Iron absorption by excised grapevine roots

Excised roots from cuttings of Vitis vinifera cv. Verduzzo and of two rootstocks V. berlandieri x V. riparia 420 A and V. berlandieri x V. rupestris 1103 P. were tested for iron absorbed from FeEDTA solutions.Absorption rates decreased with time. At 0-2 °C iron absorption was only 50-60 % inhibited. BPDS, a specific chelator for Fe2+, inhibited almost completely absorption showing that reduction from Fe3+ to Fe2+ was needed both at 30 °C and at 0-2 °C. As pH increased from 5 to 8 absorption rate doubled for the cv. Verduzzo, increased about 5 times for 1103 P. and about 10 times for 420 A. Also the apparent kinetic constants of absorption were very different in the three grapevines: both Vmax and Km were in the order: 1103 P.> Verduzzo > 420 A. The presence of a conspicuous part of not exchangeable absorption apparently not dependent on metabolism and the possibility of characterizing cultivars and rootstocks as to nutritional requirements through ion absorption measurements are discussed.Absorption du fer par les racines coupées de la vigneDes racines coupées de x cv. Verduzzo et des porte-greffes V. berlandieri x V. riparia 420 A et V. berlandieri x V. rupestris 1103 P. ont été étudiées quant au fer absorbé de solutions de FeEDTA. La vitesse d'absorption diminue en fonction du temps. A 0-2 °C l'absorption est inhibée seulement de 50--60 %. Le BPDS, chélant spécifique du Fe2+, inhibe presque complètement l'absorption, ce qui démontre que la réduction Fe3+ -> Fe2+ est nécessaire à 0-2 °C ainsi qu'à 30 °C. Lorsque le pH passe de 5 à 8 la vitesse d'absorption se redouble pour le cv. Verduzzo, elle augmente d'à peu près cinq fois pour le 1103 P. et d'environ dix fois pour le 420 A. Les constantes ciné tiques apparentes de l'absorption sont aussi très différentes pour les trois vignes: Vmax  et Km sont toutes les deux de l'ordre de 1103 P. > Verduzzo > 420 A.On discute la présence d'une part remarquable· de l'absorption qui n'est pas échangeable et qui apparemment ne dépend pas du mé tabolisme, ainsi que la possibilité de caractériser les cultivars et les por te-greffes suivant leurs besoins en substances nutritives minérales au moyen de mesurages de l'absorption des ions

Mapping the Evolution of "Clusters": A Meta-analysis

This paper presents a meta-analysis of the “cluster literature” contained in scientific journals from 1969 to 2007. Thanks to an original database we study the evolution of a stream of literature which focuses on a research object which is both a theoretical puzzle and an empirical widespread evidence. We identify different growth stages, from take-off to development and maturity. We test the existence of a life-cycle within the authorships and we discover the existence of a substitutability relation between different collaborative behaviours. We study the relationships between a “spatial” and an “industrial” approach within the textual corpus of cluster literature and we show the existence of a “predatory” interaction. We detect the relevance of clustering behaviours in the location of authors working on clusters and in measuring the influence of geographical distance in co-authorship. We measure the extent of a convergence process of the vocabulary of scientists working on clusters.Cluster, Life-Cycle, Cluster Literature, Textual Analysis, Agglomeration, Co-Authorship

Extraction and preliminary characterization of microsomal (Mg2+ + K+)-ATPase activity of grapevine roots

The microsomal fraction extracted from grapevine roots obtained from woody cuttings possesses Mg2+-dependent, monovalent cation-stimulated ATPase activity. Addition of BSA, PVPP, choline-CI, ethanolamine, glycerol-1-P besides EDTA and DTT to the homogenizing medium as preservative compounds was required in order to achieve a successful isolation.When microsomes were extracted according to HODGES and LEONARD (1974) by homogenizing root tissue in the presence of EDTA and DTT, the enzyme activity exhibited inhibition by Mg2+ only partially relieved by K+, and properties of acid phosphatase rather than ATPase.Cation-stimulated ATPase of microsomes protected during homogenization was further characterized and it showed optimum activity at pH 7.0 in the presence of Mg2+ plus K+ . It was specific as a triphosphatase and Mg2+, rather than other divalent cations, was preferred as a cofactor. As monovalent stimulating cation, only NH4+ could substitute for K+ with equivalent efficiency. The kinetics of K+ stimulation showed a biphasic pattern.Biochemical bases of ion uptake by grapevine seem to be similar to those clarified for annual plants

Clustering dynamics and the location of high-tech firms

The location of productive activities and the emergence of clustering dynamics has been an important research topic since the early works of Weber (1929) and Marshall (1920 and 1921). This thesis aims at relating the processes of firms' location decision and the development of high-tech clusters within an encompassing theoretical and empirical framework. The thesis shows the empirical relevance of the clustering of high-tech sectors and highlights the importance of the issue through the construction and use of an original database on the location of high-tech establishments and employment (at two different geographical levels) in four major industrialised countries. It also contains a critical review of a number of different streams of theoretical and empirical literature which are directly connected, or which have been explicitly put in connection by the author, with the topic of study. In the thesis we develop a composite modelling framework for analysing firms' location decisions and the growth of high-tech clusters, and we empirically test a number of crucial hypotheses in order to draw some guidelines for economic policy. The models presented in the theoretical chapter derive from two different streams of literature. The first derives from the analysis of population ecology, the second from the theory of innovation diffusion. These modelling frameworks have stressed the existence of a critical mass and a maximum dimension of the cluster and their effects on the early and late phases of development within the "life cycle" of a cluster. They also highlighted the role of rank, stock, order and epidemics effects in the location decision of an individual firm which has to decide whether to locate into a developing cluster. The empirical evidence presented in the thesis has focused on the crucial elements of the location process by verifying the empirical relevance of different locational factors, has stressed the relative importance of agglomeration versus scale economies in determining the industrial specialisation of an area, and has measured the competitive effects which arise between the development of different clusters and the synergistic effects which are generated within the cluster. Finally the thesis presents empirical evidence which shows that local competition and industrial specialisation are the key elements for the success of an industrial cluster. A final chapter extracts some crucial policy conclusions on the role of entry versus growth policies, on the different development path that an industrial cluster may follow depending on the excludability condition, presents an original taxonomy of specific policies, applies some of these findings to a brief survey of the phenomenon of science parks and finally produces a series of guidelines for policy makers. The conclusion summarises the results obtained in the thesis and present a brief agenda for future research

Special issue on the 13th international conference on computational management science

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International networks of knowledge flows: an econometric analysis

In this paper we address the manifold nature of knowledge through the analysis of four distinct but complementary phenomena (Internet hyperlinks, European research networks, EPO co-patent applications, Erasmus students mobility) that characterize knowledge as an intrinsic relational structure (directly) connecting people, institutions and (indirectly) regions across five European countries. We study the structure (in terms of density, clustering and centralisation) of these networks through network analysis techniques and test the influence of geographical distance as opposed to sectoral (based on the industrial distribution of the innovative activity) and functional (based on the value of the RSII European technological leadership index) distances in shaping the strength of knowledge relations though a gravitational model. The empirical analysis shows the existence of a polarized centre-periphery hierarchy of European regions that is reflected in the structure of knowledge flows. By using a gravitational model we demonstrate that, far from the claim of the death of distance, geographic distance is still relevant for determining the structure of inter-regional knowledge flows. Functional and sectoral distances play also a crucial role suggesting that knowledge flows easily between similar (according to their scientific, technological and sectoral characteristics) regions. If the EU intends to build a truly European Research Area in which the networking of centres of excellence acts as catalysts for backward areas this target may still be far away

Space Vs. Networks in the Geography of Innovation: A European Analysis

In the last fifteen years, income differences among European Member States have been strongly narrowing while the process has been matched with a widening of the inter-regional variance within single countries. Traditionally, regional economic disparities in Europe have been ascribed to peripherality and/or to a high level of dependence on declining sectors. Nowadays regional disparities can be no longer defined only in terms of statistical differences in the values of standard macroeconomic indicators, but also according to innovative capacities and knowledge endowment. This paper provides an original framework for the interpretation of the existing relationships between innovation process and research activity in Europe and the structural and geographical features shaping the European scientific and technological map. In order to do so, we focus on two knowledge-based relational phenomena: participation in the same research networks (funded by the EU Fifth Framework Programme) and EPO co-patent applications. Using two complementary econometric techniques we try to assess those factors that determine patenting activity, distinguishing structural features, geographical and relational spillovers. Through these variables we measure the intrinsic relational structure of knowledge flows which directly connects people, institutions and, indirectly, regions, across European countries in order to test whether hierarchical relationships based on a-spatial networks between geographically distant excellence centres prevail over diffusive patterns based on spatial contiguity