The Relation of Glucose Absorption to Respiration in Potato Slices

When plant tissue displays an indifference to one or another respiratory inhibitor, it is difficult to decide whether the respiration is truly resistant or whether the repression of an inhibitor-susceptible pathway elicits compensatory activity of a new or altered kind. Since resistance is in effect defined by the unimpaired utilization of 02 in the presence of the inhibitor, indirect means must be invoked to compare the respiratory behavior in the presence and absence of inhibitor in order to resolve the question. One way to estimate and characterize respiratory activity is to observe the utilization and disposition of radioactive substrate provided exogenously at levels sufficiently low so that hopefully the metabolite provided serves to label the endogenous metabolic pool without significantly altering the latter. It was early noted that when fresh and aged potato slices were compared with respect to the utilization of C14-labeled glucose, the evolution of C1402 differed very much more markedly than did gross glucose absorption (10, 19). Since a pronounced enhancement of salt absorbing capacity is known to accompany the respiratory rise which attends aging (12, 13), the question arose as to whether apparent differences in glucose utilization reflected distinctions related to glucose absorption. Consequently some attention was given the problem of glucose absorption per se. Absorption studies in turn served to answer in part the basic question regarding the meaning of inhibitor resistance. Potato slices, markedly cyanide-sensitive when freshly prepared, may become virtually cyanide-resistant in a day (7,14). By contrast, malonate-resistant fresh potato disks normally become increasingly malonate-sensitive with time (10, 19). However, when storage organ slices are aged in bicarbonate under 5 to 10 % CO2 in air, the respiration rises as normally but remains malonate-resistant (11). Thus a means is at hand to obtain metabolically active malonateresistant tissue. The experiments which follow examine the influence of malonate on both respiration and glucose absorption in malonate-sensitive and malonate-resistant potato slices, respectively. In addition, the effect of cyanide on the 2 processes is examined in cyanide-resistant tissue.