L'excursion en Provence (Sud-Est de la France) de la Societe Internationale de Phytosociologie

Conclusions La Provence apparaît, en définitive, comme un territoire des plus variés aux divers points de vue climatique, édaphique, biotique.C'est une région d'autant plus favorable aux études phytosociologiques que la variété des milieux s'y double d'une brutalité souvent étonnante des contrastes, conduisant à la juxtaposition parfois extrêmement précise d'associations végétales très différentes, dont les limites peuvent alors être cartographiquement figurées avec une très suffisante exactitude.Cette vigueur des contrastes est surtout marquée en Provence calcaire où les divers termes des séries évolutives dérivant du Quercetum ilicis climacique ou y conduisant, se juxtaposent souvent sans transition de quelque importance.Les contrastes sont cependant moins accusés en Provence cristalline et dans la Basse-Vallée du Rhône.En Crau comme en Camargue, les associations végétales se juxtaposent souvent en ceintures parallèles ou concentriques — elles s'individualisent alors facilement —, souvent en mosaïques irrégulières, au grè des variations locales des deux facteurs déterminants: l'eau en Crau, le sel en Camargue.En Provence cristalline, les Maures étant surtout faites de roches se délitant facilement (grès, micaschistes et phyllades) sous un climat chaud et humide, le sol se reconstitue facilement après sa destruction partielle par l'érosion; les contrastes sont moins tranchés; on observe des transitions nombreuses entre les divers termes des séries évolutives, dont les limites ne peuvent être fixées qu'approximativement. Nous y avons notamment abordé le problème de la forêt de chêne-liège dont la signification est loin d'être connue, non seulement en Provence mais sur toute l'étendue de son aire, en Afrique du Nord, en Espagne, au Portugal, en France méridionale, en Italie et dans les Iles de la Méditerranée occidentale.En provence cristalline, il est certain que l'homme en a considérablement assuré l'extension, directement pour l'utilisation du liège, indirectement par la coupe et le feu, et, en bien des points de la Méditerranée occidentale, le chêne-liège se présente comme une essence cultivée.Par ailleurs rien ne permet de mettre en doute son indigénat. Mais, dans les conditions actuelles du milieu en Provence cristalline:le chêne vert est possible partout;dans les conditions naturelles de la concurrence vitale le chêne vert l'emporte sur le chêne-liège.Si, donc, la forêt originelle a comporté le chêne-liège, ce ne peut être qu'à l'état d'essence secondaire et seulement en quelques points où une faible couverture forestière lui permettait de cohabiter avec le chêne vert.Les documents cartographiques au I/20 000^e tendent à montrer, d'aileurs que, dans les conditions naturelles de reconstitution de la forêt ou dans le peuplement naturel des sols neufs (Isthme de Giens), c'est la chênaie de chêne vert, non la chênaie de chêne-liège qui s'installe.Les grandes unités phytosociologiques de la Provence paraissent être maintenant convenablement définies floristiquement; il convient donc d'en poursuivre l'étude écologique, dont certains aspects seulement les plus apparents—mais peut-être pas toujours les plus actifs-, ont été abordés.Notons enfin la démonstration faite, au cours de l'excursion, de la parfaite application possible des méthodes phytosociologiques à l'étude des groupements marins et la nécessité, particulièrement apparente en milieu marin, de considérer tout autant les animaux que les végétaux. L'avenir est bien aux biocénoses dont les grands traits ont été mis en évidence, quant à la côte de la presqu'île de Giens, par Roger Molinier.Reçu par la rédaction le 20. XII. 1958.avec la collaboration de ROGER MOLINIER pour la partie marine et G. TALLON pour la Camargue.     

Operon fusions of Mu d1(Ap,lac) to thel-proline biosynthetic genes ofescherichia coli K-12

Operon fusions to the promoter of either theproA,proB, orproC genes of the proline biosynthetic pathway were obtained by the use of the Mu d1(Ap,lac) bacteriophage. These fusions were further stabilized by transformation with plasmid pGW600 containing the wildtype Mu repressor gene or by transduction with phage pSG1. The level of -galactosidase in the fusion strains was not affected by the presence of exogenously addedl-proline or high concentrations of NaCl in the growth medium. A Tn5 insertion nearproBA increased -galactosidase expression 140- to 200-fold in strains carrying theproA-lac andproB-lac fusions, but the level of this enzyme was unaltered in strains carrying theproC-lac fusion. The Tn5 insertion increased intracellular proline concentrations 8- to 10-fold, suggesting that mechanisms other than allosteric inhibition may regulate proline biosynthesis, but did not confer osmotolerance to cells growing in a medium with a high concentration of salt.     

In vitro localization of the protein synthesis defect associated with experimental phenylketonuria

We have used a cell-free system derived from hamster brain to investigate protein synthesis during experimental phenylketonuria. In such a system the elongation inhibitor emetine impeded translation in extracts derived from both treated and control animals. On the other hand the initiation inhibitor aurintricarboxylic acid showed no effects on protein synthesis activity of treated hamsters, although it was severely inhibiting in controls. This suggests that initiation is the altered step in brain protein synthesis failure consecutive to phenylketonuria.Abbreviations ATA aurintricarboxylic acid - HPA hyperphenylalaninaemia (hyperphenylalaninaemic) - PHE phenylalanine - PKU phenylketonuria (phenylketonuric) - PR polyribosome     

Morphological and molecular characterization of fertile tetraploid somatic hybrids produced by protoplast electrofusion and PEG-induced fusion between Lycopersicon esculentum Mill. and Lycopersicon peruvianum Mill.

Summary Mesophyl protoplasts of two genotypes of cultivated tomato (Lycopersicon esculentum Mill.) and one of its wild relative species (Lycopersicon peruvianum Mill.) were fused by using electrofusion and polyethyleneglycol-induced fusion. Forty-three fertile tetraploid somatic hybrid plants, each deriving from separate calli, were recovered from both fusion procedures. Electrofusion appeared more efficient than chemical fusion for the production of somatic hybrids. These plants appeared morphologically similar, whatever the fusion procedure and tomato genotype. They had intermediate leaf, inflorescence, and flower morphology. After self-pollination, the hybrids set fruit of intermediate size and color. The hybrid nature of these plants was confirmed by isoelectric focusing of the Rubisco small subunits used as nuclear markers. L. esculentum and L. peruvianum were distinguished by means of two chloroplast markers: CF1-ATPase subunit as analyzed by isoelectro-focusing and ct DNA restriction patterns. All hybrids displayed both ct markers of only one parent with no biased transmission. Mitochondrial (mt) DNAs were prepared from flower buds by using miniaturized CsCl gradients. Preliminary analysis indicated that mt genomes from the hybrids all differed from those of both parents. mt DNA Sall restriction enzyme analysis revealed that all but two hybrids contained one novel fragment of 13.5 kb. Gene mapping experiments showed that the mt apocytochrome b and ATPase subunit 9 homologies in the somatic hybrid mt DNA resembled L. esculentum and L. peruvianum, respectively; the mt nad5 probe distinguished at least four distinct patterns in the hybrids. These results indicated that mt DNA rearrangements involving intergenomic recombinations occurred through protoplast fusion. A greater mt DNA polymorphism was induced with chemical fusion than with electrofusion.     

Implication of Pectic Components in Cell Surface Interactions between Tomato Root Cells and Fusarium oxysporum f. sp. radicis-lycopersici: A Cytochemical Study by Means of a Lectin with Polygalacturonic Acid-Binding Specificity

Aplysia gonad lectin, a polygalacturonic acid-binding lectin isolated from the sea mollusc Aplysia depilans, was complexed to colloidal gold and used for localizing polygalacturonic-acid-containing molecules in tomato root tissues infected with Fusarium oxysporum f. sp. radicis-lycopersici (FORL). Colonization of host tissues by FORL was associated with striking wall modifications including disruption and even loss of middle lamellae. According to the labeling pattern observed in host wall areas adjacent to fungal penetration channels, it is likely that FORL pectolytic enzymes act through localized wall degradation. The release of polygalacturonic acid-rich wall fragments and the accumulation of polygalacturonic acid-containing molecules in some altered phloem cells were frequently observed and considered to be specific host reactions to fungal attack. The heavy deposition of such molecules at strategic sites such as wall oppositions and intercellular spaces provides support to their implication in the plant defense system. The possible interrelation between polygalacturonic acid-containing molecules and other polymers such as lignin and phenolic compounds remains to be investigated further. The role of these molecules in host-pathogen interactions is discussed in relation to plant defense.     

Polyamines, hydroxycinnamoylputrescines, and root formation in leaf explants of tobacco cultivated in vitro: effects of the suicide inhibitors of putrescine synthesis

In vitro formation of roots is obtained directly, without intermediate growth of callus, from foliar explants of a tobacco (Nicotiana tabacum) plant cultured on Murashige and Skoog medium containing IAA. Auxin-induced root formation was accompanied by significant changes in hydroxycinnamoylputrescine levels. Increasing levels were found in leaf explants during the first 14 days in culture; this was followed by a sharp decline after 20 days. Early changes in putrescine conjugates were detected in leaf explants before the visible appearance of roots. An early and transitory accumulation of hydroxycinnamoylputrescines was observed in the roots. Free polyamines (putrescine, spermidine, and spermine) in leaf explants and roots were always at a low level and only small changes in their concentrations were observed, α-dl-difluoromethylarginine and α-dl-difluoromethylornithine, specific, irreversible inhibitors of arginine decarboxylase and ornithine decarboxylase, respectively, inhibited putrescine accumulation and root initiation and reduced the fresh and dry weights of leaf explants. These effects were reversed by free putrescine or hydroxycinnamoylputrescines. The results reported here suggest that hydroxycinnamoylputrescines are associated with root formation. The relationship among free polyamines, hydroxycinnamoylputrescines, cell division, and root formation is discussed.     

Synergistic inhibition of Escherichia coli aspartate transcarbamylase by CTP and UTP: binding studies using continuous-flow dialysis.

The allosteric control of Escherichia coli aspartate transcarbamylase (ATCase) involves feedback inhibition by both CTP and UTP, although it is only in the presence of CTP that UTP appears to inhibit the activity of the enzyme. In order to better understand the parts played by both pyrimidine nucleotides in this synergistic inhibition, binding studies were performed by continuous-flow dialysis and ultracentrifugation methods. The results obtained show that UTP binds to ATCase in the absence of CTP. Nevertheless, this binding does not induce any inhibition unless CTP is present. The mutual influence of CTP and UTP on their respective binding constants suggests that they bind to the same regulatory sites. However, the results obtained cannot be satisfactorily explained by a simple competition between the nucleotides, and it is shown that reciprocal affinity enhancements play a fundamental role. CTP enhances the affinity of UTP for the regulatory sites 80-fold, and conversely, UTP enhances the affinity of CTP 5-fold. Interestingly, the isolated regulatory subunits bind the two pyrimidine nucleotides following the same pattern as the entire enzyme. These observations indicate that the synergistic inhibition mechanism relies entirely on interactions between the two adjacent allosteric sites which belong to the same regulatory dimer.