To perform TEM, samples were frozen using a high pressure
freezer (Leica EMPACT2) at pressure 2000–2050 bar. Freeze substitution
was performed in anhydrous acetone (containing 1% OsO4
and 0.1% uranyl acetate) using a Leica EM AFS2 (automatic freeze
substitution). The samples were kept at 85 C for 3 days, and then
at 60, 20 and 0 C for one day at each temperature, and then
raised to room temperature. The Spurr’s resin was used for infiltration
and embedding. The embedded samples were cut to make
ultrathin sections at 70–90 nm using a Reichert Ultracut S or Leica
EM UC6 (Leica, Vienna, Austria), and the sections were collected
using 100 mesh copper grids. The sections were then stained with
5% uranyl acetate in 50% methanol for 10 min and 0.4% lead citrate
for 4 min. Sections were observed using a Philips CM 100 Transmission
Electron Microscope at 80 kV and the images were recorded
with Gatan Orius CCD camera. SEM was conducted with a
chemical fixation method. The samples were fixed in 2.5% glutaraldehyde
and 4% paraformaldehyde in 0.067 M sodium phosphate
buffer, pH 7.0 at room temperature for 4 h. After 320 min buffer
rinses, the samples were postfixed in 1% OsO4 in the same buffer
for 4 h at room temperature and then rinsed in three 20 min
washes with fresh buffer. Samples were dehydrated in an ethanol
series. Critical point drying was done with a Hitachi HCP-2 critical
point dryer. After coating (with Hitachi E-1010 ion sputter), a FEI
Quanta 200 scanning electron microscope at 20 kV was used for
recording images.