Transmission electron microscopy

Developing mycorrhizal tubers were sliced, then fixed with 2% glutaraldehyde in 0.1 M sodium phosphate buffer (pH 6.8) at 4 °C overnight. After rinsing three times with fresh phosphate buffer, samples were post-fixed with 1% OsO4 in the same buffer for 4 h at room temperature. Samples were dehydrated in a graded acetone series and embedded in Spurr’s resin (Electron Microscope Sciences, USA). Ultrathin sections of 70 nm were cut with a diamond knife on an ultramicrotome Ultracut E (Reichert-Jung, Vienna, Austria). These sections were stained with uranyl acetate and lead citrate. Sections were then examined and photographed using a Philips CM 100 transmission electron microscope at 80 kV.