Immunogold electron microscopy of HMGR localizations in thin unembedded cryosections of 6-d-old wild-type Arabidopsis cotyledons. A, B, and F to L, Double labeling with anti-CD1 antiserum (10-nm gold particles) and anti-BiP antiserum (15-nm particles). C, Control image of sections incubated first with anti-CD1 antiserum preadsorbed with excess recombinant HMGR1 catalytic domain, then with protein A gold (10-nm particles). D and E, Double labeling with anti-CD1 antiserum (10-nm particles) and anti-α-TIP antiserum (15-nm particles). In all images (except H and J), arrowheads indicate site(s) of HMGR-specific 10-nm gold particles. Arrows indicate site(s) of BiP- or α-TIP-specific 15-nm particles. In images H and J, arrowheads point to regions that are shown at higher magnification in I (H), K, and L (J). v, Vacuole. Bars = 200 nm (C, D, and H), 500 nm (J), and 100 nm (all others).