According to biologists, plant roots can seek out warm patches, in the soil. They have shown that roots can detect and respond to tiny changes in temperature.
They found that maize roots can detect a difference in temperature as small as 0.05 C degrees. This may sound impressive but according to biologists, it is nowhere close to being a world record. Previously it was shown temperature differences which are one-hundredth of this size could be detected by slime moulds.
In response to gravity roots grow usually grow straight down. The root bends towards the warm side if one side of the root is warmer in comparison to the other.
In order to bring difference in temperature, special aluminum block with two parallel channels running through it was constructed. By piping cold water through one channel and hot water through the other they were able to create a temperature gradient between the two. The researchers, attached agar, a jelly-like substance, to the metal between the channels to provide a surface for the roots to grow down.
It was found that maize roots are most sensitive to temperature differences at around 15 degree Celsius, which is a normal soil temperature for maize. At higher temperatures of around 32 degree Celsius the researchers found that the roots do not respond to temperature differences at all.
This shows that the response is important in nature. This is actually of considerable advantage. If roots went straight down, they would very quickly get out of the nutrient-rich zone. Instead roots which use this ability will stay in the warm, upper layer of soil, where nutrients are most plentiful.
The biologists do not know how roots detect temperature differences. All biological thermometers are still a mystery. Almost nothing is known about temperature sensing in any organism. It is clear that humans sense hot and cold, but on a molecular level it is not clear what they are using for a thermometer.
One idea is that temperature sensing might involve fats or lipids which are embedded in biological membranes. Cells could gauge the temperature by monitoring when particular lipids solidify or melt.
In the bacterium Escherichia coli, temperature sensing has been linked to a protein which is involved in detecting the concentration of a particular nutrient. E coli uses the protein to help direct its movement towards high concentrations of the nutrient and regions of optimal temperatures. Scientists do not know if other organisms do this.
A biologist suggests that the root’s thermometer might be in its apex. This is where roots sense both gravity and moisture and it is possible that the three root senses are linked.
No one knows if shoots can sense differences in temperature. But shoots will normally grow towards warmth anyway because they grow towards the light.