SEPTAL PORE APPARATUS OF THE SMUT USTACYSTIS-WALDSTEINIAE

The septal pore apparatus in intercellular hyphae of Ustacystis waldst einiae was analyzed by serial-section electron microscopy using chemic ally fixed and high pressure frozen/freeze substituted samples. Septa have a central ''simple'' pore with rounded, non-swollen margins. Howe ver, the pore apparatus is a highly complex structure, differing signi ficantly from that found in ''simple''- and complex-septate basidiomyc etes. Three features are typical: 1) the pore canal is traversed by tw o symmetrically arranged bands, 2) a dome shaped membranous cap, intim ately attached to the plasma membrane, encloses the pore on both sides , and 3) a thin electron transparent layer and a layer of medium elect ron density cover the cytoplasmic side of the membranous cap. From our observations of septal pore morphology we suggest a general absence o f transport of organelles including ribosomes through the pore.