Functional Analysis of Cellulose and Xyloglucan in the Walls of Stomatal Guard Cells of Arabidopsis.

Yue Rui,Charles T Anderson

doi:10.1104/pp.15.01066

Abstract

Stomatal guard cells are pairs of specialized epidermal cells that control water and CO2 exchange between the plant and the environment. To fulfill the functions of stomatal opening and closure that are driven by changes in turgor pressure, guard cell walls must be both strong and flexible, but how the structure and dynamics of guard cell walls enable stomatal function remains poorly understood. To address this question, we applied cell biological and genetic analyses to investigate guard cell walls and their relationship to stomatal function in Arabidopsis (Arabidopsis thaliana). Using live-cell spinning disk confocal microscopy, we measured the motility of cellulose synthase (CESA)-containing complexes labeled by green fluorescent protein (GFP)-CESA3 and observed a reduced proportion of GFP-CESA3 particles colocalizing with microtubules upon stomatal closure. Imaging cellulose organization in guard cells revealed a relatively uniform distribution of cellulose in the open state and a more fibrillar pattern in the closed state, indicating that cellulose microfibrils undergo dynamic reorganization during stomatal movements. In cesa3(je5) mutants defective in cellulose synthesis and xxt1 xxt2 mutants lacking the hemicellulose xyloglucan, stomatal apertures, changes in guard cell length, and cellulose reorganization were aberrant during fusicoccin-induced stomatal opening or abscisic acid-induced stomatal closure, indicating that sufficient cellulose and xyloglucan are required for normal guard cell dynamics. Together, these results provide new insights into how guard cell walls allow stomata to function as responsive mediators of gas exchange at the plant surface.

Highlights

Stomatal guard cells are pairs of specialized epidermal cells that control water and CO2 exchange between the plant and the environment
Young seedlings were used in this experiment because preliminary analyses demonstrated that there is a dramatic reduction in fluorescent protein (FP)-CESA1/3/6 particle density mm22 in guard cells from 1 to 2 weeks after germination (Supplemental Fig. S1)
To validate that stomatal guard cells from young seedlings respond to abscisic acid (ABA) and dark treatments, which are normally used to induce stomatal closure in mature leaves, we carried out stomatal closure assays in 6-d-old seedlings expressing green fluorescent protein (GFP)-CESA3 and visualized stomatal apertures by staining with propidium iodide (PI), a fluorescent dye that highlights cell outlines

Summary

Introduction

Stomatal guard cells are pairs of specialized epidermal cells that control water and CO2 exchange between the plant and the environment. In cesa3je mutants defective in cellulose synthesis and xxt xxt mutants lacking the hemicellulose xyloglucan, stomatal apertures, changes in guard cell length, and cellulose reorganization were aberrant during fusicoccin-induced stomatal opening or abscisic acid-induced stomatal closure, indicating that sufficient cellulose and xyloglucan are required for normal guard cell dynamics Together, these results provide new insights into how guard cell walls allow stomata to function as responsive mediators of gas exchange at the plant surface. Despite these advances in our understanding of CSC behavior, CSC dynamics have not been reported in guard cells, and it remains unknown whether CSC distribution, motility, and/or association with MTs are altered as stomata open or close, during which MTs in guard cell have been reported to undergo dynamic rearrangements and changes in abundance (Eisinger et al, 2012a, 2012b)

Methods

Results

Discussion

Conclusion