Root tip contact with low-phosphate media reprograms plant root architecture

Plant roots are able to sense soil nutrient availability. In order to acquire heterogeneously distributed water and minerals, they optimize their root architecture. One poorly understood plant response to soil phosphate (P(i)) deficiency is a reduction in primary root growth with an increase in the number and length of lateral roots. Here we show that physical contact of the Arabidopsis thaliana primary root tip with low-P(i) medium is necessary and sufficient to arrest root growth. We further show that loss-of-function mutations in Low Phosphate Root1 (LPR1) and its close paralog LPR2 strongly reduce this inhibition. LPR1 was previously mapped as a major quantitative trait locus (QTL); the molecular origin of this QTL is explained by the differential allelic expression of LPR1 in the root cap. These results provide strong evidence for the involvement of the root cap in sensing nutrient deficiency, responding to it, or both. LPR1 and LPR2 encode multicopper oxidases (MCOs), highlighting the essential role of MCOs for plant development.     

Identification of an oviposition-regulating pheromone in the European grapevine moth,Lobesia botrana (Lepidoptera: Tortricidae)

The oviposition of the European grapevine moth (EGVM)Lobesia botrana can be deterred by an extract of conspecific eggs corresponding to 20 egg equivalents. The reduction of the oviposition behavior is dose-dependent. Nine chemicals have been extracted from the eggs and identified as straight chain fatty acids and esters of fatty acids. A mixture of these rather simple molecules induces the same levels of deterrence as the total extract. It might be possible to use oviposition regulating pheromone in the future for the control of EGVM populations.     

Effects of mistletoe (Viscum album L.) extracts on cultured tumor cells

Summary Bacterially fermented mistletoe preparations (BFMP) were tested on rat hepatoma tissue culture (HTC) cells and human leukemia Molt 4 cells. A dose-dependent inhibition of the growth rate of the cells was observed. For both cell lines, cytostatic concentrations, expressed in weight of fresh plant, were 0.5 mg/ml culture medium for oak BFMP and 1 mg/ml for apple tree BFMP. However, the action of the two preparations was markedly different on each cell line. Non-viable HTC cells were not stained by trypan blue while non-viable Molt 4 cells were fully colored by this reagent. A lysis of cellular membranes of HTC cells was observed by electron microscopy. Furthermore, oak BFMP inhibited the growth of virus transformed 3T3-SV40 cells more than that of non-transformed 3T3 cells. In contrast to BFMP, non-fermented extracts and a purified mistletoe lectin showed a greater inhibition of the growth of Molt 4 cells than of HTC cells. Samples withdrawn at different times during fermentation gradually lost their inhibitory effect on the growth of Molt 4 cells while their action on HTC cells increased up to the 4th day of fermentation. These results are discussed in relation to the cytotoxic substances of mistletoe already characterized.The bacterially fermented mistletoe preparations, named BFMP in the text, were obtained from the Hiscia Institute, CH-4144 Arlesheim, Switzerland, under the name of Iscador. For oak BFMP, mistletoe was fromQuercus petraea Liebl. andQuercus robur L.; for apple tree BFMP fromMalus domestica Borkh.     

Association of tyrosine kinase p56lck with CD4 inhibits the induction of growth through the alpha beta T-cell receptor.

The membrane glycoprotein CD4 enhances antigen-mediated activation of T cells restricted by class II molecules of the major histocompatibility complex (MHC). This positive function has been attributed to the protein tyrosine kinase p56lck (ref. 4), which is noncovalently associated with the cytoplasmic portion of CD4, and is activated on CD4 aggregation. Antigen presentation by MHC class II molecules coaggregates CD4 and the T-cell antigen receptor (TCR alpha beta-CD3). Thus, the mutual specificity of CD4 and TCR alpha beta for the MHC-antigen complex results in the juxtaposition of p56lck and TCR alpha beta-CD3. In contrast, anti-CD4 antibodies can abrogate antigen-induced, as well as anti-TCR-induced T-cell activation, indicating that CD4 might also transduce negative signals. The molecular basis for this opposing function remains unclear. Here we show that the CD4-p56lck complex prohibits the induction of activation signals through the TCR-CD3 complex when not specifically included in the signalling process. This negative effect does not require anti-CD4 treatment, indicating that the induction of distinct negative signals is probably not involved. Rather, the results demonstrate that the CD4-p56lck complex provides prerequisite signals for antigen-receptor-induced T-cell growth and thus characterize a molecular mechanism for functional constraints imposed on T-cell activation by the MHC.     

Clustering and clique partitioning: Simulated annealing and tabu search approaches

We study the application of simulated annealing and tabu search to the solution of the clique partitioning problem. We illustrate the effecveness of these techniques by computational results associated not only with randomly generated problems, but also with real-life problems arising from applications concerning the optimal aggregation of binary relations into an equivalence relation. The need for these approaches is emphasized by the example of a special class of instances of the clique partitioning problem for which the most commonly used heuristics perform arbitrarily badly, while tabu search systematically obtains the optimal solution.

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Résumé Nous étudions dans cet article l'application du recuit simulé et de la méthode de recherche tabou dans la résolution du problème de partitionnement de graphes en cliques. Nous illustrons l'efficacité de ces techniques par des résultats numériques associés soit à des problèmes génerés au hasard, soit à des problèmes réels concernant l'agrégation de relations binaires dans une relation d'équivalence. L'intérêt de ces approches est mis en évidence à travers une classe de problèmes pour lesquels les heuristiques les plus connues ont une performance arbitrairement mauvaise, tandis que la méthode de recherche tabou obtient systématiquement des solutions optimales.

     

La pseudohémoglobine et le catabolisme des composés hémiques

Summary (1) Coupled oxidation by atmospheric oxygen of systems containing hæmoglobin and various reducing agents results in the successive formation of oxyhæm, oxohæm, and pseudohæm from the prosthetic group of hæmoglobin.(2) Of the verdoglobins, sulfhæmoglobin is analogous to oxohæm whereas choleglobin and pseudohæmoglobin are pseudohæms and apparently identical.(3) It is at present impossible to decide whether the green intermediate in the physiological formation of bilirubin is sulfhæmoglobin or pseudohæmoglobin.(4) Part of the bilirubin formed in the body is probably derived from catalase, hæmatin, myoglobin and the cytochromes.

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Conférence principale, présentée à la Société suisse de biologie médicale lors de la 127me Assemblée générale de la Société helvétique des sciences naturelles à Genève, le 31 août 1947.     

Operational and Strategic Decisions in Hospitality. Lessons from an Action Research Process

Systemic Practice and Action Research - The aim of this article is to find measures that reduce personnel costs in a catering company through the optimization of routes and tasks for staff to...     

A Brief Crack of Light?

This is a contribution to an inquiry into the historical meaning of Professor Checkland's soft systems thinking. Heidegger's picture of the present postmodern (or high-modern) epoch provides a context for unfolding that historical meaning. The discussion is focused on the possibility that Checkland's thinking could represent one of the "brief cracks" in the solid neo-instrumental way of appearing (whatever-is-the-case) that characterizes our present epoch.