The use of colloid gold labelling in the detection of plasma membrane from symbiotic and non-symbiotic Glycine max root cells

Glycine max L. Merr. cv. Maple Arrow protoplasts were prepared from both tissue-cultured root cells and symbiotically-infected (fix+) nodule cells. Whilst both cell types showed glucan synthetase II (GS II; EC 2.4.1.29) activity, neither cell type, whole or gently disrupted, showed glucan synthetase I activity. After sucrose density gradient centrifugation one of the several GS II activity peaks co-sedimented with the single radioactive particulate peak from [125I]-labelled protoplasts at 1.14 g ml−1. This peak is presumed to be the plasma membrane peak because labelling of protoplasts with colloidal gold prior to disruption moved the 125I peak and the corresponding glucan synthetase II activity into denser regions of the gradient, leaving endoplasmic reticulum-contaminating IDPase (EC 3.1.3.31) and other glucan synthetase II peaks unmoved. Results are discussed in relation to various strategies of plasma membrane isolation.