No description available.

No description available.

No description available.

The initiation and development of adventitious roots in cuttings are highly complex processes, influenced by both endogenous and exogenous factors. These vary from the environmental factors prior to the striking of the cutting, to the anatomical and physiological factors, within the stem. Encompassed are the nutrient status, physiological age and degree of differentiation of the tissues, and the balance of endogenous rooting inhibitors and/or promoters (including hormones). The role of cytokinins in root initiation and development has been perceived as that of an inhibitor. This investigation considered several aspects of the role played by cytokinins in the process of root development. A qualitative/quantitative analysis of the cytokinin-like activity in stem cuttings of several plants, including both easy- and difficult-to-root species was conducted on a comparative basis. There was no clear correlation between the type / level of cytokinins detected in the cuttings and the relative ease of root formation. Both qualitative and quantitative changes in the compounds exhibiting activity in the soybean callus bioassay were observed over the period of root formation in Impatiens stem cuttings. The effects on root formation in cuttings of exogenously applied auxins and cytokinins were investigated. Auxins generally promoted root number and elongation at relatively high concentrations (10[-4] M), but showed less effect on lateral root initiation and development. At high concentrations, cytokinins strongly inhibited root development, but did promote lateral root growth. In suspension culture, the effect of these hormones differed slightly, with IAA and IBA having no significant effect on root development, but NAA strongly stimulating lateral root initiation. Zeatin (10¯¹¹ M) significantly increased root length and the number of lateral roots produced. The effect of treatment of the stem cuttings with potassium permanganate and centrifugation was examined. While both these treatments have been perceived to increase root production in cuttings, no significant improvement in rooting ability following centrifugation (relative to the control) was observed. Impatiens cuttings centrifuged in the presence of distilled water showed a significantly reduced rooting ability relative to those centrifuged in the dry state. Treatment with an 8-hour pulse in 0.05 % potassium permanganate significantly increased the average root length. These treatments had an effect on the cytokinin levels and distribution in the stem cuttings. Slightly higher levels of cytokinins were associated with the increase in root number and length in both experiments. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

No description available.

This investigation confirmed that plant reaction to Al was directed through the disruption of intercellular co-ordination existing between the cell populations comprising the root meristem. The first detectable response to A1 in the root involved disruption of Golgi apparatus function in the cap periphery. Ultrastructural changes in the cap periphery coincided with the presence of A1 in these cells. Conspicuous physiological changes involving cell enlargement, cell metabolism and root elongation were identified in cells initially remote from the site(s) of A1 uptake. Communication between A1-damaged peripheral root cap cells and the cell populations of the cap and proximal meristems, quiescent centre and region of cell growth was therefore indicated. A decrease in amyloplast numbers in response to increasing AI concentration coincided with diminished Golgi apparatus activity in the peripheral cap. These changes preceded detectable reductions in mitotic activity, indicated by decreases in cap volume and root length, and it was consequently suggested that control of intercellular activities in the root meristem may be directed through polysaccharide metabolism. Low concentrations of A1 (≤ 1,25 mg dm ¯³) produced a positive growth response in the primary root. This coincided with an increase in mean cap volume and these events were interpreted as an A1-induced release of the proximal meristem from growth inhibition originating in the cap. Experiments which followed the effect of decapping on the morphology of quiescent centre cells in the presence and absence of A1 supported the existence of a Golgi apparatus-derived morphogen involved in the control of Golgi apparatus secretory activity and plastid differentiation. In contrast to the controls (0 ABA). treatment of decapped roots with 2 X 10[-4] and 5 X 10[-5] M abscisic acid inhibited the development of Golgi apparatus secretory activity and plastid differentiation. It is postulated therefore, that an early response to AI may involve inhibition of the basipetal movement of an endogenous growth inhibitor originating in the cap, which may be ABA. The presence of A1 in the nutrient solution caused an efflux of H[+] from the root. Some of the more adverse plant responses to AI were initiated at A1 concentrations where the molar ratio of charge between Ca[2+] and A1[3+] favoured A1. An hypothesis for an electrophysiological plant response to A1 involving membrane hyperpolarisation by Al ions is developed. Chemical analysis of plant fractions did not connect A1-induced nutrient disorders with the primary expression of A1 toxicity. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

Root disease is a serious concern for the softwood timber industry. This thesis reports on the development of a root disease detection procedure that applies lidar data integrated with imaging spectrometer data. Photosynthetic pigments are frequently cited as one of the most responsive indicators of vegetation stress. This study estimated pigment content from needle and canopy reflectance and characterized the sensitivity of these pigments to a fungal-mediated stress. Samples were collected from the Greater Victoria Watershed District on Vancouver Island, BC, Canada. Lab reflectance measurements were made and pigments were extracted. Reflectance spectra were transformed into derivative spectra and a continuum removal band depth analysis was conducted. Reflectance metrics were generated and used in modeling pigment content. Chlorophyll-a was found to be significantly affected by the disease in the needle level portion of this study. The predictive power of reflectance attributes were assessed and yielded strong coefficients of determination (R2>0.80). Samples exhibiting stress responses affected by root disease were discriminated. It was determined that younger trees were more severely affected by the root pathogen than mature colonized trees. In the canopy level component of the study, chlorophyll-a was estimated through the application of partial least squares regression and achieved an R2 value of 0.82. Continuum removal metrics, which proved to be good estimators at the needle level, were found to be insufficient at the canopy level. Through the use of hyperspectral forest chemistry products, potential root disease sites can be identified. / Graduate

Photocopy (positive) of typescript. / Thesis (Ph. D.)--University of Hawaii, 1964. / Bibliography: leaves 158-161. / xi, 171 l illus., tables

Thesis (Ph. D.)--University of Adelaide, Dept of Soil Science, 1987. / Includes bibliographical references (leaves 207-222).

Thesis (D. Sc.)--University of Adelaide, 1988. / Comprised of the author's previously published works. Includes bibliographical references.