The specific activity of the ('32)P labeled sediment-P taken up by submersed macrophytes was shown to be identical to the specific activity of the sediment mobile P, as measured by isotopic dilution. The mobile P therefore represents the sediment-P available to aquatic macrophytes. / The ability to accurately measure the specific activity of the available sediment-P was applied to problems pertaining to the role of macrophytes in P cycling. The relative contribution of water and sediments in supplying P to macrophytes was measured by growing macrophytes in situ, rooted in ('32)P labeled sediments, and with the shoot in free contact with the unlabeled overlying water. Macrophytes grown in mesotrophic and eutrophic sites derived more than 95% of their P from the sediments alone. When grown in a hypertrophic site, the sediments still supplied 70% of the P. / Rates of P release by macrophytes and significance to their periphyton and surrounding phytoplankton were estimated by using fully labeled plants. The periphyton derived only 6.5% of its P form the macrophytes. Myriophyllum released 0.32 ug.g('-1).h('-1) P, most of which being readily available to phytoplankton. / The high vertical mobility of the available sediment-P was demonstrated both by experimental manipulations and direct observations.

No description available.

The present investigation is concerned with the relation between environmental factors and the ability to transfer. Although many studies in the past have shown that differences in environment result in differences in I.Q., as measured by conventional intelligence tests, there has been less research measuring environmental effects on learning and transfer abilities. The typical approachof studies which deal with either differences in intelligence, or in learning and transfer abilities, has been to select subjects from different environments and, by testing, demonstrate significant differences in the ability in question. Using this method, the results invariably favor subjects from whichever is the "better" environment in the study. The present study treats environment as an independant variable, holding I.Q. constant, and attempts to show differences in transfer ability, the dependent variable, under these conditions. On the basis of the theoretical considerations and empirical results reviewed below, it was hypothesized that, with I.Q. held constant,children raised in a "restricted" environment would show greater facility for transfer than children from a "free" environment. [...]

Cottonwoods (Populus sp.) and willows (Salix sp.) are generally limited to riparian landscapes in semi-arid regions of western North America. Water availability is a major determining factor for the establishment, growth and survival of these plants. Willows generally occur closer to the stream and at lower elevations than cottonwoods, suggesting reduced drought tolerance and increased flood tolerance. In the present thesis project, three related studies were conducted to investigate this hypothesis. Firstly, tolerable rates of water table decline and the impacts of the corresponding drought stress were investigated by growing cottonwoods and willows under water table decline rates from 0 to 12 cm/d. Willow saplings responded similarly to cottonwood saplings, but willow seedlings were more vulnerable than cottonwood seedlings to rapid rates of water table decline. In the second study, will saplings tolerated elevated water tables of 0 to 7.5 cm below substrate surface and the resulting flood stress for 152 days slightly better than cottonwood saplings. Finally, mature cottonwoods along Willow Creek, Alberta experienced water table decline from 1996 to 1998 due to water pumping in a nearby gravel pit; the water table recovered in 1999. The cottownwoods displayed physiological changes indicating drought stress in 1998 and recovered following restoration of the water table. This confirmed the cottonwoods' reliance on the water table as their primary moisture source. These studies indicate that the spatial separation of willows and cottonwoods may be particularly related to reduced drought tolerance of willows and these display only slightly increased flood tolerance of willos and these display only slightly increased flood tolerances. The studies confirm that both willows and cottonwoods are physiologically dependent on a sufficient riparian water table. / 85 leaves : ill. ; 28 cm.

Cottonwoods are poplar trees that are adapted to riparian zones that are naturally occasionally flooded. Like all Salicaceae, cottonwoods are dioecious and prior studies have indicated that males are more drought-tolerant than females and found more often in poorer, drier sites. We investigated sex differentiation of cottonwoods in response to the opposite water-stress, flood, and predicted that the increased water-stress tolerance of males in drought would also apply to flood-stress. Twenty-one clones of male and female narrowleaf cottonwoods (Populus angustifolia) were grown in a greenhouse along with three female clones of the hybrid native lanceleaf cottonwood (P. x acuminata) for comparison. It was anticipated that the hybrids would show the fastest growth owing to the genetic contribution from the P. deltoides parent and its rapid intrinsic growth rate. Flood reduced heights and the numbers and sizes of leaves and roots, and consequently dry weights, abaxial stomatal conductance and leaf chlorophyll. Inundation increased carbon:nitrogen, but did not alter stomatal density, leaf water potential, or δ13C. The hybrid saplings were much larger than the narrowleaf saplings but their proportional growth reduction with flooding was greater than in the female P. angustifolia, suggesting higher flood-tolerance of the narrowleaf cottonwood. P. angustifolia sexes performed similarly under reference conditions but the males were proportionally more inhibited by flood, suggesting sex differentiation in flood-tolerance. This study indicates that riparian cottonwoods are reasonably flood-tolerant but slight differences exist between the sexes and to a greater extent, across taxa. While prior studies have indicated males are apparently more tolerant of drought, females are probably more flood-tolerant. / xiii, 117 leaves : ill. ; 29 cm

For over 100 years, cancer radiation therapy has provided patients with increased survival rates. Despite this success, radiation exposure poses a threat to the progeny of exposed parents. It causes transgenerational genome instability that is linked to transgenerational carcinogenesis. The exact mechanisms in which this instability occurs have yet to be discovered. Current evidence points to their epigenetic nature, specifically changes in DNA methylation. Using mouse and rat models, this thesis investigated the transgenerational effects of radiation in the offspring from parents who received whole body or localized exposure to ionizing radiation (IR). Both types of exposure resulted in significant global DNA hypomethylation in the somatic tissues of the progeny. These changes were paralleled by the significantly decreased levels of methyltransferases and methyl-CpG-binding protein. In summary, our results suggest that both localized and whole body parental exposures to IR result in transgenerational epigenetic instability within the unexposed offspring. / vii, 106 leaves : ill. ; 29 cm.

Bystander effects are traditionally known as a phenomenon whereby unexposed cells exhibit the molecular symptoms of stress exposure when adjacent or nearby cells are traversed by ionizing radiation. However, the realm of bystander effects can be expanded to include any systemic changes to cellular homeostasis in response to a number of biotic or abiotic stresses, in any molecular system. This thesis encompasses three independent experiments looking at bystander and bystander-like responses in both plant and animal models. In plants, an investigation into the regulation of small RNAs has given us some insights into the regulation of the plant hormone auxin in both stress-treated and systemic (bystander) leaves. Another plant model shows that a bystander-like plant-plant signal can be induced upon ionizing radiation to increase the genome instability of neighbouring unexposed (bystander) plants. In animals, it is shown that the microRNAome is largely affected in the bystander cells in a three-dimensional human tissue model. In silico and bioinfomatic analysis of this data provide us with clues as to the nature of bystander signalling in this human ‘in vivo’ model. / xiv, 141 p. : ill. ; 29 cm.

Asymmetric localization of PIN proteins controls directionality of auxin transport and many aspects of plant development. The Arabidopsis mutant, unhinged-1 (unh-1), has defects to leaf veins and other root and shoot phenotypes. I identify UNH as the Arabidopsis VPS51 homologue, a member of the Arabidopsis GARP complex, and show that UNH interacts with VPS52, another member of the complex. I also show that UNH co-localizes with SYP61, a trans Golgi network marker. The GARP complex in yeast and metazoans retrieves vacuolar sorting receptors to the TGN and is important in sorting proteins for lysosomal degradation. PIN1 expression in the margin of unh-1 leaves is expanded and the unh leaf phenotype is suppressed by pin1 mutation, supporting the idea that the phenotype results from expanded PIN expression. My results suggest the UNH is important to restrict expression of PIN1 within the margin, likely by targeting PIN1 to the lytic vacuole. / xv, 100 leaves : ill. ; 29 cm

No description available.

No description available.