Mechanical control of morphogenesis at the shoot apex

Abstract

Morphogenesis does not just require the correct expression of patterning genes; these genes must induce the precise mechanical changes necessary to produce a new form. Mechanical characterization of plant growth is not new; however, in recent years, new technologies and interdisciplinary collaborations have made it feasible in young tissues such as the shoot apex. Analysis of tissues where active growth and developmental patterning are taking place has revealed biologically significant variability in mechanical properties and has even suggested that mechanical changes in the tissue can feed back to direct morphogenesis. Here, an overview is given of the current understanding of the mechanical dynamics and its influence on cellular and developmental processes in the shoot apex. We are only starting to uncover the mechanical basis of morphogenesis, and many exciting questions remain to be answered.

Diffuse Growth of Plant Cell Walls

“…This is a complex topic beyond the scope of this review, but readers are referred to reviews that assess the varied approaches and interpretations of these stiffness measurements (Milani et al, 2013;Mosca et al, 2017). AFMbased stiffness maps of the shoot apical meristem have been compared with maps of cell shape, cell division, auxin flow, gene expression, and cytoskeletal patterns Robinson et al, 2013;de Reuille et al, 2014;Sassi et al, 2014). These studies contribute to sophisticated models of meristem morphogenesis and phyllotaxis in which wall stress, mechanics, enlargement, and the cytoskeleton play interacting roles Kierzkowski et al, 2013;Sampathkumar et al, 2014b), concepts rooted in the pioneering efforts of Paul Green to understand the biophysics of meristem dynamics (Green et al, 1996).…”

Leaf development and morphogenesis

“…Accumulating evidence points to the potential role of mechanics in the regulation of leaf positioning and initiation, either as a signal or via differential tissue properties (Robinson et al, 2013). Tissue and cell geometry, mechanical stresses, cellulose and microtubule orientation and growth directions have long been proposed to be involved in morphogenesis, both in plants and animals (Green, 1980;Thompson, 1942).…”

Two tonoplast MATE proteins function as turgor-regulating chloride channels in Arabidopsis

“…vacuole | root hair | stomata | drought W ithin a plant cell, turgor pressure pushes the plasma membrane against the cell wall to generate a specific cell size and shape (1)(2)(3). Hence, turgor pressure is the driving force for cell expansion and growth.…”

“…At the tissue level, the structural strength of tissues depends on both the cell wall rigidity and turgor pressure in each cell. The tissues remain turgid when turgor pressure rises and wilt when turgor falls below a certain threshold (2)(3)(4). Therefore, turgor is essential for cell growth and morphology, tissue architecture, and overall strength of all plants.…”