Phytotoxicity of orellanine, a mushroom toxin.

Orellanine, a toxic principle of Cortinarius orellanus Fr., efficiently inhibited the photosynthetic activity of duckweed, Lemna minor L., at a concentration of 0.4 mM. A lower concentration (0.06 mM) blocked the O2 production in isolated spinach class A chloroplasts. However, no effect was observed on thylakoids (class C chloroplasts), showing that orellanine does not interfere with the chloroplastic electron transfer chain and that orellanine does not act like methylviologen (paraquat) in green plants, as previously suggested. An electrochemical study of orellanine and related compounds showed that orellanine can neither be reduced by electrons derived from H2O nor from NADPH, as is methylviologen in plant and animal cells, respectively.