Structure et composition chimique élémentaire de quelques coquilles d'œufs de dinosaures du Jurassique et du Crétacé d'Amérique du Nord

Structure and chemical composition of some dinosaur eggshells from Jurassic and Cretaceous of North America. Microstructural analyses of some dinosaur eggshells from Jurassic and Cretaceous sites of North America show a large variability in the state of preservation. Outer and inner surfaces are often hidden by secondary deposits, and the tubercles or ridges and spherolites are not visible. Chemical analyses show that some fragments are strongly enriched in Si. There is a good correlation between the preservation of the structures and the chemical contents. Diagenetic processes are different from those described in the samples from Southern France.     

Distribution,Circulation et Evolution des Eléments Nutritifs,en Particulier du Phosphore Minéral,dans l'Etang de Berre. Influence des Eaux Duranciennes.

Distribution, Circulation and Evolution of Nutrients, Inorganic Phosphorus Particularly, in Lake Etang de Berre. Influence of River Durance Waters Nutrients, phosphorus in particular, were studied at five locations in the brackish lake Etang de Berre's waters in order to examine vertical and horizontal distributions, seasonal and annual evolutions, and circulation. The phosphorus cycle was surveyed taking into account the extensive freshwater input from the river Durance which was recently deviated into the Etang de Berre. Of primary importance is the phenomenon of trapped nutrients in the deepest layer of the lake, corresponding to the occurrence of a pycnocline (halocline). This layer is in a steady state characterized by anoxic conditions and shows denitrification processes.     

Influence du Régime Alimentaire sur la Composition Chimique Elémentaire de Nebalia bipes (Crustacea,Leptostraca)

Effect of Diet on the Elementary Chemical Composition of Nebalia bipes (Crustacea, Leptostraca) Changes in carbon, hydrogen and nitrogen contents of Nebalia bipes were studied under different artificial feeding conditions. Using a multifactor ANOVA, highly significant variations were observed according to diet. C:N ratio, which was 4.99 ± 0.31 in control animals, exhibited extreme values of 3.96 ± 0.09 and 5.52 ± 0.49. From a trophic point of view, the results demonstrate the large possibilities of N. bipes to exploit very different resources. The variability of its elementary chemical composition expressed in C:N ratio is compared to other generalist species.     

Biosynthèse de la cellulose bacterienne deutériée: étude par R. M. N. du taux d'incorporation et de la localisation du deutérium

The use of the NMR spectra (250 MHz) of cellulose triacetate allows the determination of the percentage of deuterium bonded to each of the six carbon atoms of the monomer residue (except for H_?1 and one of the protons bonded to C₆ where the signals overlap). Deuterated derivatives of D -glucose and/or deuterated water were used for the biosynthesis of bacterial cellulose by Acetobacter xylinum. Analysis of NMR spectra of acetylated samples gives the following results. About 90% of the protons linked to C₁ and C₆ come from the D -glucose used in the nutrition medium, whereas 10% are exchanged with other sources of protons. Over 40% of the protons linked to C₂, C₃, C₄, and C₅ arise from the water of the nutrition medium. Discrepancies between results of biosynthesis from deuterated water and from deuterated D -glucose can only be explained if more than one enzymatic process is involved in the biosynthesis of bacterial cellulose.     

Effets d'un régulateur de croissance d'insectes,le fénoxycarbe,sur la diapause du psylle du poirier Cacopsylla pyri

The nature of the responses of the sheep blowfly Lucilia sericata Meigen (Diptera: Calliphoridae) to carrion odours and carbon dioxide were examined in a windtunnel in the laboratory and the attractiveness of carrion-bait was examined in the field. In the wind tunnel, gravid 9-day-old females increased both the number and duration of their flights, in response to carrion odours. In addition, linear velocity was reduced and the sinuosity of flight increased in the presence of these odours. With 3-day-old females, the response to carrrion odour depended on previous exposure to proteinaceous material. Protein deprived females showed kinetic responses to carrionodour which were similar to those of gravid females. No such changes were observed in protein-fed females. No responses to CO₂ were observed. In the field, the importance of olfactory cues in bait location was demonstrated by the absence of L. sericata from sticky targets lacking an odour bait. Increased bait concentration did not affect the age, sex ratio or ratio of L. sericata to other Lucilia spp. caught, but did increase the numbers caught. Analysis of the reproductive status of females caught, indicated that a greater number of gravid females were caught than expected, while a lower number of females in the final stages of vitellogenesis were caught than expected. The results show that the responses of L. sericata to odours are complex, and are dependent on both exogenous and endogenous stimuli, the latter including the stage of ovarian development.     

Influence du substrat sur la répartition des Crustacés stygobies interstitiels du Haut-Atlas occidental

The interstitial stygobiont distributions of two rivers in the western High Atlas is analyzed in relation with sediment granulometry. Sixteen stations were sampled along the rivers N'Fis and Zat and their tributaries. Granulometry analyses were performed. Three grain size sediment types constitute the subterranean biotopes and reflect the local hydrodynamical conditions. The main rivers stations, which undergo frequent natural or human disturbances, are characterized by a high content of fine sediment; in contrast, tributaries stations show coarse and well-classified sediments due to more stable biotopes and more regular hydrological conditions. The 92 taxa group 28 stygobiontic species with 11 crustaceans species. PCA. based on 16 stations, three faunistic richness indexes and three granulometric factors display a high correlation between coarse grain-size content and the richness of stygobiontic taxa. A high silt content both limits the interstitial taxa and excludes crustaceans that occur only in coarse gravels. The granulometric preferenda in the species of the amphipod genus Metacrangonyx and isopods Microcerberus. Microcharon and Typhlocirolana are shown on Shepard triangular diagrams. Cohabitation of several species of the same genus could be explained by the occupancy of different ecological niches resulting from the grain-size proportion.     

Le genre d'échinide s dans les dans les localités du Pliocène et du Pléistocène d'Emilie (Italie du Nord)

The study of well-preserved Pliocene and Pleistocene s from Emi from Emilia is used to analyze the morphological variations of Mediterranean populations, to depict the relationship between fasciole shape and other morphological characteristics and to describe previously unpublished pedicellar valves. These new data allow to be two species distinguished: s (Müller) a (Müller) and s Pomel; six s Pomel; six species closely related to s are synonymi are synonymized: s and it and s Pomel, i Pomel, i and itS. and s Checchia-R Checchia-Rispoli, x Simonelli a Simonelli and the recent species from Mediterranean, s Mortensen Mortensen. s can be disti can be distinguished from s by its hear by its heart-shaped subanal fasciole, when the s one is reni one is reniform. Moreover, the frontal groove of s is deeper, t is deeper, the primary tubercles of the interambulacra 1 and 4 are less numerous, the petals are shorter and narrower, the labrum is shorter. As far as pedicellariae are concerned, the jags of the large tridentate ones are stronger and the base of the globiferous ones is bigger. Palaeoecological observations on outcrops of the Stirone River, in Parme region, show similar environmental affinities between fossil populations and recent populations from Mediterranean. The s fossils fossils seem to be preserved within their life environment, that is to say in shore sandy substrates.

Résumé

L'étude d'un groupe de spécimens bien conservés appartenant au genre Spatangus, trouvés, dans des localités pliocènes et pléistocènes de l'Émilie, permet d'exposer l'étendue de la variation dans les populations fossiles méditerranéennes, de rechercher les relations entre la forme du fasciole sous-anal et les autres caractères morphologiques et de décrire les valves des pédicellaires, qui n'étaient pas connues jusqu'alors. Ces nouvelles données conduisent à reconnaître deux espèces différentes : s (Müller) e (Müller) et s Pomel ; six Pomel ; six espèces voisines de s doivent prob doivent probablement tomber en synonymie : s et itS et s Pomel, i Pomel, i et itS. a et s Checchia-R Checchia-Rispoli, x Simonelli e Simonelli et l'espèce vivant actuellement en Méditerranée, s Mortensen Mortensen. Des observations paléoécologiques sur un échantillon fossile récolté sur les bords de la rivière Stirone près de Parme montrent des affinités bionomiques semblables chez les populations fossiles et celles vivant en Méditerranée.     

Teneurs en éléments majeurs et traces de spirulines (Arthrospira platensis) originaires de France,du Tchad,du Togo,du Niger,du Mali,du Burkina-Faso et de République centrafricaine

Data on mineral elements in spirulinas being limited, we analyzed macrominerals and trace elements of samples from France and Africa. Spirulinas cultivated in France have a composition in macromineral elements similar to those of the literature. The entire contents of trace elements are low. Unlike marine cyanobacteria, they do not concentrate rare-earth elements. Spirulina harvested in Chad has high levels in macrominerals and trace elements, due to traditional drying and harvesting methods. Rare-earth element levels are attributed to this pollution and not to their concentration in spirulinas, because rare-earth element normalized profiles of spirulina are strictly parallel to those of ouadis mud and very different from those of ouadis water. Despite the sometimes high content of total As, normal water consumption in Chad presents no health problems. Spirulinas grown in Togo, Niger, Mali, Burkina-Faso and Central African Republic have chemical compositions similar to those of Chad spirulinas, but with a lower content of macromineral and trace elements, reflecting a lower mineral pollution. Rare-earth element normalized patterns dismiss an aeolian pollution and the pollution is rather of pedological origin. They show no toxicity problem except spirulinas from Burkina-Faso, whose Pb content is too high. The variability of composition of spirulinas can be largely attributed to the mineral pollution of the samples. Significant levels of rare-earth elements sometimes found in the literature reflect this pollution.     

Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

Réponses électroantennographiques de deux parasitoïdes Ichneumonidés,Diadromus pulchellus et D. collaris,aux odeurs de végétaux,du phytophage-hôte Acrolepiopsis assectella et du partenaire sexuel

Résumé Chez Diadromus pulchellus WSM et D. collaris Gr., Hyménoptères Ichneumonidés parasitoïdes spécialistes des nymphes d'A. assectella lépidoptère inféodé aux Allium, des EAG sont enregistrés en réponse à l'odeur du poireau sain ou attaqué par les larves du phytophage, odeurs actives par ailleurs sur leur comportement locomoteur (cinèses). Le thiosulfinate de dipropyle (Ti-P₂) très spécifique et abondant dans les Allium, et instable, est le mieux perçu par les deux parasitoïdes mais n'a aucun effet locomoteur chez D. pulchellus contrairement aux disulfures et thiosulfonates, plus stables et moins spécifiques. Les propriétés de l'acétate d'éthyle, actif sur l'antenne des deux parasitoïdes, et sur la locomotion de D. pulchellus expliqueraient en partie les activités biologiques du poireau attaqué sur ces parasitoïdes. Des EAG sont aussi obtenus chez les deux espèces avec l'odeur du chou et de composés soufrés plus ou moins spécifiques des Crucifères. Le thiocyanate de méthyle (TCN-M), le plus actif sur l'antenne et seul efficace sur le comportement locomoteur (de D. pulchellus), expliquerait en partie l'installation reconnue de D. collaris sur Plutella maculipennis spécialiste des Crucifères et rend celle de D. pulchelles vraisemblable.L'odeur des larves de dernier stade d'A. assectella est seule efficace sur l'antenne et la locomotion des femelles de D. pulchellus. Les mâles de ce dernier réagissent (EAG, locomotion) à des odeurs de cocons de l'hôte et particulièrement à ceux occupés par une femelle de leur espèce.     

Conséquences du traitement préalable par le précocène 2 sur les réponses du criquet migrateur,Locusta migratoria, à un apport en hormone juvénile exogène

Un apport unique de 10 g d'hormone juvénile 1, réalisé chez des criquets du dernier stade larvaire à corpora allata intacts ou préalablement soumis à une application de precocène 2, provoque, à la mue suivante, l'apparition d'individus dont les caractéristiques sont intermédiaires entre celles du dernier stade larvaire et celles de l'imago. Cependant, les criquets traités par le précocène 2 présentent des variations phénotypiques plus prononcées, se traduisant par un maintien accru des caractéristiques larvaires. Les études ultrastructurales montrent que les corpora allata dégénèrent rapidement sous l'action des 400 g de précocène 2.

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Summary In fifth instar locusts, with intact corpora allata or previously subjected to precocene 2 action, a single injection of 10 g juvenile hormone 1 leads, at the next molt, to the appearance of individuals displaying characters ranging from the typical larval to the typical imaginal ones. But, unexpectedly, the phenotypic variations are more marked in the precocene 2 treated locusts, and are typified by an increased retention of larval characters. Electron microscopic studies indicate that the use of 400 g of precocene 2 rapidly leads to the degeneration of the corpora allata.

     

Les Diatomées des Sédiments Holocènes du Bassin du Lac Afrera (Giulietti) (Afar Septentrional,Ethiopie). Essai de Reconstitution de l'Évolution du Milieu

The calcareous holocene sediments found in the outlying areas around Lake Afrera (Ethiopia) contain diatoms in abundance, some of which seem to be new species. Qualitative and quantitative studies, with informatory treatment of the data, allow us to reconstruct the main characteristics of the sedimentation conditions and their variations in the course of time. During periods of warm and humid climatic conditions, the basin was progressively filled up with alkaline, lightly saline and quickly eutrophic water. At this time, the lake covered an area of 250 km². This period occurred from 9800 years B. P. to around 7800 years B. P. It was followed by a short interruption, showed by important modifications in the diatom flora and a marked increase in the depth and salinity of the water. It has been hypothesized that this phenomenon had a tectonic origin. Soon thereafter, the previous ecological conditions reappeared. In the following period the lake began to dry up and the diatoms began to disappear. The present-day highly saline Lake Afrera is all that remains of this large holocene water area. Diatoms of the Holocene Sediments in the Afrera Lake Basin. (Northern Afar, Ethiopia). Reconstruction of the Environmental Evolution     

Mesure d'une activité métabolique in vivo. Cas du catabolisme purique chez le Pharbitis nil

In vivo measurement of a metabolic activity. — Purine catabolism in Pharbitis nil cotyledons. To study the influence of light and darkness on the level of purine degradation, an in vivo method of measuring this catabolic pathway has been developed. Cotyledon discs of Pharbitis nil were incubated in an aqueous solution of hypoxanthine-8-¹⁴C. This purine base was first oxidized by a NAD⁺ dependent xanthine dehydrogenase. The metabolic flow was expressed either by the quantity of products (xanthine + uric acid + allantoin + allantoic acid) or by the rate of hypoxanthine degradation in the discs. This easy, reproducible and very sensitive technique of measurement has been investigated with respect to several variables including tissue quantity, length of incubation time, hypoxanthine and NAD⁺ concentrations, and pH. The quantity of products varied proportionally with the tissue quantity but the catabolic rate was not linked to this. The best conditions of measurement were to incubate discs for at least 60 min in distilled water containing only hypoxanthine-8-¹⁴C at low concentrations (below 0.25 mM). The values obtained represent the actual in vivo level of the studied metabolic pathway. The NAD⁺ concentration within the tissue does not seem to be a limiting factor for hypoxanthine degradation, the hypoxanthine concentration itself appears to be the only limiting factor in endogenous purine catabolism.     

Les Invertébrés Planctoniques du Lac Volvi (Macédoine,Grèce). The Planktonic Invertebrates of Lake Volvi (Macedonia,Greece)

The planktonic invertebrates found in Lake Volvi are presented. There are 26 species of Rotifera, 1 Bivalve (larva), 13 Cladocera, 5 Copepoda, 1 Branchiura and 1 Diptera (larva). Many of these are new for the Greek fauna, though they are common in Europe. The discovery of some other species extends the knwown bounds of their geographical distribution in Greece. The lack of large-sized forms is considered to be due to strong predation by Alosa macedonica. (Pisces, Clupeidae). A comparison is given to the planktonic invertebrates of other Balkan lakes. There is a remarkable similarity with the fauna of Lake Doïrani.     

Ammotragus europaeus : une nouvelle espèce de Caprini (Bovidae, Mammalia) du Pléistocène inférieur à la grotte du Vallonnet (France)

Ammotragus europaeus: a new species of Caprini (Bovidae, Mammalia) from the Early Pleistocene site of Vallonnet (France). A new species of the genus Ammotragus is described from the assemblage III of Vallonnet cave (Roquebrune-Cap-Martin, Alpes-Maritimes, France). These remains were interpreted as Ovis, but the re-study of the dental collection from the site and a first study of a partial braincase with the basal internal region of the horn-core pedicels, the parietals, the temporals, and the basisphenoid bones, show anatomical differences with the Caprini genera Ovis, Capra, and Hemitragus and the Ovibovini genus Soergelia. At the opposite, anatomical similarities of the Vallonnet material to the extant North-African Caprini genus Ammotragus are observed. The age of Vallonnet cave is dated by palaeomagnetic techniques at about 1.0 Ma. Teeth remains similar to the Vallonnet species have been found at Fuente Nueva-3 (Orce, Andalusia, Spain). To cite this article: P.-É. Moullé et al., C. R. Palevol 3 (2004).     

Estuary–ocean connectivity: fast physics,slow biology

Estuaries are connected to both land and ocean so their physical, chemical, and biological dynamics are influenced by climate patterns over watersheds and ocean basins. We explored climate‐driven oceanic variability as a source of estuarine variability by comparing monthly time series of temperature and chlorophyll‐a inside San Francisco Bay with those in adjacent shelf waters of the California Current System (CCS) that are strongly responsive to wind‐driven upwelling. Monthly temperature fluctuations inside and outside the Bay were synchronous, but their correlations weakened with distance from the ocean. These results illustrate how variability of coastal water temperature (and associated properties such as nitrate and oxygen) propagates into estuaries through fast water exchanges that dissipate along the estuary. Unexpectedly, there was no correlation between monthly chlorophyll‐a variability inside and outside the Bay. However, at the annual scale Bay chlorophyll‐a was significantly correlated with the Spring Transition Index (STI) that sets biological production supporting fish recruitment in the CCS. Wind forcing of the CCS shifted in the late 1990s when the STI advanced 40 days. This shift was followed, with lags of 1–3 years, by 3‐ to 19‐fold increased abundances of five ocean‐produced demersal fish and crustaceans and 2.5‐fold increase of summer chlorophyll‐a in the Bay. These changes reflect a slow biological process of estuary–ocean connectivity operating through the immigration of fish and crustaceans that prey on bivalves, reduce their grazing pressure, and allow phytoplankton biomass to build. We identified clear signals of climate‐mediated oceanic variability in this estuary and discovered that the response patterns vary with the process of connectivity and the timescale of ocean variability. This result has important implications for managing nutrient inputs to estuaries connected to upwelling systems, and for assessing their responses to changing patterns of upwelling timing and intensity as the planet continues to warm.     

Common trade‐offs between xylem resistance to cavitation and other physiological traits do not hold among unrelated Populus deltoides ×Populus nigra hybrids

We examined the relationships between xylem resistance to cavitation and 16 structural and functional traits across eight unrelated Populus deltoides×Populus nigra genotypes grown under two contrasting water regimes. The xylem water potential inducing 50% loss of hydraulic conductance (Ψ₅₀) varied from ?1.60 to ?2.40 MPa. Drought‐acclimated trees displayed a safer xylem, although the extent of the response was largely genotype dependant, with Ψ₅₀ being decreased by as far as 0.60 MPa. At the tissue level, there was no clear relationship between xylem safety and either xylem water transport efficiency or xylem biomechanics; the only structural trait to be strongly associated with Ψ₅₀ was the double vessel wall thickness, genotypes exhibiting a thicker double wall being more resistant. At the leaf level, increased cavitation resistance was associated with decreased stomatal conductance, while no relationship could be identified with traits associated with carbon uptake or bulk leaf carbon isotope discrimination, a surrogate of intrinsic water‐use efficiency. At the whole‐plant level, increased safety was associated with higher shoot growth potential under well‐irrigated regime only. We conclude that common trade‐offs between xylem resistance to cavitation and other physiological traits that are observed across species may not necessarily hold true at narrower scales.     

Capacité photosynthétique du phytoplancton de la couche aphotique dans le fjord du Saguenay. Photosynthetic Capacity of Deep Phytoplankton in the Saguenay Fjord

Abnormally high chlorophyll values have been observed in the deep layer of the Saguenay Fjord, Québec, Canada. Experiments were conducted to assess the capability of this darkened phytoplankton to photosynthetize upon reillumination. It was found that photosynthetic capacity is well retained by deep phytoplankton of the Saguenay, as shown by relatively high production rates, a low tidal variability of these rates and very high P : B ratios.     

Interaction entre la cochenille du manioc Phenacoccus manihoti et ses différentes plantes-hôtes: étude de la teneur de la sève en acide aminé et en sucre

Résumé L'analyse (acides aminés et sucres) d'extrait de feuille, de 5 variétés de manioc (Manihot esculenta), du Faux caoutchouc (Hybride deM. esculenta x M.glaziovii), du Poinsettia (Euphorbia pulcherrina) et du Talinum (Talinum triangularae), caractérisés par différents degrés de résistance par antibiose à la cochenille du manioc (Phenacoccus manihoti (Mat. Ferr.)) (Homoptera: Pseudococcidae), a été réalisée sur des extraits obtenus par centrifugation du matériel foliaire. Les teneurs en acids aminés, très différentes d'une plante à l'autre, apparaissent aussi importantes entre les variétés de l'espèce manioc qu'entre les différentes espèces végétales avec respectivement un rapport de variation de 4,5 et 5,5. De même, les teneurs en sucres (exprimées en équivalent saccharose), sont très différentes d'une plante à l'autre avec un rapport de variation de 1 à 33 entre les deux extrêmes, si l'on ne considère que l'espèceM. esculenta, il n'est plus que de 3,5.Des différences dans les proportions relatives des acids aminés libres d'extrait de feuille sont observées aussi bien entre les variétés de manioc qu'entre les espèces végétales. Cependant pour toutes les plantes étudiées l'acide glutamique, la glutamine, l'ethanolamine, et l'alanine représentent près de 50% des acides aminés de l'extrait de feuille; l'acide aspertique, l'asparagine et la sérine près de 20% tandis que la tyrosine, la méthionine, l'isoleucine, la leucine et la lysine sont présents en très faibles pourcentages.Le degré de résistance à la cochenille du manioc des différentes plantes-hôtes n'a pu être relié, ni à la teneur de leur extrait de feuille en acides aminés et en sucres, ni à leur composition relative en acides aminés. Il n'a pu être non plus relié au rapport Sucres/Acides aminés Nos résultats suggèrent que des caractéristiques biochimiques autres que celles étudiées dans ce travail interviennent dans les mécanismes de résistance vis-à-vis de la cochenille du manioc.

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Summary The levels of sugars and amino acids were determined in leaf extracts from a number of plants showing different levels of resistance to the cassava mealybug,Phenacoccus manihoti (Homoptera: Pseudococcidae). There were five varieties of cassava (Manihot esculenta), as well as a hybrid obtained by crossingM. esculenta andM. glaziovii, poinsettia (Euphorbia pulcherrina) and talinum (Talinum triangularae). The variability in the total concentration of amino acid concentrations was as great between varieties of cassava as at the species level. In contrast, there was much less variability in the concentration of sugars at the intervarietal that at the interspecies level.While there were both intervarietal and interspecific differences in the amino acid composition, glutamic acid, glutamine, ethanolamine and alanine represented nearly 50% of the total in all plants examined. Aspartic acid, asparagine and serine accounted for approximately 20%, while tyrosine, methionine, isoleucine, leucine and lysine are present at low levels.The different levels of resistance noted in the different plants were not associated with the concentrations of either amino acids or sugars, the ratios of sugar/amino concentrations or the amino acid compositions obtained from leaf extracts. This suggests that other aspects of plant chemistry confer resistance to cassava mealybugs.

     

Séquences tripeptidiques typiques du collagène: étude conformationnelle quantique

Theoretical and experimental investigations on the conformations of synthetic polytripeptides, with Gly-R₂-R₃ general repetitive sequence, are of great interest for the comprehension of the factors wich contribute to the triple helix stabilization.Using appropriate molecules as models, we have investigated by the PCILO method the intrinsic conformational possibilities of each « in situresidue for the following cases: Gly-imino-imino, Gly-amino-imino and Gly-imino-amino which represent the most important sequences occuring in the primary structure of collagen. The computations were carried out taking into account the two pyrrolidine ring puckerings and the preferential side-chains orientations.Extending our previous work concerning the isomeric polytripeptides Gly-X-Pro and Gly-Pro-X with X {Pro, Phe} we have studied the cases of X {Ala, Ser}. In this brief communication, we present a preliminary synthesis of these recent results.