Controlling Influence of Thickness on Development & Type of Respiratory Activity in Potato Slices

Abstract

The respiration of potato slices kept in air increases 4- to 5-fold in the course of a day, and changes qualitatively as well. It has been demonstrated that it is the development of the respiratory increment which is controlled by tissue thickness, and not respiratory activity per se. The classical explanations for the inverse relationship between thickness and respiration rate, namely oxygen availability and wounding, have been ruled out, and the hypothesis is presented that regulation of respiratory development represents a negative feedback process in which control is effected by a volatile respiratory product. It is argued that the product in question cannot be formed in proportion to the total respiration, and hence is not CO2. It is suggested that the respiration which develops with aging is in large measure qualitatively distinct from the basal respiration, and gives rise to a respiratory product which in turn eventually represses further development. Although in all but the thinnest disks the rise in respiration is most pronounced at the disk surface, it is a salient feature of respiratory ontogeny in slices of moderate thickness that the respiratory rise proceeds for some time throughout the tissue mass. As aging progresses, development is repressed in deeper seated tissue, the rise continuing in superficial cell layers and persisting longest at the surface. Both the depth of the poorly defined zone of markedly elevated activity, and the magnitude of respiration therein, are considered to vary inversely with disk thickness. It is suggested, in view of the profound physiological changes attending the respiratory transformations described herein, and in recognition of the fact that the latter are governed by distances of but several cell diameters, that the proposed mechanism whereby respiratory ontogeny is controlled may have general implications with respect to development.