Abstract:
Growth rates of etiolated Avena sativa coleoptiles in pH 7.0
buffered medium are stimulated in a synergistic manner by IAA and 320
~l/l carbon dioxide. The suggestion that carbon dioxide stimulated
growth involves dark fixation is supported by the ability of 1 mM
malate to replace carbon dioxide, with neither factor able to stimulate
growth in the presence of the other (Bown, Dymock and Aung, 1974).
The regulation of Avena coleoptile growth by ethylene has been
investigated in the light of this data and the well documented
antagonism between carbon dioxide and ethylene in the regulation of
developmental processes. The influence of various permutations of
ethylene, IAA, carbon dioxide and malate on the rates of growth,
l4c-bicarbonate incorporation, l4C-bicarbonate fixation, and malate
decarboxylation have been investigated.
In the presence of 320 ~l/l carbon dioxide, 10.8 ~l/l ethylene
inhibited growth both in the absence and presence of 20 ~M IAA with
inhibition times, of 8-10 and 12-13 minutes respectively. In contrast
ethylene inhibition of growth was not significant in the absence of
growth stimulation by CO2 or 1 mM malate, and the normal growth
increases in response to CO2 and malate were blocked by the simultaneous
application of ethylene. The rates of incorporation and dark
fixation of l4C-bicerbonate were not measurably. influenced by
ethylene, IAA or malate, either prior to or during the changes in
growth ,ates induced by these agents.
The data does not support the hypothesis that ethylene inhibition
of growth results from an inhibition of dark fixation, but suggests
that ethylene may inhibit a process which is subsequent to fixation.
