Sugar Accumulation as a Mechanism for Freezing Tolerance in Cold-Stored 'Danshaku' Potato Tuber (Solanum tuberosum L.)

Abstract

Tissue samples from cold-stored (0°C) 'Danshaku' potato tuber which underwent low temperature sweetening (LTS) were analyzed by differential scanning calorimetry (DSC) using a heating rate of 5°C /min. Results showed that LTS significantly lowered the onset temperature of melting. Tubers stored at 10°C did not sweeten and showed insignificant reduction of onset temperature. Total sugar levels were significantly related to Tp, To and Te while off was significantly related to moisture content of the sample. The primary endotherm (average To=-3. 86°C) representing extracellular melting of water was observed for tubers stored at 10°C and 0°C ; a secondary endotherm representing freezing of intracellular water was observed in 41.18% of tissue samples from tubers stored at 10°C (average To=-3.22°C). Only 11.11% of tissue samples from tubers stored at 0°C showed a secondary endotherm (average To=-12.20°C), implying that high sugar levels reduced lethal intracellular freezing in cellular compartments. Hence, sugar accumulation induced by cold conditions may be a mechanism to delay freezing and reduce its harmful effects on cell compartmentation and function.