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1. Cycadodendron galtieri gen. nov. et sp. nov.: An Early Permian Gymnosperm Stem with Cycadalean Affinity

   https://doi.org/10.1086/727458  

   Luthardt, Ludwig; Rößler, Ronny; Stevenson, Dennis (November 2023, International Journal of Plant Sciences)

   Tomescu, Alexandru M.F. (Ed.)

   Premise of research: In our modern flora, the Cycadales represent one of the oldest-known gymnosperm clades, with their evolutionary roots tracing back to the late Paleozoic. Their radiation and wide distribution in the Mesozoic are well documented by numerous fossils. In contrast, the fossil record of late Paleozoic forms is restricted to a few specimens, thus leaving open questions on the origin and early evolution of cycads. A petrified stem with cycadalean affinity has been found in Saxony (central-eastern Germany) in Holocene gravel deposits of the Zwickauer Mulde river as a result of fluvial transportation from its original lower Permian locality. Methodology: The specimen was sectioned transversely, radially, and tangentially. Its provenance was clarified by comparing fossil woods of various localities in the upstream catchment area. Samples of these localities were exposed to ultraviolet light of different wavelengths, revealing distinctive fluorescence patterns related to specific geochemical conditions during the fossilization process. Plant anatomical studies were performed by macroscopic and microscopic documentation, including photo scanning, microscopic photography, and anatomical measurements. Pivotal results: Cycadodendron galtieri gen. nov. et sp. nov. originates from the Chemnitz Fossil Lagerstätte, an autochthonous floral assemblage of early Permian age (291 Ma; Sakmarian–Artinskian) that has been buried and conserved by pyroclastics in a geological instant. Several anatomical characteristics provide evidence for its cycadalean affinity: (1) a wide pith with numerous scattered medullary bundles, (2) a pith-peripheral vascular system with endarch primary xylem bundles, (3) at least nine successive vascular segments with secondary xylem and phloem, (4) araucarioid-type pitting of secondary xylem tracheids, and (5) primary rays and medullary bundles traversing the vascular segments. Conclusions: Cycadodendron galtieri gen. nov. et sp. nov. provides insights into stem anatomical characteristics of the oldest-known cycads, for example, revealing that polyxyly was an early-derived feature in cycad evolution. Its provenance reveals that the arborescent but generally small taxon was part of intramontane forested landscapes thriving on a well-drained mineral substrate in an alluvial plain setting and experiencing seasonally dry paleoclimate. 

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2. Palaeocupressinoxylon uniseriale n. gen. n. sp., a gymnospermous wood from the upper Permian of Central Taodonggou, southern Bogda Mountains, northwestern China

   https://doi.org/10.1016/j.palwor.2019.06.002  

   Wan, M.L.; Yang, W.; Wang, J. (January 2020, Palaeoworld)

   A silicified wood, Palaeocupressinoxylon uniseriale n. gen. n. sp., is described from the upper Permian of the Central Taodonggou section,Turpan–Hami Basin, Xinjiang Uygur Autonomous Region, northwestern China. Multidisciplinary data including U–Pb ID–TIMS zircon dating,vertebrate and invertebrate biostratigraphic, and cyclostratigraphic correlation from current and previous studies indicate that the fossil bearinginterval is Wuchiapingian (late Permian) in age. The pycnoxylic wood consists of thick-walled tracheids and parenchymatous rays. It is characterizedby separated uniseriate radial tracheidal pits, uniseriate ray cells, and cupressoid cross-field pitting. The absence of growth rings in the wood,together with the occurrence of Argillisols, Gleysols, and Histosols above and below the fossil interval, suggests that a stable landscape and aperennially humid climate prevailed in the Taodonggou area during the Wuchiapingian. 

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3. Determination of ring-level dynamic modulus of elasticity in loblolly pine from measurements of ultrasonic velocity and specific gravity

   https://doi.org/10.1093/forestry/cpac063  

   Dahlen, Joseph; Auty, David; Eberhardt, Thomas L.; Schimleck, Laurence; Pokhrel, Nawa Raj; Achim, ed., Alexis (February 2023, Forestry)

   Abstract Wood stiffness (modulus of elasticity, MOE) is an important property for conifer wood, with the variability in MOE largely being a function of both the specific gravity (SG) (wood density) and the angle of the microfibrils within the S2 layer of longitudinal tracheids. Rapid analysis techniques can be used together to quantify MOE; while SG can be determined with relative ease, this is not the case for microfibril angle, requiring expensive X-ray diffraction equipment. An alternative to microfibril angle is to measure longitudinal acoustic velocity. The objective of this study was to measure and then model the within tree variation in dynamic MOE (MOEdyn) by developing the methodology to measure ultrasonic velocity (USV) in radial samples from pith to bark using ultrasonic frequencies (>20 kHz). A total of 419 pith-to-bark radial strips, collected from multiple height levels in 92 loblolly pine (Pinus taeda) trees, were processed to obtain matching SG (2mm longitudinal) and USV (8.2-mm longitudinal) samples. Ring-by-ring SG was measured using X-ray densitometry and time-of-flight USV was measured at a 10-mm radial resolution from pith to bark. A subset of samples was sent to SilviScan to determine microfibril angle using X-ray diffraction. The relationship between microfibril angle and USV was strong (R2 = 0.91, RMSE = 2.6°). Nonlinear mixed-effects models were then developed to predict radial variation in SG, USV and MOEdyn. Fixed effects for the models, which included cambial age and height of disk within tree, had pseudo R2 values of 0.67 for SG (RMSE = 0.051), 0.71 for USV (RMSE = 316 m/s) and 0.69 for MOEdyn (RMSE = 1.9 GPa). When combined with SG measurements from X-ray densitometry, USV measurements from pith to bark are a powerful tool for assessing variability in wood stiffness. 

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4. Brachypodium distachyon MAP20 functions in metaxylem pit development and contributes to drought recovery

   https://doi.org/10.1111/nph.16383  

   Smertenko, Tetyana; Turner, Glenn; Fahy, Deirdre; Brew‐Appiah, Rhoda A. T.; Alfaro‐Aco, Raymundo; de Almeida Engler, Janice; Sanguinet, Karen A.; Smertenko, Andrei (February 2020, New Phytologist)

   Summary Pits are regions in the cell walls of plant tracheary elements that lack secondary walls. Each pit consists of a space within the secondary wall called a pit chamber, and a modified primary wall called the pit membrane. The pit membrane facilitates transport of solutions between vessel cells and restricts embolisms during drought. Here we analyzed the role of an angiosperm‐specific TPX2‐like microtubule protein MAP20 in pit formation usingBrachypodium distachyonas a model system.Live cell imaging was used to analyze the interaction of MAP20 with microtubules and the impact of MAP20 on microtubule dynamics. MAP20‐specific antibody was used to study expression and localization of MAP20 in different cell types during vascular bundle development. We used an artificial microRNAs (amiRNA) knockdown approach to determine the function ofMAP20.MAP20 is expressed during the late stages of vascular bundle development and localizes around forming pits and under secondary cell wall thickenings in metaxylem cells. MAP20 suppresses microtubule depolymerization; however, unlike the animal TPX2 counterpart, MAP20 does not cooperate with the γ‐tubulin ring complex in microtubule nucleation. Knockdown ofMAP20causes bigger pits, thinner pit membranes, perturbed vasculature development, lower reproductive potential and higher drought susceptibility.We conclude thatMAP20may contribute to drought adaptation by modulating pit size and pit membrane thickness in metaxylem. 

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5. Limited effects of xylem anatomy on embolism resistance in cycad leaves

   Jiang, Guo-Feng; Qin, Bo-Tao; Pang, Yu-Kun; Qin, Lan-Li; Pereira, Luciano; Roddy, Adam B (July 2024, New phytologist)

   • Drought-induced xylem embolism is a primary cause of plant mortality. Although ~70% of cycads are threatened by extinction and extant cycads diversified during a period of increasing aridification, the vulnerability of cycads to embolism spread has been overlooked. • We quantified the vulnerability to drought-induced embolism, pressure-volume curves, in situ water potentials, and a suite of xylem anatomical traits of leaf pinnae and rachises for 20 cycad species. We tested whether anatomical traits were linked to hydraulic safety in cycads. • Compared to other major vascular plant clades, cycads exhibited similar embolism resistance to angiosperms and pteridophytes but were more vulnerable to embolism than non-cycad gymnosperms. All 20 cycads had both tracheids and vessels, the proportions of which were unrelated to embolism resistance. Only vessel pit membrane fraction was positively correlated to embolism resistance, contrary to angiosperms. Water potential at turgor loss was significantly correlated to embolism resistance among cycads. • Our results show that cycads exhibit low resistance to xylem embolism and that xylem anatomical traits–particularly vessels–may influence embolism resistance together with tracheids. This study highlights the importance of understanding the mechanisms of drought resistance in evolutionarily unique and threatened lineages like the cycads. 

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