RESPIRATION RATE IN PLANTS
249
olism which affect the development of the induced respiration can be
gained from certain experiments by Beevers, Sharpensteen, and others.
Beevers (1953) noted a threefold increase in the respiratory rate of
freshly cut carrot disks upon exposing them to ΙΟ
5 Μ dinitrophenol at
pH 5.0. It is noteworthy that the concentration of dinitrophenol that
causes a maximal stimulation of respiration fails to affect the respiratory
quotient, whereas higher concentrations (10~
4 M) raise the R.Q. from
approximately 1.0 to 2.2. This experiment, taken together with the observations of Steward et ah (1940) and of Appleman and Smith (1936)
on the frequently inverse relationship of sugar concentration to respiratory rate in potato tissue, clearly indicates that the primary factor limiting respiration in many of the tissues under consideration, when in the
presence of plentiful oxygen, is not substrate level. This point is made
more emphatically in experiments by Sharpensteen (1953) in which the
immediate stimulation of respiration by dinitrophenol progressively diminished as the developed respiration rose. The increase of respiration
with time in potato was shown to have a high temperature coefficient.
The induced respiration failed to appear at 0 to 2° C, but developed in
the usual way, even after 36 hours, upon transfer to 25° C. Surprisingly,
however, if the disks were preincubated at 25° C. for 2 hours before
being placed in the cold, the induced respiration was fully evoked by
an additional 40 hours of incubation in the cold.
Because dinitrophenol is known to uncouple respiration and oxidative
phosphorylation, the experiments of Beevers and of Sharpensteen strongly
suggest that the primary limitation of respiration in the tissues under
study is imposed either by an endogenous limitation in the amount
of phosphate acceptors, or by a limitation imposed upon one or more
systems which either utilize high-energy phosphate, or transfer phosphate
from carrier substances such as ATP. The previously considered experiments pertaining to the stimulation of respiration by dinitrophenol are
not incompatible with the concept that induced respiration represents
merely a quantitative respiratory rise. The experiments of Laties (1954)
suggest, however, that such an interpretation is inadequate. Laties has
shown that the respiratory rise exhibited by slices of large-rooted chicory
(Cichorium
intybus) quantitatively resembles that which occurs in
potato. That is to say, the respiration is multiplied several fold upon
incubation of the tissue overnight in an aerated solution, at room temperature. However, whereas the initial respiration was shown to be
completely insensitive to malonate inhibition, the respiratory increment
was entirely repressed by malonate. The addition of dinitrophenol to
freshly cut disks raised the the respiratory rate at once to that of 24-hour
incubated tissue. The dinitrophenol-induced increment was also com-
249
olism which affect the development of the induced respiration can be
gained from certain experiments by Beevers, Sharpensteen, and others.
Beevers (1953) noted a threefold increase in the respiratory rate of
freshly cut carrot disks upon exposing them to ΙΟ
5 Μ dinitrophenol at
pH 5.0. It is noteworthy that the concentration of dinitrophenol that
causes a maximal stimulation of respiration fails to affect the respiratory
quotient, whereas higher concentrations (10~
4 M) raise the R.Q. from
approximately 1.0 to 2.2. This experiment, taken together with the observations of Steward et ah (1940) and of Appleman and Smith (1936)
on the frequently inverse relationship of sugar concentration to respiratory rate in potato tissue, clearly indicates that the primary factor limiting respiration in many of the tissues under consideration, when in the
presence of plentiful oxygen, is not substrate level. This point is made
more emphatically in experiments by Sharpensteen (1953) in which the
immediate stimulation of respiration by dinitrophenol progressively diminished as the developed respiration rose. The increase of respiration
with time in potato was shown to have a high temperature coefficient.
The induced respiration failed to appear at 0 to 2° C, but developed in
the usual way, even after 36 hours, upon transfer to 25° C. Surprisingly,
however, if the disks were preincubated at 25° C. for 2 hours before
being placed in the cold, the induced respiration was fully evoked by
an additional 40 hours of incubation in the cold.
Because dinitrophenol is known to uncouple respiration and oxidative
phosphorylation, the experiments of Beevers and of Sharpensteen strongly
suggest that the primary limitation of respiration in the tissues under
study is imposed either by an endogenous limitation in the amount
of phosphate acceptors, or by a limitation imposed upon one or more
systems which either utilize high-energy phosphate, or transfer phosphate
from carrier substances such as ATP. The previously considered experiments pertaining to the stimulation of respiration by dinitrophenol are
not incompatible with the concept that induced respiration represents
merely a quantitative respiratory rise. The experiments of Laties (1954)
suggest, however, that such an interpretation is inadequate. Laties has
shown that the respiratory rise exhibited by slices of large-rooted chicory
(Cichorium
intybus) quantitatively resembles that which occurs in
potato. That is to say, the respiration is multiplied several fold upon
incubation of the tissue overnight in an aerated solution, at room temperature. However, whereas the initial respiration was shown to be
completely insensitive to malonate inhibition, the respiratory increment
was entirely repressed by malonate. The addition of dinitrophenol to
freshly cut disks raised the the respiratory rate at once to that of 24-hour
incubated tissue. The dinitrophenol-induced increment was also com-