Auxin transport under saline growth conditions

Zusammenfassung Ein erhöhter Salzgehalt des Substrats hemmt das Koleoptilen-Längenwachstum vonZea mays, onne indessen einen Einfluss auf den Auxintransport und dessen Polarität auszuüben.

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I am thankful to the Pakistan and Danish Atomic Energy Commissions for the award of a fellowship under which the above work was carried out, and to my colleagues at Risø for their help and hospitality.     

Estimation of diffusible auxin under saline growth conditions

Zusammenfassung Der Auxingehalt von Koleoptilenspitzen vonZea mays L.-Keimlingen wird durch saline Wachstumsbedingungen herabgesetzt.

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Part of the work supported by a grant from USDA under the PL-480 research programme.     

Food-induced changes in UV-absorption spectra of isolated chromatin from liver of rats under controlled feeding schedules

Summary We have measured the UV-spectra of liver chromatin extracted at 2 different times of day, corresponding to low or high rate of RNA synthesis from rats maintained under controlled feeding schedules. Results show that food intake does modify the UV-spectra of liver chromatin.     

Food-induced changes in UV-absorption spectra of isolated chromatin from liver of rats under controlled feeding schedules.

We have measured the UV-spectra of liver chromatin extracted at 2 different times of day, corresponding to low or high rate of RNA synthesis from rats maintained under controlled feeding schedules. Results show that food intake does modify the UV-spectra of liver chromatin.     

TRPM6 kinase activity regulates TRPM7 trafficking and inhibits cellular growth under hypomagnesic conditions

The channel kinases TRPM6 and TRPM7 are both members of the melastatin-related transient receptor potential (TRPM) subfamily of ion channels and the only known fusions of an ion channel pore with a kinase domain. TRPM6 and TRPM7 form functional, tetrameric channel complexes at the plasma membrane by heteromerization. TRPM6 was previously shown to cross-phosphorylate TRPM7 on threonine residues, but not vice versa. Genetic studies demonstrated that TRPM6 and TRPM7 fulfill non-redundant functions and that each channel contributes uniquely to the regulation of Mg²⁺ homeostasis. Although there are indications that TRPM6 and TRPM7 can influence each other’s cellular distribution and activity, little is known about the functional relationship between these two channel-kinases. In the present study, we examined how TRPM6 kinase activity influences TRPM7 serine phosphorylation, intracellular trafficking, and cell surface expression of TRPM7, as well as Mg²⁺-dependent cellular growth. We found TRPM7 serine phosphorylation via the TRPM6 kinase, but no TRPM6 serine phosphorylation via the TRPM7 kinase. Intracellular trafficking of TRPM7 was altered in HEK-293 epithelial kidney cells and DT40 B cells in the presence of TRPM6 with intact kinase activity, independently of the availability of extracellular Mg²⁺, but TRPM6/7 surface labeling experiments indicate comparable levels of the TRPM6/7 channels at the plasma membrane. Furthermore, using a complementation approach in TRPM7-deficient DT40 B-cells, we demonstrated that wild-type TRPM6 inhibited cell growth under hypomagnesic cell culture conditions in cells co-expressing TRPM6 and TRPM7; however, co-expression of a TRPM6 kinase dead mutant had no effect—a similar phenotype was also observed in TRPM6/7 co-expressing HEK-293 cells. Our results provide first clues about how heteromer formation between TRPM6 and TRPM7 influences the biological activity of these ion channels. We show that TRPM6 regulates TRPM7 intracellular trafficking and TRPM7-dependent cell growth. All these effects are dependent upon the presence of an active TRPM6 kinase domain. Dysregulated Mg²⁺-homeostasis causes or exacerbates many pathologies. As TRPM6 and TRPM7 are expressed simultaneously in numerous cell types, understanding how their relationship impacts regulation of Mg²⁺-uptake is thus important knowledge.     

Innovators and imitators in innovation diffusion modelling

We examine the theoretical underpinnings of the Bass innovation diffusion model and show that, contrary to the present understanding in the literature, it does not describe the behavioural theory of an innovator-imitator dichotomy within the adopting population as was intended. Rather, this model describes the behaviour of a homogeneous population in which it is assumed that product adoption occurs as a result of exposure to a news source or from the binary interaction between adopters and non-adopters. We provide an alternative framework in which the innovator-imitator explanation of diffusion is explicitly incorporated. In the so-called two-compartment model the innovators and imitators constitute two distinct but interacting subpopulations. However, the added structural complexity cannot be supported by the available diffusion data, resulting in unsatisfactory model estimation results. This suggests that the innovator-imitator population dichotomy assumed to underlie the present understanding of the innovation diffusion process may be inappropriate. Replacing it with the assumption of a homogeneous population could have potentially important implications for new product advertising strategies.     

Gene controlled condensation in individual chromosomes

Summary When cells were irradiated with variable doses of gamma rays, 0.33% showed the appearance of single decondensed chromosomes (SDC) at the moment at which all the other chromosomes of the complement exhibited the normal condensed state corresponding to metaphase stages. Several hypotheses are discussed to explain the origin of SDC. It appears that the most reasonable mechanism to explain our observations is to assume that the process of chromosome condensation is independently controlled in each individual chromosome by a gene/s located in each one of the chromosomes of the complement. A radiation-induced deficiency in one of these genes may produce an impairement in the normal process of condensation of the carrier chromosome which would give rise to SDC.This work was supported by grants from CIC and CONICET.Acknowledgments. I wish to thank Dr J.M. Andrieu who kindly performed the irradiation of the specimens.     

Transport and diffusion of Tau protein in neurons

In highly polarized and elongated cells such as neurons, Tau protein must enter and move down the axon to fulfill its biological task of stabilizing axonal microtubules. Therefore, cellular systems for distributing Tau molecules are needed. This review discusses different mechanisms that have been proposed to contribute to the dispersion of Tau molecules in neurons. They include (1) directed transport along microtubules as cargo of tubulin complexes and/or motor proteins, (2) diffusion, either through the cytosolic space or along microtubules, and (3) mRNA-based mechanisms such as transport of Tau mRNA into axons and local translation. Diffusion along the microtubule lattice or through the cytosol appear to be the major mechanisms for axonal distribution of Tau protein in the short-to-intermediate range over distances of up to a millimetre. The high diffusion coefficients ensure that Tau can distribute evenly throughout the axonal volume as well as along microtubules. Motor protein-dependent transport of Tau dominates over longer distances and time scales. At low near-physiological levels, Tau is co-transported along with short microtubules from cell bodies into axons by cytoplasmic dynein and kinesin family members at rates of slow axonal transport.     

A study of macromolecular diffusion through native porcine mucus

A diffusion chamber technique based on time-lag analysis for the estimation of effective diffusion coefficients of radiolabelled macromolecules of varying molecular weights through native mucus gel is reported. For all solutes studied, a reduction in effective diffusion coefficients was observed with a retardation of solute flux in both aqueus and mucus layers. Over the molecular weight range of solutes investigated (126–186 000 Daltons), a consistent effect of molecular weight was evident with regard to the retarding effect of mucus. No apparent or absolute molecular weight cut-off for macromolecular transfer was exhibited. However, at high molecular weights (>30 000 Daltons) the retardation was greatly enhanced. The results confirm that mucus can be regarded as a gel with finite pores, but that it does not constitute an absolute barrier to even high molecular weight solutes.     

The diffusion coefficient of sodium in barnacle muscle fibres

Zusammenfassung In Muskelfasern der Entenmuschel (Balanus nubilus undBalanus aquila) beträgt der Natrium Diffusions-Koeffizient 2,2×10^–6 cm²/sec.

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Acknowledgment. This work was supported in part by grants from the Office of Naval Research and the National Science Foundation.     

Agar diffusion plates: The recording of experimental data

Zusammenfassung Ein Auswertungsverfahren der Antigen-Antikörper-Analyse mittels der Geléediffusionsmethode vonOuchterlony wird beschrieben.Die Muster des Niederschlags im Versuch werden angefärbt und der Agar-Gelée-Nährboden mit dem Muster wird durch Austrocknung konserviert.So gefärbte und getrocknete Präparate können, visuell geprüft, als Negative oder Diapositive verwendet werden.     

The diffusion of scientific innovations: A role typology

How do scientific innovations spread within and across scientific communities? In this paper, we propose a general account of the diffusion of scientific innovations. This account acknowledges that novel ideas must be elaborated on and conceptually translated before they can be adopted and applied to field-specific problems. We motivate our account by examining an exemplary case of knowledge diffusion, namely, the early spread of theories of rational decision-making. These theories were grounded in a set of novel mathematical tools and concepts that originated in John von Neumann and Oskar Morgenstern's Theory of Games and Economic Behavior (1944/1947) and subsequently spread widely across the social and behavioral sciences. Introducing a network-based diffusion measure, we trace the spread of those tools and concepts into distinct research areas. We furthermore present an analytically tractable typology for classifying publications according to their roles in the diffusion process. The proposed framework allows for a systematic examination of the conditions under which scientific innovations spread within and across preexisting and newly emerging scientific communities.     

Gel diffusion methods for determination of protease and protease-inhibiting activities

Zusammenfassung Es werden zwei Methoden (Diffusion und Elektrophorese in Agarose-Kasein) für quantitative und qualitative Bestimmung von Inhibitoren und Aktivatoren verschiedener Proteasen beschrieben und die Trypsininhibitoren in Kolostrum, Serum und Urin von neugeborenen Schweinen besonders untersucht.

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Financial support: The Foundation of DirectorPåhlsson, Malmö, and the Foundation ofC. F. Lundström. Technical assistance: MrsMarie Adler-Maihofer.     

A study of macromolecular diffusion through native porcine mucus.

A diffusion chamber technique based on time-lag analysis for the estimation of effective diffusion coefficients of radiolabelled macromolecules of varying molecular weights through native mucus gel is reported. For all solutes studied, a reduction in effective diffusion coefficients was observed with a retardation of solute flux in both aqueous and mucus layers. Over the molecular weight range of solutes investigated (126-186,000 Daltons), a consistent effect of molecular weight was evident with regard to the retarding effect of mucus. No apparent or absolute molecular weight cut-off for macromolecular transfer was exhibited. However, at high molecular weights (greater than 30,000 Daltons) the retardation was greatly enhanced. The results confirm that mucus can be regarded as a gel with finite pores, but that it does not constitute an absolute barrier to even high molecular weight solutes.