Fickle sunshine slows down Rubisco and limits photosynthetic
productivity of crops

Date:
January 20, 2022
Source:
Carl R. Woese Institute for Genomic Biology, University of Illinois
at Urbana-Champaign
Summary:
A team of researchers discovered an imperfection in how Rubisco
functions in cowpea and how they can improve it across crops to
increase productivity.



FULL STORY ==========================================================================
All of the carbon in our bodies, in food, and in the entire biosphere,
results from the assimilation 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. Researchers from Lancaster University are working to improve
the sustainable productivity of key crops in sub-Saharan Africa have
discovered a new imperfection in the way Rubisco functions in cowpea
and believe this imperfection is likely shared with other crops.


========================================================================== "Rubisco plays a central role in photosynthesis and frequently limits
carbon assimilation in crop plants," said Elizabete Carmo-Silva, professor
of crop physiology at Lancaster. "Leaves adjust the activity of Rubisco
to the abundance of solar energy. However, we found that this adjustment
is imperfect, and frequently there is a mismatch between how active
Rubisco is and how much solar energy is available for photosynthesis."
Cowpea is grown throughout Africa because of its high protein content but
is particularly important in West Africa, where it is the most important
source of vegetable protein. In a recent study, published in Nature
Plants, Carmo-Silva and Senior Research Associate Sam Taylor found that
as cowpea leaves go into the shade, the activity of the enzyme Rubisco
drops more rapidly than was previously appreciated.

This is important because every day, as the sun inevitably tracks across
the sky above crops in farmers' fields, leaves cast their neighbors
from sunlight into the shade and back again. When a shaded leaf comes
back into the sun, Rubisco activity takes several minutes to gear up to
the new abundance of solar energy, resulting in missed opportunities to
convert that energy into sugars.

By adding up the effect of those lost minutes of productivity across a
day, this has been estimated to cost at least 20 percent of potential
carbon dioxide uptake.

"Photosynthetic responses are not immediate. Leaves take quite a few
minutes to adjust when going from shade to high light, and during
those minutes the leaf is not assimilating as much CO2 as it has the
light energy for, so there is a substantial loss," said Carmo-Silva,
who is leading this research for the Realizing Increased Photosynthetic Efficiency (RIPE) project. "We set out to identify differences among
cowpea varieties that affect the speed of activation, to try and identify
which ones are faster." This project is part of Realizing Increased Photosynthetic Efficiency (RIPE), an international research project that
aims to increase global food production by developing food crops that
more efficiently turn the sun's energy into food, with support from the
U.K. Foreign, Commonwealth & Development Office, the Foundation for Food & Agriculture Research, and the Bill & Melinda Gates Foundation.

The amount of carbon lost during the Rubisco process depends not only on
the speed with which Rubisco can be re-activated but also on the starting point: the Rubisco activity at the moment when sunlight returns. This
factor is determined by the speed of natural de-activation of Rubisco
that happens in the shade. Faster de-activation means a bigger hit on
carbon assimilation in farmers' crops.

The researchers used a high-throughput biochemical method to show that
cowpea leaves only need to be in shade for as little as five minutes
for Rubisco activity to bottom out, so even brief shading of leaves will
lower the plant's photosynthetic productivity.

"We're not exactly clear what the mechanism is from the sun to shade
that takes Rubisco activation down, but we have found that the process
is quite quick," said Taylor. "If it was a slow process, you could go
back into the sun several minutes after shade and there wouldn't be a
great loss, but, really, you only need to be in shade for minutes for
the majority of that drop in activity to have happened." Despite these challenges, there are reasons to be optimistic. Only four different
types of cowpea were measured from the 1000s of variants that exist,
but the researchers did find differences in the speed at which Rubisco
de- activated. This holds out hope that within the wider gene pool of
cowpea, plants with much slower rates of Rubisco de-activation can be
found. That would allow targeted breeding for cowpea, and perhaps other
crops, improving productivity by minimizing the impact had by this newly identified imperfection in Rubisco function.

========================================================================== Story Source: Materials provided by Carl_R._Woese_Institute_for_Genomic_Biology,_University of_Illinois_at_Urbana-Champaign. Original written by Allie Arp. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Samuel H. Taylor, Emmanuel Gonzalez-Escobar, Rhiannon Page, Martin
A. J.

Parry, Stephen P. Long, Elizabete Carmo-Silva. Faster than expected
Rubisco deactivation in shade reduces cowpea photosynthetic
potential in variable light conditions. Nature Plants, 2022; DOI:
10.1038/s41477-021- 01068-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220120125339.htm

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