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Tissue culture cells of Streptanthus tortuosus (Kell.) var. orbiculatus (Greene) Hall (Cruciferae), having a viruslike particle in their nucleoli, the STV cell line, contain "supergranal" chloroplasts. Freeze-fracture studies of chloroplasts of a control cell line, which lacks the viruslike particles, reveal two complementary faces similar to those observed in spinach chloroplasts. Replicas of freeze-fractured STV supergranal chloroplasts, however, show that one membrane face (B) contains widely spaced 80 A particles and the other face (C) is essentially smooth. Isolated STV supergranal chloroplasts lack photosystem II activity as indicated by their inability to reduce dichlorophenolindophenol and are unable to reduce NADP with electrons from photosystem II or from ascorbate-reduced dichlorophenolindophenol. However, partial photosystem I activity is indicated by the reduction of methyl viologen with electrons from dichlorophenolindophenol-ascorbate. This supports the concept that there is not a direct correspondence between grana formation and photosystem II activity. Electrophoresis shows that all of the major polypeptide bands present in the STV supergranal chloroplasts are also present in the control chloroplast membranes. One band, molecular weight 33,000, is present in a greatly increased amount in the STV supergranal chloroplast membranes and may be associated with grana stacking.

Photosynthetic Activity and Membrane Polypeptide Composition of Supergranal Chloroplasts from Plant Tissue Cultures Containing a Viruslike Particle