Figures 15–23 in Cell structure and microtubule organisation during gametogenesis of Ulva mutabilis Føyn (Chlorophyta)

Figures 15–23: Transmission electron micrographs of developing gametangia and complete gametes of Ulva mUtabilis. (15) Metaphase nucleus of developing gametangium. The nuclear envelope (NE) is still intact with gaps only at poles (arrows). Spindle microtubules (MT) traverse the nucleoplasm, but do not radiate out of the centrosome (C), which is attached to the external membrane. Scale bar: 0.5 µm. (16) Developing gametangium, in which first nuclear division is completed. Note that furrowing membranes (arrow) are growing between daughter nuclei (N). Scale bar: 2.6 µm. (17) Advanced stage of gamete formation, showing the furrowing membrane (arrow) development separating two daughter nuclei (N). The centrosome-like structures (C) are not connected to the nuclei, but to the external membrane. Scale bar: 0.7 µm. (18) Developing furrowing membranes and vesicles (probably of dictyosome origin, see white arrow). Note increased number of active dictyosomes (D) and membranes of ER close to developing furrow. Scale bar: 0.8 µm. (19) Fully developed gametangium before gamete release. Gametes are still connected to each other by thin cytoplasmic bridges (arrows). Scale bar: 3 µm. (20) Part of fully developed gamete at high magnification. Basal bodies (BB) of flagella are visible close to surrounding membrane. Scale bar: 0.3 µm. (21) Longitudinal section of gamete, showing nucleus, chloroplast with a pyrenoid (P) and starch grains (S) and one of the two flagella. Note that gamete is still connected to neighbouring gametes (arrows). Scale bar: 1 µm. (22 and 23) Detail of cytoplasmic bridges connecting neighbouring gametes. Note the dark-stained borders of cytoplasmic bridge and microtubules close to membrane. Scale bars: 0.5 and 0.1 µm.