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

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Abstract
When slices of potato tuber tissue are aged (aerated 24 hours at 25[degree]C), their metabolic characteristics are altered. Changes in phosphate metabolism were studied by feeding P32-phosphate to the tissues, extracting the phosphate esters (PEs) and separating the PEs by 2-dimensional paper chromatography. The amounts of the various PEs were estimated from their radioactivity. The soluble PE pattern was not affected by aging, but ribonucleic acid synthesis was much more active in the aged tissue. The course and rate of PE formation was studied. The PEs became labelled in the same order in both tissues (nucleotide triphosphates were first to label) but at different rates (5 times more rapidly in the aged tissue). Measurements of respiration rate, rate of PE synthesis and amounts of PEs were used to calculate the efficiency of phosphorylation (P/O ratio). The in vivo P/O ratios were 0.25 for fresh tissue and more than 0.6 for aged tissue. Thus respiration in aged tissue was more effecient as well as more rapid, supporting suggestions that the respiration path changes during aging. The data also revealed that inorganic phosphate in both tissues exists in at least 2 pools: the metabolic pool contains 5% and the nonmetabolic pool contains 95%. Phosphate entering the tissue moves into the metabolic pool first. The half-time of equilibration of the 2 pools is at least 8 hours.