Cortical Actin Filament Organization in Developing and Functioning Stomatal Complexes of Zea mays and Triticum turgidum Emmanuel Panteris, 1 Basil Galatis, 1 * Hartmut Quader, 2 and Panagiotis Apostolakos 1 1 Department of Botany, Faculty of Biology, University of Athens, Athens, Greece 2 Biocenter Klein Flottbek, University of Hamburg, Hamburg, Germany Cortical actin filament (AF) organization was studied in detail in developing sto- matal complexes of the grasses Zea mays and Triticum turgidum. AF arrays dur- ing the whole stomatal complex development are dynamic, partly following the pattern of cortical microtubule (MT) organization. They also exhibit particular patterns of organization, spatially and temporarily restricted. Among AF arrays, the radial ones that underlie young guard cell (GC) periclinal walls, those that line the bulbous GC ends and the AF ring at the junction between subsidiary cells (SCs) and GCs are described here for the first time. Although many similarities in cortical AF organization exist among the stomatal cells of both plants studied, considerable differences have also been observed between them. Our data reveal that the expanding areas of stomatal cell walls are lined by distinct cortical AF aggregations that probably protect the plasmalemma against mechanical stresses. Experimental AF disruption does not seem to affect detectably stomatal cell mor- phogenesis. Moreover, the structural and experimental data of this study revealed that, in contrast to the elliptical stomata, in the dumbbell-shaped ones the AFs and MTs seem not to be involved in the mechanism of opening and closing of the sto- matal pore. Cell Motil. Cytoskeleton 64: 531–548, 2007. ' 2007 Wiley-Liss, Inc. Key words: actin filament; stomatal complex; Triticum turgidum; Zea mays INTRODUCTION Stomatal complexes are structurally and function- ally highly differentiated cell systems, the cytoskeleton of which plays a unique role in their development and function. In particular, in all the stomatal cells examined so far, cortical microtubules (MTs) seem to: (a) be involved in the polarization that precedes asymmetrical divisions, (b) be implicated in the determination of cell division plane, and (c) control their morphogenesis [reviewed by Hepler, 1981; Palevitz, 1981, 1982; Sack, 1987; Galatis and Apostolakos, 2004; Lucas et al., 2006]. The MTs persist in differentiated elliptical sto- mata, suggesting that they might be involved in their function [see Galatis and Apostolakos, 2004]. In contrast to MTs, cortical actin filament (AF) orga- nization and function have been studied mostly in elliptical stomata, where AFs usually form cortical arrays coaligned with cortical MTs. For instance, in differentiating and func- Emmanuel Panteris’ present address is Department of Botany, School of Biology, Aristostle University of Thessaloniki, Thessaloniki GR- 541 24, Greece. *Correspondence to: B. Galatis, Department of Botany, Faculty of Biology, University of Athens, Athens GR-15784, Greece. E-mail: bgalatis@biol.uoa.gr This article contains supplementary material available via the Internet at http://www.interscience.wiley.com/jpages/0886-1544/suppmat. Contract grant sponsor: DAAD; Contract grant number: IKYDA- 2002; Contract grant sponsors: State Scholarship Foundation of Greece; Hellenic Ministry of National Education and Religious Affairs, and EU (project Pythagoras). Received 6 November 2006; Accepted 6 February 2007 Published online 18 April 2007 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/cm.20203 ' 2007 Wiley-Liss, Inc. Cell Motility and the Cytoskeleton 64: 531–548 (2007)