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Item Modulation of enteric neural activity and its influence on brain function and behaviour : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Manawatu, New Zealand(Massey University, 2024) Parkar, Nabil JamilThe gut-brain axis (GBA) facilitates bidirectional communication between the enteric nervous system (ENS) of the gastrointestinal (GI) tract and the central nervous system (CNS). The location of the ENS along the GI tract enables it to serve as a relay station along the GBA. A key regulator of the GBA is the diverse population of microbial communities inhabiting the GI tract, known as the gut microbiota. Due to its proximity to the ENS, gut microbes significantly influence ENS functions, such as gut motility, and also impact brain function and behavior. A diverse and healthy gut microbiota is crucial for normal GI physiology and mental health. Understanding the physiological host factors that influence and control the gut microbiota is essential for grasping its variability in health and states of dysbiosis. Movement of luminal content along the GI tract, primarily driven by rhythmic contractions of GI smooth muscles, affects gut microbiota growth and population dynamics. This research involved a series of ex vivo and behavioral experiments in rodents to better understand ENS control of gut motility and its impact on anxiety-related behavior. Initially, the effect of a specific pharmacological agent on colonic motility patterns was evaluated using ex vivo techniques. Observations from this study provided fundamental insights into ENS function and its regulation of colonic motility, laying the foundation for further research on how altered colonic motility via ENS manipulation affects gut microbiota composition and anxiety-related behavior. The second study investigated whether pharmacological modulation of the ENS, resulting in reduced colonic motility, affected the gut microbiota. Results revealed significant changes in gut microbiota composition, including decreased abundance of certain bacterial species and alterations in community structure. The final study aimed to understand the relationship between ENS manipulation, brain function, and behavior by inducing changes in gut motility. Anxiety-related behavior was assessed in rats using open field and elevated plus maze tests, focusing on those exposed to a pharmacological agent that slowed colonic motility via specific ENS receptors. To determine if behavior changes involved specific neural pathways, brain gene expression in key regions was studied. Additionally, the potential relationship between gut microbiota and brain function was explored, assessing if ENS modulation and behavioral effects correlated with changes in gene expression and microbiota profiles in the large intestine. Findings indicated that ENS modulation altered anxiety-related behavior in a sex-specific manner, with female rats showing increased anxiety and corresponding changes in brain and proximal colon gene expression compared to males. This study highlighted sexually dimorphic gut-brain communication and suggested multiple genes/pathways may influence anxiety-related behavior in females. This comprehensive exploration through three interrelated studies has provided new insights into the regional specificity of ENS receptors in regulating colonic motility, the impact of slowed gut transit on microbiota composition, and the physiological consequences of ENS modulation on brain function and anxiety, with associated sex differences. A combined analysis of these findings discusses their implications for understanding the ENS as a key player in regulating the gut-brain axis.Item Characterising the responses of farm mammals to a thoracic squeeze and the relationship to tonic immobility : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Holdsworth, Sophia EllenApplying compression to the thorax of newborn farm mammals causes immobility accompanied by reduced responsiveness. Traditionally, this response was proposed to arise in neonatal foals due to the ‘thoracic squeeze’ mimicking the compression occurring during birth. Recent findings regarding the responses to the squeeze suggest a link to Tonic Immobility (TI). TI is a temporary and reversible state of reduced responsiveness and immobility with characteristic physiological changes. It is elicited by the collective actions of handling and sustained physical contact with additional pressure (restraint) and may be facilitated by inversion. TI is reported in young and adult animals of numerous species. The aim of this thesis was to examine whether responses to the thoracic squeeze are consistent with TI. First, behavioural responses to a squeeze were explored in lambs, with a focus on determining whether responses persisted beyond the neonatal period. Cortisol responses of healthy neonatal piglets to the squeeze were then investigated to explore similarities in Hypothalamic-Pituitary-Adrenal responses between the squeeze and TI. The final study examined electroencephalographic (EEG) responses of healthy neonatal piglets to a thoracic squeeze under light anaesthesia, to determine whether the squeeze causes changes in brain activity or exerts anti-nociceptive effects such as those reported during TI. The results demonstrated that responses to a thoracic squeeze persist beyond the neonatal period in lambs, and responses are generalised across multiple mammalian species. Furthermore, cortisol responses of piglets to a thoracic squeeze followed a similar pattern to that previously observed during TI in other species. Also consistent with some TI studies, the initial handling and restraint required to apply the squeeze appeared to induce the cortisol response in piglets. No inferences could be made about the effects of a thoracic squeeze on state of awareness in neonatal piglets, or the squeeze’s effect on nociception due to methodological limitations. Nevertheless, the results of this research support the hypothesis that the thoracic squeeze may be classified as a stimulus for inducing TI. Further work is required to characterise the effects of the squeeze on awareness and nociception and to explore the affective experiences of animals subjected to the squeeze.Item Applying welfare science to cetacean strandings : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University, Albany, New Zealand(Massey University, 2022) Boys, Rebecca MAnimal welfare science can provide critical knowledge to inform ethical wildlife management and human intervention efforts. Despite live stranding events being recognised by the International Whaling Commission as a major welfare concern for free-ranging cetaceans, little research has to date, been conducted on stranded cetacean welfare. Live cetacean stranding events offer a quintessential exemplar of wildlife management, where assessment or integration of welfare has been limited in the decision-making process. This thesis contributes new understanding of how welfare science can be applied to cetacean stranding events to inform decision-making processes. Here, the first welfare-centric data regarding live stranded cetaceans is presented. Specifically, this research presents novel contributions to science via: (1) conceptualisation of stranded cetacean welfare and survival likelihood; (2) recognition of key knowledge gaps and concerns that must be addressed to ensure optimal welfare and survival likelihood outcomes; (3) identification of potential valuable and practical indicators for assessing stranded cetacean welfare and survival likelihood; (4) evidenced feasibility of welfare indicator application to live cetacean stranding events; (5) incorporation of indicators to undertake holistic welfare assessments; (6) identification of potential welfare implications of strandings management, including efficacy of euthanasia; and (7) provision of key recommendations and requirements to ensure humane end-of-life outcomes for non-viable stranded cetaceans. This thesis documents inextricable links between animal welfare and survival likelihood of stranded cetaceans and demonstrates a clear need for integration of welfare science alongside conservation biology at live stranding events. Systematic, standardised data collection and welfare-centric assessment of stranded cetaceans can, if applied scientifically, inform intervention decisions, to ensure consistent guidance and improve strandings management to safeguard humane outcomes for affected cetaceans. Collectively, this research provides a significant contribution to the current scientific understanding of stranded cetacean welfare, by providing key knowledge required for the development of a welfare assessment framework that can support decision-making at stranding events.Item Abiotic stress effects associated with climate change on yield and tuber quality of potato cultivars in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, School of Agriculture and Environment, Massey University, Manawatu, New Zealand(Massey University, 2021) Siano, AllanThe recent weather anomalies in New Zealand, particularly the summer heatwaves of 2017/18 and 2018/19, hottest and third hottest on record, respectively, have seemingly affected potato production. The purpose of this research is to determine how abiotic stress commonly associated with climate change, e.g., drought and heat, is affecting the current potato production in New Zealand, define its effects on yield and tuber quality of commercial potato cultivars, and determine if cultivars exhibit differential susceptibility. Secondary climate data in the past 60 years (1958–2018) during the potato growing months of October to March showed an increasing trend for temperature in Ohakune (+0.53 °C), Opiki (+0.36 °C), and Hastings (+0.28 °C) as well as a decreasing trend for rainfall in Ohakune (-24.8 mm) and Hastings (-48.7 mm). The increase in temperature also increased the number of days with supra-optimal atmospheric temperatures believed to delay (>25 °C) or inhibit (>30 °C) tuber growth in Hastings by 57 days (2017/18 season) and in Opiki by 103 days (2018/19 season). Baseline data from a preliminary study during the 2017/18 growing season showed that abiotic stress associated with the extreme weather conditions apparently affected the yield and tuber quality, with cultivars showing differential susceptibility. Up to 85% unmarketable tubers were recorded among the samples collected, which was attributed to the high incidence of a wide array of tuber physiological disorders. The multi-environment trial in the 2018/19 growing season showed that abiotic stress had significant effects on the different morpho-agronomic and physiological functions of the potato crop and ultimately affected the yield and tuber quality. Abiotic stress increased the incidence of tuber physiological disorders, e.g., tuber malformation, growth cracks, and second growth, which reduced the total yield and marketable yield by up to 43.3% and 45.1%, respectively. Additionally, genotype × environment analysis showed that cultivar ‘Taurus’ is the most stable and adaptable cultivar across trial sites (wide adaptation). At the same time, cultivars ‘Hermes’ and ‘Snowden’ are tolerant to heat and drought stress (Opiki) and heat stress alone (Hastings) (specific adaptation), respectively. The glasshouse and plant growth chamber trial revealed that drought stress (DS) generally reduced the plant height, number of leaves, and canopy cover but enhanced the formation of more but smaller stomata and glandular and non-glandular trichomes. DS also encouraged the closing of the stomatal aperture potentially to reduce water loss, thereby reducing the transpiration rate (E), stomatal conductance (gS), and net photosynthesis (PN), which potentially affected the final yield. Conversely, heat stress (HS) increased the plant height, canopy cover, and number of leaves and developed more and larger stomata. HS also stimulated stomatal opening, leading to enhanced E and gS and improved PN at the vegetative stage. On the other hand, in general, the combination of drought and heat stress exacerbated the adverse effects of each abiotic stress type on the different morpho-physiological parameters. As established in the various component trials of this research, different abiotic stresses associated with climate change have a significant effect on the morpho-agronomic and physiological functions of potato crops and negatively impacts the yield and tuber quality. Breeding of new cultivars, and mass selection of existing cultivars should be conducted through multi-environment trials to identify adaptable cultivars that can be used to mitigate the effects of abiotic stresses associated with climate change on potato crops in the field and to increase the resiliency of the New Zealand potato industry.Item Stress and reproduction in domestic cats (Felis catus) as a model for endangered felids : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph.D.) Animal Science Group, Massey University, Palmerston North, New Zealand(Massey University, 2021) Andrews, ChristopherCaptive breeding programs are a vital component of the conservation strategies for felids, but these programs are often hindered by poor reproductive performance. Knowledge of reproductive biology is crucial to improving in situ and ex situ felid breeding programs. This thesis provided the first comprehensive systematic review of the literature available on the reproductive biology of the extant felid species. It was concluded that the high prevalence of teratospermia and highly variable oestrous cycles in felids contribute towards their poor reproductive performance in captivity. The captive environment has been linked to reduced ejaculate quality and ovarian quiescence in felids, but it is difficult to elucidate whether this is due to captivity-related stress (i.e., elevated glucocorticoid (GC) concentrations) or other factors associated with captivity. This thesis aimed to determine whether a simulated endocrine stress response (GC treatment) altered the testicular and ovarian function of felids using the domestic cat as a model species. While epididymal sperm motility was unaffected by GC treatments, the percentage of morphological abnormal sperm was higher in GC-treated cats than in control cats. This would likely have an adverse effect on fertility as morphologically abnormal sperm are rarely involved in the fertilisation process. Glucocorticoid treatments did not affect the ovarian response of cats in which follicular growth and development was stimulated by exogenous gonadotrophins. However, ooplasm and zona pellucida morphology was graded poorer in GC-treated animals than control animals. Whether this corresponds to a reduction in fertility is unclear as the fertilisation capabilities of oocytes were not assessed. It would be worth investigating whether GC administration affects the natural oestrous cycles of cats, as elevated GC concentrations associated with captivity have been linked to ovarian quiescence. However, this would require an accurate and minimally invasive (i.e., low stress) method for monitoring the ovarian cycles of domestic cats. Thus, this thesis investigated whether accelerometry and infrared thermography could be used to monitor the ovarian function of cats. It was found that accelerometry could be used to detect an increase in activity of cats following the induction of follicular growth with equine chorionic gonadotrophin (eCG). Infrared thermography also identified changes in perivulvar temperature (PVT) driven by follicular development and ovulation, with PVT increasing as follicular growth occurred and decreasing following ovulation. Both methods show promise; however, further investigation into the use of accelerometry and IR thermography for monitoring ovarian function is needed. In conclusion, the results of thesis indicate that GC have adverse effects on the testicular and ovarian function of domestic cats. Thus, there is an urgent need to further investigate the effects of captivity-related stress on the reproductive performance of non-domestic felids. Furthermore, this thesis assessed two promising non-invasive methods for monitoring the ovarian activity of cats, with the findings being highly applicable for the management and breeding of non-domestic felids in captivity.Item A search for biomarkers of ovine pre-partum vaginal prolapse : a thesis presented to Massey University in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Biochemistry, Massey University, New Zealand(Massey University, 2019) Brown, StuartOvine pre-partum vaginal prolapse (known as bearings in sheep) occurs within a few weeks prior to lambing and unless treated both ewes and unborn lambs will die. Rates of prolapse in New Zealand vary from 0.1 to 5% per annum, varying between season and farms and is a worldwide problem. Much research has been undertaken over many years to determine the cause of this condition but no clear etiology has emerged. In this study plasma samples were collected prior to prolapse occurring in order to determine physiological changes leading to prolapse. 650 ewes were ear tagged and blood sampled on one day prior to lambing, 28 of these ewes subsequently prolapsed. The date of occurrence and tag number of prolapsing ewes was recorded to enable a comparison of the plasma profile of prolapsing ewes and non-prolapsing ewes. An improved method for running sheep plasma on 2D gels was developed resulting in improved protein spot resolution along with a lower coefficient of variation for spot volume. Using this improved method samples were subjected to 2D DIGE (two dimensional differential in gel electrophoresis) to determine if there were differences between the two groups of ewes. One of the differences was in haptoglobin, a major acute phase protein in ruminants, in which some isoforms were upregulated approximately 3 fold prior to prolapse occurring. This may indicate an inflammatory response due to either infection or injury. A good correlation was found between total haptoglobin spot volume data and quantitative haptoglobin assay data from the same samples (r² = 0.91) validating the haptoglobin gel spot data. Another finding was that alpha-1B-glycoprotein was down regulated close to prolapse, however the biological significance of this is unknown. It was also found that there was a negative correlation between cortisol and days to prolapse from sampling (r² = 0.36) i.e. ewes closest to prolapse had higher plasma cortisol concentrations than controls. These findings in conjunction with a literature search, field observations and an argument from logic lead the author to propose that chronic stress or anxiety may raise intra-abdominal pressure and contribute to the development of prolapse.Item Sensing and signalling intercalary growth in Epichloë festucae : a thesis presented in the partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Genetics at Massey University, Manawatu, New Zealand(Massey University, 2019) Ozturk, AslinurEpichloë festucae is a seed-transmitted symbiont that colonises the aerial parts of grasses and provides protection from biotic and abiotic stress. Although fungal hyphae normally extend at apical tips, exceptions to polar growth characterise the ecology of many important species. Recently, E. festucae has been shown to undergo intercalary growth during host colonization, where hyphae elongate and new compartments are created between existing compartments. Intercalary growth enables the synchronized growth of E. festucae hyphae and plant cells, and rapid hyphal elongation in plant intercellular tissue. Intercalary growth in E. festucae in vitro has been shown to be stimulated by mechanical stretch, mimicking the forces thought to be imposed on hyphae in plants due to their attachment to growing host cells. This research also showed that the High Affinity Calcium Uptake (HAC) and Cell Wall Integrity (CWI) systems influence intercalary growth, however, the mechanisms that regulate cell wall plasticity and compartmentalization are still largely unknown. The aim of this study was to identify the global gene responses to mechanical stress in E. festucae and to further investigate the roles of HACS and CWI in cell wall plasticity and intercalary growth. First, the role of E. festucae MidA, a homolog of the S. cerevisiae Mid1 stress-activated calcium influx channel complex, was addressed to better understand its involvement in intercalary growth and host colonisation. E. festucae MidA had been partly characterized previously and found to regulate vegetative growth, cell wall morphology, calcium influx and colonisation of the intercalary growth zone of ryegrass leaves. In this study, L. perenne seedlings were inoculated with E. festucae wild type, ΔmidA, and midA complementation strains. The effects of midA deletion on rates of plant colonisation, and the phenotype of infected plants was determined, and found to be the same as the wild type, although hyphae were more difficult to detect. The biomass of the different strains in host tissues, enriched either for the shoot apex (including the meristem) or surrounding leaf tissues, was quantified. The results revealed that E. festucae ΔmidA colonization in both tissue types was reduced compared to wild type (WT), but the effect was most convincing during growth in leaf tissues. These findings suggests that MidA function is required for host colonization, particularly in the leaf expansion zone where intercalary growth occurs. The role of MidA in cell wall plasticity and hyphal growth responses to mechanical stretch was next addressed. E. festucae WT and ΔmidA strains were grown on Potato Dextrose Agar (PDA), with or without 50 mM CaCl2 supplementation in a custom stretching device. When grown on PDA without calcium supplementation, the cell walls of WT and midA-complemented deletion strains were able to withstand mechanical stretching equivalent to 6.5% of their hyphal length (applied over approximately 15 min). However, when grown in the presence of 50 mM CaCl2, wild type hyphae and midA-complemented deletion strains were able to withstand 26% of mechanical stretch without visible evidence of cell wall fracture. In contract, ΔmidA strains grown on PDA alone were damaged after 2% of mechanical stress. Supplemental calcium was able to partly rescue this defect, and the ΔmidA strains were able to undergo 8.9% of stretch in PDA plus 50 mM CaCl2. These findings showed that supplemental calcium increases the resilience of E. festucae cell walls to mechanical stretch, and that midA is required for this, presumably by facilitating calcium influx and cell wall plasticity. Next, a transcriptomics study was conducted on E. festucae cultures undergoing various degrees of stretch. Hyphae were grown in vitro on silicon membranes and stretching forces applied to induce intercalary compartment extension and division, as observed in developing leaves. In cultures harvested 5 min after stretch, 105 genes were differentially expressed, whereas after 3 h, that number increased to 403. Analysis of these genes suggested that reprogramming of primary metabolism and plasma membrane organisation occurs almost immediately in response to mechanical stress, and mobilisation of cell wall enzymes and hyphal growth occurs over a longer time period. Finally, previous research as shown that deletion of E. festucae WscA, a homologue of the S. cerevisiae mechano-sensor Wsc1, induced cell wall and hyphal growth defects during growth in culture, however deletion strains were able to colonise ryegrass plants similarly to the wild type. To further elucidate the role of the CWI pathway in intercalary growth, a comprehensive bioinformatics study was co nducted to identify additional E. festucae Wsc proteins which may function upstream of the CWI pathway. A putative E. festucae WscB homolog was identified, plus a new putative cell wall protein with a unique domain. Phylogenetic analysis showed similar proteins in 17 other Epichloë species and entomopathogenic fungi, suggesting the presence of an E. festucae sensor protein that has been evolutionarily conserved. Vectors to delete these genes were constructed and E. festucae antibiotic-resistant colonies recovered. The putative deletion mutants of both strains were very small and compact compared to wild type growth in culture. Efforts to confirm the deletion loci and functionally characterise the mutants will be part of future research. In conclusion, a transcriptomics study has revealed that mechanical stretching induces metabolic changes during early and late responses in E. festucae, promoting early induction of primary metabolism and later changes associated with hyphal growth and cell wall remodelling. Moreover, further investigation of MidA revealed its importance for cell wall plasticity during intercalary expansion, and indicated that calcium is an essential requirement for hyphal resilience to mechanical stretch. Finally a new protein was discovered that responded to mechanical stress and could be a potential mechanosensor protein. This PhD project attempted to broaden our understanding of intercalary growth in E. festucae and pave the way for future studies on mechanical stress response in fungi.Item Regulation of postharvest inflorescence senescence in Arabidopsis thaliana : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand(Massey University, 2020) Xu, XiSenescence is critical for plant survival and fitness as it ensures the most efficient use of nutrients for development and production of offspring. Senescence is a genetically controlled and hormone-mediated programme. Besides being induced in an age-dependent manner, senescence can also be initiated precociously from harvest-induced stress such as light- and sugar-deprivation. Understanding the biological mechanisms behind dark-mediated senescence is important as it helps to provide a new strategy for extending shelf life of crop plants. This project aims to understand the regulation of dark-induced inflorescence senescence in model plant Arabidopsis thaliana by using a forward genetic approach. Arabidopsis mutants showing accelerated and delayed inflorescence senescence (named ais and dis) were identified previously. Here, I rescreened 23 mutants and confirmed the altered time to senescence phenotype of nine mutants, including two ais and seven dis mutants. Of those, the dis2, dis9, dis15 and dis51 mutants were used for further analysis. The delayed degreening phenotype was also observed in detached dark-held leaves of dis2 and dis51 mutants, indicating that the causal mutations affected genes that regulate both leaf and inflorescence senescence. Segregation analysis was used to determine the genetic nature of dis traits in the dis2 and dis51 mutants. The dis2 trait was found to be monogenic recessive while the dis51 trait is dual-genic recessive. The dis2 mutant showed an extended “stay-green” phenotype and retained higher chlorophyll (Chl) b than Chl a. These findings were consistent with a lesion in the NON-YELLOW COLORING1 (NYC1) gene. Sequencing revealed a C/T transition in exon 8 of NYC1, which caused a highly conserved proline to be substituted by serine at amino acid position 360 of the NYC1 protein. By contrast, dis51 retained a similar amount of Chl a and Chl b. One of the genetic lesions in this mutant was mapped to a ~665 kb region at the top arm of chromosome 5 by using High Resolution Melt (HRM)-based mapping technology. The ETHYLENE INSENSITIVE2 (EIN2) gene was considered as a promising candidate because similar phenotypes were observed in ein2 mutants and dis51 seedlings did not show triple response when treated with the ethylene precursor ACC in the dark. PCR-based sequencing showed a G to A mutation in exon 6 of EIN2, resulting in a premature stop codon, which thereby resulted in a truncated EIN2 protein missing part of the C-terminal region that is required for ethylene signal transduction. In addition, the dis51 mutant emitted a pleasant aroma, which is abnormal in Arabidopsis. Four compounds (benzaldehyde, benzyl alcohol, phenylacetaldehyde and phenylethanol) were detected by using GC-MS analysis. However, it is not clear if the mutation causing the aroma phenotype also contributed to the dis51 phenotype. The mutations in the dis9 and dis15 mutants were previously mapped to chromosome 3 and chromosome 2, respectively. Here, further HRM and whole genome sequencing (WGS) data analyses were used to identify the causal mutation in the dis9 mutant. The mutation changed a highly conserved Ser-97 to Phe in the active site of strigolactone (SL) receptor gene DWARF14 (D14), likely causing loss-of-activity. Since dis15 showed similar phenotypes to dis9, I hypothesised that the genetic lesion in dis15 may also have occurred in an SL pathway gene. The MORE AXIALLY GROWTH1 (MAX1) SL biosynthesis gene was present within the previously mapped region of this mutant. By using WGS data, I found a G/A mutation in the coding region of MAX1. The mutation in MAX1 substituted a highly conserved Gly-469 (G469) with Arg (R) in the haem-iron ligand signature of the Cytochrome P450 proteins. Using a N. benthamiana transient expression system, I found that the G469R substitution caused loss-of-activity of MAX1. In addition, the delayed sepal degreening of dis9 and dis15 was also observed in planta, suggesting a role of SL in regulation of both developmental and dark-induced sepal/inflorescence senescence. nCounter transcript counting technology was used to investigate the relationship between SL biosynthesis and signalling, sugar signalling and dark-induced senescence. There was no evidence of SL biosynthesis during the normal night in the inflorescences. During the extended night, the expression patterns of the SL biosynthetic gene MAX3 and signalling gene SUPPRESSOR OF MAX2-LIKE7 (SMXL7) best correlated with the sugar-responsive senescence regulatory genes [ARABIDOPSIS NAC DOMAIN CONTAINING PROTEIN92 (ANAC092) and NAC-LIKE, ACTIVATED BY AP3/PI (NAP)] and senescence marker gene (SENESCENCE-ASSOCIATED GENE12; SAG12), suggesting an interaction between SL and sugar signalling in controlling dark-induced inflorescence senescence. ANAC092 and NAP were further induced in the max1 mutant by the SL analogue, GR24, suggesting they are SL-inducible genes. The overall findings in this project reflect a complex regulatory network, which involves multiple phytohormones and degradation pathways, during dark-induced inflorescence senescence in Arabidopsis. Here, I proposed a model in which prolonged darkness first causes sugar-starvation in the excised inflorescence; the plant hormones ethylene and SL subsequently work together to regulate inflorescence senescence, including NYC1-regulated Chl degradation.Item Drought stress responses of the Medicago truncatula - Ensifer meliloti symbiosis on nodule senescence and nitrogen fixation : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand(Massey University, 2018) Dhanushkodi, RamadossWhile the use of nitrogen (N) fertilizer has provided many benefits to agriculture, incessant use of it can reduce soil organic matter and fertility resulting in lower crop yields. Legume plants can fix its own N2 through symbiotic nitrogen fixation (SNF) to promote plant growth by developing facultative root organs called nodules. Therefore, increasing the rate of SNF to reduce dependence on N fertilizer is a promising strategy for sustainable legume production. In legume cultivation this symbiotic process confronts two major challenges. First, SNF is suppressed by readily available N in the soil and second, the early senescence of N-fixing nodules can limit any further fixation to occur. Previous reports show that N fertilizer supresses SNF activity in many legumes and supports plant growth better than SNF. Moreover, suppression of SNF can also be induced by drought stress which causes early nodule senescence and subsequent reduced rates of plant growth. This thesis addresses the process of SNF suppression in two Medicago truncatula selected genotypes in response to external N treatment and also delivers a molecular view on the regulation of drought-induced nodule senescence processes.--Shortened abstractItem The time course of corticosterone responses in kororā (little penguin, Eudyptula minor) : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Zoology at Massey University(Massey University, 2017) Long, Kar HuiWhen birds and other vertebrates perceive a situation to be threatening the hypothalamopituitary-adrenal (HPA) axis is activated and glucocorticoid hormones are secreted from the adrenal gland. Activation of the HPA axis in response to a stimulus perceived to be threatening is called a stress response. The main glucocorticoid hormone in birds is corticosterone. Corticosterone responses of birds are typically measured by the collection of an initial blood sample when a bird is captured or picked up, then the collection of further blood samples until 30 to 60 minutes has elapsed, at which time the bird is released. Whilst this standard sampling protocol provides information on the size of the corticosterone response, it does not provide any indication of how long it takes for corticosterone concentrations to return to initial values. The main objective of this thesis was to characterise the total duration of the corticosterone response of free-living kororā (little penguins, Eudyptula minor). Little penguins at Oamaru were picked up from their nestboxes and initial blood samples collected. Birds were handled and then restrained by being placed in a box. Further blood samples were collected 15, 30 and 60 min after the birds were first picked up. Birds were then returned to their nest boxes and an additional blood sample collected 15, 30, 60, 120, 240, or 360 min later. Mean corticosterone concentrations declined to initial values two hours after birds were returned to nest boxes. The rates at which corticosterone concentrations increased when a stressor was present and then decreased when the stressor was no longer present were positively correlated. Seasonal changes in corticosterone responses in little penguins were also investigated in this study. Mean corticosterone responses were similar in winter and in the pre-laying period, whereas mean responses were lower in birds during early chick rearing. Corticosterone responses during the pre-laying period were greater in male than female little penguins. The current study is the first to document the complete corticosterone responses of free-living penguins and provides information about changes of corticosterone concentrations after a stressor is removed from the free-living individuals. It is also the first to reveal that free-living penguins with relatively high corticosterone responses to a stressor had relatively high rates of corticosterone decline.