Effect of Storm Events on Benthic Nitrifying Activity

Storm events resulted in a marked reduction in the benthic nitrifying activity of a stream receiving geothermal inputs of ammonium. Subsequently, nitrifying activity demonstrated a logarithmic increase until a stable activity was reached 10 to 12 days after the storm event. The rate of increase of poststorm nitrifying activity was used to calculate the nitrifier growth rate in situ (0.0075 to 0.0116 h⁻¹) which was lower than the growth rates observed for laboratory cultures of nitrifying bacteria isolated from the sediments (0.0233 to 0.0990 h⁻¹).     

Predictions of stream nutrient and sediment yield changes following restoration of forested riparian buffers

Riparian tree planting is widely recognised as a means to improve water quality and stream habitat. However, shading of riparian pasture grasses can lead to channel widening, and riparian shade may limit the growth of macrophytes and algae that assimilate dissolved nutrients from the water column. We investigated concerns that riparian management could lead to increased yields of nutrients and sediments through a conceptual modelling exercise. A simple model of the trade-off between interception of nutrients in runoff by forest buffers versus reduction of in-stream uptake due to shade, predicted that a buffer strip alongside a small headwater stream would reduce nutrient export, while a buffer strip instigated as an isolated patch alongside a larger stream (c. >2.5 km² upstream catchment size) would increase nutrient export, as the relative amount of nutrients trapped by the buffer decreases as the nutrient load present in the stream water increases. However, in these larger streams with width exceeding approximately 6 m, sufficient light may reach the streambed for plant and algal growth, which in turn would promote instream nutrient processing. At the peak of streambank erosion after planting, predicted total sediment yield (hillslope plus bank sources) was appreciably higher than the hillslope pasture yield, but sediment yield stabilised c. 35–40 years after planting. When planting was extended over 40 years in the model, the sediment yield never exceeded that in pasture before planting. This conceptual modelling exercise shows that riparian tree planting programmes should commence in the headwaters and progress downstream to avoid nutrient yield increases. Significant sediment yield from bank stored sediment of small streams can be expected until the channel reaches the more stable, original forested width, but progressive planting may decrease the peak loads of sediment.     

Leopard predation on gelada monkeys at Guassa,Ethiopia

Predation is widely believed to exert strong selective pressure on primate behavior and ecology but is difficult to study and rarely observed. In this study, we describe seven encounters between lone wild leopards (Panthera pardus) and herds of geladas (Theropithecus gelada) over a 6-year period in an intact Afroalpine grassland ecosystem at the Guassa Community Conservation Area, Ethiopia. Three encounters consisted of attempted predation on geladas by leopards, one of which was successful. All three attacks occurred in low-visibility microhabitats (dominated by tussock graminoids, mima mounds, or tall shrubs) that provided leopards with hidden viewsheds from which to ambush geladas. An additional four encounters did not result in an attempted attack but still document the consistently fearful responses of geladas to leopards. In encounters with leopards, geladas typically gave alarm calls (n = 7 of 7 encounters), reduced interindividual distances (n = 5), and collectively fled towards or remained at their sleeping cliffs (n = 7), the only significant refugia in the open-country habitat at Guassa. Geladas did not engage in mobbing behavior towards leopards. Encounters with leopards tended to occur on days when gelada herd sizes were small, raising the possibility that leopards, as ambush hunters, might stalk geladas on days when fewer eyes and ears make them less likely to be detected. We compare the behavioral responses of geladas to leopards at Guassa with those previously reported at Arsi and the Simien Mountains and discuss how gelada vulnerability and responses to leopards compare with those of other primate species living in habitats containing more refugia. Lastly, we briefly consider how living in multilevel societies may represent an adaptive response by geladas and other open-country primates to predation pressure from leopards and other large carnivores.     

Evidence for Metabolic Domains within the Matrix Compartment of Pea Leaf Mitochondria : Implications for Photorespiratory Metabolism

The simultaneous oxidation of malate and of glycine was investigated in pea (Pisum sativum) leaf mitochondria. Adding malate to state 4 glycine oxidation did not inhibit, and under some conditions stimulated, glycine oxidation. State 4 oxygen uptake with glycine is restricted because of the control exerted by the membrane potential but reoxidation of NADH by oxaloacetate reduction can still occur. Thus, malate addition stimulates glycine metabolism by producing oxaloacetate. The malate dehydrogenase (EC 1.1.1.37) enzyme fraction remote from glycine decarboxylase (EC 2.1.2.10) oxidizes malate whereas that closely associated with it produces malate, i.e. they function in opposite directions. It is shown that these opposing directions of malate dehydrogenase activity occur within the same mitochondrial matrix compartment and not in different mitochondrial populations. It is concluded that metabolic domains containing different complements of mitochondrial enzymes exist within the one mitochondrial matrix without physical barriers separating them. The differential spatial organization within the matrix may account for the previously reported limited access of some enzymes to the respiratory electron transport chain. The implications for leaf mitochondrial metabolism are discussed.     

The Caenorhabditis elegans spe‐49 gene is required for fertilization and encodes a sperm‐specific transmembrane protein homologous to SPE‐42

Fertilization, the fusion of sperm and oocyte to form a zygote, is the first and arguably the most important cell–cell interaction event in an organism’s life. Forward and reverse genetic approaches in the nematode Caenorhabditis elegans have identified many genes that are required for gametogenesis and fertilization and thus are beginning to elucidate the molecular pathways that underlie these processes. We identified an allele of the spe‐49 gene in a second filial generation (F₂) mutagenesis screen for spermatogenesis‐defective (spe) mutants. Mutant worms for spe‐49 produce sperm that have normal morphology, activate to form ameboid spermatozoa, and can migrate to and maintain their position in the hermaphrodite reproductive tract but fail to fertilize oocytes. This phenotype puts spe‐49 in the spe‐9 class of late‐acting genes that function in sperm at the time of fertilization. We cloned the spe‐49 gene through a combination of deficiency mapping, transgenic rescue, and genomic sequencing. spe‐49 messenger RNA (mRNA) is enriched in male germ cells, and the complementary DNA (cDNA) encodes a predicted 772‐amino‐acid six‐pass transmembrane protein that is homologous to SPE‐42. Indeed, SPE‐49 and SPE‐42 have identical predicted membrane topology and domain structure, including a large extracellular domain with six conserved cysteine residues, a DC‐STAMP domain, and a C‐terminal cytoplasmic domain containing a C4–C4 RING finger motif. The presence of two SPE‐42 homologs in animal genomes from worms to humans suggests that these proteins are highly conserved components of the molecular apparatus required for the sperm–oocyte recognition, binding, and fusion.     

Contribution of buried distal amino acid residues in horse liver alcohol dehydrogenase to structure and catalysis

The dynamics of enzyme catalysis range from the slow time scale (～ms) for substrate binding and conformational changes to the fast time (～ps) scale for reorganization of substrates in the chemical step. The contribution of global dynamics to catalysis by alcohol dehydrogenase was tested by substituting five different, conserved amino acid residues that are distal from the active site and located in the hinge region for the conformational change or in hydrophobic clusters. X‐ray crystallography shows that the structures for the G173A, V197I, I220 (V, L, or F), V222I, and F322L enzymes complexed with NAD⁺ and an analogue of benzyl alcohol are almost identical, except for small perturbations at the sites of substitution. The enzymes have very similar kinetic constants for the oxidation of benzyl alcohol and reduction of benzaldehyde as compared to the wild‐type enzyme, and the rates of conformational changes are not altered. Less conservative substitutions of these amino acid residues, such as G173(V, E, K, or R), V197(G, S, or T), I220(G, S, T, or N), and V222(G, S, or T) produced unstable or poorly expressed proteins, indicating that the residues are critical for global stability. The enzyme scaffold accommodates conservative substitutions of distal residues, and there is no evidence that fast, global dynamics significantly affect the rate constants for hydride transfers. In contrast, other studies show that proximal residues significantly participate in catalysis.     

Poplar and shrub willow energy crops in the United States: field trial results from the multiyear regional feedstock partnership and yield potential maps based on the PRISM‐ELM model

To increase the understanding of poplar and willow perennial woody crops and facilitate their deployment for the production of biofuels, bioproducts, and bioenergy, there is a need for broadscale yield maps. For national analysis of woody and herbaceous crops production potential, biomass feedstock yield maps should be developed using a common framework. This study developed willow and poplar potential yield maps by combining data from a network of willow and poplar field trials and the modeling power of PRISM‐ELM. Yields of the top three willow cultivars across 17 sites ranged from 3.60 to 14.6 Mg ha^?1 yr^?1 dry weight, while the yields from 17 poplar trials ranged from 7.5 to 15.2 Mg ha^?1 yr^?1. Relationships between the environmental suitability estimates from the PRISM‐ELM model and results from field trials had an R² of 0.60 for poplar and 0.81 for willow. The resulting potential yield maps reflected the range of poplar and willow yields that have been reported in the literature. Poplar covered a larger geographic range than willow, which likely reflects the poplar breeding efforts that have occurred for many more decades using genotypes from a broader range of environments than willow. While the field trial data sets used to develop these models represent the most complete information at the time, there is a need to expand and improve the model by monitoring trials over multiple cutting cycles and across a broader range of environmental gradients. Despite some limitations, the results of these models represent a dramatic improvement in projections of potential yield of poplar and willow crops across the United States.     

Rapid decarboxylation of the products of dark fixation of CO2 in roots of pisum and Plantago

Seedlings of Pisum sativum and excised roots of Plantago major and P. lanceolata were given, in the dark, a pulse of ¹⁴CO₂ in air followed by a chase in ¹²CO₂ in air. A very substantial proportion of the ¹⁴C fixed into organic compounds in the pulse was lost from the tissues in the chase. The activity of NAD malic enzyme in extracts of roots of all three species exceeded their rate of respiration. Azide, 2-n-butylmalonate, and salicylhydroxamic acid each inhibited CO₂ fixation by excised roots of pea. The first two compounds inhibited respiratory gas exchange, but the third stimulated it. Arguments are presented for the widespread diversion of phosphoenolpyruvate from glycolysis to oxaloacetate and thence to malate in the cytosol followed by transport of the malate into the mitochondria for conversion to pyruvate via NAD malic enzyme. No differences, in the above respects, were found between the two species of Plantago.     

Analysis of lens cell fate and eye morphogenesis in transgenic mice ablated for cells of the lens lineage

Transgenic mice carrying the diphtheria toxin A gene driven by mouse gamma 2-crystallin promoter sequences manifest microphthalmia due to ablation of fiber cells in the ocular lens. Here we map ablation events in the lens by crossing animals hemizygous for the ablation construct with transgenic mice homozygous for the in situ lacZ reporter gene driven by identical gamma 2-crystallin promoter sequences. By comparing the spatial distribution of lacZ-expressing cells and the profile of gamma-crystallin gene expression in the lenses of normal and microphthalmic offspring, the contributions of specific cell types to lens development were examined. The results suggest that phenotypically and developmentally distinct populations of lens fiber cells are able to contribute to the lens nucleus during organogenesis. We also show that dosage of the transgene and its site of integration influence the extent of ablation. In those mice homozygous for the transgene and completely lacking cells of the lens lineage, we show that the sclera, cornea, and ciliary epithelium are reduced in size but, otherwise, reasonably well formed. In contrast, the anterior chamber, iris, and vitreous body are not discernible while the sensory retina is highly convoluted and extensively fills the vitreous chamber.