PROTONOPHORIC ACTIVITY OF EUTYPINE, A TOXIN FROM EUTYPA-LATA, IN PLANT-MITOCHONDRIA

Eutypine is a toxin produced by Eutypa lata, the causal agent of the d ying-arm disease of grapevine. We have previously shown that this toxi n behaves as a lipophylic weak acid (pK = 6.2) and induces drastic cha nges in both the respiration and energy balance of grapevine cells. In the present study, the molecular mode of action of eutypine at the mi tochondrial level, using methyl-eutypine, the unprotonable derivative of the toxin, has been investigated. The effects of these molecules on mitochondrial respiration and membrane potential were compared using isolated mitochondria hom grapevine cells in suspension cultures or po tato tuber mitochondria. Eutypine induces marked stimulation of oxygen consumption and a depolarizing effect, while methyl-eutypine exhibits a very small effect on both the rate of oxygen uptake and membrane po tential. For high eutypine concentrations, a mixed effect correspondin g to a direct inhibition of electron transport and uncoupling can be o bserved. In addition, below 200 mu M, eutypine displays a linear relat ionship between oxidation rate and membrane potential similar to that of the classical protonophore carbonyl cyanide-m-chlorophenylhydrazone (CCCP). However, unlike CCCP, eutypine induces a potential-dependent proton conductance that can be due to the potential-dependent migratio n of the dissociated form of the toxin across the membrane. It is conc luded that eutypine uncouples mitochondrial oxidative phosphorylation and decreases the ADP/O ratio in grapevine cells by increasing the pro ton leaks via a cyclic protonophore mechanism. The physiological aspec ts of these results are discussed. (C) 1996 Academic Press, Inc.