title: Exploiting transplastomically modified Rubisco to rapidly measure natural diversity in its carbon isotope discrimination using tuneable diode laser spectroscopy.
abstract: Carbon isotope discrimination (Δ) during C3 photosynthesis is dominated by the fractionation occurring during CO2-fixation by the enzyme Rubisco. While knowing the fractionation by enzymes is pivotal to fully understanding plant carbon metabolism, little is known about variation in the discrimination factor of Rubisco (b) as it is difficult to measure using existing in vitro methodologies. Tuneable diode laser absorption spectroscopy has improved the ability to make rapid measurements of Δ concurrently with photosynthetic gas exchange. This study used this technique to estimate b in vivo in five tobacco (Nicotiana tabacum L. cv Petit Havana [N,N]) genotypes expressing alternative Rubisco isoforms. For transplastomic tobacco producing Rhodospirillum rubrum Rubisco b was 23.8±0.7‰, while Rubisco containing the large subunit Leu-335-Val mutation had a b-value of 13.9±0.7‰. These values were significantly less than that for Rubisco from wild-type tobacco (b=29‰), a C3 species. Transplastomic tobacco producing chimeric Rubisco comprising tobacco Rubisco small subunits and the catalytic large subunits from either the C4 species Flaveria bidentis or the C3-C4 species Flaveria floridana had b-values of 27.8±0.8 and 28.6±0.6‰, respectively. These values were not significantly different from tobacco Rubisco.
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 0200, Australia susanne.caemmerer@anu.edu.au.
authors.forename: Susanne
authors.initials: S
authors.lastname: von Caemmerer
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 0200, Australia.
authors.forename: Youshi
authors.initials: Y
authors.lastname: Tazoe
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 0200, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
authors.affiliation: Research School of Biology, The Australian National University, Canberra ACT 0200, Australia.
authors.forename: Spencer M
authors.initials: SM
authors.lastname: Whitney
mesh_terms: D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D037142:Flaveria / Q000201:enzymology* / Q000235:genetics; D005838:Genotype; D054023:Lasers, Semiconductor; D010788:Photosynthesis; D018526:Plant Transpiration; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics* / Q000378:metabolism; D013057:Spectrum Analysis / Q000379:methods*; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase
keywords: C4 photosynthesis; Flaveria; Rubisco; carbon isotope discrimination; tobacco; tuneable diode laser spectroscopy.