For the first time, researchers have determined the touch response of cereals such as barley, wheat and oats at the molecular and genetic levels. The research shows that touching probably strengthens the defences of cereal crops and makes them less attractive to insects.
All plants are exposed to the elements and other organisms and are therefore affected by wind, rain, herbivores, insects, obstacles, neighbouring plants and other phenomena that affect the plants’ ability to grow.
Although researchers have long known how mechanical stimulation affects crops, this is the first time that researchers have determined what actually happens genetically inside the plants when they are touched.
The research shows that the plants react immediately to touch and that the molecular activity peaks about 25 minutes after plants are touched. The research also shows which signalling pathways are activated, and this can make companies within plant breeding more knowledgeable about the potentially beneficial effects of touching plants, and how, for example, this can be used to create higher yielding and more resistant cereal crops.
“For example, when cereal plants are touched, stress hormones are activated that are also active in defending the plants against larvae. The plants respond similarly to the adrenaline response in humans, and touch also causes plants to make stronger cell walls. This knowledge may be used to develop treatments for cereals that make them more robust and resistant to attack without needing pesticides,” explains a researcher behind the study, Olivier Van Aken, Senior Lecturer, Department of Biology, Lund University, Sweden.
The research has been published in The Plant Journal.
Mechanical stimulation is common in Japan
Plants do not grow independently of their surroundings.
Wind often makes trees close to the beach lower, stronger and more lopsided than trees further inland.
Similarly, individual trees in a field are often shorter and have larger crowns than trees in a forest, where they need to grow tall and slender to maximise exposure to sunlight.
Mechanical stimulation is used in both Japan and Africa to promote plant growth. Many farmers physically manipulate seedlings to make them stronger so that they can withstand more environmental stress later.
Researchers have long been interested in how this physical treatment affects plants at the genetic and molecular levels. Although this has been thoroughly determined in the model plant Arabidopsis, the new study is the first to determine the molecular mechanisms in wheat, oats and barley.
“When we began the study, we were surprised that no one had studied this before – especially because of the great interest in developing more resistant plants. One problem associated with wheat and barley is that they often grow so tall that they become vulnerable to wind and rain, which can flatten the plants so that the grains germinate on the ground before they can be harvested. Many farmers therefore use shorter lower-yielding varieties of these cereals. But understanding the molecular mechanisms behind plants’ response to external influences could lead to determining how to stimulate these high-yield crops to grow less tall by exposing them to mechanical stress,” says Olivier Van Aken.
In-depth analysis of touch response at the molecular level
The researchers brushed the leaves of cereal crops with a soft dustpan brush.
They then analysed messenger RNA, which represents the molecular genetic stage between genes and proteins, to determine the genetic and molecular response to touch at different times from 10 minutes to 4 hours afterwards.
The researchers also analysed whether brushing one leaf on a plant creates a response in other leaves.
Finally, they investigated which signalling pathways and functions the expressed genes are part of.
Plants respond very rapidly. Arabidopsis responds after a few seconds, and cereal plants probably respond after a few seconds, but the researchers only measured after 10 minutes.
The signal peaked at 25 minutes and then decreased.
The researchers also found that brushing certain leaves of oats and barley caused a signal in other leaves.
“After just a few minutes, the first genes begin to be expressed, and hundreds to thousands of genes end up having their expression changed following touching. That shows how important touch is for the plant,” explains Olivier Van Aken.
Touch increases the production of stress hormones
The most interesting part of the study, however, was the genes that touch activates.
First, the genes necessary for the entire response are activated. These include genes for kinases and transcription factors, which play a role in the entire molecular machinery that translates genes into proteins. This is like turning the key in the ignition of a car to make it start.
Then the genes involved in building cell walls are activated. This applies to genes for producing lignin and cellulose. The increased production of these biomolecules helps to strengthen the cell walls.
The research also shows that the calcium signalling changes drastically inside the plant cells. This is because calcium normally resides between the cells, but when the cells are damaged, calcium can leak into the cells and participate in several signalling pathways.
Damage to the cells also increases the production of jasmonic acid, a stress hormone that is released as part of the plants’ defences when insects start feeding on the leaves.
“In addition, several secondary metabolites are activated; we do not know their function, but perhaps they are also involved in the plants’ defences,” says Olivier Van Aken.
Plants can be anaesthetised with drugs intended for humans
The study determined how cereal crops respond when exposed to mechanical stress, and according to Olivier Van Aken, this can be used in developing more resistant crops.
Using the new knowledge, plant breeders can see which genes in plants are affected by mechanical stress, and they can perhaps be activated or deactivated with the aim of making the plants more robust – for example, so that they do not topple over in the wind or can better defend themselves against insects.
Olivier Van Aken hopes to learn more about how plants in general sense that they are being touched.
In this context, researchers from Czechia have shown that anaesthetics intended for humans can prevent plants from reacting to being touched. In Arabidopsis, researchers also found the same genes that humans use to sense touch, but they do not seem to have the same effect in plants.
Thus, a link is still missing between touch and how the touch response is activated.
“There is still much to be understood at the fundamental level. In addition, we are also very interested in determining how we can translate this fundamental understanding into practice that is actually relevant for crops,” concludes Olivier Van Aken.