The response of net photosynthetic CO2 uptake (A) to increasing leaf intercellular CO2 concentration (ci) 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 (Vc,max) and RuBP regeneration (Jmax) rates were calculated from the steady-state measurements of the A to ci response curves. In plants with reductions in SBPase activity of between 9% and 60%, maximum RuBP regeneration capacity declined linearly (r2 = 0.79) and no significant change in apparent in vivo Rubisco activity (Vc.max) was observed in these plants. No correlation between Vc,max and a decrease in capacity for RuBP regeneration was observed (r2=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.
ASJC Scopus subject areas
- Plant Science