Minisymposium 8: Photosynthesis: Carbon

Abs # 18001: Analysis of photosynthesis and carbon metabolism in the transgenic tobacco plants having algal fructose-1,6-bisphosphatase-II or sedoheptulose-1,7-bisphosphatase in chloroplasts

Presenter:	Tamoi, Masahiro , tamoi@nara.kindai.ac.jp
Authors	Tamoi, Masahiro  (A)   Miyagawa, Yoshiko  (A)   Nagaoka, Miki  (A)   Shigeoka, Shigeru  (A)
Affiliations:	(A): Fac. Agriculture, Kinki University

We demonstrated previously that transgenic tobacco plants expressing cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase (FBP/SBPase) in chloroplasts exhibit increased photosynthetic CO₂ fixation capacity and final dry matter under atmospheric conditions (360 ppm CO₂). The final dry matter of the transgenic plants was 1.5-fold larger than that of the wild-type plants. The transgenic plants showed 1.24-fold higher photosynthetic CO₂ fixation than the wild-type plants. These data suggest that fructose-1,6-bisphosphatase (FBPase) and/or sedoheptulose-1,7-bisphosphatase (SBPase) is one of the limiting factors participating in the regulation of the carbon flow through the Calvin cycle (Nature Biotechnol. 19, 965-969, 2001). To clarify the contributions of FBPase and/or SBPase to the regeneration of ribulose-1,5-bisphosphate (RuBP) in the Calvin cycle and the increase in the photosynthesis rate, here we generated transgenic tobacco plants (TpF) expressing cyanobacterial FBPase-II or Chlamydomonas SBPase (TpS) in chloroplasts. In TpF-11 plants with 2.3-fold higher FBPase activity in chloroplasts than wild-type plants, the amount of final dry matter and the rate of photosynthetic CO₂ fixation were 1.3-fold and 1.15-fold higher, respectively, than those in wild-type tobacco plants. Interestingly, the in vivo activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in TpF-11 was approx. 1.1-fold higher than that in wild-type plants, but there was no change of the maximal activity of Rubisco. The level of ribulose-1,5-bisphosphate (RuBP) in TpF-11 was 1.4-fold higher than that in wild-type plants. However, another transgenic plant (TpF-9), which had a 1.7-fold higher level of FBPase activity than the wild-type plants, did not show an increased rate of photosynthesis or growth. These data suggest that an increase in the chloroplastic FBPase level correlated with an increase in the RuBP level has a positive effect on the photosynthetic capacity and the growth in transgenic plants, while a slight increase in the FBPase level seems to contribute to the starch synthesis rather than the RuBP regeneration in chloroplasts. We are currently doing the comprehensive analyses of TpS plants concerning the growth, photosynthesis, and activities of enzymes and levels of intermediates in the Calvin cycle.