Hexagonal clustering of intramembrane particles in the plasmalemma of Ustilago avenae after fungicide treatment

The plasmalemma of sporidia of Ustilago avenae has been investigated by means of the freezeetching technique after treatment with the fungicide, triadimenol (5 μg ml^?1, 10 and 17 hr). The control samples are characterized in the exponential and stationary growth phases by homogeneous plasmatic fracture (PF) and extraplasmatic fracture (EF) faces with a random intramembrane particle (IMP) distribution. Treatment with triadimenol induces clusters of similar size IMPs in hexagonal arrangement. In between the flat clusters the plasmalemma is significantly deformed, showing hemispherical pits and protrusions on both membrane fracture halves. In the stationary growth phase no hexagonal clustering of the IMPs is observed under the described conditions.