Probing water compartments and membrane permeability in plant cells by H NMR relaxation measurements.

(1)H NMR relaxation times (T(1) and T(2)) in parenchyma tissue of apple can identify three populations of water with different relaxation characteristics. By following the uptake of Mn(2+) ions in the tissue it is shown that the observed relaxation times originate from particular water compartments: the vacuole, the cytoplasm, and the cell wall/extracellular space.Proton exchange between these compartments is controlled by the plasmalemma and tonoplast membranes. During the Mn(2+) penetration experiment, conditions occur that cause the relaxation times of protons of cytoplasmic water to be much shorter than their residence time in the cytoplasm. Then the tonoplast permeability coefficient P(d) for water can be calculated from the vacuolar T(1) and T(2) values to be 2.44 10(-5) m.s(-1).