Short-distance And Long-distance Transport Process Of Polycyclic Aromatic Hydrocarbons In Plant Roots

Because polycyclic aromatic hydrocarbons(PAHs)are high residual in the environment,can accumulate in plant and enter human body through the food chain,their absorption and migration process in the soil-plant system has been paid more attention.The mechanisms underlying uptake and transport of PAHs in plants,are able to provide strategies for reducing PAH accumulation in crops for food safety,and improving phytoremediation of PAH-contaminated soils or water by agronomic practices.However,little is available regarding the short-distance and long-distance transport of PAHs in plants.Here,we investigated the method for extracting plant apoplast solution in plant roots,analyzed characteristic differences of PAH uptake in plant apoplast and symplast,determined xylem sap components,and finally explored the impact factors affecting PAH uptake in plant apoplast and symplast.The main results obtained are as follows:Phenanthrene extracted from wheat root apoplast solution increases with an increase in vaccum degree,vaccum time,centrifugal speed and centrifugal time.Glucose-6-phosphate dehydrogenase(G6PGH)activity in wheat root apoplast solution is enhanced with increasing vaccum degree,vaccum time,centrifugal speed and centrifugal time.For the vaccum infiltration centrifugation extraction,the optimum vaccum degree is 70 kPa,the optimum vaccum time is 10 min,the optimum centrifugal speed is 3068 r·min-1,and the optimum centrifugal time is 15 min.Within a certain time,phenanthrene in wheat root apoplast and symplast increases with extraction time,and increases with an increment of phenanthrene in nutrient solution.Wheat root apoplast and symplast have maximum absorption capacity of phenanthrene at 35?.Under the same conditions,there is significant difference in phenanthrene absorption between wheat root apoplast and symplast.The phenanthrene in wheat root symplast is higher than in wheat root apoplast.Kinetics and thermodynamics of phenanthrene absorption in wheat root apoplast and symplast indicate that the higher the temperature,the greater the reaction rate constant is,the activation energies of phenanthrene absorption in wheat apoplast and symplast are positive,and the activation energy for symplast absorption of phenanthrene is lower than for apoplast absorption,suggesting that the symplast absorption occurs more easily than the apoplast absorption.Phenanthrene in corn xylem sap is significantly higher than in wheat xylem sap(P<0.05).The amount of xylem sap in wheat and corn is decresed by phenanthrene.In xylem sap of the treatment with phenanthrene,soluble protein and formic acid increase,and nitrogen,potassium,phosphorus and pH reduce,indicating that the long-distance transport of phenanthrene is related to soluble proteins,and phenanthrene has a inhibitory effect on long-distance transport of plant nutrients.Darkness and cuting wheat aboveground can decrease the phenanthrene in wheat root apoplast.The symplast phenanthrene is much larger at 25? than at 4?.2,4-DNP and vanadate sodium inhibite phenanthrene uptake in wheat root symplast.