Crassulacean acid metabolism 428874 225417458 2008-07-13T16:04:59Z 86.69.105.188 /* Biochemistry of Crassulacean Acid Metabolism */ <!--{{Expand|date=January 2007}}--> [[Image:Pineapple1.JPG|right|thumb|The [[Pineapple]] is a CAM plant]] '''Crassulacean acid metabolism''', also known as '''CAM photosynthesis''', is an elaborate [[carbon fixation]] pathway in some [[plant]]s. These plants fix carbon dioxide ({{co2}}) during the night, storing it as the four carbon acid malate. The {{co2}} is released during the day, where it is concentrated around the [[enzyme]] [[RuBisCO]], increasing the efficiency of photosynthesis. The CAM pathway allows stomata to remain shut during the day; therefore it is especially common in plants adapted to arid conditions. ==Historical background== CAM was first discovered in the late 1940s. It was observed by the botanists Ranson and Thomas, in the [[Crassulaceae]] family of succulents (which includes [[jade plant]]s and [[sedum]]s).<ref>{{cite journal |author=Ranson S. L. |coauthors=Thomas M |year=1960 |title=Crassulacean acid metabolism |journal=Annual Rev Plant Physiol |volume=11 |pages=81–110 |doi=10.1146/annurev.pp.11.060160.000501 }}</ref> Its name refers to acid metabolism in Crassulaceae, not the metabolism of Crassulacean acid. ==Overview of CAM: a two-part cycle== CAM is a mechanism whereby {{co2}} is concentrated around RuBisCO by day, while the enzyme is operating at peak capacity. This concentration of {{co2}} increases RuBisCO's efficiency, as it is prone to operate in the "reverse" direction via [[photorespiration]] - utilising oxygen to break down the reaction products the plant would rather it was producing. It differs from [[C4 carbon fixation|{{c4}} metabolism]], which ''spatially'' concentrates {{co2}} around RuBisCO. ===During the night=== CAM plants open their stomata during the cooler and more humid night-time hours, permitting the uptake of carbon dioxide with the minimum water loss. The carbon dioxide is converted to soluble molecules, which can be readily stored by the plant at a sensible concentration. The precise chemical pathway involves a three-carbon compound [[phosphoenolpyruvate]] (PEP), to which a {{co2}} molecule is added via carboxylation - forming a new molecule, [[oxaloacetate]]. This is then reduced, forming '''[[malate]]'''. Oxaloacetate and malate are built around a skeleton of four carbons - hence the term {{c4}}. Malate can be readily stored by the plant in vacuoles within individual cells. ===The next day...=== Malate can be broken down on demand, releasing a molecule of {{co2}} as it is converted to [[pyruvate]]. The pyruvate can be phosphorylated (i.e. have a phosphate group added by the "energy carrier" [[Adenosine triphosphate|ATP]]) to regenerate the PEP with which we started, ready to be spurred into action the next night. But it is the release of {{co2}} that makes the cycle worth the plant's while. It is directed to the [[stroma]] of [[chloroplasts]]: the sites at which photosynthesis is most active. There, it is provided to RuBisCO in great concentrations, increasing the efficiency of the molecule, and therefore producing more sugars per unit photosynthesis. ==The benefits of CAM== A great deal of energy is expended during CAM by the production and subsequent destruction of malate. This is in part countered by the increased efficiency of RuBisCO, but the more important benefit to the plant is the ability to leave leaf stomata closed during the day.{{Verify source|date=February 2008}} CAM plants are most common in {{wict|arid}} environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evapotranspiration, allowing CAM plants to grow in environments that would otherwise be far too dry. {{c3}} plants, for example, lose 97% of the water they uptake through the roots to transpiration<ref name=Raven2001>{{cite journal | author = Raven, J.A. | coauthors = Edwards, D. | year = 2001 | title = Roots: evolutionary origins and biogeochemical significance | journal = Journal of Experimental Botany | volume = 52 | issue = 90001 | pages = 381–401 | doi = 10.1093/jexbot/52.suppl_1.381 | doi_brokendate = 2008-06-20 }}</ref> - a high cost avoided by CAM plants. ==Comparison with {{c4}} metabolism== [[Image:Crassula_Ovata.jpg|thumb|CAM is named after the family Crassulaceae, to which [[Jade plant]] belongs]] The [[C4 carbon fixation|{{c4}} pathway]] bears resemblance to CAM; both act to concentrate {{co2}} around RuBisCO, thereby increasing its efficiency. CAM concentrates it in time, providing {{co2}} during the day, and not at night, when respiration is the dominant reaction.{{Verify source|date=February 2008}} {{c4}} plants, on the contrary, concentrate {{co2}} spatially, with a RuBisCO reaction centre in a "[[bundle sheath]] cell" being inundated with {{co2}}. ==How to spot a CAM plant== CAM can be considered an adaptation to arid conditions. CAM plants often display other [[xerophytic]] characters, such as thick, reduced leaves with a low [[surface area|surface-area]]-to-volume ratio; thick [[cuticle]]; and [[stomata]] sunken into pits. Some shed their leaves during the dry season; others (the succulents{{Verify source|date=February 2008}}) <!--[[cacti]], [[orchids]], and [[bromeliads]]--> store water in [[vacuole]]s. CAM plants are not only good at retaining water, but use nitrogen very efficiently.{{Fact|date=February 2008}} However, due to their stomata being closed by day, they are less efficient at {{co2}} absorption. This limits the amount of carbon they have available for growth. CAM plants can also be recognised as plants which have sour tasting leaves increasing during nights but sweet tasting leaves increasing during days. This is due to the malic acid being stored in the vacuoles of the plant cells during the night, and its being used up during the day<ref>Raven, P & Evert, R & Eichhorn, S, 2005, "Biology of Plants" (seventh edition), pp. 135 (Figure 7-26), W.H. Freeman and Company Publishers</ref>. ==Biochemistry of Crassulacean Acid Metabolism== [[Image:CAM.png|left|thumb|350px|Biochemistry of CAM]] Plants with Crassulacean Acid Metabolism (CAM plants) must control storage of [[carbon dioxide]] and its reduction to branched [[carbohydrates]] in space and time. At low temperatures (frequently at night), when CAM plants open their [[guard cells]], carbon dioxide molecules diffuse into the spongy [[mesophyll]]'s intracellular spaces and finally get into the [[cytoplasm]]. Here, they can meet [[phosphoenolpyruvate]] (PEP), which is a phosphorylated triosephosphate. During this time, CAM plants are synthesizing a protein called PEP carboxylase [[kinase]] (PEP-C kinase), which expression can be inhibited by high temperatures (frequently at daylight) and the presence of malate. PEP-C kinase phosphorylates its target enzyme PEP carboxylase (PEP-C). [[Phosphorylation]] dramatically enhanced the enzyme‘s capability to catalyze the formation of [[oxalacetate]] that can be subsequently transformed into [[malate]] by NAD malate dehydrogenase. Malate is then transported via malate shuttles into the vacuole, where it is converted into the storage form [[malic acid]]. In contrast to PEP-C kinase, PEP-C is synthesized all the time but almost inhibited at daylight either by dephosphorylation via PEP-C phosphatase or directly by binding malate. The latter is not possible at low temperatures, since malate is efficiently transported into the vacuole whereas PEP-C kinase readily inverts [[dephosphorylation]]. At daylight, CAM plants close their guard cells and discharged malate that is subsequently transported into [[chloroplast]]s. There, depending on plant species, it is cleaved into pyruvate and carbon dioxide either by malic enzyme or PEP carboxykinase. Carbon dioxide is then introduced into the [[Calvin cycle]], a coupled and self-recovering enzyme system, which is used to build branched carbohydrates. The by-product [[pyruvate]] can be further degraded in the mitochondrial [[citric acid cycle]] and therefore, provides additional carbon dioxide molecules for the calvin cycle. Alternatively, pyruvate can be also used to recover PEP via pyruvate phosphate dikinase, a high energy step, which requires [[Adenosine triphosphate|ATP]] and an additional [[phosphate]]. In the following cold night, PEP is finally exported into the cytoplasm, where it is involved in fixing carbon dioxide via malate. ==Ecological and Taxonomic Distribution of CAM Plants== The majority of plants possessing Crassulacean Acid Metabolism are either epiphytes (e.g. orchids, bromeliads) or succulent xerophytes (e.g. cacti, cactoid ''Euphorbia''s), but it is also found in hemiepiphytes (e.g. ''Clusia''), lithophytes (e.g. ''Sedum'', ''Sempervivum''), terrestrial bromeliads, hydrophytes (e.g. ''Isoetes'', ''Crassula'' (''Tillaea''), and from a halophyte (''Mesembryanthemum crystallinum''), a non-succulent terrestrial plant (''Dodonaea viscosa'') and a mangrove associate (''Sesuvium portulacastrum''). ''Portulacaria afra'' is the only plant known to display both CAM and C4 pathways. Crassulacean Acid Metabolism has evolved convergently many times<ref>http://www.werc.usgs.gov/seki/pdfs/IJPS_Keeley_Rundel.pdf</ref>. It occurs in 16,000 species (about 7% of plants), belonging to over 300 genera and around 40 families. It is found in [[quillwort]]s (relatives of [[club mosses]]), in ferns, and in [[gymnosperms]], but the great majority of CAM plants are angiosperms (flowering plants). The following list summarises the taxonomic distribution of CAM plants. {| class="wikitable" |- ! Division ! Class/Angiosperm group ! Order ! Family ! Plant Type ! Clade involved ! Type of CAM |- | [[Lycopodiophyta]] | [[Isoetopsida]] | [[Isoetales]] | Isoetaceae | hydrophyte | ''[[Isoetes]]''<ref name=Isoetids>[http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=480518&q=&uid=790851782&setcookie=yes Boston & Adams, Evidence of crassulacean acid metabolism in two North American isoetids, Aquatic Botany 15(4): 381-386 (1983)]</ref> (the sole genus of class Isoetopsida) - ''I. howellii'' (seasonally submerged), ''I. macrospora'', ''I. bolanderi'', ''I. engelmanni'', ''I. lacustris'', ''I. sinensis'', ''I. storkii'', ''I. kirkii'' | |- | [[Pteridophyta]] | [[Polypodiopsida]] | [[Polypodiales]] | [[Polypodiaceae]] | epiphyte, lithophyte | CAM is recorded from ''[[Microsorium]]'', ''[[Platycerium]]'' and ''[[Polypodium]]''<ref>[http://www.publish.csiro.au/paper/PP99001.htm Holtum & Winter, Degrees of crassulacean acid metabolism in tropical epiphytic and lithophytic ferns, Australian Journal of Plant Physiology 26(8): 749-757 (1999)]</ref>, ''[[Pyrrosia]]'' and ''[[Drymoglossum]]''<ref>[http://links.jstor.org/sici?sici=0002-8444(197610%2F12)66%3A4%3C121%3ADRTAAF%3E2.0.CO%3B2-Y Wong & Hew, Diffusive Resistance, Titratable Acidity, and {{co2}} Fixation in Two Tropical Epiphytic Ferns, American Fern Journal 66(4): 121-124 (1976)]</ref> and ''[[Microgramma (fern)|Microgramma]]'' | |- | | [[Pteridopsida]] | [[Pteridales]] | [[Vittariaceae]]<ref name=xxx>[http://dwb.unl.edu/Teacher/NSF/C11/C11Links/www.bl.rhbnc.ac.uk/plant/cam.html Crassulacean Acid Metabolism<!-- Bot generated title -->]</ref> | epiphyte | ''[[Vittaria]]''<ref>[http://orton.catie.ac.cr/cgi-bin/wxis.exe/?IsisScript=OET.xis&method=post&formato=2&cantidad=1&expresion=mfn=013247 abstract to Carter & Martin, The occurrence of Crassulacean acid metabolism among ephiphytes in a high-rainfall region of Costa Rica, Selbyana 15(2): 104-106 (1994)]</ref> ''[[Anetium citrifolium]]''<ref>[http://www.journals.uchicago.edu/doi/abs/10.1086/430334 abstract to Martin ''et al.'', The Occurrence of Crassulacean Acid Metabolism in Epiphytic Ferns, with an Emphasis on the Vittariaceae, International Journal of Plant Sciences 166(4): 623-630 (2005)]</ref> | |- | [[Cycadophyta]] | [[Cycadopsida]] | [[Cycadales]] | [[Zamiaceae]] | | ''[[Dioon]] edule''<ref>[http://www.blackwell-synergy.com/doi/abs/10.1046/j.1095-8339.2002.138002155.x Vovides et al, CAM-cycling in the cycad ''Dioon edule'' Lindl. in its natural tropical deciduous forest habitat in central Veracruz, Mexico, Botanical Journal of the Linnean Society 138(2): 155–162 (2002)]</ref> | |- | [[Pinophyta]] | [[Gnetopsida]] | [[Welwitschiales]] | [[Welwitschiaceae]] | xerophyte | ''[[Welwitschia mirabilis]]''<ref>[http://www.springerlink.com/content/g853530331684841/ Schultze, Ziegler & Stichler, Environmental control of crassulacean acid metabolism in Welwitschia mirabilis Hook. Fil. in its range of natural distribution in the Namib desert, Oecologia 24(4): 323-334 (1976)] </ref> (the sole species of the order Welwitschiales) | |- | [[Magnoliophyta]] | magnoliids | [[Magnoliales]] | [[Piperaceae]] | epiphyte | ''[[Peperomia]]''<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1064456 Sipes & Ting, Crassulacean Acid Metabolism and Crassulacean Acid Metabolism Modifications in Peperomia camptotricha, Plant Physiol. 77(1): 59-63 (1985)]</ref> | |- | | eudicots | [[Caryophyllales]] | [[Plantaginaceae]] | hydrophyte | ''[[Littorella]] uniflora''<ref name=Isoetids/> | |- | | | | [[Aizoaceae]] | xerophyte | widespread in the family; ''[[Mesembryanthemum crystallinum]]'' is a rare instance of an halophyte which displays CAM<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1062660 Chu, Dai, Ku & Edwards, Induction of Crassulacean Acid Metabolism in the Facultative Halophyte ''Mesembryanthemum crystallinum'' by Abscisic Acid, Plant Physiol. 93(3): 1253–1260 (1990)]</ref> | |- | | | | [[Cactaceae]] | xerophyte | all cacti have obligate Crassulacean Acid Metabolism in their stems; those few cacti with leaves have C3 Metabolism in those leaves; seedlings have C3 Metabolism. | |- | | | | [[Portulacaceae]] | xerophyte | recorded in approximately half of the genera (note: Portulacaceae is paraphyletic with respect to Cactaceae and Didieraceae)<ref>[http://www.journals.uchicago.edu/doi/abs/10.1086/319569?journalCode=ijps Guralnick & Jackson, The Occurrence and Phylogenetics of Crassulacean Acid Metabolism in the Portulacaceae, Int. J Plant Sci. 162(2): 257–262 (2001)]</ref> | |- | | | | [[Didiereaceae]] | xerophyte | | |- | | | [[Saxifragales]] | [[Crassulaceae]] | hydrophyte, xerophyte, lithophyte | CAM is widespread in the family | |- | | eudicots (rosids) | [[Vitales]] | [[Vitaceae]]<ref name=Tansley/> | | ''[[Cissus]]''<ref name=Nelson>[http://www.publish.csiro.au/nid/102/display/citation/paper/FP04195.htm Nelson, Sage & Sage, Functional Leaf Anatomy of plants with Crassulacean Acid Metabolism, Functional Plant Biology 32: 409-419 (2005)]</ref>, ''[[Cyphostemma]]'' | |- | | | [[Malpighiales]] | [[Clusiaceae]] | hemiepiphyte | ''[[Clusia]]''<ref name=Luttge2004>[http://aob.oxfordjournals.org/cgi/content/abstract/93/6/629, Lüttge, Ecophysiology of Crassulacean Acid Metabolism (CAM), Annals of Botany 93: 629-652 (2004)]</ref> <ref name=Nelson/> | |- | | | | [[Euphorbiaceae]]<ref name=Tansley>[http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-8137.1985.tb02815.x Cockburn, Variation in Photosynthetic Acid Metabolism in Vascular Plants: CAM and Related Phenomena, New Phytologist 101(1): 3-24 (1985)]</ref> | | CAM is found is some species of ''[[Euphorbia]]''<ref name=Nelson/> <ref name=Bender>[http://www.plantphysiol.org/cgi/content/abstract/52/5/427 Bender et al, 13C/12C Ratio Changes in Crassulacean Acid Mechanism Plants, Plant Physiology 52: 427-430 (1973)]</ref> including some formerly placed in the sunk genera ''[[Monadenium]]''<ref name=Nelson/>, ''[[Pedilanthus]]''<ref name=Bender/> and ''[[Synadenium]]''. C4 photosynthesis is also found in ''Euphorbia'' (subgenus ''Chamaesyce''). | |- | | | | [[Passifloraceae]]<ref name=xxx/> | xerophyte | ''[[Adenium]]''{{Fact|date=February 2008}} | |- | | | [[Geraniales]] | [[Geraniaceae]] | | CAM is found in some succulent species of ''[[Pelargonium]]''<ref>[http://www.amjbot.org/cgi/content/abstract/90/1/135 Jones, Cardon & Czaja, A phylogenetic view of low-level CAM in ''Pelargonium'' (Geraniaceae), American Journal of Botany 90: 135-142 (2003)]</ref>, and is also reported from ''[[Geranium pratense]]''{{Fact|date=February 2008}} | |- | | | [[Cucurbitales]] | [[Cucurbitaceae]] | | ''[[Xerosicyos]] danguyi''<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=159093 Bastide, Sipes, Hann & Ting, Plant Physiol. 103(4): 1089–1096 (1993)]</ref>, ''[[Dendrosicyos]] socotrana''{{Fact|date=February 2008}}, ''[[Momordica]]''{{Fact|date=February 2008}} | |- | | | [[Celastrales]] | [[Celastraceae]] | | | |- | | | [[Oxalidales]] | [[Oxalidaceae]] | | | |- | | | [[Brassicales]] | [[Moringaceae]] | | ''[[Moringa]]''{{Fact|date=February 2008}} | |- | | | [[Sapindales]] | [[Sapindaceae]] | | ''[[Dodonaea viscosa]]'' | |- | | | | [[Zygophyllaceae]] | | ''[[Zygophyllum]]''{{Fact|date=February 2008}} | |- | | eudicots (asterids) | [[Ericales]] | [[Ebenaceae]] | | | |- | | | [[Solanales]] | [[Convolvulaceae]] | | ''[[Ipomaea]]''{{Fact|date=February 2008}} | |- | | | [[Gentianales]] | [[Rubiaceae]] | epiphyte | ''[[Hydnophytum]]'' and ''[[Myrmecodia]]'' | |- | | | | [[Apocynaceae]] | | CAM is found in subfamily Asclepidioideae'' ([[Hoya]]''<ref name=Nelson/>, ''[[Dischidia]]'', ''[[Ceropegia]]'', ''[[Stapelia]]''<ref name=Bender/>, ''[[Caralluma]] negevensis'', ''[[Frerea]] indica''<ref>[http://www.springerlink.com/content/g0huvn11174g28v0/ abstract to Lange & Zuber, ''Frerea indica'', a stem succulent CAM plant with deciduous C<SUB>3</SUB> leaves, Oecologia 31(1): 67-72 (1977)]</ref>, ''[[Adenium]]'', ''[[Huernia]]''), and also in ''[[Carissa]]''{{Fact|date=February 2008}} and ''[[Akocanthera]]''{{Fact|date=February 2008}} | |- | | | [[Lamiales]] | [[Gesneriaceae]] | epiphyte | CAM was found ''[[Codonanthe]] crassifolia'', but not in 3 other genera<ref>[abstract to http://links.jstor.org/sici?sici=0002-9122(198603)73:3%3C336:CAMITG%3E2.0.CO;2-H Guralnick et al, Crassulacean Acid Metabolism in the Gesneriaceae, American Journal of Botany 73(3): 336-345 (1986)]</ref> | |- | | | | [[Lamiaceae]] | | ''[[Plectranthus]] marrubioides'', ''[[Coleus]]''{{Fact|date=February 2008}} | |- | | | [[Apiales]] | [[Apiaceae]] | hydrophyte | ''[[Lilaeopsis]] lacustris'' | |- | | | [[Asterales]] | [[Asteraceae]]<ref name=Tansley/> | | some species of ''[[Senecio]]''<ref>[http://links.jstor.org/sici?sici=0006-8071(198806)149%3A2%3C142%3AAOSACI%3E2.0.CO%3B2-8 Fioretti & Alfani, Anatomy of Succulence and CAM in 15 Species of ''Senecio'', Botanical Gazette 149(2): 142-152 (1988)]</ref> | |- | [[Magnoliophyta]] | monocots | [[Alismatales]] | [[Hydrocharitaceae]] | hydrophyte | ''[[Hydrilla]]''<ref name=Tansley/>, ''[[Vallisneria]]'' | |- | | | | [[Alismataceae]] | | ''[[Sagittaria]]'' | |- | | | | [[Araceae]] | | ''[[Zamioculcas]] zamiifolia'' is the only CAM plant in Araceae, and the only non-aquatic CAM plant in Alismatales<ref>[http://www.amjbot.org/cgi/content/abstract/94/10/1670 Holtum, Winter, Weeks and Sexton, Crassulacean acid metabolism in the ZZ plant, ''Zamioculcas zamiifolia'' (Araceae), American Journal of Botany 94: 1670-1676 (2007)]</ref> | |- | | | [[Poales]] | [[Bromeliaceae]] | epiphyte | Bromelioideae (91%), ''[[Puya]]'' (24%), ''[[Dyckia]]'' and related genera (all), ''[[Hechtia]]'' (all), ''[[Tillandsia]]'' (many)<ref>[http://www.pnas.org/cgi/reprint/0400366101v1Crayn, Winter & Smith, Multiple origins of crassulacean acid metabolism and the epiphytic habit in the Neotropical family Bromeliaceae, PNAS 101(10): 3703-3708 (2004)]</ref> | |- | | | | [[Cyperaceae]] | hydrophyte | ''[[Scirpus]]''<ref name=Tansley/>, ''[[Eleocharis]]'' | |- | | | [[Asparagales]] | [[Orchidaceae]] | epiphyte | | |- | | | | [[Agavaceae]]<ref name=Luttge2004/> | xerophyte | ''[[Agave]]''<ref name=Nelson/>, ''[[Hesperaloe]]'', ''[[Yucca]]'' | |- | | | | [[Asphodelaceae]]<ref name=Tansley/> | xerophyte | ''[[Aloe]]''<ref name=Nelson/>, ''[[Gasteria]]''<ref name=Nelson/> and ''[[Haworthia]]'' | |- | | | | [[Ruscaceae]]<ref name=Tansley/> | | ''[[Sansevieria]]''<ref name=Nelson/>, ''[[Dracaena]]''{{Fact|date=February 2008}} | |- | | | [[Commelinales]] | [[Commelinaceae]] | | ''[[Callisia]]''<ref name=Nelson/>, ''[[Tradescantia]]'', ''[[Tripogandra]]'' | |} ==See also== *[[C4 plants]] *[[RuBisCO]] ==References== <references/> [[Category:Photosynthesis]] ''' [[cs:CAM cyklus]] [[da:CAM-plante]] [[de:CAM-Pflanze]] [[es:Metabolismo ácido de las Crassulaceae]] [[fr:Métabolisme acide crassulacéen]] [[ko:CAM 식물]] [[it:Fotosintesi CAM]] [[he:CAM]] [[ja:CAM型光合成]] [[pl:Fotosynteza CAM]] [[fi:CAM-yhteyttäminen]] [[vi:Thực vật CAM]] [[tr:CAM bitkileri]] [[zh:景天酸代謝植物]]