No description available.

The rhizosphere and rhizoplane environments of higher plant roots are specialised microhabitats for soil organisms. These organisms include nematodes which are capable of responding to attractants from roots over several centimetres (Rode, 1962, 1969). The aim of this project was to investigate the various aspects of chemotaxis in host finding by nematodes, and the relative importance of electrotaxis in this process. This involved experimentation on root diffusate as a whole, on various ions etc which may be attractive components of root diffusate, on interference by lectins on the host finding process and finally into nematode response to applied electrical fields with comparison to field strengths measured at root surfaces. The working hypothesis used throughout this project was the occurrence of long distance attraction via a non-specific factor which is replaced by a more specific factor as the distance between host and parasite is reduced. Examination of the diffusate as a whole clearly demonstrated that nematode attraction is a directed response. It also gave some support to the theory of successive attractive factors, with each successive factor being of higher molecular weight and lower diffusibility. The response to H+, OH-, Na+, five amino acids and cAMP was tested. The two pH extremes were equally attractive, the Na+ and amino acids were neither attractive nor repulsive and the cAMP was repulsive at the higher concentration used. These results suggested that the ions might have a secondary involvement in attraction by stimulating the initial movement of the nematodes but would be non-specific. Any attraction to amino acids noted by other workers e.g. Bird (1959) might be due to the acidic nature of the amino acids tested. Experiments were carried out using concanavalin A to interfere with host finding as suggested by Marban-Mendoza et al. (1987) through its effects on surface carbohydrates. The experiments produced some evidence to support this theory, and further experiments were made to try to elucidate the mechanism. The results from this further work indicate the effect in pH dependent via changes in aggregate size, but also that there may be a dilution involvement as well. Application of electrical fields to the nematodes produced directional movement, but at voltages approximately 1,000 times that measured at the root surfaces with the vibrating probe. It is therfore concluded that chemotaxis is the primary means by which nematodes locate their host plants, but the possibility of electrotaxis being used to locate specific feeding sites is discussed.

30 clones of Betula pendula were produced using micro-propagation techniques and screened for root system variation. Shoot variation was assessed and the root systems divided into 3 root types; fine, woody, and non-woody. Dry weights, lengths, and various ratios were used in the analysis. There were differences in all the characteristics measured. Root system size could not usefully be predicted from shoot size. Four clones with contrasting root systems were chosen for further experiments. A sequential harvest experiment showed that all the characteristics changed with time, and that the clones grew and developed at different rates. Root distribution and development differed between the clones. A water status experiment indicated differences in rooting depth distribution which could be related to drought avoidance, but no growth differences were found. Two different nitrogen levels were used to show that root system differences had little effect on nitrogen uptake. One clone exhibited growth patterns which suggested that it would grow well in areas of chronic nutrient deficiency. The clone responses to phosphorus deficiency and mycorrhizal infection were also tested. One clone again showed growth patterns resembling those found in areas of chronic nutrient deficiency. Another clone responded poorly to mycorrhizal growth at high phosphorus concentrations. Ranking comparisons to the ranks found during the sequential harvest experiment showed that size was more important than age in determining development. Clone 14 seemed to be less plastic than the other clones, and shoot height and structural root production were controlled more by genotype than environment. The methods used, and some useful characteristics, were discussed in the context of tree selection programmes. Many suggestions for future work are given. These suggestions work towards the ultimate aim of the project to select root system types specifically suited to different environments.

Root tip demography of a 43 year old Sitka spruce stand was determined over a two year period. A total of 35,300 root tips were examined. A total of 14 mycorrhizal and 4 non-mycorrhizal root tip types were recognised. One mycorrhizal type, formed by Tylospora fibrillosa, made up 67% of the root tips examined, the rest each made up less than 5% of the population. The level of infection was high, with c. 94% of the root tips infected with mycorrhizal fungi. There were marked short term fluctuations in the numbers and relative abundance of some of the types, as well as longer term, unidirectional increases in the dominant type and decreases in the numbers and relative abundance of non-mycorrhizal root tips. The effect of the addition of carbon and nitrogen was examined. Carbon addition had very little effect on the mycorrhizal population as a whole. Nitrogen, on the other hand, had a very marked effect on several of the root tip types. The relative abundance and the numbers of Tylospora fibrillosa mycorrhizas were both reduced by the addition of nitrogen, whereas the relative abundance and numbers of non-mycorrhizal tips increased. A large gradient of weight of organic matter and moisture existed on the site and this was shown to strongly influence the spatial distribution of the root tip types. Russula ochroleuca mycorrhizas were shown to have a positive association with organic matter and moisture. The occurrence of E-type mycorrhizas was negatively correlated with the accumulation of organic matter, which supports the idea that these mycorrhizas are primarily associated with mineral soil. Finally, the population structure of T.fibrillosa was examined using somatic incompatibility (SI) to determine the clone size of the fungus on the site. No SI was found between any of the isolates, even when collected 20m apart. This could mean that either T.fibrillosa does not exhibit SI or that the clone from which the isolates were collected was larger than 20m across.

AIM: To assess root parallelism after Invisalign® treatment. MATERIALS AND METHODS: The sample consisted of 101 patients (mean age: 22.7 years, 29 males, 72 females) treated non-extraction with Invisalign® by one orthodontist. Root angulations were assessed using the 4-point angulation tool (Dolphin imaging©); the long axes of adjacent teeth were traced, yielding a convergence/divergence angle. Acceptable root parallelism was assessed if the root angulation did not converge/diverge more than 7 degrees. Sites evaluated: between 1st molars and 2nd premolars, 2nd and 1st premolars, lateral and central incisors, and between central incisors in all four quadrants. The average change in mesio-distal root angulation was assessed between pre- and post-treatment panoramic radiographs. RESULTS: Paired t-tests were used to analyze the average change in mesiodistal root angulation. Statistically significant differences were obtained indicating a reduction in the convergence/divergence angles between teeth #16-15, #15-14, #11-21, #24-25, #25-26, #45-44, #42-41, #41-31, #31-32, and #34-35 (at p-value <0.05). The average change in root angulation was not affected (p>0.05) by age (Pearson correlation coefficient), gender, occlusion type (I, II, or III), or elastic use (unpaired, 2 sample t-test at p<0.05). Intra and inter-rater reliability for 20% of the studied sample was assessed using the interclass correlation coefficient 3 test. All measured areas except teeth #16-15, #26-25, and #36-35 yielded good ICC reliability scores above 0.7. CONCLUSION: Root parallelism was improved post-Invisalign® treatment in ten of the fourteen areas evaluated. Thus, Invisalign® may be an effective treatment modality in controlling root angulation in non-extraction cases. / May 2016

No description available.

Thesis (M.D.S.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 67-83) Also available in print.

Thesis (M.D.S.)--University of Hong Kong, 1993. / Includes bibliographical references (p. 105-125). Also available in print.

Considerable evidence exists that the majority of low tension water flow through highly structured clayey soil occurs in a small fraction of total pore space and that the flow paths converge as depth increases. In structured clayey soils, water tends to flow in locations where macroporosity is high and roots tend to enjoy this condition as well. Water reduces the strength and mechanical impedance of the soil. Mechanical impedance of clayey soils tends to be extremely high when the soils are dry so one might expect that there would be a positive spatial correlation between the location of roots and the location of water flow paths in highly structured clayey soils. Understanding the relationship between the location of roots in soil relative to the location of water flow paths is important in understanding how plants obtain nutrients and water for growth, and it would also be of considerable importance in phytoremediation research and research into the prevention of groundwater contamination. This experiment was designed to map the locations of flow paths and roots and then measure the spatial association of the two. A pasture on Ship’s clay along the Brazos River was chosen as the research site. Three plots were irrigated with an Erioglaucine dye solution used to stain flow paths. After irrigation the soil was excavated to a depth of 25 cm. On the resulting horizontal plane the dye stain pattern was mapped using photography. The locations of roots were mapped on clear plastic sheets. During mapping the roots were categorized by size. The mapping procedure was repeated at depth of 45 cm and 75 cm for all plots. The root maps were overlaid on the photographic images and analyzed for a spatial association. There was no evidence the smallest (> 1 mm diameter) roots were not randomly distributed. The results did show that the larger roots were not randomly distributed, and evidence pointed to a clustering of roots in and around the dye stained flow paths. However, the data fell short of establishing a spatial association. The lack of more conclusive data was likely the result of inaccuracies in the mapping.

Thesis (M.D.S.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 67-83).