Mm. Millard et al., MAGNETIC-RESONANCE-IMAGING (MRI) OF WATER DURING COLD-ACCLIMATION ANDFREEZING IN WINTER-WHEAT, Plant, cell and environment, 18(5), 1995, pp. 535-544
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.