Investigating the mechanisms of the formation of spiral grain and interlocked grain in wood. (2020)
Type of ContentTheses / Dissertations
Thesis DisciplinePlant Biotechnology
Degree NameMaster of Science
PublisherUniversity of Canterbury
Spiral grain is the deviation of grain angle away from the stem axis, where the grain forms a helical array around the pith. In radiata pine, trees are initially straight- grained but develop a left-handed twist in the first year of growth that increases in severity in the several subsequent growth rings until reaching a maximum angle that is often above 5o from vertical. After this, grain angles slowly decrease and sometimes shift to right-handed (Cown et al., 1991; Harris, 1989). Most northern hemisphere gymnosperms follow this pattern in which grain is initially left-handed (Harris, 1989), and they retain this left-to-right pattern when grown in the southern hemisphere suggesting that spiral grain formation is under genetic control. Genetic control of grain direction is also supported by the partial heritability of grain angle severity in radiata pine (Gapare et al., 2007).Suggestions have, however, been made that southern hemisphere gymnosperms develop an initially right-handed twist before shifting back towards the left (Edwards et al., 2007; Kubler, 1991; Ohkura, 1958), although these suggestions are based on observation of only two Australian species, and none that are indigenous to New Zealand. It has been further suggested that any difference in spiralling direction between trees originating in different hemispheres might be caused by an interaction between predominant wind directions, and growth of the young trees towards the sun (Gapare et al., 2007).
While serial sectioning approaches are traditionally used to observe cell development, they are time consuming in both technique and data analysis and can generally only be applied to smaller samples. Additionally, 3D reconstructions can be confounded by section distortion, misalignment or tearing, severely reducing the accuracy of the model generated. A novel method for measuring grain in whole stems of young trees that utilises X-ray microtomography (μCT) has been developed. This technique allows whole stem sections of young trees to be imaged and reconstructed, thereby allowing in-situ tracheid angle measurements. Using this technique, several northern hemisphere species grown in New Zealand were analysed and no changes were observed in the grain patterns from the change in hemisphere suggesting that spiral grain is under strong genetic control. Additionally, the analysis of southern hemisphere gymnosperms with this technique demonstrated that the left-handed to right-handed pattern is common among all coniferous species regardless of hemisphere
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