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 integra tion 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 atte ntion to difficulties with this hypothesis and the areas where further or b etter evidence is needed. We conclude that there is strong correlative evid ence for a link between sucrose metabolism and the level of expression of k ey genes, but that a number of different mechanisms may be involved. (C) 20 00 Elsevier Science Ireland Ltd. All rights reserved.