Fig. 2: Localisation of the fertilisation tubule and eyespot in wild-type CC-125 (mt⁺) and mating type-reversed CC-3712 (mid mt^–) gametes.

The fertilisation tubule and nucleus were reacted with an anti-actin antibody (a, c) and DAPI (b, d), respectively. Spatial positioning of the fertilisation tubules and eyespots was visualised by FE-SEM (e–i). a, b Wild-type mt⁺ gamete. The fertilisation tubule was elongated from the cell apex. c, d CC-3712 gamete. The fertilisation tubule was extended from the cell apex. e Side view of the wild-type mt⁺ gamete. The fertilisation tubule was present on the side of the beat plane opposite the eyespot. f Top view of the wild-type mt⁺ gamete. The fertilisation tubule was situated on the intersection point of the two lateral ridges overlying the 1s and 2d roots. g Side view of the CC-3712 gamete. h Tilted image of g. The fertilisation tubule was present on the side of the beat plane opposite the eyespot. i Enlarged image of the cell anterior of a CC-3712 gamete. The fertilisation tubule was elongated from the flagellar base close to the #1 flagellum. Arrows and arrowheads indicate fertilisation tubules and eyespots, respectively. #1: no. 1 flagellum, #2: no. 2 flagellum, 1d, 1s, 2d and 2s: lateral ridges overlying 1d, 1s, 2d and 2s microtubular roots, respectively, N: nucleus.