270
GEORGE G. LATIES
enates. Fritz and Beevers concluded that cytochrome oxidase is in fact
present in the roots and shoots of 12-day-old seedlings, although at a
considerably diminished concentration. Honda (1955) has come to an
entirely similar conclusion. It should be noted that James and Boulter
have confined their attention to the apical centimeter of the barley
root, while others have routinely utilized the entire root or a large part
of it. Futhermore, James and Boulter have suggested that the trend of
the ontogenetic changes in the terminal oxidase pattern which occurs in
barley root tips in the first week appears to reverse itself thereafter. It
is of particular interest that just as the metabolically linked water uptake
in potato slices may be completely inhibited by carbon monoxide at
concentrations which affect the respiration but little (Hackett et al.,
1953; Thimann et al., 1954), so salt absorption by barley roots can be
completely abolished by carbon monoxide under conditions where considerable respiratory activity persists (Ordin and Jacobson, 1955). It
is significant that inhibition by carbon monoxide in both instances is
completely light-reversible.
Much of what is deduced regarding the relation between the salt
absorption process and the activity of one or another terminal oxidase
is based upon inhibition experiments, in particular inhibition by carbon
monoxide. In this regard, before a final judgment is made consideration
must be given to one or more newly discovered cytochromes which may
function as terminal oxidases and which are resistant to both CO and
cyanide inhibition (Martin and Morton, 1955, 1956; W. D. Bonner and
Yocum, 1956). The interesting possibility that salt accumulation may be
linked to the operation of a terminal oxidase other than a cytochromelike oxidase is certainly not excluded. Russell (1954) has presented
evidence which relates the salt absorption process in barley root tips of
young seedlings to respiration mediated by ascorbic acid oxidase.
The foregoing discussion has stressed the direct role of oxidative phosphorylation in the process of salt accumulation. Lundegárdh (1953a,
1954) and Conway (1953) have postulated the operation of a redox
pump as a means of doing osmotic work, in which case energy coupling
would be effected in the direct sense described by Goddard (1946), and
oxidative phosphorylation, if it occurred at all, would have but an indirect effect on the accumulation process.
The redox pump, according to Lundegardh's suggestion, would work
in the following way. The iron of cytochrome oxidase, having a net
positive charge in the oxidized form, would combine with an anion from
the environment. Upon reduction of cytochrome oxidase (by reduced
cytochrome c), the anion would presumably leave the iron of the oxidase and proceed to the now positively charged iron of cytochrome c.
GEORGE G. LATIES
enates. Fritz and Beevers concluded that cytochrome oxidase is in fact
present in the roots and shoots of 12-day-old seedlings, although at a
considerably diminished concentration. Honda (1955) has come to an
entirely similar conclusion. It should be noted that James and Boulter
have confined their attention to the apical centimeter of the barley
root, while others have routinely utilized the entire root or a large part
of it. Futhermore, James and Boulter have suggested that the trend of
the ontogenetic changes in the terminal oxidase pattern which occurs in
barley root tips in the first week appears to reverse itself thereafter. It
is of particular interest that just as the metabolically linked water uptake
in potato slices may be completely inhibited by carbon monoxide at
concentrations which affect the respiration but little (Hackett et al.,
1953; Thimann et al., 1954), so salt absorption by barley roots can be
completely abolished by carbon monoxide under conditions where considerable respiratory activity persists (Ordin and Jacobson, 1955). It
is significant that inhibition by carbon monoxide in both instances is
completely light-reversible.
Much of what is deduced regarding the relation between the salt
absorption process and the activity of one or another terminal oxidase
is based upon inhibition experiments, in particular inhibition by carbon
monoxide. In this regard, before a final judgment is made consideration
must be given to one or more newly discovered cytochromes which may
function as terminal oxidases and which are resistant to both CO and
cyanide inhibition (Martin and Morton, 1955, 1956; W. D. Bonner and
Yocum, 1956). The interesting possibility that salt accumulation may be
linked to the operation of a terminal oxidase other than a cytochromelike oxidase is certainly not excluded. Russell (1954) has presented
evidence which relates the salt absorption process in barley root tips of
young seedlings to respiration mediated by ascorbic acid oxidase.
The foregoing discussion has stressed the direct role of oxidative phosphorylation in the process of salt accumulation. Lundegárdh (1953a,
1954) and Conway (1953) have postulated the operation of a redox
pump as a means of doing osmotic work, in which case energy coupling
would be effected in the direct sense described by Goddard (1946), and
oxidative phosphorylation, if it occurred at all, would have but an indirect effect on the accumulation process.
The redox pump, according to Lundegardh's suggestion, would work
in the following way. The iron of cytochrome oxidase, having a net
positive charge in the oxidized form, would combine with an anion from
the environment. Upon reduction of cytochrome oxidase (by reduced
cytochrome c), the anion would presumably leave the iron of the oxidase and proceed to the now positively charged iron of cytochrome c.