Studies of natriuretic peptides in Tradescantia

The idea that plant development and physiological responses to the environment are governed largely by the five classical hormones is being superseded by the view that a much larger range of very different molecules also have such functions in plants. Recent evidence suggests that natriuretic peptides (NPs) known to function in vertebrates as regulators of salt and water balance may also play this role in plants. This thesis adds experimental results obtained in vitro and in situ that contribute to further establishing NPs as novel endogenous regulators in plants.

Diverse roles of the Mediator complex in plants

Since its original discovery in yeast, the Mediator complex has been identified in a wide range of organisms across the eukaryotic kingdom. Despite being experimentally purified from a number of fungal and metazoan organisms, it was not until 2007, thirteen years after its initial discovery, that the Mediator complex was successfully isolated from plants. With a number of papers now beginning to emerge on the plant Mediator complex, this review aims to provide an overview of the diverse functions that have been identified for individual plant Mediator subunits. In addition to demonstrating roles in plant development, flowering, hormone signaling and biotic and abiotic stress tolerance; recent findings have revealed novel functions for plant Mediator subunits, including mRNA, miRNA and rRNA processing, as well as controlling DNA and protein stability. These diverse activities have expanded the known functions of the Mediator complex and demonstrate a variety of new insights that have been gained from investigations into the plant Mediator complex. Future directions for research into this multi-functional protein complex will be discussed.

Functional genomic analysis of systemic cell division regulation in legumes

Legumes develop root nodules from pluripotent stem cells in the rootpericycle in response to mitogenic activation by a decorated chitin-likenodulation factor synthesized in Rhizobium bacteria. The soybean genes encoding the receptor for such signals were cloned using map-based cloning approaches. Pluripotent cells in the root pericycle and the outer or inner cortex undergo repeated cell divisions to initiate a composite nodule primordium that develops to a functional nitrogen-fixing nodule. The process itself is autoregulated, leading to the characteristic nodulation of the upper root system. Autoregulation of nodulation (AON) in all legumes is controlled in part by a leucine-rich repeat receptor kinase gene (GmNARK). Mutations of GmNARK, and its other legume orthologues, result in abundant nodulation caused by the loss of a yet-undefined negative nodulation repressor system. AON receptor kinases are involved in perception of a long distance, root-derived signal, to negatively control nodule proliferation. GmNARK and LjHAR1 are expressed in phloem parenchyma. GmNARK kinase domain interacts with Kinase Associated Protein Phosphatase (KAPP). NARK gene expression did not mirror biological NARK activity in nodulation control, as q-RT-PCR in soybean revealed high NARK expression in roots, root tips, leaves, petioles, stems and hypocotyls, while shoot and root apical meristems were devoid of NARK RNA. High through-put transcript analysis in soybean leaf and root indicated that major genes involved in JA synthesis or response are preferentially down-regulated in leaf but not root of wild type, but not NARK mutants, suggesting that AON signaling may in part be controlled by events relating to hormone metabolism. Ethylene and abscisic acid insensitive mutants of L. japonicus are described. Nodulation in legumes has significance to global economies and ecologies, as the nitrogen input into the biosphere allows food, feed and biofuel production without the inherent costs associated with nitrogen fertilization [1]. Nodulation involves the production of a new organ capable of nitrogen fixation [2] and as such is an excellent system to study plant – microbe interaction, plant development, long distance signaling and functional genomics of stem cell proliferation [3, 4]. Concerted international effort over the last 20 years, using a combination of induced mutagenesis followed by gene discovery (forward genetics), and molecular/biochemical approaches revealed a complex developmental pathway that ‘loans’ genetic programs from various sources and orchestrates these into a novel contribution. We report our laboratory’s contribution to the present analysis in the field.

Urbanization impacts on mammals across urban-forest edges and a predictive model of edge effects

With accelerating rates of urbanization worldwide, a better understanding of ecological processes at the wildland-urban interface is critical to conserve biodiversity. We explored the effects of high and low-density housing developments on forest-dwelling mammals. Based on habitat characteristics, we expected a gradual decline in species abundance across forest-urban edges and an increased decline rate in higher contrast edges. We surveyed arboreal mammals in sites of high and low housing density along 600 m transects that spanned urban areas and areas turn on adjacent native forest. We also surveyed forest controls to test whether edge effects extended beyond our edge transects. We fitted models describing richness, total abundance and individual species abundance. Low-density housing developments provided suitable habitat for most arboreal mammals. In contrast, high-density housing developments had lower species richness, total abundance and individual species abundance, but supported the highest abundances of an urban adapter (Trichosurus vulpecula). We did not find the predicted gradual decline in species abundance. Of four species analysed, three exhibited no response to the proximity of urban boundaries, but spilled over into adjacent urban habitat to differing extents. One species (Petaurus australis) had an extended negative response to urban boundaries, suggesting that urban development has impacts beyond 300 m into adjacent forest. Our empirical work demonstrates that high-density housing developments have negative effects on both community and species level responses, except for one urban adapter. We developed a new predictive model of edge effects based on our results and the literature. To predict animal responses across edges, our framework integrates for first time: (1) habitat quality/preference, (2) species response with the proximity to the adjacent habitat, and (3) spillover extent/sensitivity to adjacent habitat boundaries. This framework will allow scientists, managers and planners better understand and predict both species responses across edges and impacts of development in mosaic landscapes.

Plant-pathogen interactions: toward development of next-generation disease-resistant plants

Briskly evolving phytopathogens are dire threats to our food supplies and threaten global food security. From the recent advances made toward high-throughput sequencing technologies, understanding of pathogenesis and effector biology, and plant innate immunity, translation of these means into new control tools is being introduced to develop durable disease resistance. Effectoromics as a powerful genetic tool for uncovering effector-target genes, both susceptibility genes and executor resistance genes in effector-assisted breeding, open up new avenues to improve resistance. TALENs (Transcription Activator-Like Effector Nucleases), engineered nucleases and CRISPR (Clustered Regulatory Interspaced Short Palindromic Repeats)/Cas9 systems are breakthrough and powerful techniques for genome editing, providing efficient mechanisms for targeted crop protection strategies in disease resistance programs. In this review, major advances in plant disease management to confer durable disease resistance and novel strategies for boosting plant innate immunity are highlighted.

Development of disease caused by Phytophthora cinnamomi in mature Xanthorrhoe australis

Over the past 30 years, heathland and open forest communities in south-eastern Australia dominated by Xanthorrhoea australis R.Br. have been severely affected by disease caused by Phytophthora cinnamomi Rands. The disease has caused a sharp decline in numbers of individuals within populations of X. australis; however, the etiology of the disease is unclear. The characteristics and disease symptoms induced by P. cinnamomi were analysed within nine mature X. australis plants that had been removed from the field. Seven plants showed typical disease symptoms that ranged from chlorotic leaves through to plant death. Plants showing disease symptoms had different numbers of infected roots, ranging from 0% in one dead plant, 40% infected roots in a plant showing yellowing of leaf tips and 67 and 86%, respectively, in two plants with severe chlorosis. There was variation within the roots, with some infected close to the stem while others were infected at more distal regions. Within stems of all plants, P. cinnamomi was difficult to isolate but was found in the desmium and stem apex and was associated with massive lesions within the central area of the stem. The symptoms of disease in X. australis are caused by a combination of damage to tissues of the roots and stem that may lead to a reduction in water and mineral transport throughout the plant.

Community development and ecology : exploring the links

This paper will explore connections between the concepts of community development and ecology. Initially the tendency was to think there should be a total melding of the principles and practices of community development with those of an ecological understanding but on reflection this has not and indeed is not necessarily the case. The relative epistemological positioning of two different groups, one strongly associating with social justice and the need for people to be at the centre of our economic, environmental and social understanding; and the other clearly seeing the plant and ecology/environment being paramount. While there are a myriad of connections the focus of much community development has been around human welfare based on principles of social, political and economic justice. This has at times been to the detriment of ecological sustainability. Conversely ecology and particularly aspects of deep ecology have focussed on the 'other than human' aspects of the planet and at times seemed almost 'anti 'human and overlooking the need to work with the social almost entirely. This paper briefly outlines the historical separation of the social from the ecological then goes on to explore alternative understandings that bring together principles of community development and ecology. Three examples are used to highlight the principles and practices that are being used across diverse contexts but all informed by common norms and values that are consistent with both community development and ecology. Concepts such as subsidiarity, participation and empowerment that form the basis of community development praxis are critical to the development of local sustainability. The combination of these aspects is evidenced in the three examples. Each is very clearly located in the local context and is built on sound ecological and community development understandings but each is also well aware that the need for a broader perspective is imperative to achieving global goals.

Development and use of a model system to monitor clubroot disease progression with an Australian field collection of Plasmodiophora brassicae

A modified sand–liquid culture method facilitated easy visualisation of the primary life cycle stages of Plasmodiophora brassicae within clean root hairs of the Arabidopsis host. Pathogen penetration occurred from day 4 onwards and then primary plasmodia developed within the host root. Several Arabidopsis ecotypes tested in varying growth conditions showed differences in disease expression. Defined growth cabinet conditions were found most suitable for studying disease progression in the ecotypes and for achieving uniform infection and disease development. Arabidopsis ecotypes Ta-0 and Tsu-0 known to be partially resistant to a German single-spore isolate of P. brassicae were susceptible to an Australian (Victorian) field population of P. brassicae. The European clubroot differential test was used to confirm virulence and describe the pathotype of the Victorian field population. Knowledge of the interaction of an Australian population of P. brassicae with its host will provide valuable information on a disease which is very difficult to control.

A soil-free plant growth system to facilitate analysis of plant pathogen interactions in roots

Analysis of the interaction of pathogens with plant roots is often complicated by the growth of plants in a soil substrate. A soil-free plant growth system (SPS) was developed that removes the need for a substrate while supporting the growth of seedlings in a nutrient rich, oxygenated environment. The model legume Lupinus angustifolius was used to compare the growth of seedlings within soil and the SPS. Seedlings grown under both conditions were similar in morphology, anatomy and health (measured by leaf chlorophyll abundance) and importantly there was little difference in root growth and development although straighter and fuller root systems were achieved in the SPS. The ease of access to the root system proved efficient for the analysis of root and pathogen interactions with no interference from soil or adhering particulate matter. Following inoculation of L. angustifolius roots with Phytophthora cinnamomi the host/pathogen interaction was easily observed and tissues sampled undamaged.

Towards development of a quality cost model for automotive stamping

The current work used discrete event simulation techniques to model the economics of quality within an actual automotive stamping plant. Automotive stamping is a complex, capital intensive process requiring part-specific tooling and specialised machinery. Quality control and quality improvement is difficult in the stamping environment due to the general lack of process understanding and the large number to interacting variables. These factors have prevented the widespread use of statistical process control. In this work, a model of the quality control techniques used at the Ford Geelong Stamping plant is developed and indirectly validated against results from production. To date, most discrete event models are of systems where the quality control process is clearly defined by the rules of statistical process control. However, the quality control technique used within the stamping plant is for the operator to perform a 100% visual inspection while unloading the finished panels. In the developed model, control is enacted after a cumulative count of defective items is observed, thereby approximating the operator who allows a number of defective panels to accumulate before resetting the line. Analysis of this model found that the cost sensitivity to inspection error is dependent upon the level of control and that the level of control determines line utilisation. Additional analysis of this model demonstrated that additional inspection processes would lead to more stable cost structures but these structures many not necessarily be lower cost. The model was subsequently applied to investigate the economics of quality improvement. The quality problem of panel blemishes, induced by slivers (small metal fragments), was chosen as a case stuffy. Errors of 20-30% were observed during direct validation of the cost model and it was concluded that the use of discrete event simulation models for applications requiring high accuracy would not be possible unless the production system was of low complexity. However, the model could be used to evaluate the sensitivity of input factors and investigating the effects of a number of potential improvement opportunities. Therefore, the research concluded that it is possible to use discrete event simulation to determine the quality economics of an actual stamping plant. However, limitations imposed by inability of the model to consider a number of external factors, such as continuous improvement, operator working conditions or wear and the lack of reliable quality data, result in low cost accuracy. Despite this, it still can be demonstrated that discrete event simulation has significant benefits over the alternate modelling methods.

Abscisic acid regulation of plant defence responses during pathogen attack

The plant hormone, abscisic acid (ABA), has previously been shown to have an impact on the resistance or susceptibility of plants to pathogens. In this thesis, it was shown that ABA had a regulatory effect on an extensive array of plant defence responses in three different plant and pathogen interaction combinations as well as following the application of an abiotic elicitor. In unique studies using ABA deficient mutants of Arabidopsis, exogenous ABA addition or ABA biosynthesis inhibitor application and simulated drought stress, ABA was shown to have a profound effect on the outcome of interactions between plants and pathogens of differing lifestyles and from different kingdoms. The systems used included a model plant and an important agricultural species: Arabidopsis thaliana (Arabidopsis) and Peronospora parasitica (a biotrophic Oomycete pathogen), Arabidopsis and Pseudomonas syringae pathovar tomato (a biotrophic bacterial pathogen) and an unrelated plant species, soybean (Glycine max) and Phytophthora sojae (a hemibiotrophic Oomycete pathogen), Generally, a higher than basal endogenous ABA concentration within plant tissues at the time of avirulent pathogen inoculation, caused an interaction shift towards what phenotypically resembled susceptibility. Conversely, a lower than basal endogenous ABA concentration in plants inoculated with a virulent pathogen caused a shift towards resistance. An extensive suppressive effect of ABA on defence responses was revealed by a range of techniques that included histochemical, biochemical and molecular approaches. A universal effect of ABA on suppression or induction of the phenylpropanoid pathway via regulation of the key entry point gene, phenylalanine ammonia-lyase (PAL), when stimulated by biotic or abiotic elicitors was shown. ABA also influenced a wide variety of other defence-related components such as: the development of a hypersensitive response (HR), the accumulation of the reactive oxyden species, hydrogen peroxide and the cell wall strengthening compounds lignin and callose, accumulation of SA and the phytoalexin, glyceollin and the transcription of the SA-dependent pathogenesis- related gene (PR-1). The near genome-wide microarray gene expression analysis of an ABA induced susceptible interaction also revealed an yet unprecedented insight into the great diversity of defence responses that were influenced by ABA that included: disease resistance like proteins, antimicrobial proteins as well as phenylpropanoid and tryptophan pathway enzymes. Subtle differences were found in the number and type of defence responses that were regulated by ABA in each type of plant and pathogen interaction that was studied. This thesis has clearly identified in plant/pathogen interactions previously unknown and important roles for ABA in the regulation of many defence responses.

Procedural justice and Australian environment : the case of the Wonthaggi water desalination plant

Drier conditions in Australia have compelled governments to implement various projects to address current or impending water shortages. Such projects have not always been popular with the local community who are directly affected by this infrastructure, with 'procedural justice' emerging as a critical issue. This paper analyses issues of public perceptions of 'procedural justice' in implementing environmental projects in regional areas, in the context of the recently approved desalination plant in the regional Victorian town of Wonthaggi. Drawing on both qualitative and quantitative data from a survey of 316 Wonthaggi residents, we show that one of the major predictors of residents' resistance toward accepting the building of the desalination plant was explained by perceptions of procedural injustice. We further argue that inadequate attention to the particular political history of the region has compounded the sense that the plant implementation has been unfair. Attention to such political histories is vital to avoiding conflict with local stakeholders and to the successful and ethical implementation of development projects in regional areas.

Cellular and molecular components of plant defence against pathogens

This project investigated how plants respond to invading pathogens using microscopic, biochemical and genetic approaches. The development of transgenic plants containing the green fluorescent protein cloned from jellyfish enabled a new approach to studying plant defence genes. In particular, the role and involvement of the plant gene PAL1 was analysed.

Plant bioactive determinations using flow analysis, chromatography with chemiluminescence detection

The development of rapid analytical methodologies for the determination of plant bioactives including antioxidants, amino acids and opium alkaloids was investigated using novel flow analysis and liquid chromatographic techniques. These methodologies were applied to the wine, food and pharmaceutical industries.