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Fig. 2. Time course of cortical MT array reorganisation in polarised zygotes. (A-H) Polarisation, germination and mitosis entry in the same zygote. Light direction is from the left. (A-E) All sections are projected to reflect the shape of the zygote. (A) 17 hours (B) 19 hours, (C) 21 hours and (D) 23 hours AF showing progressive localisation of cortical MTs towards the rhizoid pole (projection of all sections). (E) 26 hours AF (projection of all sections). The rhizoid has germinated and long cortical MTs are absent in the zygotes with a prophase spindle but bright tubulin structures remain at the rhizoid collar. (F-H) Different areas of the same 26-hour-old zygote showing that tubulin structures at the collar start at the cortex and go deep inside the cytoplasm: (F) Cortical area through the upper 10 µm of the same zygote. Bright tubulin structures are localised as a collar around the rhizoid subapex. (G) Cytoplasmic area (11-22 µm) and (H) nuclear area (32-37 µm) with the prophase spindle. (I-N) MT reorganisation during rhizoid elongation (projection of all sections). (I) 17 hours AF with cortical MTs localised to the rhizoid hemisphere. (J,K,L) 19, 22 and 24 hours AF showing rhizoid emergence and the parallel arrangement of MTs to the rhizoid axis. (M,N) 25 and 27 hours AF: MTs depolymerise from the rhizoid tip to bright cortical star-shaped structures located at the collar. (O-Q) Projection of all sections during rhizoid germination and growth. (O) 16 hours AF showing convergence of MTs towards the site of rhizoid emergence. (P) 20 hours AF: MT bundles form a crescent at the periphery of the growing rhizoid. (Q) 27 hours AF showing disappearance of MTs from the rhizoid apex and MT bundles parallel to the growth axis extending from the rhizoid collar to a region below the apex. (R-U) Cortical network disappearance during mitosis and reformation after mitosis (projection of all sections). In this zygote rhizoid germination occurred downwards out of the horizontal scanning plane but on the right side of the zygote. (R) 16-hour-old zygote. Cortical MTs are more localised to the rhizoid hemisphere and the nuclear envelope is labelled. (S) 20 hours AF. Cortical MTs are more focused to the rhizoid and all cortical MTs are shortening. (T) Aster nucleation begins 26 hours AF showing mitosis entry. Both asters are detected in the cell centre. Only cortical star-shaped structures remain at the cortex (arrows). (U) 38-hour-old zygote showing reformation of the cortical network, particularly at the rhizoid pole. Bar, 15 µm.
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