We don’t want to alarm vegetarians, and there is no reason to think plants have feelings. Still, they are more like us than we knew, using important neurotransmitters to signal environmental stress. The discovery has profound implications from crop science to understanding the way certain drugs operate.
"We've known for a long time that the animal neurotransmitter GABA (gamma-aminobutyric acid) is produced by plants under stress, for example when they encounter drought, salinity, viruses, acidic soils or extreme temperatures," said Dr Matthew Gilliham of the University of Adelaide.
However, Gilliham told IFLScience that GABA “was thought to have a purely metabolic role”, with its production being a way for plants to cope with the stress better, rather than being a signaling mechanism.
In Nature Communications, however, a team led by Gilliham has shown that GABA provides a signal instructing a protein in the membranes of plant cells to alter electrical conductivity, preventing the passage of negatively charged ions from inside the cells to outside them.
This wasn’t detected previously, Gilliham told IFLScience, because the protein that responds to GABA in plants is quite different from the one in animals. “If you look at the two proteins, they are very different in structure and identity,” Gilliham said. “But there is one tiny part that is similar, the bit that responds to GABA.”
The differences between the proteins open questions as to whether the usage of the same transmitter is a coincidence. “It is possible it came from a common ancestor or evolved separately, or it could have been transferred between organisms by bacteria,” says Gilliham. “We’re yet to really explore that, and it raises interesting questions.”
Irrespective of origins, the authors believe the discovery opens the way to advances in crop management. “The major stresses agricultural crops face like pathogens and poor environmental conditions account for most yield losses around the planet – and consequently food shortages,” said co-lead author Professor Stephen Tyerman, “By identifying how plants use GABA as a stress signal we have a new tool to help in the global effort to breed more stress-resilient crops to fight food insecurity.”
While wild plants have evolved their responses to stress over millions of years, presumably with evolutionary benefits, Gilliham says, the crops we rely on are different. “Our crops have been domesticated over time and been bred to do well in good conditions, but not necessarily poor conditions,” Gilliham told IFLScience. “If we can study the ways they respond to stress we may find out how to help them adapt better to bad weather or salty environments.”
The fact that such different branches of the tree of life have put GABA to use demonstrates its value as a signal transmitter. Gilliham told IFLScience that this is probably because it can be released so rapidly. “Insects can walk across a leaf and the GABA concentration will increase in seconds,” he said.
Some drugs that interact with GABA-signaling proteins are derived from plants, and the team suspects that we may for the first time be able to learn why they work.