266
GEORGE G. LATIES
The point has already been made that one way in which a variety of
cellular processes could be thought to stimulate respiration is by the
utilization of phosphate-bond energy, with the attendant regeneration of
phosphate acceptors. Dinitrophenol, in uncoupling oxidation from phosphorylation, could be expected to stimulate respiration at least as much,
and possibly more, than any physiological process which exerts its effect
upon respiration through the regeneration of phosphate acceptors.
Furthermore, dinitrophenol should, and does, prevent those physiological
acts which depend on oxidative phosphorylation. Therefore, one means
for distinguishing whether it is the presence of salt, or the absorption
act, which stimulates respiration would be to ascertain whether dinitrophenol precludes a response to salt. If a respiratory stimulation by
salt is perceived in the presence of that concentration of dinitrophenol
which normally educes the greatest respiratory stimulus, then the effect
of salt in such a case in all likelihood has nothing to do with the absorption process. By the same token, it would be unreasonable to expect the
salt absorption process to stimulate respiration in tissue where the respiration rate is not increased by dinitrophenol.
Experiments in which both salt and dinitrophenol have been presented
simultaneously have been carried out by Honda (1956) with barley
roots, and by Robertson et al. (1951) with carrot slices. Honda studied
the respiratory behavior of 5 mm. segments taken successively from the
root tip to 30 mm. behind the tip. In the apical segments there was considerable response to dinitrophenol and relatively little response to
KBr, whereas in the most distal segments studied there was little response
to dinitrophenol and considerable response to salt. The observations
argue against the stimulation of respiration by the absorption process
and favor the contention of Handley and Overstreet that ions may
stimulate the respiration directly.
When the respiration rate of barley roots was expressed as a function
of the distance from the tip, the rate was found to fall off sharply in
the first 10 mm. and to decrease little thereafter. However, when the
rate was expressed as a function of the concentration of cold, trichloroacetic acid (TCA)-insoluble phosphate in the segments, the relationship was linear. Thus both the quantity of cold TCA-insoluble phosphate (presumably a measure primarily of ribose nucleic acid) and the
respiration are highest in the tip and fall rapidly with distance from
the tip.
When Honda described the respiration rate in terms of the oxygen
consumed per unit of cold TCA-insoluble phosphate (the specific respiration rate) he found that the specific respiration rate rose precipitously
at 10 to 15 mm. from the tip, and approached no discernible limit. If,
GEORGE G. LATIES
The point has already been made that one way in which a variety of
cellular processes could be thought to stimulate respiration is by the
utilization of phosphate-bond energy, with the attendant regeneration of
phosphate acceptors. Dinitrophenol, in uncoupling oxidation from phosphorylation, could be expected to stimulate respiration at least as much,
and possibly more, than any physiological process which exerts its effect
upon respiration through the regeneration of phosphate acceptors.
Furthermore, dinitrophenol should, and does, prevent those physiological
acts which depend on oxidative phosphorylation. Therefore, one means
for distinguishing whether it is the presence of salt, or the absorption
act, which stimulates respiration would be to ascertain whether dinitrophenol precludes a response to salt. If a respiratory stimulation by
salt is perceived in the presence of that concentration of dinitrophenol
which normally educes the greatest respiratory stimulus, then the effect
of salt in such a case in all likelihood has nothing to do with the absorption process. By the same token, it would be unreasonable to expect the
salt absorption process to stimulate respiration in tissue where the respiration rate is not increased by dinitrophenol.
Experiments in which both salt and dinitrophenol have been presented
simultaneously have been carried out by Honda (1956) with barley
roots, and by Robertson et al. (1951) with carrot slices. Honda studied
the respiratory behavior of 5 mm. segments taken successively from the
root tip to 30 mm. behind the tip. In the apical segments there was considerable response to dinitrophenol and relatively little response to
KBr, whereas in the most distal segments studied there was little response
to dinitrophenol and considerable response to salt. The observations
argue against the stimulation of respiration by the absorption process
and favor the contention of Handley and Overstreet that ions may
stimulate the respiration directly.
When the respiration rate of barley roots was expressed as a function
of the distance from the tip, the rate was found to fall off sharply in
the first 10 mm. and to decrease little thereafter. However, when the
rate was expressed as a function of the concentration of cold, trichloroacetic acid (TCA)-insoluble phosphate in the segments, the relationship was linear. Thus both the quantity of cold TCA-insoluble phosphate (presumably a measure primarily of ribose nucleic acid) and the
respiration are highest in the tip and fall rapidly with distance from
the tip.
When Honda described the respiration rate in terms of the oxygen
consumed per unit of cold TCA-insoluble phosphate (the specific respiration rate) he found that the specific respiration rate rose precipitously
at 10 to 15 mm. from the tip, and approached no discernible limit. If,