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Ion fluxes in plants related to acid growth


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Arif, Idam 1993 , 'Ion fluxes in plants related to acid growth', PhD thesis, University of Tasmania.

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The walls of plant cells are considered as a system containing weak acid
polymers where the interaction of ions on the polymers obeys Manning
condensation theory and Donnan theory (the Weak Acid Donnan Manning, or
WADM, model). When protons are extruded to the walls during the growth of
plant cells, the pH of the walls and therefore the ionic conditions of the walls
change with time. The Microelectrode Ion Flux Estimation (MthE) technique
was used to measure simultaneously proton and calcium fluxes during the
fusicoccin- or IAA-induced growth of 4-day-old split coleoptile segments of
Avena sativa L. and 6- to 7-day-old peeled epicotyl segments of Pisum sativurn
L. line 107.
The WADM model for fluxes is now extended to analyse the change of
the ionic condition in the walls, as well as the ion fluxes outside the walls,
during proton extrusion from the cells to the cell walls. The analysis shows that
when there is calcium condensation in the walls, proton extrusion from the cells
to the cell walls causes effluxes of both protons and calcium outside the walls.
However when the walls are considered as a classical Dorman system only,
which is a special case of the WADM model for fluxes, proton extrusion from
the cells to the cell walls would not cause any calcium release from the walls.
Fusicoccin induces immediate and transient proton and calcium effluxes
from oat segments preincubated 4.5 hours. The fusicoccin-induced proton
efflux saturates at 115 nmol. m-2 s-1 for 10-3 mole m-3 fusicoccin. The fusicoccininduced
calcium efflux saturates at about 120 nmol. m-2 s-1. On peas, the
fusicoccin-induced proton and calcium effluxes are smaller than on oats. When
the WADM model for fluxes is applied to the observed data of both oats and
peas, the calculated proton and calcium effluxes match well with the observed
effluxes. This indicates that proton-calcium exchange happens in the walls
during fusicoccin-induced proton extrusion across the plasmalemma and that the
observed calcium efflux is the evidence for the validity of the model. IAA at 10-2 mole m-3 induces proton efflux with a lag of about 13
minutes on oats. The proton efflux is smaller when the preincubation time is
shorter (15 or 5 nmol. m-2 s-1 for 4.5 or 1 hour preincubation). IAA also induces
biphasic calcium efflux but without a noticeable lag. The increase of the calcium
efflux induced by IAA is about 30 nmol. On pea segments preincubated
for 4.5 hours, IAA at 10-2 mole m-3 causes, without a noticeable lag, transient
proton and calcium effluxes, lasting about 15 minutes. The IAA-induced proton
and calcium effluxes are about 5 and 25 nmol. m-2 s-1 respectively. The
responses to IAA of oats and peas are also consistent with the proton-calcium
exchange in the walls during IAA-induced proton extrusion.
The WADM model does not specify the function of condensed calcium
in the walls that is released during proton extrusion from the cells to the cell
walls. In this present work, it is discussed that condensed calcium may serve a
role of stiffening the walls and therefore the proton-calcium exchange during
proton extrusion has some role, as well as other processes, in causing wall
Proton flux determination by measuring the electrochemical potential
gradient of protons can be in error when the measurements are carried out in
buffered solutions and the error depends on the pH of the solutions. Analysis is
done to quantify this error and take it into account.
Besides proton and calcium fluxes, potassium flux and membrane
potential were also measured. Fusicoccin induces immediate potassium efflux
and membrane hyperpolarization on both oats and peas where their magnitudes
depend on the fusicoccin concentration. On both plants, IAA does not cause any
significant effects on potassium flux. IAA induces transient membrane
hyperpolarization with a lag of about 7 minutes on oats. On peas, IAA causes
transient membrane hyperpolarization without a noticeable lag and it is followed
by membrane depolarization. Solid-state chloride rnicroelectrodes were specially
developed to measure the flux of chloride during IAA action on oats. IAA does
not cause any significant change on chloride flux. The effects of some
treatments, such as cutting, preincubation time and solution change are also

Item Type: Thesis - PhD
Authors/Creators:Arif, Idam
Keywords: Plants, Motion of fluids in, Indoleacetic acid
Copyright Holders: The Author
Copyright Information:

Copyright 1993 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1993. Includes bibliographical references (p. 207-218)

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