Characteristics And Mechanisms Of Arsenic Uptake And Accumulation By Different Populations Of Pteris Vittata

Arsenic(As)contamination has become a global environmental issue for years,with the most severe problem occurring in Southeast Asia and China.There have been attracted particular interests for years since the first As-hyperaccumulator,Pteris vittata L.,was identified.The mechanisms of accumulation and metabolism of As in P.vittata could contribute to the optimization of phytoremediation.P.vittata has developed different populations in the long-term evolution process.It has been showed that there were significant differences in As accumulation and tolerance among different populations of P.vittata.However,it is still not clear about the characteristics and mechanisms of As uptake in different populations of P.vittata.Therefore,field investigation,hydroponic experiments,pot trial and manual simulation were carried out in order to: 1)investigate the effect of phosphate on the kinetics of As(V)absorption by different populations of P.vittata;2)characterize the root exudates of different populations of P.vittata and 3)compare arsenate reductase activities in different populations of P.vittata.The preliminary conclusions are as follow:(1)The kinetics study showed that the concentration-dependent influx of arsenate in nonmetallicolous and metallicolous populations of P.vittata followed Michaelis–Menten kinetics under phosphate treatment and that phosphate could decrease the arsenate influx rate in the plant.Nonmetallicolous populations exhibited lower Km and higher ?(Vmax/Km)value than that in metallicolous populations in the presence of phosphate,indicating that the former possessed greater ability to absorb As than the latter.With phosphate concentrations increasing,the affinity of transport protein for arsenate was reduced both in nonmetallicolous populations and in metallicolous populations of P.vittata.(2)Both nonmetallicolous and metallicolous populations of P.vittata possess more efficient As uptake under As(III)treatments than those in As(V)treatments.However,P.vittata had lower ability to transfer As from roots to fronds under As(V)treatment than that of As(III).(3)It seemed that As species had insignificant effects on root exudates of P.vittata.Three organic acids including oxalic,malic and succinic acid were detected in root exudates from four populations of P.vittata,with oxalic acids being predominant.Nonmetallicolouspopulations secreted more oxalic acid than metallicolous populations.(4)Root exudates from nonmetallicolous populations could mobilize more As from As-contaminated soil than those from metallicolous populations.The simulation experiment further showed that the mobilization ability of oxalic acid in the root exudates was the strongest.(5)There were significant differences in the distribution of As species in the fronds of four populations of P.vittata.The As(III)concentrations were significantly higher in the fronds of nonmetallicolous populations than metallicolous populations,and the former also had a higher percentage of arsenite than the latter.(6)There were obvious differences in arsenic reductase activity among four populations of P.vittata.Nonmetallicolous populations had higher arsenate reductase activity than metallicolous populations.