Light is not only a source of energy, but also an important signal that regulates many light-dependent growths in a plant.
Light is first detected by photoreceptor in the shoot of a plant. Physiological processes in the plant are mediated by light signaling molecules.
For more than three decades, scientists have been speculating whether roots are also able to perceive light.
They had shown that a special photoreceptor in plants that detects light of the wavelength red/far-red is surprisingly also expressed in the roots.
However, it remained unclear how this root photoreceptor was activated.
In a new study, researchers developed a highly sensitive optical detector along with the idea to compare plants with “blind” and “sighted” roots.
They genetically modified the plants in a way that the photoreceptor was only silenced in their roots, but not in their shoots.
Hence, these plants had “blind” roots. The scientists grew these modified plants along with control plants; their roots were in the dark soil and their shoots exposed to light, just like in nature.
The optical detector system was used to measure light that was transmitted in the stem down to the roots.
With this approach, the researchers showed clearly and without ambiguity that light is transmitted into the roots via vascular bundles.
Even if the intensity of the transmitted light was low, it was sufficient to activate the photoreceptors, trigger downstream light signaling, and influence growth in the control plants.
These results are crucial for further research projects. The work proves that roots are able to perceive light, even though they are usually found belowground.
It is of major importance for ecological research to show the relevance of this study for plants growing in their natural habitat.
To find out, the scientists want to perform experiments with another plant species, the coyote tobacco Nicotiana attenuata, a model plant in ecology, which is adapted to an extremely strong exposition to light.
The researchers propose that the newly found sensory modality of roots is enhancing the ecological performance of plants in nature, by allowing for a better timing of resource allocations for growth, reproduction and defense.
Citation: Lee HJ, et al. (2016). Stem-piped light activates phytochrome B to trigger light responses in Arabidopsis thaliana roots. Science Signaling. 9: ra106. DOI: http://dx.doi.org/10.1126/scisignal.aaf6530.
Figure legend: This Knowridge.com image is credited to Rakesh Santhanam, Angela Overmeyer / Max Planck Institute for Chemical Ecology.