Fig. 2. Protein trafficking from mesophyll to epidermal cells in the Arabidopsis leaf. GFP fusion reporters were expressed using the mesophyll-specific pRbcS2b-GAL4/UAS-reporter system. The tissue specificity of the promoter is shown by the expression of the cell-autonomous mGFP5-ER reporter. (A-C) Expanded leaves of transgenic plants expressing mGFP5-ER showed GFP fluorescence in mesophyll and epidermal guard cells, but not in epidermal pavement cells. (D-L) In contrast, the presence of GFPKN1 (D-F), GFPTVCV MP (G-I) and free GFP (J-L) under the same promoter was detected in all epidermal and subepidermal cells. (F) GFPKN1 and (I) GFPTVCV MP localized to puncta (arrowheads) that were not observed in plants expressing free GFP (L). Hand-made cross sections (A-B,D-E,G-H,J-K) were imaged by using red and green channels (left column) and green channel only (middle column) of the confocal microscope. Paradermal images are shown in (C,F,I,L). Left panels of A and D show bright-field images of mGFP5-ER and GFPKN1 plant sections, respectively. (M-O) Immunolocalization using an anti-KN1 antiserum was performed on leaf sections of wild-type (M, red box is magnified in upper panel of O) and GFPKN1 expressing plants (N, red box is magnified in lower panel of O). GFPKN1 protein was detected in nuclei of epidermal cells and in mesophyll cells. Arrows indicate nuclear localization of GFP and GFP fusions (F, I, L) and KN1 protein (O). Scale bars: 50 µm (A,B,D,E,G,H,J,K,M); 25 µm (C,F,I,L,N,O).