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    The disordered- and ordered-state structures of κ-carrageenan : an X-ray scattering, molecular dynamics, and density-functional theory study : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University, Palmerston North, New Zealand
    (Massey University, 2022) Westberry, Benjamin
    κ-carrageenan is a biopolymer extracted from marine algae. It exists in aqueous solution, at high temperatures and/or low salt concentrations as a ‘disordered-state’, and at low temperatures and in the presence of certain salts as an ‘ordered-state’. The transition between disordered- and ordered-states involves molecular structural changes, which are essential to its interesting viscoelastic properties that are routinely exploited in a plethora of applications. Despite this, the molecular conformations of the disordered- and ordered-states, as well as the details of the transitional pathway connecting them, remain a source of contention. While decades of research have amassed a vast trove of information on the disorder-order transition, an atomistic understanding of the structure in solution has remained elusive. This study takes advantages of recent advances in computational capabilities in order to simulate κ-carrageenan solutions on length scales of ∼10 nm over μs time scales, and thus develop atomistic models of the disordered- and ordered-states. Both models are used to calculate wide-angle X-ray scattering profiles, and these are subsequently validated by comparison to data obtained at a synchrotron facility. The models will be further explored using density functional theory to calculate their expected optical rotation behaviour, which finds that the formation of double-helices from single chains is able to explain the increase in optical rotation measured experimentally when transitioning from the disordered to ordered-state. Structural analysis of both experimentally-verified models find the disordered-state to have a significant amount of residual helical secondary-structure, whereas the ordered-state is mostly double-helical. Crucially, simulations show that the ordered-state arises spontaneously from the so-called disordered-state at a rate dependant on salt concentration, without prior uni-molecular changes. The findings of this research are the most detailed model of the disorder-order transition to-date, and demonstrate that the existing paradigm of a ‘coil-to-helix’ transition is in need of revision.
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    Evaluation of seaweed extract and two resistant peach varieties for control of peach leaf curl disease (Taphrina deformans) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science at Massey University
    (Massey University, 1989) Blakeley, Joanne Elizabeth
    The effectiveness of seaweed extracts for the control of peach leaf curl (Taphrina deformans) on Red Diamond nectarines was compared with a copper fungicide and with two varieties of peach claimed resistant to peach leaf curl. Field and laboratory tests were undertaken. The peach varieties Winiata Gold and Gordon's Glory were tolerant to peach leaf curl under conditions of severe disease pressure. They were more effective than seaweed extracts in the control of the fungus. The seaweed extract, Seagro, did not control peach leaf curl disease on Red Diamond nectarines planted in a randomised complete block design in Palmerston North in 1987. No evidence of fungicidal properties was found in the second year of the study when there were eleven infection periods suitable for the leaf curl fungus. In this season both seaweed extract and copper oxychloride fungicide were ineffective. In laboratory experiments, the seaweed extracts Response, Ecklonia and Carpophyllum had no effect on T. deformans growth. In vitro, T. deformans grew well on a media of potato dextrose agar and 1% peptone. Satisfactory growth was also obtained on whole potato extract but the ease of preparation of the commercial agar mix made it the best option for this study. T. deformans grew more slowly on malt agar and peptone and did not grow at all on Czapek media. Acidifying the PDA media to a pH of 3.5 did not significantly affect T. deformans growth. Quick laboratory tests for comparison of fungal growth on different fungicide/seaweed extract amended PDA plates were compared. The measurement of light absorbance of cell suspensions with a spectrophotometer was quicker than counting cells using a haemacytometer. The petri dish zonal inhibition technique was useful for quantifying the effectiveness of some fungicides against T. deformans. Streptomycin, Benlate, and Rovral had little or no effect on the growth of Taphrina deformans in vitro but Saprol inhibited growth.