No description available.

Tagetes minuta L. is a weedy herb that has been a rich source of fragrant oils, used as in the perfume and flavour industry. T. minuta achenes germinate erratically under field conditions. However, at the optimal germination temperature of 25 °C, 100 % germination is attained within 48 h of imbibition. The achenes are thermoinhibited at 35 °C. The aims of this project were to assess the role of cytokinins (CKs) in normal germination at 25 °C, and to investigate the factors that regulate thermoinhibition at 35 °C. CKs were extracted from achenes germinating at 25 °C at 0, 24; 48; 96 and 144 h after imbibition. Two different purification techniques were used, namely Dowex cation exchange resin followed by paper chromatography, or high performance liquid chromatography (HPLC). CK-like activity was tested with the soybean callus bioassay. With both techniques, a peak in CK-like activity appeared 24 h after imbibition, which coincides with the period during which most of the achenes germinated. For quantitative analysis, HPLC\mass spectrometry (MS) techniques were used. The isoprenoid CKs were far more abundant in T. minuta achenes than the aromatic CKs. cis-Zeatin (cZ) and its derivatives were the most abundant CKs. In total, 19 CK compounds were detected, including 4 free bases and a number of corresponding conjugates. Benzyladenine (BA) was the only aromatic CK detected. There was no common time at which active free base maximal concentrations were detected, suggesting that different CKs may have specific roles in the germination process, and thus peak at different times. This in turn suggests that germination is not a single process, but rather a correlative process involving a number of events, with specific CKs having specific roles relating to these correlative events. There is sufficient evidence obtained from both the soybean callus bioassay and HPLC/MS analysis to suggest that CKs have an active role in T. minuta germination. A decline in free BA during germination without corresponding conjugation, suggests that BA is actively used in early germination processes, possibly in the stimulation of DNA synthesis. Secondly, there was a distinct dihydrozeatin (DHZ) peak obtained at 24 h. Roughly 75 % of the achenes germinate between 16 and 26 h, thus it is likely that DHZ has an active role during the germination of T. minuta. Although CKs are probably not involved in the breaking of dormancy per se, the distinct peak in CK-like activity obtained in the bioassays, 24 h after imbibition, suggests that CKs have an active role in the germination of T. minuta. With respect to the regulation of thermoinhibition, a number of exogenous treatments were applied, including hormones [gibberellins (GA₄₊₇), abscisic acid (ABA), ethylene and a number of CKs], adenosine triphosphate (ATP) and incubation in 100 % oxygen. ABA was extracted from thermoinhibited and germinating achenes to assess the role of ABA in thermoinhibition and germination. While exogenous 0.1 mg L¯¹ GA₄₊₇ application slightly improved normal germination at 25°C, no treatments were effective in alleviating thermoinhbibition in T. minuta achenes. Thermoinhibition in T. minuta achenes may be under hormonal regulation, as there is strong evidence for the role of ABA in the maintenance of dormancy and thermoinhbition. High ABA levels were found in dry control samples. Additionally, exogenous ABA application inhibited normal germination, and the commencement of germination was accompanied by a decrease in endogenous ABA levels. A number of experiments relating to the imposition of thermoinhibition were carried out. Thermoinhibition appears to be very rapidly imposed. Germination is rapidly inhibited following shifting to higher thermoinhibitory temperatures, even after prolonged exposure to optimal germination temperatures. Results suggest active de novo biosynthesis of ABA in thermoinhibited achenes. Active biosynthesis of ABA during thermoinhibition suggests that this phytohormone is essential in the maintenance of thermoinhibition of T. minuta achenes. It thus appears that ABA is synthesized in the achenes in response to elevated temperatures that are unfavourable for germination to proceed. Unfavourable environmental conditions result in an achene-mediated inhibition of germination, which appears to be initiated and maintained by elevated levels of endogenous ABA. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

No description available.

Seeds of wild rice (Zizania palustris var. interior) have been reported to show highest survival when dehydrated at 25 QC. It has also been reported that axis cells sustained least damage at this drying temperature. In the present study, a linear relationship between drying rate and dehydration temperature was established. Whereas highest positive tetrazolium staining and lowest leakage were recorded for seeds that were dehydrated at 25 QC, maximum germination was recorded for seeds dried at 20 QC. A proportion of seeds showed the presence of glasses, irrespective of the dehydration temperatures used. Parameters of the glass to liquid transition, however, correlated with neither water content nor sugar profiles. The ratio of raffinose to sucrose was similar among all the treatments. A hydroperoxide test revealed a linear relationship between peroxide levels and temperature of drying although the levels of fatty acids were not correlated with hydroperoxide levels. Butanal levels and total aldehydes evolved, on the other hand, showed a high negative correlation with peroxide levels. Electron microscopy showed that the variability and relative abundance of peripheral membrane complexes (PMCs) was the highest for cells of embryonic axes dehydrated at 25 QC and the lowest for embryonic axes of seeds dried at 10 QC. Furthermore, intramembrane particles (IMPs) were evenly distributed in cells of axes dried at 25 or 37 QC. In contrast, membranes of cells of axes dehydrated at 10 QC showed large IMP-free areas. The relative abundance of IMPs was the highest for cells of embryonic axes dried at 25 QC, and the lowest for cells of axes dehydrated at 10 QC. From these observations, it is suggested that membrane phase transition, with the concomitant elimination of proteins, accompanies dehydration of Z. paluslris seeds at 10 QC, whereas at 37 QC peroxidation may predominate. / Thesis (M.Sc.)-University of Natal, Durban, 1996.

Buddleia davidii is a weed naturalized in New Zealand. It invades radiata pine plantations and causes major growth reduction and economic losses. Modelling its germination for predicting its occurrence will help foresters minimise its influence in forest plantations. Germination experiments have been carried out in laboratory to assess the influence of seed origin, defoliation, temperature and water stress on germination. Defoliation treatments did not significantly affect germination. The pattern of germination for seeds from four different places within New Zealand revealed so little difference that there is no need to define different models according to the site considered. However this similarity in germination pattern is limited to New Zealand and cannot be generalised to other countries where germination appears to be significantly different. The germination of Buddleia davidii seed appeared to be a function of hydrothermal time. The base, optimum and ceiling temperatures for Buddleia are respectively 9, 25 and from 30 to 35?, and Buddleia seed germinate between 0 and approximately -6 bars. In constant conditions, the predicted germination for Buddleia davidii with the thermal time model was limited to sub-optimal temperatures and the hydrotime and hydrothermal time models described well the germination pattern at any temperature and water potential. The modified hydrothermal time model proposed by Alvarado and Bradford (2002) most accurately predicted germination although it tended to overestimate the asymptotes. Overall the hydrothermal time model allowed prediction of actual timing of germination with much accuracy. This threshold model can therefore be used for modelling the germination of Buddleia davidii subjected to constant temperature and water potential conditions.

No description available.

In Scotland, bilberry is well known as a member of the dwarf shrub community on moorlands, which provide valuable habitats for wildlife. Recently it has been envisaged that bilberry populations could play an important role in improving the dwarf shrub vegetation in degraded moorland areas. This study was therefore undertaken to investigate the above-ground growth dynamics of bilberry with emphasis on responses to grazing by sheep and seedling establishment. The leaf production of bilberry was increased by higher nitrogen availability. High nitrogen supply also led to greater activation of dormant buds. Abortion of buds was less when nitrogen was continuously supplied. The reproductive capacity of bilberry was shown to be decreased by herbage removal. In contrast flowering was increased following supply of high nitrogen in glasshouse conditions. Almost all the flowers developed into fruits in the field, but a very low production of fruits was reported from bilberry plants that were grown in the glasshouse. Results of a series of laboratory experiments on seed production, germination, seed storage and evaluation of a moorland seed bank confirmed that the scanty seedling recruitment of bilberry was due to the limited production of 'germinable' seeds in berries and risks imposed by the environment after dispersal particularly when seeds are in the litter layer and/or soil. This could suggest that limited picking of bilberry fruits would not have a detrimental effect on establishment of bilberry populations in moorlands. Therefore, areas could be identified which were suitable for public access and berry exploitation in Scotland. The berry production was estimated approximately to be about 3220-9660 tones per year in this zone.

Common heliotrope (Heliotropium europaeum L.) is an herbaceous Mediterranean summer annual that grows on areas devoid of vegetation in the dry-land cropping region located in the north-west of the state of Victoria, Australia. This region is known as the Mallee, and common heliotrope is considered a weed here because it transpires soil water that could otherwise be used by ensuing crops, and is toxic to livestock. / In this study, laboratory experiments have shown that germination of seeds of common heliotrope is not limited by light, cold treatment, or a leacheable inhibitor. Temperature and water potential (and perhaps depth inhibition) are the principal environmental factors that limit germination. Although 100 % of seeds will germinate under optimal conditions, these conditions are rarely met in the field, and the percentage of seeds that germinate at sub-optimal conditions changes seasonally and between Australian populations. This is the principal mechanism of dormancy in the species, ensuring that seeds do not germinate when conditions are unfavourable for continued growth and that in the field, germination of a seed population is fractional, spreading risk temporally. Germination of seeds of common heliotrope does not conform to the assumptions of the hydrothermal time model frequently used to predict field emergence of weed species. / Field observations and simulated rainfall experiments on a consistent soil type (Calcarosol with a clay loam surface texture and clay subsoil) indicated that approximately 20 mm of rainfall is the minimum amount required for germination and emergence of common heliotrope. Field experiments using lysimeters indicated that this is also the amount required for minimal reproduction on the same soil type. Although common heliotrope can successfully reproduce upon the rainfall event which causes its germination, its growth is indeterminate, and further access to moisture will result in massively increased reproductive output. Plants will continue to grow and produce seed over summer until they are killed by drought or senesce in autumn. Laboratory and field studies showed that root growth in common heliotrope is relatively slow, and is opportunistic in areas where moisture becomes available. / Simulation of soil water and temperature fluxes showed that soil type has a large impact on the amount and duration of water potential that seeds and plants are exposed to. In the case of common heliotrope, this is critical in determining regional prevalence and distribution in the north-west of Victoria. It is recommended that studies of arid species reliant on isolated rainfall events for emergence should consider absolute water availability and not in terms of rainfall amount alone. / Analysis of long term summer rainfall data from the Victorian Mallee indicates that there is potential for reducing the cost of controlling common heliotrope by using residual pre-emergent sulfonylurea or triazine herbicides, instead of the traditional post-emergent herbicides or cultivation. More information is needed on the efficacy of such residual herbicides on common heliotrope and other summer weeds, and their impact on subsequent crops before the full potential of this management option is known. Reduced cost of control could also be achieved by economic analysis of the likely benefits of controlling each emerging cohort of common heliotrope, and a framework for decision making is suggested.

The Lycopodiaceae is an ancient and cosmopolitan family of fern allies that include an estimated 35 Huperzia species occurring throughout the South-East Asian and Australian region. Thirteen species naturally occur in Australia and are found mainly in the tropical rainforests of far north Queensland. Over the past decade, there has been renewed interest in Huperzia and their respective Huperzine alkaloid concentrations following the discovery of Huperzine A (HupA) and Huperzine B (HupB) alkaloids in H. serrata (Thunb. ex Murray) Trevis. Both alkaloids are of pharmaceutical interest since they are highly selective and potent reversible inhibitors of acetylcholine esterase. Huperzine alkaloid concentrations of Australasian Huperzia have not been well documented, and no prior studies have been undertaken to investigate the amenability of Australasian Huperzia to alternative propagation techniques such as axenic culture. / This research presents an extensive screen of 16 Australasian Huperzia species to investigate their Huperzine alkaloid concentrations. HupA (0.032 to 1.012 mg g-1 DW) was detected in ten out of the sixteen Huperzia species examined, while HupB (0.008 to 0.339 mg g-1 DW) was detected in eight. From this extensive study, H. elmeri (Herter) Holub was observed as the species with the greatest potential to yield high Huperzine-containing individuals. In addition, the screen established that Australasian Huperzia generally contain higher HupA levels than H. serrata, the main source of commercial HupA, which on average only contains 0.082 mg g-1 DW HupA. The fractionation and spectrometric analysis of alkaloids as part of the screen led to the discovery of three Huperzine alkaloids co-occurring within the same plant: HupA, HupB and Huperzine C, isolated from an individual of an Australian H. carinata (Desv. Ex Poir.) Trevis. / The potential of establishing axenic cultures of Australasian Huperzia was also investigated in this research. Actively growing axenic cultures of H. carinata, H. squarrosa (C.Forster) Trevisan, H. phlegmaria (L.) Rothm. and H. phlegmarioidies (Gaudich.) Rothm., together with callus and cell suspension cultures of H. carinata and H. phlegmaria, were successfully established. The results suggest that culturing in total darkness is essential to allow for optimal callus and cell suspension growth. In addition, this study also investigated the possibilities of germinating various Huperzia spores, by both symbiotic and asymbiotic means. Germination of H. squarrosa spores was achieved by both symbiotic and asymbiotic means, and was only observed in cultures which were kept in the dark, implying that there is a form of photo-inhibition mechanism preventing spores from germinating when they are exposed to light. Beneficial effects of various types of spore treatments prior to sowing, in terms of increased spore germination was also observed. / In conclusion, the results presented suggest that Australasian Huperzia are indeed a potentially valuable resource for Huperzine alkaloids. The investigations into the conditions required for the successful introduction and maintenance of Australasian Huperzia in axenic culture has also further extended our understanding of these plants, and their amenability towards axenic culture conditions as a means of alternative propagation.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.