The problem of whether leghaemoglobin is synthesized on plant of bacterial ribosomes in root nodules of yellow lupin has been examined. 2. Leghaemoglobin, soluble plant protein and soluble bacteroid protein were labelled with 14C administered by uptake of 14CO2. 3. Exposure of roots to 1 mM D-threo-chloramphenicol resulted in inhibition of soluble bacteroid protein synthesis, but leghaemoglobin synthesis and soluble plant protein synthesis were unaffected. This result is consistent with leghaemoglobin being synthesized on plant ribosomes. 4. After nitrogen-fixing plants had been supplied with a pulse of 14CO2, the decay of specific radioactivity of nodule protein fractions was observed. Leghaemoglobin had an apparent half-life of 18 days and is a stable protein in nitrogen-fixing yellow lupin nodules.
