Two New Discoveries Point to Breakthroughs in Frost Resistance

photo by Andreas Øverland | Flickr CC license
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FAFDL Columnist: Patty Johnson | Patty is owner operator of Pannill’s Gate Farm, Orange, VA.

 


Renewable Fuel Standards come and go, but you never know where the research will take you.

Having survived introduced species, modern cultivation practices and the Renewable Fuels Standard, Prairie Cordgrass (Spartina pectinata), a native warm season perennial is showing new value as a tool to help other plant species thrive in changing conditions.

Typically forming a monoculture along ponds and slow moving streams, prairie cordgrass’ role in stream-bank stabilization has long been known, while its potential as a bio-mass crop – competitive and high-yielding in marginal areas with little chance of becoming invasive – means that it’s been widely studied. But it’s the plant’s genetic strategies for adapting to abiotic stresses – salt, flooding, and more importantly, rapid freezing – that make it so appealing to researchers and commercial interests. How does a plant protect itself from an event that occurs over the time-frame of minutes, and then repair itself when that stress is gone?

photo by Matt Lavin | Flickr CC license

Researchers at the University of Illinois have isolated genetic traits that allow prairie cordgrass to survive stress from frost. If these traits can be transferred to crops, it would be hugely valuable.

After observing that prairie cordgrass had survived a late-April frost had damaged its neighbors, University of Illinois agronomist D.K. Lee set about trying to isolate the genetic and biological characteristics of the frost resistance he’d observed.

Lee already knew that prairie cordgrass, Spartina pectinata, was especially tolerant of flooding and salt stress, but this discovery confirmed his suspicion that cordgrass was tolerant of freezing, too. Being tolerant of environmental stress factors is important for biomass crops, because they are often grown on so-called marginal land where conditions are far from perfect. With its tolerance of several major stress factors, cordgrass has the potential to be grown in more places than other perennial energy crops.

The next step for Lee and his research group was to identify the molecular changes that keep cordgrass perky in cold weather.
“Unlike salt and flooding stress, freezing usually happens abruptly. The plant has to react quickly. To find out what was happening at the molecular level, we grew cordgrass in a growth chamber at 25 degrees Celsius and then abruptly moved them into another growth chamber set to -5 degrees.

“We looked at gene expression within five minutes after exposure to freezing temperatures. We found some unique genes being activated right away and then different ones turning on 30 minutes later,” Lee says.

The team suspects that the initial genetic response protects the cells from freezing. Typically, ice crystals form in the spaces outside the cell when a plant is exposed to freezing temperatures. Once these “seed crystals” form, they grow quickly and burst the living cells. To avoid this, cordgrass may quickly pump ions outside the cell, keeping ice crystals from forming or growing. The secondary reactions that occur after 30 minutes may have to do with repairing damaged cells, allowing the plant to recover more quickly.

Lee says the findings just scratch the surface; much more needs to be done to fully understand the genetic mechanisms that allow cordgrass to avoid tissue damage during freezing temperatures. Once the system is fully understood in cordgrass, the hope is that it can be applied to other crops.

“Corn farmers are always looking to plant earlier in the spring,” Lee says. “They think if they plant early, they could see a yield benefit. Currently, crop insurance won’t cover corn if farmers plant before a certain date, because there’s a big risk of frost. If we understand more about freezing tolerance, we could eventually apply it to annual crops and potentially expand the production area for crops such as corn.”

By identifying and understanding the biological mechanisms that allow Prairie Cordgrass to react to the sudden stress of freezing, researchers will hopefully have another tool to help improve the stress tolerance of commercial crop species. Meanwhile in Germany, researchers have identified plant hormones – brassinosteroids – in brassica crops that have the ability to protect those plants against frost in addition to other stressors.

While wild-type varieties often still managed to survive temperatures of six degrees below zero, most of the mutants already displayed clear signs of damage at this point, which demonstrates the essential role steroid hormones play in this process. By analyzing the process, the researchers found that brassinosteroids increase frost resistance by regulating a protein called CESTA. This protein uses a signal cascade to control gene expression. In this manner, it in turn influences the protein composition of the cells, which among other things appears to lead to a change in the fatty acid composition. This ensures that the plant stocks up on a type of ‘winter fat’ on a molecular level, thereby protecting it from potential cold damage.

. . . She’s convinced that “our discovery that brassinosteroids boost both growth and cold resistance will open up new possibilities for bringing out both characteristics in plants.” She asserts that it’s also possible to spray crop plants with brassinosteroids to achieve both effects. “That may be a viable method — at least, that’s what the findings suggest.”

Brassicas encompass a wide variety of crops, from mustard, to canola, to cabbages and broccoli. Figuring out how to dail brassinosteroids expression up and down, breed them into other crops or create sprayable brassinosteroids could make this discovery a pretty big deal.

Watch this space.

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