title: Small decreases in SBPase cause a linear decline in the apparent RuBP regeneration rate, but do not affect Rubisco carboxylation capacity.
abstract: The response of net photosynthetic CO(2) uptake (A) to increasing leaf intercellular CO(2) concentration (c(i)) was determined in antisense Nicotiana tabacum plants, derived from six independent transformation lines, displaying a range of sedoheptulose-1, 7-bisphosphatase (SBPase) activities. The maximum in vivo ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (V(c,max)) and RuBP regeneration (J(max)) rates were calculated from the steady-state measurements of the A to c(i) response curves. In plants with reductions in SBPase activity of between 9% and 60%, maximum RuBP regeneration capacity declined linearly (r(2)=0.79) and no significant change in apparent in vivo Rubisco activity (V(c,max)) was observed in these plants. No correlation between V(c,max) and a decrease in capacity for RuBP regeneration was observed (r(2)=0.14) in the SBPase antisense plants. These data demonstrate that small decreases in SBPase activity limit photosynthetic carbon assimilation by reducing the capacity for RuBP regeneration.
authors.affiliation: Department of Biological Sciences, John Tabor Laboratories, University of Essex, Colchester CO4 3SQ, UK.
authors.forename: E P
authors.initials: EP
authors.lastname: Harrison
authors.forename: H
authors.initials: H
authors.lastname: Olcer
authors.forename: J C
authors.initials: JC
authors.lastname: Lloyd
authors.forename: S P
authors.initials: SP
authors.lastname: Long
authors.forename: C A
authors.initials: CA
authors.lastname: Raines
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D007700:Kinetics; D010641:Phenotype; D010788:Photosynthesis / Q000502:physiology*; D030821:Plants, Genetically Modified; D012273:Ribulose-Bisphosphate Carboxylase / Q000096:biosynthesis / Q000378:metabolism*; D012274:Ribulosephosphates / Q000378:metabolism*; D013403:Sugar Phosphates / Q000096:biosynthesis / Q000378:metabolism*; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics
chemical_list: D012274:Ribulosephosphates; D013403:Sugar Phosphates; D002245:Carbon Dioxide; C001933:ribulose-1,5 diphosphate; C022079:sedoheptulose 1,7-bisphosphate; D012273:Ribulose-Bisphosphate Carboxylase