Institut de Biologie StructuraleGrenoble / France

Contact person(s) related to this article / PELLEQUER Jean-Luc


Nanobiomechanics is the study of stiffness of biological materials such as cells or organs.

An AFM standardized procedure in nanomechanics

Procedure that allows a reliable determination of the elastic (Young’s) modulus of soft
samples, including living cells, by atomic force microscopy (AFM).

Following the European COST TD1002 project that we coordinated between 2010 and 2014, a multi-site and multi-machine round-robin study has been developed to improve the quantification of the elastic Young modulus of cells. This study produced a protocol called SNAP (temporarily named Dubrovnik procedure). The essence of the protocol is to improve the calibration of AFM instruments using pre-calibrated cantilevers whose spring constants have been experimentally determined. This allows a better calibration of the photodiode sensitivity. Once the procedure is applied, variability of elasticity measurements dropped to 1% on hydrogels. Below is shown the improve results (on the right) when the protocol was applied on eukaryotic cells MDCK C11. This is typically a joint project where it is difficult to assign a participatory hierarchy. However, the major role of Hans Oberleithner in the development of this action must be emphasized, as well as the driving role of Manfred Radmacher and also of Hermann Schillers in setting up and distributing the samples for the whole group.

Schillers H, Rianna C, Schäpe J, Luque T, Doschke H, Wälte M, Uriarte JJ, Campillo N, Michanetzis GP, Bobrowska J, Dumitru A, Herruzo ET, Bovio S, Parot P, Galluzzi M, Podestà A, Puricelli L, Scheuring S, Missirlis Y, Garcia R, Odorico M, Teulon JM, Lafont F, Lekka M, Rico F, Rigato A, Pellequer J-L, Oberleithner H, Navajas D and Radmacher M (2017) Standardized Nanomechanical Atomic force microscopy Procedure (SNAP) for measuring soft and biological samples. Sci. Rep. 7 : 5117.

Nanomechanics and plant growth

Establish a link between root plant growth and cell surface elasticity

Plant growth is extremely sensitive to environmental constraints that act in fine on the cell wall activity. Relaxing or blocking cell walls allow roots to grow or to stop growing, respectively. In the model plant Arabidopsis, it has been shown that external phosphate limitation (-Pi) quickly and irreversibly block the plant root growth (figure below). Three genes have been identified (stop1, almt1 et lpr1) whose activities are necessary for this response, suggesting that the growth stop is an active process and not due to a metabolic deficiency. It has been also shown that the quick arrest in cell elongation depends on the activity of peroxidases, a set of enzymes that build covalent bonds in the polymeric parietal backbone. If these bonds are responsible for the growth arrest, then it should be expected to have some impact on the mechanical properties of cell walls. To test this hypothesis, AFM has been used in the nanomechanics mode. An increase in the cell wall rigidity has been demonstrated in absence of Pi in the root elongation zone using AFM nanoindendations. These results suggest a simple scenario where the deficiency in Pi trigger a stiffening of cell walls which prevent their elongation. The nanoindentation results confirm causality between peroxidase activity and cell elongation arrest. Finally, these results demonstrate that AFM is an excellent technique allowing a precise measurement of a rapid change in the plant root state in a living organism.
AFM measurements were performed by Christian Godon and curve analyses were performed by Jean-Marie Teulon on seedlings produced by Christian and whose seeds were provided by Thierry Desnos.

Balzergue C, Dartevelle T, Godon C, Laugier E, Meisrimler C, Teulon J-M, Creff A, Bissler M, Brouchoud C, Hagège A, Müller J, Chiarenza S, Javot H, Becuwe-Linka N, David P, Péret B, Delannoy E, Thibaud M-C, Armengaud J, Abel S, Pellequer J-L, Nussaume L and Desnos T (2017) Low phosphate activates STOP1-ALMT1 to rapidly inhibit root cell elongation. Nat. Commun. 8 : 15300.