V.
DETERMINING
FACTORS IN
CELL
GROWTH
211
Haesloop, 1958; Schroeder and Spector, 1957; Bradley and Crane, 1957
andSkjestad, 1957).
With these varied reports, the definition of gibberellins becomes
more obscure and difficult. Thus, when considering the vast array of
substances, natural and synthetic, now known to affect growth by cell
enlargement, the crucial problem is not what they are called but what
they do, how they do it, and where they occur in plants.
The most useful generalizations concern the origin of these stimuli.
Formation in the shoot apex (including young leaves) and basipetal
movement still seem to be cardinal features of an 'auxin'. If the gibberellins remained as products only of fungal metabolism, only affecting
growth in pathological situations, they would have but limited interest.
However, the recent evidence (MacMillan and Suter, 1958; Phinney
et al., 1957; West and Phinney, 1959) that gibberellin-like substances
have been isolated in small amounts not only from a large number of
runner bean seeds (Phaseolus multiflorus), but also from 9 genera of
flowering plants is highly suggestive. The work of Phinney et al. (1957)
and Lang, Sandoval and Bedri (1957) indicates that endosperm of a
cucurbitaceous seed (Echinocystis) is also a reservoir of substances which
satisfy the physiological criteria of gibberellins, for they act to promote
cell enlargement in the seedling and induce bolting and flowering in
Hyoscyamus and Samolus.
After the elapse of nearly three decades since the discovery of the first
natural auxin (now known to be indoleacetic acid) and after the study
of a very large number of synthetic auxins and herbicides, there is no
clear-cut definition of an auxin excepting that based on cell elongation
from which all other effects seem to stem, although lateral bud inhibition
and control of abscission are secondary criteria. In cell enlargement the
vacuole increases in size; therefore the auxin might intervene at any
point in metabolism which might increase the concentration of salts, or
solutes, in the vacuole and thus steepen the 'diffusion pressure deficit'
between external solution and vacuole. Auxin-induced water movement,
or reduced wall pressures, attributable to such effects have been variously
described. In fact, Bonner, Ordin and Cleland (1956) have attributed
to a reduction in the wall pressure, the increase in water uptake that
occurs. Moreover, Ketellaper (1953) and Kobayashi et al. (1956) claim
that there is no appreciable increase in osmotic pressure during the
elongation of Avena coleoptile cells. The possibility that auxin-induced
growth may be due to an increased permeability to water is not
acceptable for roots which are normally water saturated, according to
Burström (1957). While auxin effects on respiration have been conceived,
no auxin-induced metabolic reaction which would clearly affect the
prior accumulation of solutes in cells has emerged. During cell enlargeH
A.M. X
DETERMINING
FACTORS IN
CELL
GROWTH
211
Haesloop, 1958; Schroeder and Spector, 1957; Bradley and Crane, 1957
andSkjestad, 1957).
With these varied reports, the definition of gibberellins becomes
more obscure and difficult. Thus, when considering the vast array of
substances, natural and synthetic, now known to affect growth by cell
enlargement, the crucial problem is not what they are called but what
they do, how they do it, and where they occur in plants.
The most useful generalizations concern the origin of these stimuli.
Formation in the shoot apex (including young leaves) and basipetal
movement still seem to be cardinal features of an 'auxin'. If the gibberellins remained as products only of fungal metabolism, only affecting
growth in pathological situations, they would have but limited interest.
However, the recent evidence (MacMillan and Suter, 1958; Phinney
et al., 1957; West and Phinney, 1959) that gibberellin-like substances
have been isolated in small amounts not only from a large number of
runner bean seeds (Phaseolus multiflorus), but also from 9 genera of
flowering plants is highly suggestive. The work of Phinney et al. (1957)
and Lang, Sandoval and Bedri (1957) indicates that endosperm of a
cucurbitaceous seed (Echinocystis) is also a reservoir of substances which
satisfy the physiological criteria of gibberellins, for they act to promote
cell enlargement in the seedling and induce bolting and flowering in
Hyoscyamus and Samolus.
After the elapse of nearly three decades since the discovery of the first
natural auxin (now known to be indoleacetic acid) and after the study
of a very large number of synthetic auxins and herbicides, there is no
clear-cut definition of an auxin excepting that based on cell elongation
from which all other effects seem to stem, although lateral bud inhibition
and control of abscission are secondary criteria. In cell enlargement the
vacuole increases in size; therefore the auxin might intervene at any
point in metabolism which might increase the concentration of salts, or
solutes, in the vacuole and thus steepen the 'diffusion pressure deficit'
between external solution and vacuole. Auxin-induced water movement,
or reduced wall pressures, attributable to such effects have been variously
described. In fact, Bonner, Ordin and Cleland (1956) have attributed
to a reduction in the wall pressure, the increase in water uptake that
occurs. Moreover, Ketellaper (1953) and Kobayashi et al. (1956) claim
that there is no appreciable increase in osmotic pressure during the
elongation of Avena coleoptile cells. The possibility that auxin-induced
growth may be due to an increased permeability to water is not
acceptable for roots which are normally water saturated, according to
Burström (1957). While auxin effects on respiration have been conceived,
no auxin-induced metabolic reaction which would clearly affect the
prior accumulation of solutes in cells has emerged. During cell enlargeH
A.M. X