School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe role of tubulins in secondary cell wall deposition in woody tree species( 2020)Woody trees are an essential source of timber, pulp, paper and biofuel, and advances in biotechnology provide opportunities for the improvement of traits of interest for specific end uses. Cellulose microfibrils, the basic structural component of plant cell walls, are responsible to a large degree for wood mechanical and physiological properties. The angle between the direction of the helical windings of cellulose microfibrils in plant secondary cell walls, or microfibril angle (MFA), plays critical roles in a tree’s development and has become a subject of major interest in forest biotechnology, particularly in detailed studies of the secondary cell wall of xylary (wood) cells. While our knowledge of how exactly the cellulose synthase complex (CSC) acts in response to environmental and genetic cues remains sketchy, guidance of cellulose deposition has been repeatedly accredited to microtubules, a cytoskeleton component formed of protein dimers of alfa- and beta-tubulin. Nevertheless, few studies explore the cytoskeleton roles in secondary cell wall deposition in woody tree species. Reaction wood (RW) develops in response to gravitational stimulus through a series of changes at the cellular and molecular levels. Tubulin genes have been previously reported to be upregulated during RW formation and differences in their expression might lead to differences in microtubule assembly. This differential microtubule organisation might be related to changes on cell wall morphology, including MFA. In this study, cortical microtubule array organisation was therefore assessed in samples from trees forming RW and stems growing upright (normal wood). To further investigate if perturbation of microtubule organisation would impact wood formation, microtubule-interacting drugs were applied to wood tissue depositing SCW in vivo and in vitro. Together, results indicate that tubulins play an essential role in cellulose deposition in the secondary cell wall of woody tree species to ensure appropriate microfibril orientation.
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ItemUse of near infrared spectroscopy to detect non-recoverable collapse caused by tension wood in Eucalyptus globulus( 2012)Eucalyptus globulus is widely planted around the world. The wood is mainly used for fibreboard, paper and firewood. Use for sawn and engineered wood products can be limited because of the development of non-recoverable collapse caused by tension wood, which can severely distort wood surfaces and affect sawing and drying performance, leading to increased processing costs, lower yield (recovery) and thus reduced product value. In tension wood, cellulose content, microfibril angle (MFA), density, and stiffness (MOE) are altered compared to normal wood. The study investigated the calibration and application of near infrared (NIR) spectroscopy to measure these wood properties and detect non-recoverable collapse. Radial, bark to pith, wood cores were sampled from 175 trees in a 20 year old E. globulus silvicultural trial at Tostaree, Victoria, Australia. NIR spectra were measured at 1 mm intervals along the cores after drying to 12% estimated moisture content (EMC). Tangential shrinkage of the cores was measured at 8 points across each core after reconditioning to 12% MC. Spectra were measured on an additional 20 cores that were also analysed using SilviScan-3 to measure MFA, density and MOE, and NIR Partial Least Squares (PLS) Regression calibrations were developed. The calibrations were used to predict wood properties in the 175 cores, which were then related to the measured tangential shrinkage and non-recoverable collapse. NIR-predicted wood properties at points of non-recoverable collapse were consistent with the presence of tension wood (i.e. high cellulose, low MFA, high density and high MOE). Cellulose content and MOE were the best multiple regression predictors of tangential shrinkage. An NIR calibration developed to directly predict tangential shrinkage qualitatively identified zones of high shrinkage, but tended to under-predict measured shrinkage values. Tangential shrinkage, or the incidence of high tangential shrinkage, was not or only weakly correlated with tree size, height to diameter ratio, or lean. Silvicultural treatments (thinning intensity, fertilizer application) did not affect tangential shrinkage or tension wood formation. Generally, the incidence of non-recoverable collapse was greater in the wood grown since age 10 years. The study demonstrated that NIR predicted wood properties can be used to detect non-recoverable collapse caused by tension wood. The methodology has potential use in plantation and log assessment, wood processing, and tree breeding.