Abstract
The state of water in cells in biological systems has been studied extensively by NMR (nuclear magnetic resonance) spectroscopy. The longitudinal (T_1) or transverse (T_2) relaxation times of water protons provide invaluable information about the dynamic state of tissue water. For a decade, we have been studying changes in NMR relaxation behaviors in plants that resulted from the influence of various types of environmental stress. Our studies revealed that although Ti in plant tissues is primarily influenced by water contents, they are influenced not only by inherent factors in plants such as age, species, tissues and organs, but also by extrinsic conditions including environmental stresses. The Ti relaxation times are also influenced by the state of water balance in cells and tissues. Water balance is implied by total water contents, distribution of water in different compartments and interactions of water, macromolecules and secondary metabolites such as phenol derivatives in plants. In plant materials, however, the interpretation of the data in Tx needs special care different from the study of animal materials because plant cells contain characteristic organella such as chloroplasts, vacuoles and cell walls, and also the presence of unique water conducting systems (vascular bundles). Consequently, it is clear that the T_1 measurement in plants can be used for monitoring the primary response to various types of environmental stresses such as freezing, chilling, heat, salt, UV radiation and biotic (insect gall formation) stress and for a comparative evaluation of the stress sensitivities.
