Abstract
BackgroundLeaf venation traits are important for many research fields such as systematics and evolutionary biology, plant physiology, climate change, and paleoecology. In spite of an increasing demand for vein trait data, studies are often still data-limited because the development of methods that allow rapid generation of large sets of vein data has lagged behind. Recently, non-destructive X-ray technology has proven useful as an alternative to traditional slow and destructive chemical-based methods. Non-destructive techniques more readily allow the use of herbarium specimens, which provide an invaluable but underexploited resource of vein data and related environmental information. The utility of 2D X-ray technology and microfocus X-ray computed tomography, however, has been compromised by insufficient image resolution. Here, we advanced X-ray technology by increasing image resolution and throughput without the application of contrast agents.ResultsFor 2D contact microradiography, we developed a method which allowed us to achieve image resolutions of up to 7 µm, i.e. a 3.6-fold increase compared to the industrial standard (25 µm resolution). Vein tracing was further optimized with our image processing standards that were specifically adjusted for different types of leaf structure and the needs of higher imaging throughput. Based on a test dataset, in 91% of the samples the 7 µm approach led to a significant improvement in estimations of minor vein density compared to the industrial standard. Using microfocus X-ray computed tomography, very high-resolution images were obtained from a virtual 3D–2D transformation process, which was superior to that of 3D images.ConclusionsOur 2D X-ray method with a significantly improved resolution advances rapid non-destructive bulk scanning at a quality that in many cases is sufficient to determine key venation traits. Together with our high-resolution microfocus X-ray computed tomography method, both non-destructive approaches will help in vein trait data mining from museum collections, which provide an underexploited resource of historical and recent data on environmental and evolutionary change. In spite of the significant increase in effective image resolution, a combination of high-throughput and full visibility of the vein network (including the smallest veins and their connectivity) remains challenging, however.
Highlights
Leaf venation traits are important for many research fields such as systematics and evolutionary biology, plant physiology, climate change, and paleoecology
Without the network complexity achieved in angiosperms, photosynthetic capacity and evapotranspiration rates would not have reached the levels required to establish and maintain, for example, the highly productive megathermal tropical rainforests [3, 4]. The discovery of such linkages during the last years has led to increasing demands for leaf venation data to Schneider et al Plant Methods (2018) 14:7 corroborate previous findings and to detect new relationships in a broad array of research fields ranging from plant physiology and systematics to macroecology and paleoecology
Paradermal sections using a handheld razor blade with subsequent bleaching are an alternative, even though destructive method [10, 11], but are challenging for many species and only allow the removal of small areas of leaf tissue. None of these methods provide the required acceleration of the preparation process, nor the versatility to be applicable to leaves from herbarium specimens, which are an invaluable and still underexploited resource for leaf venation data and associated environmental information, but should not be subjected to invasive methods
Summary
Leaf venation traits are important for many research fields such as systematics and evolutionary biology, plant physiology, climate change, and paleoecology. Vein networks are one of the key structures of leaves and fulfil a series of important functions, including the transport of water and carbohydrates, providing mechanic The discovery of such linkages during the last years has led to increasing demands for leaf venation data to Schneider et al Plant Methods (2018) 14:7 corroborate previous findings and to detect new relationships in a broad array of research fields ranging from plant physiology and systematics to macroecology and paleoecology. Paradermal sections using a handheld razor blade with subsequent bleaching are an alternative, even though destructive method [10, 11], but are challenging for many species and only allow the removal of small areas of leaf tissue None of these methods provide the required acceleration of the preparation process, nor the versatility to be applicable to leaves from herbarium specimens, which are an invaluable and still underexploited resource for leaf venation data and associated environmental information, but should not be subjected to invasive methods. X-ray technology is both fast and morphologically non-destructive (i.e. disregarding deleterious effects at the molecular level) and, has the advantage of being appropriate for leaf samples from herbarium collections
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