Gas exchange and ultrastructural analysis of transgenic potato plants expressing mRNA antisense construct targeted to the cp-fructose-1,6-bisphosphate phosphatase

Measurements of the net photosynthetic (P-N), respiration (R) and transpiration (E) rates, leaf conductances (g(H20)) and intercellular CO2 concentrations (C-i), along with the transmission electron microscopy were utilized in order to study differences in photosynthetic traits of transgenic and wild-type (Wt) potato. plants. We used transgenic plants expressing different levels of the chloroplastic isoform of fructose-1,6-bisphosphate phosphatase (FBPase), which had been created via the mRNA antisense technique. A significant reduction of the P-N was found only with FBPase activities below 36 % compared to the Wt, and under irradiances that exceeded 300 mu mol m(-2) s(-1). Progressive attenuation of the FBPase activity caused further P-N reduction. The CO2 compensation concentration and compensation irradiance were identical in the transgenic and Wt plants. Under anoxic conditions a 30 % increase of the P-N occurred in all the plants. The R during the dark period was similar both in the Wt and FBPase-antisense plants. The size and number of starch grains were significantly lower in plants with the FBPase activities below 36 %. Shift to a higher amount of small grana stacks occurred within chloroplasts of the transgenic plants.