Material for transmission electron microscopy was washed in buffer,
post-fixed in a 1% solution of osmium tetroxide in 0.1 M phosphate
buffer, dehydrated in an ethanol series and embedded in Spurr's
epoxy resin (Spurr, 1969). Samples were then sectioned at 130 nm
using a diamond knife in a Leica UCT ultramicrotome (Leica Microscopy
Systems Ltd., Heerbrugg, Switzerland), mounted on copper sample
grids and stained sequentially with a saturated solution of uranyl acetate
in 50% ethanol followed by aqueous lead citrate (Roland, 1978). Transmission
electron microscopy was carried out using a JEOL JEM-1200EXII
transmission electron microscope (JEOL Tokyo, Japan) operating at an
accelerating voltage of 80 kV.