Age of potato seed-tubers influences protein synthesis during sprouting

The effect of seed-tuber age on the ability of tuber tissue to synthesize protein during sprouting was examined. As seed-tuber age advanced from 4 to 32 months (at 4°C, 95% relative humidity), soluble protein concentration of tubers decreased linearly, with a concomitant increase in free amino acid concentration. The age-induced loss of tuber protein may thus be due to increased proteolysis, decreased protein synthesis, or both. Five- and 17-month-old seed-tubers were compared for their ability to incorporate radiolabeled amino acids into soluble protein at equivalent stages of sprout development. Tuber respiration was profiled through each sprouting stage to characterize the physiological status of the seed-tubers prior to incorporation studies. Five-month-old seed-tubers maintained a constant rate of respiration during sprouting. In contrast, respiration of 17-month-old tubers increased as sprout dry matter increased, resulting in a 2- to 3-fold greater respiratory rate from the older tubers, relative to the younger tubers, at similar stages of sprout development. Prior to sprouting, the rate of incorporation of amino acids into trichloroacetic acid-precipitable protein of tissue from 5-month-old tubers was 2. 9-fold higher than that from 17-month-old tubers. More importantly, protein-synthetic capacity of tissue from younger tubers increased about 1. 7-fold during sprout development. Despite the higher respiratory activity and faster total sprout dry matter accumulation from older seed-tubers, protein synthesis remained at a low and constant level through all stages of sprouting. Protein-synthetic capacity thus declines with advancing tuber age, and this may contribute to reduced growth potential during the latter stages of establishment by affecting the ability of seed-tubers to synthesize enzymes involved in mobilization and translocation of tuber reserves to developing plants.