Plastid

Plastids ( from Ancient Greek πλαστός plastos "formed" ) are cell organelles of plants and algae that have emerged from endosymbiontisch living cells. You will be required, among others, for photosynthesis and have a private annular genome ( plastome or plastid genome) and their own ribosomes ( Plastoribosomen ). More plastid components are available for the plastid replication, transcription and translation. A distinction is made between simple plastids, which are due to a primary Endosymbioseereignis and are surrounded by two envelope membranes, as well as complex plastids arose through secondary or tertiary endosymbiosis and have so three or four envelope membranes.

The simple plastids of Glaucocystophyceen, red algae, green algae ( Chlorophyta ) and terrestrial plants ( Embryophyta ) probably come from a primary endosymbiosis and are monophyletic, that is, the three groups of algae and land plants ( Embryophyta ) originate from a common unicellular ancestor, whose descendants in three evolutionary lineages segregating. The plastids of Glaucocystophyceen be called cyanelles, use as light -harvesting phycobilisomes and are still surrounded by a rest of a bacterial cell wall. The plastids of red algae called rhodoplasts also contain phycobilisomes, but no bacterial cell wall more. The chloroplasts of green algae and higher plants no longer form phycobilisomes contain chlorophyll b and form starch in the plastids.

In vascular plants, a distinction alongside the term chloroplasts, which is a part of the evolutionary line and one for the photosynthetically active plastids, between: Gerontoplasten and etioplasts as developments in the chloroplasts, chromoplasts and the leucoplasts ( amyloplasts, elaioplasts and Proteinoplasten ). You can develop from the proplastids.

The remaining algae from the evolutionary lineages of Stramenopilen, Haptophyta, Cryptophyceae, Chlorarachniophyta and Euglenozoa form complex plastids. The host cells are not related to those of the Plantae ( red algae, green algae, so-called higher plants and presumably also Glaucocystophyceen ), but their plastids, which originate most likely from secondary endosymbiosis. The photosynthetically active representatives of Euglenozoa ( = Euglenida ) and the Chlorarachniophyta received their plastids by recording a green alga, that contain complex chloroplasts, all the rest are due to red algae, so complex rhodoplasts. In dinoflagellates the possibilities of secondary endosymbiosis events endosymbioses find with red algae, haptophyte tertiary endosymbiosis with and cryptophyceae to unstable Kleptoplastiden that are digested again. Since the 1990s it has plastidenähnliche cell organelles found in various protozoa, the Apicomplexa. About the " Apikoplasten " said cellular constituents have about the malaria parasites of the genus Plasmodium. According to current knowledge, these are complex rhodoplasts. Come in a cell several plastids are present, they are usually connected to each other via Stromuli.

Division

For a long time it was unknown how plastids divide and change shape. Today we know that bacteria have a cytoskeleton, whose proteins are evolutionary precursors of the eukaryotic cytoskeleton. Experiments on the moss Physcomitrella patens (including with knockout mosses ) it is known that the FtsZ proteins, tubulin homologs are involved not only in the chloroplast division, but can also form a complex network in the plastids. They fulfill similar functions as the cytoskeleton in the cytoplasm.