. At the end of the experiment, five leaf tissue samples from each treatment were taken for electron microscope ex- amination. Leaf fragments were fixed in 2% paraformaldehyde and 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2), post-fixed in 1% osmium tetroxide and 0.8% potassium ferrocyanide in the same buffer, dehydrated in a graded acetone series and em- bedded in Spurr’s resin. Thin sections (0.5 µm) were used to select zones to explore under the electron mi- croscope. Ultrathin (50-80 nm) sections were cut with an ultramicrotome (Leica Ultracut UCT, Germany) us- ing a diamond knife. They were then mounted on Cu grids and post-stained, first with 2% uranyl acetate for 10 min, then with lead citrate for 20 min. Observations were made with a Jeol EM 1010 transmission electron microscope, operated at 80 kV.