Survival of teleost larvae requires growth and development which depend upon endocrine processes. In this dissertation I have examined the ontogeny of elements of the thyroid hormone (TH) and corticosteroid (CS) systems in red drum (Sciaenops ocellatus). Basal cortisol production was first detected 3 days post-hatch (DPH) and a cortisol stress response was present from 6 DPH forward. Changes in steroidogenic enzyme mRNA (CYP11B and CYP21) levels did not correlate with these events. The time necessary to reach peak cortisol levels as well as return to basal levels declined as larvae developed. A second set of studies examined ontogenetic patterns in levels of mRNAs encoding thyroid (soTR[alpha] and soTR[beta]) and corticosteroid (soGR) hormone receptors and assessed the regulation of these mRNAs by exogenous triiodothyronine (T3) and cortisol. soTR[alpha], soTR[beta] and soGR were expressed in all stages of red drum examined. soTR[alpha] levels increased during the time when surging TH levels have been reported. soTR[beta] levels did not differ significantly during development. soGR levels were strongly correlated with those of soTR[alpha]. T3 up-regulated soTR[alpha] and soTR[beta] levels in 7 DPH, but not older larvae. Cross-regulation of receptor mRNAs by exogenous treatment with T3 or cortisol was not observed. Finally, I assessed the influence of a common herbicide, atrazine, on receptor mRNA, TH levels and growth of red drum. In two experiments, red drum exposed to environmentally relevant levels of atrazine did not alter hormone receptor mRNA levels, or TH content. However, atrazine did depress growth in some instances. In conclusion, the expression patterns of hormone receptor mRNA in embryos suggests receptor proteins could be activated by maternal hormones prior to the onset of endogenous hormone production. A correlation between soTR[alpha] and soGR mRNA levels suggests coordinated function of TH and CS systems, although regulatory interactions between these systems were not evident under the conditions in this study. Patterns in soTR[alpha] and soTR[beta] mRNA levels support an important role for TH in the larval to juvenile transformation of red drum larvae. The results also support growing evidence indicating atrazine exposure effects larval growth and may impact their survival in the wild. / text

Stress has been shown to exacerbate cell death and cognitive deficits after ischemic injury in rodents, however, little is known of the effects of stress on motor recovery. The objective of this present thesis is to examine the effects of chronic stress on skilled motor recovery after devascularization lesion in rats. It was found that pre-lesion stress induced the most behavioural impairments, while post-lesion stress exacerbated infarct volume. The effects of chronic multiple stress on skilled motor recovery after lesion was also examined. Chronic multiple stress did not modulate skilled motor recovery nor did it have any influence on infarct volume. Additionally, stress had effect on edema after devascularization lesion. The present thesis suggests that the time of exposure to chronic stress in respect to the ischemic lesion, in addition to the type of stress, will differentially affect recovery and compensation in rats. / xii, 122 leaves : ill. ; 29 cm.

Homologous recombination represents a DNA repair pathway. Its role in a plant cell is not limited to double strand break repair. It also extends to genome evolution via rearranging of DNA sequences, and has an important application in foreign DNA integration in the plant genome. Our study demonstrated that effects exerted by stress on homologous recombination and genome stability are not restricted to the exposed generation. The progeny of plants exposed to stress exhibited elevated spontaneous homologous recombination, changes in DNA methylation and higher tolerance to stress. These heritable changes are mediated by an unknown stress-inducible epigenetic signal. Furthermore, we demonstrated that using factors that enhance homologous recombination can improve the efficiency of genetic transformation by Agrobacterium. We have developed and patented a plant growth medium enhancing homologous recombination and significantly increasing the transformation frequency. The role of several other chemicals for the improvement of transformation was also evaluated. / xxi, 246 leaves : ill. ; 29 cm. --

As anthropogenic demands on water resources intensify instream flow needs are becoming an increasingly important area of study, particularly over winter months during which time little is known about the behaviour and physiology of fishes. This thesis addresses the implications of water withdrawal from a small in situ stream on brook trout (Salvelinus fontinalis) during the winter of 2007 and 2008 in the Rocky Mountains. Water was withdrawn from one of two stream enclosures reducing the discharge by 50% and 75%, for 4hrs daily. Behaviour was monitored using radio transmitters that were externally attached to the small trout. Changes in physiology were monitored by measuring stress hormone levels and by measuring predicted body composition parameters using bioelectrical impedance analysis. Trout reacted to water withdrawal by being more active, but this change in behaviour did not elicit detectable changes in physiology. / x, 129 leaves : ill. ; 29 cm. --

Cowpea (Vigna unguiculata. L) is an important African crop. However, it is also an underutilized grain legume. Consequently, there is not enough research data on cowpea seed physiology. Whereas there is evidence of cowpea being a drought tolerant crop, there is no evidence to associate plant drought tolerance with seed quality in response to water stress. This study sought to understand the effect of production site and water stress on cowpea seed quality development with respect to germination capacity and vigour. Patterns of raffinose family of oligosaccharides (RFO) during seed development to mature dry stage were used to physiologically relate seed performance to water stress. The effect of water stress and exogenous ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development and germination was investigated. RFOs are known for their roles in desiccation sensitivity but no studies have shown their significance in cowpeas. Seeds of six cowpea cultivars were produced at two distinct growth sites characterised by irrigated and dry land conditions. The seeds were assessed during six developmental stages, for water content, dry matter accumulation, and performance. Harvested seeds were then planted in a pot experiment under controlled conditions to examine the effect of water stress on seed quality development and data collected during three developmental stages. Harvested seeds from the pot experiment were subsequently analyzed for changes in RFO accumulation during development using gas chromatography. The seeds were also used to investigate the effect of water stress and ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development in cowpea. In addition, this study evaluated the use of image analysis as a method that can be used to objectively determine seed coat colour variation in cowpea. Statistical variation in individual seed’s solute leakage for cowpea cultivars differing in seed coat colour and produced under different environmental conditions was explored and correlations were done between seed conductivity test with other aspects of seed performance during germination. Furthermore the results of the conductivity test were compared with accelerated aging test, in relation to seed performance. The study provided evidence that cowpea seed lots produced under different environmental, and possibly management conditions may not differ with respect to seed quality as determined by germination capacity and vigour. However, significant differences between sites with respect to seed maturation patterns determined by water content and dry matter accumulation were observed. Adverse maternal environmental effects on the subsequent performance of seeds in a drought tolerant crop may not necessarily lead to poor performance. Cultivar differences in response to simulated drought conditions at the whole plant and tissue level can be considerable and highly variable; however, these differences may not have adverse effects on the germination and vigour of the seeds. Drought avoidance mechanisms at the whole plant level in cowpea are quite efficient in allowing the species to adapt to simulated drought conditions. These mechanisms may allow the cowpea cultivars to maintain metabolism and restore conditions for their continued growth under water stress; and produce few seeds of high germination capacity and vigour. Stachyose was found to be the predominant member of the raffinose family of oligosaccharides in cowpea. It is suggested that stachyose accumulation could be used as an indicator of stress tolerance in cowpea. However, the relationship between RFO concentration and the acquisition of desiccation remained as a matter of speculation in the present study and is still generally inconclusive. There was no evidence to suggest the acquisition of maximum desiccation tolerance is associated with maximum seed vigour. It is suggested in cowpea, which is drought tolerant, that maximum vigour does not necessarily imply the acquisition of maximum desiccation tolerance; rather there is a minimum level of desiccation tolerance that is required for the development of optimal seed vigour. The use of an in vivo approach in the study of LEA function in cowpea enabled the accurate comparison of two different groups of LEA proteins in developing cowpea seeds under conditions of water stress and in relation to germination and vigour. Both group 1 LEA and group 2 LEA (dehydrin) were shown to increase in concentration in response to water stress. In addition group 1 LEA protein was observed to be relatively abundant in cowpea seeds. A maternal influence on LEA protein gene expression under conditions of water stress, which may induce dehydrin accumulation vii during the earlier stages of seed development, was implied by the observation that dehydrin-like proteins were induced after two weeks of development in cowpea plants subjected to stress during the vegetative phase. In addition, the exogenous application of ABA delayed radicle protrusion; this was associated with a delay in the disappearance of LEA proteins and is suggestive of a relationship between LEA protein accumulation and the acquisition of desiccation tolerance. The study has demonstrated that image analysis can objectively discriminate seed coat colour variation in cowpea. Dark coloured seeds in general performed better than light coloured seeds; however seed coat colour was not always associated with better performance. A newly developed Aging Stress Differential Index (ASDI) has been used in this study to demonstrate a link between seed coat colour and sensitivity to water stress. The ASDI correlated well with the observations relating stress tolerance to stachyose accumulation. The skewed distribution patterns in individual electrical conductivity and the presence of extreme values may have implications with respect to the suitability of using standard statistical analyses which compare mean values to evaluate such data. In addition variation in individual electrical conductivity may also be influenced by cultivar differences and the chemical composition of the seed coat. Therefore associations between seed coat colour and electrical conductivity as a measure of performance should be treated with caution. The AA test does reflect changes in seed vigour, however ranked electrical conductivity values after AA did not consistently reflect differences in seed performance between cultivars and sites, and they did not correlate well with other aspects of performance. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Thesis (MScFor)--Stellenbosch University 2002. / ENGLISH ABSTRACT: One of the greatest .limitations to the productivity of a plantation forest is poor nutrient status of the soil. Empirical application of corrective treatments are marginally successful in some cases, but because of limited understanding of the soiltree system, most nutritional problems go unnoticed or are accepted as a conceivable growth constraint. The aim of this investigation was to identify nutrient growth problems through field observations and to determine means of confirming these nutrient imbalances. Poor and abnormal growth of pine trees in the following areas were investigated: (i) The North Eastern Cape: Ugie and Maclear Districts (ii) The Natal Midlands: Mooi River area (iii) Mpumalanga: .Graskop and Kaapsche Hoop areas (iv) Southwestern Cape: Jonkershoek Plantation The study was conducted as nursery trials at the University of Stellenbosch and field trials at the various locations. Soils from the different regions were collected and used as growing media to test the growth response of five timber species (Pinus patula, P. elliottii, P. taeda, P. greggii and Eucalyptus nitens) under controlled conditions to various nutrient treatments. Indicator plants (cauliflower and soya) were included in these bio-assays. In the field trials nutrients were applied to seedlings and established stands of various ages by means of foliar and soil application. In the nursery trials and the trials where seedlings were planted in the field, plant performance was measured by quantitative means. The reaction of established stands to nutrient treatments were however less vigorous and qualitative means (e.g. colour changes) were used for assessment. Field observations in the North Eastern Cape and the Natal Midlands indicated possible boron, iron and molybdenum deficiencies and thus the work concentrates on these elements. Foliar and soil analyses reinforced these observations with marginal to deficient levels for boron and molybdenum being detected. The yellowing of foliage during the dry season was symptomatic of ineffective nitrogen assimilation and pointed to a molybdenum deficiency while seasonal growth tip dieback, resm exudation, sinuous tree limbs and bushy trees were classical boron deficiency symptoms. Potted trials indicated positive reaction to the application of boron and molybdenum deficiency symptoms were observed on indicator plants. Conclusive evidence of a boron deficiency in some of the pot trials, the planted field trials and the tree evaluation field trials remain elusive due to toxicity experienced as a result of an over-application of the nutrient. The occurrence of multiple deficiencies (phosphorous and calcium) further complicated the findings. The Mpumalanga observations indicated severe nutrient imbalance due to manganese toxicity (strong iron antagonism). The discolouring of the foliage on some sites towards the end of the winter was thought to be an induced molybdenum deficiency on the weathered and acidic red soils. Positive reaction to molybdenum application occurred in a single. tree evaluation trial, but because of soil oxidisation during collection, the effect of manganese toxicity was diluted in the pot trials. Foliar analyses indicated that foliar application of iron was unsuccessful and that other means should be considered to ensure uptake of this nutrient. / AFRIKAANSE OPSOMMING: Die lae vrugbaarheid van grond is een van die grootste beperkings tot die produktiwiteit van plantasie bosbou. Empiriese toedienings van kunsmisstowwe is in sekere gevalle suksesvol tot die bekamping van onvrugbaarheid. Weens gebrekkige kennis t.o.v die grond-boom sisteem word baie van die voedingstof probleme egter onkundig oorgeslaan' of word dit as natuurlike beperking in die produksie konteks aanvaar. Die doel van hierdie ondersoek was om swak boomgroei in die veld waar te neem en om bevestigende metodes te vind waarmee hierdie probleme as voedingstoftekorte geëien kan word. Swak en abnormale boomgroei van denne is in die volgende gebiede ondersoek: (i) Die Noordoos Kaap: Ugie- en Maclear Distrikte (ii) Die Natal Middelande: Mooirivier area (iii) Mpumalanga: Graskop- en Kaapsche Hoop areas (iv) Suidwes Kaap: Jonkershoek Plantasie Die ondersoek is uitgevoer as kwekery proewe by die Universiteit van Stellenbosch en as veldproewe in die onderskeie areas. Grond is uit die verskilende gebiede versamel en as groeimeduim gebruik om die groei-reaksie van vyf verskillende houtspesies (Pinus patula, P. elliottii, P. taeda, P. greggii en Eucalyptus nitens) onder beheerde klimaatsomstandighede te ondersoek. Daar is ook gebruik gemaak van indikator spesies (blomkool en soya) vir diagnose van visuele tekort simptome. Beide saailinge en reeds gevestigde bome is in die veldproewe gebruik. Voedingstowwe is by aanplanting toegedien, of in die geval van groter bome, as blaar- of grondtoedienings. Waar dit moontlik was (meestal in die geval van die saailinge) is die reaksie op die toegediende voedingstowwe met kwantitatiewe metodes bepaal. Daar moes egter van alternatiewe kwalitatiewe metodes gebruik gemaak word om die reaksie by die ouer en groter bome te bepaal. Gevolglik is verandering in bladkleur t.o.v. 'n basiskleur onder andere as maatstaf gebruik. Waarnemings van swak boomgroei in die Noordoos Kaap en die Natal Middelande het gedui op moontlike boor, yster en/of molibdeen tekorte. Lae vlakke van hierdie elemente in blaar- en grondanalises het hierdie waarnemings bevestig. Die geel verkleuring van die naalde gedurende die droë seisoen is simptomaties van oneffektiewe stikstof assimilasie en dui op 'n molibdeen tekort. Die waarneming van seisoenale terugsterwing van groeipunte, gebuigde stamme en takke, gomuitskeiding en bome met bosagtige voorkoms is eienskappe van 'n boor tekort. In die potproewe was daar positiewe reaksie op die toediening van boor en tekort simptome van molibdeen is in die indikator plante waargeneem. In van die potproewe, die saailing veldproewe en ander veldproewe kon daar egter nie uitsluitsel tot die effektiwiteit van boor gevind word nie aangesien toedienings te heftig was en toksisiteit ervaar is. Diagnose van enkel element voedingstof tekorte word bemoeilik deur van die proewe wat ook dui op veelvoudige voedingstoftekorte (veral fosfaat en kalsium). In Mpumalanga is daar waargeneem dat drastiese voedingstof wanbalanse a.g.v. mangaan toksisiteit aanwesig is (veral 'n sterk Fe antagonisme). Die bladverkleuring op sekere proefopstande aan die einde van die winter is ook 'n aanduiding van geïnduseerde molibdeen tekorte wat op die verweerde en suur rooi gronde van die omgewing verwag kan word. Daar was dan ook positiewe reaksie op die toediening van molibdeen, hoewel slegs byeen proefopstand. Die inherente nadeel van potproewe is op die mangaanryk gronde geopenbaar deurdat belugting (gedurende grond versameling) die effek van mangaan toksisiteit verminder het. Die gebruik van blaaranalises is ook voordelig aangewend om te bepaal dat die toediening van yster as blaartoediening onsuksesvol was en dat ander metodes ondersoek moet word om opname van die element te verseker.

Orientador: Marcelo Menossi Teixeira, Andrea Akemi Hoshino / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-21T05:45:50Z (GMT). No. of bitstreams: 1 Souza_CesarBuenode_D.pdf: 2755272 bytes, checksum: 945d7a45c10893c9a58603f1e04813ef (MD5) Previous issue date: 2012 / Resumo: O Brasil é o maior produtor mundial de cana-de-açúcar e no cenário atual, em que o aumento na busca por energia renovável é visível, o aumento na produtividade da cana é de extremo interesse para o setor sucroalcooleiro. Estresses abióticos influenciam grandemente a produtividade de espécies como a cana e, sendo assim, estudos relacionados com a tentativa de diminuir esse impacto na produtividade são de grande importância. A seca é o estresse ambiental que mais causa prejuízos ao agronegócio e por esse motivo é muito desejável que se desenvolvam novas variedades de cana-de-açúcar que sejam mais tolerantes a esses estresses e com isso o setor sucroalcooleiro será largamente beneficiado. A transgenia é uma das ferramentas utilizadas na produção de novos cultivares comerciais com características agronômicas interessantes e, para o seu sucesso, a identificação de genes com potencial para melhorar essas características faz-se necessária. Sendo assim, o maior objetivo desse trabalho foi a avaliação do potencial biotecnológico de seis genes de cana-de-açúcar que são modulados por seca. Os genes aqui estudados tiveram seu perfil de resposta a seca anteriormente avaliado por microarranjos de DNA e foram selecionados como candidatos para a produção de um novo cultivar de cana-de-açúcar que seja mais tolerante a estresses abióticos. Esses genes foram analisados em plantas transgênicas de tabaco, cana-de-açúcar e/ou Brachypodium. A superexpressão de dois genes de cana em tabaco conferiu maior tolerância a seca e salinidade das plantas transgênicas quando comparadas às selvagens e a proteção de seus usos na produção de plantas tolerantes a estresses abióticos foi solicitada. Há evidências de que um terceiro gene de cana conferira tolerância ao estresse oxidativo em plantas transgências de cana. Além disso, outros três genes de cana foram inseridos em Brachypodium, mas os eventos gerados ainda não foram avaliados. Com o trabalho desevolvido foi, portanto, possível gerar plantas transgênicas tolerantes a estresses abióticos e com isso é possível concluir que a seleção de genes candidatos para melhorias de características agronômicas de interesse através de microarranjos é algo que deve ser explorado e pode-se concluir, ainda, que alguns dos genes analisados estão envolvidos na resposta a seca e/ou aos estresses ambientais em geral / Abstract: Brasil is the largest producer of sugarcane in the world and the seeking for renewable energy is currently visible what makes the increase of sugarcane productivity highly desirable. Abiotic stresses greatly influence the productivity of species such sugarcane. Therefore, studies related to the reduction of these impacts on productivity are highly important. Drought is the environmental stress that causes more damage to agribusiness and because of it the development of new cultivars with higher tolerance to abiotic stresses is desirable since the sugar and ethanol sector will be largely benefited. Transgenic plants production is one of the tools that have been used in the development of new cultivars with interesting agronomic traits and for its success identifying genes that can improve these characteristics is necessary. Thus, the main objective of this study was evaluating the biotechnological potential of six drought-modulated genes from sugarcane. The genes studied here have their drought response profile previously showed by microarray and were selected as candidates for the production of a new sugarcane cultivar with higher tolerance to abiotic stresses. These genes were analyzed in transgenic tobacco, sugarcane and/or Brachypodium plants. The overexpression of two sugarcane genes in tobacco conferred higher drought and salinity tolerance in tobacco plants compared to wild-type and the protection of their uses in the production of plants with higher tolerance to abiotic stress was requested. There are evidences that a third sugarcane gene confers tolerance to oxidative stress in transgenic sugarcane. Furthermore, three other genes were inserted in Brachypodium but these transgenic events were not yet analyzed. With this work was possible to produce transgenic plants that are tolerant to abiotic stresses what let us to conclude that the selection of candidate genes to improve agronomic traits by microarrays is useful and that some of the analyzed genes are involved into drought and/or abiotic stresses in general responses / Doutorado / Genetica Vegetal e Melhoramento / Mestre em Genética e Biologia Molecular

Vegetation stress as a form of degradation is a widespread problem in many catchments in the Eastern Cape province. The Keiskamma is one of the catchments where considerable parts of the thicket biome are stressed. This necessitates an assessment of the status of the thicket biome by way of detecting vegetation stress in the area. The underpinnings of vegetation stress are investigated in this study. As a basic method to evaluate the thicket condition, remotely sensed data were acquired. High resolution ASTER imagery for the Keiskamma area at two different dates (2001 and 2005) was used to compute SVI and NDVI as indicators of vegetation stress conditions. A Digital Elevation Model (DEM) was used to derive slope angle and aspect. By way of digitizing from ortho-photo maps, various land-use types were mapped using Arc View GIS. The relationship between land use, terrain, soil erosion and vegetation stress was established. Field based techniques comprising stomatal conductance measurements were used and compared to remotely sensed data. The SVI and NDVI resultant images expressed similarities in areas depicting vegetation stress conditions at both epochs. A strong linear regression between NDVI and stomatal conductance measurements (mmol/m²) serve to confirm that the NDVI is a reliable indicator of vegetation stress condition. Slope angle and aspect were found to have a significant influence on vegetation stress conditions. Similarly variations in soil moisture and soil surface condition have strong implications for vegetation stress. Amongst other land-use types, abandoned lands were found to have the lowest NDVI values implying an association with the worst vegetation stress scenarios. It was concluded that an element of persistent stress conditions exists amongst the thicket vegetation of the Keiskamma catchment. This was mainly due to land use activities in the area.

Quality protein maize (QPM) has enhanced levels of two essential amino acids, lysine and tryptophan compared to normal maize. This makes QPM an important cereal crop in communities where maize is a staple crop. The main abiotic factor to QPM production is drought stress. Little information is available on the effect of drought stress on QPM. Therefore, the objectives of this study were to: (i) conduct diversity analysis of QPM inbred lines using morpho-agronomic and simple sequence repeat markers, (ii) screen available QPM inbred lines and F1 progeny for tolerance to seedling drought stress, (iii) determine the combining ability and type of gene action of QPM inbred lines for tolerance to seedling drought stress, grain yield and endosperm modification. The study was conducted in South Africa, at the University of Fort Hare. Morphological characterisation of 21 inbred lines was done using quantitative and qualitative traits. A randomised complete block design with three replicates was used for characterizing the inbred lines in the field. Genstat statistical software, version 12 (Genstat ®, 2009) was used for analysis of variance (ANOVA) and descriptive statistics. Analysis of variance was performed on all quantitative data for morphological traits. Data for qualitative traits was tabulated in their nominal classes. Traits that contributed most to the variation were days to anthesis, days to silking, anthesis-silking interval, plant height, number of kernel rows, ear length and grain yield. Cluster analysis grouped the inbred lines into three main clusters. The first cluster was characterised by tall and average yielding lines, while the second cluster showed the least anthesis-silking interval, and had the highest yield. Cluster three consisted of lines that were early maturing, but were the least yielding. Genetic distances between maize inbred lines were quantified by using 27 simple sequence repeat markers. The genetic distances between genotypes was computed using Roger’s (1972) genetic distances. Cluster analysis was then carried out using the neighbour-joining tree method using Power Marker software version 3.25. A dendrogram generated from the genetic study of the inbred lines revealed three groups that concurred with expectations based upon pedigree data. These groups were not identical to the groups generated using morpho-agronomic characterisation. Twenty one QPM inbred lines were crossed using a North Carolina design II mating scheme. These were divided into seven sets, each with three inbred lines. The three inbred lines in one set were used as females and crossed with three inbred lines in another set consisting of males. Each inbred line was used as a female in one set, and as a male in a second set. Sixty three hybrids (7 sets x 9 hybrids) were formed and evaluated in October 2011, using a 6x8 alpha-lattice incomplete block design with three replicates under glasshouse and optimum field conditions. A randomised complete block design with three replicates was used for the 21 parental inbred lines. Traits recorded for the glasshouse study were, canopy temperature, chlorophyll content, leaf roll, stem diameter, plant height, leaf number, leaf area, fresh and dry root and shoot weights. Data for the various traits for each environment, 25 percent (stress treatment) and 75 percent (non-stress) of field capacity, were subjected to analysis of variance using the unbalanced treatment design in Genstat statistical package Edition 12. Where varietal differences were found, means were separated using Tukey’s test. Genetic analyses for grain yield and agronomic traits were performed using a fixed effects model in JMP 10 following Residual Maximum Likelihood procedure (REML). From the results, inbred lines that were not previously classified into heterotic groups and drought tolerance categories were classified based on their total dry weight performance and drought susceptibility index. Inbred lines L18, L9, L8, L6 and L3, in order of their drought tolerance index were the best performers under greenhouse conditions and could be recommended for breeding new varieties that are tolerant to seedling drought stress. Evaluation of maize seedlings tolerant to drought stress under glasshouse conditions revealed that cross combination L18 x L11 was drought tolerant, while cross L20 x L7 was susceptible. Total dry weight was used as the major criteria for classifying F1 maize seedlings as being resistant or susceptible. General combining ability effects accounted for 67.43 percent of the genetic variation for total dry weight, while specific combining ability effects contributed 37.57 percent. This indicated that additive gene effects were more important than non-additive gene action in controlling this trait. In the field study (non-drought), the experimental design was a 6x8 alpha lattice incomplete block design with three replicates. On an adjacent field a randomised complete block design with three replicates was used to evaluate the parental inbred lines. The following variables were recorded: plant height, ear height, ears per plant, endosperm modification, days to silking and days to anthesis, anthesis-silking interval, number of kernels per row, number of rows per ear and grain yield. General analyses for the incomplete lattice block design and randomised complete block design for hybrid and inbred data respectively were performed using JMP 10 statistical software. Means were separated using the Tukey's test. Genetic analyses of data for grain yield and agronomic traits were conducted using a fixed effects model using REML in JMP 10. The importance of both GCA (51 percent) and SCA (49 percent) was observed for grain yield. A preponderance of GCA existed for ear height, days to anthesis, anthesis-silking interval, ears per plant and number of kernels per row, indicating that predominantly, additive gene effects controlled hybrid performance under optimum field conditions. The highest heritability was observed for days to silking (48.27 percent) suggesting that yield could be improved through selection for this trait. Under field conditions, variation in time to maturity was observed. This implies that these inbred lines can be recommended for utilisation in different agro-ecologies. Early maturing lines such as L18 can be used to introduce earliness in local cultivars, while early maturing single crosses such as L18 x L2, L5 x L9, L3 x L4 and L2 x L21 could be recommended for maize growers in drought prone areas such as the former Ciskei. Single crosses L18xL11, L16xL18, L8xL21 and L9xL6 had good tolerance to seedling drought stress. On the other hand, single crosses L18xL11 and L11xL13 had high grain yield and good endosperm modification. All these single crosses could be recommended for commercial production after evaluation across locations in the Eastern Cape Province. Alternatively they can be crossed with other superior inbreds to generate three or four way hybrids, which could then be evaluated for potential use by farmers in the Eastern Cape.

Plankerbverzahnungen zählen zu den Vertretern der Kupplungsverzahnungen, mit deren Hilfe zwei Bauteile koaxial miteinander verbunden werden können. Neben einer hohen Winkelgenauigkeit zeichnen sie sich durch eine enorme Drehmomentkapazität bei gleichzeitig geringem Montageaufwand aus. Die zur Leistungsübertragung erforderliche Vorspannkraft kann über eine zentrale Spannschraube oder mehrere dezentral, auf einem gemeinsamen Teilkreis, angeordnete Spannschrauben erzeugt werden. Diese Arbeit liefert einen Beitrag zur beanspruchungsgerechten Dimensionierung von Plankerbverzahnungen mit zentraler und dezentraler Verschraubung. Es wird eine Berechnungsmethode zur Bestimmung der Tragfähigkeit des Zahnfußes, der Zahnflanke und der Spannschrauben vorgestellt und anhand von Beispielrechnungen erläutert. Neben den umfangreichen theoretischen Betrachtungen werden die Ergebnisse zahlreicher experimenteller Untersuchungen präsentiert. Diese dienen der Gewinnung von grundlegenden Aussagen zur Stützwirkung und zum Mittelspannungseinfluss an einfach und mehrfach gekerbten Proben sowie zur Verifizierung des Tragfähigkeitsnachweises.