施硼对水稻幼苗吸收和分泌砷的影响

Effects of Boron Treatment on Arsenic Uptake and Efflux in Rice Seedlings

通过3组水培试验研究了营养液不同供硼(B)浓度和叶面施B对水稻(Oryza sativa L.)幼苗吸收、转运和分泌砷(As)的影响.在10μmol·L-1三价砷[As(Ⅲ)]或五价砷[As(Ⅴ)]处理下,营养液B浓度没有显著影响水稻体内As(Ⅲ)、As(Ⅴ)和总As的含量、转移系数和根吸收效率.叶面施B使得水稻幼苗地上部的B含量显著增加15.8倍,使得As(Ⅴ)处理条件下的根部As含量和As根吸收效率分别显著降低20.9%和18.0%,As(Ⅲ)处理条件下的根部As含量和As根吸收效率分别降低12.6%和13.8%(P<0.05),而地上部As含量降低不显著(P>0.05).在As(Ⅴ)处理下,叶面施B使根部B含量显著降低达47.1%,而As(Ⅲ)处理下根部B含量无显著变化.As(Ⅴ)处理下的水稻根部B含量平均比As(Ⅲ)处理高85.3%(P<0.05).叶面施B后,As(Ⅴ)处理下水稻根部中总As含量和As(Ⅴ)含量均与根部B含量呈显著正相关(P<0.05).As(Ⅲ)预处理后水稻幼苗根系外泌的As总量比As(Ⅴ)预处理高105.2%.叶面施B使As(Ⅲ)预处理水稻的As外泌量增加14.0%~16.9%(P>0.05),对As(Ⅴ)预处理的水稻As外泌无影响.水稻根部有45.9%~70.7%的As可以在1周内被外排到生长介质中.结果表明,营养液供B浓度为As浓度的4倍时仍不能减少水稻幼苗对As的吸收累积,而叶面施B有助于减少水稻对As的吸收.B通道不是As(Ⅲ)进入水稻根系的主要途径;As(Ⅴ)在水稻中的迁移分配机制可能与B的迁移运输有关.

The impacts of boron（ B） root application and foliar spray on arsenic（ As） uptake,translocation,and efflux by/in rice seedlings（ Oryza sativa L.） were investigated in three hydroponic experiments. The addition of B to culture medium did not alter concentrations of arsenite（ As[Ⅲ]）,arsenate（ As[Ⅴ]）,and total As,nor did it alter transfer coefficients or uptake efficiency of As in rice seedlings under either As（ Ⅲ） or As（ Ⅴ） exposure. Foliar B supply increased shoot B concentrations 15. 8-fold,and decreased root As concentrations and As uptake efficiency by 20. 9% and 18. 0% under As（ Ⅴ） treatment,and by 12. 6% and 13. 8% under As（ Ⅲ） treatment,respectively,yet did not significantly decrease shoot As concentrations（ P〈0. 05）. Interestingly,foliar B supply reduced root B concentrations by up to 47. 1% under exposure to As（ Ⅴ） but not As（ Ⅲ）,and corresponding root B concentrations were 85. 3% higher in As（ Ⅴ） treatment than in As（ Ⅲ） treatment on average（ P〈0. 05）. Both total As and As（ Ⅴ） concentrations were positively related to B concentration in rice roots under As（ Ⅴ） treatment following foliar B supply（ P〈0. 05）. Rice seedlings extruded 105. 2% more As after As（ Ⅲ）-pretreatment than after As（ Ⅴ）-pretreatment. Foliar B supply increased the amount of As excreted by As（ Ⅲ）-pretreated rice root by 14. 0%-16. 9%（ P〈0. 05）,and had no effect on the As efflux of As（ Ⅴ）-pretreatment seedlings. A range of 45. 9%-70. 7% of root As was excreted to solution during one week. These results indicate that the root application of B at four times the concentration of As can slightly decrease As accumulation by rice,whereas foliar B supply is conducive to a decline in As acquisition by rice roots. It is likely that the B channel is at least not the main pathway for As（ Ⅲ）entering into rice roots,and the As（ Ⅴ） distribution mechanism in rice plants may be shared with that of B.