Editing Pyrenoid (section)

==Discovery==

Pyrenoids were first described in 1803 by [[Jean Pierre Étienne Vaucher|Vaucher]]<ref>{{cite book|author=Vaucher, J.-P.|year=1803|title=Histoire des conferves d'eau douce, contenant leurs différens modes de reproduction, et la description de leurs principales espèces, suivie de l'histoire des trémelles et des ulves d'eau douce|publisher=J. J. Paschoud|location=Geneva|url=https://www.biodiversitylibrary.org/item/43432#page/9/mode/1up}}</ref> (cited in Brown et al.<ref>Brown, R.M., Arnott, H.J., Bisalputra, T., and Hoffman, L.R. (1967). The pyrenoid: Its structure, distribution, and function. Journal of Phycology, 3(Suppl. 1), 5-7.</ref>). The term was first coined by Schmitz<ref>Schmitz, F. (1882). Die Chromatophoren der Algen. Vergleichende untersuchungen über Bau und Entwicklung der Chlorophyllkörper und der analogen Farbstoffkörper der Algen. M. Cohen & Sohn (F. Cohen), Bonn, Germany.</ref> who also observed how algal chloroplasts formed de novo during cell division, leading [[Andreas Franz Wilhelm Schimper|Schimper]] to propose that chloroplasts were autonomous, and to surmise that all green plants had originated through the “unification of a colourless organism with one uniformly tinged with chlorophyll".<ref>Schimper, A.F.W. (1883). Über die Entwicklung der Chlorophyllkörner und Farbkörper. Botanische Zeitung , 41, 105-120, 126-131, 137-160.</ref> From these pioneering observations, [[Konstantin Mereschkowski|Mereschkowski]] eventually proposed, in the early 20th century, the [[endosymbiotic theory|symbiogenetic theory]] and the genetic independence of chloroplasts.

In the following half-century, [[phycology|phycologists]] often used the pyrenoid as a taxonomic marker, but physiologists long failed to appreciate the importance of pyrenoids in aquatic photosynthesis. The classical paradigm, which prevailed until the early 1980s, was that the pyrenoid was the site of starch synthesis.<ref>Griffiths, D.J. (1980). The pyrenoid and its role in algal metabolism. Science Progress, 66, 537-553.</ref> Microscopic observations were easily misleading as a starch sheath often encloses pyrenoids. The discovery of pyrenoid deficient mutants with normal starch grains in the green alga ''Chlamydomonas reinhardtii'',<ref>Goodenough, U.W. and Levine, R.P. (1970). Chloroplast structure and function in AC-20, a mutant strain of ''Chlamydomonas reinhardtii''. III. Chloroplast ribosomes and membrane organization. J Cell Biol , 44, 547-562.</ref> as well as starchless mutants with perfectly formed pyrenoids,<ref>Villarejo, A., Plumed, M., and Ramazanov, Z. (1996). The induction of the CO<sub>2</sub> concentrating mechanism in a starch-less mutant of ''Chlamydomonas reinhardtii''. Physiol Plant, 98, 798-802.</ref> eventually discredited this hypothesis.

It was not before the early 1970s that the proteinaceous nature of the pyrenoid was elucidated, when pyrenoids were successfully isolated from a green alga,<ref name = bazinga>Holdsworth, R.H. (1971). The isolation and partial characterization of the pyrenoid protein of ''Eremosphaera viridis''. ''J Cell Biol'', 51, 499-513.</ref> and showed that up to 90% of it was composed of biochemically active RuBisCO. In the following decade, more and more evidence emerged that algae were capable of accumulating intracellular pools of DIC, and converting these to CO<sub>2</sub>, in concentrations far exceeding that of the surrounding medium. Badger and Price first suggested the function of the pyrenoid to be analogous to that of the carboxysome in cyanobacteria, in being associated with CCM activity.<ref>Badger, M. R., & Price, G. D. (1992). The CO<sub>2</sub> concentrating mechanism in cyanobacteria and microalgae. Physiologia Plantarum, 84(4), 606-615.</ref> CCM activity in algal and cyanobacterial photobionts of lichen associations was also identified using gas exchange and [[Biological carbon fixation#Carbon isotope discrimination|carbon isotope discrimination]]<ref>Máguas, C., Griffiths, H., Ehleringer, J., & Serodio, J. (1993). Characterization of photobiont associations in lichens using carbon isotope discrimination techniques. Stable Isotopes and Plant Carbon-Water Relations, 201-212.</ref> and associated with the pyrenoid by Palmqvist<ref>Palmqvist, K. (1993). Photosynthetic CO<sub>2</sub>-use efficiency in lichens and their isolated photobionts: the possible role of a CO<sub>2</sub>-concentrating mechanism. ''Planta'', 191(1), 48-56.</ref> and Badger et al.<ref>Badger, M. R., Pfanz, H., Büdel, B., Heber, U., & Lange, O. L. (1993). Evidence for the functioning of photosynthetic CO<sub>2</sub>-concentrating mechanisms in lichens containing green algal and cyanobacterial photobionts. ''Planta'',191(1), 57-70.</ref> The Hornwort CCM was later characterized by Smith and Griffiths.<ref>Smith, E. C., & Griffiths, H. (1996). A pyrenoid-based carbon-concentrating mechanism is present in terrestrial bryophytes of the class Anthocerotae. ''Planta'', 200(2), 203-212.</ref>

From there on, the pyrenoid was studied in the wider context of carbon acquisition in algae, but has yet to be given a precise molecular definition.

[[File:Scenedesmus quadricauda close up DIC Image-1.tif|thumb|300px|right|Differential interference contrast micrograph of ''Scenedesmus quadricauda'' with the pyrenoid (central four circular structures) clearly visible.]]