Leaves were cut with a razor to a length of 5 mm and a width
of 1–2 mm, and fixed with 2.5% glutaraldehyde for 2–3 h. Leaves
were then washed two to three times with buffer solution (potassium
phosphate buffer, pH 7.4) and fixed with buffer solution at 4 ◦C
for 12 h. Samples were then treated with 1 mL 2% osmium tetroxide
(OsO4) and 1 mL Dalton fixative solution (K2Cr2O7 0.5 mL + 3.4%
NaCl 0.5 mL) for 1 h and 30 min, and dehydrated by incubation in
an ethanol gradient (30%, 50%, 70% and 90%, 10 min each).