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

Pea plants (Pisum sativum L.) were supplied with external phosphatefor differing periods of time, so that their phosphorus statusvaried, 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 quantityof vacuolar P₁ per unit fresh weight of root tip changed considerably,whereas the quantity of cytoplasmic P₁ per unit fresh weightof root tip did not alter. The relative volumes of the cytoplasmand the vacuole in pea root tips seemed to be little affectedby differences in phosphorus nutrition, and this implied thatthe 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 negativelycorrelated with the vacuolar P₁ concentration, but there wasno clear correlation with the concentration of P₁ in the cytoplasm. Key words: Compartmentation, Cytoplasm, Vacuole, Concentration, Absorption