Figure 1.

Shade avoidance in Arabidopsis thaliana. Characteristic changes to the visible light spectrum (low R: FR and low blue) occur due to the presence of neighboring plants. These shade signals trigger increased transcript abundance and activity of specific XTHs. Shade also triggers an acidification of the apoplast. This provides the optimal milieu for the action of XTHs and other cell wall modifying proteins such as expansins. The coordinated action of these proteins modifies the cell wall thereby facilitating cellular expansion and resulting in enhanced petiole elongation and hyponasty. These morphological responses help a plant overtop competing vegetation.