Uptake Of Silver By Wheat Root System In The Presence Of Silver Nanoparticles Or It And Silver Ion

At present,domestic research on nanomaterials is in full swing,especially for plant and silver nanoparticles?AgNPs?interaction research is still very limited.AgNPs are widely used in consumer products,easily discharged to the environment,and harmful to plants and the human health.In this study,the effects of deoxygenation,air exposure and wheat root exudates on the dissolution of AgNPs were studied.After that,the effects of cysteine on the detoxification of AgNPs or Ag⁺,and the uptake rate constants of AgNPs and Ag⁺were investigated.The absorption model of wheat uptaking Ag was established and accumulated.The main research results are as follows:The effect of dissolved oxygen on the dissolution of AgNPs helps to better evaluate its bioavailability and toxicity in soil or water.The results of deoxygenation and air exposure experiments showed that there was no significant difference,no upward trend,in the Ag⁺concentration of AgNPs within 150 min in the condition of deoxidation,maintaining at a stable level(below 4?g·L^-1).However,the Ag⁺dissolved in AgNPs was increasing at air exposure,and up to 25.9?g·L^-1 at 150 min.This suggests that oxygen can significantly affect the dissolution of AgNPs.At the same time,this also provides a new method for distinguishing particles and Ag⁺.The effects of wheat root exudates on the dissolution of AgNPs were investated.The root exudates of wheat were extracted by nutrient solution,and AgNPs were mixed with root exudates under deoxidation condition to investigate the effect of root exudates on the dissolution of AgNPs.It was found that the dissolution of AgNPs exhibited a certain inhibitory effect?p>0.05?in low concentrations of root exudates(0.5-10 mg·L^-1,TOC).However,AgNPs released more Ag⁺?p<0.05?in high concentrations of root exudates(20-40 mg·L^-1)and the Ag⁺concentrations stabilized after 12 h.This may be due to the presence of a certain amount of organic matter in the root exudates,which can combine with Ag⁺.When the root exudates were high,it may destroy the balance of AgNPs dissolution,and promote the dissolution of AgNPs.However,the Ag⁺concentration would be decresed at low concentration of root exudates,which may be not destroy the balance of AgNPs dissolution.Under the experimental conditions,the concentration of root exudates secreted by wheat was about 0.82 mg·L^-1,which did not significantly affect the dissolution of AgNPs.The uptake and accumulation of particles under deoxidation and air exposure conditions were investigated.Through the chlorophyll fluorescence parameters and SEM microstructure analysis,it was found that deoxidation and air exposure did not affect the physiological characteristics of wheat.After the experiments of Ag⁺exposure(2-10?g·L^-1),it found that the accumulation of Ag in wheat tissue would be no significantly different in the low Ag⁺concentrations(below 4?g·L^-1).Based on the above experimental results,wheat could uptake particles from AgNPs solutions(0.1,1,4,10 mg·L^-1)under deoxidation,which there were lots of particles and a small amount of Ag⁺(less than 4?g·L^-1).It indicating that wheat can absorb particles from the solution and accumulate in the tissues.At the same time,it was found that the accumulation of Ag in the wheat shoots in the exposure of 10 mg·L^-1 AgNPs.It suggested that AgNPs could be uptake and transferd within plant tissues.Compared with deoxidation,the uptake and accumulation of Ag increased significantly under air exposure.At the concentration of 0.1-1 mg·L^-1,the contribution rate of AgNPs particles to total Ag accumulation in wheat was about 30%,while the contribution rate increased to about 50%at 4-10 mg·L^-1.This suggests that the uptake of Ag⁺may account for the dominant effect at low Ag⁺concentrations.The bioavailability and toxicity of Ag⁺were reduced by L-cysteine,which could complex with Ag⁺.It helped to explore the uptake and accumulation of AgNPs in wheat.Through the concentrations of CAT and MDA in the wheat which be exposed in AgNPs,AgNOs,AgNPs-cysteine and AgNO₃-cysteine solution,it found that L-cysteine was able to effectively relieve the toxicity of Ag⁺and particles were also toxic to wheat.The changes of Ag concentrations in the wheat tissues under AgNPs,AgNOs,AgNPs-cysteine and AgNO3-cysteine solution shows the uptake mechanism of AgNPs and Ag⁺was different and wheat could uptake particles.L-cysteine not only reduces the toxicity of Ag⁺,but also reduces the uptake rate constant of Ag⁺by wheat.The uptake rate constants of different forms of Ag?ie,dissolved Ag⁺,particles and Ag-cysteine?were different:k_u,_diss(275.4L·kg^-1·h^-1)>k_{u,Ag-cysteine}(210.8L·kg^-1·h^-1)>k_u,NP(1.6L·kg^-1·h^-1).In this experiment,the absorption model of Ag was established,and it was proved that it could accurately reflect the uptake of Ag in different forms.The results can provide basic data for studying the uptake and accumulation of AgNPs in plants,and can further investage the uptake mechanism of plant on AgNPs.The experimental results provide data support for the risk assessment of nanomaterials.