Fluorescence depolarization study of randomly oriented and magneto-oriented spinach chloroplasts in suspension

The degree of polarization of fluorescence (P) of chlorophyll a in vivo has been measured using suspensions of either randomly oriented or magnetically oriented spinach chloroplasts. In the latter case the viewing direction was perpendicular to the plane of the oriented photosynthetic membranes. P decreases from 3.5% (unoriented) to 1.5% when the chloroplasts are oriented in a 13 Kgauss magnetic field. This decrease can be explained by the anisotropic optical properties of the membranes. The residual 1.5% polarization is shown to reflect the depolarization by energy transfer. Similar effects have been observed with Chlorella.