A P-31-NMR STUDY OF THE UPTAKE AND COMPARTMENTATION OF MANGANESE BY MAIZE ROOTS

The uptake and compartmentation of manganese by maize roots, from solutions containing between 1 mu M and 1 mM Mn2+, was monitored in vivo by P-31 nuclear magnetic resonance (NMR) spectroscopy. Qualitatively, NMR provided a convenient method for observing the effects of pH, anoxia, metabolic inhibitors, and competition with magnesium on the uptake of manganese and the results highlighted the role of the vacuole as a sink for Mn2+. Quantitatively, it was established that root tissues could maintain a low concentration of free Mn2+ in the cytoplasm during manganese uptake and that there is a non-equilibrium distribution of Mn2+ between the cytoplasm and the vacuole. Typically exposure to Mn2+ in the range 10-100 mu M resulted in a submicromolar pool of Mn2+ in the cytoplasm and a vacuolar pool of 10 mu M and it was concluded that the movement of Mn2+ out of the cytoplasm must be energy consuming. Overall the results draw attention to the similarity between the subcellular distribution of manganese and calcium and provide some support for the suggestion that manganese, like calcium, might have a control function in normal cells.