Composition and spatial heterogeneity of submersed vegetation in a softwater lake in Wisconsin

Big Muskellunge Lake, a softwater lake (pH 7.5–8.0, alkalinity 0.36 meq/L) in northern Wisconsin, harbors a diverse (25 species) submersed macrophyte vegetation. The present submersed flora combines species generally thought distinct in their ecological affinities, and is very similar to that reported in 1935. The only differences are the apparent loss of three previously infrequent Potamogeton species, and the addition to the flora of two infrequent Potamogeton species and the now abundant Elodea canadensis. Dramatic differences in composition and pattern of the vegetation occurred between sites of contrasting exposure and sediment type. Substantial compositional variation, at scales ranging from tens of centimeters to tens of meters, occurred along transects of contiguous quadrats at uniform depth and exposure. Analyses of species sequences along line transects detected significant segregation of species that is most plausibly explained by biotic factors such as colonization, clonal growth, and competition. Heterogeneity at small scales of a few meters or less is common in Big Muskellunge Lake. Such pattern has been neglected in macrophyte ecology, in spite of its significance for neighbor relationships which may critically influence growth and reproduction of aquatic plants.     

Structure and properties of pectin gels in plant cell walls

Abstract This review deals with recent advances in the structural characterization of pectins and the gels which they form, in relation to auxin-induced extension growth, the ripening of fruit, and cellular recognition. Pectins are block polysaccharides. Heavily branched, largely methyl-esterified blocks alternate with unbranched blocks of varying degrees of esterification. The unbranched, non-esterified blocks can aggregate through calcium binding to form the junction zones that hold a gel together. The aggregates are of two, or possibly four, chains at low calcium levels, and larger with excess calcium. The fall in wall pH during auxin-induced growth activates glycanase enzymes. These may attack some components of the pectic fraction, as well as xyloglucans. Pectin-bound calcium ions may be displaced but this probably has little effect on gel strength. Pectins may be cross-linked by diferulate esters when growth stops. The softening of ripe fruit is due to loss of cohesion in the pectin gel. In apples this results from replacement of the pectins by more esterified forms. In many other fruits it results from depolymerization by polygalacturonases, assisted by pectinesterases, so that the remaining segments are too short for effective calcium binding. Pectins have a further role in the recognition reactions between plant cells and some of their bacterial and fungal pathogens.     

Recent advances in methods of direct optical resolution

Very great advances have been made in the field of direct optical resolution of organic compounds by chromatographic techniques. Chiral capillary gas chromatography now permits a determination of the enantiomeric composition of a few nanograms of a compound present in a mixture of many others. Coupled with high resolution mass spectrometry the technique will additionally permit structural elucidation; of great interest in pheromone research and related areas. Analytical separations of enantiomers are now also carried out by high-performance liquid chromatography (HPLC) methods based on a variety of principles. Basically, two main types are used, differing as to whether the mobile phase has to be a chiral medium or not. Two-dimensional HPLC, whereby compounds separated on a non-chiral column are progressively and automatically transferred to a chiral column for optical resolution, has been used successsfully for chiral amino acid separations. Many different chiral sorbents for preparative LC and HPLC resolutions have been prepared; some of these are now used in columns capable of producing pure enantiomers from a given racemate at a rate of the order of one gram/hour in continuous, automatic HPLC procedures. Apart from all important applications of these results of optical resolution technology, an increased knowledge of the underlying chiral recognition phenomena responsible for enantioselection has also been achieved.     

Recognition of sodium- and potassium-dependent adenosine triphosphatase on mouse lymphoid cells by means of a monoclonal antibody

Summary Previous evidence has established the similarity between (Na⁺+K⁺)-ATPase (ATP phosphohydrolase, EC.3.6.1.3) and the antigen recognized by the rat antimouse monoclonal antibody anti-BSP-3. This antibody has been used for investigation of the surface expression and biochemical analysis of the enzyme in different mouse lymphoid populations. The BSP-3 determinant is found on almost all thymocytes and concanavalin A-induced thymocytes, to a lesser extent on bone marrow cells and also on a minor population of spleen cells. Spleen cells from athymic mice are negative. The (Na⁺+ K⁺)-ATPase purified from mouse thymus by affinity chromatography migrates in SDS-polyacrylamide gels in the form of two polypeptide chains of 105000 and 51000 daltons. Chains of the same molecular weight, fractionated on SDS-PAGE from microsomes of mouse thymuses, are shown to react with subunit-specific polyclonal antisera against ATPase in immunoblotting experiments. Immunoprecipitation with anti-BSP-3 from surface iodinated thymocytes yields only the small subunit. Comparison of the chains isolated from thymus and brain shows molecular weight differences in both subunits. These results, and variations in the reactivity pattern of the anti-BSP-3 antibody on several cell types, may indicate a possible heterogeneity of the (Na⁺+K⁺)ATPase expressed by various tissues and cells.     

Cell interactions in the generation of chaetae pattern inDrosophila

Summary We have already shown that theachaetae-scute complex (AS-C) ofDrosophila is regulated by two genes,hairy andextramacrochaetae. Using mutants in these genes, we have analysed how different levels of expression of AS-C affect the pattern of chaetae. The results indicate that the spatial distribution of chaetae results from cell interactions, probably by a mechanism of lateral inhibition. The results are discussed in view of the different theories of pattern formation.     

Analytical treatment of pattern formation in the Gierer-Meinhardt model of morphogenesis

Summary We first perform a linear stability analysis of the Gierer-Meinhardt model to determine the critical parameters where the homogeneous distribution of activator and inhibitor concentrations becomes unstable. There are two kinds of instabilities, namely, one leading to spatial patterns and another one leading to temporal oscillations. Focussing our attention on spatial pattern formation we solve the corresponding nonlinear equations by means of our previously introduced method of generalized Ginzburg-Landau equations. We explicitly consider the two-dimensional case and find both rolls and hexagon-like structures. The impact of different boundary conditions on the resulting patterns is also discussed. The occurrence of the new patterns has all the features of nonequilibrium phase transitions.     

Cell clones and pattern formation: Developmental restrictions in the compound eye ofDrosophila

Summary Five regions of the compound eye have been found to be preferential boundaries for clones of labelledMinute ⁺ cells, and to act restrictively on the growth of cell clones after a given developmental stage. One of these regions is topographically related to the line of pattern inversion existing at the level of the equator. The results of experiments showing independency of origin of restriction lines and line of pattern inversion are reported.     

Lectin involvement in root-hair tip adhesion as related to the Rhizobium-clover symbiosis

Contact of adjacent root hairs of seedlings of white clover ( Trifolium repens L. cv. Ladino and Louisiana Nolin) led to cell-cell adhesion of root hair tips. The involvement of the root lectin, trifoliin A, in this phenomen was examined in slide cultures of axenically grown seedlings. Trifoliin A was detected by indirect immunofluorescence on root hair tips, which had adhered to one another. Seedlings grown under conditions which specifically reduce the levels of this lectin on the root surface (e.g., in the presence of 15 m M NO₃– or 5 m M 2-deoxy- d -glucose) had significantly fewer adhesions of root hair tips. In addition, flushing the slide cultures with 20 m M 2-deoxy- d -glucose resulted in an immediate 4-fold reduction in frequency of tip adhesions. These results are consistent with the lectin cross-bridging model, which predicts that cell-cell adhesions would occur when trifoliin A on root hair tips contacts complementary glycosylated receptors on neighboring root hairs.     

New versatile cloning and sequencing vectors based on bacteriophage M13

A new pair of cloning and sequencing vectors based on bacteriophage M13mp7 has been developed. These vectors (M13tg130 and M13tg131) contain, in addition to the EcoRI, BamHI, HindIII, SmaI, SalI and PstI sites present in other vectors [cf., M13mp8 and M13mp9, Messing and Vieira, Gene 19 (1982) 269-276], unique restriction recognition sequences for the enzymes EcoRV, KpnI, SphI, SstI and XbaI. A restriction site for the enzyme BglII has been incorporated into the polylinker region of one of the vector pair to permit rapid discrimination between the two vectors.