Study Reveals Important Step in Photosynthesis Evolution
The finding, captured with electron microscope images, offers a glimpse at how scientists think early organisms acquired free-living chloroplasts, the structures responsible for converting light into food. This event is thought to be a critical first step in the evolution of photosynthetic algae and land plants, which helped raise oxygen levels in Earth’s atmosphere and paved the way for the rise of animals.
In a paper that appears in the June 17 issue of Current Biology and is available online, Eunsoo Kim, an assistant curator in the Museum’s Division of Invertebrate Zoology, and her colleague Shinichiro Mauyama, a postdoctoral researcher at Japan’s National Institute for Basic Biology, identify a mechanism by which a green alga that resembles early ancestors of the group engulfs bacteria. Their work provides conclusive evidence for a process that had been proposed but not definitely shown.
“This behavior had previously been suggested but we had not had clear microscopic evidence until this study,” Kim said. “These results offer important clues to an evolutionary event that fundamentally changed the trajectory of the evolution of not just photosynthetic algae and land plants, but also animals.”
In green algae and land plants, photosynthesis, or the conversion of light into food, is carried out by a specialized cell structure known as a chloroplast. The origin of chloroplast is linked to endosymbiosis, a process in which a single-celled eukaryote—an organism whose cells contain a nucleus—captures a free-living photosynthetic cyanobacterium but does not digest it, allowing the photosynthetic cell to eventually evolve into a chloroplast. The specific feeding mechanisms for this process, however, have remained largely unknown until now.
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