In each category of Zn deficiency, one typical leaf at the middle of the shoot with
typical symptoms was selected at 10:00 am on 10 June. All the tissues were sampled
from the middle regions of leaves adjacent to the main veins and prepared according
to Stefanowska et al. (2002). An area approximately 25 mm2 at the central site
along the main vein was cut out with a knife and served as the fixed material. The samples were fixed in 2% glutaraldehyde with 0.1 M sodium cacodylate buffer (pH 7.2) and then postfixed in 1% osmium tetroxide with 0.1 M sodium cacodylate buffer
(pH 7.2).