connections among CMFs can be weakened and loosened, creating
gaps where newly synthesized components are deposited. This
process releases the wall tension, which enables the wall to expand
and the cell to grow [1, 7, 8]. Accessing the cell wall mechanical
properties remains a challenge due to the heterogeneous size of the
wall components and their complex interactions. Highly sensitive
biophysical tools need to be used to understand the interplay
between the molecular players involved in the cell wall modifications and mechanics. These tools can provide information about
some mechanical measures such as wall stiffness or creep rate.
In the recent decade, new methods to measure the mechanical
forces in plant tissues have been developed [9], among which,
stretching the tissues (using an extensometer) or pressing on the
cells or cell regions (applying an indenter) are the most common.
An extensometer consists of two clamps (to grab the material) and a
force sensor that records the force while pulling the sample. This
tool can give information about how much force needs to be
applied to break tissue integrity and it is also well suited to measure
creep rates, wall extensibility, and yield threshold in various plant
[10–12] and animal organs [13]. On the other hand, the indentation techniques gather information by touching the surface with a
mechanical probe, which brings insights into the elasticity and the
turgor pressure of the cells on the surface. The indenter size determines the scale of observations, which can be conducted at cellular
and tissue levels (microscale) or subcellular level (nanoscale).
Microindentation has been used to measure the mechanical forces
in single cells [14–16] and multicellular organisms [17–
19]. Nanoindentation is known as atomic force microscopy
(AFM), which is able to image molecular structures at the nanoscale. Most of the indentation measurements are nondestructive
and can be carried on live material; however, this technique is
sensitive to any uncontrolled movements and the sample requires
a solid stabilization.
AFM is characterized by a high precision movement of a
mechanical probe, which allows a very accurate scan and detailed
reconstruction of the topography and the measurement of the
mechanical properties. More in detail, AFM consists of a springlike cantilever with a tiny tip to scan the surface of the sample
(Fig. 1a), piezo crystals (moving the cantilever in XYZ directions
and generating its oscillations), a laser and a detector (recording the
motion and deflection of the cantilever) and a motorized probe
holder and/or stage for the sample to move in XYZ directions. The
AFM hardware is controlled by computer software that shows the
measurements obtained. AFM is usually connected to a microscope, which allows taking an optical image or movie while indenting the sample, but it can also be combined with confocal
microscopy and RAMAN spectroscopy.
350
Mateusz Majda
gaps where newly synthesized components are deposited. This
process releases the wall tension, which enables the wall to expand
and the cell to grow [1, 7, 8]. Accessing the cell wall mechanical
properties remains a challenge due to the heterogeneous size of the
wall components and their complex interactions. Highly sensitive
biophysical tools need to be used to understand the interplay
between the molecular players involved in the cell wall modifications and mechanics. These tools can provide information about
some mechanical measures such as wall stiffness or creep rate.
In the recent decade, new methods to measure the mechanical
forces in plant tissues have been developed [9], among which,
stretching the tissues (using an extensometer) or pressing on the
cells or cell regions (applying an indenter) are the most common.
An extensometer consists of two clamps (to grab the material) and a
force sensor that records the force while pulling the sample. This
tool can give information about how much force needs to be
applied to break tissue integrity and it is also well suited to measure
creep rates, wall extensibility, and yield threshold in various plant
[10–12] and animal organs [13]. On the other hand, the indentation techniques gather information by touching the surface with a
mechanical probe, which brings insights into the elasticity and the
turgor pressure of the cells on the surface. The indenter size determines the scale of observations, which can be conducted at cellular
and tissue levels (microscale) or subcellular level (nanoscale).
Microindentation has been used to measure the mechanical forces
in single cells [14–16] and multicellular organisms [17–
19]. Nanoindentation is known as atomic force microscopy
(AFM), which is able to image molecular structures at the nanoscale. Most of the indentation measurements are nondestructive
and can be carried on live material; however, this technique is
sensitive to any uncontrolled movements and the sample requires
a solid stabilization.
AFM is characterized by a high precision movement of a
mechanical probe, which allows a very accurate scan and detailed
reconstruction of the topography and the measurement of the
mechanical properties. More in detail, AFM consists of a springlike cantilever with a tiny tip to scan the surface of the sample
(Fig. 1a), piezo crystals (moving the cantilever in XYZ directions
and generating its oscillations), a laser and a detector (recording the
motion and deflection of the cantilever) and a motorized probe
holder and/or stage for the sample to move in XYZ directions. The
AFM hardware is controlled by computer software that shows the
measurements obtained. AFM is usually connected to a microscope, which allows taking an optical image or movie while indenting the sample, but it can also be combined with confocal
microscopy and RAMAN spectroscopy.
350
Mateusz Majda