When testing Chl d and Chl a at the wavelengths they each need to split water molecules, the team showed that whole-cell energy storage in A. marina was just as—and sometimes more— efficient than the S. leopoliensis cells using Chl a. For the first time, the team showed that oxygenic photosynthesis can operate well at longer wavelengths.
This discovery makes A. marina and Chl d very interesting for scientists trying to find life on extrasolar planets that orbit stars beyond our solar system. [The Strangest Alien Planets]
Nancy Kiang of the NASA Goddard Institute for Space Studies (GISS) explained, "Chl d extends the useful solar radiation for oxygenic photosynthesis by 18 percent — meaning life can use more wavelengths of light (i.e. more types of light-producing stars) to survive. This implies a lot of cool things."
Kiang emphasized the implications that the findings could have in the search for life on alien planets, and the future of life here on Earth. For instance, Kiang said that A. marina appears to have evolved relatively recently, occupying a light niche that is produced by leftover photons from Chl a organisms. Since it can use more solar radiation than Chl a organisms, might our planet evolve to have Chl d outcompete Chl a?
Also, "planets orbiting red dwarf stars may not get much visible light, but they'll get a lot of NIR light," she said. "So, now we know it would still make sense to look for oxygenic photosynthesis on such planets, and we could look for pigment signatures in the NIR."
Finally, Kiang said the discovery could have implications for the development of renewable energy sources.
"Biomimicry of photosynthesis continues to be a quest in the development of renewable energy, but no one has yet developed an artificial system as good as nature to split water," she noted. "For renewable energy that depends on sunlight, do the lower energy photons used with Chl d mean that we don't need such strong artificial catalysts for producing hydrogen fuel and biofuels?"
The findings could completely change our understanding of a biological reaction that is essential to the modern biosphere of Earth, researchers say. The results may also open new doors for the future of humankind in areas like renewable energy. But for NASA, the study could also have implications for the future of life on Earth and beyond that are truly far out.
This work was conducted by NASA Postdoctoral Program fellow Steven P. Mielke, under the advisement of Nancy Y. Kiang at GISS, in the laboratory of David Mauzerall at Rockefeller University in New York City, and in collaboration with Robert Blankenship at Washington University in St. Louis, MO, and Marilyn Gunner at City College of New York.
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