Effects of Cytosolic FBPase on Photosynthetic Carbon Metabolism Under High CO₂ Conditions

Abstract

We generated transgenic tobacco plants expressing cyanobacterial fructose-1, 6-/ sedoheptulose-1,7-bisphosphatase in cytosol. Under atmospheric (360 ppm) CO₂ conditions, though sucrose/hexose/starch ratio in the transgenic plants was slightly changed compared with wildtype plants, there were no significant differences in growth, photosynthetic activity, and fresh weight between the wild-type and transgenic plants. On the other hand, under high (1,200 ppm) CO₂ conditions, lateral shoot, leaf number, and fresh weight of transgenic plants significantly increased compared with those in the wild-type plants. Transgenic plants had increased photosynthetic activity compared to the wild-type plants. The level of hexose of wild type accumulated in upper leaves, while levels of sucrose and starch of transgenic plants accumulated in lower leaves and lateral shoots. These findings suggest that the cytosolic fructose-1,6-bisphosphatase contributes to the efficient conversion of hexose into sucrose, and that the change of carbon partitioning affects photosynthetic capacity, hormone biosynthesis, and morphogenesis.