Iron Specifically Protects Corn Protoplasts from T-Toxin of Cochliobolus heterostrophus

Ferric ion reduced the damaging effects of T-toxin, a series of linear beta-polyketols produced by the pathogenic fungus Cochliobolus heterostrophus, on leaf mesophyll protoplasts from susceptible T-cytoplasm corn. Of nine metals tested, only ferric and ferrous ions had this effect. Despite the presence of 12 available oxygen atoms in each T-toxin molecule, there was no evidence for the formation of an aqueous Fe(2+)- or Fe(3+)-T-toxin complex. The protective effect of iron was eliminated by a molar excess of EDTA. Iron had no effect on the sensitivity of T-cytoplasm mitochondria to T-toxin, even at a 1000-fold molar excess, nor did it protect roots of T-cytoplasm corn seedlings from inhibition by T-toxin. The mechanism by which iron specifically protects protoplasts from T-toxin is not understood, but time lapse experiments suggest that iron acts on some intracellular site to modify T-toxin sensitivity and not on a transport system at the cell surface.