Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2009
Publication Date: 7/18/2009
Citation: Rosenthal, D.M., Raines, C.A., Ort, D.R. 2009. Over Expression of Sedoheptulose 1,7, bisphosphatase (SBPase) Significantly Improves Carbon Assimilation at Elevated CO2 [abstract]. Plant Biology Annual Meeting. Paper No. P45034. Interpretive Summary:
Technical Abstract: Biochemical models of photosynthesis (A) show that it is most frequently limited by the slowest of two processes, maximum carboxylation capacity of the enzyme Rubisco (Vc,max) or the regeneration of RuBP via electron transport (J). At current CO2 levels Rubisco is not saturated by its substrate, therefore elevating CO2 increases the velocity of carboxylation. At light saturation the transition between Rubisco limited and RuBP limited photosynthesis occurs at current ambient CO2. Therefore, in the future leaf A should be increasingly limited by RuBP regeneration, as CO2 is predicted to increase by 50% by 2050 to ca. 550 ppm. If this is the case then plant engineered to have an increased capacity to regenerate RuBP should have a greater stimulation of photosynthesis and productivity at elevated CO2 relative to wild type plants. We tested this hypothesis by growing three transgenic tobacco lines over expressing the enzyme SBPase and compared their response to wild type tobacco in greenhouse growth chambers in near ambient (400ppm) and at elevated (750 ppm) CO2. Increased light saturated A of transgenic lines in elevated CO2 was associated with a 2 to 4 fold greater increase in the quantum yield of electron flux through PSII (Phi PSII) than that of wild type plants. As a result, plants over expressing SBPase exhibited a 45% increase of light saturated photosynthetic rates (A) whereas wild type plants only had a 35% increase at elevated CO2. In vivo Rubisco capacity (Vc,max) was down regulated in both WT and transgenic plants. However, downregulation of carboxylation capacity in transgenic plants was 1/2 to 1/3 of that in wild type plants. Over expressing this enzyme alone could significantly increase carbon assimilation, growth, and crop productivity in the future.