Factors affecting the survival of over-wintering tree roots during waterlogging were investigated. Die-back of roots covered by high Winter water tables results in shallow rooted trees susceptible to wind-throw. Such is the scale of the problem in Britain, this research is considered to be of practical relevance. Sitka spruce (Picea sitchensis (Bong.) Carr.) and Lodgepole pine (Pinus contorta Douglas ex Loudon) were chosen, being the most predominant species planted and showing differing susceptibility to flooding. Sitka spruce is considered flood-intolerant (Crawford 1982) and Lodgepole pine highly-tolerant (Minore 1968). In both species, waterlogging the whole root system for 3 months severely reduced the carbohydrate content of the distal 15cm root, reflecting almost total depletion of starch reserve and varying degrees of glucose depletion. In Sitka spruce, depletion depended on the date of flood-initiation, being most severe after flooding from October when root respiration rate was higher, rather than November as the roots became dormant. Flooding injury was reflected in decreased tri-phenyl tetrazolium chloride reduction and loss of respiratory capacity. Greater loss of aerobic (as compared to anaerobic) respiration capacity after flooding suggested damage to the aerobic pathway, either directly through anoxia or indirectly due to depletion of sugars important in cell maintenance. Injury appeared to be greater when respiratory activity at flood-initiation was high. Aeration from stem lenticels ameliorated flood-injury and carbohydrate depletion in Lodgepole pine, although the roots appeared to have no metabolic adaptation to anoxia. Increased soil temperature during Winter flooding increased carbohydrate depletion in the distal root and reduced viability relative to seedlings flooded at ambient temperature. Carbohydrate depletion during cold storage and its effect on survival of soil waterlogging at out-planting was determined in Sitka spruce. Cold storage leads to increased root growth and slightly superior flood-tolerance when compared to nursery over-wintered seedlings, presumably due to the more dormant state of stored seedlings.

No description available.

A recently discovered peptide hormone, pituitary adenylate cyclase-activating polypeptide (PACAP) regulates several endocrine systems affecting essential physiological processes such as metabolism, growth, reproduction, and the stress response. PACAP acts as a hypophysiotropic factor, is a potent secretogogue of insulin, regulates production and release of catecholamines from the adrenal medulla and acts as a neuromodulator in the sympathetic and parasympathetic nervous system. The primary structure of PACAP has been highly conserved during the evolution of chordates suggesting it plays an important physiological role. The objective of my thesis was to identify PACAP’s primary physiological function and to determine if it is essential for survival by generating a mouse line deficient in PACAP through targeted disruption of the PACAP gene locus. Postnatal PACAP expression was examined to determine sites of peripheral PACAP production. In addition, several splice variants of the PACAP gene with alternate 5’untranslated regions were identified suggesting a complex system for regulating expression of the mouse PACAP gene. A targeting vector that allows tissue specific or developmental stage specific knockout of the PACAP gene was constructed in the event that PACAP gene deletion resulted in embryonic lethality. PACAP null mice were generated from homologously recombined embryonic stem cells. Initial characterization of the PACAP null mice determined that in the absence of PACAP, mice died within the first two postnatal weeks with abnormal lipid metabolism. Lipid accumulation was present in liver, heart and skeletal muscle and serum lipids were high. Mitochondrial dysfunction in the liver was not the cause of the lipid accumulation, as P-oxidative function was normal. I conclude that PACAP null mice are unable to regulate lipid release from white adipose tissue stores, resulting in a flood of lipids to non-adipose tissues. The abnormal distribution of lipids observed in the PACAP null mice is characteristic of diabetes type 2, yet classical insulin resistance is not observed. Thus, elevated insulin levels were accompanied by low blood glucose levels and the response to a glucose challenge was normal. The uncontrolled release of free fatty acids may result if glucose that is taken up by cells can not be utilized and an alternate energy source is required or if white adipocytes only are insulin resistant. The PACAP null mice were temperature sensitive, in that when raised at 21“C they exhibited metabolic dysfunction and died by two weeks of age. At 24°C most (85%) of the mice survived to adulthood with no obvious signs of metabolic dysfunction. We have determined that the inability of the PACAP null pups to thermoregulate normally when exposed to a lower environmental temperature may be associated with decreased norepinephrine levels to the brown adipose tissue. PACAP may be important for the production and release of catecholamines in the adrenal gland or within the sympathetic nervous system in times of prolonged stress. A mechanistic connection between the lipid abnormalities and the temperature sensitivity in the PACAP null pups has yet to be made. Catecholamines affect a wide range of tissues and the problems associated with insulin regulation within the PACAP null mice may be due to the imbalance in catecholamine production. As one of two main stress response systems, the sympathetic nervous system elicits a vital coping mechanism in times of stress and PACAP’s ability to regulate this system may explain why the primary structure of PACAP has remained so highly conserved. PACAP is a wide acting hormone and therefore the metabolic problems seen in the PACAP null mice may result from altered regulation of several endocrine systems at once. Targeted disruption of the PACAP gene in mouse has revealed a role for PACAP in the regulation of lipid metabolism and in the sympathetic control of thermoregulation. / Graduate

The incorporation of Si1-xGex alloy heterostructures into conventional Si processes has been proposed as a means of improving the operating frequency and overall performance of Si field effect transistors. One parameter expected to benefit from this approach is the hole mobility, which would have important implications for high speed CMOS applications. Measured values of the hole mobility, however, have failed to live up to early expectations, and much ongoing research is directed at understanding whether this is an intrinsic limitation (e.g. due to alloy disorder scattering), or due to imperfections arising in the growth and fabrication process. In this thesis, a detailed theoretical study is presented of the hole mobility in single sub-band Si1-xGex heterostructures.

No description available.

Plants regulate many physiological processes in response to adverse environmental stresses. This study focused on the seed germination and seedling establishment stage and investigated the molecular signaling events when abiotic stresses, such as osmotic, water and temperature, were applied. Seeds of Arabidopsis, mutants or wild type, were used to identify the signaling components. Cold-pretreatment (stratification) is widely used to break seed dormancy and improve germination rate. Stratification at 4. significantly broke the seed dormancy of Arabidopsis in wild-type, cyp707a2, sleepy1 and sleepy1/cyp707a2, but not in ga3ox1. Stratification and exogenous ABA treatment strongly enhanced the expression and the activity of a-amylase in the freshly harvested seeds among the wild-type and those mutants, which have relatively high ABA content. Similarly, the expression of RGL2 and ABI5 were also substantially suppressed by stratification. These results suggest that stratification firstly leads to GA biosynthesis and unlocks the inhibition of RGL2 on the expression of a-amylase. Stratification also relieves the inhibition of ABA on the germination process but the inhibition of ABA on seedling development is not affected. We have isolated an Arabidopsis mutant, dsptp1, which is hyposensitive to osmotic stress during seed germination and seedling establishment, indicated by exhibiting higher seed germination rate, lower inhibition in root elongation under osmotic stress, and more tolerance to drought compared with the wild type (Col0) plants. Osmotic stress and drought enhanced AtDsPTP1 expression in seed coats, the bases of rosette leaves and roots. Compared with the wild type, the dsptp1 mutant increased proline accumulation, reduced MDA content and ion leakage, and enhanced antioxidant enzyme activity under osmotic stress. AtDsPTP1 regulated the transcript levels of various dehydration responsive genes, ABA biosynthesis and metabolic enzyme gene under osmotic stress, resulting in reduced accumulation of ABA in dsptp1 mutant plants than wild type in response to osmotic stress. AtDsPTP1 also mediated the ABA signaling pathway under osmotic stress by suppressing the expression of ABI1 and enhancing the expression of the positive regulators ABI3 and ABI5 in ABA signaling. These data suggest that AtDsPTP1 positively regulates ABA accumulation and signaling during seed germination and seedling establishment in Arabidopsis under osmotic stress. To further investigate the regulation mechanism of DsPTP1 in osmotic stress and drought signaling, we analyzed the water holding capacity between wild type and dsptp1 mutant. The dsptp1 mutant exhibited enhanced water holding capacity compared to wild type under osmotic stress resulting from reduced water loss and increased relative water content, which shall contribute the osmotic and drought tolerance. To identify the signaling components, we investigated the activity of MAPKs under osmotic and drought stress and found that the DsPTP1 differentially regulates the activities of MAPK6 and a p38 MAPK, which is inferred as MAPK12 according to its molecular weight in Arabidopsis under osmotic and salt stress. However, there is no direct interaction between DsPTP1 and 20 MAPKs indicated by the results of the of specific interaction test. These results suggest that the differential regulation of MAPK6 and MAPK12 by DsPTP1 is indirect. In addition, we screened the interaction proteins of DsPTP1 under abiotic stress. Seventeen positive clones were acquired from the sequencing results. More work need to be done to confirmed the positive interactions and the signaling cascades. In summary, seed germination and seedling growth are closely regulated by environmental cues. This should be the result of evolutionary selection since successful new growth from the seed embryo depends on the sensitive perception of environmental conditions and effective regulation of many physiological processes that are involved. We have demonstrated that plant hormones, especially ABA, play central regulative roles during such regulations. Many other signaling components, such as protein kinases and phosphatases, are also involved. Identifying the detailed signaling pathways should be the focus of further research.

Predation is one of the basic mechanisms of population growth control. Using a mathematical model, we explore the impact of predation in a prey population structured into two age classes, juveniles and adults, assuming a generalist predator. The specific predation pressure is represented for each of the two age classes by either no predation or Holling type II or Holling type III functional responses in various combinations. We distinguish two scenarios. In the first one, we seek for potential Allee effects or multiple stable states in the prey population, and explore the conditions at which the predation is more effective on juveniles than adults and vice versa. The most interesting finding here is the occurrence of bistability, or a predator-pit-like behaviour, when predators consume only juvenile prey, via a Holling type II functional response, an observation not described previously. In case only adults or both age classes are killed by predators exhibiting a type II functional response, the Allee effect occurs frequently. Multiple positive stable states are commonly observed if one of the age classes is exploited via a type III functional response. In the second scenario, we assume that the prey feeds on a resource and that the resource together with the prey undergoes outbreak dynamics, and we examine possibilities of control of such outbreaks using age-specific predation. Predation was proven to be able to suppress the prey population successfully. In some cases, an oscillation-free resource-prey-predator coexistence was detected.

No description available.

No description available.

M.Sc. (Zoology) / Please refer to full text to view abstract