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Biomedical subjects

A Sievers

Publications and source records attributed to A Sievers.

At least 37 records · Page 2Linked to original sources
PubMed1996

Possible use of a 3-D clinostat to analyze plant growth processes under microgravity conditions.

A three-dimensional (3-D) clinostat equipped with two rotation axes placed at right angles was constructed, and various growth processes of higher plants grown on this clinostat were compared with ground controls, with plants grown on the conventional horizontal clinostat, and with those under real microgravity in space. On the 3-D clinostat, cress roots developed a normal root cap and the statocytes showed the typical polar organization except a random distribution of statoliths. The structural features of clinostatted statocytes were fundamentally similar to those observed under real microgravity. The graviresponse of cress roots grown on the 3-D clinostat was the same as the control roots. On the 3-D clinostat, shoots and roots exhibited a spontaneous curvature as well as an altered growth direction. Such an automorphogenesis was sometimes exaggerated when plants were subjected to the horizontal rotation, whereas the curvature was suppressed on the vertical rotation. These discrepancies in curvature between the 3-D clinostat and the conventional ones appear to be brought about by the centrifugal force produced. Thus, the 3-D clinostat was proven as a useful device to simulate microgravity.

Cell Wall↗
PubMed1996

Structure of cress root statocytes in microgravity (Bion-10 mission).

Experiments on primary roots of Lepidium sativum L. have been performed on board the Bion-10 satellite. The experimental set-up was extremely miniaturized and completely automatic. The results demonstrate the effectiveness of the instrumentation. The spatial orientation, growth, root cap differentiation and statocyte structure of roots grown under microgravity (MG) have been compared with control roots grown on the ground (GC) and in a 1G-reference centrifuge in space (RC). Root length and cap shape did not differ between MG and control samples. Under MG, the mean distance of the statoliths from the distal cell wall of the statocytes increased significantly, the mean distance of the mitochondria decreased and the nucleus did not change its position in comparison to both controls. The number and the shape of the amyloplasts (statoliths) were not influenced by the space flight factors, but their size as well as their relative area in the cell decreased. The number of starch grains per statolith as well as their size and shape changed under MG. In MG and RC samples the number of lipid bodies in the statocytes was higher and the relative area larger than in GC samples. The relative area occupied by vacuoles was greater in RC statocytes than in GC and MG statocytes. These results partly confirm and, in addition, extend the data from earlier experiments in space.

Microscopy, Electron↗
PubMed1996

Gravity sensing in tip-growing cells.

In addition to the statocytes of roots and shoots, a number of tip-growing cells also sense gravity, which influences the cells' growth and development. Since these tip-growing cells are highly suitable for observations in vivo, the movement and sedimentation of their statoliths can be studied in detail. Experimental manipulation by centrifugation, drug application, optical tweezers or microgravity can be monitored by light microscopy. The statoliths are localized in distinct cytoplasmic areas by interactions with actin filaments or microtubules, and their sedimentation seems to be narrowly confined. Since gravisensing and the graviresponse take place within the same cell, the gravitropic signal transduction chain is not complicated by signal transmission between sensing and responding cells. Studies on tip-growing cells have now enabled the formulation of models explaining positive and negative gravitropism.

Actins↗
PubMed1996

Differential proton secretion in the apical elongation zone caused by gravistimulation is induced by a signal from the root cap.

The extracellular proton activity along primary roots of Phleum pratense L. was measured using proton-selective microelectrodes. Removal of the root cap caused a reduction of the proton influx in the transitional region between the meristem and the apical elongation zone of the vertical root and inhibited the development of pH differences between the physically upper and lower flanks of the gravistimulated root. Disruption of the actin filament system of the root with 5 mmol m-3 cytochalasin D did not result in an altered proton flux and pH pattern compared with untreated vertical control roots, but inhibited the gravity-induced development of pH differences between the physically upper and lower root flanks as well as gravitropic curvature. These results provide evidence that pH changes following gravistimulation are induced by a signal transmitted from the root cap and that the actin filament system is involved in the gravity perception/transduction mechanism.

Cytochalasin D↗
PubMed1995

Clinical and epidemiologic features of infection with Mycobacterium genavense. Swiss HIV Cohort Study.

OBJECTIVES: To characterize clinical and epidemiologic features of infections with Mycobacterium genavense. DESIGN: Case series and case-control studies. Patients with M genavense were compared with two control groups: CD4 controls were matched on the basis of CD4 counts, and Mycobacterium avium-intracellulare complex controls had disseminated infection with M avium-intracellulare complex. RESULTS: Fifty-four patients with disseminated infections caused by M genavense were found, from Europe (37), North America (15), and Australia (two). All were infected with human immunodeficiency virus. The median CD4 count was 0.016 x 10(9)/L (16/mm3) (range, 0.001 to 0.082 x 10(9)/L). Eighty-seven percent had fever and weight loss, 44% had diarrhea, 43% had splenomegaly, 39% had hepatomegaly, and 72% had anemia. In Swiss university hospitals, M genavense was responsible for 12.8% of nontuberculous disseminated mycobacterial infections in patients with human immunodeficiency virus from 1990 to 1992. The median survival was 190 days after the first isolation of M genavense. Among the patients who had been treated with at least two antimycobacterial drugs for 1 month or more, median survival was 263 days (95% confidence interval, 144 to 382 days), compared with 81 days (95% confidence interval, 73 to 89 days) for those not treated (P = .0009). Survival in patients with M genavense was similar to the survival of M avium-intracellulare complex controls. However, patients with similar CD4 counts (CD4 controls) survived longer (median, 342 days; 95% confidence interval, 269 to 415 days; P < .0003). CONCLUSIONS: Infection with M genavense may be responsible for more than 10% of disseminated nontuberculous mycobacterial infections in patients with human immunodeficiency virus infection. Its clinical presentation and response to treatment are similar to those of infection with M avium-intracellulare complex.

AIDS-Related Opportunistic Infections↗
PubMed1995

Unequal distribution of osmiophilic particles in the epidermal periplasmic space of upper and lower flanks of gravi-responding rye coleoptiles.

In various studies, auxin (IAA)-induced coleoptile growth has been reported to be closely correlated with an increased occurrence of osmiophilic particles (OPs) at the inner surface of the outer, growth-limiting epidermal cell wall, indicating a possible function related to the mechanism of IAA-induced wall loosening. In order to test whether changes in cell elongation rates of upper and lower flanks (UFs, LFs, respectively) during graviresponsive growth are reflected in appropriate changes in the occurrence of OPs, rye (Secale cereale L.) coleoptiles either as segments or as part of intact seedlings, were gravitropically stimulated by positioning them horizontally for 2 h. Ultrastructural analyses within the UFs and LFs of the upward-bending coleoptiles revealed a distinct imbalance in the occurrence of OPs. The number of OPs per transverse epidermal cell section of the elongation-inhibited UF on average amounted to twice the number of OPs counted in epidermal cell sections of the faster-growing LF. As a hypothesis, the results lead us to suggest that OPs are involved in the mechanism of wall loosening and that temporary growth inhibition of epidermal cells of the UF during upward bending is mediated by inhibition of OP entry into the cell walls. Thereby, more OPs accumulate near the inner surface of the outer wall of epidermal cells of the UF compared with the LF.

Cell Wall↗
PubMed1995

Gravity induced changes in intracellular potentials in statocytes of cress roots.

Two glass microelectrodes were inserted from opposite sides of the root cap into statocytes of Lepidium sativum L. immersed in medium with or without cytochalasin D (CD). Intracellular potentials (Eis) of statocytes were measured with reference to an earthed electrode in the bathing solution. In the absence of CD, Ei values were -160 +/- 2 mV (n = 52) in vertical roots. During the recording of Eis, the roots were tilted from the vertical by 45 degrees so that in a tilted root one electrode was on the upper side and the other on the lower side; after 5 min the roots were returned to the vertical. At approximately 64 s after tilting (lasting 5-15 s) there was a transient lowering of Ei (more negative) by an average of 4.7 mV on both the upper and lower sides (n = 52). In some cases, this decrease in Ei was preceded by a transitory increase. Returning the roots to the vertical resulted in a response similar to that obtained by tilting. In roots treated with CD at a concentration of 3 (microM for 1 h, the initial Ei was -145 +/- 2 mV (n = 43), and the lowering of Ei on position change (tilting or returning) was smaller (2.0 mV) in some statocytes (n = 50) and higher (8.1 mV) in others (n = 14) compared to control roots (without and with DMSO). A higher concentration (10 microM) of CD and longer treatment (2 h) further reduced the decrease in Ei (1.1 mV) on position change (n = 26). The observed effects of CD support the hypothesis that statoliths in statocytes are anchored by actin filaments to the plasma membrane and/or to the cortical endoplasmic reticulum. Movement of statoliths during the first step of graviperception may lead to stress changes in actin filaments, affecting the transmembrane potential and also the Ei.

Brassicaceae↗
PubMed1994

Variation in velocity of cytoplasmic streaming and gravity effect in characean internodal cells measured by laser-Doppler-velocimetry.

Velocities of cytoplasmic streaming were measured in internodal cells of Nitella flexilis L. and Chara corallina Klein ex Willd. by laser-Doppler-velocimetry to investigate the possibility of non-statolith-based perception of gravity. This was recently proposed, based on a report of gravity-dependent polarity of cytoplasmic streaming. Our measurements revealed large spatial and temporal variation in streaming velocity within a cell, independent of the position of the cell with respect to the direction of gravity. In 58% of the horizontally positioned cells the velocities of acropetal and basipetal streaming, measured at opposite locations in the cell, differed significantly. In 45% of these, basipetal streaming was faster than acropetal streaming. In 60% of the vertically positioned cells however the difference was significant, downward streaming was faster in only 61% of these. When cell positions were changed from vertical to horizontal and vice versa the cells reacted variably. A significant difference between velocities in one direction, before and after the change, was observed in approx. 70% of the measurements, but the velocity was faster in the downward direction, as the second position, in only 70% of the significantly different. The ratio of basipetal to acropetal streaming velocities at opposite locations of a cell was quite variable within groups of cells with a particular orientation (horizontal, normal vertical, inverted vertical). On average, however, the ratio was close to 1.00 in the horizontal position and approx. 1.03 in the normal vertical position (basipetal streaming directed downwards), which indicates a small direct effect of gravity on streaming velocity. Individual cells, however, showed an increased, as well as a decreased, ratio when moved from the horizontal to the vertical position. No discernible effect of media (either Ca(2+)-buffered medium or 1.2% agar in distilled water) on the streaming velocities was observed. The above mentioned phenomenon of graviperception is not supported by our data.

Actins↗
PubMed1994

Differential flank growth.

With the mathematical basis for the precise analysis of developmental processes in plants, the patterns of growth in phototropic and gravitropic responses have become better understood. A detailed temporal and spatial quantification of a growth process is an important tool for evaluating hypotheses about the underlying physiological mechanisms. Studies of growth rates and curvature show that the original Cholodny-Went hypothesis cannot explain the complex growth patterns during tropic responses of shoots and roots. In addition, regulating factors other than the lateral redistribution of hormones must be taken into account. Electrophysiological studies on roots led to a modification of the Cholodny-Went hypothesis in that redistributions of bioelectrical activities are observed.

Electrophysiology↗
PubMed1994

The diagnostic use of the polymerase chain reaction for the detection of Mycobacterium tuberculosis.

Detection of Mycobacterium tuberculosis by microscopy is difficult in specimens containing fewer than 10(4) bacteria/mL and growth in culture can take up to 6 wks. In this study the Polymerase Chain Reaction (PCR) was investigated as a rapid diagnostic technique for the detection of M. tuberculosis. The presence of DNA polymerase inhibitors in sputum specimens poses a potentially serious problem as false negative results can occur. In this study polymerase inhibitors were detected by inclusion of an internal plasmid control in each test. DNA from specimens in which the internal control failed to amplify was purified with a DNA binding matrix before retesting by PCR. A total of 169 sputum specimens were examined and 4 were found to have inhibitors. The correlation between detection of M. tuberculosis by PCR with a combination of culture, Ziehl-Neelsen (ZN) staining and patient history was 97.6%. This study confirms that PCR offers a more sensitive and rapid alternative for the detection of M. tuberculosis to ZN staining and culture, with results being available within 24 hrs of a specimen being received in the laboratory.

Base Sequence↗
PubMed1994

Role of the microtubule cytoskeleton in gravisensing Chara rhizoids.

The arrangement of the microtubule cytoskeleton in tip-growing and gravisensing Chara rhizoids has been documented by immunofluorescence microscopy. Predominantly axially oriented undulating bundles of cortical microtubules were found in the basal zone of the rhizoids and colocalized with the microfilament bundles underlying the cytoplasmic streaming. Microtubules penetrate the subapical zone, forming a three-dimensional network that envelops the nucleus and organelles. Microtubules are present up to 5 to 10 microns basal from the apical cytoplasmic region containing the statoliths. No microtubules were found in the apical zone of the rhizoid which is the site of tip growth and gravitropism. Depolymerization of microtubules by application of oryzalin does not affect cytoplasmic streaming and gravitropic growth until the relatively stationary and polarly organized apical and subapical cytoplasm is converted into streaming cytoplasm. When the statoliths and the apical cytoplasm are included in the cytoplasmic streaming, tip growth and gravitropism are stopped. Oryzalin-induced disruption of the microtubule cytoskeleton also results in a rearrangement of the dense network of apical and subapical microfilaments into thicker bundles, whereas disruption of the microfilament cytoskeleton by cytochalasin D had no effect on the organization of the microtubule cytoskeleton. It is, therefore, concluded that the arrangement of microtubules is essential for the polar cytoplasmic zonation and the functionally polar organization of the actin cytoskeleton which is responsible for the motile processes in rhizoids. Microtubules are not involved in the primary events of gravitropism in Chara rhizoids.

Chlorophyta↗
PubMed1993

Statoliths pull on microfilaments: experiments under microgravity.

Previous videomicroscopy of Chara rhizoids during parabolic flights of rockets showed that the weightless statoliths moved basipetally. A hypothesis was offered that the removal of gravity force disturbed the initial balance between this force and the basipetally acting forces generated in a dynamic interaction of statoliths with microfilaments (MFs). The prediction of this hypothesis that the statoliths would not be displaced basipetally during the microgravity phase (MG-phase) after disorganizing the MFs was tested by videomicroscopy of a rhizoid treated with cytochalasin D (CD) immediately before the flight. The prediction was fully supported by the flight experiment. Additionally, by chemical fixation of many rhizoids at the end of the MG-phase it was shown that all rhizoids treated with CD before the flight had statoliths at the same location. i.e., sedimented an the apical cell wall, while all untreated rhizoids had statoliths considerably displaced basipetally from their normal position. Thus, a dynamical interaction involving shearing forces between MFs and statoliths appears highly probable.

Actin Cytoskeleton↗
PubMed1993

Centrifugation causes adaptation of microfilaments: studies on the transport of statoliths in gravity sensing Chara rhizoids.

The actin cytoskeleton is involved in the positioning of statoliths in tip growing Chara rhizoids. The balance between the acropetally acting gravity force and the basipetally acting net outcome of cytoskeletal force results in the dynamically stable position of the statoliths 10-30 micrometers above the cell tip. A change of the direction and/or the amount of one of these forces in a vertically growing rhizoid results in a dislocation of statoliths. Centrifugation was used as a tool to study the characteristics of the interaction between statoliths and microfilaments (MFs). Acropetal and basipetal accelerations up to 6.5 g were applied with the newly constructed slow-rotating-centrifuge-microscope (NIZEMI). Higher accelerations were applied by means of a conventional centrifuge, namely acropetally 10-200 g and basipetally 10-70 g. During acropetal accelerations (1.4-6g), statoliths were displaced to a new stable position nearer to the cell vertex (12-6.5 micrometers distance to the apical cell wall, respectively), but they did not sediment on the apical cell wall. The original position of the statoliths was reestablished within 30 s after centrifugation. Sedimentation of statoliths and reduction of the growth rates of the rhizoids were observed during acropetal accelerations higher than 50 g. When not only the amount but also the direction of the acceleration were changed in comparison to the natural condition, i.e., during basipetal accelerations (1.0-6.5 g), statoliths were displaced into the subapical zone (up to 90 micrometers distance to the apical cell wall); after 15-20 min the retransport of statoliths to the apex against the direction of acceleration started. Finally, the natural position in the tip was reestablished against the direction of continuous centrifugation. Retransport was observed during accelerations up to 70 g. Under the 1 g condition that followed the retransported statoliths showed an up to 5-fold increase in sedimentation time onto the lateral cell wall when placed horizontally. During basipetal centrifugations > or = 70 g all statoliths entered the basal vacuolar part of the rhizoid where they were cotransported in the streaming cytoplasm. It is concluded that the MF system is able to adapt to higher mass accelerations and that the MF system of the polarly growing rhizoid is polarly organized.

Acceleration↗
PubMed1993

DNA restriction fragment analysis to define an extended cluster of tuberculosis in homeless men and their associates.

A cluster of tuberculosis in men associated with shelters for the homeless in Melbourne, diagnosed between April 1984 and July 1991, was reviewed with respect to the genetic relatedness of the infecting strains. Relatedness was determined by examination of Southern blot analyses of restriction enzyme-digested genomic DNA, using probes for repetitive sequences. From the initial 24 cases selected, isolates were available from 19, and 18 were identical. A total of 571 other Australian and Solomon Islands strains were examined for relatedness to these strains. Nine additional case strains were found to be identical; all were from recent Melbourne residents and at least 7 were epidemiologically related to the original case cluster. The identification of a single infecting strain of Mycobacterium tuberculosis in these 27 cases suggests that reactivation disease in this group may not be as important as infection or reinfection from another case or cases.

Adult↗
PubMed1993

Mycobacteria in stool specimens: the nonvalue of smears for predicting culture results.

A previous recommendation suggests that stool be cultured for mycobacteria only if the smear is positive. We have correlated smear and culture results of 2,176 stool specimens submitted for mycobacterial culture. The sensitivity, specificity, and positive and negative predictive values for smears to predict culture results are 34, 99, 90, and 87%, respectively. We recommend that the stool smear not be used as a screening technique to decide which specimens from at-risk patients should be cultured because it lacks the necessary sensitivity.

AIDS-Related Opportunistic Infections↗
PubMed1993

Aspiration pneumonia in stroke.

Aspiration pneumonia developed within 1 year in 29 of 60 stroke patients referred for videofluoroscopic evaluation of poststroke dysphagia and drawn from a total population of 304 acute stroke patients. The presence of vallecular pooling, piriform pooling, or bolus penetration to or through the true vocal cords on videofluoroscopy did not correlate with the development of aspiration pneumonia. Kinematic pharyngeal transit times did show a significant correlation with the development of aspiration pneumonia (time of first movement, p = .038; time of arrival of bolus at valleculae, p = .0008; time of return of epiglottis to resting position, p = .0001). Those patients with total kinematic pharyngeal transit times (Em) of less than 2.00 sec were at little or no risk for aspiration pneumonia (0%), those with 2.01 to 5.00sec at moderate risk (38.5%), and those with more than 5.00sec were at marked risk (90%).

Cerebrovascular Disorders↗
PubMed1993

Characteristic and differential calcium signals from cell structures of the root cap detected by energy-filtering electron microscopy (EELS/ESI).

Characteristic calcium signals were analyzed in structures of three cell types of the root cap of cress: statocytes, meristematic cells and secretion cells. Twenty-four hour-old roots were fixed with glutaraldehyde (postfixed with osmiate/potassium bichromate) or with potassium permanganate. No visible precipitates were formed, but calcium signals typical for different cell structures could be detected by means of energy-filtering transmission electron microscopy (EELS/ESI). In statocytes, calcium signals were recorded from the plasma membrane, the membranes of the endoplasmic reticulum, the amyloplast envelope and the mitochondrial membranes. In contrast to the excitable statocytes, the two other, non-excitable cell types, meristematic and secretion cells, exhibited much lower intensities of the calcium signals recorded from the same membrane systems. The revealed characteristic calcium-related properties of the different membrane systems may be related to the special function of statocytes, namely transduction of the gravity stimulus. In all three cell types, additional calcium signals were recorded from cell structures with well known calcium contents, i.e., mitochondrial granules, starch grains and cell walls. For the first time, clear calcium signals were detected from the lipid bodies which are mobilized during the developmental stage of the examined roots. It is supposed that free fatty acids and lipases are the binding sites for calcium. The reliability of the applied method is especially proven by comparison of the electron microscopic images from lipid bodies according to the two different fixation methods. After glutaraldehyde fixation followed by osmiate/potassium bichromate postfixation, the lipid bodies were well fixed and appeared homogeneously grey with homogeneous calcium signals. However, due to potassium permanganate fixation the lipid bodies were only partly fixed; they had an electron-lucid core, from which the lipids are lost during the dehydration procedure, without calcium signals and an electron-dense border zone, which is a reaction product of potassium permanganate with triacylglycerols, with calcium signals.

Calcium↗