Changes in Sugars and Activities of Sucrose Phosphate Synthase, Sucrose Synthase, and Invertase during Potato Tuber (Russet Burbank) Reconditioning at 10 °C in Air and 2.53 kPa Oxygen after Storage for 28 Days at 1 °C

Abstract

Potato tubers (Solanum tuberosum `Russet Burbank') were stored at 1 °C in air for 28 days and then transferred to 10 °C in either air or 2.53 kPa O2. During cold storage there was an increase in sucrose, glucose, and fructose. The activities of extractable sucrose phosphate synthase (SPS) and invertase increased by 2.2- and 7.7-fold, respectively, during 28 days at 1 °C. The activity of sucrose synthase (SS) remained constant at 1 °C and was similar to that found in tubers kept continuously at 10 °C. With the transfer of tubers from 1 to 10 °C, there was an initial sharp rise in respiration which peaked at ≈7 days, followed by a gradual decline. Sucrose declined rapidly during reconditioning, while glucose and fructose declined more slowly. With the transfer of tubers from 1 to 10 °C, the activity of SS increased sharply after 7 days at 10 °C, to be followed by a decline to the levels found in control tubers. The activities of both extractable SPS and invertase decreased during reconditioning, reaching the values of the control tubers within ≈15 days. Low O2 inhibited the decrease in sugars and suppressed the rise in SS activity, but it did not alter the decrease in SPS and invertase. Western blot analysis showed that the amount of SPS protein remained unchanged at 1 and 10 °C. These results indicate that the activity of SPS is regulated by factors other than the amount of its protein. The activities of the above three enzymes showed no changes in tubers kept at 10 °C continuously. In control tubers SPS showed the highest activity, followed by SS and invertase.