1997 Volume 5 Issue 3 Pages 91-99
NMR micro-imaging provides a powerful tool for studying the changes in biological systems that occur upon cooling to subfreezing temperatures. Since the method is non-invasive, the changes can be followed in the one sample so that any dynamic processes that occur may be observed. In the present work the freezing behaviours (of water) in a wintering maple stem, a potato stem and pure water as a control were followed using NMR microimaging over the temperature range of 3 to −17°C. The images provide a clear indication of the highly organized and non-random nature of the freezing behaviours in wintering plant tissues (e.g., the maple stem) as well as contrasting behaviours between the images of the pure water, potato and maple stems as the temperature was decreased. The various factors that contribute to image intensity including NMR relaxation times, spectrometer performance and NMR spin populations, and how their respective contributions change with temperature are considered in detail. An in depth understanding of these processes is important for making valid interpretations and comparisons of images of plant materials taken at different temperatures (nonfreezing and subfreezing).
