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Biomedical subjects

H E Zieschang

Publications and source records attributed to H E Zieschang.

5 recordsLinked to original sources
PubMed1997

Modelling of root growth and bending in two dimensions.

A special co-ordinate system is developed for modelling the gravitropic bending of plant roots. It is based on the Local Theory of Curves in differential geometry and describes, in one dimension, growth events that may actually occur in two, or even three, dimensions. With knowledge of the spatial distributions of relative elemental growth rates (RELELs) for the upper and lower flanks of a gravistimulated root, and also their temporal dependencies, it is possible to compute the development of curvature along the root and hence describe the time-course of gravitropic bending. In addition, the RELEL distributions give information about the velocity field and the basipetal displacement of points along the root's surface. According to the Fundamental Theorem of Local Curve Theory, the x and y co-ordinates of the root in its bending plane are then determined from the associated values of local curvature and local velocity. With the aid of this model, possible mathematical growth functions that correspond to biological mechanisms involved in differential growth can be tested. Hence, the model can help not only to distinguish the role of various physiological or biophysical parameters in the bending process, but also to validate hypotheses that make assumptions concerning their relative importance. However, since the model is constructed at the level of the organ and treats the root as a fluid continuum, none of the parameters relate to cellular behaviour; the parameters must instead necessarily apply to properties that impinge on the behaviour of the external boundary of the root.

Gravitropism↗
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↗
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↗
PubMed1991

Graviresponse and the localization of its initiating cells in roots of Phleum pratense L.

Roots of Phleum pratense L. were photographed during both vertical growth and gravitropic bending, and positions of anticlinal rhizodermal cell walls were digitized on the physically upper and lower flanks of the root in the curvature plane. By using B-splines, arc lengths of these positions, i.e. distances along the root surface, values of curvature, and relative elemental rates of elongation were estimated. The whole graviresponse can be divided into phases according to growth-rate values: (i) an increase of rates on the upper side of the root and a decrease on the lower side during the first 1-1 1/2 h after the root has been moved from the vertical to a horizontal position, (ii) a transient equality of the rates on both sides, (iii) 2-3 h after the beginning of graviresponse, the growth gradient is inverted, and (iv) finally, after about 4 h, the growth rates of both flanks are approximately equal again. Curvature begins 15-20 min after horizontal placement of the root. During the first 2 h of graviresponse, plots of curvature versus arc length show one maximum value. After 2-2 1/2 h, two maximum values can be observed, the apical one near the root tip always keeping the same distance from the tip, the other one drifting basipetally relative to the growing tip. By evaluating photographs of high magnification, a group of six rhizodermal cells on each side of the root was identified which are the first cells showing gravitropic bending. These cells are located at the beginning of the elongation zone, enclosing the region 480-680 micrometers from the root tip. These cells might be target cells for a signal which the statenchyma, the site of graviperception, sends to the reacting zone of gravicurvature.

Gravitropism↗