RESPIRATION RATE IN PLANTS
251
tically, as a consequence of the diminution of wall pressure following
enzymatic transformation of the cell wall, or whether water is actually
secreted into the cell by a pumping mechanism that derives its energy
from cellular respiration, the uptake is in either case metabolically induced. Thimann (1951) has discussed the various concepts of metabolic
water absorption at considerable length, while the broader aspects of the
water relations of cells and tissues have been reviewed by Kramer
(1955, 1956b, c). Mercer (1955) has compared the evidence in favor
of the osmotic pressure and pump theories of water movement. We wish
now to examine the relationship of water absorption to the respiratory
metabolism of the cell.
In accordance with the suggestion of Thimann (1951), growth will be
considered in its simplest aspect, namely, as an irreversible increase in
volume. Since under certain conditions irreversible increases in volume
can be achieved without any concomitant increase in cellular protein
or of cell wall components (see Thimann, 1952), the minimal and basic
requirement for growth remains the absorption of water. For this reason
the following discussion will treat alike those examples of directionally
oriented growth, such as the increase in length of Avena coleoptiles and
Pisum epicotyl sections, and growth involving a more or less nonoriented increase in cell size, such as is to be observed in disks of tuberous
organs. Neither the growth of Avena coleoptile sections nor that of
potato disks is accompanied by cell division, while the extent of cell
division occasionally described in Pisum sections (Thimann, 1951) is
of so trivial an order that it fails to account for the observed growth.
Although growth may occur without an increase of cellular protein or of
cell wall components, it is not meant to imply that such is usually the
case—especially with reference to the cell wall components. It is simply
pertinent to remember that the aspects of growth involving water absorption and synthesis of cellular materials are not inextricably linked.
The intimate relation of growth and respiratory metabolism has been
recognized since the early demonstration by Bonner (see Thimann,
1952) that growth of Avena coleoptile sections is inhibited by the respiratory poison, cyanide. The consequent deduction that the effect of cyanide is due primarily to inhibition of some one or more heavy metal
terminal oxidases of respiration has been borne out by the demonstration
that the growth process depends upon aerobiosis in Avena coleoptiles,
in Pisum stems (Hackett and Schneiderman, 1953), and in potato disks
(Hackett et al, 1953). The fact that growth cannot be maintained
anaerobically in tissues like potato, although it is capable of at least
some degree of anaerobic fermentation, suggests either that the energy
requirements of growth are not met by the fermentative process, or else
251
tically, as a consequence of the diminution of wall pressure following
enzymatic transformation of the cell wall, or whether water is actually
secreted into the cell by a pumping mechanism that derives its energy
from cellular respiration, the uptake is in either case metabolically induced. Thimann (1951) has discussed the various concepts of metabolic
water absorption at considerable length, while the broader aspects of the
water relations of cells and tissues have been reviewed by Kramer
(1955, 1956b, c). Mercer (1955) has compared the evidence in favor
of the osmotic pressure and pump theories of water movement. We wish
now to examine the relationship of water absorption to the respiratory
metabolism of the cell.
In accordance with the suggestion of Thimann (1951), growth will be
considered in its simplest aspect, namely, as an irreversible increase in
volume. Since under certain conditions irreversible increases in volume
can be achieved without any concomitant increase in cellular protein
or of cell wall components (see Thimann, 1952), the minimal and basic
requirement for growth remains the absorption of water. For this reason
the following discussion will treat alike those examples of directionally
oriented growth, such as the increase in length of Avena coleoptiles and
Pisum epicotyl sections, and growth involving a more or less nonoriented increase in cell size, such as is to be observed in disks of tuberous
organs. Neither the growth of Avena coleoptile sections nor that of
potato disks is accompanied by cell division, while the extent of cell
division occasionally described in Pisum sections (Thimann, 1951) is
of so trivial an order that it fails to account for the observed growth.
Although growth may occur without an increase of cellular protein or of
cell wall components, it is not meant to imply that such is usually the
case—especially with reference to the cell wall components. It is simply
pertinent to remember that the aspects of growth involving water absorption and synthesis of cellular materials are not inextricably linked.
The intimate relation of growth and respiratory metabolism has been
recognized since the early demonstration by Bonner (see Thimann,
1952) that growth of Avena coleoptile sections is inhibited by the respiratory poison, cyanide. The consequent deduction that the effect of cyanide is due primarily to inhibition of some one or more heavy metal
terminal oxidases of respiration has been borne out by the demonstration
that the growth process depends upon aerobiosis in Avena coleoptiles,
in Pisum stems (Hackett and Schneiderman, 1953), and in potato disks
(Hackett et al, 1953). The fact that growth cannot be maintained
anaerobically in tissues like potato, although it is capable of at least
some degree of anaerobic fermentation, suggests either that the energy
requirements of growth are not met by the fermentative process, or else