Global ETD Search

1	Ecophysiology and Biomechanics of <i>Equisetum Giganteum</i> in South America Husby, Chad Eric 24 March 2009 (has links) Equisetum giganteum L., a giant horsetail, is one of the largest living members of an ancient group of non-flowering plants with a history extending back 377 million years. Its hollow upright stems grow to over 5 m in height. Equisetum giganteum occupies a wide range of habitats in southern South America. Colonies of this horsetail occupy large areas of the Atacama river valleys, including those with sufficiently high groundwater salinity to significantly reduce floristic diversity. The purpose of this research was to study the ecophysiological and biomechanical properties that allow E. giganteum to successfully colonize a range of habitats, varying in salinity and exposure. Stem ecophysiological behavior was measured via steady state porometry (stomatal conductance), thermocouple psychrometry (water potential), chlorophyll fluorescence, and ion specific electrodes (xylem fluid solutes). Stem biomechanical properties were measured via a 3-point bending apparatus and cross sectional imaging. Equisetum giganteum stems exhibit mechanical characteristics of semi-self-supporting plants, requiring mutual support or support of other vegetation when they grow tall. The mean elastic moduli (4.3 Chile, 4.0 Argentina) of E. giganteum in South America is by far the largest measured in any living horsetail. Stomatal behavior of E. giganteum is consistent with that of typical C3 vascular plants, although absolute values of maximum late morning stomatal conductance are very low in comparison to typical plants from mesic habitats. The internode stomata exhibit strong light response. However, the environmental sensitivity of stomatal conductance appeared less in young developing stems, possibly due to higher cuticular conductance. Exclusion of sodium (Na) and preferential accumulation of potassium (K) at the root level appears to be the key mechanism of salinity tolerance in E. giganteum. Overall stomatal conductance and chlorophyll fluorescence were little affected by salinity, ranging from very low levels up to half strength seawater. This suggests a high degree of salinity stress tolerance. The capacity of E. giganteum to adapt to a wide variety of environments in southern South America has allowed it to thrive despite tremendous environmental changes during their long tenure on Earth. salinity tolerance pteridophyte water potential xylem guttation chlorophyll fluorescence
2	A Centrin Homologue Is a Component of the Multilayered Structure in Bryophytes and Pteridophytes Vaughn, K. C., Sherman, T. D., Renzaglia, Karen S. 01 March 1993 (has links) The multilayered structure (MLS), a component of the locomotory complex of plant sperm, has been utilized extensively by taxonomists in establishing phylogenetic relationships between the lower plants and algae. Unfortunately, there has been almost no biochemical characterization of the MLS and, in those studies that did attempt a characterization, conflicting results were obtained. We utilized antisera to the calcium-binding protein centrin to probe thin sections of the mid-stage spermatids of the anthocerote Phaeoceros laevis, the hepatic Sphaerocarpos texanus, and the pteridophyte Ceratopteris richardii embedded in L. R. White resin. The lamellar strip (LS; layers S2-S4) of the MLS in each of these species is labelled strongly with anti-centrin, but the S1 layer, composed of microtubules, is not. In Ceratopteris, centrin is also detected in the amorphous electron opaque material that connects the basal bodies of the flagella. Both the MLS and the amorphous zones are putative microtubule organizing centers. Extracts from axenic cultures of Ceratopteris subjected for electrophoresis and Western blotting revealed a reactive band at 19.3 kDa, a protein similar in molecular mass to algal centrin. These data indicate that the MLS is composed at least partially of the protein centrin or a protein antigenically-related to centrin. This report is the first electron microscopic immunocytochemical demonstration that a centrin homologue is found in land plants and that it occurs at putative microtubule organizing centers. bryophyte spermatid centrin microtubule organizing center multilayered structure pteridophyte spermatid
3	Systematics of Eastern North American Bracken Fern Speer, William D. 07 May 1997 (has links) The cosmopolitan Pteridium aquilinum (L.) Kuhn is widespread throughout eastern North American, where it is represented primarily by Tryon's (1941) var. latiusculum (Desv.) Underw. and var. pseudocaudatum (Clute) Heller. The taxonomy of Pteridium is controversial. Fourteen isozyme loci and 12 morphological characters were used to assess the taxonomic relationship of these two varieties. Isozyme data indicated a high mean genetic identity (I = 0.976) between eleven bracken populations. Strong patterns of geographic variation for isozyme allele frequencies were also observed. The isozyme results did not separate the two taxa. Numerical analysis of the morphology distinguished the two taxa when the qualitative characters were used alone or in conjunction with some of the quantitative traits. All qualitative characters differed significantly between the two taxa. No perceptible geographic pattern of variation was observed. Morphological distinctiveness was maintained even in those localities where both taxa were present, with few or no intermediates being found. Isozyme evidence suggestive of gene flow between the two varieties was found at Greensboro, NC, where the two morphotypes were easily recognizable. The isozyme evidence strongly indicates conspecificity, while the morphological evidence supports their status at the varietal level. / Master of Science plant systematics allozyme pteridophyte univariate analysis multivariate analysis clinal variation
4	Taxonomic revision of the genus <Sticherus> (Gleicheniaceae - Pteridophyta) in the Neotropics / Revisión Taxonómica del género <Sticherus> (Gleicheniaceae - Pteridophyta) en el Neotrópico Gonzales Rocabado, María Jasivia 02 July 2003 (has links) No description available. 32 Biologie W Biologie WW Pflanzensystematik Pflanzentaxonomie WWL 000 Farne Pteridophyte Mathematics and Natural Science species concept scales morphology taxonomy farne Sticherus Gleicheniaceae Pteridophy pseudodichotomous branching pattern dormant buds fork of axes tropical America Sticherus Gleicheniaceae Pteridophyta pantropische Farngattung Arten Konzept schuppen Ruheknospen Gabelwinkeln fiederschnittige Achsen taxonomische Geschichte Morphologie intragenerische Verwandtschaften 42.53 Pteridophyta (Farne)

1

Page generated in 0.0525 seconds