240
GEORGE G. LATIES
no question of fermentation in whole tubers in air. As has been mentioned, the R.Q. of whole tuber respiration is 1.0, and Barker and El
Saifi (1952) found no fermentation in potato tubers until the external
po 2
w a s
sharply reduced. The most reasonable way out of this paradox
is to suppose that it is not primarily diminished oxygen tension which
limits respiration in potato slices, but rather a volatile product of metabolism. The validity of this hypothesis will be further discussed below.
In the early experiments of Steward et al. (1932), measurements of
respiration were made in 12-hour periods after cutting, and although the
rate during the first 12 hours was somewhat more than 10 times the bulk
rate mentioned above, it is not precluded that this enormous rise above
the bulk rate actually developed during the interval of measurement.
However, Schade et al. (1948) and Sharpensteen (1953) have done careful manometric measurements of the respiration of potato slices immediately after cutting. From their data it is clear that the respiration of
thin slices of potato (0.5-0.75 mm. thick) is approximately 10 times
as great as that of equal masses of potato tissue in bulk, at the earliest
time at which a measurement can be made. Similarly, Turner (1940;
Turner and Hanly, 1949) has shown that the respiration of freshly cut
1 mm. thick slices of carrot is four to five times the bulk rate immediately
after cutting.
Steward et al. (1932), on the basis of their work and a review of the
earlier literature, expressed an opinion that wound respiration was entirely attributable to the exposure of removed tissue to higher oxygen tensions than those experienced within the intact root or tuber. A serious
question has been raised with respect to this interpretation as a consequence of the work of Burton (1950), Scott, and Denny (see Goddard
and Meeuse, 1950). Burton has indicated that at storage temperatures
of 5° C. to 15° C. the concentration of oxygen in solution in the tissue
fluids of potato is from 81 to 93% of that to be expected if the tissue were
in equilibrium with air. That is to say, the tissue fluid is in apparent
equilibrium with a gas mixture containing 17 to 19.5% of oxygen. At
temperatures of 25° G, the tissue is still 55% saturated, compared to
the calculated value for full equilibrium with air. Thus even at 25° C.
the oxygen concentration, in the gas phase within the potato is approximately 12%. These values agree well with the reports of Scott (in Goddard and Meeuse, 1950). The analysis of Burton is particularly useful,
since it includes not only the composition of the gas phase within the
potato, but the concentration of dissolved gas within the tissue fluids as
well. Surprisingly, perhaps, Burton has concluded that even at 25° C.
there is an apparent equilibrium between the oxygen dissolved in the
liquid phase and that in the gas phase within the tuber—the gas phase
GEORGE G. LATIES
no question of fermentation in whole tubers in air. As has been mentioned, the R.Q. of whole tuber respiration is 1.0, and Barker and El
Saifi (1952) found no fermentation in potato tubers until the external
po 2
w a s
sharply reduced. The most reasonable way out of this paradox
is to suppose that it is not primarily diminished oxygen tension which
limits respiration in potato slices, but rather a volatile product of metabolism. The validity of this hypothesis will be further discussed below.
In the early experiments of Steward et al. (1932), measurements of
respiration were made in 12-hour periods after cutting, and although the
rate during the first 12 hours was somewhat more than 10 times the bulk
rate mentioned above, it is not precluded that this enormous rise above
the bulk rate actually developed during the interval of measurement.
However, Schade et al. (1948) and Sharpensteen (1953) have done careful manometric measurements of the respiration of potato slices immediately after cutting. From their data it is clear that the respiration of
thin slices of potato (0.5-0.75 mm. thick) is approximately 10 times
as great as that of equal masses of potato tissue in bulk, at the earliest
time at which a measurement can be made. Similarly, Turner (1940;
Turner and Hanly, 1949) has shown that the respiration of freshly cut
1 mm. thick slices of carrot is four to five times the bulk rate immediately
after cutting.
Steward et al. (1932), on the basis of their work and a review of the
earlier literature, expressed an opinion that wound respiration was entirely attributable to the exposure of removed tissue to higher oxygen tensions than those experienced within the intact root or tuber. A serious
question has been raised with respect to this interpretation as a consequence of the work of Burton (1950), Scott, and Denny (see Goddard
and Meeuse, 1950). Burton has indicated that at storage temperatures
of 5° C. to 15° C. the concentration of oxygen in solution in the tissue
fluids of potato is from 81 to 93% of that to be expected if the tissue were
in equilibrium with air. That is to say, the tissue fluid is in apparent
equilibrium with a gas mixture containing 17 to 19.5% of oxygen. At
temperatures of 25° G, the tissue is still 55% saturated, compared to
the calculated value for full equilibrium with air. Thus even at 25° C.
the oxygen concentration, in the gas phase within the potato is approximately 12%. These values agree well with the reports of Scott (in Goddard and Meeuse, 1950). The analysis of Burton is particularly useful,
since it includes not only the composition of the gas phase within the
potato, but the concentration of dissolved gas within the tissue fluids as
well. Surprisingly, perhaps, Burton has concluded that even at 25° C.
there is an apparent equilibrium between the oxygen dissolved in the
liquid phase and that in the gas phase within the tuber—the gas phase