Mechanical Measurements on Living Plant Cells by Micro- indentation with Cellular Force Microscopy - Plant Cell Morphogenesis: Methods and Protocols - page 135

Fig. 3 The quality of experimental data depends on sample movement during the measurements. ( a , b ) Shows
correct data, for a properly immobilized onion peel. The force-indentation curve ( a ) represents 3 loading/
unloading cycles of a total duration of 7 s. The height map ( b ) refl ects the proper shape of the sample (here,
two adjacent cells). ( c , d ) Shows artifacts in data acquired along a tomato stem that was laid horizontal for the
experiment. The gravitropic response induced an upward movement of the sample. Force-indentation curve
( c ) shows a drift in the position during the 3 loading-unloading cycles, in contrast with the overlapping curves
of the previous example ( a ). The distance between curves at maximal force (7 μ N) shows a movement of

approximately 50 nm/s (3 m/min). The height map ( d ) presents a characteristic zigzag shape in the XZ plane.

This artifact is due to the upward movement of the sample over time while the probe goes back and forth along
the X -axis to scan the surface

μ

made only for the parts of the sample which are perpendicular to
the force sensor axis. This can be achieved by performing a scan
grid of the tissue surface and detecting the surface slope (Fig. 1 ).
The grid size and lateral resolution should be suffi cient to recog-
nize individual cells and compute the indentation angle accurately
at each point. However, too high a resolution slows down the
experiment and makes it more invasive. Force-indentation curves
can be acquired up to a predefi ned force threshold or indentation
depth. The step size in Z direction should be adjusted so that the