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Biomedical subjects

H R Hohl

Publications and source records attributed to H R Hohl.

At least 19 recordsLinked to original sources
PubMed1990

Actin and tubulin cytoskeletons in germlings of the oomycete fungus Phytophthora infestans.

Actin and tubulins of Phytophthora infestans germlings were detected with monoclonal antibodies on Western blots of crude extracts separated by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The Mr of actin was approximately 43,000, whereas alpha- and beta-tubulin, which migrated as a single band, had an Mr of 53,000. Rhodamine-phalloin revealed peripheral patches of actin in ungerminated cysts. In young germlings, actin fibers were visible in the conversion zone between cyst and germ tube and as connections between actin patches and the incipient germ tube. Actin patches also occurred throughout the peripheral cytoplasm of longer germ tubes, except for the hyphal apex, which commonly contained actin fibers, but actin patches only exceptionally. Associations between patches and fibers were frequent. A monoclonal antibody specific for actin also stained fibers, but in addition it revealed diffuse staining of the apex and fine granular structures, indicative of the presence of G-actin or of single actin filaments. Cysts incubated with a monoclonal antibody against tubulin contained an array of cytoplasmic microtubules (MTs) that arise from a nucleus-associated center. Some of these MTs circumflexed the nucleus, whereas others extended to the cyst periphery. In germ tubes, axially oriented MT bundles extended from the nucleus-associated center into the proximal and distal cytoplasm. Their density was highest near the nucleus, and their number decreased towards the tip, with only a few remaining at the extreme apex. Bundles of MTs were continuous from the nucleus to the subapical region, reaching lengths of up to 20 microns. Ultrastructurally the bundles consisted of as many as 10 MTs. The architecture of the actin and tubulin cytoskeletons in germ tubes of P. infestans bolsters the hypothesis that they maintain the spatial organization of the hyphal protoplast and support or accomplish intrahyphal movements.

Actins↗
PubMed1978

Plasma membrane alterations as a result of heat activation in Dictyostelium spores.

At the end of heat activation the distribution of spore plasma membrane particles between the two fracture faces (PF and EF) is drastically changed. While in dormant spores the particle number ratio of PF/EF was about 1;1, it increased up to 9:1 in heat activated sproes, indicating a subtle change in plasma membrane properties. The permeability of spores increased within 30 min following heat activation as determined by efflux measurements of radioactively labelled spores. At the onset of swelling this efflux was accelerated. During germination the osmotically active material within the spores increased, part of which could be recovered from the supernatant. The combined experiments point to the plasma membrane as possible target site of heat activation in this system.

Cell Membrane↗
PubMed1976

Hyphal tip growth in Phytophthora. Gradient distribution and ultrahistochemistry of enzymes.

Germinating cysts and isolated walls from germinating cysts incorporated 14C-UDPG into wall material of which 22.5 and 15% respectively were insoluble in boiling 1 N HCl, indicating that part of the synthetase activity is located in the wall itself. A combination of Urografin and Ficoll density gradients was used to separate various intracellular fractions. A consistent separation of beta-glucanase and UDPG-transferase enriched fractions was achieved. The beta-glucanase fraction contained dictyosome vesicles and fragments along with some plasma membranes. The UDPG-transferase fraction was relatively rich in membranes resembling rough and smooth ER. The results suggest the two enzymes are transported to the wall by different intracellular routes, and two types of vesicle may be involved. Alkaline phosphatase, beta-glucosidase and acid phosphatase were found extracellularly and their distribution in density gradients determined. The results of histochemical staining for acid phosphatase, alkaline phosphatase and polysaccharide are described and compared with the biochemical data. beta-1,3-glucanase, found intra- and extracellularly, induced distorted growth of germ tubes and also removed most of the apical wall when added to the incubation medium. None of these responses were observed with cellulase. Determinations of the osmotic pressure of germinating cysts and incubation medium revealed that the turgor of germinating cysts amounts to about 1.8 at under the conditions used.

Acid Phosphatase↗
PubMed1975

Histochemical and biochemical evidence for the presence of microbodies in phytophthora palmivora.

Using the diaminobenzidine (DAB) reaction catalase activity could be demonstrated histochemically in cytoplasmic structures of Phytophthora palmivora bearing general ultrastructural features of microbodies. These socalled U-bodies sediment together with the catalase activity in Ficoll-Sorbitol-Sucrose gradients following prior purification by differential centrifugation.

3,3'-Diaminobenzidine↗
PubMed1975

Ultrastructural changes and a second mode of flagellar degeneration during ageing of Phytophthora palmivora sporangia.

Ageing of sporangia in Phytophthora palmivora is accompanied by a gradual breakdown of flagella, a transformation of the 'fingerprint' vacuoles, extensive vacuolization of the cytoplasm, accumulation of bundles of microtubules (mastigonemes)contained within cisternae of the rough endoplasmic reticulum, formation of a germination wall lining the inside of the sporangial wall and production of secondary sporangia. The mechanism of flagellar degeneration differs from that observed in directly germinating sporangia. In ageing sporangia and in sporangia induced to germinate directly with germ tubes, there is a close correlation between loss of competence for zoosporogenesis and breakdown of the flagella.

Endoplasmic Reticulum↗
PubMed1969

Ultrastructural changes during germination of Dictyostelium discoideum spores.

Spores of Dictyostelium discoideum undergo significant changes in fine structure during germination. The mitochondria progressively become less dense and lose their peripherally attached ribosomes, and the tubuli become more pronounced as germination proceeds. During this period, the three-layered spore wall breaks down in two stages: first, the outer and middle layers are ruptured as a unit, and, second, the inner wall is breached. Crystals and dark (lipid) bodies disappear shortly before or during emergence of the myxamoebae. Autophagic vacuoles are found in dormant spores and throughout the entire germination process. The addition of cycloheximide to germinating spores inhibited the loss of the crystals and dark (lipid) bodies. In addition, the drug inhibited the breakdown of the inner wall layer. Cycloheximide did not prevent the formation of the water expulsion vesicle or the apparent function of the autophagic vacuoles.

Cell Membrane↗