MAGNETIC-RESONANCE-IMAGING (MRI) OF WATER DURING COLD-ACCLIMATION ANDFREEZING IN WINTER-WHEAT

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance i maging (MRI) were used to analyse changes in the physical state of wat er in wheat crowns during cold acclimation and during the freezing/tha wing cycle. Spectroscopically measured average spin-spin relaxation ti mes (T-2) decreased during cold acclimation and increased when plants were grown at normal temperatures. Spin-spin relaxation times were acc urately approximated by mono-exponential rates for water relaxation on a pixel basis in images, Spin-spin relaxation images whose contrast i s proportional to T-2 times were calculated allowing association of wa ter relaxation with regions of tissue in spin-echo images during accli mation 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 and T-2 times decreased dramatically between -4 degrees C and -8 degrees C as a result of a decrease in water mobilit y during freezing. Images collected during thawing were diffuse with l ess structure and relaxation times were longer, consistent with water redistribution in tissue after membrane damage.