286
GEORGE G. LATIES
(see Daly, 1954; Ducet and Rosenberg, 1953). Stenlid (1949a) suggested that the apparent loss of a cyanide-sensitve or azide-sensitive
respiration in older leaves simply reflects a less effective penetration into
the older leaves of the heavy metal oxidase inhibitors. In any event, the
occurrence of cytochrome oxidase in extracts from a great variety of
mature leaves, and from tissues of members of more than 20 separate
families of the higher plants, has been demonstrated by Webster (1952).
Webster (1954) has also, by means of the photoreversible inhibition of
the respiration with CO, demonstrated the actual participation of cytochrome oxidase in the respiration of the roots of 9 species of plants. The
association of certain enzymes of the tricarboxylic acid cycle with intact
mitochondria was demonstrated in etiolated bean cotyledons and etiolated
young bean leaves (Brummond and Burris, 1954; see also Davis, 1953,
for the young etiolated pea seedling), but was not demonstrable in
green cotyledons or in older leaves. Old leaves were found to contain
the components of the tricarboxylic acid cycle, but not all of them were
in association with the mitochondria. In all parts of the pea plant, however, including the mature green leaves, Smillie (1956) found all the
enzymes of the tricarboxylic acid cycle in the mitochondria. Furthermore, Ohmura (1955) has been able to show tricarboxylic cycle activity
and oxidative phosphorylation by particles isolated from mature spinach
leaves.
In general, it appears that cytochrome oxidase may frequently be present yet difficult to demonstrate in vivo. Such appears to be the case
in aged potato slices (Thimann et al, 1954), in the coleoptiles of 3- to
4-day-old Avena seedlings (Albaum and Eichel, 1943), in many leaves
(Webster, 1952) and in barley and wheat roots (James and Boulter,
1955; Honda, 1955). Although in those instances where cytochrome
oxidase cannot be demonstrated in vivo it is often difficult to decide
from respiration studies whether cytochrome oxidase is inoperative or
whether its activity is simply masked, it is significant that energydependent physiological activities in these cases respond to carbon
monoxide inhibition and to the light reversal thereof just like cytochrome
oxidase (Hackett et al, 1953; Hackett and Schneiderman, 1953; Ordin
and Jacobson, 1955; Lundegárdh, 1951a).
Unless it should develop that the TPN-mediated direct oxidation pathway observed in mature tissues (Gibbs and Beevers, 1955) is phosphorylative in vivo, and linked to the cytochrome oxidase system, the
preceding observation, taken together with the known occurrence in
carbon-monoxide-resistant tissues, of mitochondria which can carry out
the tricarboxylic acid cycle, appears to strengthen the contention that useful cellular energy is derived from the operation of the tricarboxylic
GEORGE G. LATIES
(see Daly, 1954; Ducet and Rosenberg, 1953). Stenlid (1949a) suggested that the apparent loss of a cyanide-sensitve or azide-sensitive
respiration in older leaves simply reflects a less effective penetration into
the older leaves of the heavy metal oxidase inhibitors. In any event, the
occurrence of cytochrome oxidase in extracts from a great variety of
mature leaves, and from tissues of members of more than 20 separate
families of the higher plants, has been demonstrated by Webster (1952).
Webster (1954) has also, by means of the photoreversible inhibition of
the respiration with CO, demonstrated the actual participation of cytochrome oxidase in the respiration of the roots of 9 species of plants. The
association of certain enzymes of the tricarboxylic acid cycle with intact
mitochondria was demonstrated in etiolated bean cotyledons and etiolated
young bean leaves (Brummond and Burris, 1954; see also Davis, 1953,
for the young etiolated pea seedling), but was not demonstrable in
green cotyledons or in older leaves. Old leaves were found to contain
the components of the tricarboxylic acid cycle, but not all of them were
in association with the mitochondria. In all parts of the pea plant, however, including the mature green leaves, Smillie (1956) found all the
enzymes of the tricarboxylic acid cycle in the mitochondria. Furthermore, Ohmura (1955) has been able to show tricarboxylic cycle activity
and oxidative phosphorylation by particles isolated from mature spinach
leaves.
In general, it appears that cytochrome oxidase may frequently be present yet difficult to demonstrate in vivo. Such appears to be the case
in aged potato slices (Thimann et al, 1954), in the coleoptiles of 3- to
4-day-old Avena seedlings (Albaum and Eichel, 1943), in many leaves
(Webster, 1952) and in barley and wheat roots (James and Boulter,
1955; Honda, 1955). Although in those instances where cytochrome
oxidase cannot be demonstrated in vivo it is often difficult to decide
from respiration studies whether cytochrome oxidase is inoperative or
whether its activity is simply masked, it is significant that energydependent physiological activities in these cases respond to carbon
monoxide inhibition and to the light reversal thereof just like cytochrome
oxidase (Hackett et al, 1953; Hackett and Schneiderman, 1953; Ordin
and Jacobson, 1955; Lundegárdh, 1951a).
Unless it should develop that the TPN-mediated direct oxidation pathway observed in mature tissues (Gibbs and Beevers, 1955) is phosphorylative in vivo, and linked to the cytochrome oxidase system, the
preceding observation, taken together with the known occurrence in
carbon-monoxide-resistant tissues, of mitochondria which can carry out
the tricarboxylic acid cycle, appears to strengthen the contention that useful cellular energy is derived from the operation of the tricarboxylic