Phosphorylation by Barley Root Mitochondria & Phosphate Absorption by Barley Roots

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Abstract
Mitochondria were isolated from roots of 6-day old barley seedlings by differential centrifugatlon of root homogenates. The mitochondria faction contains three-fourths of the total phosphorylative activity of the homogenate. The mitochondria respire and esterify phosphate at steady rates in phosphate concentrations from 10-4 to 10-1 [image]. Relative turnover rates, concentration effects, and interactions of different substrates in the mitochondria parallel their effects on phosphate absorption by roots. Phosphorylation and respiration for mitochondria and roots are similarly inhibited by azide, ammonium hydroxide, barbiturates and acetate. Dinitrophenol competitively uncouples mltochondrial phosphorylation and root absorption without inhibiting respiration. The mitochondria appear to be the partlculate site of the rate limiting step for phosphate absorption.