Science has a way of opening our eyes, of surprising us — even on topics we think we understand.
Even photosynthesis, the process by which plants and other organisms harvest light for energy, has surprises in store. A recent discovery has confirmed that this most basic and necessary process can occur under much different circumstances, including under longer wavelengths of light.
"The new form of photosynthesis made us rethink what we thought was possible. It also changes how we understand the key events at the heart of standard photosynthesis," explains Bill Rutherford, a professor at Imperial College London and lead author of the study that outlined this new photosynethesizing process in a statement. "This is textbook-changing stuff."
Pushing the limits of chlorophyll's abilities
If you need a refresher, photosynthesis is the process by which plants, algae and cyanobacteria collect sunlight using the green pigment chlorophyll-a. This pigment also uses collected sunlight to create biochemicals that are useful to the plant. One of the beneficial byproducts of the process is oxygen.
That's the basic gist of the energy process. Chlorophyll-a excels at absorbing certain wavelengths of visible light, particularly blue and red. Red is at the end of the spectrum, and thus was considered the "red limit" of photosynthesis, or the absolute minimum amount of energy that was needed for photosynthesis to occur. Indeed, the "red limit" is used in astrobiology to determine whether or not complex life can occur on other planets.
Things shifted in 1996 with the discovery of chlorophyll-d in the cyanobacterium Acaryochloris marina, an organism that grows under the green sea squirt. Acaryochloris can absorb light that is slightly longer than red, putting it just outside the visual spectrum. It broke the "red limit" as it were, and a good thing for this cyanobacterium, since visible red light doesn't always reach the depths of the ocean. However, chlorophyll-d was considered something of a one-hit wonder since it was only found in Acaryochloris.
Our understanding of photosynthesis changed again in 2010 with the discovery of chlorophyll-f. Chlorophyll-f was more of a question mark than anything, with its role in the photosynthesis unclear. Researchers weren't sure if it simply collected the energy and handed it over to chlorophyll-a, or if it performed some other function.
Now, however, with a study published in Science, we've learned that chlorophyll-f can serve as chlorophyll-a's understudy, stepping up in infrared light environments.
Using Chroococcidiopsis thermalis, an extremely hardy genus of cynaobacterium that some think could survive just fine on Mars, researchers tested how chlorophyll would react when exposed to different kinds of light and shade. What they found was that chlorophyll-a systems basically shut down when grown in near-infrared light. Chlorophyll-f takes over in these instances, doing all the photosynthesizing.
Researchers believed that moving beyond the red limit would be harmful, but the study shows that this isn't the case, at least within stable environments.
"Finding a type of photosynthesis that works beyond the red limit changes our understanding of the energy requirements of photosynthesis," one of the study's co-authors, Andrea Fantuzzi, said in the statement. "This provides insights into light energy use and into mechanisms that protect the systems against damage by light."
Those insights in turn could also help us engineer crops to perform a more efficient kind of photosynthesis thanks to an ability to do so under a wider variety of light conditions.