Characteristic Changes in Relaxation Times of Water Protons in Vigna radiata Seedlings Exposed to Temperature Stress

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Water protons in hypocotyl tissues from etiolated seedlings of Vigna radiata that were exposed to temperature stress showed characteristic relaxation behaviors for ^1H-NMR. Cold stress treatment (0℃) caused gradual prolongation of NMR relaxation times (T_1). After exposure of tissues to cold stress for 24 h, T_1 returned to the initial value as a result of subsequent incubation at normal temperature (20℃). By contrast, heat stress treatment (40℃) induced a time-dependent decrease in T_1, which did not return completely to the initial value upon subsequent incubation at 20℃ after exposure to heat stress for 4 h. We examined changes in various physical factors that influence the response of T_1 to temperature stress, namely, water content and the concentrations of protein, diamagnetic (K^+, Na^+, Ca^<2+> and Mg^<2+>) and paramagnetic (Mn^<2+> and Fe^<2+>) ions in the tissues. From the relationships between T_1 and these factors in vitro, we could not interpret the responses of T_1 to the temperature stress only in terms of a change in water content. A synergistic effect of an Mn^<2+>_protein complex and pH might be essential for the mechanism of changes in T_1 that are due to cold stress. The influence of heat stress on structural water in tissues is discussed in terms of water-protein interactions.
日本植物生理学会の論文