RESPIRATION RATE IN PLANTS
265
response to the auxin-induced water uptake, the further presentation
of salt produced no respiratory stimulation. It may be deduced that the
maximum respiratory rate of which a tissue is capable may be elicited
by the performance of work of whatever kind, whether salt accumulation,
water uptake, or various other endergonic processes.
The concept just presented has important implications with respect to
the relationship of the magnitude of the salt respiration to the quantity of
salt absorbed. According to this, the extent to which salt accumulation
stimulates respiration will depend upon the extent to which the respiration is limited by the level of phosphate acceptor within the cell. For
example, in Hanson and Bonner's experiments, the addition of salt elicited
a respiratory response in tissue untreated with auxin, whereas the same
tissue, when metabolically absorbing water, showed no respiratory response to neutral salt although the accumulation of salt could be demonstrated. Here, then, part of the phosphorylative metabolism linked to
water uptake may be thought to have been diverted to the process of
salt accumulation, with no net effect upon the respiration. Both water
uptake and salt accumulation were shown to be completely inhibited
by dinitrophenol, yet apart from their mutual dependence on the
energy metabolism of the cell these processes were demonstrably independent.
Recently, Handley and Overstreet (1955) have questioned whether
the respiratory stimulation evoked in barley roots by neutral salts is
dependent upon the absorption process per se. They emphasize, in
agreement with an earlier observation by Milthorpe and Robertson
(1948), that the salt respiration persists for a considerable time after
the transfer of roots to a salt-free environment. They demonstrate,
furthermore, that the magnitude of the salt respiration associated with
the absorption in unit time of a given amount of bromide ion is dependent upon the nature of the associated cation (see Steward and Preston,
1941). Middleton (1956), too, has cast doubt on the hypothesis that
the salt respiration is intimately related to salt absorption.
It is therefore urgent to distinguish between the direct effect of certain ions on the respiration, and the nonspecific stimulation of respiration reputedly brought about in general by the act of ion absorption.
Presumably, certain cations may stimulate respiration apart from the
absorption process (Handley and Overstreet, 1955; Robertson and
Wilkins, 1948). There is little doubt that potassium in particular affects
both growth (Cooil, 1952; Brown and Sutcliffe, 1950) and respiration
(Steward and Preston, 1941; Handley and Overstreet, 1955). As a consequence, the numerous experiments in which KCl has been employed
to demonstrate salt respiration are open to more than one interpretation.
265
response to the auxin-induced water uptake, the further presentation
of salt produced no respiratory stimulation. It may be deduced that the
maximum respiratory rate of which a tissue is capable may be elicited
by the performance of work of whatever kind, whether salt accumulation,
water uptake, or various other endergonic processes.
The concept just presented has important implications with respect to
the relationship of the magnitude of the salt respiration to the quantity of
salt absorbed. According to this, the extent to which salt accumulation
stimulates respiration will depend upon the extent to which the respiration is limited by the level of phosphate acceptor within the cell. For
example, in Hanson and Bonner's experiments, the addition of salt elicited
a respiratory response in tissue untreated with auxin, whereas the same
tissue, when metabolically absorbing water, showed no respiratory response to neutral salt although the accumulation of salt could be demonstrated. Here, then, part of the phosphorylative metabolism linked to
water uptake may be thought to have been diverted to the process of
salt accumulation, with no net effect upon the respiration. Both water
uptake and salt accumulation were shown to be completely inhibited
by dinitrophenol, yet apart from their mutual dependence on the
energy metabolism of the cell these processes were demonstrably independent.
Recently, Handley and Overstreet (1955) have questioned whether
the respiratory stimulation evoked in barley roots by neutral salts is
dependent upon the absorption process per se. They emphasize, in
agreement with an earlier observation by Milthorpe and Robertson
(1948), that the salt respiration persists for a considerable time after
the transfer of roots to a salt-free environment. They demonstrate,
furthermore, that the magnitude of the salt respiration associated with
the absorption in unit time of a given amount of bromide ion is dependent upon the nature of the associated cation (see Steward and Preston,
1941). Middleton (1956), too, has cast doubt on the hypothesis that
the salt respiration is intimately related to salt absorption.
It is therefore urgent to distinguish between the direct effect of certain ions on the respiration, and the nonspecific stimulation of respiration reputedly brought about in general by the act of ion absorption.
Presumably, certain cations may stimulate respiration apart from the
absorption process (Handley and Overstreet, 1955; Robertson and
Wilkins, 1948). There is little doubt that potassium in particular affects
both growth (Cooil, 1952; Brown and Sutcliffe, 1950) and respiration
(Steward and Preston, 1941; Handley and Overstreet, 1955). As a consequence, the numerous experiments in which KCl has been employed
to demonstrate salt respiration are open to more than one interpretation.