While it is now recognised that transport within the endomembrane system may occur via membranous tubules, spatial regulation of this process is poorly understood. We have investigated the role of the cytoskeleton in regulating the motility and morphology of the motile vacuole system in hyphae of the fungus Pisolithus tinctorius by studying (1) the effects of anti-microtubule (oryzalin, nocodazole) and anti-actin drugs (cytochalasins, latrunculin) on vacuolar activity, monitored by fluorescence microscopy of living cells; and (2) the ultrastructural relationship of microtubules, actin microfilaments, and vacuoles in hyphae prepared by rapid-freezing and freeze-substitution. Anti-microtubule drugs reduced the tubular component of the vacuole system in a dose-dependent and reversible manner, the extent of which correlated strongly with the degree of disruption of the microtubule network (monitored by immunofluorescence microscopy). The highest doses of anti-microtubule drugs completely eliminated tubular vacuoles, and only spherical vacuoles were observed. In contrast, anti-actin drugs did not reduce the frequency of tubular vacuoles or the motility of these vacuoles, even though immunofluorescence microscopy confirmed perturbation of microfilament organisation. Electron microscopy showed that vacuoles were always accompanied by microtubules. Bundles of microtubules were found running in parallel along the length of tubular vacuoles and individual microtubules were often within one microtubule diameter of a vacuole membrane. Our results strongly support a role for microtubules, but not actin microfilaments, in the spatial regulation of vacuole motility and morphology in fungal hyphae.
Abstract. Flagellar scales were isolated from the flagellate green alga Scherffelia dubia. The flagellar scales consist mainly of acidic polysaccharides (70%) and glycoproteins (10%), and monosaccharide analyses show that the scales contain high amounts of unusual 2-keto-sugar acids. Approximately, 72 mol % of total carbohydrate is 3-deoxy-manno-2-octulosonic acid, 3-deoxy-5-O-methylmanno-2-octulosonic acid and 3-deoxy-lyxo-2-heptulosaric acid. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the presence of at least 18 different scale-associated proteins (SAPs), ranging in apparent molecular mass from 77 kDa to over 300 kDa. Lectin blot analyses performed in combination with glycosidase treatment, showed that SAPs contained N-glycans of the highmannose type and the hybrid type, as well as a complex type that was not immunologically related to higher-plant complex glycans. Most of the SAPs were present in two or possibly three high-molecular-weight complexes. In these complexes, individual polypeptides are cross-linked by disulfide bridges. A polyclonal antibody was raised against a SAP of 126kDa (SAP126), a glycoprotein present in a high-molecular-weight complex. The SAP126 antibody was used to localize the protein between scale layer and flagellar membrane. We suggest that these highmolecular-weight complexes link scales to the flagellar membrane.Key words: Flagellar membrane -Glycoprotein immunolocalization -Lectin -Scale -Scherffelia Dedicated to Professor Eberhard Schnepf on the occasion of his 65th birthday Abbreviations: AAA = Aleuria aurantia agglutinin; DSA = Datura stramonium agglutinin; DTT = dithiothreitol; GNA = Galanthus nivalis agglutinin; RCA = Ricinus communis agglutinin; SAP = Scale-associated protein; TBS = Tris-buffered saline Correspondence
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