C4 carbon fixation - wikipedia C carbon fixation Kranz anatomy allows C carbon fixation. A : Mesophyll Cell B : Chloroplast C : Vascular Tissue D: Bundle Sheath Cell E : Stomate F : Vascular Tissue : provides continuous source of water 1 ) Carbon is fixed to produce oxaloacetate by PEP carboxylase. 2 ) The four carbon molecule then exits the cell and enters the chloroplasts of bundle sheath cells. 3 ) It is then broken down releasing carbon dioxide and producing pyruvate. Carbon dioxide combines with ribulose bisphosphate and proceeds to the Calvin Cycle. 4 ) Pyruvate re-enters the mesophyll cell. It then reacts with ATP to produce the beginning compound of the C4 cycle. C carbon fixation or the Hatch - Slack pathway is a photosynthetic process in some plants. It is the first step in extracting carbon from carbon dioxide to be able to use it in sugar and other biomolecules. It is one of three known processes for carbon fixation. The C in one of the names refers to the 4 - carbon molecule that is the first product of this type of carbon fixation. C fixation is an elaboration of the more common C carbon fixation and is believed to have evolved more recently. C overcomes the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in the process of photorespiration. This is achieved by ensuring that RuBisCO works in an environment where there is a lot of carbon dioxide and very little oxygen. CO is shuttled via malate or aspartate from mesophyll cells to bundle - sheath cells. In these bundle - sheath cells CO is released by decarboxylation of the malate. C4 plants use PEP carboxylase to capture more CO in the mesophyll cells. PEP Carboxylase ( 3 carbons ) binds to CO to make oxaloacetic acid ( OAA ). The OAA then makes malate ( 4 carbons ). Malate enters bundle sheath cells and releases the CO. These additional steps, however, require more energy in the form of ATP. Using this extra energy, C plants are able to more efficiently fix carbon in drought, high temperatures, and limitations of nitrogen or CO. Since the more common C pathway does not require this extra energy, it is more efficient in the other conditions. The naming Hatch - Slack pathway is in honor of Marshall Davidson Hatch and C.R. Slack, who elucidated it in Australia in 1966. Contents 1 C pathway 2 C Kranz leaf anatomy 3 The evolution and advantages of the C pathway 4 Plants that use C carbon fixation 4.1 Converting C plants to C 5 See also 6 References 7 External links C pathway NADP - ME type C pathway NAD - ME type C pathway PEPCK type C pathway The first experiments indicating that some plants do not use C carbon fixation but instead produce malate and aspartate in the first step of carbon fixation were done in the 1950s and early 1960s by Hugo P. Kortschak and Yuri Karpilov. The C pathway was elucidated by Marshall Davidson Hatch and C.R. Slack, in Australia, in 1966 ; it is sometimes called the Hatch - Slack pathway. In C plants, the first step in the light - independent reactions of photosynthesis involves the fixation of CO by the enzyme RuBisCO into 3 - phosphoglycerate. However, due to the dual carboxylase and oxygenase activity of RuBisCo, some part of the substrate is oxidized rather than carboxylated, resulting in loss of substrate and consumption of energy, in what is known as photorespiration. In order to bypass the photorespiration pathway, C plants have developed a mechanism to efficiently deliver CO to the RuBisCO enzyme. They utilize their specific leaf anatomy where chloroplasts exist not only in the mesophyll cells in the outer part of their leaves but in the bundle sheath cells as well. Instead of direct fixation to RuBisCO in the Calvin cycle, CO is incorporated into a 4 - carbon organic acid, which has the ability to regenerate CO in the chloroplasts of the bundle sheath cells. Bundle sheath cells can then utilize this CO to generate carbohydrates by the conventional C pathway. The first step in the pathway is the conversion of pyruvate to phosphoenolpyruvate ( PEP ), by the enzyme pyruvate orthophosphate dikinase. This reaction requires inorganic phosphate and ATP plus pyruvate, producing phosphoenolpyruvate, AMP, and inorganic pyrophosphate ( PPi ). The next step is the fixation of CO into oxaloacetate by the enzyme PEP carboxylase. Both of these steps occur in the mesophyll cells : pyruvate + P + ATP → PEP + AMP + PP PEP + CO → oxaloacetate PEP carboxylase has a lower Km for HCO − 3 -- and, hence, higher affinity -- than RuBisCO. Furthermore, O is a very poor substrate for this enzyme. Thus, at relatively low concentrations of CO, most CO will be fixed by this pathway. The product is usually converted to malate, a simple organic compound, which is transported to the bundle - sheath cells surrounding a nearby vein. Here, it is decarboxylated to produce CO and pyruvate. The CO now enters the Calvin cycle and the pyruvate is transported back to the mesophyll cell. Since every CO molecule has to be fixed twice, first by 4 - carbon organic acid and second by RuBisCO, the C pathway uses more energy than the C pathway. The C pathway requires 18 molecules of ATP for the synthesis of one molecule of glucose, whereas the C pathway requires 30 molecules of ATP. This energy debt is more than paid for by avoiding losing more than half of photosynthetic carbon in photorespiration as occurs in some tropical plants, making it an adaptive mechanism for minimizing the loss. There are several variants of this pathway : The 4 - carbon acid transported from mesophyll cells may be malate, as above, or aspartate. The 3 - carbon acid transported back from bundle - sheath cells may be pyruvate, as above, or alanine. The enzyme that catalyses decarboxylation in bundle - sheath cells differs. In maize and sugarcane, the enzyme is NADP - malic enzyme ; in millet, it is NAD - malic enzyme ; and, in Panicum maximum, it is PEP carboxykinase. C kranz leaf anatomy Cross section of a maize leaf, a C plant. Kranz anatomy ( rings of cells ) shown. Drawing based on microscopic images courtesy of Cambridge University Plant Sciences Department. The C plants often possess a characteristic leaf anatomy called kranz anatomy, from the German word for wreath. Their vascular bundles are surrounded by two rings of cells ; the inner ring, called bundle sheath cells, contains starch - rich chloroplasts lacking grana, which differ from those in mesophyll cells present as the outer ring. Hence, the chloroplasts are called dimorphic. The primary function of kranz anatomy is to provide a site in which CO can be concentrated around RuBisCO, thereby avoiding photorespiration. In order to maintain a significantly higher CO concentration in the bundle sheath compared to the mesophyll, the boundary layer of the kranz has a low conductance to CO, a property that may be enhanced by the presence of suberin. Although most C plants exhibit kranz anatomy, there are, however, a few species that operate a limited C cycle without any distinct bundle sheath tissue. Suaeda aralocaspica, Bienertia cycloptera, Bienertia sinuspersici and Bienertia kavirense ( all chenopods ) are terrestrial plants that inhabit dry, salty depressions in the deserts of the Middle East. These plants have been shown to operate single - cell C CO-concentrating mechanisms, which are unique among the known C mechanisms. Although the cytology of both genera differs slightly, the basic principle is that fluid - filled vacuoles are employed to divide the cell into two separate areas. Carboxylation enzymes in the cytosol can, therefore, be kept separate from decarboxylase enzymes and RuBisCO in the chloroplasts, and a diffusive barrier can be established between the chloroplasts ( which contain RuBisCO ) and the cytosol. This enables a bundle - sheath - type area and a mesophyll - type area to be established within a single cell. Although this does allow a limited C cycle to operate, it is relatively inefficient, with the occurrence of much leakage of CO from around RuBisCO. There is also evidence for the exhibiting of inducible C photosynthesis by non-kranz aquatic macrophyte Hydrilla verticillata under warm conditions, although the mechanism by which CO leakage from around RuBisCO is minimised is currently uncertain. The evolution and advantages of the C pathway Further information : Evolutionary history of plants § Evolution of photosynthetic pathways C plants have a competitive advantage over plants possessing the more common C carbon fixation pathway under conditions of drought, high temperatures, and nitrogen or CO limitation. When grown in the same environment, at 30 ° C, C grasses lose approximately 833 molecules of water per CO molecule that is fixed, whereas C grasses lose only 277. This increased water use efficiency of C grasses means that soil moisture is conserved, allowing them to grow for longer in arid environments. C carbon fixation has evolved on up to 61 independent occasions in 19 different families of plants, making it a prime example of convergent evolution. This convergence may have been facilitated by the fact that many potential evolutionary pathways to a C phenotype exist, many of which involve initial evolutionary steps not directly related to photosynthesis. C plants arose around 35 million years ago during the Oligocene ( precisely when is difficult to determine ) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene Period. C metabolism originated when grasses migrated from the shady forest undercanopy to more open environments, where the high sunlight gave it an advantage over the C pathway. Drought was not necessary for its innovation ; rather, the increased resistance to water stress was a by - product of the pathway and allowed C plants to more readily colonise arid environments. Today, C plants represent about 5 % of Earth 's plant biomass and 3 % of its known plant species. Despite this scarcity, they account for about 23 % of terrestrial carbon fixation. Increasing the proportion of C plants on earth could assist biosequestration of CO and represent an important climate change avoidance strategy. Present - day C plants are concentrated in the tropics and subtropics ( below latitudes of 45 ° ) where the high air temperature contributes to higher possible levels of oxygenase activity by RuBisCO, which increases rates of photorespiration in C plants. Plants that use C carbon fixation Maize ( or corn ) is a common C4 plant. About 8,100 plant species use C carbon fixation, which represents about 3 % of all terrestrial species of plants. All these 8,100 species are angiosperms. C carbon fixation is less common in dicots than in monocots, with only 4.5 % of dicots using the C pathway, compared to 40 % of monocots. Despite this, only three families of monocots utilise C carbon fixation compared to 15 dicot families. Of the monocot clades containing C plants, the grass ( Poaceae ) species use the C photosynthetic pathway most. Forty - six percent of grasses are C and together account for 61 % of C species. These include the food crops maize, sugar cane, millet, and sorghum. Of the dicot clades containing C species, the order Caryophyllales contains the most species. Of the families in the Caryophyllales, the Chenopodiaceae use C carbon fixation the most, with 550 out of 1,400 species using it. About 250 of the 1000 species of the related Amaranthaceae also use C. Members of the sedge family Cyperaceae, and members of numerous families of Eudicots - including Asteraceae ( the daisy family ), Brassicaceae ( the cabbage family ), and Euphorbiaceae ( the spurge family ) - also use C. Trees which use C include Paulownia. Converting C plants to C Given the advantages of C, a group of scientists from institutions around the world are working on the C Rice Project to turn rice, a C plant, into a C plant by studying the C plants maize and Brachypodium. As rice is the world 's most important human food -- it is the staple food for more than half the planet -- having rice that is more efficient at converting sunlight into grain could have significant global benefits towards improving food security. The team claim C rice could produce up to 50 % more grain -- and be able to do it with less water and nutrients. The researchers have already identified genes needed for C photosynthesis in rice and are now looking towards developing a prototype C rice plant. In 2012, the Government of the United Kingdom along with the Bill & Melinda Gates Foundation provided $14 million over 3 years towards the C Rice Project at the International Rice Research Institute. See also C photosynthesis CAM photosynthesis C photosynthesis References Jump up ^ Slack, CR ; Hatch, MD ( 1967 ). `` Comparative studies on the activity of carboxylases and other enzymes in relation to the new pathway of photosynthetic carbon dioxide fixation in tropical grasses '' ( PDF ). The Biochemical Journal. 103 ( 3 ) : 660 -- 5. doi : 10.1042 / bj1030660. PMC 1270465. PMID 4292834. Retrieved 2010 - 04 - 08. Jump up ^ Nickell, Louis G. ( 1993 ). `` A tribute to Hugo P. Kortschak : The man, the scientist and the discoverer of C photosynthesis ''. Photosynthesis Research. 35 ( 2 ) : 201 -- 204. doi : 10.1007 / BF00014751. Jump up ^ Hatch, Marshall D. ( 2002 ). `` C ( 4 ) photosynthesis : Discovery and resolution ''. Photosynthesis Research. 73 ( 1 -- 3 ) : 251 -- 6. doi : 10.1023 / A : 1020471718805. PMID 16245128. 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PMID 12207654. Jump up ^ Akhani, Hossein ; Barroca, João ; Koteeva, Nuria ; Voznesenskaya, Elena ; Franceschi, Vincent ; Edwards, Gerald ; Ghaffari, Seyed Mahmood ; Ziegler, Hubert ( 2005 ). `` Bienertia sinuspersici ( Chenopodiaceae ) : A New Species from Southwest Asia and Discovery of a Third Terrestrial C Plant Without Kranz Anatomy ''. Systematic Botany. 30 ( 2 ) : 290 -- 301. doi : 10.1600 / 0363644054223684. Jump up ^ Akhani, H ; Chatrenoor, T ; Dehghani, M ; Khoshravesh, R ; Mahdavi, P. ; Matinzadeh, Z. ( 2012 ). `` A new species of Bienertia ( Chenopodiaceae ) from Iranian salt deserts : a third species of the genus and discovery of a fourth terrestrial C4 plant without Kranz anatomy ''. Plant Biosystems. 146 : 550 -- 559. doi : 10.1080 / 11263504.2012. 662921. Jump up ^ Holaday, A.S. ; Bowes, G. ( 1980 ). `` C Acid Metabolism and Dark CO Fixation in a Submersed Aquatic Macrophyte ( Hydrilla verticillata ) ''. 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( 2016 - 07 - 01 ). `` A portrait of the C4 photosynthetic family on the 50th anniversary of its discovery : species number, evolutionary lineages, and Hall of Fame ''. Journal of Experimental Botany. 67 ( 14 ) : 4039 -- 4056. doi : 10.1093 / jxb / erw156. ISSN 0022 - 0957. PMID 27053721. Jump up ^ Sage, Rowan ; Russell Monson ( 1999 ). `` 16 ''. C Plant Biology. pp. 551 -- 580. ISBN 0 - 12 - 614440 - 0. Jump up ^ Zhu XG, Long SP, Ort DR ( 2008 ). `` What is the maximum efficiency with which photosynthesis can convert solar energy into biomass ? ''. Current Opinion in Biotechnology. 19 ( 2 ) : 153 -- 159. doi : 10.1016 / j. copbio. 2008.02. 004. PMID 18374559. Jump up ^ Kadereit, G ; Borsch, T ; Weising, K ; Freitag, H ( 2003 ). `` Phylogeny of Amaranthaceae and Chenopodiaceae and the Evolution of C Photosynthesis ''. International Journal of Plant Sciences. 164 ( 6 ) : 959 -- 86. doi : 10.1086 / 378649. Jump up ^ Slewinski. `` Scarecrow Plays a Role in Establishing Kranz Anatomy in Maize Leaves ''. Jump up ^ Gilles van Kote ( 2012 - 01 - 24 ). `` Researchers aim to flick the high - carbon switch on rice ''. The Guardian. Retrieved 2012 - 11 - 10. Jump up ^ Von Caemmerer, S. ; Quick, W.P. ; Furbank, R.T. ( 2012 ). `` The Development of C4 Rice : Current Progress and Future Challenges ''. Science. 336 ( 6089 ) : 1671 -- 1672. Bibcode : 2012Sci... 336.1671 V. doi : 10.1126 / science. 1220177. PMID 22745421. Jump up ^ Hibberd, J.M. ; Sheehy, J.E. ; Langdale, J.A. ( 2008 ). `` Using C4 photosynthesis to increase the yield of rice -- rationale and feasibility ''. Current Opinion in Plant Biology. 11 ( 2 ) : 228 -- 231. doi : 10.1016 / j. pbi. 2007.11. 002. PMID 18203653. Jump up ^ Munawan Hasan ( 2012 - 11 - 06 ). `` C rice project gets financial boost ''. The News. Retrieved 2012 - 11 - 10. External links Khan Academy, video lecture Retrieved from `` https://en.wikipedia.org/w/index.php?title=C4_carbon_fixation&oldid=815720604 '' Categories : Photosynthesis Hidden categories : All articles with unsourced statements Articles with unsourced statements from July 2010 Talk Contents About Wikipedia Català Čeština Deutsch Español Esperanto Français Galego 한국어 עברית 日本 語 Norsk Polski Português Русский Slovenčina Suomi தமிழ் Türkçe Українська Tiếng Việt 中文 Edit links This page was last edited on 16 December 2017, at 17 : 49. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where does calvin cycle occur in c4 plants
Answer: bundle-sheath cells surrounding a nearby vein