Changes in respiratory metabolism during sprouting of aged seed-potato tubers

Abstract

Seed-potato tubers stored for more than 8 months lose apical dominance and sprout with reduced vigor compared with younger tubers. To determine if age-reduced vigor is associated with less efficient respiratory activity, contributions of the different modes of respiration were measured in tissue from 7- and 19-month-old tubers at 6-day intervals over an 18-day sprouting period. Although respiration rate of tissue from the two tuber ages was equal at planting, it increased for both during sprouting, reaching a level 51% higher in tissue from old tubers by the end of the study. Tuber age and time had no effect on cytochrome-mediated respiration, which averaged 18 nmol O2/(min∙g fresh weight) over the study interval. However, the rate of alternative respiration of tissue from old tubers increased through day 12, reaching a level 30-fold greater than that of tissue from young tubers. As a percentage of total respiration, residual respiration was relatively constant (26%) in both ages of tissue during sprouting. In young tuber tissue, alternative respiration decreased from 9 to 1% of the total by day 12. Over the same period, the proportion of alternative respiration in old tissue increased from 14 to 28%, and this occurred with a concomitant decrease in the proportion of cytochrome-mediated respiration. During sprouting, old tubers appeared to be generating higher levels of ATP through a combination of the cytochrome-mediated and alternative pathways compared with young tubers; however, the increased energy-metabolizing ability of old seed tubers is less efficient at meeting the demands of sprout growth, as indicated by the lower weight of sprouts produced. Key words: potato, age-reduced vigor, respiration, sprouting.