An investigation into the role of oxalate in the leaves of Pisonia grandis

"Pisonia grands R. Br. (Nyctaginaceae) is a large tropical tree whose distribution is restricted to coral cays, in particular those with high seasonal nesting seabird populations. These trees are often the dominant plant species found on coral cays. This is the case for the chosen study site on North West Island, a coral cay which lies off the Central Queensland coast within the Mackay Capricorn section of the Great Barrier Reef. Coral cays are almost entirely composed of coral rubble and sand and as a result the substrate pH (c. 9.0) and many ions are found as insoluble salts. The high pH, abundance of calcium, lack of water and high seasonal input of nitrates from nesting seabirds, are possible influences on the biosynthesis of oxalates which are found in high concentrations in P. grandis. The aims of this study are twofold. The first aim was to investigate the influence of environmental factors, such as pH and nitrate concentration, on the biosynthesis of oxalate in Pisonia grandis leaf. The second aim was to purify and characterise the enzyme glycolic acid oxidase (E.C. 1.1.3.1) (GAO), an enzyme involved in the biosynthesis of oxalate..." --abstract.. Pisonia grandis R. Br. (Nyctaginaceae) is a large tropical tree whose distribution is restricted to coral cays, in particular those with high seasonal nesting seabird populations. These trees are often the most dominant plant species found on coral cays. This is the case for the chosen study site on North West Island, a coral cay which lies off the Central Queensland coast within the Mackay Capricorn section of the Great Barrier Reef. Coral cays are almost entirely composed of coral rubble and sand and as a result the substrate pH is high (c. 9.0) and many ions are found as insoluble salts. The high pH, abundance of calcium, lack of water and high seasonal input of nitrates from nesting seabirds, are possible influences on the biosynthesis of oxalates which are found in high concentrations in P. grandis. The aims of this study were twofold. The first aim was to investigate the influence of environmental factors, such as pH and nitrate concentration, on the biosynthesis of oxalate in Pisonia grandis leaf. The second aim was to purify and characterise the enzyme glycolic acid oxidase (E.C. 1.1 .3.1) (GAO), an enzyme involved in the biosynthesis of oxalate. P. grandis was grown in a hydroponic system which was constructed in a glasshouse. The effect of variations in light intensity, pH and the concentrations of nitrate, calcium and sodium chloride in the nutrient sol ution on leaf oxalate concentration was investigated. A small diurnal variation in leaf soluble oxalate concentration was observed (O.5mmol/g DW at 07:00hrs and 0.62 mmol/g/DW at 19:00hrs) which was consistent with the notion that an intermediate in the formation of oxalate was derived from photosynthesis or photorespiration. In all other experimental regimes leaf oxalate concentrations were shown to vary in response to changes in the excess cation content of the leaves. These hydroponic studies suggested that changes in leaf excess cation concentration, and associated changes in intracellular pH, stimulate changes in the biosynthesis of oxalate in Pisonia. GAO was isolated to purity from the leaves of P. grandis and was found to be similar to GAO from other sources. The holoenzyme was found to be a hexamer (M.Wt. 250000) of subunits with molecular weight 44000. In vitro, with glycolate substrate, GAO had a pH optima of 7.0 and a Km of O.4mM. The enzyme exhibited partial competitive inhibition by oxalate (Ki 2.75mM) and was irreversibly inhibited by phydroxymercuribenzoate. Phenyllactate and iodoacetate did not inhibitthe enzyme preparation. These studies were repeated for glyoxylate and lactate as the enzyme substrates. The pH optima determined for GAO in vitro with glycolate and glyoxylate substrates, in conjunction with the pH optima reported for aminotransferase enzymes, supports the notion that leaf oxalate participates in a biochemical pH stat within the leaves of Pisonia grandis

Recognitive justice : renewed commitment to socially just schooling

The contribution of schools to the production and maintenance of educational inequalities is no secret, yet the continued support for the promotion of differential educational outcomes on the basis of the social groups to which students belong is clearly unjust. This paper discusses the 'ideal' arrangements to promote success in schooling for all students while also critiquing arrangements that are less-than-ideal. In rethinking these matters, the paper draws on the notion of 'recognitive justice': a process model of social justice that includes a positive regard for social difference and the centrality of socially democratic processes. Issues that emerge for teachers and schools include: fostering self-respect and facilitating students' positive self-identities; promoting the development of students' abilities and encouraging expressions of their experiences; and establishing meaningful involvement in schooling premised on self-determination

Activist dispositions for social justice in advantaged and disadvantaged contexts of schooling

This article advances current conceptions of teacher activism through an exploration of the social justice dispositions of teachers in advantaged and disadvantaged contexts of schooling. We interrogate the practices of teachers in a government school, with a high proportion of refugee students and students from low socio-economic backgrounds, in a high-fees, multi-campus independent school, and in a disadvantaged Systemic Catholic school to illustrate how Bourdieu’s notion of dispositions (which are constitutive of the habitus) and Fraser’s distinction between affirmative and transformative justice are together productive of four types of teacher activism. Specifically, we show that activist dispositions can be characterised as either affirmative or transformative in stance and as either internally or externally focused in relation to the education field. We argue that the social, cultural and material conditions of schools are linked to teachers’ activist dispositions and conclude with the challenge for redressing educational inequalities by fostering a transformative activism in teachers’ practices

A laserball calibration device for the SNO+ scintillator phase

Located 2 km underground in SNOLAB, Sudbury, Canada, SNO+ is a large scale liquid scintillator experiment that primarily aims to search for neutrinoless double beta decay. Whilst SNO+ has light and radioactive calibration sources external to the inner volume, an internally deployed optical source is necessary for the full characterization of the detector model. A laser diffuser ball developed for SNO has previously demonstrated to be an effective optical calibration device for both SNO and SNO+ water phase. Since the introduction of liquid scintillator for SNO+, the material compatibility, cleanliness, and radiopurity requirements of any materials in contact with the internal medium have increased. Improving on the original SNO laserball design, a new laserball calibration device has been developed for the SNO+ scintillator phase with the goal of measuring the optical properties of the detector and performing routine PMT gain and timing calibrations. Simulations have been written to model the diffusion properties to optimise optical and temporal performance for calibration. Prototype laserballs have been built and characterised, demonstrating sub-ns timing resolution and a quasi-isotropic light distribution.</p

A laserball calibration device for the SNO+ scintillator phase

Located 2 km underground in SNOLAB, Sudbury, Canada, SNO+ is a large scale liquid scintillator experiment that primarily aims to search for neutrinoless double beta decay. Whilst SNO+ has light and radioactive calibration sources external to the inner volume, an internally deployed optical source is necessary for the full characterization of the detector model. A laser diffuser ball developed for SNO has previously demonstrated to be an effective optical calibration device for both SNO and SNO+ water phase. Since the introduction of liquid scintillator for SNO+, the material compatibility, cleanliness, and radiopurity requirements of any materials in contact with the internal medium have increased. Improving on the original SNO laserball design, a new laserball calibration device has been developed for the SNO+ scintillator phase with the goal of measuring the optical properties of the detector and performing routine PMT gain and timing calibrations. Simulations have been written to model the diffusion properties to optimise optical and temporal performance for calibration. Prototype laserballs have been built and characterised, demonstrating sub-ns timing resolution and a quasi-isotropic light distribution.</p

A series of fortunate readers : a collaborative review article of important Australasian YA writing

This review article is a collaborative autoethnographic exploration of Australasian Young Adult writing compiled by the contributors of the ‘Why YA?: Researching, writing and publishing YA fiction in Australasia’ TEXT Special issue. The contributors to the special issue were asked to produce a brief review of what they considered an important Australasian YA text, and why. While the range of narratives examined in this article (and the special issue as a whole) demonstrates the valuable variety of the field, this review article also serves to demonstrate the personal pleasure which each of the contributors takes in the genre