Role of cell wall anisotropy on guard cell mechanics in Arabidopsis thaliana.

Abstract

The function of plant stomata is regulated by nanoscale cellular components and turgor pressure in flanking guard cells that control stomatal pore size to facilitate gas exchange and photosynthesis. Cell wall nanostructure plays a critical role in stomatal behavior. Stomatal aperture is regulated by tuning the mechanical properties of guard cell walls and by water uptake or release by the cells. However, the specific mechanical roles of different wall components, especially in newly maturing guard cells, are unclear. Here, we used a combination of molecular genetics, nanoindentation in normal and lateral directions, computational modeling, and microscopy to investigate the influences of wall components and maturation on wall mechanics and turgor pressure in stomatal guard cells. Lateral indentation measurements allow the unique anisotropic properties of each guard cell to be quantified with respect to age and genotype, including mutants with lower cellulose content and with lower or higher pectin molecular weight. Our results highlight the significance of cellulose in modulating the dynamics of guard cells by affecting wall anisotropy and emphasize the role of pectin modification for tuning stomatal responses to environmental stimuli. Our nanoindentation measurements when combined with finite element modeling allow the wall modulus, anisotropy, and turgor pressure to be measured. We also found that both cell wall mechanics and turgor pressure undergo significant changes during stomatal maturation. The role of cell wall architecture in determining anisotropic wall mechanics is also discussed. Together, these results provide new insights of wall mechanics and their effect on stomatal function and growth in plants.