Lichens toGunnera — with emphasis onAzolla

Summary N₂-fixing cyanobacteria occur in symbiotic associations with fungi (ascomycetes) as lichens and with a few green plants. The associated cyanobacterium is always a species ofNostoc orAnabaena. Only a small number of plant genera are involved but there is a remarkable range of host diversity. Associations occur with several bryophytes (e.g.Anthoceros, Blasia, Cavicularia), a pteridophyte (Azolla), cycads (nine genera includingMacrozamia andEncephalartos) and an angiosperm (Gunnera). Except forGunnera, where the cyanobacterium penetrates the plant cells, the cyanobacteria are extracellular with specialized morphological modifications and/or structures of the host plant organs providing an environment which facilitates interaction with the prokaryote.Salient aspects of current knowledge pertaining to the establishment, perpetuation, and functioning of the individual symbioses are summarized. Where possible this includes information concerning recognition and specificity, mode(s) of infection, morphological modifications/adaptations of the host plant and a synopsis of morphological, physiological and biochemical changes common to the symbiotic cyanobacteria. The latter encompasses heterocyst frequencies, enzymes involved in ammonia assimilation, photosynthetic capability and metabolic interaction with the host.TheAzolla-Anabaena symbioses, which have potential agronomic significance as an alternative nitrogen source and maintain continuity with the endophyte through the sexual cycle, are emphasized.     

Molecular mobility and nucleocytoplasmic flux in hepatoma cells

Fluorescence microphotolysis (photobleaching) was used to measure, in single polyethylene glycol-induced polykaryons of hepatoma tissue culture cells, nucleocytoplasmic flux and intracellular mobility for a series of dextrans ranging in molecular mass from 3 to 150 kD and for bovine serum albumin. For the dextrans, the cytoplasmic and the nucleoplasmic translational diffusion coefficients amounted to approximately 9 and approximately 15%, respectively, of the value in dilute buffer. The diffusion coefficients depended inversely on molecular radius, suggesting that diffusion was dominated by viscosity effects. By application of the Stokes-Einstein equation, cytoplasmic and nucleoplasmic viscosities were derived to be 6.6 and 8.1 cP, respectively, at 23 degrees C. Between 10 and 37 degrees C nucleoplasmic diffusion coefficients increased by approximately 45-85%, whereas cytoplasmic diffusion coefficients were virtually independent of temperature. In contrast to that of the dextrans, diffusion of bovine serum albumin was more restricted. In the cytoplasm the diffusion coefficient was approximately 1.5% of the value in dilute buffer; in the nucleus albumin was largely immobile. This indicated that albumin mobility is dominated by association with immobile cellular structures. Nucleocytoplasmic flux of dextrans depended inversely on molecular mass with an exclusion limit between 17 and 41 kD. This agrees with previous measurements on primary hepatocytes (Peters, R., 1984, EMBO [Eur. Mol. Biol. Organ.] J. 3:1831-1836), suggesting that in both cell types the nuclear envelope has properties of a molecular sieve with a functional pore radius of approximately 55 A.     

Purification of gamma-glutamyltransferase by phenyl boronate affinity chromatography. Studies on the acceptor specificity of transpeptidation by rat kidney gamma-glutamyltransferase

gamma-Glutamyltransferase has been purified from rat kidney by a novel procedure using phenyl boronate affinity chromatography. The highly purified enzyme has been studied with respect to acceptor specificity for a number of amino acids, amino acid analogues, dipeptides and tripeptides. The acceptor activity is specific for L-amino acids. The amino acids and the majority of the essential amino acids are poor acceptors while the sulphur-containing amino acids are the best acceptors. The acceptor activity is modulated by the substitution of the amino acid side chain. Substitution of the side chain at the delta, gamma or beta positions results in a proportionally decreasing ability to act as acceptor. The carbonyl moiety of the gamma-carboxy group of the acceptor appears to be essential for acceptor activity, absence of an alpha-carboxy carbonyl group increases the Kappm of the acceptor approximately 100-fold.     

Mechanical constraints canalizing the evolutionary transformation of tetrapod limbs

A reconstruction of the anagenetic transformations from fins to tetrapod limbs is represented considering the self-evident mechanical constraints which must have limited the construction and thus the function and the transformation.     

A Mouse β-Globin Mutant That Is an Exact Model of Hemoglobin Rainier in Man

A mutation induced by ethylnitrosourea in a spermatogonial stem cell of a 101/H mouse has resulted in a structurally altered beta-diffuse major globin in one of his offspring. The mutant hemoglobin is associated with polycythemia, rubor, increased oxygen affinity and decreased hem-hem interaction. The mutant haplotype has been designated Hbbd4, polycythemia. Amino acid analysis of the mutant globin has shown that a single substitution beta 145 Tyr----Cys has occurred, and it is proposed that ethylnitrosourea induced an A----G transition in the tyrosine codon (TAC----TGC). This murine polycythemia is homologous with hemoglobin Rainier in man, in which the amino acid substitution is also beta 145 Tyr----Cys and which is associated with similar physiological consequences.     

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Desensitization of the turkey erythrocyte beta-adrenergic receptor in a cell-free system. Evidence that multiple protein kinases can phosphorylate and desensitize the receptor

We have used a recently developed cell-free system (cell lysate) derived from turkey erythrocytes to explore the potential role of cAMP-activated and other protein kinase systems in desensitizing the adenylate cyclase-coupled beta-adrenergic receptor. Desensitization by the agonist isoproterenol required more than simple occupancy of the receptor by the agonist since under conditions where adenylate cyclase was not activated, no desensitization occurred. As in whole cells, addition of cyclic nucleotides to the cell lysate produced only approximately 50% of the maximal isoproterenol-induced desensitization obtainable. Addition of the purified cAMP-dependent protein kinase holoenzyme plus isoproterenol to isolated turkey erythrocyte plasma membranes mimicked the submaximal desensitization induced in lysates by cAMP. This effect was entirely blocked by the specific inhibitor of the cAMP-dependent protein kinase. By contrast, maximal desensitization induced in lysates by isoproterenol was only approximately 50% attenuated by the protein kinase inhibitor. In the lysate preparations, isoproterenol was also shown to induce, in a stereospecific fashion, phosphorylation of the beta-adrenergic receptor. Phosphorylation promoted by isoproterenol was attenuated by cAMP-dependent protein kinase inhibitor to the same extent as desensitization (i.e. approximately 50%). Phorbol diesters also promoted receptor desensitization and phosphorylation in cell lysates. The desensitization was mimicked by incubation of isolated turkey erythrocyte membranes with partially purified preparations of protein kinase C plus phorbol diesters. In the cell lysate, calmodulin also promoted receptor phosphorylation and desensitization which was blocked by EGTA. Desensitization of adenylate cyclase by isoproterenol, phorbol diesters, and calmodulin was not observed to be additive. These findings suggest that: (a) multiple protein kinase systems, including cAMP-dependent, protein kinase C-dependent, and Ca2+/calmodulin-dependent kinases, are capable of regulating beta-adrenergic receptor function via phosphorylation reactions and that (b) cAMP may not be the sole mediator of isoproterenol-induced phosphorylation and desensitization in these cells.     

On the sexual reproduction ofDictyosiphon foeniculaceus (Phaeophyceae,Dictyosiphonales)

Dictyosiphon foeniculaceus from Sweden and Newfoundland was studied in laboratory culture. Zoids from unilocular sporangia developed into dioecious microscopic filamentous gametophytes which produced uniseriate plurilocular gametangia in low temperatures (0 to 8 °C). Zygotes and unfused isogametes gave rise to filamentous protonemata on which parenchymatous macroscopic sporophytes were formed. Isolates from Sweden and Newfoundland were interfertile. Although formed in culture, genetically unisexual sporophytes were not detected in nature. Female gametes ofD. foeniculaceus produced a sexual pheromone. It was identified as finavarrene, which is also known as the sperm attractant inAscophyllum nodosum.     

The ultrastructure of the midgut and the formation of peritrophic membranes in a harvestman,Phalangium opilio (Chelicerata Phalangida)

Summary The ultrastructure of the midgut epithelium of Phalangium opilio was examined. In the anterior part of the midgut the epithelium consists of three different types of cells, called resorption, digestion, and excretion cells according to their presumed functions. Excretion cells may represent old digestion cells. The relation between resorption and digestion cells needs further investigation. The epithelium of the posterior part of the midgut consists of two types, transport and secretion cells, which seem to serve mainly for the resorption of water and the secretion of peritrophic membranes, respectively.Peritrophic membranes are secreted by the anterior midgut epithelium mainly in a period between 2 and 4 h after feeding. Chitin or chitin precursors could be localized in vesicles and in the brush border of midgut cells, and in the peritrophic membranes, using colloidal gold labelled with wheat germ agglutinin. Two different textures of chitin-containing microfibrils were found in the peritrophic membranes, either a random or a hexagonal texture. The latter results if the microfibrils polymerize between the basal parts of the microvilli. Irregularities of the hexagonal texture can be correlated with an irregular pattern of the microvilli. In the posterior midgut peritrophic membranes with a random texture, chitin-containing microfibrils are continuously secreted in the form of patches.