Longitudinal sections of sieve elements (SE) in mature stem labeled with TLP1 antiserum. Panels A-C show bright field images and panels D-F the corresponding immunofluorescent images. The stem section in panel D was treated without the primary antibody, E was treated with preimmune serum, and F was treated with TLP1 antiserum. Asterisks indicate position of sieve plate. Scale bar = 20 μm.