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

Abstract

The aim of this work was to investigate the role of fructose 2,6‐bisphosphate (Fru 2,6‐P 2 ) during photosynthesis. The level of Fru 2,6‐P 2 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‐P 2 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‐P 2 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‐P 2 levels ( C = +3.35 for 206–268% increase in 6‐PF‐2‐K activity). Transgenic plants contained Fru 2,6‐P 2 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‐P 2 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‐P 2 contributes to the regulation of carbon partitioning in tobacco leaves by inhibiting sucrose synthesis.