Leaf samples were separated and cut into 0.5 cm × 0.5 cm pieces, and then fixed with 2.5% glutaraldehyde for 12 h. After at least three rinses with 0.1 M PBS, the samples were fixed with 1.0% osmium tetroxide (OsO4) for 2 h, followed by three rinses with PBS. Subsequently, the samples were dehydrated in an acetone dilution series from 30 to 100%, embedded in Spurr’s resin (Ted Pella, United States), and cut into thin sections (70–90 nm). Lastly, these sections were observed by transmission electron microscopy at 80 kV. At least five dependent samples and more than 16 individual chloroplasts were observed for each treatment.