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.

Overexpression of Plastid Transketolase in Tobacco Results in a Thiamine Auxotrophic Phenotype

“…One area of research on the C3 cycle has been to identify enzymes that limit carbon fixation with a view to improving photosynthesis and yield (Raines, 2006;Zhu et al, 2007;Stitt et al, 2010). Using antisense technology it has been shown that sedoheptulose-1,7-bisphosphatase (SBPase), a highly regulated enzyme catalyzing a nonreversible reaction in the regenerative phase of the C3 cycle, limits carbon fixation and plant growth (Harrison et al, 1998;Raines et al, 1999;Harrison et al, 2001;Olçer et al, 2001;Raines, 2003;Lawson et al, 2006;Raines and Paul, 2006). This led to the hypothesis that by increasing the level of this enzyme it might be possible to increase photosynthesis.…”

Systems Analysis of the Response of Photosynthesis, Metabolism, and Growth to an Increase in Irradiance in the Photosynthetic Model OrganismChlamydomonas reinhardtii

“…However, systematic application of reverse genetics has revealed that several enzymes that are involved in the regeneration of RuBP also exert control over the rate of photosynthesis in some conditions (Anderson, 1992;Kossmann et al, 1994;Haake et al, 1998Haake et al, , 1999Harrison et al, 1998Harrison et al, , 2001Henkes et al, 2001;Miyagawa et al, 2001;Olçer et al, 2001;Lefebvre et al, 2005;Lawson et al, 2006;Rosenthal et al, 2011). Recently, evolutionary models have predicted that an increase in SBPase abundance would increase the rate of photosynthesis (Zhu et al, 2007).…”

Diversity of regulatory mechanisms of photosynthetic carbon metabolism in plants and algae

“…In order to determine the limiting steps of the Calvin cycle and factors that influence carbon allocation, a large number of studies have examined the regulation of carbohydrate metabolism in photosynthetic CO 2 fixation in plant leaves. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] The findings obtained indicated that a number of enzymes involved in the Calvin cycle were present in the protein level in excess than that required to sustain a continued rate of CO 2 fixation. In contrast, especially in the antisense plants of chloroplastic FBPase or SBPase, the rate of photosynthesis was significantly diminished in proportion to the decrease in respective enzyme activities due to a decrease in the RuBP regeneration capacity in the Calvin cycle.…”