Roles of alcohol dehydrogenase, lactate dehydrogenase and pyruvate decarboxylase in low‐temperature sweetening in tolerant and susceptible varieties of potato (Solanum tuberosum)

Abstract

Low‐temperature sweetening (LTS) results when tubers of potato (Solanum tuberosum) are stored at temperatures below 9–10°C with the accumulation of sucrose and reducing sugars glucose and fructose. Our earlier study showed that the LTS‐tolerant varieties have higher ethanol and lactate tissue levels compared with the LTS‐susceptible variety Monona (Blenkinsop et al. 2003), which led us to investigate the role of the anaerobic respiratory pathway in LTS tolerance. The anaerobic respiratory enzymes alcohol dehydrogenase (ADH), l‐lactate dehydrogenase (LDH) and pyruvate decarboxylase (PDC) were, therefore, investigated in LTS‐tolerant and ‐susceptible potato varieties. A positive correlation (P≤ 0.05) was observed between reducing sugar concentration and the KM of PDC, with the LTS‐tolerant ND 860‐2 possessing a lower KM and reducing sugar content than the LTS‐susceptible Monona variety. The moderately LTS‐tolerant variety, Snowden, exhibited intermediate behavior between the two aforementioned cultivars at 4°C. The isozyme profile of the tolerant varieties differed from the susceptible variety. Two groups of LDH isozyme families were observed in all varieties with the exception of ND 860‐2, where the second group appeared only during low‐temperature exposure. Moreover, the tolerant variety possessed one additional ADH isozyme. Gene expression levels of these enzymes were higher in ND 860‐2 as compared with Monona at 4°C. The above results suggest that the anaerobic respiratory enzymes contribute to LTS‐tolerance.