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Abstract

Measurements of electric potential differences between
points on the surface of etiolated Avena coleoptiles have been made
with a reliable, new technique. These show that an electric wave
moves down an intact coleoptile when its apex is illuminated, or down
a decapitated coleoptile when indole acetic acid (IAA) is applied to
its cut top.
It is postulated that auxin-requiring electric oscillators
in the coleoptile are the source of the wave and that they are synchron
ised by a sudden change in the stream of auxin moving down from the
top. It is shown that the electric wave provides a useful technique
for studying auxin transport under altered environmental or metabolic
conditions.
Carbon 14 tracer studies confirm the suggestion, arising
from the electric measurements, that IAA, moving from a source on the
top of a decapitated coleoptile, possesses a definite front moving at
constant speed. This speed depends on the ambient temperature.
Graphs have been obtained relating concentration of mobile and
immobilised
14C-IAA to both distance and time after application
of the IAA at several concentrations to the top of the decapitated
coleoptile. At the lowest concentrations of IAA applied the graphs
of concentration against distance are linear from near the top of the
coleoptile to the front of the IAA stream. Linearity exists in the region
of the f'ront even with concentrations above 0.4 mgm/litre applied.
Further experiments show that there is much 14c-IAA in the
coleoptile that is mobile but is not actually moving with the speed of
the front of the stream, so that the very concept of a "stream" to
describe IAA transport must be questioned.
Effects of IAA application for a short time are investigated,
as is the effect of tri-iodobenzoic acid on IAA transport.
Design, construction and operation of an inexpensive, reliable,
low-background G-M counting system, developed specially for the 14c
tracer experiments, is described.
A mathematical treatment of the results shows their inter
relationships, their dependence on the rate of uptake of IAA from the
source into the transport system and on the rate of immobilisation of
IAA in the coleoptile. Both the rate of uptake and the rate of immobil
isation increase with time. The treatment shows also how results of
other workers, on the export of IAA from the base of a coleoptile
section, can be predicted from the present work.
Theoretical models of auxin transport are discussed in the
light of the results and analysis. It is clear that diffusion cannot
play a major part in the normal transport of auxin in the coleoptile
and that each cell must pass on to the next nearly all the auxin that
it initially receives.
A survey of the literature on auxin transport up to 1965
is presented as an appendix.

Item Type:	Thesis - PhD
Authors/Creators:	Newman, Ian A
Keywords:	Electrophysiology of plants, Auxin metabolism
Copyright Holders:	The Author
Copyright Information:	Copyright 1968 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, 1968. Includes bibliography
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