RESPIRATION RATE IN PLANTS
229
above inhibitors than was the initial endogenous activity, except in the
case of iodoacetate. The existence of two or more respiratory systems in
Avena* is also indirectly indicated in certain starvation experiments (Bonner, 1948). In these experiments the respiration of fresh Avena sections was inhibited only 12% by 0.02 Μ malonate, whereas sections prepared from seedlings from which the endosperm had been removed 48
hours previously were inhibited 93% by the same concentration of
malonate. Although, in view of the fact that malonate is a competitive
inhibitor of succinic dehydrogenase, the difference of response to
malonate could be ascribed to the varying levels of succinate in starved
and unstarved tissue, it is equally possible that starvation (or aging)
brings about the demise of one respiratory system more effectively than
of another (see section on Wound Respiration). The very low level of
succinate in unstarved coleoptile tissue, which is equalled or exceeded
by the succinate concentration in starved tissue, favors the latter interpretation.
Whenever Avena sections must first be incubated for 24 hours before
a response to organic acids can be perceived, then malonate inhibition
of the respiration of fresh sections is minimal (Bonner, 1948); whereas
whenever fresh sections do respond to organic acids, malonate inhibition
is extensive (Bonner, 1949). The situation is analogous in chicory root
disks (Laties, 1954). In these the respiration of freshly cut disks is
resistant to malonate and unresponsive to additions of malate, whereas
the respiratory increment developed during incubation is inhibited by
malonate and restored by malate. Dinitrophenol added to fresh chicory
disks evokes at once a malonate-sensitive respiratory rise. The behavior
of chicory disks is apparently similar to that in a number of fleshy roots
and tubers. An ever-increasing body of evidence thus points to the
coexistence in a variety of tissues of two or more respiratory systems, at
least one of which is phosphorylative in nature and is frequently severely
curtailed in activity either by a paucity of phosphate acceptor, or by a
limited activity of the phosphate-transferring systems.
2. Regulation in Mitochondrial
Systems
The previously developed concept of the nature of rate regulation, as
indirectly deduced from numerous experiments with intact tissue, has
been amply reaffirmed by a great many investigations dealing with the
respiratory characteristics of isolated plant mitochondria. Hackett
(1955) has comprehensively reviewed the enzymological and physiological aspects of mitochondrial activity in plants.
Mitochondrial preparations from a great variety of plant sources have
been demonstrated to require the classical components of phosphory-
229
above inhibitors than was the initial endogenous activity, except in the
case of iodoacetate. The existence of two or more respiratory systems in
Avena* is also indirectly indicated in certain starvation experiments (Bonner, 1948). In these experiments the respiration of fresh Avena sections was inhibited only 12% by 0.02 Μ malonate, whereas sections prepared from seedlings from which the endosperm had been removed 48
hours previously were inhibited 93% by the same concentration of
malonate. Although, in view of the fact that malonate is a competitive
inhibitor of succinic dehydrogenase, the difference of response to
malonate could be ascribed to the varying levels of succinate in starved
and unstarved tissue, it is equally possible that starvation (or aging)
brings about the demise of one respiratory system more effectively than
of another (see section on Wound Respiration). The very low level of
succinate in unstarved coleoptile tissue, which is equalled or exceeded
by the succinate concentration in starved tissue, favors the latter interpretation.
Whenever Avena sections must first be incubated for 24 hours before
a response to organic acids can be perceived, then malonate inhibition
of the respiration of fresh sections is minimal (Bonner, 1948); whereas
whenever fresh sections do respond to organic acids, malonate inhibition
is extensive (Bonner, 1949). The situation is analogous in chicory root
disks (Laties, 1954). In these the respiration of freshly cut disks is
resistant to malonate and unresponsive to additions of malate, whereas
the respiratory increment developed during incubation is inhibited by
malonate and restored by malate. Dinitrophenol added to fresh chicory
disks evokes at once a malonate-sensitive respiratory rise. The behavior
of chicory disks is apparently similar to that in a number of fleshy roots
and tubers. An ever-increasing body of evidence thus points to the
coexistence in a variety of tissues of two or more respiratory systems, at
least one of which is phosphorylative in nature and is frequently severely
curtailed in activity either by a paucity of phosphate acceptor, or by a
limited activity of the phosphate-transferring systems.
2. Regulation in Mitochondrial
Systems
The previously developed concept of the nature of rate regulation, as
indirectly deduced from numerous experiments with intact tissue, has
been amply reaffirmed by a great many investigations dealing with the
respiratory characteristics of isolated plant mitochondria. Hackett
(1955) has comprehensively reviewed the enzymological and physiological aspects of mitochondrial activity in plants.
Mitochondrial preparations from a great variety of plant sources have
been demonstrated to require the classical components of phosphory-