Pflugmacher S, Wiegand C, Beattie K A, Krause E, Steinberg C E, Codd G A
Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
Environ Toxicol Chem. 2001 Apr;20(4):846-52. doi: 10.1897/1551-5028(2001)020<0846:ueamoc>2.0.co;2.
The commonly occurring cyanobacterial toxin microcystin-LR (MC-LR) was rapidly taken up by the emergent reed plant Phragmites australis with clear distribution in the different cormus parts of the plant. Highest uptake was detected in the stem, followed by the rhizome. Enzyme extracts of the rhizome system, the stem, and the leaf revealed the presence of soluble glutathione S-transferases (sGST) measured with the model substrate 1-chloro-2,4-dinitrobenzene. A significant elevation of sGST activity in the rhizome and stem parts of P. australis was detected after a 24-h exposure to 0.5 microg/L MC-LR. Rhizome, stem, and leaf tissues were also able to conjugate several microcystin 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 detected in the pkat/mg range in the stem of P. australis. For MC-LR, a complete metabolism from the formation of a glutathione conjugate to the degradation 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-glutamylcysteine and a cysteine conjugate was demonstrated by comparison with chemically formed reference compounds and by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This is the first evidence for the uptake and metabolism of cyanobacterial toxins by an emergent aquatic macrophyte.
常见的蓝藻毒素微囊藻毒素-LR（MC-LR）能被挺水植物芦苇迅速吸收，并在植物的不同茎部有明显分布。在茎中检测到的吸收量最高，其次是根茎。根茎系统、茎和叶的酶提取物显示存在可溶谷胱甘肽S-转移酶（sGST），用模型底物1-氯-2,4-二硝基苯进行测定。在暴露于0.5微克/升的MC-LR 24小时后，检测到芦苇根茎和茎部的sGST活性显著升高。根茎、茎和叶组织也能够结合几种微囊藻毒素。然而，以相关蓝藻毒素节球藻毒素为底物时，未检测到化学或酶促结合。在芦苇茎中，毒素底物的谷胱甘肽S-转移酶活性最高在pkat/毫克范围内。对于MC-LR，报道了其在植物所有茎部从形成谷胱甘肽结合物到半胱氨酸结合物降解的完全代谢过程。通过与化学合成的参考化合物比较以及基质辅助激光解吸/电离飞行时间质谱法，证明了MC-LR-谷胱甘肽结合物逐步降解为γ-谷氨酰半胱氨酸和半胱氨酸结合物。这是挺水水生大型植物吸收和代谢蓝藻毒素的首个证据。
