response of palisade parenchyma plastids to sugar exposure. A) Increase of stromule frequency in mesophyll cells after vacuum infiltration of either APW or APW supplemented with 40 mM glucose, 40 mM sucrose, or 40 mM sorbitol. Error bars indicate the 99% confidence intervals. For absolute values of SF see additional file 2 panel B. B - E) 'Stacked' and inverted epifluorescence images showing leaf tissue either at 0 h (B), 1 h (C), 2 h (D) or 3 h (E) after infiltration of 40 mM glucose solution. The plastids of epidermal cells appear in dark, while the larger mesophyll chloroplasts appear brighter. Note the increasing proportion of plastids in both tissues that form stromules. The asterisk highlights mesophyll chloroplasts with stromules. Size bar corresponds to 10 μm.