Subcellular Distribution of Inorganic Phosphate, and Levels of Nucleoside Triphosphate, in Mature Maize Roots at Low External Phosphate Concentrations: Measurements with31P-NMR

Abstract

Maize plants were grown in nutrient solution without phosphate, or in which inorganic phosphate (Pi) was maintained at nearly constant concentrations of 1 μM, 10 μM or 0.5 mM. In vivo 31 P-NMR measurements showed that there was no discernible difference in the cytoplasmic Pi content (μmol cm -3 root volume) of the mature roots of plants exposed to 1 μM, 10 μM or 0.5 mM external phosphate for up to 12 d. However, the vacuolar Pi content of the mature roots varied about 10-fold between these three groups. The cytoplasmic Pi content of roots receiving no external phosphate decreased significantly after about 7 d total growth, and at about this time the vacuolar pool of Pi became too small for accurate measurement