Summary: Whereas the morphogenesis of developing organisms is relatively well understood at the molecular level, the contribution of the mechanical properties of the cells to shape changes remains largely unknown, mainly because of the lack of quantified biophysical parameters at cellular or subcellular resolution. Here we designed an atomic force microscopy approach to investigate the elastic modulus of the outer cell wall in living shoot apical meristems (SAMs). SAMs are highly organized structures that contain the plant stem cells, and generate all of the aerial organs of the plant. Building on modeling and experimental data, we designed a protocol that is able to measure very local properties, i.e. within 40–100 nm deep into the wall of living meristematic cells. We identified three levels of complexity at the meristem surface, with significant heterogeneity in stiffness at regional, cellular and even subcellular levels. Strikingly, we found that the outer cell wall was much stiffer at the tip of the meristem (5 ± 2 MPa on average), covering the stem cell pool, than on the flanks of the meristem (1.5 ± 0.7 MPa on average). Altogether, these results demonstrate the existence of a multiscale spatialization of the mechanical properties of the meristem surface, in addition to the previously established molecular and cytological zonation of the SAM, correlating with regional growth rate distribution.

Measurements of fluid motion during thin-layer electrochemical growth reveal that convection arising from concentration gradients that are transverse to gravity is immediate and substantial for experimental conditions typical to many studies in the literature. A particle tracking technique is used to determine and follow the time evolution of the convective velocity field. The contribution of buoyancy driven convection to local and global transport is compared to that arising from diffusion. A transition is observed from a regime in which the convection rolls near each electrode grow as ${\mathit{t}}^{4/5}$ to a regime with the roll size growing as ${\mathit{t}}^{1/2}$. Convection generated by electric fields can also be important in electrodeposition experiments; the measured electroconvective velocities are found to be much smaller than those predicted by the theory of Fleury and Chazalviel.

We report experimental evidence indicating that two-dimensional zinc electrodeposition clusters in the limit of small ionic concentration and small voltage are self-similar with generalized dimensions $D_q=1.66\mathrm{}\pm 0.08$. Small-mass clusters obtained in a numerical simulation of diffusion-limited aggregation in a strip geometry are also found to be self-similar, with $D_q=1.60\mathrm{}\pm 0.02$. These results suggest that electrodeposition and diffusion-limited clusters have a similar geometrical structure.