Plant Roots in the Dark See Light

rootsLight is not only a source of energy for plants but also an important signal which regulates many light-dependent growth processes allowing it to effectively adapt to its environment.

Light is first detected by photoreceptors in the shoot of a plant. For more than three decades, scientists have been speculating whether roots are also able to perceive light. A new study appears to confirm that is the case.

Previous studies had shown that a special photoreceptor in plants which 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 an interdisciplinary effort, molecular biologists and optical physicists developed a highly sensitive optical detector along with the idea to compare plants with “blind” and “sighted” roots.

They used plants of the thale cress Arabidopsis thaliana, a model organism in plant research, which were genetically modified 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 which was transmitted in the stem down to the roots.

The results showed that roots do indeed perceive light even though they are typically below the ground.

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2 Comments

  1. Ian Ashdown says:

    The story here is not that roots perceive light, but that the light (at least in this particular species) respond to light incident on leaves and stem being conducted through the translucent cells to the roots.

    Far-red light penetrates loose soil to a depth of several centimeters, where it can trigger the growth of buried seeds by activating phytochrome. This has been known for half a century. Once sprouted, the roots continue to respond to both value and far-red light, which is perceived by phytochrome and cryptochrome photoreceptors in the roots. This has been known for the past 20 years or more.

    So, an interesting story, but not as novel as the summary article above (from http://www.phys.org) suggests.

  2. Doug Steel says:

    I appreciated this article and especially Ian’s comments. Coming from a biological perspective (but not botanical!) and taking Ian’s insights into consideration, the most primitive animal responses to light involve locomotion (light avoidance or seeking). It would make sense that roots might do the same thing, growing horizontally or vertically using light as a cue. It is also possible that roots might use light as a means of establishing a certain degree of structural density – once a root network had grown to a certain extent, it would block a proportion of the penetrating light and serve as a cue to stop growing. These are strictly idle speculations, but they have a basis in how other lower organisms such as flatworms resound to light cues.

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