Diatom Reproduction

The ability to reproduce sexually is closely associated with cell size. It is the most prevalent method of restoring cell size, and is often triggered when the size of a cell is less than a critical level (usually smaller than half of the original size for most species). The process of sexual reproduction is different for centric and pennate diatoms.

Sexual reproduction is oogamous in centric diatoms. A male gametangial cell first undergoes a series of differentiated divisions to form a limited number (usually four) microspores, or sperm mother cells. The microspores then undergo meiosis to form flagellated sperm. Oogonial female cells produce one or two eggs; the resulting female protoplast facilitates sperm entry by one of many mechanisms depending on the species. Fertilization forms a zygote which enlarges by water uptake to form an auxospore. The auxospore is often spherical in shape and with different valve morphology than a normal valve. Division of the auxospore produces cells of the maximum size for that species. Sexual reproduction is isogamous in pennate diatoms. Gametangial cells pair up and undergo meiosis. Only one or two nuclei of the meiotic tetrad is sexually functional. The gametes are amoeboid and their emergence from their respective frustles is associated with the production of mucilage which embeds the copulating cells. The gametes conjugate to produce one or two auxospores per pair of parents (depending on the species). As in centric, diatoms the auxospore divides to produce cells of restored size.