197,072 research outputs found
Pinguicula grandiflora (Lentibulariaceae), specie nuova per la flora italiana
No full textThe occurrence of Pinguicula grandiflora subsp. grandiflora, previously unknown for the Italian flora, is reported for the Rutor Valley (Valle d’Aosta, Western Italian Alps). A single population of less than 100 individuals was recorded at 2135 m a.s.l., while no other population was found in the surroundings, where only Pinguicula leptoceras and P. vulgaris grow. The autochthony of the population and the biogeographic significance of the finding are discussed as well as the implications for its conservation
A comparison between different treeline types shows contrasting responses to climate fluctuations
No full textTreeline position is mainly determined by growth season temperature, but the response of treelines to climate warming is not uniform worldwide. We compared treeline structure, dynamics and thermal profile in nearby areas with different treeline type, species composition and bioclimatic conditions. We performed a detailed survey of different treeline types in three areas of Italian Alps and northern Apennines. Every tree individual was recorded along altitudinal transects from the closed forest to the species limit. Treeline structure and dynamics were described through altitudinal limits of tree height, density and age. Data were elaborated by principal components analysis. Temperature regime of the three sites was assessed from homogeneous historical climatic data. Treeline was different in the three areas for species composition, shape and dynamics. Both Alpine sites showed diffuse treeline, but only one showed advancing dynamics. Apennine treeline was abrupt and static, with higher temperature at the tree limit. Our study showed the variable dynamics of treelines within a relatively restricted area and the connection between treeline shape and dynamics. An important role is played by species composition, determined by bioclimatic and historical features. These factors should be taken into account when modelling future treeline dynamics at global scale
Growth forms and age estimation for treeline species
No full textThe correct evaluation of the age of small tree individuals is of great importance in ecological studies, and can be performed if growth units are identifiable even under strong environmental constraints. We aimed to
assess the reliability of age evaluation of small individuals of four species commonly occurring at the treeline in the Alps and the Apennines (N Italy), Picea abies, Pinus
cembra, Larix decidua and Fagus sylvatica. A total of 224 individuals were sampled along an altitudinal gradient up to the treeline. For each species, we assessed the growth
architecture and the appearance of annual growth units; for each individual, age and evaluation uncertainty were estimated.
To verify the estimation a core or a cross-section was obtained. The estimated age was compared with the tree-ring age through linear regression and reduced chi
square test, and the estimation accuracy was evaluated as function of tree age, dimension and environmental parameters. A good estimation was possible for all species, even when loss of vertical growth occurred. The highest error occurred for Larix, the lowest for Pinus; the error was generally correlated with tree age and dimension, and was affected by altitude and geomorphology. Good reduced chi square values were reached considering only the youngest individuals for Fagus and Picea and the smallest for Fagus and Larix; the uncertainty was generally underestimated for Pinus. Even though reliable age estimation could be
obtained, a realistic and species-specific evaluation of the estimation uncertainties is necessary to assess estimation accuracy for ecological studies
Late Holocene soil evolution and treeline fluctuations in the Northern Apennines
No full textThe aim of this study is the reconstruction of Late Holocene soil evolution and environmental changes at the treeline of Northern Apennines (Italy) through field observation, pedoanthracological analysis, soil micromorphology and dendrochronology. Nine soil profiles across the present treeline (c. 1750 m) between 1700 and 2000 m were described. Physical and chemical analyses, and pedoanthracological and micromorphological observations were carried out. Tree ring analysis was also performed to outline recent disturbance events. All soils consisted of two superimposed units. The lowermost unit consisted of a well developed B horizon resulting from intense brunification process, frequently overtopped by a dark Ab horizon. The superficial unit was up to 1 m thick, consisting of colluvium deposits with poorly developed pedogenesis. Below the present treeline, charcoals were observed in the B horizon of the buried soils: Abies and Fagus dominated the anthracological assemblages. Abies charcoals were AMS dated to 790–670 cal BP. Above the treeline, a charcoal assemblage dominated by Abies and Laburnum was found in the buried B horizon. A Laburnum charcoal sample was dated to 3920–3700 cal BP. In the Ab horizon another assemblage dominated by Abies, Laburnum and Vaccinium with abundant insect remains was observed, dated to late Middle Ages. Soil data suggest a recent phase of marked slope instability. Tree ring analysis indicated that this phase occurred at least during the 18th and early 19th century. These analyses, together with previous archaeological evidence, indicate the occurrence of forests well above the present treeline in the Early-Mid Holocene. The lowering of the treeline probably started during Late Holocene, but woody vegetation (open forest or treed heathland) occurred at high altitude until recent times. The colluvial episodes and the burial of paleosols probably took place through successive events during modern times. The dominance or co-dominance of fir at the treeline lasted until historical times. The multi-proxy approach allowed previous archaeological data to be put in a wider context, to give better spatial and temporal extent to treeline fluctuations, and to achieve high resolution for the analysis of the most recent time span
Synthesis of photoactivable probes for the study of glycosphingolipid-protein interactions
No full textSYNTHESIS OF PHOTOACTIVABLE PROBES FOR THE STUDY OF GLYCOSPHINGOLIPID-PROTEIN INTERACTIONS
Giuseppina Brasile,1 Federica Compostella,1 Laura Mauri,2Sandro Sonnino2 and Fiamma Ronchetti1
Dipartimento di Chimica, Biochimica e Biotecnologie per la Medicina, Università di Milano
1Via Saldini 50, 20133-Milano, Italy; 2Via Fratelli Cervi 93, 20190- Segrate (Milano), Italy
E-mail:[email protected]
It is widely accepted that glycosphingolipids (GSLs) at the level of the plasma membrane can affect the biological functions of protein molecules, such as cell surface receptors or transporters. The interactions between GSLs and proteins belonging to specific membrane microdomains, called lipid rafts, could be responsible for the modulation of the functional properties of membrane proteins participating in signal transduction. GSL-protein interactions can be investigated by cell photolabelling experiments using radioactive photoactivable GSLs, which yield, when illuminated, a very reactive intermediate that covalently binds to the molecules in the environment, i.e. proteins.1,2
In this context, we have designed a fatty acid probe with two nitrophenylazide photoactivable groups, one at position 2 and the other at the end of the acyl chain. The conjugation of the fatty acid to a radioactive sphingoglycolipid generates a species to be used for photolabelling experiments. In this way, the simultaneous identification of the proteins belonging to both the leaflets of the plasma membrane, the cytoplasmatic and the extracellular one, will be realized.
Herein we describe a general synthetic strategy to obtain not commercially available α,ω-diamino acids, the synthetic precursors of the labelled fatty acids, which we have applied to the synthesis of a C-18 derivative. Furthermore, it will be described the preparation of a photolabelled radioactive GSL as a case study.
1. Aureli M., Prioni S., Mauri L. Loberto N., Casellato R., Ciampa M.G., Chigorno V., Prinetti, A.; Sonnino S. J. Lipid Res. 2010, 51, 798-808
2. Mauri L., Prioni S., Loberto N., Chigorno V., Prinetti A., Sonnino S. Glycoconj. J. 2004, 20, 11-23
Schede per una Lista Rossa della Flora vascolare e crittogamica Italiana: Pinguicula grandiflora Lam.
No full textA 2,3-carbamate-bearing allyl galactosamine donor for the synthesis of repeating alfa-(1 4)-linked galactosamine units
No full textThe 1,2-cis-linked 2-amino-2-deoxy sugar structure is found in various oligosaccharides of biological importance. The repeating GalpNAc--(1→4)-GalpNAc unit constitutes for example an essential motif incorporated in a range of oligosaccharides, e.g. the repeating unit of the O-antigen moiety of the lipopolysaccharide from Escherichia Coli O142 or Sphaerotilus natans.[1] Vi antigen is instead a linear homopolymer of -(1→4)-linked N-acetyl galactosaminuronic monomers, with a variable degree of O-acetylation at the C3 position. Vi antigen is a capsular polysaccharide found mainly in Salmonella typhi and Salmonella paratyphi C, two serotypes of Salmonella that are responsible for severe infection in humans.[2]
Although in the past years there has been much progress in carbohydrate chemistry, 1,2-cis-selective glycosylation of gluco- or galactosamines is still a challenge. 2-Azidoglycosyl donors, developed many years ago, are still employed for the synthesis of 2-amino-2-deoxy -glycosides, even if glycosylations suffer of low selectivity. Progress in resolving these issues has been made with the development of donors carrying a 2,3-trans-carbamate group, which has attracted much attention as a stereodirecting protection in glycosylation reactions. The fused carbamate ring proved to be a non-participating group and favors the formation of -glycosides. So far, different studies have demonstrated that 2,3-oxazolidinone protected thioglycosides are highly efficient substrates for the synthesis of -linked glycosides.[3]
Herein we report a new 2,3-oxazolidinone protected galactosamine donor, bearing an allyl group at the anomeric position. The allyl group, in addition to its traditional role as a valuable anomeric protecting group, can also be converted into a good leaving group for glycosylation. Thus, the allyl glycoside is first isomerized to the corresponding prop-1-enyl glycoside, which, after chemoselective activation of the anomeric enol ether moiety with a suitable electrophile in the presence of the glycosyl acceptor, leads to the formation of the disaccharide product.[4] This method has the advantage that prop-1-enyl glycoside can be directly derived from allyl glycoside with a variety of facile and highly effective isomerization methods and immediately subjected to glycosylation.
Herein we describe the synthesis of a galactosamine building block, which has the anomeric position protected by an allyl group, and positions 2 and 3 involved in the formation of an oxazolidinone ring. The proper donor and acceptor to perform a -(1→4) glycosylation have been obtained from this common building block. The new 2,3-oxazolidinone protected allyl galactosamine donor has been subjected to glycosylation reactions to study its reactivity and the stereoselectivity of the process.
1. a) Landersjö, C.; Widmalm, G. Biopolymers 2002, 64,283; b) Takeda, M.; Nakamori, T.; Hatta, M.; Yamada, H.; Koizumi,
J.I. Int. J. Biol. Macromol. 2003, 33, 245
2. a) Daniels, E.M.; Schneerson, R.; Egan, W.M.; Szu, S.C.; Robbins, J.B. Infect. Immun. 1989, 57, 31592; b) Heyns, K.;
Kiessling, G. Carbohydr. Res. 1967, 3, 340
3. See for examples: a) Kerns R.J., Zha C., Benakli K.,. Liang Y.Z, Tetrahedron Lett. 2003, 44, 8069; b) Olsson, J. D. M.;
Eriksson, L.; Lahmann, M.; Oscarson, S. J. Org. Chem: 2008, 73, 7181; c) Yang, L.; Ye, X-S. Carbohydr. Res. 2010, 345,
1713; d) Yang, L.; Zhu, J. ; Zheng, X-J. ; Tai, G. ; Ye, X-S. Chem. Eur. J. 2011, 17, 14518
4. Wang, Y.; Zhang, X.; Wang, P. Org. Biomol. Chem. 2010, 8, 4322 and references herein reported.
We acknowledge MIUR-Italy (PRIN 2008) for financial support
Micromorphological evidences of contrasting pedogenetic processes in Alpine paleosols in the central Italian Alps
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