Cell wall-related and biomechanics mechanisms in stomatal function and development
Open Access
- Author:
- Chen, Yintong
- Graduate Program:
- Molecular, Cellular, and Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 11, 2021
- Committee Members:
- James Wang, Outside Unit & Field Member
Sarah Assmann, Major Field Member
Daniel Cosgrove, Major Field Member
Charles Anderson, Chair & Dissertation Advisor
Gabriele Monshausen, Major Field Member
Melissa Rolls, Program Head/Chair - Keywords:
- Guard cell
Stomata
Plant cell wall
Cell biomechanics - Abstract:
- Stomata are microscopic pores on the leaf surface that are flanked by guard cells. The degree to which stomata are open or closed controls the rate of CO2 influx and water loss in plants and is important for plant physiology. Homogalacturonan (HG) is a major component of the guard cell wall and its proper metabolism is required for normal stomatal dynamics; however, the function of HG in guard cell mechanics is elusive. Employing genetic, physiological, mechanical, modeling, and biochemical approaches, we revealed that an HG degrading enzyme, PECTATE LYASE-LIKE12, contributes to the softening of guard cell walls by reducing calcium crosslinkable HG and unexpectedly is required for proper pressurization of guard cells. Our findings expand the understanding of HG metabolism in stomatal dynamics and aid in elucidating the mechanisms underlying stomatal function. As a leaf develops, stomatal conductance first increases then decreases, suggesting that stomatal dynamics change over the course of development. However, the maturation process of guard cells is not yet well defined, which limits our understanding of the mechanical changes that occur in developing stomata. Using time-series imaging, plasmolysis, and cell ablation, we ruled out cell wall mechanics and turgor pressure as factors contributing to wider dynamic range in mature stomata and discovered that mature stomata are more open than young stomata because they are locked in an open state. These results expand our knowledge of the mechanical changes that occur as stomatal guard cells age. The “see-saw” hypothesis proposes that opposing changes in turgor pressure between guard cells and subsidiary cells is the reason that grass stomata, which consist of narrow guard cells flanked by larger subsidiary cells, have faster stomatal dynamics than eudicot stomata, which are flanked by wider, kidney-shaped guard cells. A similar hypothesis is proposed for Arabidopsis stomata, which are surrounded by puzzle piece-shaped pavement cells, but neither of these hypotheses have been empirically tested. Using time-series imaging, we observed distinct behaviors between neighboring and non-neighboring pavement cells during stomatal opening and closing. Ablating pavement cells results in stomatal complexes becoming wider and shorter, suggesting the presence of a compression force from the flanking side which might originate from pavement cells, but the mechanical impacts of junctional side pavement cells that abut the top and bottom of each stomatal complex remain to be elucidated. Data collected in this project will be combined with computational mechanical modeling to characterize and predict the mechanical interactions between guard cells and surrounding cells. In summary, the data collected in these projects have revealed mechanical mechanisms underlying the influence of cell wall modification and stomatal maturation on stomatal dynamics, and shed light on the mechanical impacts of interactions between guard cells and pavement cells in determining stomatal geometry. These findings open new potential avenues for improving stomatal function and water use efficiency in plants.