Abstract
To clarify the contributions of fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase (SBPase) to the increase in the photosynthetic rate, we generated transgenic tobacco plants expressing cyanobacterial FBPase-II (TpF) or Chlamydomonas SBPase in chloroplasts (TpS). In TpF-11 plants with 2.3-fold higher FBPase activity, final dry matter and photosynthetic activity were 1.30- and 1.15-fold higher, respectively, than those in wild-type plants. However, TpF-9 plants with 1.7-fold higher FBPase activity did not show these phenotypes. On the other hand, TpS-11 and TpS-10 with 1.6- and 4.3-fold higher SBPase activity, respectively, showed the increased photosynthetic activity and growth rate, but TpS-2 plants with 1.3-fold higher SBPase activity did not show these phenotypes. These data suggest that both FBPase and SBPase are the limiting factors for the RuBP regeneration in the Calvin cycle and that FBPase contributes to partitioning of fixed carbon for RuBP regeneration or starch synthesis.
