Morphological characterization of HRP-rhodopsin-carrying vesicular tubules in the basal OS axonemes. Electron micrographs of longitudinal (A–C) and cross-sectional (D) views of proximal OS axonemes of HRP-rhodopsin transfected rods showing the membrane tubules with (white arrows) or without (white arrowheads) dark DAB precipitates. The intensity of DAB labeling in the branches or distal tips of the tubules is comparable to that of adjacent discs (curved black arrows). The diameter of the distal ends of these tubules is also similar to that of the disc membrane. Black arrows point to DAB-labeled small vesicles. Scale bars in nm.