Quantifying the plant actin cytoskeleton response to applied pressure using nanoindentation

Area of Science:

• Plant biology
• Cellular defense mechanisms
• Mechanobiology

Background:

• Plants and animals detect pathogen signals for defense.
• Plant cell walls provide a barrier, reinforced by the actin cytoskeleton during infection.
• The physical forces triggering plant defense responses are not well understood.

Purpose of the Study:

• To quantify the magnitude and duration of mechanical forces that trigger plant defense responses.
• To investigate the role of the actin cytoskeleton in plant mechanical sensing.

Main Methods:

• Mechanical stimulation of Arabidopsis hypocotyls using a tungsten microneedle and nanoindentation with a diamond spherical tip.
• Confocal microscopy to observe actin cytoskeleton reorganisation in epidermal cells.
• Quantification of force and contact time required to elicit a response.

Main Results:

• Actin cytoskeleton reorganisation in Arabidopsis epidermal cells occurred within 116 ± 49 seconds.
• A force as small as 4 μN applied for 21.6 seconds was sufficient to trigger actin reorganisation.
• The detected force threshold is significantly lower than the invasive forces of common plant pathogens.

Conclusions:

• Plant cells possess mechanosensory capabilities to detect and respond to physical stimuli.
• The actin cytoskeleton plays a crucial role in mediating plant responses to mechanical stress.
• This study provides the first quantification of mechanical force thresholds for plant defense.