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Ion fluxes from protoplasts and split segments of oat coleoptiles relating to the mode of action of growth substances

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Juswono, Unggul Pundjung (1997) Ion fluxes from protoplasts and split segments of oat coleoptiles relating to the mode of action of growth substances. Research Master thesis, University of Tasmania.

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Abstract

Indole 3 acetic acid (IAA) is the major plant growth substance that
causes normal plant elongation and the bending responses to light and gravity.
The mechanism by which IAA causes cell wall loosening to produce elongation
growth of plant stems is still in controversy. The most accepted hypothesis for
the mode of action of IAA is the acid growth hypothesis, which states that
auxin regulates wall loosening by causing a pH drop in the cell wall.
Many questions are left in relation to the involvement of ions in the
mechanism of wall loosening. The investigation of ion fluxes from plant cells
in the presence and absence of the cell walls may contribute to the explanation
of the involvement of these ions.
The study of proton fluxes on opposite sides of protoplasts shows an
asymmetric pattern and polarity of the flux. This leads to the conclusion that
the protoplasts must have polarity to allow pH regulation in the cytoplasm.
Estimation of the change in the cytoplasmic pH due to observed influx or
efflux of protons shows that the cytoplasmic buffering capacity alone is not
capable of neutralising the observed proton flux.
IAA and fusicoccin (FC) stimulate proton extrusion from protoplasts by
factors of about three and two times the control. It must be stimulation of active
proton transport that is caused by these substances. IAA also enhances the
calcium efflux which may be a way to maintain the cytoplasmic free calcium at
a low level. As with protoplasts, IAA and FC also enhance proton and calcium
effluxes from epidermal and parenchymal cells of split oat coleoptiles. Ion
fluxes from the epidermal cells are larger than those from the parenchymal
cells. It could be that the epidermal cells are more sensitive to the growth
substances. However, the effects of IAA and FC on ion fluxes from the
parenchymal cells are still observable.
There is no time delay in enhancement of proton and calcium fluxes
from protoplasts and segments by IAA and FC. This is in contrast with results
of other workers in observing the effect of IAA. However, enhancement of
proton and calcium fluxes by FC is larger than for IAA.
The calcium appearing in the external medium may come from a
compartment inside the cell and from the cell wall. The cell walls contribute
about 75 to 90 % of the total amount of the emerging calcium. The calcium
from the walls results from the exchange of the extruded protons from inside
the cell with the condensed calcium in the wall. This is in agreement with the
Weak Acid Donnan Manning (WADM) model for cell wall ion exchange.

Item Type: Thesis (Research Master)
Copyright Holders: The Author
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Additional Information:

Examines the mechanism by which indole 3 acetic acid (IAA) causes cell wall loosening to produce elongation growth of plant stems. Thesis (M.Sc.)--University of Tasmania, 1998. Includes bibliographical references. Examines the mechanism by which indole 3 acetic acid (IAA) causes cell wall loosening to produce elongation growth of plant stems

Date Deposited: 19 Dec 2014 02:36
Last Modified: 04 Dec 2016 22:10
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