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D Volkmann

Publications and source records attributed to D Volkmann.

52 records · Page 3Linked to original sources
PubMed1994

Monoclonal antibody CRA against a fraction of actin from cress roots recognizes its antigen in different plant species.

The globular cytoskeletal protein G-actin was isolated from the crude extract of soluble proteins from cress (Lepidium sativum L.) roots. The crude extract was loaded onto a deoxyribonuclease (DNase) I-affinity chromatography column and subsequently eluted with EGTA and urea. The fraction eluted with 2 mM EGTA was characterized by molecular weight determination, binding to DNase I, isoelectric focusing, and immunoblotting. These samples clearly showed one main 43,000 dalton protein with a pI value between 5.5 and 5.7. This polypeptide is an isoform of actin. It was stained using commercially available monoclonal and polyclonal actin antibodies. We used the EGTA fraction as plant actin antigen to produce a monoclonal cress root actin antibody. Antibodies (CRA) showed specific labelings on Western immunoblots against a 43,000 dalton protein of the cress root crude extract. Under the fluorescence microscope CRA detected actin in fixed statenchyma cells of cress roots. This antibody also demonstrated intact bundles of actin filaments in unfixed internodal cells of Chara australis. On the basis of these results we concluded that we had obtained a new monoclonal antibody (CRA) against actin from cress roots. We also found a cress root actin-binding protein antibody (CRAB) showing a filament staining pattern in internodal cells of Chara.

Actins↗
PubMed1992

[Research under reduced gravity. Part II: experiments in variable gravitational fields].

Recently, the reduced gravitational field of space laboratories, rockets, or satellites in Earth orbits offers a gravitational field which is variable from 10(-4) g to 1 g by the use of centrifuges. Especially with plants, data concerning gravisensitivity are based on experiments with clinostats. First experiments in reduced gravitational fields, however, demonstrate the uncertainty of these results. Thus, the main task of gravitational biologists is to test the validity of results obtained with the aid of clinostats. On this basis it should be possible to find a common mechanism to explain the influence of gravity on organisms. Experiments under reduced gravity in sounding rockets provided new knowledge on the perception of the gravity stimulus in plant cells.

Biological Science Disciplines↗
PubMed1992

[Research under reduced gravity. Part I: bases of gravitational biology].

The orientation of organisms in space and their morphogenesis in relation to the gravitational field of the Earth are the main topics of research in the field of gravitational biology. For more than 100 years clinostats provided the only possibility to simulate physiological weightlessness. In contrast to animals, plants are characterized by intracellular gravireceptors. Nevertheless, there are some indications, e.g., the minimal energy of approx. 10(-18) J triggering a gravity-dependent response, for similar mechanisms of gravity perception. Stretch-activated ion channels might be the common structural basis.

Biological Science Disciplines↗
PubMed1991

Oriented movement of statoliths studied in a reduced gravitational field during parabolic flights of rockets.

During five rocket flights (TEXUS 18, 19, 21, 23 and 25), experiments were performed to investigate the behaviour of statoliths in rhizoids of the green alga Charo globularia Thuill. and in statocytes of cress (Lepidium sativum L.) roots, when the gravitational field changed to approx. l0(-4) g (i.e. microgravity) during the parabolic flight (lasting for 301-390 s) of the rockets. The position of statoliths was only slightly influenced by the conditions during launch, e.g. vibration, acceleration and rotation of the rocket. Within approx. 6 min of microgravity conditions the shape of the statolith complex in the rhizoids changed from a transversely oriented lens into a longitudinally oriented spindle. The center of the statolith complex moved approx. 14 micrometers and 3.6 micrometers in rhizoids and root statocytes, respectively, in the opposite direction to the originally acting gravity vector. The kinetics of statolith displacement in rhizoids demonstrate that the velocity was nearly constant under microgravity whereas it decreased remarkably after inversion of rhizoids on Earth. It can be concluded that on Earth the position of statoliths in both rhizoids and root statocytes depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by microfilaments.

Actin Cytoskeleton↗
PubMed1991

Automatic fixation facility for plant seedlings in the TEXUS Sounding Rocket Programme.

Automatic chemical fixation of plant seedlings within a 6 min period of reduced gravity (10(-4)g) was performed on three ballistic rocket flights provided by the German Sounding Rocket Programme TEXUS (Technologische Experimente unter Schwerelosigkeit = Technological Experiments in Microgravity). The described TEXUS experiment module consists of a standard experiment housing with batteries, cooling and heating systems, timer, and a data recording unit. Typically, 60 min before launch an experiment plug-in unit containing chambers with the plant material, the fixation system, and the temperature sensors is installed into the module which is already integrated in the payload section of the sounding rocket (late access). During the ballistic flight plant chambers are rapidly filled at pre-selected instants to preserve the cell structure of gravity sensing cells. After landing the plant material is processed for transmission electron microscopy. Up to now three experiments were successfully performed with cress roots (Lepidium sativum L.). Detailed improvements resulted in an automatic fixation facility which in principle can be used in unmanned missions.

Acceleration↗
PubMed1988

Microgravity and the organisms: results of the Spacelab mission D1.

During the Spacelab mission D1 different organisms were investigated at the unicellular and multicellular level respectively. Microgravity affects growth and development of the organisms in a different manner, some processes are enhanced, others are inhibited. On the other hand, there are a lot of parameters. e.g. circadian rhythm or cell and organ polarity, which seem to be exclusively under genetical control.

Adaptation, Physiological↗
PubMed1984

A freeze-fracture electron microscope study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller).

Two strains of Trichomonas vaginalis, JH162A , with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces ( PFs ) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad . In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of approximately 9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae , as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta -type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.

Animals↗
PubMed1983

A freeze-fracture study on the differentiation of Golgi and plasma membranes in plant cells.

Dictyosomes, Golgi vesicles, and plasma membranes were investigated after freeze-fracture in cells from growing root tips of cress (Lepidium sativum L.), that are distinguishable by different cellulose content of the cell wall, into (i) meristematic cells during early formation of the cell plate, (ii) statocytes of the root cap, and (iii) cortex cells of the differentiation zone. The results of this study show that the number of intramembrane particles (imps) is high in dictyosome cisternae, but low in membranes of budding or dictyosome-derived vesicles. Imps are disperse in the vesicle membranes of meristematic cells (i), but are often grouped into clusters in vesicle membranes of statocytes (ii), and of cortex cells (iii). For the number of particle aggregates in vesicle membranes, the following relation holds: (i) < (ii) < (iii). The number of particles on both fracture faces (PF and EF) of the plasma membrane differs widely between the cell types investigated. There are approximately 250, 1400, and 3100 imps microns-2 on the PF and 50, 500, and 300 on the EF of (i), (ii), and (iii), respectively. The structural complexity of the plasma membrane as judged by the degree of particle aggregations on the PF and the number of cellulose microfibrils in the cell wall show the same relationship: (i) < (ii) < (iii). Thus, the strong correlation between the distribution of imps in vesicle membranes, the structural complexity of the plasma membrane, and the content of cellulose microfibrils indicate that selection of imps during vesicle formation at dictyosome cisternae is an integral component of biogenesis and structural differentiation of plant plasma membranes.

Brassica↗
PubMed1977

Ultrastructure of gravity-perceiving cells in plant roots.

The root cap is the gravity-perceiving organ of plant roots. The central statenchyma consists of polarly organized statocytes which are characterized by sedimentable amyloplasts and by a striking distal endoplasmic reticulum (e.r. complex). During the normal downwards orientated growth of the root, the amyloplasts are sedimented onto the e.r. complex. Some observations indicate that the amyloplasts stress the e.r. complex by their sedimentation. The stress possibly influences the structural and functional state of the e.r. membranes. Therefore, graviperception is probably a function of differential stress on the e.r. complexes. The amyloplasts are partly or totally separated from the e.r. complex under experimental conditions such as deviations of the roots from the perpendicular between 30 and 180 degrees, rotation of the roots on the horizontal klinostat at 2 rev/min and at 55-120 rev/min, and placing the roots into an electric field at 2000-3000 V/cm. These are important facts for an understanding of the nature of graviperception. Spacelab experiments may help to verify the interpretation of results obtained in the experiments in simulated weightlessness.

Brassicaceae↗