Three- and four-dimensional imaging techniques are a prerequisite for spatially resolving the form–structure–function relationships in plants. However, choosing the right imaging method is a difficult and time-consuming process as the imaging principles, advantages and limitations, as well as the appropriate fields of application first need to be compared. The present study aims to provide an overview of three imaging methods that allow for imaging opaque, large and thick (>5 mm, up to several centimeters), hierarchically organized plant samples that can have complex geometries. We compare light microscopy of serial thin sections followed by 3D reconstruction (LMTS3D) as an optical imaging technique, micro-computed tomography (µ-CT) based on ionizing radiation, and magnetic resonance imaging (MRI) which uses the natural magnetic properties of a sample for image acquisition. We discuss the most important imaging principles, advantages, and limitations, and suggest fields of application for each imaging technique (LMTS, µ-CT, and MRI) with regard to static (at a given time; 3D) and dynamic (at different time points; quasi 4D) structural and functional plant imaging.
Key message A conspicuous 'finger-like' branching morphology is described for three arborescent Araliaceae species with a focus on the three-dimensional vascular bundle arrangement in leaf insertion and stem-branch attachment regions during ontogenetic development. Abstract The central aim of this study is to gain a deeper understanding of the structure and development in leaf insertions and stem-branch attachments of the arborescent Araliaceae species: Schefflera arboricola, Fatsia japonica and Polyscias balfouriana. Therefore, the vascular bundle arrangement in the leaf insertion zone and ontogenetic development of the stem-branch attachment after decapitation were analyzed, with a special focus on their conspicuous 'finger-like' branching morphology that, to our knowledge, is unique to the Araliaceae. Decortication of adult ramifications allows for a morphological analysis of the woody strands in the stem-branch attachment regions. Via high-resolution microscopy of serial thin-sections and 3D reconstructions, as well as cryotome sections, anatomical analysis was carried out of the course and arrangement of vascular bundles through leaf insertions and later developing ramifications, including a comparative analysis of the different ontogenetic stages. All three species investigated present a 'finger-like' branching morphology with variations in the number and arrangement of the woody strands. Thin-sectioning reveals a conspicuous pattern of leaf trace emergence from the main stem, proceeding into the leaf and the early developing ramifications. Vascular bundle derivatives contribute to the vascular integration of leaves and axillary buds. The described 'finger-like' branching morphology in the investigated Araliaceae species represents a sophisticated mode of vascular integration in leaf insertion zones and developing ramifications. In combination with forthcoming biomechanical experiments, this analysis shall serve as a basis for biomimetic translations into textile technology (fiber-reinforced branched composite materials) and civil engineering (optimization of branched building structures).
Ivy (Hedera helix L., Araliaceae) is an abundant, evergreen, rootclimbing liana, widespread across most of Europe and western Asia (Schnitzler, 1995;Metcalfe, 2005). Its phenotype is mainly characterized by differences in the morphology and growth habits of the juvenile and adult phases (Jones, 1999;Metcalfe, 2005). Typically, juvenile plant stems initially grow as prostrate, plagiotropic shoots on the ground, and this phase can persist for a prolonged time (Wareing and Frydman, 1976). As they make contact with an adequate support, newly developed shoots grow as climbing axes, attached to the support via adventitious roots (Melzer et al., 2010(Melzer et al., , 2012. Juvenile shoots additionally occur in the form of "searchers" or vine tips-i.e., self-supporting tip regions of climbing axes (Gartner and Rowe, 2000). The adult phase of H. helix consists of orthotropic self-supporting shoots, which bear flowers and fruits for reproduction. Besides these differences in growth habits, the ontogenetic change from the juvenile to the adult reproductive phase is distinguished by other vegetative traits, for example, leaf shapelobed in juvenile and entire in adult phase (Stein and Fosket, 1969;Zotz et al., 2011), phyllotaxis-alternate in juvenile and helical in adult phase (Stein and Fosket, 1969;Poethig, 1990), and adventitious roots-present only in the juvenile phase (Stein and Fosket, 1969).Besides the relevance of H. helix to horticulture, including interest in its phase change, research on H. helix has focused mainly on its ecology (
The huge rachis of Raphia matombe is intensely used by local people in Northern Angola for the construction of stools, chairs, shelfs, beds, or baskets. This is not only because it is a charming, fast-growing, renewable, and locally abundant material with a high aesthetic value but also due to its extremely light weight structure. Nevertheless, up to now the anatomical and mechanical features of rachises have hardly been studied, although monocotyledonous stem tissues have been the subject of numerous papers. This study presents an analysis of the rachis of Raphia matombe and its material gradients over its whole length and cross-sectional area. The modulus of elasticity increased from the inner towards the outer layers, whereas no clear axial gradient from the base to the apex was found. However, the specific modulus of elasticity increased from the base to the apex in relation to the density, reaching maximum values of 19.0 MPa/kgm-³. Still, the high anatomical and mechanical heterogeneity of the rachis impede quick and easy processing.
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