RESPIRATION RATE IN PLANTS
277
the increase in surface area rather than to the increase in volume (Pearson and Robertson, 1953). The respiratory rate per unit fresh weight of
disks is consistently higher than that of the whole fruit after the first
50 days from full blossom. However, the respiratory pattern with time
is the same whether respiratory measurements are made upon whole
fruit, or upon disks freshly cut from whole fruit. In each case the climacteric begins at approximately 190 days from full blossom and continues
for some 30 days or longer thereafter.
Pearson and Robertson (1953) have also described the changes in
concentration within the cell of protein, starch, soluble nitrogen, and
organic acids as a function of time from full blossom. A decided maximum with respect to starch concentration is perceived at approximately
150 days from full blossom. After that time the starch content drops
steadily until the starch has entirely disappeared in about 270 days. The
concentration of protein per cell increases up till 120 days, following
which the protein level remains almost constant until well beyond the
beginning of the climacteric, when a slight rise in protein content again
takes place. Whereas Pearson and Robertson studied the changes in
apple fruits left on the tree up until the time of chemical analysis or
respiratory measurement, Hulme (1948, 1954) carried out the same type
of studies on detached fruits kept in storage. Hulme consistently noted
a pronounced increase in protein synthesis which began either concomitantly with, or shortly after, the onset of the respiratory climacteric.
The approximate coincidence of the two events was observed whether
the climacteric occurred naturally in mature or immature fruit, or
whether the climacteric was induced by ethylene. Pearson and Robertson attribute the climacteric rise "to the increased demands of synthetic processes to maintain the protein content of the cells." Hulme
stresses the net synthesis of protein which takes place during the climacteric. The synthetic processes presumably utilize ATP and thereby lower
the ATP/ADP ratio, with the consequence that respiration is increased.
It is not clear why a greater demand should be placed upon the ATP
pool for the maintenance of protein than for its synthesis in the first
place. In this regard an estimation of the extent of protein degradation
during maturation unobscured by concomitant synthesis would be of
great interest.
Since at approximately 110 days from full blossom both starch and
protein are being synthesized (see Fig. 8, Pearson and Robertson, 1954),
at a time when the respiration rate is low (compared to the climacteric
period) and is rising but slowly, it seems unlikely that the abrupt and
extensive respiratory rise which characterizes the climacteric should be
the consequence of a drastic diminution in the ATP/ADP ratio en-
277
the increase in surface area rather than to the increase in volume (Pearson and Robertson, 1953). The respiratory rate per unit fresh weight of
disks is consistently higher than that of the whole fruit after the first
50 days from full blossom. However, the respiratory pattern with time
is the same whether respiratory measurements are made upon whole
fruit, or upon disks freshly cut from whole fruit. In each case the climacteric begins at approximately 190 days from full blossom and continues
for some 30 days or longer thereafter.
Pearson and Robertson (1953) have also described the changes in
concentration within the cell of protein, starch, soluble nitrogen, and
organic acids as a function of time from full blossom. A decided maximum with respect to starch concentration is perceived at approximately
150 days from full blossom. After that time the starch content drops
steadily until the starch has entirely disappeared in about 270 days. The
concentration of protein per cell increases up till 120 days, following
which the protein level remains almost constant until well beyond the
beginning of the climacteric, when a slight rise in protein content again
takes place. Whereas Pearson and Robertson studied the changes in
apple fruits left on the tree up until the time of chemical analysis or
respiratory measurement, Hulme (1948, 1954) carried out the same type
of studies on detached fruits kept in storage. Hulme consistently noted
a pronounced increase in protein synthesis which began either concomitantly with, or shortly after, the onset of the respiratory climacteric.
The approximate coincidence of the two events was observed whether
the climacteric occurred naturally in mature or immature fruit, or
whether the climacteric was induced by ethylene. Pearson and Robertson attribute the climacteric rise "to the increased demands of synthetic processes to maintain the protein content of the cells." Hulme
stresses the net synthesis of protein which takes place during the climacteric. The synthetic processes presumably utilize ATP and thereby lower
the ATP/ADP ratio, with the consequence that respiration is increased.
It is not clear why a greater demand should be placed upon the ATP
pool for the maintenance of protein than for its synthesis in the first
place. In this regard an estimation of the extent of protein degradation
during maturation unobscured by concomitant synthesis would be of
great interest.
Since at approximately 110 days from full blossom both starch and
protein are being synthesized (see Fig. 8, Pearson and Robertson, 1954),
at a time when the respiration rate is low (compared to the climacteric
period) and is rising but slowly, it seems unlikely that the abrupt and
extensive respiratory rise which characterizes the climacteric should be
the consequence of a drastic diminution in the ATP/ADP ratio en-