Most plant toxicology tests developed in support of environmental laws use a single stress applied to an individual plant. While tests using individual species or stresses require fewer resources and are easier to interpret, they are under increasing criticism for being unrealistic and missing important ecological interactions. The objective of this research was to increase our understanding of how plants and plant communities respond to a variety of stressors. Model plant communities of spring wheat (Triticum aestivum) and wild oats (Avena fatua) were planted at three densities and five proportions in the field. Puccinia recondita, the causal agent of wheat leaf rust, was inoculated on half of the plots. Disease severity was estimated as percent of wheat flag leaves covered by rust lesions. Plants were harvested at maturity and measured. Seeding density rarely had a significant influence on rust severity, probably because tiller density differed little as a result of compensation due to increased tillering at low seeding densities. In contrast, increasing the proportion of wheat in mixtures with wild oats consistently increased wheat leaf rust severity. There was no evidence to suggest that wild oats acted as a barrier to inoculum movement. Wild oats' effect on wheat leaf rust was probably through its competitive reduction of wheat tiller density. Both wheat and wild oats seed weight decreased as the proportion of wild oats increased in mixtures. This indicates that intraspecific competition was stronger in wild oats than was intraspecific competition with wheat in these mixtures. Wild oats generally did not respond to the presence of leaf rust on wheat, while wheat was negatively impacted. Thus, there was little competitive advantage to wild oats when its competitor (wheat) was diseased. A small subset of the field treatments was treated with ozone, because of the limited space available in the open-top ozone exposure chambers. Wheat height and aboveground biomass generally decreased with ozone exposure and with increasing disease severity in both years, while total grain weight decreased significantly only with disease and only in one year. There was no interaction between ozone and disease, regardless of cultivar, density, or plant response variable measured. There was little evidence that ozone exposure affected the severity of wheat leaf rust. In general, there seemed to be a lack of interactions among the different stressors and the results varied considerably depending on year and wheat cultivar. / Graduation date: 1998

Various aspects of the energetic response to handling stress in juvenile coho salmon (Oncorhynchus kisutch) were examined. Fish were subjected to four different handling stressors in a Blazka-style respirometer. Stressed fish had rates of oxygen consumption that were higher than controls. The magnitude of the increase ranged from 139 to 198% of the control value, and appeared roughly related to the severity of the stressor. The post-stress increase in oxygen consumption also appeared to vary seasonally, with less of a stress effect on respiration observed in the spring as compared to the fall. Elevation in oxygen consumption following stress was largely eliminated within 1 h post-stress, but metabolic rate may have remained slightly elevated for an additional 2 h. Plasma cortisol and lactate titers also increased significantly following handling stressors. Oxygen consumption was positively correlated with both plasma cortisol and lactate after a moderate stressor, but no correlation was found after more severe stressors. Whole body lactate concentration was significantly elevated following stress, reaching levels almost 500% higher than controls. By 5 h post-stress whole body lactate had returned to control levels. The mechanism of excess post-stress oxygen consumption remains unclear. Fish given exogenous cortisol did not experience an increase in oxygen consumption, so it is unlikely that cortisol alone has a major effect on metabolic rate. Similarities between the energetic responses to both stress and exercise suggest that the results of exercise physiology may provide a basis for understanding the energetic response to stress. / Graduation date: 1993

Thesis (M. App. Sc.)--University of Queensland, 2001. / Includes bibliographical references.

No description available.

Sorghum (Sorghum bicolor L., Moench) and pearl millet (Pennisetum americanum L., Leeke) were intercropped under soil moisture non-stress and stress at Marana, Arizona during summer 1987. Effects of soil moisture stress and inter-row competition between sorghum and pearl millet on grain yield, 50% bloom, plant height, head length, head exsertion, 1000 grain weight, and number of effective tillers were evaluated. Interplot competition significantly reduced grain yield and head exsertion of peal millet. In sorghum, only plant height was significantly different due to competition. Agronomic characters were significantly different due to the effect of soil moisture stress except head length in pearl millet and head length, 1000 seed weight, and number of effective tillers in sorghum. Sorghum growing in a neighbor plot greatly suppressed millet grain yield under soil moisture stress. Relative yield total of the cereals under intercrop was less than unity under soil moisture stress.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

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.

Jiang, Tiantian. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 61-75). / Abstracts in English and Chinese. / Thesis/Assessment Committee --- p.ii / Statement --- p.iii / Abstract --- p.iv / 摘要 --- p.v / Acknowledgements --- p.vi / List of Figures and Tables --- p.vii / Chapter Part 1 --- Introduction --- p.-0- / Chapter 1.1 --- Brassinosteriods (BRs) and BR signaling --- p.-0- / Chapter 1.1.1 --- Discovery of BRs --- p.-2- / Chapter 1.1.2 --- Functions of BRs --- p.-4- / Chapter 1.1.3 --- BR signaling pathway --- p.-6- / Chapter 1.2 --- Nitrogen (N) and N responses --- p.-10- / Chapter 1.2.1 --- Hormones involved in plant N responses --- p.-11- / Chapter 1.3 --- Anthocyanin and anthocyanin synthesis --- p.-13- / Chapter 1.3.1 --- Anthocyanin structures --- p.-13- / Chapter 1.3.2 --- Functions of anthocyanins --- p.-14- / Chapter 1.3.3 --- Biosynthesis of anthocyanins --- p.-14- / Chapter 1.3.4 --- Regulations of anthocyanin biosynthesis --- p.-15- / Chapter 1.4 --- Hormones and plant nutrient stresses --- p.-19- / Chapter Part 2 --- Materials and Methods --- p.-20- / Chapter 2.1 --- Plant materials and growth conditions --- p.-20- / Chapter 2.2 --- Measurement of anthocyanin content --- p.-21- / Chapter 2.3 --- Yeast two-hybrid (Y2H) assay --- p.-22- / Chapter 2.4 --- Bimolecular fluorescence complementation (BiFC) assays --- p.-23- / Chapter 2.5 --- Quantitative real-time PCR --- p.-25- / Chapter 2.6 --- Electrophoretic mobility shift assay (EMSA) and competition assay --- p.-26- / Chapter 2.7 --- Histochemical staining of GUS activity --- p.-28- / Chapter Part 3 --- Results --- p.-29- / Chapter 3.1 --- 24-epibrassinolide (24-eBR) increases plant tolerance to N-starvation in Arabidopsis - --- p.-29- / Chapter 3.2 --- BR treatment enhances anthocyanin accumulation under N deprivation conditions --- p.-31- / Chapter 3.3 --- BZR1 interacts with PAP1 in vitro and in vivo --- p.-35- / Chapter 3.4 --- BR and BZR1 promote the expression of the 'late' anthocyanin biosynthetic genes during N deprivation - --- p.-39- / Chapter 3.5 --- BZR1 binds to the promoter of DFR --- p.-43- / Chapter 3.6 --- BR-enhanced anthocyanin accumulation is specific to N-deprivation --- p.-46- / Chapter 3.7 --- BZR1 differently regulates PAP1 and PAP2 --- p.-48- / Chapter 3.8 --- Endogenous GL3 is required for BR-enhanced anthocyanin biosynthesis --- p.-52- / Chapter 3.9 --- N status affects the expression of BR biosynthetic gene CPD --- p.-52- / Chapter Part 4 --- Discussion --- p.-54- / Chapter 4.1 --- BRs confer plant tolerance to low-N stress and the tolerance is mediated by BR enhancement of low-N-induced anthocyanin biosynthesis --- p.-54- / Chapter 4.2 --- BRs enhance anthocyanin accumulation under N starvation through BZR1-PAP1 interaction or direct control of the expression of anthocyanin biosynthetic genes --- p.-55- / Chapter 4.3 --- BRs are specifically involved in low-N induced anthocyanin production --- p.-56- / Chapter 4.4 --- Transcription factors that specifically control BR-regulated anthocyanin biosynthesis --- p.-57- / Chapter 4.5 --- DFR is an important target of BR-regulation of anthocyanin biosynthesis --- p.-58- / Chapter Part 5: --- Conculsions --- p.-59- / Chapter Part 6: --- References --- p.-61-

The development of assays for stress in marine fishes is vital for studying the impacts of bycatch in fisheries and for determining the health of fish being cultured or used in research. This research developed behavioral and physiological assays for stress in juvenile sablefish, Anoplopoma fimbria, a species that comprises a valuable North Pacific fishery and is often a substantial part of incidental discard. The effects of conditions, intrinsic or extrinsic to the fish, on the variability of the stress response were also investigated. A moderate stress of 15 minutes in air was used to elicit an acute stress response. Behavioral responses and physiological values were evaluated at 1, 5, and 24 hours after the 15 minute air stress, and were compared with control fish that received only a minimal air stress. In the first series of experiments, behavioral patterns and changes in behavior over time of stressed and control fish were determined, and the protocols and time course for measuring behavioral effects of stress were established. In the second series of experiments, physiological assays were added to the behavioral protocols developed during the first series of experiments. The behavioral assays included activity levels, swimming speed at capture, and appetitive behavioral patterns in response to a chemical food stimulus (squid extract), and to a visual food stimulus (squid without odor). These behaviors are ecologically relevant in terms of performance and survival. All of these behaviors were sensitive to stress. In general, behavioral responses were depressed by stress at 1 hour, followed by recovery to control levels by 5 hours. However, the intensity of behavioral responses was affected by feeding history (1 or 5 days of food deprivation) and group influence (recovering alone or in visual contact with 3 conspecifics), which therefore affected the ability of the behavioral responses to assess stress. The behavioral assays were less capable of detecting differences between stressed and control fish when the responses of control fish were depressed as a consequence ofbeing fed the day before. Visual contact with conspecifics facilitated recovery of activity in stressed fish, but therefore also resulted in apparent activity responses to chemical food stimulus that were more likely attributable to activity increases of conspecifics than to appetitive behavior. The focus of attention of isolated fish on activity of conspecifics often interfered with visual detection of food. The physiological assays included plasma concentrations of cortisol, glucose, and lactate, all of which proved to be sensitive measures of stress in sablefish. These parameters were elevated by stress at 1 hour, followed by a decreasing trend to 5 and 24 hours. The physiological assays were affected by feeding history, and an effect of group influence was also indicated. Cortisol and lactate levels in stressed fish fed the day before recovered faster than for stressed fish that were deprived of food for 5 days. Glucose levels in stressed fish fed the day before were not elevated above controls. These results suggested an alleviating effect of feeding on the biochemical stress response. At 5 hours, cortisol and glucose were elevated above baseline levels in both solitary stressed fish and in stressed fish influenced by a group, but also for controls influenced by a group, suggesting an exacerbating effect of isolated fish being in visual contact with groups. There were critical cortisol, glucose and lactate thresholds (180 ng/ml, 140 mg/dl, and 175 mg/dl, respectively) above which no appetitive behavioral responses occurred. These clear demarcation levels are extremely valuable for linking behavioral and physiological responses. These results indicate that behavioral and physiological assays are sensitive indicators of stress in sablefish, although the magnitude, time courses, and correlation of responses may be affected by factors intrinsic and extrinsic to the fish that may vary before and during recovery. There was a correspondence between behavioral and physiological indications of stress shortly after the stressor had been removed and levels of stress were still severe. However, there was a temporal discrepancy after partial recovery had occurred, at which time recovery of physiological norms had not yet been established although behavioral responses had recovered. While behavioral patterns may readjust quickly, the persistence of an energetic load during recovery from stress, as indicated by continued physiological perturbations, may compromise ability to respond to additional stressors. / Graduation date: 2001

Graduation date: 1997