144
L. W. WOODSTOCK
The respiratory uncoupler, dinitrophenol, failed to reduce the degree
of correlation between respiratory rates and seedling growth when applied
to intact seeds, even at concentrations which were growth inhibiting. When
barley was ground to a dry powder, respiration per gram dry weight was
initially higher than for intact seeds, indicating that possible injury to
mitochondria by grinding was compensated by better aeration. In contrast
to intact seeds, however, respiration of meal from low-vigor seeds declined
with time. Respiratory rates of ground barley were significantly correlated
with the growth potential of the seeds (Fig. 3a). Dinitrophenol (DNP)
markedly reduced the degree of correlation between respiration and growth
when applied to ground barley (Fig. 3b), suggesting that its failure to do
so in intact seeds was due to its inability to reach active sites.
Significance oj relationships between respiration during imbibition and subsequent seedling growth: Metabolic processes during imbibition are evidently
related to the capacity of the seed for growth. The above data show that
differences in seedling growth are preceded by differences in respiration
during the initial 6 hrs of germination; i.e., either by changes in Q02 (seed),
changes in RQ, or both. What is the nature of this relationship? Four
alternative interpretations of the data may be suggested: (a) Respiratory
energy is limiting for the synthetic processes required for growth, as
suggested by PFEFFER [10], (b) the rates of the synthetic processes set the
pace, i.e., the more rapidly A TP is converted to ADP by the biosynthetic
reactions, the more rapid will be the respiratory rates, (c) the respiratory
and synthetic processes are mutually independent and are controlled by
some other mechanism, and Cd) the respiratory and synthetic processes
are mutually independent, but are equally susceptible to injurious treatments and tend to "degenerate" during storage at approximately the same
rates.
The fact that there was, in some cases, poor correspondence between
respiration and growth (e.g., certain corn lots had similar growth rates,
but differed in respiratory rates) might be taken as evidence in favor of
alternative (d) above. Lack of correspondence then would be ascribed to
differences in rates of degradation of the respiratory and growth mechanisms
in certain lots. If alternative (d) is indeed correct, then there is no direct
cause-and-effect relationship between respiration and growth and the
correlations might be regarded as "fortuitous". There are, however,
several difficulties with this alternative. Most important is the widespread
occurrence of the correlations between respiration and seedling growth.
It is not likely that similar correlations in such varied experimental systems
are due to chance. Furthermore, alternative (d) offers no explanation for
the negative correlation between RQ and growth. Perhaps the lack of
correspondence in some of the corn lots might be attributed to differences
in waxy coating or endosperm composition which would influence both
L. W. WOODSTOCK
The respiratory uncoupler, dinitrophenol, failed to reduce the degree
of correlation between respiratory rates and seedling growth when applied
to intact seeds, even at concentrations which were growth inhibiting. When
barley was ground to a dry powder, respiration per gram dry weight was
initially higher than for intact seeds, indicating that possible injury to
mitochondria by grinding was compensated by better aeration. In contrast
to intact seeds, however, respiration of meal from low-vigor seeds declined
with time. Respiratory rates of ground barley were significantly correlated
with the growth potential of the seeds (Fig. 3a). Dinitrophenol (DNP)
markedly reduced the degree of correlation between respiration and growth
when applied to ground barley (Fig. 3b), suggesting that its failure to do
so in intact seeds was due to its inability to reach active sites.
Significance oj relationships between respiration during imbibition and subsequent seedling growth: Metabolic processes during imbibition are evidently
related to the capacity of the seed for growth. The above data show that
differences in seedling growth are preceded by differences in respiration
during the initial 6 hrs of germination; i.e., either by changes in Q02 (seed),
changes in RQ, or both. What is the nature of this relationship? Four
alternative interpretations of the data may be suggested: (a) Respiratory
energy is limiting for the synthetic processes required for growth, as
suggested by PFEFFER [10], (b) the rates of the synthetic processes set the
pace, i.e., the more rapidly A TP is converted to ADP by the biosynthetic
reactions, the more rapid will be the respiratory rates, (c) the respiratory
and synthetic processes are mutually independent and are controlled by
some other mechanism, and Cd) the respiratory and synthetic processes
are mutually independent, but are equally susceptible to injurious treatments and tend to "degenerate" during storage at approximately the same
rates.
The fact that there was, in some cases, poor correspondence between
respiration and growth (e.g., certain corn lots had similar growth rates,
but differed in respiratory rates) might be taken as evidence in favor of
alternative (d) above. Lack of correspondence then would be ascribed to
differences in rates of degradation of the respiratory and growth mechanisms
in certain lots. If alternative (d) is indeed correct, then there is no direct
cause-and-effect relationship between respiration and growth and the
correlations might be regarded as "fortuitous". There are, however,
several difficulties with this alternative. Most important is the widespread
occurrence of the correlations between respiration and seedling growth.
It is not likely that similar correlations in such varied experimental systems
are due to chance. Furthermore, alternative (d) offers no explanation for
the negative correlation between RQ and growth. Perhaps the lack of
correspondence in some of the corn lots might be attributed to differences
in waxy coating or endosperm composition which would influence both