Nuclear magnetic resonance studies of sodium and potassium in etiolated pea stem

Based on nuclear magnetic resonance (NMR) spectroscopy and other evidence, it has been argued that tissues accumulate, and retain, ions in a binding process by a highly structured water-protoplasm system; thus active membrane transport need not be involved. Recent evidence has accounted for the loss of resonance intensity usually found when investigating quadrupolar ions in animal tissue. Using continuous wave NMR spectroscopy, we have examined two quadrupolar ions, Na(+) and K(+), in pea stem cells where about 90% of the ion content is in the largely aqueous vacuoles having a membrane barrier. The NMR resonances from these ions correspond to almost 100% of that expected from independent measurements of total ion content. This indicates that the ions are retained as free ions after accumulation. The small fraction which is NMR invisible may represent ions in an ordered, anisotropic environment, such as that in the wall or cytoplasm.