Thesis--Bonn University.

Thesis (M.S.)--Ohio State University, 1987. / Includes bibliographical references (leaves 102-104). Available online via OhioLINK's ETD Center

Thesis (M.S.)--Ohio State University, 1985. / Includes bibliographical references (leaves 86-87). Available online via OhioLINK's ETD Center

Intraspecific variation within the genetic model plant Arabidopsis thaliana has been used to research numerous potentially adaptive and economically important traits. In this thesis I used this tool to investigate root morphology and adaptation of plants to edaphic conditions. Firstly I tested local adaptation of chosen A. thaliana wild genotypes collected from north eastern Scotland, to two soil types with contrasting textures. When local adaptation is defined as fitness advantage (reproductive output) in local soil, I did not find clear signs of local adaptation. Additionally, I observed significant phenotypic variation between collected accessions for both mineral nutrient uptake and growth in the two soil types. Together these results may suggest the mixing of adapted genotypes due to extensive human disturbance in north eastern Scotland. Secondly I focused on two linked aspects of root biology: endodermal development and root system architecture. The characteristic features of the endodermis include Casparian strips (CS) that form a barrier to apoplastic transport. Some mutants with an altered CS are sensitive to growth on media with elevated magnesium (Mg) and reduced calcium (Ca). In order to potentially identify novel alleles of genes involved in CS biosynthesis I took advantage of this growth phenotype and performed genome wide association (GWA) analysis on response of plants to low Ca/Mg ratio of the growth medium. As a result I compiled a list of genes for the future research by choosing candidate genes identified in the GWA study for both plant weight and elemental composition. This list was further refined using knowledge on gene expression in the endodermis. Accessions with the most extreme response to this low Ca/Mg treatment were analysed further. I identify a link between both lateral root number and total root length with performance on growth medium containing a low Ca/Mg ratio.

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Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in Arizona in order to determine the effect of aeration, flooding, and exogenously applied benzyladenine (BA) on growth and cytokinin production at different growth stages. The structural changes in roots at different soil environments were also studied. Fresh and dry weight of roots and shoots and root exudate were collected at various stages of growth. Results showed that aerated plants significantly outperformed flooded and BA treated plants due to increased root and shoot output. The level of cytokinin in root exudate was higher during the early phase of vegetative growth. At the time of bud formation and anthesis, the level of cytokinin declined. In the vegetative stage, the competition between removed sinks and the rest of the shoot was reduced and, as a result, more cytokinin was believed to come from the roots to the shoots. Besides, additional carbohydrates were available to the roots. Determination of cytokinins in aerated plants showed a significant increase. However, in flooded plants, a smaller amount of cytokinin was detected. This is believed to be due to death of root apices, a major site for cytokinin production. Under experimental conditions, the application of BA to foliage of flooded plants had an adverse effect on growth of roots and shoot of tomato plants. However, a slight increase in cytokinin level was detected. Histological studies showed an increase in air-spaces (aerenchyma) in roots of flooded plants. This acclimation improved survival in inadequately aerated plants that were waterlogged.

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