Mechanical Stress Initiates and Sustains the Morphogenesis of Wavy Leaf Epidermal Cells

Abstract

Summary: Pavement cells form wavy interlocking patterns in the leaf epidermis of many plants. We use computational mechanics to simulate the morphogenetic process based on microtubule organization and cell wall chemistry. Based on the in silico simulations and experimental evidence, we suggest that a multistep process underlies the morphogenesis of pavement cells. The in silico model predicts alternatingly located, feedback-augmented mechanical heterogeneity of the periclinal and anticlinal walls. It suggests that the emergence of waves is created by a stiffening of the emerging indented sides, an effect that matches cellulose and de-esterified pectin patterns in the cell wall. Further, conceptual evidence for mechanical buckling of the cell walls is provided, a mechanism that has the potential to initiate wavy patterns de novo and may precede chemical and geometrical symmetry breaking. : Plant epidermal pavement cells often exhibit wavy shapes. A mechanical model by Bidhendi et al. predicts local mechanical heterogeneity to underlie wavy morphogenesis, preceded by buckling triggering microtubule polarization. A positive feedback loop involves polarized deposition of cellulose microfibrils and pectin de-esterification stiffening cell wall regions at indentation sides of waves. Keywords: pavement cells, morphogenesis, plant cell mechanics, lobes, buckling, pectin, cellulose, feedback loop, stress and strain, leaf epidermis