Relationship of nuclear magnetic resonance relaxation time to water content and cold hardiness in flower buds of evergreen azalea

The longitudinal relaxation time (T₁) of water protons in florets of R. × akebono flower buds was measured with a pulse NMR spectrometer to determine the relationship of T₁ to water content and cold hardiness (supercooling ability). Seasonal changes of T₁ in florets were closely correlated with water content and supercooling ability of florets. T₁ of florets was short for acclimated buds having a low water content and long for non-acclimated buds having a high water content. Flower buds collected in November and stored at 0 and 5°C for 4 weeks had shorter T₁ values than buds stored at 10°C even though the floret water content and supercooling ability were similar. Thus, the short T₁ of cold acclimated buds hardened naturally or by storage at low temperatures is due to a combination of both reduced water content and temperature.