Thesis (Ph. D.)--University of Michigan, 1920. / "Reprinted from the American journal of botany, vol. VII, November, 1920." Includes bibliographical references (p. 404-406).

Thesis (Ph. D.)--University of Michigan, 1920. / "Reprinted from the American journal of botany, vol. VII, November, 1920." Includes bibliographical references (p. 404-406).

The continuum theory provides a framework in which the growth of a plant root as a dynamic process involving interactions among transport of water and solute, cell division, and the subsequent cell elongation can be described. A plant root is modeled as a one-dimensional, multi-phase, mathematical continuum. The network of cell walls constitute the solid phase of the system. The symplast and the apoplast pathways reside in this network of cell walls. Water and carbohydrates move in opposite directions through the apoplast and symplast pathways within the deforming network of cell walls. The division and elongation of cells depends on the mechanical stress imposed on the cell walls, the rate of metabolic stress relaxation process, and the physical properties of the cell walls. The model consists of five systems of differential equations. The kinematic equations are derived which allow, specifically, the different roles of cell division and elongation in root growth to be considered. These provide the reference system of the model. Equations of water transport in the coupled system of apoplast and symplast pathways are derived from considerations of theories of transport in the porous media and the cellular and membrane properties of the plant root. Equations of solute transport are derived by considering, specifically, the mechanisms involved in solute transport both at the membranes separating individual cells and within the cytoplasm. The rate of cell elongation is described as a function of the mechanical stress in the cell walls, the viscoelastic properties of the cell walls, and a metabolically controlled strain energy relaxation process. Growth in the meristem is modeled as the result of continuous cell elongation and division. The equations of water and solute transport, cell elongation, and meristem growth are solved simultaneously under the reference system provided by the kinematic theory. The model is used to examine the effects of soil water stress, soil resistance to root penetration, and temperature, as well as the carbohydrate supply from the upper part of the plant on the dynamic process of root elongation. The close correspondence between the material coordinate system and the underlying cellular structure of the root allows the comparison between the continuum theory and the results of cell growth studies. Agreement of the model predictions of the pattern of growth along the root axis, as well as the effects of temperature and soil water stress on root growth, with the experimental measurements reported in the literature provides the justification for the theories. / Graduation date: 1991

Extracts of gelling agents have been shown to stimulate rooting and this study was initiated to investigate the presence of root stimulating substances in gelling agents. After screening a number of gelling agents, four were selected, namely; Agar Bacteriological, Agar Commercial Gel, Difco Bacto Agar and Gelrite were selected and examined for the presence of root-stimulating substances using mungbean bioassay. Water extracts of Agar Bacteriological, Agar Commercial Gel and Difco Bactol Agar stimulated rooting of mungbean cuttings. Addition of Charcoal neither reduced nor increased rooting produced by the water extract of the first two agars but when added in conjunction with Difco Bacto Agar rooting was reduced. Autoclaving, however reduced rooting in extracts of the gelling agents. The possibility that root-stimulating substances may not be the same in all the gelling agents can not be excluded. Extraction of Gelrite with water was problematical and was therefore excluded. IBA solution and water extracts of the gelling agents separately promoted good rooting in mungbeans cuttings. Rooting in extracts of autoclaved frozen-thawed gelling agents was poor, however, IBA + gelling agents gave high rooting at the 100% concentration and this could possibly be due to an additive effect of the IBA. Addition of charcoal reduced rooting significantly in extracts of IBA + gelling agents. Using 80% acidic methanol, reasonable levels of rooting substances were obtained from the residue extract of this complex (IBA + gelling agent+charcoal) of all the gelling agents except Gelrite indicating that root-promoting substances were adsorbed by charcoal. The low rooting in the presence of the Gelrite extract was attributed to the matrix of the polymer of the Gelrite. Ethyl acetate fractionated extracts (EA-pH 8.0; EA-pH 3.0; and Aqueous) obtained from the four gelling agents stimulated rooting indicating the presence of numerous root promoting substances. Gelrite gave good rooting with both the 50 and 100% concentrations of all the fractions. Purified water and ethanol extracts of the gelling agents exhibited auxin-like activity when separated by paper chromatography and compared with IBA and IAA standards. Using HPLC, IAA was quantified in all the gelling agents with Difco Bacto Agar and Agar Commercial Gel having the highest IAA concentration and Gelrite the lowest IAA concentration. IAA concentration in Agar Bacteriological was a third of the level detected in Difco Bacto Agar. The information from this work may enable researchers to consider gelling agents as sources of auxin-like compounds and other plant hormones as well as support media for use in tissue culture procedures and also increase the enthuse for further research into the nutrient types and levels in gelling agents. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

No description available.

Kelpak®, a seaweed concentrate (SWC) prepared from the brown seaweed Ecklonia maxima (Osbeck) Papenfuss, improves overall plant mass and fruit yield in a variety of crops. The main active principals isolated from Kelpak® are cytokinins and auxins. Although these compounds are partly responsible for the growth promoting effect observed with Kelpak® application, they do not fully account for the complete effect of Kelpak® treatment. For this reason the focus has turned to polyamines (PAs) which are found in all cells of plants, animals and microorganisms, including eukaryotic algae. Polyamines also have growth promoting effects in plants. A study was carried out to investigate the PA levels in E. maxima and Kelpak® through a biennial cycle and to investigate if the PAs present in Kelpak® may have an effect on root growth, alleviating nutrient deficiency and the transport and accumulation of PAs in plants. To determine the amount of PA in the stipes, fronds and SWC prepared from E. maxima, samples were collected monthly over a two-year period (June 2009-June 2011). Extracts were benzoylated and quantified using a Varian HPLC. Putrescine concentrations ranged from 15.98-54.46 μg.g⁻¹, 6.01-40.46 μg.g⁻¹ and 50.66-220.49 μg.g⁻¹ DW in the stipe, fronds and SWC, respectively. Spermine concentrations ranged from 1.02-35.44 μg.g⁻¹, 1.05-26.92 μg.g⁻¹ and 7.28-118.52 μg.g⁻¹ DW in the stipe, fronds and SWC, respectively. Spermidine concentrations fell below the detection threshold. This is the first report of PAs being detected in a SWC. The seasonal pattern established for the stipe, frond and SWC followed the same trend over a biennial cycle. Polyamines accumulated in the seaweed tissue during periods of active growth and as a stress response elicited by rough wave action. This PA trend was similar to the cytokinin trend reported by MOONEY and VAN STADEN (1984b) for Sargassum heterophyllum which suggests that PAs play an important role in the hormone cascade during active growth. Routine monthly screening of Kelpak® carried out in the Research Centre for Plant Growth and Development indicated that Kelpak® consistently resulted in more rooting in the mung bean bioassay than the IBA control. The potential root promoting effect of PAs were investigated. Individually applied PAs did not increase rooting in the mung bean bioassay, but a synergistic relationship was observed between Put (10⁻³ M) and IBA (10⁻⁴ M). When applied together, rooting increased significantly above Put (10⁻³ M) and IBA (10⁻⁴ M) applied separately. The Put-auxin combination produced a similar number of roots to those treated with Kelpak®. It is possible that the PAs present in Kelpak® have a synergistic effect with auxins present in Kelpak® to promote root development and growth. Several physiological effects of Kelpak® and PAs on plant growth were investigated in a series of pot trials. Kelpak® significantly improved the growth of P- and K-deficient okra seedlings and masked the detrimental effects exerted by P- and K-deficiency. The application of PAs (10⁻⁴ M) significantly improved the seedling vigour index (SVI) of okra seedlings subjected to N-deficiency. The statistical difference was attributed to the N-containing growth regulators and polyamines being degraded and metabolized by the okra seedlings. Polyamine application did not alleviate P- and K-deficiency but increased root growth significantly in seedlings receiving an adequate supply of nutrients. It is likely that the additional PAs supported auxin-mediated root growth. A pot trial with okra plants was conducted to establish if the PAs in Kelpak®, applied as a soil drench or foliar application, are absorbed and translocated in a plant. Plants were also treated with Put, Spm, Spd to establish if PAs can be absorbed and translocated. Once the fruit had matured, plants were harvested and the endogenous PA content quantified by HPLC in the roots, stems and fruits. Applying PAs as a soil drench was not as effective as a foliar spray at increasing the PA content in the different plant parts. Kelpak® treatment (0.4%) did not contribute more PAs in any plant part. Spermidine concentrations were higher, in the various plant parts, than Put or Spm, irrespective of the mode of application. The application of Put, Spd and Spm increased Spd concentrations in the roots. Considering that Spd is the main PA produced in the roots and that exogenously applied PAs are readily converted to Spd, it seems evident that Spd is the preferred PA for long-distance transport in plants. The cytokinins and auxins in Kelpak® play an important role in stimulating growth in plants. It is, however, the totality of different compounds in Kelpak® that gives it its unique growth stimulating ability. Polyamines, occurring within the seaweed contribute to this activity, having an active role in root production and thus increased plant growth. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Drought resistance among genotypes of Port-Orford-cedar (Chamaecyparis lawsoniana (A. Murr.) Pan., Cupressaceae) seedlings was evaluated both in the field and in the greenhouse. Field water potentials (��) of 5-year-old seedlings were measured at two high-elevation plantation sites where summer drought occurs. Measurements of �� were compared to survival two years prior at the same site. The north coastal breeding zone 1 had significantly lower mid-day �� and lower survival than the southern interior breeding zone 6. Percent survival at 3 years was significantly correlated with mid-day ��. A second assessment of drought resistance was performed in the greenhouse on 1-0 seedlings. Root growth potential (RGP) was measured in the winter under non-stress conditions and following a drought in the summer. Differences among breeding zones were opposite in pattern from outplanting measurements of survival and water potential; therefore, RGP may not be a good predictor of drought resistance or survival among different genotypes within a single species. Low-elevation, coastal families had greater root growth than inland, high elevation sources. Greater root growth occurred in seedlings with more shoot mass. Little regional specialization in RGP across the species' range was indicated as there was greater variation among families than among breeding zones. In the summer RGP test following drought, only the two extremes of the range were evaluated; both north coastal and southern interior families showed decreased root growth compared to the winter RGP under non-stress conditions. Despite significantly higher predawn �� in inland, high elevation families, lower elevation coastal families had significantly more roots. Change in chlorophyll fluorescence yield measured on foliage of droughted plants was positively correlated with the absolute value of predawn ��; however, it was not a sensitive predictor of predawn �� (R��=0.06) at the levels used in this study. Lower levels of �� may be necessary to produce severe stress to damage Port-Orford-cedar foliage. / Graduation date: 2003

No description available.

Athletic field rootzones are often sand-based for improved drainage. Sand-based rootzones may have stability issues if turfgrass is not fully established. Our objective was to use organic amendments to improve the stability of sand-based fields during the turfgrass establishment period and avoid overuse of inorganic materials, which have negative effects. We tested coconut coir, peat and wheat straw at 1% organic material, peat at 2% organic material, and an inorganic stabilizing fiber, StaLok, in the top 10 cm of the rootzone. Surface hardness, volumetric water content, traction, penetration resistance and visual quality were measured 2 to 4 months after construction of the plots. Surface hardness was greatest in the inorganic stabilizer and the wheat straw treatments. The kinetic penetration had no differences between the wheat straw (33.78-51.10 kPa) and the StaLok fibers (34.99-56.23 kPa). Wheat straw could be used to stabilize sand-based fields as an organic alternative to inorganic fibers.

Root growth potential CRGP) is the measure of seedling ability to grow new roots. Loblolly pine (Pinus taeda L.) seedlings from 5 seedlots were raised at two widely separated nurseries (Summerville, SC and New Kent, VA). In Experiment I, RGP was determined during the fall and winter of 1984-85 and 1985-86, and several morphological traits were measured. In Experiment II seedlings from the same seedlots were lifted during February 1985 and 1986 at both nurseries, and cold stored until subsequent outplanting; subsamples of outplanted seedlings were used for RGP determinations. Root growth potential varied significantly by family, nursery, and lift date, and first order interactions were significant. Generally, the RGP of Summerville raised seedlings was higher than that of New Kent raised seedlings. RGP was not strongly correlated with common measures of shoot morphology, but RGP was consistently well correlated with lateral root dry weight. In Experiment II, RGP varied significantly by family, nursery, and storage duration. The family x nursery effect was the only significant interaction. Summerville raised seedlings had higher RGP on each planting date. During each year RGP declined rapidly in storage. First year survival was significantly correlated with RGP (r = .52, p < .001). Height increment and RGP were also strongly correlated (r = .80, p < .001). These relationships and their implications for nursery management were discussed. / M.S.