Organelle found within the chloroplasts of algae and hornworts
Not to be confused with pyrena, a nutlet within a drupaceous fruit.
Cross section of a Chlamydomonas reinhardtii algae cell, a 3D representation
Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae,[1] and in a single group of land plants, the hornworts.[2] Pyrenoids are associated with the operation of a carbon-concentrating mechanism (CCM). Their main function is to act as centres of carbon dioxide (CO2) fixation, by generating and maintaining a CO2 rich environment around the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Pyrenoids therefore seem to have a role analogous to that of carboxysomes in cyanobacteria.
Algae are restricted to aqueous environments, even in aquatic habitats, and this has implications for their ability to access CO2 for photosynthesis. CO2 diffuses 10,000 times slower in water than in air, and is also slow to equilibrate. The result of this is that water, as a medium, is often easily depleted of CO2 and is slow to gain CO2 from the air. Finally, CO2 equilibrates with bicarbonate (HCO3−) when dissolved in water, and does so on a pH-dependent basis. In sea water for example, the pH is such that dissolved inorganic carbon (DIC) is mainly found in the form of HCO3−. The net result of this is a low concentration of free CO2 that is barely sufficient for an algal RuBisCO to run at a quarter of its maximum velocity, and thus, CO2 availability may sometimes represent a major limitation of algal photosynthesis.
^Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. Annu. Rev. Plant Biol., 56, 99-131. PMID 15862091
^Villarreal, J. C., & Renner, S. S. (2012) Hornwort pyrenoids, carbon-concentrating structures, evolved and were lost at least five times during the last 100 million years. Proceedings of the National Academy of Sciences,109(46), 1873-1887. PMID 23115334
Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae, and in a single group of land plants, the hornworts. Pyrenoids are...
Starch can also accumulate around the pyrenoids when CO2 is scarce. Pyrenoids can divide to form new pyrenoids, or be produced "de novo". Thylakoids (sometimes...
cup-shaped chloroplast, which has a single large pyrenoid where starch is formed from photosynthetic products. Pyrenoid with starch sheath is present in the posterior...
proteins and sends them out of the cell Cell wall; outer membrane of the cell Pyrenoid; center of carbon fixation Chromatophore; pigment carrying membrane structure...
intensely-colored green chloroplast, their flagellated cell bodies, the presence of a pyrenoid within the chloroplast, and a scale-produced thecal-wall. Species within...
of the monoplastidic species, a cellular structure called a pyrenoid is absent. The pyrenoid, which is both a food storing organ and enables a more efficient...
reticulate, cup-shaped, spiral, or ribbon shaped. They have one or more pyrenoids to preserve protein and starch. The latter chlorophyll type is not known...
worldwide. The species name pyrenoidosa refers to the presence of a prominent pyrenoid within the Chlorella chloroplast. Auxenochlorella pyrenoidosa has been...
accumulate within the cell from where they diffuse into the carboxysomes. Pyrenoids in algae and hornworts also act to concentrate CO2 around RuBisCO. The...
of RuBisCO is densely packed into a single subcellular compartment: the pyrenoid. Carbon dioxide is concentrated in this compartment using a combination...
the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may...
hydroxyproline-rich glycoproteins, a large cup-shaped chloroplast, a large pyrenoid, and an eyespot apparatus that senses light. Chlamydomonas species are...
protection techniques for shipping and storage include the application of pyrenoids[citation needed], as well as hermetic storage in sealed bags or containers...
nucleus, a single parietal chloroplast and a single pyrenoid lacking a starch sheath (or no pyrenoid at all). Reproduction occurs asexually by autospores...
cell has a single girdle-like and parietal chloroplast and two to many pyrenoids are present in each chloroplast. Reproduction in Ulothrix takes place...
and traditionally has been distinguished mainly through the absence of a pyrenoid. Species of Chloromonas occupy a variety of habitats, including soil, temporary...
including C4 carbon fixation, crassulacean acid metabolism, and the use of pyrenoid. Rubisco side activities can lead to useless or inhibitory by-products...
single chloroplast which contains a central pyrenoid surrounded by grains of starch, as well as another pyrenoid (called the pseudopyrenoid) near the edge...
length and has a single cup-like chloroplast that often contains a central pyrenoid. The chloroplast can hold large amounts of β-carotene, which makes it appear...
base, an eyespot, and a large cup-shaped chloroplast with at least one pyrenoid. The colonies co-ordinate their flagellar movement to create a rolling...
Cells have one nucleus and a single parietal chloroplast with a single pyrenoid. Reproduction in Sphaerocystis occurs by the formation of autospores or...
single chloroplast is present, filling nearly the entire cell; it lacks a pyrenoid. It is commonly used as a bioindicator species to assess the levels of...
become visible as slimy green mats. Spirogyra has a cell wall, nucleus, pyrenoid, and spiral chloroplasts. Spirogyra can reproduce both sexually and asexually...
containing chloroplasts composed of thylakoids present in clusters of three. A pyrenoid protrudes from each chloroplast and is encased along with the chloroplast...
there is a large thick central piece containing a single large pyrenoid. From the pyrenoid, there are many irregularly arranged lobes that branch out to...
the filament. Cells may have either a pyrenoid (transparent structure) in each of its lobes or a single pyrenoid in the middle of the cell. The nucleus...
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