Analogs of methionyl-tRNA synthetase substrates containing photolabile groups.

Three photolabile analogs of substrates of methionyl-tRNA synthetase were synthesized. In one, the 4-thiouridine at the 8 position of E. coli tRNAfMet was alkylated with [14C]p-azidobromoacetanilide. In the second, [14C]p-azidobenzoic acid hydrazide was condensed with the 3'-terminal dialdehyde of periodate-oxidized Escherichia coli tRNAfMet. The modified tRNAs could be purified by chromatography on benzoylated DEAE-cellulose. The third photolabile compound was [3H]methioninyl-8-azido-adenosine 5'-phosphate, an analog of the methionyl adenylate intermediate in the aminoacylation reaction. Irradiation of each of these compounds in the presence of equimolar amounts of E. coli methionyl-tRNA synthetase of micrometer concentrations gave 5-15% crosslinking.     

Photosynthesis in submersed macrophytes of a temperate lake

The photosynthetic carbon fixation pathways and levels of carbon-fixing enzymes of four dominant submersed macrophytes of Lawrence Lake, southern Michigan, were investigated during the main growth season (May to November). All four species (Scirpus subterminalis Torr., Najas flexilis (Willd.) Rostk. and Schmidt, Potamogeton praelongus Wulf., and Myriophyllum heterophyllum Michx.) were C₃ plants based on their patterns of ¹⁴C pulse-chase incorporation. High levels of phosphoenolpyruvate carboxylase were also found in these species. These levels, as well as the ribulose 1,5-biphosphate carboxylase/phosphoenolpyruvate carboxylase ratio of the leaves, varied throughout the growing season and exhibited highest values in July. No shift in carbon fixation pathways, however, could be detected from July to October. The possible functions of phosphoenolypyruvate carboxylase in these plants, as well as the significance of C₃ metabolism in submersed plants of temperate lakes, are delineated.     

Synthesis and properties of fatty acid starch esters

Being completely bio-based, fatty acid starch esters (FASEs) are attractive materials that represent an alternative to crude oil-based plastics. In this study, two synthesis methods were compared in terms of their efficiency, toxicity and, especially, product solubility with starch laurate (C₁₂) as model compound. Laurates (DS > 2) were obtained through transesterification of fatty acid vinylesters in DMSO or reaction with fatty acid chlorides in pyridine. The latter lead to higher DS-values in a shorter reaction time. But due to the much better solubility of the products compared to lauroyl chloride esterified ones, vinylester-transesterification was preferred to optimize reaction parameters, where reaction time could be shortened to 2 h. FASEs C₆–C₁₈ were also successfully prepared via transesterification. To determine the DS of the resulting starch laurates, the efficient ATR-IR method was compared with common methods (elementary analysis, ¹H NMR). Molar masses (M_w) of the highly soluble starch laurates were analyzed using SEC-MALLS (THF). High recovery rates (>80%) attest to the outstanding solubility of products obtained through transesterification, caused by a slight disintegration during synthesis. Particle size distributions (DLS) demonstrated stable dissolutions in CHCl₃ of vinyl laurate esterified – contrary to lauroyl chloride esterified starch. For all highly soluble FASEs (C₆–C₁₈), formation of concentrated solutions (10 wt%) is feasible.     

Compensatory Hemagglutinin Mutations Alter Antigenic Properties of Influenza Viruses

Influenza viruses routinely acquire mutations in antigenic sites on the globular head of the hemagglutinin (HA) protein. Since these antigenic sites are near the receptor binding pocket of HA, many antigenic mutations simultaneously alter the receptor binding properties of HA. We previously reported that a K165E mutation in the Sa antigenic site of A/Puerto Rico/8/34 (PR8) HA is associated with secondary neuraminidase (NA) mutations that decrease NA activity. Here, using reverse genetics, we show that the K165E HA mutation dramatically decreases HA binding to sialic acid receptors on cell surfaces. We sequentially passaged reverse-genetics-derived PR8 viruses with the K165E antigenic HA mutation in fertilized chicken eggs, and to our surprise, viruses with secondary NA mutations did not emerge. Instead, viruses with secondary HA mutations emerged in 3 independent passaging experiments, and each of these mutations increased HA binding to sialic acid receptors. Importantly, these compensatory HA mutations were located in the Ca antigenic site and prevented binding of Ca-specific monoclonal antibodies. Taken together, these data indicate that HA antigenic mutations that alter receptor binding avidity can be compensated for by secondary HA or NA mutations. Antigenic diversification of influenza viruses can therefore occur irrespective of direct antibody pressure, since compensatory HA mutations can be located in distinct antibody binding sites.     

A survey of seasonal bark proteins in eight temperate hardwoods

Summary Bark proteins of eight temperate hardwoods were analyzed by SDS-PAGE at monthly intervals to determine whether an accumulation of specific proteins, potential storage proteins, occurred in the fall at the time of leaf senescence. Storage proteins were identified as proteins that accumulated during the fall and were present in reduced amounts in the summer. Total protein levels were higher in the winter than in the summer in Fagus sylvatica, Fraxinus americana, Tilia americana, Alnus glulinosa, Betula papyrifera and Querus rubra, but not in Gleditsia triacanthos or Robinia pseudoacacia. Betula contained the most abundant storage protein, although in all species minor bands, which fluctuated seasonally, could be identified. With the exception of Alnus and Betula, results generally correlated with previous microscopy studies of these tree species, which showed varying amounts of protein storage vacuoles present in phloem parenchyma cells during the winter, but not during the summer.     

Modelling expected trout ranges under current and future water temperature regimes in the Eastern Cape,South Africa

Different values have resulted in conflicts between anglers and conservation lobbies in the management of trout in South Africa. Key to the conflict is the demarcation of boundaries to areas in which brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss currently occur, or are likely to establish following stocking for angling. To provide a longer-term perspective on these areas, we developed models to link salmonid biological thermal thresholds to elevation. These, when applied spatially using a digital elevation model with a probability of occurrence model, provided the basis for estimating potentially available thermal habitat for these two cold water species. Here, we acknowledge that other variables (stocking history; river connectivity) also play a role in understanding trout distributions. Using a simple scenario of an increase in mean daily water temperatures of 2 °C, we demonstrated that both brown and rainbow trout are likely to exhibit considerable range reductions in the future. Because it is possible that these range restrictions will result in an increasing desire to introduce trout into areas above their current distribution limits for the maintenance of angling opportunities, conservation managers should prioritise these areas, with management interventions seeking to understand what will help to limit introductions.     

Global diversity of oligochaetous clitellates (“Oligochaeta”; Clitellata) in freshwater

One of the predicted consequences of climate change is an increase in the occurrence of extreme rainfall and a subsequent increase in frequency of high flow events in rivers. High flow events have the potential to impact estuarine communities like mussel assemblages due to decreased salinity and/or the transport of sediments, organic matter and nutrients from the terrestrial environment to the estuary. The impact of two high flow events was investigated using mussels located within the Conwy estuary, North Wales, using the ‘Beyond BACI’ approach. Three study sites were chosen, the potentially impacted site (Conwy) and two control sites located outside the estuary. Sampling took place over 18 months with samples being collected before and after each event. On each sampling occasion, the following data were collected: the total haemocyte count (THC) and condition index (CI) of the mussels and the diversity (Hlog_e) of their associated macrofauna. A significant effect of the first event (22nd October 2004) was found on the CI of the Conwy mussels, whereas a significant effect of the second event (10th October 2005) was found on mussel THC. No effect of either event was found on the diversity of the associated fauna. The results of this study suggest that any increase in the number or intensity of heavy precipitation or high flow events have potential implications for the health and resilience of estuarine mussel populations. Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan Challenges to Marine Ecosystems     

Nutrient additions by waterfowl to lakes and reservoirs: predicting their effects on productivity and water quality

Lakes and reservoirs provide water for human needs and habitat for aquatic birds. Managers of such waters may ask whether nutrients added by waterfowl degrade water quality. For lakes and reservoirs where primary productivity is limited by phosphorus (P), we developed a procedure that integrates annual P loads from waterfowl and other external sources, applies a nutrient load-response model, and determines whether waterfowl that used the lake or reservoir degraded water quality. Annual P loading by waterfowl can be derived from a figure in this report, using the days per year that each kind spent on any lake or reservoir. In our example, over 6500 Canada geese (Branta canadensis) and 4200 ducks (mostly mallards, Anas platyrhynchos) added 4462 kg of carbon (C), 280 kg of nitrogen (N), and 88 kg of P y^–1 to Wintergreen Lake in southwestern Michigan, mostly during their migration. These amounts were 69% of all C, 27% of all N, and 70% of all P that entered the lake from external sources. Loads from all external sources totaled 840 mg P m^–2 y^–1. Application of a nutrient load-response model to this concentration, the hydraulic load (0.25 m y^–1), and the water residence time (9.7 y) of Wintergreen Lake yielded an average annual concentration of total P in the lake of 818 mg m^–3 that classified the lake as hypertrophic. This trophic classification agreed with independent measures of primary productivity, chlorophyll-a, total P, total N, and Secchi disk transparency made in Wintergreen Lake. Our procedure showed that waterfowl caused low water quality in Wintergreen Lake.Contribution 824 of the National Fisheries Research Center-Great Lakes, 1451 Green Road, Ann Arbor, Michigan 48105, U.S.A. and 722 of the Kellogg Biological Station, Michigan State University.     

Heterogeneity of phosphorus distribution in a patterned landscape,the Florida Everglades

The biologically mediated transfer of nutrients from one part of a landscape to another may create nutrient gradients or subsidize the productivity at specific locations. If limited, this focused redistribution of the nutrient may create non-random landscape patterns that are unrelated to underlying environmental gradients. The Florida Everglades, USA, is a large freshwater wetland that is patterned with tree islands, elevated areas that support woody vegetation. A survey of 12 tree islands found total soil phosphorus levels 3–114 times greater on the island head than the surrounding marsh, indicating that the Florida Everglades is not a homogeneous oligotrophic system. It was estimated that historically 67% of the phosphorus entering the central Everglades was sequestered on tree islands, which are ~3.8% of the total land area. This internal redistribution of phosphorus onto tree islands due to the establishment of trees may be one reason that marshes have remained oligotrophic and may explain the spatial differentiation of the patterned Everglades landscape.     

Effects of nutrient and soil moisture on competition between shape Carex stricta,shape Phalaris arundinacea,and shape Typha latifolia

We investigated the importance of nutrients, soil moisture, arbuscular mycorrhizal fungi (AMF), and interspecific competition levels on the biomass allocation patterns of three wetland perennial plant species, Carex stricta Lam., Phalaris arundinacea L., and Typha latifolia L. A factorial experiment was conducted with high-low nutrient levels, high-low soil moisture levels, and with and without AMF inoculation. Under the experimental conditions, plant inoculation by AMF was too low to create a treatment and the AMF treatment was dropped from the total analysis. P. arundinacea and T. latifolia biomass were 73% and 77% higher, respectively, in the high nutrient treatment compared to the low nutrient treatment. Biomass allocation between shoots and roots remained relatively constant between environmental treatments, although shoot:root ratios of P. arundinacea declined in the low nutrient treatment. For C. stricta, the high nutrient and soil moisture treatments resulted in an increase in biomass of 50% and 15%, respectively. Shoot:root ratios were nearly constant among all environmental conditions. Biomass of T. latifolia and C. stricta was greatly decreased when grown with P. arundinacea. The rapid, initial height growth of P. arundinacea produced a spreading, horizontal canopy that overshadowed the vertical leaves of T. latifolia and C. stricta throughout the study. This pattern was repeated in both high and low nutrient and soil moisture treatments. When grown with P. arundinacea, C. stricta and T. latifolia significantly increased their mean shoot height, regardless of the nutrient or soil moisture level. The results of this experiment suggest that C. stricta and T. latifolia were light limited when growing with P. arundinacea and that canopy architecture is more important for biomass allocation than the other environmental conditions tested. The results also suggest that Phalaris arundinacea is an inherently better competitor (sensu Grime 1979) than C. stricta or T. latifolia.