Turnover Rates of Phosphate Esters in Fresh and Aged Slices of Potato Tuber Tissue

In recent years, a number of studies have been made on the respiration of slices of potato tuber tissue (1, 6,7, 8, 9, 11, 12, 13, 16, 17). When the slices or disks are freshly cut, they have a respiration rate similar to that of the intact tuber. This tissue has been termed fresh tissue. When the fresh disks are kept by aerating them in distilled water or 10-4 M CaSO4 at 00, the low respiration rate is maintained; but when the disks are aerated at 250, the respiration rate rises threeto fourfold over about 18 hours. This phenomenon has been termed aging, and disks treated in this way are aged disks. Aging does not merely involve a simple increase in respiration rate: the sensitivity of the respiration to various inhibitors alters markedly (1, 6, 11, 16, 17), and the tissue shows a marked increase in its ability to accumulate salts, particularly phosphate (6, 9, 13). Such observations have led to suggestions that aging involves a major change in the cellular processes (7). Some authors (6,17) have suggested that there is a modification of the respiration chain in the region between DPNH and cytochrome c; while others (1, 16) have suggested that there are changes in the relative importance of the pentose phosphate and the tricarboxylic acid cycle respiration paths. The results of experiments by Loughman (9) indicate that the respiration changes are closely associated with changes in the phosphate metabolism. Therefore experiments have been carried out to examine in more detail the phosphate metabolism of fresh and aged potato tuber slices, with a view to learning more about the nature of the aging process.