Carbon metabolism in leaves of transgenic tobacco (Nicotiana tabacum L.) containing elevated fructose 2,6‐bisphosphate levels

Summary The aim of this work was to investigate the role of fructose 2,6‐bisphosphate (Fru 2,6‐P2) during photosynthesis. The level of Fru 2,6‐P2 in tobacco plants was elevated by the introduction of a modified mammalian gene encoding 6‐phosphofructo‐2‐kinase (6‐PF‐2‐K). Estimates of the metabolite control coefficient (C) for Fru 2,6‐P2 levels in response to increased 6‐PF‐2‐K activity, suggest that small increases in 6‐PF‐2‐K activity have little effect upon steady‐state Fru 2,6‐P2 levels (C = +0.08 for a 0–58% increase in 6‐PF‐2‐K activity). However, larger changes resulted in dramatic rises in Fru 2,6‐P2 levels (C = +3.35 for 206–268% increase in 6‐PF‐2‐K activity). Transgenic plants contained Fru 2,6‐P2 levels in the dark that ranged from 104 to 230% of the level in wild‐type tobacco. Plants with altered levels of Fru 2,6‐P2 were used to determine the effects of this signal metabolite upon carbohydrate metabolism during the initial phase of the light period. Here we provide direct evidence that Fru 2,6‐P2 contributes to the regulation of carbon partitioning in tobacco leaves by inhibiting sucrose synthesis.