Shining a light on the protection mechanism of plants against excess sunlight
In a world first, scientists have mapped how plants dispel excess sunlight as heat. Future understanding of this process could have the potential to protect and improve crop yields.
It is well-known that plants rely on sunlight for the crucial process of photosynthesis, which allows them to convert solar energy into sugar molecules and store them for later use. However, excess sunlight can be problematic for plants by causing ‘photodamage’ — dehydrated and damaged leaves.
While it has long been accepted plants can protect themselves from photodamage by dissipating excess light as heat, exactly how this process occurs has been a subject of debate in scientific circles. Now, for the first time, scientists have been able to directly observe one mechanism.
A team from the Massachusetts Institute of Technology (MIT), the University of Pavia, and the University of Verona, used a process known as spectroscopy to observe excess energy being transferred from chlorophyll (the green pigment found in leaves) to other pigments known as carotenoids, which have the ability to release energy as heat.
Gabriela Schlau-Cohen is an Assistant Professor at MIT, and senior author of the study. She said this was the first time chlorophyll-to-carotenoid energy transfer has been observed in the light-harvesting complex of green plants.
“That's the simplest proposal, but no one's been able to find this photophysical pathway until now," Schlau-Cohen said.
One of the reasons the process had been so difficult to observe is the high speed at which it occurs, and the fact previous methods were only able to measure a small section of the spectrum of visible light.
For this study, the research team used a technique developed by Schlau-Cohen, which allowed them to look at a broader range of energy levels, spanning red to blue light. As a result, they were able to monitor energy transfer between chlorophylls, which absorb red light, and carotenoids, which absorb blue and green light.
"By broadening the spectral bandwidth, we could look at the connection between the blue and the red ranges, allowing us to map out the changes in energy level," said Schlau-Cohen.
The researchers observed after the carotenoids accepted the excess energy, most of it was discharged as heat, preventing light-induced cell damage.
However, an important mystery remains — which is, how exactly does excess sunlight trigger the protective mechanism? The researchers are now exploring whether the organisation of chlorophylls and carotenoids within the chloroplast membrane could be responsible for activating photoprotection.
The team is hopeful an improved understanding of photoprotection could support the development of new approaches to protecting and improving crop yields.