Barium accumulation in the metalliferous fern Athyrium yokoscense

The fern Athyrium yokoscense is a Cd hyperaccumulator, and can attain a high concentration of Cd in the fronds. The present study determined that Ba is also accumulated in the fronds. The contents of Ba, evaluated in 24 individuals, were 443 mg kg(-1) dw on average, with a maximum of 1020 mg kg(-1) dw. Another Cd hyperaccumulator, Arabidopsis halleri, which also colonized the same site as A. yokoscense, did not accumulate Ba, indicating that Cd hyperaccumulation does not necessarily imply the ability to accumulate Ba. We characterized Ba tolerance and accumulation in A. yokoscense by examining the effects of Ba on the growth and uptake of essential nutrients in A. yokoscense gametophytes. We used gametophytes of the fern Ceratopteris richardii as a control. When grown in the presence of 1 mM Ba, fresh weights of the A. yokoscense and C. richardii gametophytes decreased to 65 and 30 %, respectively, indicating that A. yokoscense was relatively tolerant to Ba. The C. richardii gametophytes showed marked decreases in K content in the presence of exogenous Ba, while the K content was little affected in the A. yokoscense gametophytes. These results imply that Ba accumulation and tolerance in A. yokoscense may be related to the K uptake mechanisms of this fern.