Transport, cytoplasmic accumulation and mechanism of action of the toxin eutypine in Vitis vinifera cells

Abstract

The mechanism of the toxic action of eutypine, 4-hydroxy-3-(3-methyl-3-butene-l-ynyl) benzaldehyde, a toxin produced by the fungus Eutypa lata , the agent of dying arm disease of the grapevine, was investigated with cell suspension cultures of Vitis vinifera cv. Gamay and l4 C-labelled eutypine. The study of the chemical characteristics of eutypine revealed that the toxin is a weak acid (pKa = 6.2), which also has a lipophilic character (water/octanol partition coefficient of 86). Eutypine was rapidly taken up by the cells and accumulated against a concentration gradient. Uptake showed no saturation at high eutypine concentration, and neither structural analogues of eutypine nor protein modifying reagents had an inhibitory effect on eutypine uptake. These data suggest a mechanism of passive diffusion for eutypine uptake. The eutypine accumulation observed in cells can be pardy explained by an ion trapping mechanism related to the ionization state of the toxin. It has been demonstrated that some eutypine molecules insert into cellular lipids, i.e. cell membranes. Such partition of eutypine in the cells might play a major role in the expression of its toxicity. Eutypine seems to affect the functioning of mitochondria by an uncoupling effect or by inhibiting succinate dehydrogenase activity. These results suggest that eutypine has the same properties as the uncoupling agents that act as mobile proton carriers. The reduction of the energetic charge following eutypine action could explain the symptoms observed in diseased plants.