Plant tissue diffusion-weighted

A number of isotopically different forms of water can be prepared, which greatly facilitates experimental studies. Replacing both of the usual hydrogen atoms with deuterium (2H) results in heavy water, or deuterium oxide, with a molecular weight of 20. The role of water in chemical reactions can then be studied by analyzing the deuterium content of substances involved as reactants or products. Tritium (3H), a radioactive isotope with a half-life of 12.4 years, can also be incorporated into water. Tritiated water has been used to measure water diffusion in plant tissues. Another alternative for tracing the pathway of water is to replace the usual 160 isotope with lsO. This labeling of water with lsO helped determine that the O2 evolved in photosynthesis comes from H20 and not from CO2 (Chapter 5, Section 5.5A). 

Most recently these ideas have been combined with a numerical cell model to relate S(q, A, r) to cell structure in plant parenchyma tissue.143 Using PGSE data for apple tissue a value for the plasmalemma membrane permeability was estimated. The application of this numerical cell model to mammalian tissue might enable quantitative interpretation of diffusion weighted contrast in clinical MRI. Table 6 lists a number of other applications of the PGSE method to food-related materials, although few of these studies have attempted to explore systematically the whole of the three-dimensional q—A—r space. 

Fig. 2.S. Relationship between change in tissue or cell volume or weight from its initial (natural) value and the osmotic potential of the solution in which it is immersed. The osmotic potential in which there is no change in volume or weight gives the (water potential of protoplast) of the cell or tissue. Pp is equal but opposite in sign to the DPD (diffusion pressure deficit) or SF (suction force). (From T. A. Rennet-Clark, in Plant Physiology, vol. 2, pp. 105-192, edited by F. C. Steward, Academic Press, New York, 1959.)...

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