No description available.

Appreciation of the ecological and economic values associated with healthy salt marshes has led to a recent rise in the number of marshes that are being targeted for restoration by dike removal. The success of restoration is often measured by the return of marsh plants, though this overlooks a key component of salt marshes, that of the invertebrate community within marsh sediments. To evaluate the short-term recovery of these invertebrates, sediment cores were collected across an elevational gradient in a recent dike removal marsh, one and two years post removal, and a nearby reference marsh. Abundance, richness and diversity as well as morphospecies community composition were compared across treatment groups (Reference, Removal) and elevation zone (High Marsh, Low Marsh). Morphospecies richness, abundance and diversity were significantly higher in Low Marsh samples than in High Marsh samples, though no statistically significant differences were found across treatments of the same elevation (e.g., Reference Low Marsh versus Removal Low Marsh). Pair-wise ANOSIM results found significant differences between community compositions across treatments, specifically Reference Low Marsh and Removal Low Marsh. The marsh edge, the lowest point of vascular plant growth before transitioning to tide flats, is considered a high stress environment for emergent vegetation. Plant establishment and survival in this low elevation zone is limited by the tolerance to inundation duration and frequency and anoxic sediments. Bioturbation and burrowing by macroinvertebrates increases the surface area exposed to surface water for gas exchange, increasing the depth of the redox potential discontinuity layer. Crabs that make stable, maintained burrows have been shown to increase oxygen penetration into sediment, improving plant productivity. Such crabs are not found in salt marshes of the Pacific Northwest of North America. However, other burrowing invertebrates may have a positive impact on plant health in these areas by reducing abiotic stress due to anoxic sediments, thereby allowing plants to establish and survive lower in the intertidal zone. To assess this potential relationship, study plots of Distichlis spicata were selected at equivalent elevations at the lowest point of plant establishment at the marsh edge. Focal plant rhizomes were severed from upland ramets and assigned an invertebrate abundance treatment based on a visual burrow count surrounding each plant (9 cm diameter). Focal plants were visited monthly from July to September 2016, plant health variables of chlorophyll content and chlorophyll fluorescence (photosynthetic efficiency), and sediment ORP readings were collected. Plant survivorship was significantly higher in plots with invertebrates, 96% of plants in 'With Invertebrate' plots and 50% of plants in 'No Invertebrates' plots survived the duration of the study. Plant health (chlorophyll content and chlorophyll fluorescence) generally increased with increased invertebrate presence though, not statistically significant. There may be potential for improved plant productivity and resilience to plants at the marsh edge due to invertebrate burrowing activity. This benefit could help mitigate projected losses in plant productivity due to sea level rise, though more research is needed to investigate the mechanism by which these invertebrates confer a health benefit to plants at the marsh edge.

Previous findings showed that mild chronic restraint stress causes motor impairments in rats. These behavioural impairments might be related to molecular changes in brain areas that regulate motor functions, such as the cerebellum. Little is known about the role of the cerebellum in stress-induced behavioural alteration. We hypothesized that alteration in animal behaviour after chronic restraint stress is due to brain-specific changes in miRNA and proteins encoding gene expression. Our results revealed that expression of three miRNAs and 39 mRNAs was changed significantly after two weeks of stress. Furthermore, we verified one putative target for one of the changed miRNAs and expression of four randomly selected genes. Changes in gene expression disappeared after two weeks of recovery from stress. These findings provide a novel insight into stress-related mechanisms of gene expression underlying altered behavioural performance. The observations bear implications for the prevention and treatment of stress-related disorders and disease. / xii, 109 leaves. : ill. ; 29 cm

Abiotic stresses are one of the major limiting factors of plant growth and thus crop productivity. Exposure to these stresses, including temperature and UV, cause physiological and epigenetic changes in plants. Such changes may be inherited in the progeny of stressed plants, and may change their ability to respond to stress. To understand the ability of plants to inherit an epigenetic stress memory as well as the physiological manifestations of such a memory, we propagated both stressed and control plants and compared the progeny under both normal and stressed conditions. In addition to wild-type plants we used Dicer-like mutants dcl2, dcl3 and dcl4, as Dicers have been linked to RNA-directed DNA methylation, a form of epigenetic memory. These studies revealed that leaf number decreases in the progeny of stressed plants, and bolting occurs earlier in the progeny of temperature stressed plants but later in the progeny of UV-C stressed plants. Transposons were also re-activated in the progeny of stressed plants. While heat shock transcription factor 2A increased expression in the progeny of heat stressed plants, many genes involved in DNA repair and histone modifications decreased. DCL2 and DCL3 appeared to be more important in transgenerational stress memory than DCL4. However, all dcl plants were generally not significantly different than wild-type plants, indicating that a single DCL deficiency may be compensated for by another DCL. / xiv, 246 leaves : ill. ; 29 cm

Abstract not available

Crocodilians and birds comprise sister taxa of archosaurs, the development of these vertebrates occurs within an egg case that leaves developing embryos susceptible to fluctuations in the nesting environment. Studies suggest that sub-optimal conditions alter morphological growth and cardiovascular physiology. Regulation of the cardiovascular system is immature in the subjects studied, and embryos may rely on humoral rather than neural control of the cardiovascular system. The primary focus of this dissertation was to assess regulatory mechanisms responsible for maintenance of arterial pressure and heart rate. Dehydration stress had marked effects on embryo growth, and altered baseline cardiovascular parameters, while leaving the response to humoral regulator, angiotensin II (Ang II), unaffected. However, dehydrated alligator embryos developed cholinergic tone on heart rate. Hypoxic incubated chicken embryos were reduced in embryo mass, and altered response to humoral regulatory components Ang I and adenosine in addition identifying a novel regulatory component of the cardiovascular response to acute hypoxia. Collectively, these studies add to the existing knowledge of cardiovascular physiology in embryonic archosaurs and suggest that some components of cardiovascular regulation are plastic following developmental stress.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Horticulture in the Faculty of Applied Sciences at the Cape Peninsula University of Technology, 2012 / This article based thesis includes two individual studies evaluating the role of silicon (Si) in mitigating the negative effects that are associated with sodium chloride (NaCl) induced toxicity in lettuce (Lactuca sative L. 'Eish!').

Plant form is a compromise between resource gathering, reproduction and the tolerance to physical demands of the abiotic and biotic environment. In an agricultural field in addition to the natural factors causing stress, humans also introduce physical and mechanical stresses, and chemical pesticides into the environment. Many of these factors are hazardous, since they represent stresses to which plants are unable to develop defense mechanisms. However, weeds have persisted in the agricultural environment despite the efforts to eradicate them. They have adapted to environmental changes such as crop rotation and have developed tolerance to stressors like pesticides in very short periods of times (less than 10 years), much less time than normally expected for evolutionary responses to occur. Perhaps a key to why weeds persist in stress-dominated habitats is the way they compromise between yield and survival. The mechanisms that explain which process is relevant in the control of seed production or seedling growth relate to the ecophysiology of the individual plants. However, trade-offs between plants physiological functions will have implications at both population and community levels. Climate change, air pollution and water scarcity are examples of environmental stresses that particularly affect agriculture. Herbicides are a major technological tool for agriculture and are responsible, at least in part, for significant increases in crop production during the last quarter of the century. The research presented in this dissertation was developed to understand the extent that individual responses to multiple environmental stresses can be extrapolated to population-level responses in an annual weed species. The specific objectives were to assess (1) the impact of three anthropogenic stresses (herbicide, UVB light and ozone) and their interactions on individual Italian ryegrass ontogeny and reproduction and (2) the potential evolutionary effect of these stresses and combinations on changes in population size and structure over time. Plants were capable of growth and reproductive compensation under the studied stresses. Stress factors with similar biochemical mechanisms had different effects at the individual plant and population levels of organization. Compensation occurred at all levels of organization: as individuals modifying growth and allocation to different organs and as populations modifying birth, and death rates and density dependent responses. The ability to compensate sometimes decreased with the number of stress factors (e.g. herbicide and UVB). In other cases, compensation ability increased with the number of stress factors (e.g. ozone and herbicide). / Graduation date: 2004

[No abstract available] / xi, 176 leaves : ill. (chiefly col.) ; 29 cm

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: In the brewing industry yeast cells are re-used in successive fermentations. Consequently, the state of the cells at the end of each successive fermentation could impact on the quality of the subsequent fermentations. The use of markers to evaluate the fermentative ability of yeast to resist stress enables brewers to select populations of yeast for brewing. Yeasts are typically exposed to osmotic-, ethanol- and cold-stress during the high-gravity brewing process. In this study the vitality of the yeast cells was monitored during and after each successive high-gravity brewing fermentation. This was done by measuring the cell metabolites, which included glycerol, trehalose and glycogen. Others markers that were evaluated for yeast viability were the number of budding scars, the levels of activity of the enzymes neutral trehalase and esterase and the expression level of the heat shock protein Hsp12p. Coupled to these evaluations, the growth of the yeast and the utilisation of the sugars glucose, fructose, maltose and maltotriose were monitored during the fermentations. The experiments were conducted in 2-litre E.B.C. tubes at either 14 oC or at 18oC using standard techniques. Comparable growth patterns were obtained for different re-pitching fermentations, with fermentation 1 at 18ºC and 5 and 6 at 14°C being the most active fermentations. The higher temperature encouraged more rapid growth and a greater numbers of cells. The wort attenuation was more rapid at 18°C than at 14°C. Glucose and fructose in wort were utilised prior to maltose and maltotriose. At 18°C the yeast consumed the sugars faster, with mean utilisation values of 97.3% glucose, 100% fructose, 59.9% maltose and 65.6% maltotriose. At the lower temperature of 14°C high concentrations of residual sugars remained at the end of the fermentation. All re-pitching fermentations revealed lower viabilities at 18°C in comparison to the 14°C fermentations. Simultaneously, a number of other markers were evaluated. The intracellular trehalose concentration per cell varied considerably with each fermentation. Trehalose levels at 18°C gradually increased in concentration from 48h until the end of the stationary phase. Much lower trehalose concentrations were observed in fermentations conducted at 14°C. Higher and more consistent glycerol concentrations were found in fermentations at 14°C with mean concentrations of 12 mg/g dry weight at pitching. The expression of the heat shock protein Hsp12p level increased during the fermentation but no sharp increase was detected in any particular fermentation. No increase in yeast budding scar number was observed during re-pitching fermentations. Neutral trehalase and esterase activities in fermentations at 18°C were especially high at pitching. Neutral trehalase activities at 14°C were all generally lower than in the case of fermentations at 18°C. The fermentation ability of flocculated yeast in slurry and yeast suspended in beer was investigated after exposure to various stresses. The aged yeast present in the slurry was generally found to be more resistant to stress, in particularly to osmotic stress, throughout the serial re-pitching process. The fermentation rates of both yeast types were especially sensitive to prior exposure to ethanol stress. / AFRIKAANSE OPSOMMING: In die broubedryf word gisselle herhaaldelik gebruik vir agtereenvolgende fermentasies. Derhalwe kan die toestand van die gisselle teen die einde van elke agtereenvolgende fermentasie ‘n invloed hê op die kwaliteit van die daaropvolgende fermentasies. Deur gebruik te maak van merkers om die fermentasievermoë van gis om stres te weerstaan te evalueer, stel dit bierbrouers in staat om gispopulasies te selekteer. Gedurende die hoëdigtheid brouproses word giste tipies aan osmotiese-, etanol- en koue-stres blootgestel. In hierdie studie, gedurende hoë-digtheid fermentasies, is die lewensvatbaarheid van die gisselle gedurende en na elke agtereenvolgende fermentasie gemonitor deur die volgende selmetaboliete te bepaal: gliserol, trehalose en glikogeen. Bykomende merkers vir gis lewensvatbaarheidsbepalings was: die aantal botselletsels, die vlakke van aktiwiteit van die neutrale trehalose en esterase ensieme, en die uitdrukkingsvlak van die hitteskokprotein Hsp12p. As aanvullende evaluasies is die groei van die gis en die gebruik van die suikers glukose, fruktose, maltose en maltotriose gedurende fermentasies gemonitor:. Die proewe is in 2-liter E.B.C. buise uitgevoer, by ‘n temperatuur van 14oC of 18oC, deur van standaard tegnieke gebruik te maak. Die groeipatrone van die verskillende herhaaldelike-inokulasie gistings was ongeveer dieselfde. Fermentasie 1 by 18ºC en fermentasies 5 en 6 by 14°C was die mees aktiewe fermentasies. Die hoër temperatuur het vinniger groei en ‘n groter aantal selle begunstig. Die wortattenuasie was vinniger by 18°C as by 14°C. Glukose en fruktose in mout is voor die maltose and maltotriose opgebruik. By 18°C het die gis die suikers vinniger opgebruik. Gemiddelde gebruikswaardes vir die sewe reeksgewyse fermentasies was die volgende: 97.3% glukose, 100% fruktose, 59.9% maltose en 65.6% maltotriose. Teen die einde van fermentasie by 14°C was daar hoë konsentrasies van die oorblywende suikers, hoofsaaklik na fermentasie 1. Alle herhaaldelike inokulasie fermentasies het lae lewensvatbaarheid by 18°C in vergelyking met 14°C fermentasies getoon. Ander merkers is ook gelyktydig gebruik. In die verskillende fermentasies was daar ‘n groot verskil in die intrasellulêre trehalose konsentrasie per sel. Trehalose konsentrasies by 18°C het geleidelik toegeneem, vanaf 48 uur tot aan die einde van die stationêre fase. Baie laer trehalose konsentrasies is gemeet vir fermentasies by 14°C. In fermentasies by 14°C was die gliserolkonsentrasies hoër en meer konstant. Gemiddelde konsentrasies was 12mg/g 14°droë gewig by inokulasie. Die uitdrukking van die hitteskokproteien Hsp12p vlak het gedurende fermentasie toegeneem, maar daar was geen skerp toename vir die afsonderlike fermentasies nie. Die bepaling van die aantal botselletsels per sel het daarop gewys dat die gemiddelde aantal nie toegeneem het met die veroudering van die gis gedurende reeksgewyse herhaaldelike inokulasie nie. Neutrale trehalase aktiwiteite in fermentasies by 18°C was besonders hoog, veral by inokulasie. Die neutrale trehalase aktiwiteite in die fermentasies by 14°C was in die algemeen laer as die by 18°C. Die fermentasievermoë van die geflokkuleerde gis in die sediment en gesuspendeerde gis in die bier is ondersoek na blootstelling aan verskeie tipes stres. Die verouderde gis teenwoordig in die sediment was in die algemeen meer bestand teen stres, veral aan osmotiese stres, dwarsdeur die reeksgewyse herhaaldelike inokulasie proses. Etanolstres het die gistingstempo van beide giste dieselfde geaffekteer.