A proposed role for the anaerobic pathway during low-temperature sweetening in tubers of Solanum tuberosum

Following exposure to low temperatures (i.e. < 9-10°C), tubers of potato (Solanum tuberosum ) undergo a phenomenon known as low-temperature sweetening (LTS), which results in the conversion of starch to sugars. LTS in stored potato tubers was evaluated by monitoring glycolysis, the oxidative pentose phosphate pathway, anaerobic respiration and mitochondrial respiration, in order to obtain an overview of the regulation of sugar metabolism during LTS. Carbohydrate metabolism during 4°C storage was evaluated in four different storage seasons, comparing tubers of cold-tolerant (low sugar-accumulating) clones (ND 860-2, V 0056-1 and Wis 1355-1) and cold-sensitive (high sugar-accumulating) cultivars (Novachip and Monona). Parameters measured included whole tuber respiration, concentrations of sucrose, reducing sugars, ATP, NADH, NADPH, lactate and ethanol, as well as tissue pH. In three of the four seasons of study, the cold-tolerant tubers maintained lower levels of reducing sugars, and higher levels of lactate and ethanol, relative to cold-sensitive tubers. A higher anaerobic flux in tubers of cold-tolerant genotypes may be partially responsible for a lower accumulation of reducing sugars relative to cold-sensitive tubers. This study represents the first known report on the role of the anaerobic pathway during LTS in potato tubers.