Sporophyte Development in Rhynia Gwynne-Vaughanii, an Early Devonian Vascular Land Plant from the Rhynie Chert, Aberdeenshire, UK

Sporophyte development in Rhynia gwynne-vaughanii, an Early Devonian vascular land plant from the Rhynie chert, Aberdeenshire, UK Patricia Kearney 2015 # !""# # Westfälische Wilhelms-Universität, Münster Institut für Geologie und Paläontologie Sporophyte development in Rhynia gwynne-vaughanii, an Early Devonian vascular land plant from the Rhynie chert, Aberdeenshire, UK Inaugral-Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften im Fachbereich Geowissenschaften der Mathematisch-Naturwissenschaften Fakultät der Westfälischen Wilhelms-Universität Vorgelegt von Patricia Kearney aus Cork, Irland 2015 !""# Dekan: Professor Dr. Hans Kerp Erstgutachter: Professor Dr. Hans Kerp Zweitgutachter: Professor Dr. Kai Müller Drittgutachter: Professor Dr. Ralph Thomas Becker Tag der mündlichen Prüfung: 06 Mai 2016 Tag der Promotion: 06 Mai 2016 $# ! Hiermit versichere ich, dass ich bisher noch keinen Promotionsversuch unternommen habe. Münster, den # $# # ! Hiermit versichere ich, dass ich die vorgelegte Dissertation selbst und ohne Hilfe angefertigt, alle in Anspruch genommen Quellen und Hilfsmittel in der Dissertation angeben habe und die Dissertation nicht bereits anderweilig als Prüfungsarbeit vorgelegen hat. Münster, den # $$# # ! Hiermit erkläre ich, dass ich nicht wegen eines Verbrechens, zu dem ich meine wissenschaftliche Qualifikation missbraucht habe, rechtskräftig verurteilt worden bin. Münster, den # $$$# # ! Summary While the developmental patterns and strategies of extant land plants are widely studied, the same cannot be said for the earliest land plants. The studies in this volume describe the development of the Early Devonian Rhynie chert plant, Rhynia gwynne-vaughanii, a morphologically simple vascular land plant, devoid of the many specialised organs and structures that characterise extant vascular land plants, i.e. roots and leaves. Such studies are possible because the Rhynie chert preserves some of the earliest land plants in exceptional detail, down to the cell level. Asexual vegetative propagules of Rhynia gwynne-vaughanii as well as mature shoot axes were studied using a combination of petrographic thin sectioning, light microscopy (LM) and synchrotron X-ray tomographic microscopy (SXRTM). Asexual vegetative propagules played an essential role in understanding the basic developmental pattern of the Rhynia gwynne-vaughanii shoot. Using LM, propagules are shown to have developed from two different locations on the shoot axis, from multiple epidermal cells adjacent to mature stomata, and from single cells on the hemispherical projections that dot the surface of the shoot. Propagule development in Rhynia gwynne-vaughanii resembles somatic embryogenesis, a form of asexual reproduction that occurs commonly in extant land plants, and has been studied extensively in vitro in order to understand the mechanisms controlling shoot development. The preservation of propagules at various points of shoot development allowed for the documentation of specialised tissue formation as well as overall shoot developmental morphology. Comparison of developmental morphology in Rhynia gwynne-vaughanii with that of extant land plants revealed some basic similarities with the ancestral bryophytes but in general shoot development was most similar to that of the extant early divergent lycophyte and monilophytes groups. Both LM and SRXTM show that development of the Rhynia gwynne-vaughanii shoot was directed from the shoot apical meristem (SAM). The structure of the SAM, with its tetrahedral and probably transient apical cell, core zone of isodiametric cells and superficial layer of larger square- rectangular cells, resembles that of the lycophytes and the monilophytes. Stomata, rhizoids and hemispherical projections developed from cells derived from the apical cell. For stomata and the water-conducting tracheid cells, the SAM played a primary role in their formation and ontogenetic patterns for both of these specialised tissue complexes fit within modern accepted classification schemes for the same in extant land plants. The SAM of the more primitive non-vascular Rhynie chert plant Aglaophyton major was also examined and is shown to be structurally different to that of Rhynia gwynne-vaughanii, with the cells of the core of the SAM, the superficial layer and the cells of the peripheral zone around the SAM to be of similar dimensions; the limit of the SAM within the plant axis was relatively more difficult to pinpoint than in Rhynia gwynne-vaughanii. In addition, the # $%# # ! SAM of Aglaophyton major comprises several divisional zones of vertical files of cells, deep into the core of the SAM. The SAM of Rhynia gwynne-vaughanii represents a change in SAM complexity and structure between two evolutionary important groups of land plants, a trend also seen throughout the evolution of the extant land plant groups. This increase in SAM complexity and structure within the vascular land plants accounts for the slightly more complex morphology and physiology of Rhynia gwynne-vaughanii, compared to that of Aglaophyton major, and was fundamental to the evolution of the increasingly more complex vascular plant sporophyte, as well as to terrestrial adaptation and radiation. # %# # ! Acknowledgements I would like to express gratitude to a number of people who all played a vital role in the research carried out and described in this dissertation. At the Forschungsstelle für Paläobotanik, Professor Dr. Hans Kerp, for providing a world class environment in which to carry out palaeobotany. Hagen Hass, who provided training in thin section making and was an invaluable mine of information regarding the Rhynie chert. In addition I also thank my colleagues at the Institute for Geology and Paleontology. I wish to acknowledge the Plant Origins team and thank them for their many hours of fruitful discussion on plant evolution: Principal Investigators – Dr. Liam Dolan (University of Oxford, UK); Dr. Hans Kerp (Westfälische Wilhelms-Universität, Germany); Dr. Paul Kenrick (Natural History Museum, UK); Dr. Jose Feijo (formally Dep. Biologia Vegetal Fac.Ciencias Universidade Lisboa, Portugal/Departent of Cell Biologyand Molecular Genetics, University of Maryland, USA ); Dr. Jörg Becker (Instituto Gulbenkian de Ciência, Portugal); Dr. Viktor Zársk! (Institute for Experimental Botany/ Charles University, Czech Republic); Students: Zuzanna Wawrzyniak (UK/Poland), Anamika Rawat (Czech Rep.), Agata Jarzynka (Germany/Poland), Carlos Ortiz Ramerez (Portugal), Carlos Gois Marques (UK), Bruno Catarino (UK), Marcela Hernandez Coronado (Portugal), Anna Tham (UK), and all others I met during my frequent trips to the institutes under the Plant Origins project. Work at the TOMCAT Beamline at the synchrontron Swiss Light Source (SLS), Paul Scherrer Institute, was carried out with the assistance of Dr. Martin Rücklin, (Naturalis Center for Biodiversity, Netherlands) and Dr. Phil Donoghue (School of Earth Sciences, University of Bristol),who were essential in getting the Rhynie chert to the SLS for its first systematic analysis. At the beamline the assistance of physicist Dr. Federica Marone was greatly appreciated especially in the area of rectifying issues with some samples and clarifying the methodology behind these rectifications. I also would like to thank my fellow members of the Münster Graduate School of Evolution at WWU Münster, former coordinator Dr. Rebecca Schreiber, current coordinator Dr. Vanessa Kloke, and co-supervisors Dr. Kai Müller (Institute for Evolutionary Biology) and Dr. Ralph Thomas Becker (Institute for Geology and Palaeontology). Finally, I would like to thank my family, and friends old and new. The studies in this dissertation were funded by the European Community’s Seventh Framework Programme (FP7/2007-20139) under grant agreement 238640 - Marie Curie Actions ITN Plant Origins (2011-2014) and DFG Grant agreement KE 584/13-2 Synecology of the Rhynie chert Biota II (2014-2015). # %$# # ! Contents Declarations i–iii Summary iv Acknowledgements vi Main vii List of figures and tables xi Appendix Figures xiv Main Chapter 1 Introduction and review: Land plant biology, phylogeny and evolution 1.0! Introduction 1 1.1 Land plant groups 2 1.1.1 Phylogeny of land plants - algae, bryophytes and vascular plants 3 1.1.2! Alternation of generations and reproductive biology in land plants 5 1.2 Physiological adaptation to land 6 1.2.1! Evolution of the terrestrial sporophyte shoot 7 1.2.2! Sporopollenin and a delay in spore production 8 1.2.3! Stomata 8 1.2.4! Water acquisition and physical support 9 1.3 Fossil evidence for early land plants 11 1.3.1 Lack of macrofossils for early land plants 12 # %$$# # ! Chapter 2 The Rhynie chert: History of research, geology, flora and analytical techniques 2.0 The Rhynie chert: Discovery and main scientific contributors 18 2.1 Stratigraphy and structural geology 19 2.2 Plant biota 19 2.2.1 Rhynia gwynne-vaughanii 21 2.2.2 Aglaophyton major 22 2.3 Analytical techniques 22 2.3.1 Light microscopy 22 2.3.2 Synchrotron X-ray tomographic microscopy 23 Chapter 3 Results: Light microscopy and synchrotron X-ray tomographic microscopy of asexual propagules of Rhynia gwynne-vaughanii, and light microscopy of Aglaophyton major 3.0 Introduction 31 3.1 Development of asexual propagules in Rhynia gwynne-vaughanii 31 3.1.1 Propagules developing from epidermal cells 32 3.1.2 Propagules developing from hemispherical projections 33 3.2 Stages of Development 34 3.2.1 Pre-propagules Stage I 34 3.2.2 Early Globular Stage II 34 3.2.3 Late

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