TRANSPORT, CYTOPLASMIC ACCUMULATION AND MECHANISM OF ACTION OF THE TOXIN EUTYPINE IN VITIS-VINIFERA CELLS

The mechanism of the toxic action of eutypine, 4-hydroxy-3-(3-methyl-3 -butene-1-ynyl) benzaldehyde, a toxin produced by the fungus Eutypa la ta, the agent of dying arm disease of the grapevine, was investigated with cell suspension cultures of Vitis vinifera cv. Gamay and C-14-lab elled eutypine. The study of the chemical characteristics of eutypine revealed that the toxin is a weak acid (pKa = 6.2), which also has a l ipophilic character (water/octanol partition coefficient of 86). Eutyp ine was rapidly taken up by the cells and accumulated against a concen tration gradient. Uptake showed no saturation at high eutypine concent ration, and neither structural analogues of eutypine nor protein modif ying reagents had an inhibitory effect on eutypine uptake. These data suggest a mechanism of passive diffusion for eutypine uptake. The euty pine accumulation observed in cells can be partly explained by an ion trapping mechanism related to the ionization state of the toxin. It ha s been demonstrated that some eutypine molecules insert into cellular lipids, i.e. cell membranes. Such partition of eutypine in the cells m ight play a major role in the expression of its toxicity. Eutypine see ms to affect the functioning of mitochondria by an uncoupling effect o r by inhibiting succinate dehydrogenase activity. These results sugges t that eutypine has the same properties as the uncoupling agents that act as mobile proton carriers. The reduction of the energetic charge f ollowing eutypine action could explain the symptoms observed in diseas ed plants.