Turbo-Charged Photosynthesis Could Make Crops Grow Faster While Using Fewer Nutrients

The carboxysomes in which cyanobacteria hold their photosynthesizing enzymes allow for much faster growth. ARC Centre of Excellence for Translational Photosynthesis

One of the great ironies of evolution is that almost all known life depends on one of the slowest and most inefficient enzymes on Earth. Cyanobacteria have evolved a better mechanism to deal with the slow rate at which the Rubisco enzyme processes carbon dioxide than plants. Now scientists have taken the largest step towards transferring this work-around into a plant. If the process can be completed, crop yields may increase by as much as 60 percent while fertilizer and water demands decline, making it the single largest advance in crop efficiency ever contemplated.

Both plants and cyanobacteria use Rubisco to photosynthesize carbon dioxide into sugars, which can then be converted into all the other components necessary for life. Cyanobacteria have a carbon dioxide concentration mechanism to speed up the process, and Dr Ben Long of the Australian National University is working to give plants the same capacity.

Long told IFLScience each Rubisco molecule can only process around three carbon dioxide molecules a second, while many other enzymes induce hundreds of chemical reactions in the same time. Besides being painfully slow, Rubisco often fails to differentiate CO2 from oxygen, wasting precious time and energy on the wrong molecule.

Plants have responded to this inefficiency by producing enormous amounts of Rubisco. Long told IFLScience, “In a typical leaf of a plant half the protein can be Rubisco.” Plants also respond by leaving their gas-exchanging stoma wide open, drawing in as much carbon dioxide as possible, at the cost of losing a lot of water.

Thirty-five million years ago the development of the C4 pathway gave one group of plants a slightly improved mechanism for dealing with this inefficiency, but long before that, single-celled organisms had created something much better. “Cyanobacteria use what's called a 'CO2 concentrating mechanism' to deliver large amounts of the gas into their carboxysomes, where their Rubisco is encapsulated," Long said in a statement

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