Further evidence of oxygen diffusion as the determining factor in the relation between disk thickness and respiration of potato tissue.

The effect of oxygen tension above atmospheric pO(2) on the development of respiratory capacity in potato disks has been examined. Raising the oxygen tension of the aqueous environment to 40% during the aging of 2.0 mm or 3.0 mm thick disks at 25 degrees progressively increased the respiration rate of the tissue as shown by subsequent assay in 100% oxygen. Disks 3.0 mm thick showed a greater response to increased pO(2) than did 2.0 mm disks. A comparison of center 1.0 mm sections excised from 3.0 mm disks after aging, showed that the respiration rate of internal tissue from disks aged in high pO(2) was approximately 40% greater than such tissue aged with atmospheric pO(2). The characteristic inverse relationship between respiration rate and thickness in aged disks can be modified from a concave-downwards curve to a convex-downwards curve by pretreating the tissue with increased pO(2), thus indicating that raising the pO(2) during aging can increase the thickness threshold at which the transition from tissue manifesting the respiratory characteristics of thin disks to that manifesting the characteristics of thick disks, occurs. Similarly increased pO(2) during aging can modify the hyperbolic relationship obtaining between pretreatment temperature in the range 10 degrees to 25 degrees and respiratory capacity of aged 3.0 mm disks, to approximate to the linear relationship observed with 0.75 mm disks. It is concluded that the development of respiratory capacity in disks between 0.75 mm and 3.0 mm thick is restricted by oxygen dificiency and that the characteristic inverse relationship between respiration rate and thickness in aged disks is largely attributable to this factor, the influence of which is discernible both on the development of respiratory capacity and on its subsequent assay.