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Cellular specificity of the gravitropic motor response in rootsA number of features of the gravitropic response of roots are not readily accounted for by the classical Cholodny-Went theory. These include the observations that (i) in the later stages of the response the growth gradient is reversed with no evident reversal of the auxin gradient; (ii) a major component of the acceleration of growth along the upper side occurs in the distal elongation zone (DEZ), a group of cells located between the meristem and the main elongation, not within the central elongation zone; and (iii) the initiation of differential growth in the DEZ appears to be independent of the establishment of auxin asymmetry. Alternative candidates for mediation of differential growth in the DEZ include calcium ions and protons. Gravi-induced curvature is accompanied by polar movement of calcium toward the lower side of the maize root tip and the DEZ is shown to be particularly sensitive to growth inhibition by calcium. Also, gravistimulation of maize roots causes enhanced acid efflux from the upper side of the DEZ. Evidence for gravi-induced modification of ion movements in the root tip includes changes in intracellular potentials and current flow. It is clear that there is more than one motor region in the root with regard to gravitropic responses and there is evidence that the DEZ itself consists of more than one class of responding cells. In order to gain a more complete understanding of the mechanism of gravitropic curvature, the physiological properties of the sub-zones of the root apex need to be thoroughly characterized with regard to their sensitivity to hormones, calcium, acid pH and electrical perturbations.
Document ID
20040089434
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Evans, M. L.
(The Ohio State University Columbus 43210, United States)
Ishikawa, H.
Date Acquired
August 21, 2013
Publication Date
September 1, 1997
Publication Information
Publication: Planta
Volume: 203
Issue: Suppl 1
ISSN: 0032-0935
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: IBN9-416015
CONTRACT_GRANT: NAGW-4522
CONTRACT_GRANT: IBN9-421856
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Plant Biology
Non-NASA Center

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