-1,the activity of each index of maize seedlings was the strongest and the seedling growth was the most vigorous.And the inhibitory effect of OTC on each index of maize seedlings was higher than that of CIP.And the sensitivity of underground part of maize seedlings to OTC and CIP was higher than that of aboveground part.Both the growth of maize seedlings was inhibited at high concentration(30-120 mg·L^-1)and promoted at low concentration(3-5 mg·L^-1).3–5 mg·L^-1 OTC and CIP treatment groups could increase the biomass of maize seedlings,including the increase of dry and fresh weight of maize leaves and roots,the decrease of root-shoot ratio,the robust growth of seedlings and the enhancement of vitality.And the relative water content of maize leaves increased,the relative conductivity of rice leaves decreased,and the cell permeability decreased.The activities of leaf photosynthetic enzymes PEPCase,RUBPCase,PPDK,NADP-ME and NADP-MDH increased,photosynthesis enhanced,and dry matter accumulation increased.The IAA,GA and ZR levels in maize leaves and roots was increased,and ABA and Me JA levels was decreased.The levels of GS,GOGAT and GAD related to nitrogen metabolism in roots and leaves were increased,and the GDH level was decreased.Root activity and root parameters including average diameter,root tip number,total volume,total root length and root surface area increased,and root growth was vigorous.Compared with CK,30-120 mg·L^-1 OTC and CIP treatments decreased maize seedling biomass,increased root-shoot ratio and weak seedling growth.The relative water content of maize leaves decreased,the relative conductivity of maize leaves increased,and the cell permeability increased.The decrease of leaf photosynthetic enzyme activity leads to the decrease of photosynthesis and photosynthetic productivity.The IAA,GA and ZR levels in leaves and roots of maize seedlings were decreased,and the ABA and Me JA levels were increased,GS,GOGAT and GAD levels in leaves and roots of maize seedlings were decreased,and GDH level was increased.The root activity decreased,and the parameters of root decreased accordingly.