Three‐dimensional organization of flagellar basal apparatus in Ectocarpus gametes

The flagellar basal apparatus of the brown alga Ectocarpus siliculosus was re‐investigated in details using transmission electron microscopy and electron tomography. As a result, three‐dimensional structures with spatial arrangement of bands and microtubular flagellar rootlets were observed. Fibrous structures linking the anterior flagellar basal body to the major anterior rootlet (R3) or the bypassing rootlet was newly discovered in this study. A direct attachment from the minor anterior rootlet (R4) to the anterior and posterior basal bodies was also discovered, as were attachments from the minor posterior rootlet (R1) to the deltoid striated band and from the major posterior rootlet (R2) to the posterior fibrous band. The microtubular flagellar rootlets were connected to the bands and to the anterior or posterior basal body. These bands may have a role in maintaining the spatial arrangement of the anterior and posterior flagellar basal bodies and the microtubular flagellar rootlets. A numbering system of the basal body triplets was established by tracing axonemal doublets in the serial sections. From these observations, the precise position of two flagellar basal bodies, bands, and flagellar rootlets was determined.