|Tuesday, July 06|
Narrow species concept and the unsupported subgeneric delimitations in the molecular phylogeny of Lejeunea (Lejeuneaceae)
* Gaik Ee Lee, Unviersiti Malaysia Terengganu, Malaysia
Julia Bechteler, University of Bonn
Alfons Schäfer-Verwimp, Herdwangen-Schönach
Tamás Pócs, Eszterházy University
Jochen Heinrichs, University of Munich
Incongruence of morphospecies concepts and molecular phylogenies is not uncommon in liverworts and has increased significantly over the past decade. Morphological similarity does not necessarily indicate genetic similarity and multiple accessions of morphologically similar species may nest in different main lineages of molecular phylogenies. Morphology alone was shown to be inadequate to classify liverworts of the Lejeuneaceae due to their high level of homoplasy, which has been recognized as a problem in the establishment of natural relationships among their taxa. The subcosmopolitan genus Lejeunea includes between 200 to 300 species and is well known for its extensive morphological homoplasy. Molecular data are therefore essential for reconstructing relationships between taxa and establishing robust species hypotheses. The current subgenera concepts of Lejeunea are based on morphology alone and are not supported by molecular phylogenies. We leveraged a recent molecular phylogeny of Lejeunea to demonstrate relationships among taxa from the molecular perspective and to reveal discrepancies to the traditional classification based on morphology. Morphological investigation includes 14 gametophytic characters, which were scored for each of the species in the present study. Those characters were selected due to their former use in sectional and subgeneric circumscriptions. Maximum likelihood and Bayesian inference were used for phylogenetic analyses of a dataset composed of two plastid and one nuclear marker. Our investigations point to narrow species concepts and led to a deeper understanding of morphologically vague and controversial species complexes and also identified several new species.
Liverwort oil bodies : often overlooked beautiful and distinct cell features
* Kellina L. Higgins, GeoFlora, Canada
It is well-known that liverwort oil bodies are useful features for identifying specimens -- when examined fresh. These beautiful and distinct features of liverwort cells are also elusive : they disappear a few days after being collected. As such, identification keys tend to treat oil bodies as a last resort, only when they are absolutely necessary. Generally, attempts are made to accommodate the bryologist who pulls out the specimen for identification after a field campaign (days or months or even years after collection). However, much information is lost when oil bodies are not prioritized as a crucial if not primary identification characteristic. For example, Lophozia silvicola and Lophozia ventricosa have been considered as a single species by some taxonomists. Many keys rely on length:width ratios that are notoriously difficult to ascertain and, which can be quite variable within a single shoot. Yet, L. silvicola has distinct biconcentric oil bodies that are evidently different from the simple oval ones of L. ventricosa. This presentation will present the variety of oil bodies found in Quebec liverwort taxa with an emphasis on their distinguishing shapes and sizes for identification.
Why do bryophyte gametophytes lack stomata?
* Jeffrey Duckett, Natural History Museum, United Kingdom
Silvia Pressel, Natural History Museum
Background: Although stomata are the most important structural innovation in the evolution of land plants, their absence from gametophytes, save for Devonian fossils, has long remained mysterious. The recent realisation that moss sporophytes are homoiohydric prompts a reappraisal of this enigma . Objectives: We set out to explore features of gametophytes that might preclude the presence of stomata . Methods: We used cryo-scanning electron microscopy and hypertonic sucrose to investigate bryophytes under different hydration states. Results: Whereas plasmolysis in hypertonic sucrose is universal in vascular plant and bryophyte sporophytes, bryophyte gametophytes undergo cytorrhysis (cell collapse) followed by full recovery in water thus mimicking their natural behaviour. Morphologically we see the repeated evolution in mosses, thalloid and leafy liverworts, hornworts and pteridophyte gametophytes, of unistratose lamellate structures lacking intercellular spaces whose very construction precludes stomata as does the absence of gas-filled intercellular spaces . Reversible cytological changes during dehydration, including depolymerisation of the cytoskeleton and rounding of organelles and vacuolar shrinkage are remarkably similar to those in desiccation-tolerant streptophyte algae. In contrast to the inflexible guard cell walls and fixed apertures in bryophyte stomata extreme gametophytic wall pliability is geared to cytorrhysis . Conclusions: Future research should focus on differences in cell wall composition associated with plasmolysis versus cytorrhysis. A reappraisal of the possible loss of sporophytic stomata in liverworts including highly structured placentas in basal clades, the presence of a stomatal construction toolkit in the capsule walls of Haplomitrium and plasmolysis of liverwort setal cells hint at more complex ancestry.
Rotation angle of apical cell division plane controls spiral phyllotaxis in mosses
* Masaki Shimamura, Hiroshima University, Japan
Taishi Tano, Hiroshima University
Naoya Kamamoto, Osaka University
Koichi Fujimoto, Osaka University
Phyllotaxis of bryophytes emerges from a single apical stem cell (AC) that is embedded in a growing tip of the gametophyte. To clarify the merophyte arrangement and its regulatory mechanism, we examined three moss species, Tetraphis pellucida, Physcomitrium patens, and Niphotrichum japonicum, which exhibit 1/3, 2/5, and 3/8 spiral phyllotaxis, respectively. We measured the angle between the centroids of adjacent merophytes relative to the AC centroid on cross-transverse sections and compared with a mathematical model.
Somatic embryogenesis of weevil-resistant phenotypes of Sitka spruce
* Patrick von Aderkas, University of Victoria, Canada
Natalie Prior, University of Victoria
Stefan Little, University of Victoria
Taylor Holt, University of Victoria
Emma Creasy, University of Victoria
Justin Whitehill, North Carolina State University
John King, British Columbia Ministry of Forests
Lisheng Kong, University of Victoria
A somatic embryogenic system was created using material from the Sitka spruce (Picea sitchensis) breeding program for resistance to the white pine weevil (Pissodes strobi) of the British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Embryogenic lines were derived from controlled crosses of parental genotypes previously ranked for the abundance of three physical traits: sclereid cells, constitutive resin canals and traumatic resin canals. Seeds from open-pollinated and controlled crosses of weevil-resistant and control populations were used to induce somatic embryos. Of 135 genotypes, 88.1 % produced mature embryos. Nearly all genotypes germinated. However, the overall conversion rate of somatic embryos was only 5.5 %. We used a cryopreservation method developed in house that did not use dimethylsulfoxide. Seedlings were acclimated in a greenhouse before planting in soil. Having reached a dozen years of age, the phenotypes of these trees were assessed. After trees were allowed to grow for a decade, we dissected and sectioned materials and found that we were able to confirm high sclereid abundance, typical of resistant phenotypes, in apical leaders of trees derived from somatic embryos multiplied from seed of resistant breeding stock. The initial investment in highly skilled labour is warranted, if the longer term possibilities of having unlimited material for testing can be exploited.
Using computational models to investigate vein patterning and programmed cell death in lace plant (Aponogeton madagascariensis) leaves
* Sophie Tattrie, Dalhousie University, Canada
Adam Runions, University of Calgary
Arunika Gunawardena, Dalhousie University
Programmed cell death (PCD), the genetically encoded destruction of cells, is essential in regulating several activities required to maintain health and function in both plants and animals. The lace plant (Aponogeton madagascariensis) provides a unique example of developmental PCD, which generates perforations in a regular lattice pattern over the surface of its leaves. These perforations develop in a predictable manner initiating in the center of areoles of young leaves and expanding towards the surrounding vasculature. Treating lace plants with auxin transport inhibitors or antioxidants yields leaves with fewer perforations, indicating their involvement in PCD signaling pathways. The objectives of this research are twofold; create computational models to: (1) analyze vein patterning and perforation formation when treated with known regulators, and (2) predict which cells will undergo PCD during early leaf development. Leaves will be harvested from sterile cultures and quantitative data will be collected via light microscopy to construct computational models. The number of cell layers from perforation area to veins, area of areoles, and anthocyanin location/disappearance will inform model construction. Preliminary data show perforations stop 4-5 cell layers away from veins, establishing a boundary during early leaf development that persists until maturity. To elucidate the role of regulators such as auxin in lace plant PCD, leaves from auxin-inhibitor-treated sterile cultures will be harvested and analyzed to construct models. This research will provide insight on how different regulators of PCD are integrated to precisely coordinate cell death, and has significance to medical research attempting to halt PCD in certain scenarios.