Researchers Discover Mechanism Protecting Plants Against Freezing

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Christoph Benning (view larger image)

New ground broken by an MABR researcher helps explain how plants protect themselves from freezing temperatures and could lead to discoveries related to plant tolerance of drought and other extreme conditions.

“This brings together two classic problems in plant biology,” said Christoph Benning, MABR biochemistry and molecular biology scientist. “One is that plants protect themselves against freezing; scientists long thought it had something to do with cell membranes but didn’t know exactly how. The other is the search for the gene for an enigmatic enzyme of plant lipid metabolism in the chloroplasts, shedding light on how cell membrane building blocks are made.”

In an article published online by the journal Science, Benning and then-doctoral degree candidate Eric Moellering and technical assistant Bagyalakshmi Muthan describe how a particular gene in Arabidopsis thaliana, common mustard weed, leads to the formation of a lipid that protects chloroplasts and plant cell membranes from freeze damage by a novel mechanism.

Working on his dissertation project under Benning, Moellering identified a mutant strain of Arabidopsis that can’t manufacture the lipid and linked this biochemical defect to work done by others who originally described the role of the gene in freeze tolerance but did not find the mechanism.

“One of the big problems in freezing tolerance or general stress in plants is that some species are better at surviving stress than others,” Moellering said. “We are only beginning to understand the mechanisms that allow some plants to survive while others are sensitive.”

There is no single mechanism involved in plant freezing tolerance, Moellering added, so he can’t say that his findings will lead anytime soon to genetic breakthroughs making citrus or other freezing-intolerant plants able to thrive in northern climates. But it does add to the understanding of how plants survive temperature extremes.

Much plant damage in freezing temperatures is due to cell dehydration—water is drawn out as it crystallizes, and the organelle or cell membrane shrivels as liquid volume drops. Lipids in the membranes of tolerant plants are removed and converted to oil that accumulates in droplets, the researchers said, retaining membrane integrity, keeping membranes from fusing with one another and conserving the energy by storing oil droplets. With rising concern globally about water supplies and climate change, scientists see additional reasons to understand the ways hardy plants survive.

The research, funded by the U.S. Department of Energy Office of Science-Basic Energy Sciences and the Michigan AgBioResearch, also leads to speculation that freezing itself can prompt cell proteins directly to change the composition of the membrane, without activation by gradual acclimation. That has been a major focus in the plant freezing tolerance field, the researchers said.

“This opens a huge door now for people to do this kind of research and to redirect researchers,” Benning said. “There are lots of them out there trying to understand cold, salt and drought tolerance in plants, and we’ve given them a new idea about how they can approach this problem mechanistically.”

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