Characterization of a photosynthetic mutant of Lemna lacking the cytochrome b₆-f complex

A photosynthetic mutant of Lemna perpusilla (no. 1073) has been examined by spectrophotometric and immunoblotting techniques in order to localize the site of defect. In contrast to previous conclusions (Shahak, Y., Posner, H.B. and Avron, M. (1976) Plant Physiol. 57, 577-679), neither cytochrome f nor cytochrome b₆ could be detected spectrophotometrically in the mutant. Furthermore, immunoblotting using antibodies specific for each of the four constituent subunits of the cytochrome b₆-f complex demonstrate that the entire complex is absent in the mutant. The light-harvesting chlorophyll-protein complex of Photosystem II is present in similar amounts in wild-type and mutant Lemna. However, the total amount of plastoquinone-9 is reduced by approx. 65% in the mutant strain, while the photoreducible plastoquinone-9 pool is comparable in wild-type and mutant Lemna.