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Changing proton concentrations at the surfaces of gravistimulated Phleum roots (1993)

Zieschang, Hanna E. ; Köhler, Kurt ; Sievers, Andreas

Springer

Planta 190 (1993), S. 546-554

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ISSN: 1432-2048

Keywords: Graviresponse (root) ; pH gradient (graviresponse) ; pH pattern (extracellular) ; Phleum (graviresponse) ; Proton flux

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The pH patterns at the surfaces of both vertically growing roots of Phleum pratense L. and roots tilted by 45° were recorded using H +-sensitive microelectrodes. During vertical growth the root cap exhibited lower pH values than the meristematic zone. The highest pH values were found at the border between meristematic and elongation zones. In the apical part of the elongation zone the values strongly decreased basipetally. They reached a minimum value of pH 5.4–5.5 (medium pH of about 6.0) at a distance of 700 μm from the root tip. This region of strongest acidification usually coincided with that of the highest relative rates of elongation. The region of the first visible curvature following gravistimulation was positioned at 100–200 μm more apically. The pH values increased in the basal elongation zone towards the mature zone. The H+-flux pattern around a vertically growing Phleum root was characterized by high influxes in the meristematic zone and smaller effluxes in the elongation zone. Tilting the root by 45° induced changes in the pH values of the upper and lower sides of a Phleum root. At a distance of 300–500 μm from the root tip, the upper side was strongly acidified while the pH of the lower side slightly increased compared with the values during vertical orientation. pH differences of up to 0.9 pH units between the two sides of a root were detected. These differences decreased basipetally and could not be measured more distant than 700–800 μm from the tip. Compared with a vertically growing root, the H+-flux pattern of a Phleum root tilted by 45° exhibited effluxes on the entire upper organ flank while the pattern was scarcely altered on the lower side. The curvature-initiating zone in Phleum roots is positioned within that section of the root in which pH changes occur after tilting. The region of highest pH differences, however, is nearer to the apex of the root than the curvature-initiating zone. The pH changes began 8.2 min after a root had been tilted. The bending process started after 17.2 min, i.e. after double the time needed for differential acidification. After reorienting a root, which had just begun to bend, to its previous vertical position the inversion of the pH gradient could be measured within the same mean time of about 8 min. This is again significantly earlier than the beginning of the rebending process. The results indicate that, during the graviresponse, ionic movements occur much earlier than the changes in hormonal activities reported in the literature.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00224794

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Graviresponse and the localization of its initiating cells in roots of Phleum pratense L. (1991)

Zieschang, Hanna E. ; Sievers, Andreas

Springer

Planta 184 (1991), S. 468-477

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ISSN: 1432-2048

Keywords: Curvature (root) ; Graviresponse (root) ; Phleum (graviresponse) ; Root growth ; Target cells (graviresponse)

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract 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 1–11/2h 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 2–21/2 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 μm 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.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00197894

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Root movements: Towards an understanding through attempts to model the processes involved (1994)

Barlow, Peter W. ; Zieschang, Hanna E.

Springer

Plant and soil 165 (1994), S. 293-300

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ISSN: 1573-5036

Keywords: gravitropism ; living systems theory ; nutation ; Phleum pratense L. ; simulation ; Zea mays

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proponed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00008072

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