Abstract
Temperature dependency of Arrhenius plots of ^1H-NMR relaxation times (T_1, T_2) was investigated in fresh, stored and frozen-thawed sweet potato tubers as a chilling sensitive plant. Noteworthy converse correlation in Arrhenius plots of T_2 was observed with lowering temperature from 30 to 0℃ in the fresh tuber tissues. The tubers stored at 15℃ for one year were partly injured and the frozen-thawed tubers were dead tissues judging from the results of ion leakage. Gradient in T_2 of Arrhenius plots changed at about 14℃ in the fresh tissues. On the other hand, there were no break points in T_1 and T_2 of dead tubers. Therefore, occurrence of gradient change of Arrhenius plots in T_2 at 14℃ might respond to chilling stress for the fresh tuber tissues. In dead tuber tissues temperature dependency of Arrhenius plots was clearly observed in T_1, while no temperature dependency was observed in T_2 of that tissues. In the stored tubers, temperature dependency on T_1 and T_2 indicated similar tendency observed in the dead tuber tissues. The water contents of sweet potato tubers were about 70% while that of Vigna hypototyls, which indicate liner T_1 decrease with lowering temperature, were over 95%. Thus, inverse relaxation behavior with lowering temperature seems to be partly influenced by low-level in water content of the tubers. In sugar solutions, T_2 markedly decreased at higher concentration compared to T_1 Additionally, T_1 in the sugar solutions decreased with lowering temperature while T_2 was independent upon temperature. The difference between T_1 and T_2 observed in the solutions was similar to the dead tuber tissues. That is, T_2s of the sugar solution
