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

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 K M of PDC, with the LTS-tolerant ND 860-2 possessing a lower K M 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.