The plant response to shade

This work addresses the plant response to conditions of shade. Plants grown under canopies perceive the reduction in the ratio of red (R) to far-red (FR)
light as a warning of competition, and they enhance elongation
growth in an attempt to overgrow their neighbors. Here, Dr. Ida Ruberti's
group report that the same low R/FR signal that induces hypocotyl elongation also triggers a rapid arrest of leaf primordium growth, ensuring that plant resources are redirected into extension growth. We find that the growth arrest induced by low R/FR depends on auxin-induced cytokinin breakdown in developing primordia. On the whole, therefore, these findings identify a previously unrecognized regulatory circuit underlying the plant response to shade.
Canopy shade causes a rapid and transient arrest in leaf development through auxin-induced cytokinin oxidase activity. Carabelli M, Possenti M, Sessa G, Ciolfi A, Sassi M, Morelli G, Ruberti I. Genes Dev. 2007 vol. 21:1863-8.