Sucrose and the integration of metabolism in vascular plants.

We consider the hypothesis that sucrose is a signal as well as a substrate. We suggest that the significance of sugar sensing in plants is the integration of whole-plant carbon flux so that the capacity of sources to produce sucrose matches the capacity of sinks to consume it. We pay particular attention to difficulties with this hypothesis and the areas where further or better evidence is needed. We conclude that there is strong correlative evidence for a link between sucrose metabolism and the level of expression of key genes, but that a number of different mechanisms may be involved.