Figure 4. 3D cellular architecture at the rim of the chloroplast cup.
(A) A slice from a tomographic volume and (B) corresponding 3D segmentation showing thylakoid membranes (dark green) and lumina (light green), the chloroplast envelope (blue), a starch granule (tan), and plastoglobules (purple, arrow in A). The rim of the chloroplast lobe is in close proximity to the cell wall (cw). (C–E) Three sequential slices from the same tomogram showing the thylakoid tip convergence zone at the chloroplast rim. Small vesicles (arrows in C) can be seen between the thylakoid tips and the chloroplast envelope, which loses definition in several locations (loss of intermembrane space in C–E). The arrow in D points to a circular structure in the membrane that could be a protein complex or just a single membrane bilayer. (F) In the corresponding 3D segmentation (which has been flipped 180° from B and tilted to face the chloroplast rim), the chloroplast envelope has been removed to reveal the interconnections between the thylakoid tips at the convergence zone. The tomogram was 2× binned. Unbinned pixel size: 5.7 Å. Segmented tomogram thickness: 126 nm. Scale bars: 100 nm. Figure accompanied by Video 3.