Forma, Vol. 7 (No. 2), pp. 139-146, 1992
Original Paper

How a Unicellular Green Alga Mougeotia Detects Direction of Incident Light

Nozomi Ytow and Toru Yamada

Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan

(Received November 16, 1991; Accepted May 8, 1992)

Keywords: polarization, chloroplast orientation, phototropism, selective excitation, phytochrome (chloroplast movement), Mougeotia

Abstract. A unicellular green alga Mougeotia responds to incident light according to its direction as can be observed in its chloroplast orientation. A cylindrical cell of Mougeotia detects the direction by the azimuthal distribution of excited photoreceptor molecules which are localized near the cell membrane. In this study, we calculate the distributions of the excited molecules using nine models which arise from the combinations of three possible orientations of the photoreceptor molecules and three possible conditions of incident light. It is found that the distribution of the excited molecules depends on the shape of the cell. The mechanical measurement of the chloroplast rotation can clarify the calculated distribution.