Respiration and Growth in Germinating Seeds
145
imbibition and rates of oxygen diffusion. Such differences might develop
during storage and would obscure relationships between tissue respiratory
capacity and growth.
The arguments against alternative (d) also apply to alternative (c).
Alternative (c), likewise, does not explain the inverse relationship so
frequently found between the respiratory quotients and seedling growth.
The wide occurrence of the correlations again would seem to argue against
this alternative. One would expect that under at least some circumstances
either respiration or growth would become "unstuck" from the control
mechanism which this alternative assumes. Possibly the most serious
objection to (c) is the effect of DNP on correlations between respiration
and growth in ground barley meal. The fact that a compound which
uncouples energy from respiration should reduce the degree of correlation
between respiration and growth might imply that energy plays some important role in the correlation.
The present data do not permit a definitive choice between alternatives
(a) and (b). Nevertheless, the negative correlations between RQ values
and seedling growth may be significant. The tricarboxylic acid cycle is
probably more easily injured than the glycolytic pathway or the hexosemonophosphate shunt, perhaps because it depends on the integrity of the
mitochondrial membranes [1]. If the growth effects of injurious treatments
were due to impaired mitochondrial activity, then accumulation of pyruvate
could result in enhanced decarboxylation reactions and higher RQ values.
Since mitochondria appear to be self-replicating organelles [5], injury to the
mitochondria or their progenitors at a given stage of development would
tend to be perpetuated. Such injury would show up in decreased respiratory
rates, higher RQ values, a lowered production of ATP, and decreased rates
of seedling growth. This would mean that seedling growth depends on the
general level of biosynthetic activity which, in turn, depends on A TP
generated by respiration, i. e., alternative (a). If alternative (a) is true, then
mitochondrial activit\' should be closely related to seedling growth rates.
Recent evidence for this comes from McDANIEL and SARKISSIAN [6], who
showed that heterosis in seedling vigor, measured as seedling growth, in
corn corresponds to a biochemical heterosis in mitochondria, measured as
oxygen uptake.
References
1. BONNER, W. D., JR.: In: J. BONNER and J. E. VARNER (Eds): Plant Biochemistry, p. 89. New York: Acad. Press 1965.
2. BRACHET, J.: Biochemical cytology. New York: Acad. Press 1957.
3. CHANG, C. W., and C. R. THOMPSON: Physiol. Plant 19, 911 (1966).
4. GORDON, S. A., and R. P. WEBER: Plant Physiol. 30, 200 (1955).
5. LUCK, O. J. L.: J. Cell BioI. 24, 641 (1965).
6. McDANIEL, R. Q., and 1. V. SARKISSIAN: Science 152, 1640 (1966).
10 3. Symp. Quant. Biol.
145
imbibition and rates of oxygen diffusion. Such differences might develop
during storage and would obscure relationships between tissue respiratory
capacity and growth.
The arguments against alternative (d) also apply to alternative (c).
Alternative (c), likewise, does not explain the inverse relationship so
frequently found between the respiratory quotients and seedling growth.
The wide occurrence of the correlations again would seem to argue against
this alternative. One would expect that under at least some circumstances
either respiration or growth would become "unstuck" from the control
mechanism which this alternative assumes. Possibly the most serious
objection to (c) is the effect of DNP on correlations between respiration
and growth in ground barley meal. The fact that a compound which
uncouples energy from respiration should reduce the degree of correlation
between respiration and growth might imply that energy plays some important role in the correlation.
The present data do not permit a definitive choice between alternatives
(a) and (b). Nevertheless, the negative correlations between RQ values
and seedling growth may be significant. The tricarboxylic acid cycle is
probably more easily injured than the glycolytic pathway or the hexosemonophosphate shunt, perhaps because it depends on the integrity of the
mitochondrial membranes [1]. If the growth effects of injurious treatments
were due to impaired mitochondrial activity, then accumulation of pyruvate
could result in enhanced decarboxylation reactions and higher RQ values.
Since mitochondria appear to be self-replicating organelles [5], injury to the
mitochondria or their progenitors at a given stage of development would
tend to be perpetuated. Such injury would show up in decreased respiratory
rates, higher RQ values, a lowered production of ATP, and decreased rates
of seedling growth. This would mean that seedling growth depends on the
general level of biosynthetic activity which, in turn, depends on A TP
generated by respiration, i. e., alternative (a). If alternative (a) is true, then
mitochondrial activit\' should be closely related to seedling growth rates.
Recent evidence for this comes from McDANIEL and SARKISSIAN [6], who
showed that heterosis in seedling vigor, measured as seedling growth, in
corn corresponds to a biochemical heterosis in mitochondria, measured as
oxygen uptake.
References
1. BONNER, W. D., JR.: In: J. BONNER and J. E. VARNER (Eds): Plant Biochemistry, p. 89. New York: Acad. Press 1965.
2. BRACHET, J.: Biochemical cytology. New York: Acad. Press 1957.
3. CHANG, C. W., and C. R. THOMPSON: Physiol. Plant 19, 911 (1966).
4. GORDON, S. A., and R. P. WEBER: Plant Physiol. 30, 200 (1955).
5. LUCK, O. J. L.: J. Cell BioI. 24, 641 (1965).
6. McDANIEL, R. Q., and 1. V. SARKISSIAN: Science 152, 1640 (1966).
10 3. Symp. Quant. Biol.