Plant scientists have developed a new tool called an automated confocal micro-extensometer (ACME). It allows scientists to measure spatial variation in the mechanical properties of plant cells with unprecedented accuracy.
Plant cell growth is limited to the mechanical properties surrounding a cell wall. Cell walls in the growing parts of a plant are thought to be much stretchier than those in mature parts and these local differences in cell wall extensibility affect the overall shape of a plant. Until now, it was not possible to measure cell wall extensibility in the direction of growth in living plants. A team of researchers led by Cris Kuhlemeier from the Institute of Plant Sciences at the University of Bern in Switzerland created a system that can measure that.
"Intuitively the simplest way to do this is to stretch the plant and look at how much each cell stretches," explains first author Sarah Robinson.
Using this principle, the researchers cobbled together a robotic pipeline that combines custom and commercially available parts. They designed a specialized device that holds plants in place without damaging them and then stretched them under a defined pull. The device is mounted on a microscope, controlled by software that allows the user to specify the duration and degree of stretching. High-resolution images of the plants are taken during stretching, and custom-built software uses images to compute mechanical properties in different regions of the plant. The researchers called the device ACME after the fake corporation from the Road Runner/Wile E. Coyote cartoons because they were inspired by the efforts of Wile E. Coyote.
"Thankfully, in the end, we were more successful, but some of our prototypes were less elegant and involved a lot of scotch tape," said Robinson.
Using ACME, the authors demonstrated that cells in the stems of seedlings show gradients of mechanical properties in the presence of the plant growth hormone gibberellic acid. They used their system to show that stretching induces irreversible increased cell length in living plant cells, but that the increases in cell length are partially reversed in dead plant tissues when the stretching stops. While ACME was built to accommodate small samples, it can be adapted for use with larger samples and different imaging systems.
The team made the information for the system freely available so other scientists can use ACME for their research.
ACME has many applications and scope for future use," says Sarah Robinson.
The paper on this research was published in The Plant Cell.