1987 Volume 53 Issue 2 Pages 210-226
Glyceollin, a phytoalexin produced by soybeans, partially and completely inhibited growth of young hyphae of Phytophthora capsici in liquid culture at 20 and 50μg/ml, respectively, within 4hr of incubation. Glyceollin at the same concentrations induced electrolyte leakage from hyphae immediately following the treatment and inhibited incorporation of an amino acid or nucleoside into an acid soluble “pool” fraction of hyphae. Oxygen uptake by hyphae was also inhibited by glyceollin but only after a lag period of several minutes. These results suggested that the possible primary mechanism of glyceollin action on the fungal hyphae was to interfere with the functions of plasma membrane. Ultrastructural study showed that glyceollin at the inhibitory concentrations induced characteristic alterations in the structure of fungal plasma membranes at early stages (30 to 60min) following treatment, while membrane systems of intracellular organelles remained relatively undamaged. Plasma membranes of the glyceollin-treated hyphae were flattened compared to those of the untreated hyphae and separated from cell walls at some places, and vesicle-like structures were observed between the plasma membranes and cell walls. Furthermore, plasma membranes appeared to be absent from some portions of the cell periphery. In contrast to glyceollin, some toxicants such as cycloheximide and 2, 4-dinitrophenol at the doses that completely inhibited hyphal growth did not induce significant distortion in the structure of plasma membranes, although the latter inhibitor induced electrolyte leakage as rapidly as did glyceollin. These results suggest that the observed distortion in plasma membrane structure is not a nonspecific general response of fungal hyphae due to growth inhibition caused by a variety of toxicants, but it appears to be a characteristic morphological symptom induced by glyceollin. Possible use of this morphological parameter in evaluating the role of glyceollin in soybean disease resistance is suggested.