Recent advances in polysaccharide bio-based flocculants

Natural polysaccharides, derived from biomass feedstocks, marine resources, and microorganisms, have been attracting considerable attention as benign and environmentally friendly substitutes for synthetic polymeric products. Besides many other applications, these biopolymers are rapidly emerging as viable alternatives to harmful synthetic flocculating agents for the removal of contaminants from water and wastewater. In recent years, a great deal of effort has been devoted to improve the production and performance of polysaccharide bio-based flocculants. In this review, current trends in preparation and chemical modification of polysaccharide bio-based flocculants and their flocculation performance are discussed. Aspects including mechanisms of flocculation, biosynthesis, classification, purification and characterization, chemical modification, the effect of physicochemical factors on flocculating activity, and recent applications of polysaccharide bio-based flocculants are summarized and presented.     

Detailed positron annihilation lifetime spectroscopic investigation of atrazine imprinted polymers grafted onto PE/PP non‐woven fabrics

This study presents the preparation of molecularly imprinted matrices by using radiation‐induced grafting technique onto polyethylene/polypropylene (PE/PP) non‐woven fabrics. Atrazine imprinted polymers were grafted onto PE/PP non‐woven fabrics through the use of methacrylic acid (MAA) and ethylene glycol dimethylacrylate (EGDMA) as the functional monomer and crosslinking agent, respectively. Grafted MIPs were characterized by attenuated total reflectance Fourier transform infra‐red spectroscopy (ATR‐FTIR), X‐ray photoelectron spectroscopy (XPS), elemental analysis, scanning electron microscopy (SEM), and positron annihilation lifetime spectroscopy (PALS). The average diameter of free volume holes was determined as 0.612 nm which correlates very well with the size of template molecule atrazine, 0.512 nm. Binding behaviors were investigated against various factors, such as concentration of template molecule, pH, and contact time. Furthermore, the specific selectivity of grafted MIP on non‐woven fabric was studied by using other common triazine compounds, such as simazine and metribuzine which show structural similarities to atrazine. The specific binding values for atrazine, simazine, and metribuzine were determined as 40%, 2.5%, and 1.5%, respectively.     

Coherent synthesis of genomic associations with phenotypes and home environments

Local adaptation is often studied via (i) multiple common garden experiments comparing performance of genotypes in different environments and (ii) sequencing genotypes from multiple locations and characterizing geographic patterns in allele frequency. Both approaches aim to characterize the same pattern (local adaptation), yet the complementary information from each has not yet been coherently integrated. Here, we develop a genome‐wide association model of genotype interactions with continuous environmental gradients (G × E), that is reaction norms. We present an approach to impute relative fitness, allowing us to coherently synthesize evidence from common garden and genome–environment associations. Our approach identifies loci exhibiting environmental clines where alleles are associated with higher fitness in home environments. Simulations show our approach can increase power to detect loci causing local adaptation. In a case study on Arabidopsis thaliana, most identified SNPs exhibited home allele advantage and fitness trade‐offs along climate gradients, suggesting selective gradients can maintain allelic clines. SNPs exhibiting G × E associations with fitness were enriched in genic regions, putative partial selective sweeps and associations with an adaptive phenotype (flowering time plasticity). We discuss extensions for situations where only adaptive phenotypes other than fitness are available. Many types of data may point towards the loci underlying G × E and local adaptation; coherent models of diverse data provide a principled basis for synthesis.     

Endo-xyloglucan transferase,a new class of transferase involved in cell wall construction

Cell shape in plants is constrained by cell walls, which are thick yet dynamic structures composed of crystalline cellulose microfibrils and matrix polymers. Xyloglucans are the principal component of the matrix polymers and bind tightly to the surface of cellulose microfibrils and thereby cross-link them to form an interwoven xyloglucan-cellulose network structure. Thus, cleavage and reconnection of the cross-links between xyloglucan molecules are required for the rearrangement of the cell wall architecture, the process essential for both cell wall expansion and the wall deposition occurring during cell growth and differentiation. Endoxyloglucan transferase (EXT) is a newly identified class of transferase that catalyzes molecular grafting between xyloglucan molecules. This enzyme catalyzes both endo-type splitting of a xyloglucan molecule and reconnection of a newly generated reducing terminus of the xyloglucan to the non-reducing terminus of another xyloglucan molecule, thereby mediating molecular grafting between xyloglucan cross-links in plant cell walls. Molecular cloning and sequencing of EXT-cDNAs derived from five different plant species includingA. thaliana andV. angularis has revealed that the amino acid sequence of the mature protein is extensively conserved in the five different plant species, indicating that EXT protein is ubiquitous among higher plants. This structural study has also disclosed the presence of a group of xyloglucan related proteins (XRPs) with transferase activity in higher plants. Current data strongly suggest that these proteins are involved in a wide spectrum of physiological activities including cell wall expansion and deposition in growing cell walls. Recipient of the Botanical Sociaty Award of Young Scientists, 1993.     

Coastal insect herbivore communities are affected more by local environmental conditions than by plant genotype

Abstract.

• 1 We compared the effects of plant genotype and local environment on population densities of a community of coastal insect herbivores in west-central Florida. Reciprocal transplants of four genotypes of three species of coastal plants, Borrichia frutescens, Iva frutescens and Limbricata, were made in July 1992 between a series of off-shore islands.
• 2 For each plant species, phytophagous insects with a wide range of feeding modes including gall-makers, stem borers, leaf miners and sap suckers were affected more by local environment than by plant genotype. Whereas host genotype had a significant effect on the population densities of gall-makers on B.frutescens in the spring of 1993, no significant effect on the denrities of any other insect species was found and the effect on the gall-makers on Borrichia disappeared in the summer, 1 year after the transplants had been made. In our study, local environment had by far the greatest effect on insect population densities among islands. This is an unusual result because in other studies over 80% of the insect species examined have been affected by plant genotype (Karban, 1992). This result is consistent with that reported by Stiling (1994), who censused populations of two phytophagous insects on reciprocal transplantr ot Borrichia in north Florida.
• 3 Local environment also had an effect on insect population densities within islands. This result contrasts with similar studies performed in north Florida (Stiling, 1994), where population densities did not differ within areas, and underlies how some biotic processes may change with in the same community even over relatively small changes in species range.

     

Establishing and maintaining the body plan ofAcetabularia acetabulumin the absence of cellularization

How do ‘unicellular’ organisms in which cytokinesis and karyokinesis may be uncoupled spatially delimit regions which are structurally and functionally distinct? Developmentally arrested (da) phenotypes fail to complete development and morphologically altered (ma) phenotypes ofAcetabularia acetabulummake body parts in the wrong proportions or places. When grafted to wild type, mildmadefects phenoconvert body parts of the graft partner toma. Strongmadefects convert one body part into another on their own body. These defects may tell us how the body plan of organisms which lack obvious internal partitions are established and maintained during development.     

Whence tit-for-tat?

Summary In theoretical and empirical studies of the evolution of cooperation, the tit-for-tat strategy (i.e. cooperate unless your partner did not cooperate in the previous interaction) is widely considered to be of central importance. Nevertheless, surprisingly little is known about the conditions in which tit-for-tat appears and disappears across generations in a population of interacting individuals. Here, we apply a newly developed classifier-system model (EvA) in addressing this issue when the key features of interactions are caricatured using the iterated prisoner's dilemma game. Our simple representation of behavioural strategies as algorithms composed of two interacting rules allowed us to determine conditions in which tit-for-tat can replace noncooperative strategies and vice versa. Using direct game-theoretic analysis and simulations with the EvA model, we determined that no strategy is evolutionarily stable, but larger population sizes and longer sequences of interactions between individuals can yield transient dominance by tit-for-tat. Genetic drift among behaviourally equivalent strategies is the key mechanism underlying this dominance. Our analysis suggests that tit-for-tat could be important in nature for cognitively simple organisms of limited memory capacity, in strongly kin-selected or group-selected populations, when interaction sequences between individuals are relatively short, in moderate-sized populations of widely interacting individuals and when defectors appear in the population with moderate frequency.