Using a flowering weed called Arabidopsis thaliana, researchers from Germany and South Korea discovered that the aboveground parts of the plant transmit light to its roots so that the plant can adapt its growth to the light conditions of the environment. Roots, they write, “directly perceive light that is conducted through the plant tissues,” with the stems acting as fiber-optic cables to transmit rays underground.
To confirm this hypothesis, the researchers exposed A. thaliana shoots to light, while keeping the roots from exposure, and vice versa, using an optical detector to record how much light made it underground. Some of the plants were genetically modified to turn off a photoreceptor known to detect light, found in both the aboveground parts of plants and in roots. They found that the stems conducted some wavelengths of light to the roots through the plant’s vascular system, affecting downward root growth. “Photoreception in the roots triggers a signaling chain which influences plant growth, especially the root architecture," according to a press statement from Ian Baldwin from the Max Planck Institute for Chemical Ecology, who led the study.
Scientists have hypothesized before that roots could sense light, but this is the first experiment to confirm it, according to the Max Planck Society.
[h/t New Scientist]