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.

Variation in Cyclaneusma minus isolates

Cyclaneusma minus is a plant pathogen that has financial impacts on the forestry industry. This study characterised the genetic variation in Australian and New Zealand isolates of Cyclaneusma minus using both molecular and morphological techniques and developed a PCR detection test for the presence of Cyclaneusma minus in tree plantations.

Profiling secondary metabolites of plant roots inoculated with Phytophthora cinnamomi

The soil-borne pathogen, Phytophthora cinnamomi, continues to cause severe dieback in Australian native forest species and is of great international significance due to its global distribution. This research established a protocol to successfully identify phyto-chemicals associated with the defense response of plants challenged by the disease caused by Phytophthora cinnamomi.

The clp chaperones and proteases of the human malaria parasite Plasmodium falciparum

The Clp chaperones and proteases play an important role in protein homeostasis in the cell. They are highly conserved across prokaryotes and found also in the mitochondria of eukaryotes and the chloroplasts of plants. They function mainly in the disaggregation, unfolding and degradation of native as well as misfolded proteins. Here, we provide a comprehensive analysis of the Clp chaperones and proteases in the human malaria parasite Plasmodium falciparum. The parasite contains four Clp ATPases, which we term PfClpB1, PfClpB2, PfClpC and PfClpM. One PfClpP, the proteolytic subunit, and one PfClpR, which is an inactive version of the protease, were also identified. Expression of all Clp chaperones and proteases was confirmed in blood-stage parasites. The proteins were localized to the apicoplast, a non-photosynthetic organelle that accommodates several important metabolic pathways in P. falciparum, with the exception of PfClpB2 (also known as Hsp101), which was found in the parasitophorous vacuole. Both PfClpP and PfClpR form mostly homoheptameric rings as observed by size-exclusion chromatography, analytical ultracentrifugation and electron microscopy. The X-ray structure of PfClpP showed the protein as a compacted tetradecamer similar to that observed for Streptococcus pneumoniae and Mycobacterium tuberculosis ClpPs. Our data suggest the presence of a ClpCRP complex in the apicoplast of P. falciparum.

An overview of the ecology, management and conservation of Australia's temperate woodlands

Australia’s temperate woodlands are environments of cultural and ecological importance and significant repositories of Australia’s biodiversity. Despite this, they have been heavily cleared, much remaining vegetation is in poor condition and many species of plants and animals are threatened. Here, we provide a brief overview of key issues relating to the ecology, management and policy directions for temperate woodlands, by identifying and discussing ten themes. When addressing issues relating to the conservation and management of temperate woodlands, spatial scale is very important, as are the needs for a temporal perspective and a complementary understanding of pattern and process. The extent of landscape change in many woodland environments means that woodland patches, linear networks and paddock trees are critical elements, and that there can be pervasive effects from ‘problem’ native species such as the Noisy Miner (Manorina melanocephala). These consequences of landscape change highlight the challenge to undertake active management and restoration as well as effective monitoring and long-term data collection. In developing approaches for conservation and management of temperate woodlands, it is essential to move our thinking beyond reserves to woodland conservation and management on private land, and recognise the criticality of cross-disciplinary linkages. We conclude by identifying some emerging issues in woodland conservation and management. These include the need to further develop non-traditional approaches to conservation particularly off-reserve management; the value of documenting approaches and programmes that demonstrably lead to effective change; new lessons that can be learned from intact examples of temperate woodlands; and the need to recognise how climate change and human population growth will interact with conservation and management of temperate woodlands in future decades

Influence of age on expression of DNA repair genes in Arabidopsis

Numerous studies suggest that ageing in mammals may be associated with a reduction in DNA repair, whereas little is known about the DNA repair capacity of plants as they age. In this study we examined the effects of ageing on the expression of genes thought to be involved in nucleotide excision repair (AtERCC1, AtGTF2H2, AtGTF2H5, AtXPB1, AtXPD, AtXPF) or translesion replication (AtPOLH, AtREV1, AtREV3, AtUBC2) of UV photoproducts in Arabidopsis (Arabidopsis thaliana). Two- or four-week old plants were unirradiated or treated with 254 nm ultraviolet (UV) radiation (0.75 or 1.5 kJm^-2), incubated for 3 or 9 hr, and gene expression was analysed via quantitative PCR. With the exception of AtPOLH, transcript levels for all genes investigated were at least four-fold greater in unirradiated four-week old plants than unirradiated two-week old plants. Compared to unirradiated age-matched plants, two-week old plants generally showed no consistent change in transcript levels for either UV dose or post-irradiation incubation period. On the other hand, transcript levels in four-week old plants were increased over those in two-week old plants for the majority of genes by 9 hr post-irradiation with 0.75 or 1.5 kJm^-2 UV. No other consistent responses were observed for UV treatment. Collectively, our results are consistent with the possibility that ageing may be associated with increased DNA repair capacity in plants.

Fruitful use of bioacoustic alarm stimuli as a deterrent for Crimson Rosellas (Platycercus elegans)

Birds cause considerable damage to horticultural crops in Australia each year. The playback of species-specific bioacoustic alarm stimuli has been one of the most promising methods suggested to deal with bird-problems. However, no published studies have tested this method on species of parrots, one of the main avian pests of crops in Australia and globally. Furthermore the effectiveness of this method might be reduced if alarm calls were played back that came from a non-local population. The Crimson Rosella species complex (Platycercus elegans), a parrot with considerable acoustic variation throughout its range, is considered a pest species of several commercial fruit crops. This study tested whether alarm calls from Crimson Rosellas were effective in reducing the activity of Rosellas in apple orchards. Three groups of bioacoustic stimuli were compared: control stimuli, local alarm calls and non-local alarm calls. Our results indicate that the playback of alarm calls from Crimson Rosellas is effective in reducing the activity of Rosellas in orchards over the period of study, and we did not find any difference between the use of local and non-local alarm calls. Our study suggests that playback of alarm calls may be an effective deterrent of rosellas over a broad distribution, at least for short- to medium-term use.

Comparative analyses of cadmium and zinc uptake correlated with changes in natural resistance-associated macrophage protein (NRAMP) expression in Solanum nigrum L. and Brassica rapa

Environmental context Soils contaminated with metals can pose both environmental and human health risks. This study showed that a common crop vegetable grown in the presence of cadmium and zinc readily accumulated these metals, and thus could be a source of toxicity when eaten. The work highlights potential health risks from consuming crops grown on contaminated soils. Abstract Ingestion of plants grown in heavy metal contaminated soils can cause toxicity because of metal accumulation. We compared Cd and Zn levels in Brassica rapa, a widely grown crop vegetable, with that of the hyperaccumulator Solanum nigrum L. Solanum nigrum contained 4 times more Zn and 12 times more Cd than B. rapa, relative to dry mass. In S. nigrum Cd and Zn preferentially accumulated in the roots whereas in B. rapa Cd and Zn were concentrated more in the shoots than in the roots. The different distribution of Cd and Zn in B. rapa and S. nigrum suggests the presence of distinct metal uptake mechanisms. We correlated plant metal content with the expression of a conserved putative natural resistance-associated macrophage protein (NRAMP) metal transporter in both plants. Treatment of both plants with either Cd or Zn increased expression of the NRAMP, with expression levels being higher in the roots than in the shoots. These findings provide insights into the molecular mechanisms of heavy metal processing by S. nigrum L. and the crop vegetable B. rapa that could assist in application of these plants for phytoremediation. These investigations also highlight potential health risks associated with the consumption of crops grown on contaminated soils.

The potential for indirect effects between co-flowering plants via shared pollinators depends on resource abundance, accessibility and relatedness

Co-flowering plant species commonly share flower visitors, and thus have the potential to influence each other's pollination. In this study we analysed 750 quantitative plant-pollinator networks from 28 studies representing diverse biomes worldwide. We show that the potential for one plant species to influence another indirectly via shared pollinators was greater for plants whose resources were more abundant (higher floral unit number and nectar sugar content) and more accessible. The potential indirect influence was also stronger between phylogenetically closer plant species and was independent of plant geographic origin (native vs. non-native). The positive effect of nectar sugar content and phylogenetic proximity was much more accentuated for bees than for other groups. Consequently, the impact of these factors depends on the pollination mode of plants, e.g. bee or fly pollinated. Our findings may help predict which plant species have the greatest importance in the functioning of plant-pollination networks.

Does biochar improve establishment of tree seedlings in saline sodic soils?

Reforestation of saline sodic soil is increasingly undertaken as a means of reclaiming otherwise unproductive agricultural land. Currently, restoration of degraded land is limited to species with high tolerances of salinity. Biochar application has the potential to improve physical, biological and chemical properties of these soils to allow establishment of a wider range of plants. In a glasshouse trial, we applied biochar made from Acacia pycnantha (5Mgha^-1) or no biochar to either a low (ECe 4·75 dS m^-1, ESP 6·9), a moderate (ECe 27·6 dS m^-1, ESP 29·3) or a high (ECe 49·4 dS m^-1, ESP 45·1) saline sodic soil. The regional common reforestation species Eucalyptus viminalis and Acacia mearnsii were planted as tubestock in to the soils. Early establishment indicators, including growth, plant condition and nutrition, were assessed at the end of a simulated growing season, 108days after biochar application. Application of biochar increased height, and decreased root:shoot and the concentration of Mn, N and S in plants of E.viminalis when grown in the highly saline sodic soil. Biochar application increased the concentration of B in leaves of E.viminalis and increased the concentration of P, K and S in leaves of A.mearnsii when grown in the low saline sodic soil. The results confirm that there is potential for biochar to assist in reforestation of saline sodic soils.