Microcystin-LR (0.02 mu g/ml) in the hydroculture medium of Portulaca oleracea cv., became below the detection level (<0.0001 mu g/ml) by HPLC analysis after 7 days. The toxicity of microcystin estimated with protein phosphatase inhibition assay, however, remained at 37% of the initial level, indicating that microcystin-LR was transformed by P. oleracea cv. into unknown compound(s) of lower toxicity. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.