Plants transmit light down stems to roots to ‘see’ underground
Plants can turn their roots into virtual flashlights to promote new growth by piping sunlight down their stems, New Scientist reports. Light is reflected down the stem and through the roots by receptors called phytochromes, researchers say in their paper in the journal Science Signaling. The process is similar to how fiber optic cables transmit the light signals that allow you to stream your favorite shows online.
The scientists detected the reflective properties of the phytochromes—which activate proteins that promote growth—by putting a light source at the stem and a sensor at the roots. But unlike the light glowing from your laptop, the light moving through the root system is far too dim for soil-dwelling critters to notice or for bacteria to use for photosynthesis.
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.