Fluctuating sunlight slows down the Rubisco enzyme and reduces the photosynthetic productivity of crops

Cowpea field experience. Credit: Lancaster University

Researchers from Lancaster University working to improve the sustainable productivity of staple crops in sub-Saharan Africa have discovered a defect in an important enzyme within cowpea – and they believe this deficiency is likely shared with other crops.

All the carbon in our bodies, in food, and in the entire biosphere, results from the uptake of carbon dioxide in photosynthesis by a single enzyme known to biologists as Rubisco. Not surprisingly, given its importance, this protein is the most abundant in the world.

“Robisco plays a central role in photosynthesis and greatly limits carbon uptake in crop plants,” said Elizabeth Carmo Silva, Professor of Crop Physiology at Lancaster University. “Leaves adjust Rubisco activity with solar abundance. However, we found that this adjustment is imperfect, and there is often a mismatch between how active Rubisco is and how much solar energy is available for photosynthesis.”

Cowpea is grown throughout Africa due to its high protein content but is especially important in West Africa, where it is the most important source of vegetable protein. In a new study published in nature plantsProfessor Carmo Silva and Lancaster University Research Fellow Dr Sam Taylor found that when cowpea leaves permeate the shade, the activity of the Rubisco enzyme decreases more rapidly than previously thought.

This is important because every day, as the sun travels across the sky over crops in farmers’ fields, leaves cast their neighbors from sunlight into shade and back again. When a shaded leaf returns to the sun, Rubisco’s activity takes several minutes to prepare for the new abundance of solar energy, missing opportunities to convert that energy into sugars. By adding up the effect of those minutes of lost productivity throughout the day, it is estimated that this costs at least 20 percent of potential carbon dioxide uptake.

“Photosynthetic responses are not immediate. Leaves take a few minutes to adjust when going from shade to high light, and during those minutes the leaf does not absorb as much carbon dioxide as its light energy, so there is a significant loss,” said Professor Carmo Silva, who is leading this research. The Realization of Increased Photosynthesis Efficiency (RIPE) Project “We set out to identify the differences between cowpea species that influence the speed of activation, to try to identify the fastest species.”

This project is part of the Realizing Increased Photosynthesis Efficiency (RIPE), an international research project aimed at increasing global food production by developing food crops that more efficiently convert the sun’s energy into food, with support from the UK’s Foreign, Commonwealth and Development Office, Food and Agriculture Research Foundation The Bill and Melinda Gates Foundation

The amount of carbon lost during the Rubisco process depends not only on how quickly Rubisco can be reactivated, but also on the starting point: Rubisco’s activity by the time the sunlight returns. This factor is determined by how quickly Rubisco’s natural deactivation occurs in the shadows. Rapid disruption of activation means a bigger hit to carbon uptake in farmers’ crops.

The researchers used a high-throughput biochemical method to show that cowpea leaves should only remain in the shade for five minutes until Rubisco’s activity ended, so even short leaf shading would reduce the plant’s productivity in photosynthesis.

“We’re not clear exactly what is the mechanism from sun to shade that deactivates Rubisco, but we found the process to be very rapid,” said Dr. Taylor. “If the process is slow, you can go back to the sun after several minutes of shade and there won’t be much loss, but, really, you only need to stay in the shade for minutes for the majority of that decrease in activity to happen.”

Despite these challenges, there are reasons for optimism. Only four different types of cowpea were measured out of the thousands of variants present, but the researchers found differences in the speed with which Rubisco was deactivated. This holds the hope that plants with much slower rates of Rubisco inactivation can be found within the broader gene pool of cowpeas. This will allow targeted breeding of cowpeas, and possibly other crops, and improve productivity by reducing the impact of this newly identified deficiency on the Rubisco function.

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more information:
Elizabeth Carmo Silva, faster than expected to inactivate Rubisco in the shade reduces the photosynthetic potential of cowpea in changing light conditions, nature plants (2022). DOI: 10.1038/s41477-021-01068-9. www.nature.com/articles/s41477-021-01068-9

Presented by Lancaster University

the quote: Fluctuating sunlight slows down the Rubisco enzyme and limits the photosynthetic productivity of crops (2022, Jan 20) Retrieved on Jan 21, 2022 from https://phys.org/news/2022-01-fixle-sunshine-rubisco-enzyme-limits. html

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