228
GEORGE G. LATIES
was equally effective, adenine and adenosine were without effect. As
might be anticipated from what has been said in the paragraph above,
additions of adenylate and dinitrophenol together did not produce
an additive effect on the respiration. The amount of stimulation was
the same whether one or both substances were present. Arginine also
stimulates respiration. The explanation proffered, in view of the prevalence of arginine phosphate in echinoderms (Mende and Chambers,
1953), is that it too may possibly play a role as a phosphate acceptor.
The effect of arginine as a respiratory stimulant in Avena sections is
matched by its corresponding effect upon their growth. Neither action is
exerted by any other amino acid.
In Bonner's experiments, indoleacetic acid stimulated respiration by
as much as 35%. It is of particular interest that in no case was the respiratory response to indoleacetic acid additive to that elicited by adenylate,
arginine, or dinitrophenol; nor was there any indication of synergism.
French and Beevers (1953) have made similar observations. The consensus is thus that indoleacetic acid, by allowing ATP, or some other
product of oxidative phosphorylation, to be utilized in growth, brings
about the regeneration of phosphate acceptors, and hence stimulates
respiration (see Newcomb, 1954). More will be said about this in a
subsequent section.
Commoner and Thimann (1941) early suggested that growth of Avena
coleoptiles was particularly related to a rather small fraction of the
total respiration, the fraction involving the metabolism of the dicarboxylic
organic acids. Respiratory stimulation and growth were shown to parallel
each other strikingly. Respiratory stimulation by the four-carbon dicarboxylic acids failed to occur in the absence of indoleacetic acid, and
in addition, indoleacetic acid failed to stimulate respiration in the absence of the organic acids. Iodoacetic acid abolished all growth at
5 X 10~
5 M, while inhibiting respiration only 10%. Commoner and
Thimann suggested that the fraction of the respiration inhibited by iodoacetate is that which is concerned with the oxidation of the four-carbon
acids, and which is brought into play by the presence of indoleacetic
acid.
The work of Bonner (1949) confirms and extends the suggestion of
Commoner and Thimann that at least two different respiratory systems
function in the Avena coleoptile. The respiratory increment elicited by
indoleacetic acid was shown by Bonner to be completely inhibited by
suitable concentrations of malonate, fluoride, iodoacetate, or fluoroacetate, whereas the initial respiration was inhibited only in part by each
of these inhibitors. Similarly the additional respiratory activity evoked
by dinitrophenol was shown to be more susceptible to inhibition by the
GEORGE G. LATIES
was equally effective, adenine and adenosine were without effect. As
might be anticipated from what has been said in the paragraph above,
additions of adenylate and dinitrophenol together did not produce
an additive effect on the respiration. The amount of stimulation was
the same whether one or both substances were present. Arginine also
stimulates respiration. The explanation proffered, in view of the prevalence of arginine phosphate in echinoderms (Mende and Chambers,
1953), is that it too may possibly play a role as a phosphate acceptor.
The effect of arginine as a respiratory stimulant in Avena sections is
matched by its corresponding effect upon their growth. Neither action is
exerted by any other amino acid.
In Bonner's experiments, indoleacetic acid stimulated respiration by
as much as 35%. It is of particular interest that in no case was the respiratory response to indoleacetic acid additive to that elicited by adenylate,
arginine, or dinitrophenol; nor was there any indication of synergism.
French and Beevers (1953) have made similar observations. The consensus is thus that indoleacetic acid, by allowing ATP, or some other
product of oxidative phosphorylation, to be utilized in growth, brings
about the regeneration of phosphate acceptors, and hence stimulates
respiration (see Newcomb, 1954). More will be said about this in a
subsequent section.
Commoner and Thimann (1941) early suggested that growth of Avena
coleoptiles was particularly related to a rather small fraction of the
total respiration, the fraction involving the metabolism of the dicarboxylic
organic acids. Respiratory stimulation and growth were shown to parallel
each other strikingly. Respiratory stimulation by the four-carbon dicarboxylic acids failed to occur in the absence of indoleacetic acid, and
in addition, indoleacetic acid failed to stimulate respiration in the absence of the organic acids. Iodoacetic acid abolished all growth at
5 X 10~
5 M, while inhibiting respiration only 10%. Commoner and
Thimann suggested that the fraction of the respiration inhibited by iodoacetate is that which is concerned with the oxidation of the four-carbon
acids, and which is brought into play by the presence of indoleacetic
acid.
The work of Bonner (1949) confirms and extends the suggestion of
Commoner and Thimann that at least two different respiratory systems
function in the Avena coleoptile. The respiratory increment elicited by
indoleacetic acid was shown by Bonner to be completely inhibited by
suitable concentrations of malonate, fluoride, iodoacetate, or fluoroacetate, whereas the initial respiration was inhibited only in part by each
of these inhibitors. Similarly the additional respiratory activity evoked
by dinitrophenol was shown to be more susceptible to inhibition by the