Dichroism in spinach chloroplasts

Abstract

In spinach chloroplasts oriented at steel-water interfaces parallel to the light beam a distinct dichroism is measured at about 680 nm. This dichroism is minimal upon addition of sucrose up to a final concentration of 0.18 M to the medium, the dichroic ratio amounting to 1.02. It is concluded that predominantly the Ca 680 chlorophyll type is oriented to an extent of about 2% in the plane of the chloroplast lamellae.

No indication could be obtained that the Ca 680 molecules occur at an angle other than 0° or 90° to the surface of the quantasome subunits. For reasons mentioned in DISCUSSION, it is suggested that a tangential arrangement of these molecules at the subunit surfaces seems to be more likely than a radial one. Based on the present experiments as well as on data from the literature a hypothetical model for the arrangement of the photosynthetic pigments in the quantasome is given.