Effect of As (V) treatment on the root elongation and metal accumulation of Arabidopsis thaliana accessions Col-0 and Ws-2. (a) Seedlings with different accession backgrounds (Col-0 and Ws-2) were grown on quarter-strength MS medium for 4 d and then transferred to medium with 100, 200 and 300 μM As (V) and grown for an additional 2 d (Scale bar, 2 cm ). As tolerance was determined by relative root growth after treatment. (b) Root length of plants was measured after treatment with As. Root samples were collected from 3 independent experiments (each from a pool of 7 root samples). Data are mean±SD. *P ≤ 0.05 compared with Col-0 in each concentration of As. The difference in root elongation is significant according to Student's t test. (c) Accumulation of As (V) by Arabidopsis accessions Col-0 and Ws-2 was analyzed with ICP-AES. The 4-d-old seedlings with different accession backgrounds (Col-0 and Ws-2) were transferred to medium containing 100 and 200 μM As (V) for 3h and 48 h, then root tips were collected and measured. Data are mean±SD calculated from 3 biological replicates per treatment. *P ≤ 0.05 compared with Col-0.