Advances on the Visualization of the Internal Structures of the European Mistletoe: 3D Reconstruction Using Microtomography

Abstract

The European mistletoe (Viscum album) is a dioecious epiphytic evergreen hemiparasite that develops an extensive endophyte enabling the absorption of water and mineral salts from the host tree, whereas the exophytic leaves are photosynthetically active. The attachment mode and host penetration are well studied, but little information is available about the effects of mistletoe age and sex on haustorium-host interactions. We harvested 130 plants of Viscum album ssp. album growing on host branches of Aesculus flava for morphological and anatomical investigations. Morphometric analyses of the mistletoe and the (hypertrophied) host interaction site were correlated with mistletoe age and sex. We recorded the morphology of the endophytic systems of various ages by using X-ray microtomography scans and corresponding stereomicroscopic images. For detailed anatomical studies, we examined thin stained sections of the mistletoe-host interface by light microscopy. The diameter and length of the branch hypertrophy showed a positive linear correlation with the age of the mistletoe. Correlations with their sex were only found for ratios between host branch and hypertrophy size. A female bias of about 76% was found. In a 4-year-old mistletoe, several small, almost equally sized sinkers and the connected cortical strands extend over more than 5 cm within the host branch. In older mistletoes, one main sinker was predominant and occupied an increasingly large proportion of the stem cross-section. Bands of vessels ran along the axis of the wedge-shaped haustoria and sinkers and bent sideways toward the mistletoe-host interface. At the interface, the vascular elements of the host wood changed their direction and formed vortices near the haustorium.

Elastic property and fracture mechanics of lateral branch-branch junctions in cacti: A case study of Opuntia ficus-indica and Cylindropuntia bigelovii

“…To test whether the mechanical variables were related to the mass of the lateral branch, we performed a (linear) correlation analysis using Pearson’s correlation coefficient (Pearson’s ρ). The direction (positive or negative) of the correlation is indicated by the sign of Pearson’s ρ, and its absolute value classifies the strength of the correlation, with |ρ| < 0.3 indicating no correlation, 0.3 ≤ |ρ| < 0.5 indicating a weak correlation, 0.5 ≤ |ρ| < 0.7 indicating a medium correlation, and 0.7 ≤ |ρ| indicating a strong correlation (adapted from Kampowski et al, 2017 ; Mylo et al, 2021b ).…”

The Argentine MistletoesLigaria cuneifolia(Ruiz & Pav.) Tiegh (Loranthaceae) andPhoradendron liga(Gillies ex Hook. & Arn.) Eichler (Santalaceae). Thirty Years of Research

“…[25] A comprehensive work has been performed by Barney et al [42] to compile the vast number of hosts for V. album three European subspecies. In a more recent report, Mylo et al [5] indicate that V. album ssp. album has white berries and angiosperms (e. g., Esculus, Malus, Populus and Tilia) as its exclusive hosts.…”

“…[3,4] Viscum album L. is native to Europe and western and southern Asia, but it is also found in the United States as a neophyte. [5] Theophrastus (371-287 BC) was the first to document scientific observations related to mistletoes and specifically, the parasitic role of this plant. [4] According to von Tubeuf, [6] the Greek author pointed out Part of a Special Collection on Bioactive Secondary Plant Metabolites.…”

“…[27] In the case of V. album, the parasite grows endophytically as a cortical strand under the hosts' bark while epicortical roots located on the surface of the host branch are seen in some species of Loranthaceae. [5] Phoradendron species form a holdfast, cortical strand that runs along the host branch axis and sinkers and a xylem-xylem connection is established via water-conducting vessels that run along the sinker [36] but V. album seems to grow fewer sinkers and extend further along the host branch axis. [5] As pointed out by Mathiassen et al, [27] stem parasites are the ones that should be regarded as true mistletoes.…”

“…[5] Phoradendron species form a holdfast, cortical strand that runs along the host branch axis and sinkers and a xylem-xylem connection is established via water-conducting vessels that run along the sinker [36] but V. album seems to grow fewer sinkers and extend further along the host branch axis. [5] As pointed out by Mathiassen et al, [27] stem parasites are the ones that should be regarded as true mistletoes. Agelanthus, Amyema, Ligaria, Phthirusa, Psittacanthus, Scurrula, Struthanthus Santalaceae [a] Antidaphne, Eubrachion, Lepidoceras Amphorogynaceae [b] Dendromyza, Dendrotrophe, Dufrenoya, Phacellaria Viscaceae Arceuthobium, Dendrophthora, Ginalloa, Korthalsella, Notothixos, Phoradendron, Viscum…”