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1. Quantitative relationship between cholesterol distribution and ordering of lipids in asymmetric lipid bilayers

   https://doi.org/10.1039/d0sm01709d  

   Aghaaminiha, Mohammadreza; Farnoud, Amir M.; Sharma, Sumit (March 2021, Soft Matter)

   null (Ed.)

   The plasma membrane of eukaryotic cells is known to be compositionally asymmetric. Certain phospholipids, such as sphingomyelin and phosphatidylcholine species, are predominantly localized in the outer leaflet, while phosphatidylethanolamine and phosphatidylserine species primarily reside in the inner leaflet. While phospholipid asymmetry between the membrane leaflets is well established, there is no consensus about cholesterol distribution between the two leaflets. We have performed a systematic study, via molecular simulations, of how the spatial distribution of cholesterol molecules in different “asymmetric” lipid bilayers are affected by the lipids’ backbone, head-type, unsaturation, and chain-length by considering an asymmetric bilayer mimicking the plasma membrane lipids of red blood cells, as well as seventeen other asymmetric bilayers comprising of different lipid types. Our results reveal that the distribution of cholesterol in the leaflets is solely a function of the extent of ordering of the lipids within the leaflets. The ratio of the amount of cholesterol matches the ratio of lipid order in the two leaflets, thus providing a quantitative relationship between the two. These results are understood by the observation that asymmetric bilayers with equimolar amount of lipids in the two leaflets develop tensile and compressive stresses due to differences in the extent of lipid order. These stresses are alleviated by the transfer of cholesterol from the leaflet in compressive stress to the one in tensile stress. These findings are important in understanding the biology of the cell membrane, especially with regard to the composition of the membrane leaflets. 

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2. Zamia magnifica (Zamiaceae, Cycadales): A New Rupicolous Cycad Species from Sierra Norte, Oaxaca, Mexico

   https://doi.org/10.3390/taxonomy3020017  

   Pérez-Farrera, Miguel Angel; Gutiérrez-Ortega, José Said; Martínez-Martínez, Mauricio Gerónimo; Calonje, Michael (June 2023, Taxonomy)

   Zamia magnifica (Zamiaceae), a new species endemic to Sierra Norte, Oaxaca, Mexico, is described. Zamia magnifica is characterized by having a rupicolous habit, pendent leaves bearing leaflets that are densely tomentose and pink to caramel in color when emerging, and broad oblong leaflets that are coriaceous in texture with few non-prominent denticulations and ovulate strobili with short (<4 cm) peduncles. It is compared to Z. furfuracea and Z. meermanii, the Mesoamerican Zamia species to which it shares the closest morphological resemblance. 

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3. Revisions to the fossil sporophyte record of Marsilea

   https://doi.org/10.2478/acpa-2019-0005  

   Hermsen, Elizabeth J. (June 2019, Acta Palaeobotanica)

   Abstract The fossil record of Marsilea is challenging to assess, due in part to unreliable reports and conflicting opinions regarding the proper application of the names Marsilea and Marsileaceaephyllum to fossil leaves and leaflets similar to those of modern Marsilea . Specimens examined for this study include material assigned to Marsileaceaephyllum johnhallii , purportedly the oldest fossil record of a Marsilea -like sporophyte from the Lower Cretaceous of the Dakota Formation, Kansas, U.S.A.; leaves and leaf whorls of the extinct aquatic angiosperm Fortuna from several Late Cretaceous and Paleocene localities in western North America; and leaves and leaflets resembling Marsilea from the Eocene Green River Formation, Colorado and Utah, U.S.A. Literature on the fossil record of Marsilea was also reviewed. As a result, several taxonomic changes are proposed. Marsileaceaephyllum johnhallii is reinterpreted as an aquatic angiosperm that shares some architectural features with the genus Fortuna , although Marsileaceaephyllum is here maintained as a distinct genus with an emended diagnosis; under this reinterpretation, the name Marsileaceaephyllum can no longer be applied to sporophyte organs with affinities to Marsileaceae. Three valid fossil Marsilea species are recognized on the basis of sporophyte material that includes characteristic quadrifoliolate leaves and reticulate-veined leaflets: Marsilea campanica (J. Kvaček & Herman) Hermsen, comb. nov., from the Upper Cretaceous Grünbach Formation, Austria; Marsilea mascogos Estrada-Ruiz et al., from the Upper Cretaceous Olmos Formation, Mexico; and Marsilea sprungerorum Hermsen, sp. nov., from the Eocene Green River Formation, U.S.A. The species are distinguished from one another based on leaflet dimensions. Leaves from the Eocene Wasatch Formation, U.S.A., are transferred from Marsileaceaephyllum back to Marsilea , although not assigned to a fossil species. Finally, an occurrence of Marsilea from the Oligocene of Ethiopia is reassigned to Salvinia . A critical evaluation of the fossil record of Marsilea thus indicates that (1) the oldest fossil marsileaceous sporophytes bearing Marsilea -like leaves are from the Campanian; (2) only four credible records of sporophyte material attributable to Marsilea are known; and (3) the oldest dispersed Marsilea spores are known from the Oligocene. 

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4. Zamia multidentata (Cycadales, Zamiaceae), a new arborescent species of Zamia from Acre, Brazil

   https://doi.org/10.11646/phytotaxa.598.1.2  

   SEGALLA, ROSANE; PIMENTA, RICARDO SOARES; CALONJE, MICHAEL (May 2023, Phytotaxa)

   Zamia multidentata is described and illustrated here as a new species from the Amazon basin, state of Acre, Brazil. The new species shares morphological similarities with the Amazonian species Z. hymenophyllidia, and Z. urep, to which it is compared. The combination of slender (to 6.2 cm) caulescent stems, strongly serrulate elliptic leaflets with long acuminate tips and a pronounced adaxially raised longitudinal crease, as well as seed strobili with long peduncles (15 cm +) and flat megasporophylls distinguish the new species Zamia multidentata from all other known species in the genus. 

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5. Within‐leaf variation in embolism resistance is not a rule for compound‐leaved angiosperms

   https://doi.org/10.1002/ajb216447  

   Rimer, Ian M; McAdam, Scott_A M (December 2024, American Journal of Botany)

   Abstract PremiseHydraulic segmentation, caused by the difference in embolism resistance across plant organs, provides a sacrificial layer of cheaper plant organs, like leaves, to protect more costly organs, such as stems, during drought. Within‐leaf hydraulic segmentation has been observed in two compound‐leaved tree species, with leaflets being more vulnerable than the rachis or petiole. Many herbaceous species have compound leaves, and some species have leaflets that are associated with pulvini at the base of the lamina, which could provide an anatomical means of preventing embolism from spreading within a leaf because of the higher number of vessel endings in the pulvinus. MethodsWe used the optical vulnerability method to investigate whether differences in embolism resistance were observed across the leaf tissues of six herbaceous species and one deciduous tree species with compound leaves. Our species selection included both palmately and pinnately‐compound leaved species, one of each with a pulvinus at the base of the leaflets. ResultsWe found considerable variation in embolism resistance across the species measured, but no evidence of variation in embolism resistance within the leaf. In two species with pulvini, we observed major embolism events crossing the pulvinus, spreading from the rachis or petiole into the lamina, and embolizing both tissues at the same water potential. ConclusionsWe conclude that within‐leaf hydraulic segmentation, caused by variation in embolism resistance, is not a universal phenomenon to compound‐leaved species and that the presence of a pulvinus does not provide a barrier to embolism spread in compound leaves. 

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