Arsenic speciation and transport in Pteris vittata L. and the effects on phosphorus in the xylem sap

The mechanism of arsenic (As) transport in Pteris vittata L. (Chinese brake fern), the first known arsenic-hyperaccumulating plant, is important to understand how arsenic is detoxified in the fern. The effects of arsenic concentration and form on arsenic and phosphorus in xylem sap were investigated using hydroponics systems. Ferns were subjected to 0, 10 or 50 mg As l−1 as As(III), As(V), DMA or MMA. Xylem sap was collected and analyzed for arsenic concentration and speciation and inorganic phosphorus concentrations. When arsenic was supplied as an inorganic form, As(V), was the predominant form transported in the sap. This may be due to its resemblance to phosphorus. However, when arsenic was supplied in the methylated form, the fern transported the arsenic mainly in the form supplied. The presence of arsenic in the xylem sap did not significantly affect the inorganic phosphorus concentration in the sap. Regardless of the species supplied, arsenic may be transported in the form(s) which are least harmful to the plant. The fact that arsenic was stored mostly as As(III) in the pinnae of the frond but transported as As(V) or methylated forms indicates the majority of the arsenic reduction takes place in the frond pinnae.