Life cycle of Vaucheria (yellow-green alga)
Xanthophyceae (Yellow-green algae) occur mostly in fresh water, especially at the surface or as epiphytes. Only few species are found as plankton in sea water. Some species live as aerophytes in humid places, on branches or in between mosses, or with other algae in the soil.
The chromatoplasts are green-yellow, but not truly yellow. Assimilation products are oil and chrysolaminarine. The cell wall consists often of two parts that contain pectin-compounds. Cyste formation is clearly accompanied by silicification of the cell wall. The motile stages are heterokont (with two different flagellae).
Vaucheria shows oögamy; the antheridium is formed at the end of a short protuberance of a multi-nuclear cell that is seperated by a cell wall. In the immediate vicinity later an oögonium develops in a similar way. The size of the protuberance is species-dependent: for example in
Vaucheria sessilis, like shown here below in the drawing, the buldge of the oögonium is shorter than that of the antheridium. When the apical part of the cell wall of the antheridium becomes slimy antherozoïdes are released. They penetrate into the oögoniumn, in which also part of the cell wall is degraded. The oospore arises after fusion of the cytoplasm and the nuclei of the oosphere. After meiosis, the oospore grows to form a siphonous filament.
| Life cycle of Vaucheria |
 |
| Various stages of the life cycle of Vaucheria sessilis
|
 |
| Siphonous filament of Vaucheria with protruding antheridium and oogonium in een stained slide |
 |
| Red-green anaglyph stereo projection of above slide reconstructed from optical sections acquired with a confocal laser scanning microscope (red-green glasses required |
