Date of Award

8-16-2024

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Plant & Microbial Biosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Mechanical forces are omnipresent in life on Earth and responses to force can be found across all three domains of life. The colonization of land by plants approximately 500 million years ago, an event that shaped life on Earth as we know it, involved adaptation from a relatively homogeneous fluid mechanical environment to a highly heterogeneous and mechanically diverse terrestrial environment. Evolution of multicellularity would present new mechanical challenges for land plants, not only from externally generated forces, but also from mechanical linkage to neighboring cells through the cell wall. Coordination of cell growth and an indeterminate body plan requires that individual cells within plant tissues be able to sense the growth of neighboring cells. As evidence for this process, mutations that affect cell shape, size, and number in various tissues usually leads to compensatory growth of neighboring cells to maintain well-defined organ shapes. Despite this, the role of mechanical sensation to plant growth and development is poorly understood. Additionally, disentangling the contributions of mechanical versus biochemical cues in these processes has been challenging. Here, I characterized a substrate to which individual plant cells adhere to and grow on to provide a controlled system to study how different mechanical environments affect plant cell growth and morphology. Using Nicotiana tabacum-derived Bright Yellow-2 (BY-2) cell suspensions, I showed that plant cells preferentially bind to fibrous matrices with bulk properties similar to the native cell wall, namely an overall negative surface charge, a combination of hydrophilic and hydrophobic surfaces, and an electrical potential generated by piezoelectric fibers. I found that a matrix composed of polyvinylidene tri-fluoroethylene (PVDF-TrFE) copolymer consistently worked best for BY-2 cells. Importantly, cells adhered to PVDF-TrFE continue to grow and divide but were slightly smaller than suspension-grown cells. Nevertheless, cells on PVDF-TrFE displayed stereotypical cell morphology and ~ 80% of adhered cells were viable, indicating that PVDF-TrFE is not harmful and does not significantly impair cell expansion. Finally, I used enzymatic digests of specific cell wall components to show that BY-2 cells adhere to PVDF-TrFE primarily through pectin, the same component responsible for cell-cell adhesion in land plants. To further test the utility of PVDF-TrFE as a plant growth substrate and to determine whether the mechanical environment influences cell growth and development, I used the moss Physcomitrium patens as a representative of an early land plant. I showed that P. patens bound to PVDF-TrFE substrates are not nutritionally or photosynthetically stressed and they produced morphologically normal 3D gametophores. In addition, I found that tight adhesion of P. patens filaments to PVDF-TrFE is associated with a transient reduction in tip growth rate and altered orientation of the first subapical cell division plane. Taken together, these data show that cells from evolutionarily diverse plant species adhere to PVDF-TrFE, thus providing a novel method to study how topological and mechanical cues influence critical cellular processes underlying plant growth and development.

Language

English (en)

Chair and Committee

Ram Dixit

Committee Members

Barbara Kunkel; Joe Jez; Lucia Strader; Matthew Lew

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