Secretion systems and membrane‐associated structures in rust fungi after high pressure freezing and freeze‐fracturing

Excellent preservation and new structural details can be demonstrated in rust‐infected leaf tissue after high pressure freezing and freeze‐fracturing. A tubular‐vesicular complex was the most remarkable cytoplasmic structure observed in cells of the bean rust fungus Uromyces appendiculatus var. appendiculatus during its establishement in its host Phaseolus vulgaris. In fungal cells undergoing intensive synthesis of wall material, this membranous system extended throughout the cytoplasm; in addition, vesicles were accumulated adjacent to the plasma membrane. Here, membrane‐associated configurations were observed which seem to be involved in exo‐ and/or endocytotic processes. It is assumed that the tubular‐vesicular complex belongs to the endomembraneous system of the bean rust fungus and that it is involved in the synthesis and secretion of wall material.