Growth-induced mass flows in fungal networks

Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.     

Dynamic Light Regulation of Photosynthesis (A Review)

Regulatory reactions providing the photosynthetic apparatus with the ability to respond to variations of irradiance by changes in activities of the light and the dark stages of photosynthesis within a time range of seconds and minutes are considered in the review. At the light stage, such reactions are related to the changes in both distribution of light energy between two photosystems and probability of nonphotochemical dissipation of absorbed quanta in PSI and PSII. These regulatory reactions operate in a negative feedback mode, thus avoiding overreduction of electron transport chain and minimizing the probability of generation of reactive oxygen species. The crucial role in preventing the generation of reactive oxygen species belongs to dynamic regulation of electron transport activity despite the presence of complex system of their detoxification in chloroplasts. In dark reactions of Calvin cycle, the regulatory responses involve a positive feedback principle being related to redox regulation of activities of several enzymes, which is sensitive to the reduction status of PSI acceptor side. The complex of regulatory reactions based on negative and positive feedback principles provides prolonged functioning of a chloroplast and high stability of photosynthetic activity under various light conditions.     

Mechanisms of madness: evolutionary psychiatry without evolutionary psychology

Delusions are currently characterised as false beliefs produced by incorrect inference about external reality (DSM IV). This inferential conception has proved hard to link to explanations pitched at the level of neurobiology and neuroanatomy. This paper provides that link via a neurocomputational theory, based on evolutionary considerations, of the role of the prefrontal cortex in regulating offline cognition. When pathologically neuromodulated the prefrontal cortex produces hypersalient experiences which monopolise offline cognition. The result is characteristic psychotic experiences and patterns of thought. This bottom-up account uses neural network theory to integrate recent theories of the role of dopamine in delusion with the insights of inferential accounts. It also provides a general model for evolutionary psychiatry which avoids theoretical problems imported from evolutionary psychology.     

Flavonoid synthesis in Petunia hybrida: partial characterization of dihydroflavonol-4-reductase genes

In this paper we describe the organization and expression of the genes encoding the flavonoid-biosynthetic enzyme dihydroflavonol-4-reductase (DFR) in Petunia hybrida. A nearly full-size DFR cDNA clone (1.5kb), isolated from a corolla-specific cDNA library was compared at the nucleotide level with the pallida gene from Antirrhinum majus and at the amino acid level with enzymes encoded by the pallida gene and the A1 gene from Zea mays.The P. hybrida and A. majus DFR genes transcribed in flowers contain 5 introns, at identical positions; the three introns of the A1 gene from Z. mays coincide with first three introns of the other two species. P. hybrida line V30 harbours three DFR genes (A, B, C) which were mapped by RFLP analysis on three different chromosomes (IV, II and VI respectively).Steady-state levels of DFR mRNA in the line V30 follow the same pattern during development as chalcone synthase (CHS) and chalcone flavanone isomerase (CHI) mRNA. Six mutants that accumulate dihydroflavonols in mature flowers were subjected to Northern blot analysis for the presence of DFR mRNA. Five of these mutants lack detectable levels of DFR mRNA. Four of these five also show drastically reduced levels of activity for the enzyme UDPG: flavonoid-3-O-glucosyltransferase (UFGT), which carries out the next step in flavonoid biosynthesis; these mutants might be considered as containing lesions in regulatory genes, controlling the expression of the structural genes in this part of the flavonoid biosynthetic pathway. Only the an6 mutant shows no detectable DFR mRNA but a wild-type level for UFGT activity. Since both an6 and DFR-A are located on chromosome IV and DFR-A is transcribed in floral tissues, it is postulated that the An6 locus contains the DFR structural gene. The an9 mutant shows a wild-type level of DFR mRNA and a wild-type UFGT activity.     

Population structure,spite, and the iterated Prisoner's Dilemma

Evolutionary stability (sensu Maynard Smith: Evolution and the Theory of Games, Cambridge: Cambridge University Press, 1982) of TIT FOR TAT (TFT) under the social ecology of the iterated Prisoner's Dilemma is a function of the number of pure TFT groups (dyads) in the population, relative to the social position of a focal invading defector. Defecting against TFT always raises the defector's relative intragroup fitness; when Axelrod's (Am. Polit. Sci. Rev. 75:306–318, 1981; The Evolution of Cooperation. New York: Basic Books, 1984) Evolutionary stable strategy (ESS) conditions are met, defection also lowers the absolute fitness of the defector. Here the retaliatory (punishing) character of TFT converts defection into spite, permitting pure TFT groups to sufficiently outproduce the defector for the latter's evolutionary suppression. Increasing the relative impact of spiteful defection on a population lowers the range of evolutionary stability for TFT. When individuals participate in multiple dyads, those participating in the greatest number of dyads are most likely to provide a vehicle for the successful invasion of defection. Within social networks, ESS conditions for TFT are thus individual specific. This logic is generalized to the context of an interated n-person Prisoner's Dilemma, providing a cooperative solution conceptually identical with TFT in the two-person game.     

3',5'-Cyclic Adenosine Monophosphate- and Ca2+-Calmodulin-Dependent Endogenous Protein Phosphorylation Activity in Membranes of the Bovine Chromaffin Secretory Vesicles: Identification of Two Phosphorylated Components as Tyrosine Hydroxylase and Protein Kinase Regulatory Subunit Type II

Abstract: Membranes of the secretory vesicles from bovine adrenal medulla were investigated for the presence of the endogenous protein phosphorylation activity. Seven phosphoprotein bands in the molecular weight range of 250,000 to 30,000 were observed by means of the sodium dodecyl sulphate electrophoresis and autoradiography. On the basis of the criteria of molecular weight, selective stimulation of the phosphorylation by cyclic AMP (as compared with cyclic GMP) and immunoprecipitation by specific antibodies, band 5 (molecular weight 60,300) was found to represent the phosphorylated form of the secretory vesicle-bound tyrosine hydroxylase. The electrophoretic mobility, the stimulatory and inhibitory effects of cyclic AMP in presence of Mg²⁺ and Zn,²⁺ respectively, and immunoreactivity toward antibodies showed band 6 to contain two forms of the regulatory subunits of the type II cyclic AMP-dependent protein kinase, distinguishable by their molecular weights (56,000 and 52,000, respectively). Phosphorylation of band 7 (molecular weight 29,800) was stimulated about 2 to 3 times by Ca²⁺ and calmodulin in the concentration range of both agents believed to occur in the secretory tissues under physiological conditions.     

Regulation of choline acetyltransferase/iacZ fusion gene expression in putative cholinergic neurons of drosophila melanogaster

We have analyzed the distribution of putative cholinergic neurons in whole-mount preparations of adult Drosophila melanogaster. Putative cholinergic neurons were visualized by X-gal staining of P-element transformed flies carrying a fusion gene consisting of 5′ flanking DNA from the choline acetyltransferase (ChAT) gene and a lacZ reporter gene. We have previously demonstrated that cryostat sections of transgenic flies carrying 7.4 kb of ChAT 5′ flanking DNA show reporter gene expression in a pattern essentially similar to the known distribution of ChAT protein. Whole-mount staining of these same flies by X-gal should thus represent the overall distribution of ChAT-positive neurons. Extensive staining was observed in the cephalic, thoracic, and stomodeal ganglia, primary sensory neurons in antenna, maxillary palps, labial palps, leg, wing, and male genitalia. Primary sensory neurons associated with photoreceptors and tactile receptors were not stained. We also examined the effects of partial deletions of the 7.4 kb fragment on reporter gene expression. Deletion of the 7.4 kb fragment to 1.2 kb resulted in a dramatic reduction of X-gal staining in the peripheral nervous system (PNS). This indicates that important regulatory elements for ChAT expression in the PNS exist in the distal region of the 7.4 kb fragment. The distal parts of the 7.4 kb fragment, when fused to a basal heterologous promoter, can independently confer gene expression in subsets of putative cholinergic neurons. With these constructs, however, strong ectopic expression was also observed in several non-neuronal tissues. © 1995 John Wiley & Sons, Inc.