Stomatal cell wall composition: distinctive structural patterns associated with different phylogenetic groups.
Stomatal morphology and function have remained largely conserved throughout ∼400 million years of plant evolution. However, plant cell wall composition has evolved and changed. Here stomatal cell wall composition was investigated in different vascular plant groups in attempt to understand their possible effect on stomatal function.



A renewed look at stomatal cell walls was attempted utilizing digitalized polar microscopy, confocal microscopy, histology and a numerical finite-elements simulation. The six species of vascular plants chosen for this study cover a broad structural, ecophysiological and evolutionary spectrum: ferns ( Asplenium nidus and Platycerium bifurcatum ) and angiosperms ( Arabidopsis thaliana and Commelina erecta ) with kidney-shaped stomata, and grasses (angiosperms, family Poaceae) with dumbbell-shaped stomata ( Sorghum bicolor and Triticum aestivum ).



Three distinct patterns of cellulose crystallinity in stomatal cell walls were observed: Type I (kidney-shaped stomata, ferns), Type II (kidney-shaped stomata, angiosperms) and Type III (dumbbell-shaped stomata, grasses). The different stomatal cell wall attributes investigated (cellulose crystallinity, pectins, lignin, phenolics) exhibited taxon-specific patterns, with reciprocal substitution of structural elements in the end-walls of kidney-shaped stomata. According to a numerical bio-mechanical model, the end walls of kidney-shaped stomata develop the highest stresses during opening.



The data presented demonstrate for the first time the existence of distinct spatial patterns of varying cellulose crystallinity in guard cell walls. It is also highly intriguing that in angiosperms crystalline cellulose appears to have replaced lignin that occurs in the stomatal end-walls of ferns serving a similar wall strengthening function. Such taxon-specific spatial patterns of cell wall components could imply different biomechanical functions, which in turn could be a consequence of differences in environmental selection along the course of plant evolution.
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 7610001, Israel.
Ilana
I
Shtein
Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
Yaniv
Y
Shelef
Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
Ziv
Z
Marom
The Interdepartmental Equipment Unit, The Robert H. Smith Faculty of Agriculture, Food & Environment, The Hebrew University of Jerusalem, Rehovot 7610001, Israel.
Einat
E
Zelinger
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 7610001, Israel.
Amnon
A
Schwartz
Botany and Plant Science, Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland.
Zoë A
ZA
Popper
Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
Benny
B
Bar-On
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 7610001, Israel.
Smadar
S
Harpaz-Saad
D005075:Biological Evolution; D002473:Cell Wall / Q000648:ultrastructure*; D029624:Ferns / Q000033:anatomy & histology* / Q000648:ultrastructure; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D054046:Plant Stomata / Q000648:ultrastructure*; D006109:Poaceae / Q000033:anatomy & histology / Q000648:ultrastructure
Stomata; angiosperms; biomechanics; cell wall; cellulose crystallinity; ferns; grasses; guard cells; lignin