Last updated May 10, 2018 at 11:47 am
A pair of amino acids is all that stands between survival and shrivelling for grass crops.
Just two amino acids are responsible for the drought tolerance of cereal crops, researchers have found, raising hopes that a tiny genetic tweak could improve the drought resistance of other types of edible plants.
Cereal grasses comprise about 80 per cent of all plant-based foods farmed commercially, in part because they are less vulnerable to water scarcity than other crops.
To find out why, Rainer Hedrich, Dietmar Geiger and Peter Ache from Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, examined the internal structures of barley. Their results are reported in a paper published in the journal Current Biology.
Barley’s drought resistance, they discovered, is linked to an evolutionary adaptation shared by all grasses – their guard cells. These are cells that surround breathing holes, or stomata, positioned in the leaves.
While most non-grass plants (known as dicots) have guard cells that are shaped like little kidneys, those in grasses (monocots) are dumbbell-shaped.
There is a pair of guard cells around individual stoma in grasses, while dicots have only one. Additionally, monocot guard cells are assisted by two other cells, known as subsidiary cells, positioned directly behind them.
Molecular action by the monocot guard cells and subsidiaries prompts the rapid closure of stomata, limiting water loss through evaporation, and enhancing moisture retention.
This action is catalysed by the stomata themselves, which release a stress hormone called abscisic acid (ABA) when water becomes scarce.
The hormone activates the guard cells, leading to the stomata being closed off within just a few minutes.
Hedrich and colleagues found that a protein inside the guard cells, called SLAC1, was responsible for the effect. The protein contains a “nitrate sensor”, made of two amino acids, that works alongside the stress hormone to push the guard cells into action.
“Interestingly, we found that nitrate must be present in brewing barley and other grass cereals in addition to ABA to enable the pore to close,” explains Ache.
Hedrich adds: ‘By combining the two, the barley is better able than other plants to negotiate between the extremes of ‘dying of hunger’ and ‘dying of thirst’ when facing water scarcity.”
The researchers are now studying the two-amino-acid sensor in more detail, with the eventual aim of inserting into other crops.
“If this step increases their stress tolerance, we can consider breeding optimised potatoes, tomatoes or rapeseed,” Hedrich says.