Plants just might be piping more than just carbohydrates down to their roots. A study published in Science Signalling offers the first evidence that plants may actually be piping light down underground. No this isn't a metaphor either.
The presence of photoreceptors in the roots has been a bit of a puzzle ever since they were identified. A handful of hypotheses have been put forth in attempt to explain their function. It has been suggested that these photoreceptors are able to sense minuscule amounts of light penetrating through the soil. However, this research suggests there is another mechanism.
A team of researchers based out of South Korea found that certain stem tissues efficiently conducted wavelengths of red light down to the roots. Now before we get too ahead of ourselves, it should be noted that these are minuscule amounts of light. It certainly isn't enough for photosynthesis. However, it is light. Detectors placed under the soil at the ends of roots confirmed that light was indeed being transmitted.
Light is conducted through the tissues in much the same way as fiber optic cables. It is likely that the affinity for red wavelengths in particular has to do with the fact that it can travel farther than other, more intense wavelengths.
By experimenting with gene expression and light exposure, the team was able to demonstrate that light being piped to the roots activates a transcription factor involved in root growth and response to gravity. When the researchers blocked the ability to transmit light they found that root growth was severely stunted. Taken together, these results suggest that not only do roots receive information regarding light conditions above ground, they also directly perceive it.
It should be noted that all of this research was done on a single species, Arabidopsis thaliana. The question remains how common this phenomenon is throughout the plant kingdom. Most plants have photoreceptors in their roots, suggesting this light-piping ability is widespread.
Photo Credit: Dr John Runions/Science Photo Library
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