Respiration and Growth in Germinating Seeds
137
In other cases, as in irrepairable injury and the hormonal or genetic
suppression of certain reactions, the system cannot increase the limiting
factor and a given enzyme or compound may be limiting for a measureable
period of time. Here, growth may be correlated with the activities of
particular enzymes rather than with some index of overall activity.
In an earlier study p 9], we observed a direct proportionality between
rates of root elongation and ribosenucleic acid (RNA) contents in the roots
of Zea mays. In the six inbred lines studied, a striking parallel was found
between the RNA. content in the apical 3-mm portion and the growth rate
of the entire root. The relationships, specific for RNA, were not found for
deoxyribosenucleic acid (DNA) and were independent of the size of the
root. Similar correlations were later reported [8] for seedling roots of sorghum cultured at various temperatures, where growth and RNA contents
varied as a function of temperature and sampling period. CHANG and THOMPSON [3] recently observed a direct relationship between the growth rates of
the seedling root of corn and the RNA contents of the 3-mm root tips
where differences in growth and RNA were due to treatments with sodium
fluoride and to time of measurement. These quantitative relationships
between RNA contents and growth are similar, in many respects, to
those reported for the bacteria, Aerobacter aerogenes [7]. Because of the known
involvement of RNA metabolism in enzyme synthesis [2], we suspected
that, in germinating seeds, overall levels of metabolic activity might be
more important in determining seedling growth rates than the activity
of any single enzyme.
Energy is an essential prerequisite for growth and metabolic energy
is derived from respiration. Thus, when overall metabolic activity is related
to growth, a correlation between respiration and growth is to be expected.
Many such observations have been reported. Usually, however, respiratory
rates have been measured on actively growing tissues and do not indicate
whether differences in respiration are a cause or a result of differences in
growth. Our first concern was to determine whether differences in the
respiratory rates of germinating seeds could be shown to clearly precede
differences in growth. We found that differences in the respiration of
germinating seeds do, in fact, precede differences in seedling growth.
Seeds which germinate rapidly and produce vigorously growing seedlings
have higher respiratory rates and lower respiratory quotients than nonvigorous seeds. These differences may appear as early as 1 hr after the start
of imbibition. This is many hours before rupture of the seed coat by the
elongating radicle or other morphological evidence of growth. In the
remainder of this talk a number of experiments indicating relationships
between respiration and seedling growth in different kinds of seeds will be
described. From these experiments, we will attempt to deduce something
of the nature of the relationship between respiration and growth.
137
In other cases, as in irrepairable injury and the hormonal or genetic
suppression of certain reactions, the system cannot increase the limiting
factor and a given enzyme or compound may be limiting for a measureable
period of time. Here, growth may be correlated with the activities of
particular enzymes rather than with some index of overall activity.
In an earlier study p 9], we observed a direct proportionality between
rates of root elongation and ribosenucleic acid (RNA) contents in the roots
of Zea mays. In the six inbred lines studied, a striking parallel was found
between the RNA. content in the apical 3-mm portion and the growth rate
of the entire root. The relationships, specific for RNA, were not found for
deoxyribosenucleic acid (DNA) and were independent of the size of the
root. Similar correlations were later reported [8] for seedling roots of sorghum cultured at various temperatures, where growth and RNA contents
varied as a function of temperature and sampling period. CHANG and THOMPSON [3] recently observed a direct relationship between the growth rates of
the seedling root of corn and the RNA contents of the 3-mm root tips
where differences in growth and RNA were due to treatments with sodium
fluoride and to time of measurement. These quantitative relationships
between RNA contents and growth are similar, in many respects, to
those reported for the bacteria, Aerobacter aerogenes [7]. Because of the known
involvement of RNA metabolism in enzyme synthesis [2], we suspected
that, in germinating seeds, overall levels of metabolic activity might be
more important in determining seedling growth rates than the activity
of any single enzyme.
Energy is an essential prerequisite for growth and metabolic energy
is derived from respiration. Thus, when overall metabolic activity is related
to growth, a correlation between respiration and growth is to be expected.
Many such observations have been reported. Usually, however, respiratory
rates have been measured on actively growing tissues and do not indicate
whether differences in respiration are a cause or a result of differences in
growth. Our first concern was to determine whether differences in the
respiratory rates of germinating seeds could be shown to clearly precede
differences in growth. We found that differences in the respiration of
germinating seeds do, in fact, precede differences in seedling growth.
Seeds which germinate rapidly and produce vigorously growing seedlings
have higher respiratory rates and lower respiratory quotients than nonvigorous seeds. These differences may appear as early as 1 hr after the start
of imbibition. This is many hours before rupture of the seed coat by the
elongating radicle or other morphological evidence of growth. In the
remainder of this talk a number of experiments indicating relationships
between respiration and seedling growth in different kinds of seeds will be
described. From these experiments, we will attempt to deduce something
of the nature of the relationship between respiration and growth.