title: Allocate carbon for a reason: priorities are reflected in the ¹³C/¹²C ratios of plant lipids synthesized via three independent biosynthetic pathways.
abstract: It has long been theorized that carbon allocation, in addition to the carbon source and to kinetic isotopic effects associated with a particular lipid biosynthetic pathway, plays an important role in shaping the carbon isotopic composition ((13)C/(12)C) of lipids (Park and Epstein, 1961). If the latter two factors are properly constrained, valuable information about carbon allocation during lipid biosynthesis can be obtained from carbon isotope measurements. Published work of Chikaraishi et al. (2004) showed that leaf lipids isotopic shifts from bulk leaf tissue Δδ(13)C(bk-lp) (defined as δ(13)C(bulkleaftissue)-δ(13)C(lipid)) are pathway dependent: the acetogenic (ACT) pathway synthesizing fatty lipids has the largest isotopic shift, the mevalonic acid (MVA) pathway synthesizing sterols the lowest and the phytol synthesizing 1-deoxy-D-xylulose 5-phosphate (DXP) pathway gives intermediate values. The differences in Δδ(13)C(bk-lp) between C3 and C4 plants Δδ(13)C(bk-lp,C4-C3) are also pathway-dependent: Δδ(13)C(ACT)(bk-lp,C4-C3) > Δδ(13)C(DXP(bk-lp,C4-C3) > Δδ(13)C(MVA)(bk-lp,C4-C3). These pathway-dependent differences have been interpreted as resulting from kinetic isotopic effect differences of key but unspecified biochemical reactions involved in lipids biosynthesis between C3 and C4 plants. After quantitatively considering isotopic shifts caused by (dark) respiration, export-of-carbon (to sink tissues) and photorespiration, we propose that the pathway-specific differences Δδ(13)C(bk-lp,C4-C3) can be successfully explained by C4-C3 carbon allocation (flux) differences with greatest flux into the ACT pathway and lowest into the MVA pathways (when flux is higher, isotopic shift relative to source is smaller). Highest carbon allocation to the ACT pathway appears to be tied to the most stringent role of water-loss-minimization by leaf waxes (composed mainly of fatty lipids) while the lowest carbon allocation to the MVA pathway can be largely explained by the fact that sterols act as regulatory hormones and membrane fluidity modulators in rather low concentrations.
authors.affiliation: Institute for Landscape Biogeochemistry, ZALF, Germany; Department of Chemistry, Curtin University, Perth, Australia; SKLLQG, Chinese Academy of Sciences, Xi'an, China; Leibniz Institute for Freshwater Ecology & Inland Fisheries, Germany. Electronic address: youping.zhou@zalf.de.
authors.forename: Youping
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: RSB, Australian National University, Canberra, Australia.
authors.forename: Hilary
authors.initials: H
authors.lastname: Stuart-Williams
authors.affiliation: Department of Chemistry, Curtin University, Perth, Australia.
authors.forename: Kliti
authors.initials: K
authors.lastname: Grice
authors.affiliation: Institute for Landscape Biogeochemistry, ZALF, Germany.
authors.forename: Zachary E
authors.initials: ZE
authors.lastname: Kayler
authors.affiliation: Slovenian Forestry Institute, Ljubljana, Slovenia.
authors.forename: Saša
authors.initials: S
authors.lastname: Zavadlav
authors.affiliation: Leibniz-Institut für Ostseeforschung, Rostock, Germany.
authors.forename: Angela
authors.initials: A
authors.lastname: Vogts
authors.affiliation: LUFA Nord-West, Institut für Futtermittel, Oldenburg, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Rommerskirchen
authors.affiliation: RSB, Australian National University, Canberra, Australia.
authors.forename: Graham D
authors.initials: GD
authors.lastname: Farquhar
authors.affiliation: Institute for Landscape Biogeochemistry, ZALF, Germany; Swiss Federal Institute WSL, Birmensdorf, Switzerland.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
mesh_terms: D000465:Algorithms; D053898:Biosynthetic Pathways; D002247:Carbon Isotopes / Q000378:metabolism; D003368:Gossypium / Q000737:chemistry; D008055:Lipids / Q000096:biosynthesis*; D008798:Mevalonic Acid / Q000378:metabolism; D015394:Molecular Structure; D008897:Panicum / Q000737:chemistry; D010428:Pentosephosphates / Q000737:chemistry / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry; D010944:Plants / Q000737:chemistry*; D012278:Ricinus / Q000737:chemistry; D045868:Sorghum / Q000737:chemistry; D013261:Sterols / Q000378:metabolism; D014026:Nicotiana / Q000737:chemistry; D014867:Water / Q000378:metabolism; D014885:Waxes / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry
chemical_list: C109460:1-deoxylulose 5-phosphate; D002247:Carbon Isotopes; D008055:Lipids; D010428:Pentosephosphates; D013261:Sterols; D014885:Waxes; D014867:Water; D008798:Mevalonic Acid
keywords: C(3)−C(4) difference; Carbon allocation priority; Isotope effects; Lipid biosynthetic pathways; Natural abundance carbon isotopes