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.