*4.4. Transmission Electron Microscopy*

Samples were fixed in 3% paraformaldehyde, 1.5% glutaraldehyde, 5 mM CaCl2, 2.5% sucrose, and 0.1% tannic acid in 0.1 M sodium cacodylate bu ffer, pH 7.2. After bu ffer rinse, samples were fixed in 1.0% osmium tetroxide for 1 h on ice in the dark. Following a rinse with distilled water, the samples were stained with 2.0% aqueous uranyl acetate (0.22 μm filtered) for 1 h in the dark, dehydrated using a graded series of ethanol, and embedded in Eponate 12 resin (Ted Pella, Redding, CA, USA). Samples were polymerized for 2–3 days at 37 ◦C and were stored at 60 ◦C overnight. Thin sections, 60–90 nm, were cut at a depth of 50 μm from the surface with a diamond knife using a Reichert-Jung Ultracut E ultramicrotome and placed on naked copper grids and were stained with 2% uranyl acetate in 50% methanol and observed using a Philips/FEI BioTwin CM120 TEM.
