Earth’s Most Important Biochemical Reaction: Photosynthesis Breakthrough for Increasing CO2 Uptake in Plants
Plant cells Plant cells inside a leaf seen through a microscope.
A group of proteins in plant cells plays a vastly more important role in regulation of photosynthesis than once thought, according to new research at the University of Copenhagen. The research is an important step towards fully understanding photosynthesis regulation and increasing CO2 uptake in plants to benefit the climate.
Photosynthesis Facts
- Photosynthesis is one of the most important biological processes on Earth, as it produces most of the oxygen in our atmosphere, upon which nearly all life depends.
- Photosynthesis takes place in green plants, algae and some bacteria, when solar energy converts carbon dioxide and water into oxygen and organic matter in the form of glucose.
- Glucose is then converted into nutrients and used by the plants themselves and animals
Source: Den Store Danske
Imagine being able to grow plants that could absorb even more CO2 from Earth’s atmosphere and thereby help solve the world’s climate problems. Humans have selected, bred and optimized plants to increase food production and ensure our survival for thousands of years.
But the most important and fundamental function of life on Earth – photosynthesis – has not been relevant with regards to plant selection or breeding until now, an age when greenhouse gas emissions from human activities threaten our planet. With new technologies at hand, scientists around the world are now working to understand the internal processes of plants that drive photosynthesis.
In a new study published in the scientific journal PNAS, researchers from the University of Copenhagen’s Department of Plant and Environmental Sciences have just discovered that a group of proteins in plant leaf cells, called CURT1, plays a much more important role in photosynthesis than once thought.
“We have discovered that CURT1 proteins control a plant’s development of green leaves already from the seed stage. Thus, the proteins have a major influence on how effectively photosynthesis is established,” explains Associate Professor Mathias Pribil, the study’s lead author.
Proteins that kickstart photosynthesis
CURT1 Protein Facts
- URT1 is a protein group which coordinates structural processes of the internal chloroplast membrane that makes photosynthesis function more efficiently.
- It was once thought that this protein group was only present in plants with mature leaves, and that the protein played a less important role. Scientists now know that the protein group is central to managing photosynthesis.
- The protein group also helps plant leaves increase or decrease their light-harvesting ability depending upon sunlight strength.
- Plants with a misbalanced CURT1 protein content – whether too many or too few – had a higher mortality rate and generally poorer growth.
CURT1 proteins were previously believed to play a more modest role and only be present in fully-developed leaves. But using state-of-the-art Imaging techniques (photography and computer equipment), the researchers zoomed 30,000x in on the growth of a series of experimental thale cress (Arabidopsis) plants. This allowed them to study the plants at a molecular level. The researchers could see that CURT1 proteins were present from the earliest stages of their plants’ lives.
“Emerging from the soil is a critical moment for the plant, as it is struck by sunlight and rapidly needs to get photosynthesis going to survive. Here we can see that CURT1 proteins coordinate processes that set photosynthesis in motion and allow the plant to survive, something we didn’t know before,” explains Mathias Pribil.
Photosynthesis takes place in chloroplasts, 0.005 mm long elliptical bodies in plant cells that are a kind of organ within the cells of a plant leaf. Within each chloroplast, a membrane harbours proteins and the other functions that make photosynthesis possible.
“CURT1 proteins control the shape of this membrane, making it easier for other proteins in a plant cell to move around and perform important tasks surrounding photosynthesis, depending on how the environment around the plant changes. This could be to repair light harvesting protein complexes when the sunlight is intense or to turn up a chloroplast’s ability to harvest light energy when sunlight is weak,” explains Pribil.
Plants with a misbalanced CURT1 protein content – whether too many or too few – had a higher mortality rate and generally poorer growth.
Improved CO2 uptake in the future
The new finding provides deeper insight into Earth’s most important biochemical reaction. Indeed, without plants, neither animals nor humans would exist on our planet. Thus far, the result only applies to the thale cress plant, but Pribil would be “very surprised” if the importance of CURT1 proteins for photosynthesis didn’t extend to other plants as well.
“This is an important step on the way to understanding all of the components that control photosynthesis. The question is whether we can use this new knowledge to improve the CURT1 protein complex in plants in general, so as to optimize photosynthesis,” says Mathias Pribil, who adds:
“Much of our research revolves around making photosynthesis more efficient so that plants can absorb more CO2. Just as we have selected and bred the best crops throughout the history of agriculture, it is now about helping nature become the best possible CO2 absorber,” says Mathias Pribil.
Reference: “Curvature thylakoid 1 proteins modulate prolamellar body morphology and promote organized thylakoid biogenesis in Arabidopsis thaliana” by Omar Sandoval-Ibáñez, Anurag Sharma, Michal Bykowski, Guillem Borràs-Gas, James B. Y. H. Behrendorff, Silas Mellor, Klaus Qvortrup, Julian C. Verdonk, Ralph Bock, Lucja Kowalewska and Mathias Pribil, 19 October 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2113934118
New Research Shows Plants Are Photosynthesizing More in Response to More CO2 in the Atmosphere
A new study finds that plants are photosynthesizing more in response to more carbon dioxide in the atmosphere, but nowhere near enough to remove all emissions.
Plants Buy Us Time to Slow Climate Change – But Not Enough to Stop It
New research from Berkeley Lab and UC Berkeley shows that plants are photosynthesizing more in response to more carbon dioxide in the atmosphere.
Because plants take up carbon dioxide from the atmosphere and convert it into food, forests and other similar ecosystems are considered to be some of the planet’s most important carbon sinks. In fact, the United States and many other countries that participated in last month’s UN Climate Change Conference have made nature-based solutions a critical feature of their carbon dioxide mitigation framework under the Paris Agreement.
As human activities cause more carbon dioxide to be emitted into the atmosphere, scientists have debated whether plants are responding by photosynthesizing more and sucking up even more carbon dioxide than they already do – and if so, is it a little or a lot more. Now an international team of researchers led by Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have used a novel methodology combining remote sensing, machine learning, and terrestrial biosphere models to find that plants are indeed photosynthesizing more, to the tune of 12% higher global photosynthesis from 1982 to 2020. In that same time period, global carbon dioxide concentrations in the atmosphere grew about 17%, from 360 parts per million (ppm) to 420 ppm.
The 12% increase in photosynthesis translates to 14 petagrams of additional carbon taken out of the atmosphere by plants each year, roughly the equivalent of the carbon emitted worldwide from burning fossil fuels in 2020 alone. Not all of the carbon taken out of the atmosphere through photosynthesis is stored in ecosystems, as much is later released back to the atmosphere through respiration, but the study reports a direct link between the increased photosynthesis and increased global carbon storage. The study was published in Nature.
“This is a very large increase in photosynthesis, but it’s nowhere close to removing the amount of carbon dioxide we’re putting into the atmosphere,” said Berkeley Lab scientist Trevor Keenan, lead author of the study. “It’s not stopping climate change by any means, but it is helping us slow it down.”
Measuring photosynthesis
Because carbon dioxide stays in the atmosphere decades longer than other greenhouse gases driving global warming, efforts to reduce it are critical to mitigating climate change. Plants, through photosynthesis, and soils sequester roughly a third of carbon dioxide emissions released into the atmosphere each decade from the burning of fossil fuels.
During photosynthesis, plants open tiny pores on their leaf surfaces to suck carbon dioxide from the air and produce their own food. To measure this photosynthetic activity, scientists can put a leaf in a closed chamber and quantify the dropping carbon dioxide levels in the air inside. But it’s far more difficult to measure how much carbon dioxide an entire forest takes up.
Through initiatives such as AmeriFlux, a network of measurement sites coordinated by the Department of Energy’s AmeriFlux Management Project at Berkeley Lab, scientists from across the world have built over 500 micrometeorological towers in forests and other ecosystems to measure the exchange of greenhouse gases between the atmosphere and the vegetation and soil. While these flux towers can help estimate photosynthesis rates, they’re expensive and thus limited in their geographic coverage, and few have been deployed long-term.
This explains why scientists rely on satellite images to map how much of the Earth is green and thus covered by plants, which allows them to infer global photosynthetic activity. But with rising carbon dioxide emissions, those estimates based solely on greenness become problematic.
Bringing history in the picture
Satellite images can capture the extra green to account for additional leaves plants put out due to accelerated growth. But they often don’t account for each leaf’s increased efficiency to photosynthesize. Also, this efficiency doesn’t increase at the same rate at which carbon dioxide builds up in the atmosphere.
Previous efforts to estimate how photosynthesis rates respond to increased carbon dioxide concentrations found widely varying results, from little to no effects on the low end, to very large effects on the high end.
“That magnitude is really important to understand,” said Keenan, who is also an assistant professor in UC Berkeley’s Department of Environmental Science, Policy and Management. “If the increase [in photosynthesis] is small, then we may not have the carbon sink we expect.”
So Keenan and his team of researchers took a new approach: they looked back at nearly three decades of carbon sink estimates made by the Global Carbon Project. They compared these with predictions from satellite images of the Earth taken between 1982 and 2012 and models using carbon exchange between the atmosphere and land to make carbon sink estimates.
“Our estimate of a 12% increase comes right in the middle of the other estimates,” he said. “And in the process of generating our estimate, it allowed us to re-examine the other estimates and understand why they were overly large or small. That gave us confidence in our results.”
While this study highlights the importance of protecting ecosystems that are currently helping slow down the rate of climate change, Keenan notes that it’s unclear how long forests will continue to perform this service.
“We don’t know what the future will hold as far as how plants will continue to respond to increasing carbon dioxide,” he said. “We expect it will saturate at some point, but we don’t know when or to what degree. At that point land sinks will have a much lower capacity to offset our emissions. And land sinks are currently the only nature-based solution that we have in our toolkit to combat climate change.”
Reference: “A constraint on historic growth in global photosynthesis due to increasing CO2” by T. F. Keenan, X. Luo, M. G. De Kauwe, B. E. Medlyn, I. C. Prentice, B. D. Stocker, N. G. Smith, C. Terrer, H. Wang, Y. Zhang and S. Zhou, 8 December 2021, Nature.
DOI: 10.1038/s41586-021-04096-9
The study was supported in part by NASA and the DOE Office of Science. Among the co-authors were Berkeley Lab postdoctoral fellows Nicholas Smith, Yao Zhang, Xiangzhong Luo, and Sha Zhou, all now at other institutions.
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