New research from Michigan State University reveals that photorespiration – long considered a wasteful process – is essential for producing a crucial nutrient for preventing birth defects.
For the first time, scientists have measured how much carbon flows through photorespiration to make folates, a class of compounds that includes vitamin B9 – known for its importance as a prenatal vitamin. According to the study, led by MSU researcher Berkley Walker , about 6 percent of the carbon absorbed by plants is used to make folates. That number plummets by fivefold when photorespiration is suppressed.
These findings, published in Nature Plants , could help scientists engineer plants to boost production of the nutrient important for human health. They also shed light on how a high-carbon dioxide world caused by climate change could make plants less nutritious.
"In cultures where the bulk of their calories come from rice, it's a pretty big deal if that rice is less nutritious," said Walker, an associate professor in the MSU-DOE Plant Research Laboratory and the Department of Plant Biology. "The way plants respond to changing climates is complicated. Understanding how they might adapt can help us plan better for the future."
Plants are like factories, using the raw materials of sunlight, water and carbon dioxide, or CO2, to make sugar they use for food. The foreman of this factory is an enzyme called rubisco, which grabs CO2 and feeds it into the production line.
But sometimes, rubisco gets sloppy on the job and accidentally grabs oxygen, clogging up the assembly line and producing a toxic byproduct called phosphoglycolate. That's when a recycling crew springs into action. In a process called photorespiration, plants neutralize the toxic waste and salvage it into useful compounds.
Scientists have long suspected that photorespiration supported processes like making folates. Until now, it was unclear how much carbon photorespiration contributed to making that vitamin.
To crunch the numbers, Walker and his lab tested a common model plant, called Arabidopsis thaliana. They measured the plant under conditions with or without photorespiration and measured how much CO2 the plant took in by clamping its leaves in an infrared gas analyzer. Then, they sprayed the leaves with liquid nitrogen while still clamped to freeze them immediately. This helped them understand what the leaf was doing while being measured.
Walker's team used mass spectrometry to examine the leaf's chemicals and how they incorporated CO2 over time. Then, they repeated the process for several months, measuring chemical content at different points before plugging the measurements into a computational analysis.
The results provide a stark look at how plant nutrition could change. As the CO2 in the air increases, plants need photorespiration less often. MSU's study found that in those circumstances, the carbon flow to produce vitamin B9 dropped from nearly 6 percent to about 1 percent. That's significant, as vitamin B9 is important during pregnancy to reduce the risk of neural tube defects.
"Understanding how nature makes this vitamin will help us engineer plants fortified with this nutrient," Walker said. "That may become necessary especially in cultures where people can't simply take a multivitamin to make up for less nutritious plants."
The Walker lab's next step is conducting similar experiments with crop plants grown outdoors. They want to know whether the same trends inside the lab are true for plants grown out in the field.
The National Science Foundation-funded project is another example of critical research that lays the foundation for the future.
"We need this knowledge about plants in order to engineer them for the future," Walker said. "If we don't have that foundation, we'll never to get to the application."
By Bethany Mauger
