Induction of Glutamine Synthetase During Nodule Development in Lupin

Abstract

Activity of glutamine synthetase (EC 6.3.1.2) in the soluble protein fraction of nodules from 21-day- old lupin plants was measured. On a fresh tissue weight basis, activity was approximately 500 times higher than in the soluble protein fraction from roots of inoculated plants and 300 times higher than in the bacteroid soluble protein fraction. The activity of glutamine synthetase in the bacteroids was approximately 10 times lower than in cultured rhizobia. Glutamine synthetase activity in the nodule cytoplasm was found to increase during nodule development over a time course which followed the induction of leghaemoglobin and nitrogenase. Glutaminase activity, which could be inhibited by L-5-diazo-4-oxo-norvaline, was detected in extracts of bacteroids and cultured rhizobia. The glutamine synthetases present in cultured rhizobia and in the nodule cytoplasm had different electrophoretic mobilities on polyacrylamide gels.