Magnetic resonance imaging (MRI) of water during cold acclimation and freezing in winter wheat

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) were used to analyse changes in the physical state of water in wheat crowns during cold acclimation and during the freezing/thawing cycle. Spectroscopically measured average spin‐spin relaxation times (T2) decreased during cold acclimation and increased when plants were grown at normal temperature. Spin‐spin relaxation images whose contrast is proportional toT2, times were calculated allowing association of water relaxation with regions of tissue in spin‐echo images during acclimation and freezing. Images taken during freezing revealed nonuniform freezing of tissue in crowns and roots. Acclimated and non‐acclimated wheat crowns were imaged during freezing and after thawing. Spin‐echo image signal intensity andT2times decreased dramatically between ‐4°C and ‐8°C as a result of a decrease in water mobility during freezing. Images collected during thawing were diffuse with less structure and relaxation times were longer, consistent with water redistribution in tissue after membrane damage.