Carbon dioxide (CO₂) in the air is the basis of the global food chain. Plant leaves contain proteins that collect the carbon and remove the oxygen (O₂). These proteins are virtually identical in all plants and algae, however, what this collected carbon is converted into differs widely. This poses a problem in measuring the efficiency of plants, since it is difficult to compare the amount of, say, new starch created in a potato on a scale with the new proteins in single celled algae. Now, researchers deliver a clear picture by developing a universal standard of CO₂ uptake.

Their approach rests on a “marker”, ¹³C, a heavier version of the naturally occurring carbon. They delivered ¹³C via ¹³CO₂ to the organisms, which started building molecules. At specific time points, the researchers stopped the process and counted a set of common molecules. A mass spectrometer, an instrument weighing molecules using a magnetic field, determined whether ¹³C had already been incorporated into each type of molecule. This allowed scientists to arrange the molecules in their order of carbon uptake. As the first molecules to which new carbons bind are always the same, they provide a convenient standard to measure how much ¹³C has entered the organism, irrespective of size or other characteristics. With enough time points, the researchers could follow the flow of ¹³C making its way throughout an organism, from simple sugars to fats and proteins.

Before this study, it was not known how some algae have much faster carbon uptakes than plants. The answer lies in this study’s most outstanding example: Chlorella ohadii has perfected its carbon flow, living in the desert with high illumination and few enemies. Instead of rationing, it keeps a large pool of each molecule, so no chemical reaction step ever runs out of its ingredients. Imagine a chain of connected dams: whatever the weather, the water keeps flowing steadily. In contrast with the treacherous environment and idiosyncratic reproductive adaptations of plants, Chlorella ohadii rather encapsulates a pure reactor for photosynthesis, revealing itself as a suitable model for the design of crops to feed a growing world.

Author intro: Dr. Haim Treves is now a senior lecturer at the School of Plant Sciences and Food Security at Tel-Aviv University. He joined after a post-doc fellowship in the lab of Professor Mark Stitt at the Max-Planck Institute for Molecular Plant Physiology in Potsdam-Golm, Germany, which was where this study was conducted.

Managing Correspondent: Raphael Haslecker

Original Journal Article: https://doi.org/10.1038/s41477-021-01042-5