Plastid

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Plastids (from ancient Greek πλαστός plastós "shaped") are the special cell organelles that occur in plants and algae and that have emerged from endosymbiotic cells and are used, among other things, for photosynthesis .

construction

A plastid has its own ring-shaped genome - this plastid genome is also called a plastome - and its own ribosomes , known as plastoribosomes , which are embedded in its basic plasmatic substance ( stroma ). In addition, there are other plastid-specific components for plastid replication , transcription and translation .

According to the membranes surrounding them, a distinction is made between simple plastids, which can be traced back to a primary endosymbiosis event and are surrounded by two envelope membranes, and complex plastids , which have arisen as a result of secondary or tertiary endosymbiosis and thus have three or four envelope membranes. If there are several plastids in a cell, they are usually connected to one another via stromules .

evolution

Relationships between types of plastids in vascular plants

The simple plastids of the glaucocystophyceae , red algae , green algae (Chlorophyta) and land plants (Embryophyta) probably originate from a primary endosymbiosis . They are monophyletic, i.e. H. the three groups of algae and the terrestrial plants (Embryophyta) descend from a common unicellular ancestor whose descendants split into three evolutionary lines:

  • The plastids of the glaucocystophyceae are called cyanelles (also cyanoplasts or muroplasts ), use phycobilisomes as light- harvesting complexes and are still surrounded by a remnant of a bacterial cell wall.
  • The plastids of red algae are called rhodoplasts and also contain phycobilisomes, but no longer a bacterial cell wall.
  • The chloroplasts of green algae and higher plants no longer form phycobilisomes, contain chlorophyll b and form starch in the plastids.
  • The plastids of brown algae are also called phaeoplasts .

The plastids of the amoeboid Paulinella chromatophora ( Euglyphida , see below), called chromatophores , are evidently primary chloroplasts. P. chromatophora evidently descends from an ancestor who independently and much later ingested a cyanobacterium of the genus Prochlorococcus (or Synechococcus ).

In the case of vascular plants , besides the (photosynthetically active) chloroplasts, a distinction is made between other types of plastids: the gerontoplasts and etioplasts as developments of the chloroplasts, as well as the chromoplasts and the leucoplasts , from which amyloplasts , elioplasts and proteinoplasts can arise. Proplastid is the name given to the precursor type from which the plastids can develop.

The remaining algae from the evolutionary lines of the Stramenopil , Haptophyta , Cryptophyceae , Chlorarachniophyta and Euglenozoa form complex plastids. The host cells are not related to the above-mentioned plantae (red algae, green algae, so-called higher plants and probably also glaucocystophyceae), but their plastids, which most likely originate from secondary endosymbiosis .

The photosynthetically active representatives of the Euglenozoa (= Euglenida) and the Chlorarachniophyta received their plastids by ingesting a green alga, i.e. they contain complex chloroplasts, all the rest are due to red algae, i.e. complex rhodoplasts. In dinoflagellates there are various endosymbiosis events from secondary endosymbioses with red algae, tertiary endosymbioses with haptophyceae and cryptophyceae to unstable kleptoplastids , which are digested again.

Since the 1990s, cell organelles similar to plastids have also been found in various protozoa , the apicomplexa . Malaria pathogens from the genus Plasmodium also have the cell components known as “apicoplasts” . According to the current state of knowledge, these are complex rhodoplasts .

division

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

literature

  • Patrick J. Keeling: The endosymbiotic origin, diversification and fate of plastids . In: Philosophical Transactions of the Royal Society B: Biological Sciences. Volume 365, No. 1541, 2010, pp. 729–748, PMID 20124341 , PDF (free full text access , English)

Web links

Commons : Plastids  - collection of images, videos and audio files
  • Wilfried Probst: Early Evolution and Symbiosis , Europa-Universität Flensburg, Institute for Biology and Science Education and its Didactics: §Plastiden, accessed on April 19, 2019

Individual evidence

  1. ↑ Takuro Nakayama, John M. Archibald: Evolving a photosynthetic organelle . In: BMC Biology . 10, No. 1, 2012, p. 35. doi : 10.1186 / 1741-7007-10-35 . PMID 22531210 . PMC 3337241 (free full text).
  2. ↑ ECM Nowack, H. Vogel, M. Groth, AR Grossman, M. Melkonian, G. Glöckner: Endosymbiotic Gene Transfer and Transcriptional Regulation of Transferred Genes in Paulinella chromatophora . In: Molecular Biology and Evolution . 28, No. 1, 2010, pp. 407-22. doi : 10.1093 / molbev / msq209 . PMID 20702568 .
  3. ^ Luis Delaye, Cecilio Valadez-Cano, Bernardo Pérez-Zamorano: How Really Ancient Is Paulinella Chromatophora? . In: PLoS Currents . 2016. doi : 10.1371 / currents.tol.e68a099364bb1a1e129a17b4e06b0c6b .
  4. ^ Purificación López-García, Laura Eme, David Moreira: Symbiosis in eukaryotic evolution . In: Journal of Theoretical Biology . 434, 2017, pp. 20–33. doi : 10.1016 / j.jtbi.2017.02.031 .
  5. ↑ Patricia Sánchez-Baracaldo, John A. Raven, Davide Pisani, Andrew H. Knoll: Early photosynthetic eukaryotes inhabited low-salinity habitats . In: Proceedings of the National Academy of Sciences . 114, No. 37, September 12, 2017, pp. E7737 – E7745. doi : 10.1073 / pnas.1620089114 .
  6. ↑ W Probst, European University Flensburg: § On the way to chloroplast formation
  7. ↑ René Strepp, Sirkka Scholz, Sven Kruse, Volker Speth, Ralf Reski : Plant nuclear gene knockout reveals a role in plastid division for the homolog of the bacterial cell division protein FtsZ, an ancestral tubulin. In: Proceedings of the National Academy of Sciences . Volume 95, 1998, pp. 4368-4373 (abstract) .
  8. ↑ Ralf Reski: Rings and networks: the amazing complexity of FtsZ in chloroplasts. In: Trends in Plant Science. Volume 7, 2002, pp. 103-105 (abstract) .
  9. ^ J. Kiessling, S. Kruse, SA Rensing, K. Harter, EL Decker, R. Reski: Visualization of a cytoskeleton-like FtsZ network in chloroplasts. In: Journal of Cell Biology . Volume 151, 2000, pp. 945-950 (abstract) .