Plant stems can act like fibre-optic cables, piping light from above ground down to the roots.
Plants' roots produce proteins that respond to light, but it was not clear how light reached below the ground. Chung-Mo Park of Seoul National University, Ian Baldwin of the Max Planck Institute for Chemical Ecology in Jena, Germany, and their team investigated this in thale cress (Arabidopsis thaliana). They found that illuminating the plant shoot altered gene expression in the roots, even when they prevented light from shining through the soil. Light in the red to near-infrared range was efficiently conducted through stem and root tissues.
Plants bearing a mutation in a light-responsive protein called HY5 showed abnormal root growth in response to shoot illumination, suggesting that light-sensing in plants is necessary for normal root development.