Estimation of the Freezing Injury in Flower Buds of Evergreen Azaleas by Water Proton Nuclear Magnetic Resonance Relaxation Times

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Temperature dependence of longitudinal relaxation times (T_1) of water protons in flower buds of six azalea species differing in cold hardiness and ecological distribution was investigated by pulse nuclear magnetic resonance spectroscopy. Thermal hysteresis was observed for T_1 following a slow freeze-thaw cycle. The Tl ratio (the ratio obtained from the difference between the original T_1 value in an unfrozen sample and the final T_1 after a freeze-thaw treatment, both at 20℃, divided by the original Tl) was closely correlated with the viability of florets in non-acclimated buds of R. kiusianum. If the buds were frozen to a lethal temperature and then thawed to 20℃, the T_1 ratio increased. The T_1 ratios of acclimated winter buds for the six species used were correlated with the level of cold hardiness (supercooling ability of florets determined by differential thermal analysis). The T_1 ratio of deacclimated spring buds, especially those from hardier species, markedly increased upon cooling to a lethal temperature. Species differences observed in acclimated winter buds disappeared upon deacclimation. The T_1 ratio appears to be related to the viability of florets and the degree of freezing damage (membrane disruption) in florets.
日本植物生理学会の論文