Uptake, effects, and metabolism of cyanobacterial toxins in the emergent reed plant Phragmites australis (cav.) trin. ex steud

The, commonly occurring cyanobacterial toxin microcystin-LR (MC-LR) was rap idly taken up by the emergent reed plant Phragmites australis with clear di stribution in the different cormus parts of the plant. Highest uptake was d etected in the stem, followed by the rhizome. Enzyme extracts of the rhizom e system, the stem, and the leaf revealed the presence of soluble glutathio ne S-transferases (sGST) measured with the, model substrate 1-chloro-2,4-di nitrobenzene. A significant elevation of sGST activity in the rhizome and s tem parts of P. australis was detected after a 24-h exposure to 0.5 mug/L M C-LR. Rhizome, stem, and leaf tissues were also able to conjugate several m icrocystin toxins. However, no conjugation, either chemical nor enzymatic, was detected using the related cyanobacterial toxin nodularin as substrate. Highest glutathione S-transferase activity for the toxin substrates was de tected in the pkat/mg range in the stem of P. australis. For MC-LR, a compl ete metabolism from the formation of a glutathione conjugate to the degrada tion of a cysteine conjugate in all cormus parts of the plant is reported. The stepwise degradation of the MC-LR-glutathione conjugate to a gamma -glu tamylcysteine and a cysteine conjugate was demonstrated by comparison with chemically formed reference compounds and by matrix-assisted laser desorpti on/ionization time-of-flight mass spectrometry. This is the first evidence for the uptake and metabolism of cyanobacterial toxins by an emergent aquat ic macrophyte.