Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two coexisting arid‐zone coniferous trees?

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation‐tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller interconduit pits to reduce vulnerability to embolism but more phloem tissue and larger phloem conduits compared with plants that avoid desiccation. These anatomical differences could be expected to increase in response to long‐term reduction in precipitation. To test these hypotheses, we used tridimensional synchroton X‐ray microtomograph and light microscope imaging of combined xylem and phloem tissues of 2 coniferous species: one‐seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.     

Functional morphology of Tethya species (Porifera): 1. Quantitative 3D-analysis of Tethya wilhelma by synchrotron radiation based X-ray microtomography

Rhythmic body contraction is a phenomenon in the Porifera, which is only partly understood. As a foundation for the understanding of the functional morphology of the highly contractile Tethya wilhelma, we performed a qualitative and quantitative volumetric 3D-analysis of the morphology of a complete non-contracted specimen at resolutions of 5.2 and 6.9 μm, using synchrotron radiation based X-ray computed microtomography (SR-μCT). For the first time, we were able to visualize all three major body structures of a complete poriferan without dissection of the shock-frozen, fixed and contrasted specimen in a near-to-life confirmation: poriferan tissue, mineral skeleton and aquiferous system. Applying a ‘virtual cast’ technique allowed us to analyze the structural details of the complete canal structure. Our results imply an extensive re-circulation of water inside the poriferan due to well-developed by-pass-canals, connecting excurrent and incurrent system. Nevertheless, the oscule region is strictly separated from the incurrent system. Based on our data, we developed a hypothetical flow regime for T. wilhelma, which explains the necessity of by-pass canals to minimize pressure boosts in the canal system during contraction. Additionally, re-circulation optimizes nutrient uptake, within small-sized poriferans, like T. wilhelma. Quantitative analysis allowed us to measure volumes and surfaces, displaying remarkable organizational differences between choanosome and cortex, by means of distribution of morphological elements. The surface-to-volume ratio proved to be very high, underlining the importance of the poriferan pinacoderm. We support a pinacoderm-contraction hypothesis.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .Dedicated to Prof. Dr. Michele Sarà (Genova, Italy), in honour of his 80th birthday in 2006.     

Micro‐CT X‐rays do not fragment DNA in preserved bird skins

Most zoological systematics studies are currently based on morphological features, molecular traits or a combination of both to reconstruct animals’ phylogenetic history. Increasingly, morphological studies of museum specimens are using X‐ray computed tomography to visualize internal morphology, because of its ‘non‐destructive’ nature. However, it is not known whether CT can fragment the size of DNA extracted from museum specimens, as has been demonstrated to occur in living cells. This question is of paramount importance for collections based research because X‐rays may reduce the amount of data obtainable from specimens. In our study, we tested whether exposure of museum bird skins to typical CT X‐ray energies (for visualization of the skeleton) increased DNA strand fragmentation, a key factor for the success of downstream molecular applications. For the present study, we extracted DNA from shavings of 24 prepared and dried bird skins (100⁺ years) footpads before and after CT scanning. The pre‐ and post‐CT fragmentation profiles were assessed using a capillary electrophoresis high‐precision instrument (Agilent Bioanalyzer). Comparison of the most common strand length in each DNA sample (relative mass) revealed no significant difference unexposed and exposed tissue (paired t‐test p = 0.463). In conclusion, we found no further quantifiable degradation of DNA strand length under standard X‐ray exposure obtained from our bird skins sample. Differences in museum preservation techniques probably had a greater effect on variation of pre‐CT DNA fragmentation.