RESPIRATION RATE IN PLANTS
261
merit of deuterium oxide (D 2 0) into and out of Avena coleoptile sections. They found the rate of water exchange between the cell and the
water solution to be 90 times the rate of net water movement. In summary, the energy utilized in growth appears to be consumed in metabolic
events which ultimately change the state of the cell wall, rather than in
the movement of water against an osmotic gradient.
If metabolic water absorption increases respiration by causing a regeneration of phosphate acceptor, then it should follow that indoleacetic
acid would prove to be without effect upon respiration when phosphorylation is uncoupled from respiration by means of dinitrophenol. Such is
the case. When dinitrophenol is added to Jerusalem artichoke disks the
respiration is not increased by indoleacetic acid, and conversely, when
indoleacetic-acid-induced respiration is allowed to develop, dinitrophenol
elicits little further effect (Bonner et al, 1953). The same observations
may be made with Avena coleoptiles (Bonner, 1949). As has been mentioned earlier, the respiratory increment evoked in Avena either by dinitrophenol or indoleacetic acid is qualitatively different from a large
part of the initial basal respiration, and appears to represent activity of
the tricarboxylic acid cycle (Bonner, 1949; Cooil, 1952). These observations support the view (Commoner and Thimann, 1941; Thimann and
W. D. Bonner, 1948, 1949; W. D. Bonner and Thimann, 1950) that
respiratory metabolism in which the organic acids are concerned is directly related to growth. Taken together, the above observations imply
that the tricarboxylic acid cycle represents the phosphorylative component of the respiration in Avena; that the activity of this component is
normally restricted by lack of phosphate acceptor; and that it is the tricarboxylic acid cycle metabolism which may be linked to cellular work.
There is at present insufficient evidence to extend the above concept to
other tissues, although some possibility of a comparable situation in tistues from tubers and tuberous roots has become apparent.
Disks from tubers or tuberous roots usually require a preliminary
aerobic incubation period in the presence of auxin before metabolic
water absorption begins. With potatoes the period is approximately two
days (Hackett and Thimann, 1952a, 1953); with Jerusalem artiehoke,
four hours (Hanson and Bonner, 1954; Hackett and Thimann, 1952b).
As has already been pointed out, there is a strong indication that the
metabolism of these disks changes qualitatively during a relatively short
incubation period. This qualitative change may well result in a type of
metabolism which does cellular work.
In chicory root, the entire phosphorylative type of respiration appears
to be suppressed until after somewhat less than a day's incubation
(Laties, 1954, and in press). There is some indication that the
261
merit of deuterium oxide (D 2 0) into and out of Avena coleoptile sections. They found the rate of water exchange between the cell and the
water solution to be 90 times the rate of net water movement. In summary, the energy utilized in growth appears to be consumed in metabolic
events which ultimately change the state of the cell wall, rather than in
the movement of water against an osmotic gradient.
If metabolic water absorption increases respiration by causing a regeneration of phosphate acceptor, then it should follow that indoleacetic
acid would prove to be without effect upon respiration when phosphorylation is uncoupled from respiration by means of dinitrophenol. Such is
the case. When dinitrophenol is added to Jerusalem artichoke disks the
respiration is not increased by indoleacetic acid, and conversely, when
indoleacetic-acid-induced respiration is allowed to develop, dinitrophenol
elicits little further effect (Bonner et al, 1953). The same observations
may be made with Avena coleoptiles (Bonner, 1949). As has been mentioned earlier, the respiratory increment evoked in Avena either by dinitrophenol or indoleacetic acid is qualitatively different from a large
part of the initial basal respiration, and appears to represent activity of
the tricarboxylic acid cycle (Bonner, 1949; Cooil, 1952). These observations support the view (Commoner and Thimann, 1941; Thimann and
W. D. Bonner, 1948, 1949; W. D. Bonner and Thimann, 1950) that
respiratory metabolism in which the organic acids are concerned is directly related to growth. Taken together, the above observations imply
that the tricarboxylic acid cycle represents the phosphorylative component of the respiration in Avena; that the activity of this component is
normally restricted by lack of phosphate acceptor; and that it is the tricarboxylic acid cycle metabolism which may be linked to cellular work.
There is at present insufficient evidence to extend the above concept to
other tissues, although some possibility of a comparable situation in tistues from tubers and tuberous roots has become apparent.
Disks from tubers or tuberous roots usually require a preliminary
aerobic incubation period in the presence of auxin before metabolic
water absorption begins. With potatoes the period is approximately two
days (Hackett and Thimann, 1952a, 1953); with Jerusalem artiehoke,
four hours (Hanson and Bonner, 1954; Hackett and Thimann, 1952b).
As has already been pointed out, there is a strong indication that the
metabolism of these disks changes qualitatively during a relatively short
incubation period. This qualitative change may well result in a type of
metabolism which does cellular work.
In chicory root, the entire phosphorylative type of respiration appears
to be suppressed until after somewhat less than a day's incubation
(Laties, 1954, and in press). There is some indication that the