Phosphorus Nutrition and the Intracellular Distribution of Inorganic Phosphate in Pea Root Tips: A Quantitative Study using31P-NMR

Abstract

Pea plants (Pisum sativum L.) were supplied with external phosphate for differing periods of time, so that their phosphorus status varied, and the intracellular distribution of inorganic phosphate (P1) in the roots was examined by 31P nuclear magnetic resonance. Over the range of phosphorus nutrition investigated, the quantity of vacuolar P1 per unit fresh weight of root tip changed considerably, whereas the quantity of cytoplasmic P1 per unit fresh weight of root tip did not alter. The relative volumes of the cytoplasm and the vacuole in pea root tips seemed to be little affected by differences in phosphorus nutrition, and this implied that the concentration of P1 in the cytoplasm was kept almost constant, at a level estimated to be ∼ 18 mM. The rate of absorption of 32P-labelled phosphate was negatively correlated with the vacuolar P1 concentration, but there was no clear correlation with the concentration of P1 in the cytoplasm.