Distribution of arabinan in the walls of N. alata pollen tubes grown in vitro. Arabinan epitopes were detected (green) with the monoclonal antibodies LM6 and LM13. Pollen tubes were counterstained with FM4-64 (red). A to D show 4-h (A and B) and 16-h (C and D) pollen tube shank (A and C) and tip (B and D) regions labeled with LM6. E to H show 4-h (E and F) and 16-h (G and H) pollen tube shank (E and G) and tip (F and H) regions labeled with LM13. I shows a cross section of a 4-h pollen tube shank imaged with immunogold transmission electron microscopy labeled with the monoclonal antibody LM13. PW, Fibrillar primary wall; SW, electron-lucent secondary wall. Bars = 5 µm.