THE EYESPOT MEMBRANES OF HAEMATOCOCCUS PLUVIALIS FLOTOW (CHLOROPHYCEAE): THEIR ULTRASTRUCTURE AND POSSIBLE SIGNIFICANCE IN PHOTOTAXIS

SUMMARY The eyespot region of the green flagellate alga Haematococcus pluvialis Flotow (Clorophyceae) was investigated by electron microscopy in order to identify any possible specialization of the plasmalemma and the outer chloroplast envelope membrane connected with photoreception. In this alga, the distance between the outer chloroplast membrane and the plasmalemma in the eyespot region is variable. In some thin sections in this region, the inner limiting membrane of the chloroplast is more electron dense than the outer, while the thickness of the plasmalemma opposite the eyespot shows no appreciable difference with respect to other parts of the cell. The possible functional significance of these findings and the possibility that the eyespot in Haematococcus pluvialis serves as a shading device are both discussed.