Interaction Of Uptake And Acropetal Translocation Between Phenanthrene And Phosphate In Crop Roots

Investigation regarding interaction of root uptake and translocation between polycyclic aromatic hydrocarbons(PAHs)and phosphate is beneficial for safe production of crop foods and enhancement in phytoremediation of PAH-contaminated soils or water.In this study,we assessed the interaction of uptake and acropetal translocation between phenanthrene and phosphate in wheat.The hydroponic experiment was enployed to study absorption and accumulation of phenanthrene by wheat roots and shoots under the coexistence of phenanthrene and phosphate.In the presence of phenanthrene and phosphate,we measured the activity of acid phosphatase(APase)and secreted acid phosphatase(SAPase),the concentration of phenanthrene and phosphorus in xylem sap,soluble protein and soluble sugar content changes in wheat roots and shoots,to reveal the biological mechanisms underlying the interaction of absorption and translocation between PAHs and phosphorus in crops.The main results are shown as follows:(1)Phenanthrene contents in wheat roots and shoots peak with 36.87 mg·kg-1 and 2.07 ng·kg-1,respectively,at 10 μmol·L-1 P.Phosphorus content is raised in both roots and shoots with an increase of P in the range of 0～1200 μmol·L-1.According to the paired t-test,there are no significant dinfferences(P>0.05)in P contents of wheat roots or shoots between the treatments with and without phenanthrene.P can escalate the translocation of phenanthrene from wheat roots to shoots,but phenanthrene has no significant effects on P acropetal translocation.Nutrient solution pH in the presence of phenanthrene and P increase more than that in the presence of either phenanthrene or P.(2)In phenanthrene and phenanthrene-free treatments,the presence of phosphorus has different effects on crop root enzymatic activity.At 1.0 mg·L-1 phenanthrene,the activity of acid phosphatase(APase)and secreted acid phosphatase(SAPase)gradually decreases with the phosphorus concentration,while the existence of phenanthrene can improve the activity of these two enzymes.Compared to the phenanthrene-free control,the activity of these two enzymes is increased by phenanthrene,with the increase rates of 1.31%～9.05%and 7.1%～12.60%,respectively.At 10 μmol·L-1 P,the activity of these two enzymes also gradually increases with an increment in phenanthrene concentration.There is a positive correlation between the activity of these two enzymes and phenanthrene concentration(P<0.05).(3)At 1.0 mg·L-1 phenanthrene,the concentration of phenanthrene in xylem sap increases over the P concentration range of 0～1200 μmol·L-1 with a maximum of 0.0504 mg·L-1,indicating that phosphorous escalates phenanthrene translocation from roots to shoots.In phenanthrene or phenanthrene-free treatments,there is no significant difference in P concentration in xylem sap(P>0.05).Xylem sap pH in the presence of phenanthrene and P decreases more than that in the presence of either phenanthrene or P.At 10 μmol·L-1 P,Phenanthrene in xylem sap also shows an noticeable increase over the phenanthrene concentration range of 0.2～0.6 mg·L-1 in Hoagland solution(P>0.05);while at the range of 0.6～1.0 mg·L-1 phenanthrene,the increase of phenanthrene in xylem sap is not pronounced(P>0.05).There is no significant difference in P concentration in xylem sap(P>0.05).Xylem sap pH decreases with the increase of phenanthrene concentration.(4)Under the coexistence of phenanthrene and phosphorue,the contents of soluble protein and soluble sugar are different.At 1.0 mg·L-1 phenanthrene,as the phosphorus concentration increases from 0 to 1200μmol·L-1,wheat soluble protein and soluble sugar contents increase firstly,and then decrease with a maximum at 600 μmol·L-1 and 300 μmol·L-1 P,respectively,suggesting that high or low phosphorus concentration will affect plant soluble protein and soluble sugar content.At the sane time,soluble protein and soluble sugar contents in thephenanthrene treatments are markedly higher than in the phenanthrene-free treatments(P<0.05),indicating an operation of a tolerant system against pollutant stress.At low phosphorus concentration of 10μmol·L-1,the soluble protein and soluble sugar contents rapidly and significantly increase with phenanthrene concentrations below 0.6 mg·L-1(P<0.05);when the phenanthrene concentrationis over 0.6 mg·L-1,the increase in soluble protein and soluble sugar is not significant(P>0.05).Therefore,it is concluded that the acropetal translocation of phenanthrene is coupled to phosphate。...