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Although the effect of working memory (WM) load on the magnitude of distractor interference has been studied extensively, a common characteristic in prior research is that the target and distractors belong to different objects. The present experiments investigate the effect of WM load on distractor interference when the relevant and irrelevant information is part of the same object. In two experiments, participants saw stimulus displays that consisted of a memory set followed by a Stroop color stimulus. The tasks were to respond to the color of the stimulus first and then to a memory probe. The principal manipulations were the relationship between the color and meaning of the Stroop stimulus (neutral vs. incongruent) and the level of WM load (high vs. low). The results show that WM load had little effect on the magnitude of Stroop interference. These results were consistent with previous research which shows that WM load plays a limited role in the efficiency of selective attention when the extent of attentional focus was held constant across different WM load conditions. They also emphasize the importance of stimulus structure in understanding selective attention in general, and distractor processing in particular.

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This dissertation details the effect of underpotentially deposited (UPD) Pb on the surface enhanced Raman scattering (SERS) ability of roughened polycrystalline Ag electrodes. The deposition of monolayer and submonolayer amounts of Pb results in a quenching of the SERS response for pyridine and Cl⁻ adsorbed at Ag electrodes. Various factors which may contribute to the loss of SERS intensity are investigated. The most significant factors include changes in surface roughness features brought about by Pb UPD, changes in surface electronic properties of Pb-modified Ag and changes in a chemical contribution to surface enhancement. Possible changes in surface roughness properties of the Ag electrode due to Pb deposition are examined using scanning electron microscopy (SEM) and SERS reversibility studies. SEMs of roughened Ag electrodes before and after Pb monolayer deposition show no significant change in the morphology of the larger roughness features. However, the deposition and stripping of 60 - 70% of a Pb monolayer results in a loss of ca. 50% of the original SERS intensity for both adsorbate bands. This irreversible loss of SERS intensity is attributed to the destruction of atomic scale roughness (ASR). These results suggest that ca. 50% of the observed SERS response arises from a mechanism involving ASR. In addition, the destruction of ASR is shown to be largely responsible for the quenching of SERS at higher Pb coverages. The morphology of the SERS quenching profiles at lower Pb coverages for pyridine and Cl⁻ varies as a function of excitation wavelength. Experimental quenching profiles are compared with theoretical quenching profiles based on an electromagnetic contribution to SERS. Theoretical quenching profiles are calculated using a model for electromagnetic enhancement at a overlayer-covered ellipsoids proposed by Murray. The experimental results for both adsorbates are in agreement with the theoretical predictions for laser excitation in the blue. Experimental results in the green and red wavelength regions are best explained in terms of photoassisted charge-transfer mechanisms for surface enhancement.

In two greenhouse experiments, the response of maize plants (Zea mays L.) to macro and micronutrient fertilizers was studied. The first experiment was conducted in Cairo, Egypt in which maize plants were grown on saline soils with ECₑ values of 1.42, 6.12 and 12.1 dSm⁻¹ and fertilized with N, P, K alone and in combination. It was found that maize plants produced the highest dry matter when NP fertilizers were added in the Ca-form compared to the other fertilizer treatments, and this positive response decreased with increasing salinity level. Also, it was found that application of P and K fertilizers either alone or together as PK augmented the adverse effect of salinity on dry matter and nutrients uptake. In addition, the concentration and uptake of Na⁺ ions in the shoot tissues decreased with increasing salinity level up to ECₑ 12 dSm⁻¹. This could be due to Na+ exclusion or accumulation in root tissues. However, application of N and P fertilizers tended to decrease plant content of micronutrients, particularly Fe as well as Zn at high salt levels. The second experiment was conducted in a University of Arizona campus greenhouse. A Pima soil from the Marana area was artificially salinized with NaCl, Na₂SO₄, CaCl₂, and Mg₂SO₄ salts almost to the salinity levels mentioned above. Maize plants were grown and fertilized with NP fertilizer as a basic dressing. Chelated forms of Zn, Fe, and Mn were added with two different methods; soil and foliar spray application. Two pH values of spray nutrient solutions were used; pH 6 and pH 8. Data obtained showed increased dry matter and nutrient uptake in response to spraying maize plants with Zn + Fe or Zn+ Fe + Mn at pH value of 8 at the medium salt level relative to the other treatments. However, maize plants also showed high dry matter and nutrient uptake in response to Zn + Fe + Mn soil application at the high salt level, although Zn-pH 8 gave unexpectedly high dry matter production. It seems probable that this high dry matter obtained could be due to the effect of high pH spray treatment on increasing the activity of some enzymes, e.g. PEP-carboxylase and/or ribulose 1,5 diphosphate carboxylase, as well as the increase in rate of translocating the photosynthates and this effect was augmented by the nutrient(s) applied. Also, it was found that Na uptake decreased while total chlorophyll and chlorophyll a content increased with increasing salinity level. The increase in the chlorophyll content could be due to either Na exclusion by the plants and/or the decrease plant growth due high salts.

Taurine (2-aminoethane sulfonic acid) is one of the most abundant inhibitory amino acids in the mammalian central nervous system (CNS). Substantial evidence exists to suggest that this amino acid is a physiological modulator of neuronal excitability. Taurine is also a potent anticonvulsant in a variety of animal epilepsies and in certain human epileptics. The mechanisms of these neuromodulatory and anticonvulsant actions of taurine are not known. I have investigated a proposed relationship between altered amino acid metabolism, seizure-susceptibility and the anticonvulsant action of taurine. The findings of the work presented in this dissertation indicate that in the genetically seizure-susceptible rat there are alterations in the subcellular concentration and transport of taurine. Furthermore, the data presented here indicate that these alterations in the CNS handling of taurine are not a consequence of seizure activity but rather may be contributing to the seizure-susceptibility. This supports the hypothesis that taurine is a physiological modulator of neuronal excitability and that defects in this neuromodulatory process may contribute to seizure-susceptibility. The action of taurine was found to not be mediated by a redistribution of glutamate in the brain but instead may be by increasing the conversion of glutamate to GABA.

Young barley seedlings (Hordeum vulgare L.) were stressed using nutrient solutions containing NaCl or polyethyleneglycol (PEG) and measurements were made of leaf growth, water status, proline soluble sugar contents of growing (basal) and non-growing (blade) tissues. Leaf growth ceased within seconds following exposure of seedlings to osmotic solutions with water potential values (ψ) = -3 to -11 bars but growth resumed after a lag period. Latent periods were increased and new growth rates were decreased as ψ of nutrient solutions were lowered. Growth ceased before detectable changes occurred in tissue water status but leaf basal tissues began to adjust osmotically, and reductions of 1 to 2 bars in both ψ and osmotic potential (π) usually occurred for the first 1 to 2 hours with lower reduction rates thereafter. After 1 to 3 days exposure of seedlings to solutions with different ψ, cumulative leaf elongation was reduced as the ψ of the root medium was lowered. Reductions in ψ and π of tissues in leaf basal regions paralleled growth reductions, but turgor (P) was largely unaffected by stress. In contrast, ψ, π and P of leaf blades were usually changed little regardless of the degree and duration of stress, and blade ψ were always higher than ψ of basally located cells. It is hypothesized that blades have high ψ and are generally unresponsive to stress because water in most of the mesophyll cells in this area does not exchange readily with water present in the transpiration stream. Measurements of proline contents in different sections of leaf following water stress, showed that in living tissues proline levels are dynamically related to water status of the tissue. In the basal regions where reductions in ψ and π occurred rapidly, proline levels were elevated quickly, whereas, accumulation of proline in mid-blade tissues occurred slowly and in lower concentrations. The combined data of many experiments showed a strong correlation between proline levels and tissue ψ (r = 0.93) and π (r = 0.85). Increase in total soluble sugars (TSS) and ion concentrations, contributed significantly to the stress-induced osmotic adjustment observed in the growing tissue.

Glycoproteins play a key role in cellular growth and differentiation. In order to study glycoprotein biosynthesis and processing, we have chosen the murine Immunoglobulin M (IgM) system as a model. Our system utilizes hybridoma, lymphoma and plasmacytoma cell lines which synthesize intracellular, membrane-bound and secreted IgM. Each type of IgM is synthesized during a specific phase of B-cell differentiation. We have examined the kinetics of IgM synthesis and processing in cells at each developmental stage. The rate of synthesis of membrane-bound and soluble IgM are different. Characteristic rates for membrane versus soluble IgM may be dependent on the extent of oligosaccharide processing. The membrane-bound IgM contains more high-mannose oligosaccharide than does the secreted product. In addition, we have begun to determine how protein structural requirements can affect final glycosylation patterns on the glycoprotein. Two cell lines were studied which secreted smaller than normal IgM heavy chains in tissue culture. One cell line studied (208) contains one glycosylation site, while another (562) retains three sites on the molecule synthesized in tissue culture. Studies performed on these cell lines in tissue culture indicate greater processing of the oligosaccharides on these mutant IgM molecules when compared to the parental cell line (PC700). Studies on the 208 IgM molecules synthesized in the mouse and purified from ascites fluid confirm these results. Upon injection into the mouse, the 562 cell line reverts to produce protein and carbohydrate structures characteristic of the parental cell line. Studies on the 562 protein purified from ascites fluid illustrate the need for more precisely defined cell lines and genetic engineering for the study of altered protein structures.