ABSTRACTWe investigated the genetic control of cytosolic fructose‐1,6‐bisphosphatase (cytFBPase) activity, and the relationships between sucrose synthesis capacity and photosynthesis, growth, flowering and whole‐plant carbon partitioning inFlaveria linearisLag. F1; F2, and selfed lines generated from plants with low or high cytFBPase activity were used. CytFBPase activity was controlled by one gene and inherited co‐dominantly, giving three classes of activity (low, intermediate and high). Reversed O2sensitivity of photosynthesis, which indicates an end‐product limitation on photosynthesis, was controlled by one gene and co‐segregated with low cytFBPase activity. A low activity of cytFBPase decreased the growth rate. A recessive day‐neutral flowering trait inFlaveria linearisdid not co‐segregate with cytFBPase activity. Plants with low cytFBPase activity had an increased shoot‐to‐root ratio, and flowering caused an additional shift in carbon partitioning to shoots only in plants with low cytFBPase activity. These data indicate that altering sucrose synthesis can affect photosynthesis and plant gro