A review of the literature revealed that there is a lack of depth in our knowledge of gymnospermous seeds with regard to the development and germination processes. The phytohormones, particularly the cytokinins have been implicated in these processes. The seeds of Podocarpus henkelii were thus selected as experimental material for studying the biochemical and cytokinin-like changes associated with development and germination. The development of these seeds was also followed at the ultrastructural level. These studies revealed that cellular detail within the female gametophyte only began .to form in December (early summer), approximately six weeks after fertilization had taken place. At this time some reserve protein was evident and the embryo sporophyte consisted of only a few pro-suspensor and pro-embryo cells. Concurrently, the cytokinin levels were fairly high in the female gametophyte but low in the epimatium. In both seed components two cytokinin- like compounds predominated which co-chromatographed with the free base cytokinin zeatin and its ribonucleoside. The second sample was taken in late January (mid-summer) by which time the embryo sporophyte had developed rapidly into a readily distinguishable seed component. The cellular detail indicated that much cell division had recently taken place and that the cells were currently increasing in size and accumulating starch and lipid. In the female gametophyte the soluble sugars were at the maximum level recorded during these experiments and the level of starch was increasing. The extractable cytokinin content of the seed was high at this time, particularly in the embryo sporophyte. In all three seed components cytokinin-like compounds which co-chromatographed with zeatin and ribosylzeatin were present. These high levels of cytokinin coincided with the rapid increase in both fresh and dry mass of the embryo sporophyte and female gametophyte. Ultrastructural studies of the third sample collected in mid-March (early autumn) showed that cellular changes were associated mainly with increases in cell size and the accumulation of food reserves, particularly starch. The cytokinin levels had decreased in all three seed components at this time. There was an increase in the cytokinin which co-chromatographed with glucosylzeatin in the female gametophyte. The seeds matured in late April (autumn) and had the unusual features of not drying out during maturation. Fresh seeds collected from the ground had a moisture content of ca. 62 per cent. The main food reserve was starch with relatively small amounts of protein and lipid also present. The seeds of Podocarpus henkelii germinated readily after scarification in the absence of water provided that their moisture content remained ca. 60 per cent. Seeds in which the moisture content had fallen below ca. 54 per cent required additional water for germination. The moisture content of the seeds fell rapidly under natural conditions and viability was lost below a moisture content of ca. 34 per cent. Unscarified seeds of 52 per cent moisture content placed under moist conditions at a constant 25°C took 23 weeks to achieve 68 per cent germination. These experiments showed that although the epimatium limited water uptake by the seeds it did not prevent moisture loss to the atmosphere. This appears to be the main factor contributing to the seed's inefficiency as a propagule. A small degree of after-ripening was recorded with the embryo sporophyte increasing in size with storage. This appeared to contribute to the increased rate of germination of the scarified seeds. An interesting feature of the seeds of Podocarpus henkelii is that they have the ability to fix atmospheric carbon, which is subsequently translocated from the epimatium to the female gametophyte and embryo sporophyte. The mature seeds were stored at 4°C for six weeks during which time little change had occurred at the ultrastructural level. Protein vacuoles in the embryo sporophyte had disappeared and in all three seed components cytokinin levels were low. Three days after scarification and the start of incubation, little change in cellular detail was apparent as limited rehydration was necessary due to the high moisture content. The cytokinin levels in the embryo sporophyte and epimatium had increased, whilst the levels in the female gametophyte had decreased at this time. In the embryo sporophyte lipid mobilization had commenced with these reserves apparently being metabolized within vacuoles. The rate of respiration measured in terms of increases in CO[2] evolution, increased 60 hours after the start of the incubation period, just 12 hours before ten per cent germination was recorded. Germination was accompanied by a large increase in the levels of cytokinins in the female gametophyte and embryo sporophyte. The cytokinins detected co-chromatographed with the free base cytokinin zeatin and its riboside, ribosylzeatin. Concurrently, marked ultrastructural changes were recorded with increases in the amounts of dictyosomes, endoplasmic reticulum and the formation of polyribosomes, all of which are indicative of increased metabolic activity. Similar increases in the female gametophyte were ofa lower order and occurred only after nine days of incubation. By this time the levels of cytokinins had decreased considerably. After 12 days of incubation 65 per cent of the seeds had germinated. As much of the food reserves in the female gametophyte and embryo sporophyte remained, it is suggested that these reserves are utilized for subsequent seedling establishment rather than for germination. The actual role that cytokinins play in the development and germination of these seeds is not clear. High levels of this phytohormone coincide with periods of food deposition and mobilization suggesting that they play an important part in these processes. The results of the biochemical, cytokinin and ultrastructural studies are discussed in relation to the developmental and germination processes and are compared to the data of other seeds. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1981.

xv, 217 leaves : ill., tables, graphs, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agronomy, 1977

Phytophthora cinnamomi has been recognised as a key threatening process to Australia’s biodiversity by the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999. Despite over 80 years of extensive research, its exact mode of survival is still poorly understood. It is widely accepted that thin- and thick-walled chlamydospores are the main survival propagules while oospores are assumed to play no role in the survival of the pathogen in the Australian environment, yet evidence is limited. The saprophytic ability of the pathogen is still unresolved despite the important role this could play in the ability of the pathogen to survive in the absence of susceptible hosts. This thesis aimed to investigate chlamydospores, oospores and the saprophytic ability of P. cinnamomi to determine their contribution to survival. Phytophthora cinnamomi did not show saprophytic ability in non-sterile soils. The production of thick-walled chlamydospores and selfed oospores of P. cinnamomi in vitro was documented. Thick-walled chlamydospores were sporadically formed under sterile and non-sterile conditions in vitro but exact conditions for stimulating their formation could not be determined. The formation of thick-walled chlamydospores emerging from mycelium of similar wall thickness was observed, challenging the current knowledge of chlamydospore formation. Selfed oospores were abundant in vitro on modified Ribeiro’s minimal medium in one isolate. Three other isolates tested also produced oospores but not in large numbers. Although the selfed oospores did not germinate on a range of media, at least 16 % were found to be viable using Thiozolyl Blue Tetrazolium Bromide staining and staining of the nuclei with 4´, 6-diamidino-2-phenylindole.2HCl (DAPI). This indicated the potential of selfed oospores as survival structures and their ability to exist dormantly. The ability of phosphite to kill chlamydospores and selfed oospores was studied in vitro. Results challenged the efficacy of this chemical and revealed the necessity for further study of its effect on survival propagules of P. cinnamomi in the natural environment. Phosphite was shown to induce dormancy in thin-walled chlamydospores if present during their formation in vitro. Interestingly, dormancy was only induced by phosphite in isolates previously reported as sensitive to phosphite and not those reported as tolerant. Chlamydospores were produced uniformly across the radius of the colony on control modified Ribeiro’s minimal medium but on medium containing phosphite (40 or 100 µg ml-1), chlamydospore production was initially inhibited before being stimulated during the log phase of growth. This corresponded to a point in the colony morphology where mycelial density changed from tightly packed mycelium to sparse on medium containing phosphite. This change in morphology did not occur when the pathogen was grown on liquid media refreshed every four days, and chlamydospores were evenly distributed across the radius of these colonies. This trend was not observed in selfed oospores produced in the presence of phosphite. Selfed oospore production was found to be inhibited by phosphite at the same concentrations that stimulated chlamydospore production. Isolates of P. cinnamomi were transformed using a protoplast/ polyethylene glycol method to contain the Green Fluorescent Protein and geneticin resistance genes to aid in future studies on survival properties of the organism. Although time constraints meant the stability of the transgene could not be determined, it was effective in differentiating propagules of the transformed P. cinnamomi from spores of other microrganisms in a non-sterile environment. Two different sized chlamydospores (approximately 30 µm diameter and < 20 µm diameter) were observed in preliminary trials of transformed P. cinnamomi inoculated lupin roots floated in non-sterile soil extracts and these were easily distinguished from microbial propagules of other species. The growth and pathogenicity was reduced in two putative transformants and their ability to fluoresce declined over ten subcultures but they still remained resistant to geneticin. This study has improved our knowledge on the survival abilities of P. cinnamomi in vitro and has provided a useful tool for studying these abilities under more natural glasshouse conditions. Important implications of phosphite as a control have been raised.

Thesis (doctoral)--Helsinki University of Technology, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Dallas G. Hoover, Dept. of Animal & Food Sciences. Includes bibliographical references.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.

Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references. Also available in electronic format on the Internet.

Thesis (Ph. D.)--Illinois State University, 1974. / Title from title page screen, viewed Nov. 1, 2004. Dissertation Committee: Herman Brockman, Arlan Richardson (co-chairs), Ione Rhymer, Fritz Schwalm, David Weber. Includes bibliographical references (leaves 116-128) and abstract. Also available in print.

Made available in DSpace on 2014-08-13T14:50:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-07-17Bitstream added on 2014-08-13T18:01:08Z : No. of bitstreams: 1 000738195_20141215.pdf: 138287 bytes, checksum: c29b20fe08bca3353b58f3993e889ca0 (MD5) Bitstreams deleted on 2014-12-19T18:32:44Z: 000738195_20141215.pdf,Bitstream added on 2014-12-19T18:33:33Z : No. of bitstreams: 1 000738195.pdf: 1423722 bytes, checksum: 72b36b830647082cdbd6b9d27c80cf1f (MD5) / O objetivo do presente trabalho foi descrever a morfologia da semente e as etapas do processo germinativo de Aechmea blanchetiana (Baker) L.B.Sm. Aechmea bromeliifolia (Rudge) Baker, Neoregelia marmorata (Baker) L.B.Sm., Pitcairnia flammea Lindl. e Vriesea incurvata Gaudich. As espécies apresentaram germinação epígea e criptocotiledonar, diferindo entre si nos períodos e porcentagem de germinação. Os embriões possuem posição axial com eixos embrionários curtos e cilíndricos, o endosperma contém células de amido e o tegumento é composto por células justapostas. Antes da emissão da raiz primária observa-se pilosidade em forma de anel na radícula. O envoltório das sementes de Aechmea Ruiz & Pav. e Neoregelia L.B.Sm. (Bromelioideae) apresenta mucilagem que evita a dessecação; enquanto que em Pitcairnia L’Hér. (Pitcairnioideae) as sementes apresentam alas membranáceas e em Vriesea Lindl. (Tillandsioideae) notam-se apêndices plumosos. O início do desenvolvimento pós-seminal de A. blanchetiana, A. bromeliifolia, N. marmorata (Bromelioideae) e Pitcairnia flammea (Pitcairnioideae) é marcado pela emergência da raiz primária, já em Vriesea incurvata (Tillandsioideae) observa-se a emergência do cotilédone haustorial.Os resultados obtidos no presente estudo subsidia a área de tecnologia de sementes envolvendo as espécies estudadas, assim como a taxonomia de Bromeliaceae / The aim of this study was to describe the morphology and the stages of germination of Aechmea blanchetiana (Baker) L.B.Sm. Aechmea bromeliifolia (Rudge) Baker, Neoregelia marmorata (Baker) L.B.Sm., Pitcairnia flammea Lindl. e Vriesea incurvata Gaudich. The species have epigeal and cryptocotylar germination, with different periods and germination rates. The embryos have axial position with short and cylindrical embryonic axes, the endosperm containing starch and the tegument has overlapping cells. The radicle shows ring- shaped pilosity before the issuance. The seeds of Aechmea and Neoregelia (Bromelioideae) presents mucilage that prevents drying out, Pitcairnia L'Hér. (Pitcairnioideae) has seeds with membranous wings and in Vriesea Lindl. (Tillandsioideae) the seeds show feathery appendages. In A. blanchetiana, A. bromeliifolia, N. marmorata (Bromelioideae) and Pitcairnia flammea (Pitcairnioideae) the post-seminal development starts with the emergence of primary root; to Vriesea incurvata (Tillandsioideae) we observed a haustorial cotyledon. The results obtained in this study are basis in the area of seed technology involving these species, as well as the taxonomy of Bromeliaceae

Made available in DSpace on 2015-03-03T11:52:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-27Bitstream added on 2015-03-03T12:06:08Z : No. of bitstreams: 1 000811967.pdf: 992303 bytes, checksum: 45769526368a8c41c31996dad950f71f (MD5) / O presente trabalho objetivou avaliar o efeito do estresse hídrico sobre a germinação de sementes de seis espécies (Eucalyptus brassiana, E. camaldulensis, E. grandis, E. pellita, E. resinifera e E. urophylla) e quatro híbridos (E. brassiana x E. pellita, E. brassiana x E. tereticornis, E. grandis x E. camaldulensis e E. grandis x E. urophylla) de eucalipto, submetendo-os a seis potenciais hídricos (0, -0,2, -0,4, -0,6, -0,8 e -1,0 MPa) simulados por soluções aquosas de polietilenoglicol 6000 (PEG 6000). Pretendeu-se também avaliar o efeito do condicionamento osmótico de sementes sobre a porcentagem, velocidade de emergência em viveiro, sobre o desenvolvimento de mudas e sobre a possível indução de maior tolerância dessas mudas ao déficit hídrico, em casa de vegetação. Os experimentos realizados no laboratório e em viveiro foram conduzidos em delineamento experimental inteiramente ao acaso, e o realizado na casa de vegetação foi conduzido em blocos ao acaso. Os dados foram submetidos a análise de variância com comparação de médias pelo teste de Tukey e análise de regressão. Observou-se que o aumento da restrição hídrica afeta de forma diferenciada a germinação das espécies e híbridos de eucalipto, sendo E. brassiana x E. tereticornis, E. grandis x E. camaldulensis e E. resinífera os mais tolerantes à deficiência hídrica. O osmocondicionamento proporcionou o aumento na velocidade de emergência de E. brassiana x E pellita e E. brassiana x E. tereticornis, mas prejudicou a emergência de E. grandis x E. camaldulensis e de E. urophylla x E. grandis. Na etapa realizada na casa de vegetação o osmocondicionamento resultou na diminuição da média da altura das mudas de E. resinifera, E. grandis e E. grandis x E. camaldulensis, e no aumento da média desse caráter em E. brassiana x E pellita. Não houve diferença no período de sobrevivência das mudas provenientes de sementes osmocondicionadas e ... / This research aimed valuate the effect of the water stress under the seed germination of six eucalypt species (Eucalyptus brassiana, E. camaldulensis, E. grandis, E. pellita, E. resinifera and E. urophylla) and four eucalypt hybrids (E. brassiana x E. pellita, E. brassiana x E. tereticornis, E. grandis x E. camaldulensis e E. grandis x E. urophylla), subjecting to six osmotic potentials (0, -0,2, -0,4, -0,6, -0,8 e -1,0 MPa) simulated by solutions of polyethylene glycol 6000 (PEG 6000) The aim was also to evaluate the effect of seed priming on percentage and emergence in nursery, on seedling development and the possible induction of drought tolerance to these seedlings, in greenhouse The experiments were carried out in completely randomized design, in laboratory and in nursery, and in completely randomized block in greenhouse. The data were subjected to analysis of variance and means compared by the Tukey test and regression analyses It was noted that the rising of water restriction affects in a different way the germination of the species and hybrids of eucalyptus, E. brassiana x E. tereticornis, E. grandis x E. camaldulensis and E. resinífera the most tolerant to the water deficit. The effect of the priming was little among the species and hybrids studied, giving a increasing in the emergency speed of the E. brassiana x E pellita e E. brassiana x E. tereticornis, but damaging the emergency rate of E. grandis x E. camaldulensis and de E. urophylla x E. grandis. In stage conducted in a greenhouse priming resulted in decreased of average seedling height on genotypes E. resinifera, E. grandis and E. grandis x E. camaldulensis, and increasing this characteristic of E. brassiana x E. pellita. No significant differences were found in survival time between the seedlings from primed seeds and the unprimed