SUMMARYExamination of chloroplasts from chinese cabbage leaves infected with turnip yellow mosaic virus (TYMV), using freeze-fracture techniques revealed, that the small peripheral vesicles induced by infection were present in clusters near the surface of the chloroplast, often being arranged in arrays that approximate to hexagonal. The small peripheral vesicles were flask shaped with their necks pointing to the chloroplast surface. The structure of the necks, which were only about I5 to 22 nm in diam., suggested but did not prove that they were open to the cytoplasmic space.The inner membrane of the peripheral vesicles is distinguished from other chloroplast membranes in showing no particles on either the A or the B fracture faces.In the regions where the peripheral vesicles were clustered, the number and kind of particles seen on the chloroplast membrane faces were changed compared with healthy chloroplasts or the non-vesicle bearing areas of chloroplasts from infected cells. In particular, the B face of the outer chloroplast membrane in the vesiclebearing regions had a reduced number of particles 1o nm in diam., but in" addition to these contained large numbers of particles about 5 nm in diam.In the chloroplasts of both healthy and infected tissue we frequently observed protuberances of the stroma corresponding to the mobile phase of chloroplasts postulated from light microscopic observations.
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