Phosphate absorption by Arabidopsis thaliana : the effects of phosphorus nutritional status : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology and Biotechnology at Massey University, Palmerston North, New Zealand

The effect of phosphorus nutritional status on phosphate uptake within the concentration range of the high affinity uptake mechanism, and subsequent translocation to the shoot was investigated in the plant species Arabidopsis thaliana. Plants of different nutritional status were generated by exposure to different set phosphate concentrations throughout an aseptic hydroponic growing period. Alternatively phosphorus deficiency was induced by growth at high concentrations of phosphate followed by a period of 5 days in phosphate-free hydroponic solution. In effect these growth conditions resulted in plants of distinguishable phenotypic character with respect to phosphate absorption, phosphate translocation, arsenate sensitivity and root-shoot ratio. To determine absorption kinetics nutrient depletion trials were carried out in which phosphate uptake was measured by monitoring the loss of phosphate from depletion solutions of set initial phosphate concentration to which the root systems of intact plants were exposed. Km and Vmax kinetic parameters were calculated from the depletion trial data using the software package "Igor Pro". Influx and net phosphate uptake was determined by setting the initial phosphate concentration of the depletion trials using either 32 P labelled KH 2 P0 4 or non-labelled KH 2 P0 4 respectively. Radioactivity was measured by counting the Cerenkov radiation in a scintillation counter. Non-labelled phosphate depletion was measured by either spectrophotometric assay or ion chromatography. To asses the effect of the phosphate analogue arsenate on phosphate influx, 32 P labelled phosphate uptake was measured with arsenate (KH 2 AsO 4 ) present in the depletion solution at a concentration of 20 µM. Phosphate translocation was determined by counting the Cerenkov radiation in the roots and shoots separately of plants that had been exposed to the 32 P labelled depletion solutions. Under the conditions of this project, phosphorus deficient plants exhibited alterations in the kinetic parameters Km and Vmax for phosphate uptake that were dependent on how the deficiency was induced. For plants that were grown continuously at low phosphate concentrations Km was decreased without a concomitant change in Vmax. For plants that were grown at high concentrations of phosphate followed by a 5 day period of phosphate starvation, a significant increase in Vmax was recorded without an associated change to Km. Phosphate uptake was found to be severely inhibited by the presence of arsenate in the depletion solution. Greatest inhibition however was found not to occur at the level of absorption into the plant root system but rather appeared to be at a site involved in phosphate loading into the xylem. Inhibition at this site was also found to be greatest in low phosphorus status plants. From these results it is suggested that plants of low phosphorus status possess high affinity phosphate xylem loading mechanisms, induced under conditions of phosphorus deficiency, which have a greater susceptibility to arsenate competitive inhibition and toxicity than equivalent xylem loading mechanisms in high phosphorus status plants

Polymer dynamics studied by dynamic light scattering : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University

Appendix 1 and 2 – articles have been removed due to copyright. The articles are available in the print copy held in the library.Theoretical treatments of dynamic properties of polymer solutions are reviewed. Particular emphasis is placed on the discussion of diffusion in polymer solutions. The relationship between the slow diffusion coefficient found by Dynamic Light Scattering (DLS) and the Self Diffusion Coefficient is shown. An introduction to DLS theory is given. The experimental techniques involved in DLS measurements are discussed. Concentration dependencies of the DLS observed slow diffusion coefficient in ternary polymer solutions of polystyrene-poly vinyl methyl ether-solvent have been measured. Solvents used were toluene, carbon tetrachloride and tetrachloroethylene and the polymer molar masses were 110 000 gmol -1 for both polystyrene (PS) and poly vinyl methyl ether (PVME). Solvents were chosen to be very nearly isorefractive with PVME. Toluene is very nearly an equally good solvent for the polymer pair PS and PVME, while tetrachloroethylene is equally poor for both polymers. Carbon tetrachloride is an unequal quality solvent for this polymer pair. The results of these DLS measurements are reported. Four sets of experiments are described. The first is the effect on the relationship between D 1 (the slow mode diffusion coefficient found by DLS) and D s (the self diffusion coefficient) of different mass fractions in the polymer solution. It is found the mass fraction, x, has little effect on the observed diffusion coefficient. Secondly the effect of the polymer-polymer interaction parameter, x, on the relationship between D 1 and D s is investigated. It is found solutions formed with equal quality solvents have D 1 nearly equal to D s . But solutions formed with unequal quality solvents have D 1 considerably less than D s and that these solutions suffer phase separation at lower concentration. Thirdly the effect of polymer molar mass on the relationship between D 1 and D s is investigated. These are found to be in line with those expected from literature. Fourthly the considerable discrepancy between D 1 and D s which is manifest in 110 000 gmol -1 PS/ 110 000 gmol -1 PVME/ toluene solutions at polymer volume fractions greater than 0.4 is investigated. The diffusion coefficient found, D 1 , does not fit a unique concentration power law. Two unique regions are seen with concentration exponents of -11±4 and -14.9±0.7 for the low and high concentration regions respectively. This is found to agree with results found in literature

The Hedonic Price Structure of Faculty Compensation at U.S. Colleges and Universities

Economic theory suggests that the variation in academic salaries across institutions in part reflects compensating differences associated with variation in the levels of local quality of life factors such as environmental quality and the provision of local public services. This paper presents an econometric analysis of the hedonic, or implicit price structure, of faculty compensation at U.S. colleges and universities using data from AAUP merged with data on a host of location-specific characteristics. Quality of life factors are found to be important, accounting for between 7 percent and 12.8 percent of total compensation

More on the Cohort-Component Model of Population Projection in the Context of HIV/AIDS: A Leslie Matrix Representation and New Estimates

This article presents an extension of the cohort component model of population projection (CCMPP) first formulated by Heuveline that is capable of modeling a population affected by HIV. We extend this work by developing the Leslie matrix representation of the CCMPP that greatly facilitates implementation of the model for parameter estimation and projecting. The Leslie matrix also contains information about the stable tendencies of the corresponding population, such as the stable age distribution and time to stability. We validate our reformulation of the model by comparing parameter estimates obtained through maximum likelihood and bootstrap methods to those presented by Heuveline.Africa, AIDS/HIV, cohort component method, estimation, incidence, Leslie matrices, model, prevalence