When a single leaf on a young poplar tree is mechanically wounded, wound-induced (win) mRNAs are detected in the unwounded portion of that leaf and in specific leaves that are remote from the wounded leaf. Shortly after wounding (6-8 hr), the remote leaves in which win genes are expressed can be predicted by a knowledge of photoassimilate movement patterns in vivo. When assimilate movement from a wounded leaf is blocked or the direction of assimilate movement is altered by shading, win gene expression in remote leaves is similarly blocked or altered. These data illustrate how the long-distance transduction of wound-induced signals can be manipulated in plants by altering carbon allocation.