How built-in sunblock shields plants from harmful radiation

On a bright, sunny day, it’s good to be a plant. No sunblock? No problem.

Plants, which rely so vitally on sunlight, actually protect themselves from the harmful ultraviolet (UV) rays that beat down on them. And University of Geneva (UNIGE) researchers have provided new insight into that mechanism.

In a study published Monday in the journal Proceedings of the National Academy of Sciences, the researchers identified a network of photoreceptors and enzymes that work in tandem to create a biochemical defense from radiation.

For most plant life, sunlight is an essential resource. It provides energy, stimulates growth, and can even determine when a plant should germinate or flower.

But sunlight is composed of several distinct wavelengths, with those on the shorter end having potential to do damage to living cells.

“UV is part of what’s called electromagnetic radiation, which is classified based on wavelength,” explains Thomas Tenkate, a professor of public health at Ryerson University specializing in radiation exposure, who was not involved in this study, in a phone interview with The Christian Science Monitor. “The distance between the peaks of the wave is the wavelength. The shorter the wavelength, the more energy in that wave.”

So why don’t plants burn the same way?

To make use of different wavelengths of light, plants use a number of specialized molecules. For example, the pigment chlorophyll absorbs blue and red light and facilitates photosynthesis.

Previously, researchers identified a photoreceptor, now known as UVR8, in plant cells. These proteins absorb UV-B rays – hence the name – and congregate in the cell nucleus, setting off a chain of biochemical reactions relating to UV protection.

“Simply, UVR8 sees UV radiation and then tells the cell to make sunscreen,” says Daniel Kliebenstein, a professor of plant sciences at the University of California, Davis, in an email to the Monitor. Dr. Kliebenstein, who was not involved in this study, has authored similar papers on the protective function of UVR8.

Later research found that when activated, UVR8 receptors bind to an enzyme called COP1, whose exact role in the process was unclear. But by tweaking some cells from the plant Arabidopsis thaliana, researchers have now gained new insight into the enzyme’s function.

“When the UVR8 photoreceptor or COP1 enzyme were artificially retained in the cytosol of cells, no response was observed in terms of UV tolerance or growth. These two proteins must be present in the cell nucleus for the genes involved in the response to be activated,” said Roman Ulm, professor at the Department of Botany and Plant Biology of UNIGE, in a press release.

Researchers believe that COP1 travels between the nucleus and the cytosol like a shuttle, allowing the rapid build-up of UVR8 receptors in the nucleus. This simple task allows the reaction chain to continue, leading to a physiological response in the plant body that promotes UV tolerance and growth.

It is still unclear exactly how this chain of reactions provides UV protection. Ulm and colleagues will continue to study their experimental Arabidopsis lines to better understand this mechanism.

In the meantime, human sunbathers could learn a thing or two from plants.

Some of the plant compounds involved in UV protection are “already used in sunscreen,” Kliebenstein says. Could future breakthroughs produce further bio-inspired solutions?

“I don’t see why we couldn’t learn from the mechanisms of plants," says Dr. Tenkate, "but then the genetic mechanisms of plants are different than ours.”