EYESPOT OF THE FLAGELLATE TETRASELMIS-CORDIFORMIS STEIN (CHLOROPHYCEAE) - STRUCTURAL SPECIALIZATION OF THE OUTER CHLOROPLAST MEMBRANE AND ITS POSSIBLE SIGNIFICANCE IN PHOTOTAXIS OF GREEN-ALGAE

The eyespot region of the flagellate T. cordiformis Stein (Chlorophyceae) was investigated with the freeze-fracture technique. The only fracture faces observed in this region were the 2 complementary fracture faces (PF and EF) of the outer chloroplast envelope membrane. Intramembranous particle numbers on both fracture faces of this membrane were significantly higher in the eyespot region as compared to regions outside the eyespot. Higher numbers of particles on the PF face in the eyespot region were mainly caused by an increase in particle numbers of the size class 6-8 mm, while on the EF face particle size distribution was not significantly different between eyespot and other regions. Functional implications are discussed and evidence is presented that the outer chloroplast envelope membrane may be the site of photoreceptor location in green algal phototaxis.