The particle size characteristics of fluvial suspended sediment: an overview

The particle size characteristics of suspended sediment are of fundamental importance in understanding its role in a variety of environmental processes. Existing knowledge concerning the spatial and temporal variability of the grain size composition of suspended sediment is, however, relatively limited. At the global scale, major contrasts may exist between individual rivers in the calibre of their suspended load and this may be related to a number of controls including climate, catchment geology and basin scale. Any attempt to understand the precise relationship between the grain size characteristics of suspended sediment and those of its source material must also take account of the selectivity of erosion and delivery processes. A local case study undertaken by the authors in the 1500 km² basin of the River Exe in Devon, UK is used to illustrate the considerable spatial variability that may occur within a relatively small area and the complexity of the associated controls.Available evidence concerning the temporal variability of the grain size characteristics of suspended sediment emphasises the diverse patterns of behaviour that may exist and the complexity of the controls involved. In some rivers the sediment may become coarser as flow increases, in others it may become finer, whilst in others it may exhibit a relatively constant grain size composition. Data from the local case study in the Exe basin are again used to highlight the considerable diversity in response to changing discharge that may occur within a relatively small area.Any attempt to understand the dynamics of sediment movement through a river system must also take account of the potential contrast between the ultimate and effective particle size distribution of suspended sediment in response to aggregation. Results from the Exe basin study indicate that even in rivers with relatively low solute concentrations, almost an order of magnitude difference may exist between the median particle size associated with the ultimate and effective grain size distributions.     

A major difference between the divergence patterns within the lines-1 families in mice and voles

L1 retroposons are represented in mice by subfamilies of interspersed sequences of varied abundance. Previous analyses have indicated that subfamilies are generated by duplicative transposition of a small number of members of the L1 family, the progeny of which then become a major component of the murine L1 population, and are not due to any active processes generating homology within preexisting groups of elements in a particular species. In mice, more than a third of the L1 elements belong to a clade that became active approximately 5 Mya and whose elements are > or = 95% identical. We have collected sequence information from 13 L1 elements isolated from two species of voles (Rodentia: Microtinae: Microtus and Arvicola) and have found that divergence within the vole L1 population is quite different from that in mice, in that there is no abundant subfamily of homologous elements. Individual L1 elements from voles are very divergent from one another and belong to a clade that began a period of elevated duplicative transposition approximately 13 Mya. Sequence analyses of portions of these divergent L1 elements (approximately 250 bp each) gave no evidence for concerted evolution having acted on the vole L1 elements since the split of the two vole lineages approximately 3.5 Mya; that is, the observed interspecific divergence (6.7%-24.7%) is not larger than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses showed no clustering into Arvicola and Microtus clades.      

ANALYSIS OF POLYPEPTIDES ASSOCIATED WITH SHOOT FORMATION IN TOBACCO CALLUS CULTURES

Callus lines of Nicotiana tabacum were selected for competence and lack of competence in shoot formation. Changes in total and chromosomal polypeptides in these shoot-forming and nonshoot-forming tobacco cultures were examined by twodimensional polyacrylamide gel electrophoresis. Qualitative and quantitative differences in total, nonhistone chromosomal, and basic chromosomal polypeptides were evident throughout the 7-d test period. The analysis of total proteins identified polypeptides specific to shoot-forming and nonshoot-forming tissue during the 7-d sampling period. A small number of basic chromosomal proteins were found solely in shoot-forming or nonshoot-forming tissue. One basic chromosomal protein was detected in only nonshoot-forming tissue at all sampling times. Two proteins, although present in shoot-forming tissue, were present at elevated levels in the nonshoot-forming cultures. No temporal changes in basic proteins over the 7-d incubation period were observed. Qualitative differences in total nonhistone chromosomal polypeptides in the shoot-forming and nonshoot-forming tissue were also observed. Differences in chromosomal polypeptides were observed. In contrast to the basic chromosomal proteins, temporal variation in the nonhistone chromosomal polypeptides was demonstrated. Throughout the 7-d sampling period, 29 and 12 nonhistone chromosomal polypeptides varied qualitatively in shoot-forming and nonshoot-forming callus cultures, respectively. In vitro labeling with ³²P-orthophosphate indicated that approximately 1.0% and 0.3% of the nonhistone chromosomal proteins were phosphorylated in the shoot-forming and nonshoot-forming cultures. Of these phosphorylated polypeptides, one was present in nonshoot-forming tissue and three were detected only in the shoot-forming tissue. Phosphorylation occurred at serine or threonine residues.     

The Impact of Chlorophyll-Retention Mutations,d1d2 and cyt-G1, during Embryogeny in Soybean

The ultrastructural, physiological, and molecular changes in developing and mature seeds were monitored in a control line (Glycine max [L.] Merr., cv Clark) that exhibited seed degreening and two mutant lines (d1d2 and cyt-G1) that retained chlorophyll upon seed maturation. Ultrastructural studies showed that the control line had no internal membranes, whereas stacked thylakoid membranes were detected in the green seed from the mutant lines. Pigment analyses indicated that total chlorophyll was lowest in the mature seeds of the control line. Mature d1d2 and cyt-G1 seed had elevated Chl a and Chl b levels, respectively. In both control and mutant lines, Lhcb1, Lhcb2, and RbcS mRNAs were abundant in embryos prior to cotyledon filling, declined after the onset of storage protein accumulation, and were barely detectable or undetectable in all later stages of seed development. Therefore, the chlorophyll-retention phenotype must be a result of the alteration of a process that occurs after translation of photosynthesis-related mRNAs to stabilize apoprotein and pigment levels. Furthermore, different elements controlling either the synthesis or turnover of Chl a and Chl b must be impaired in the d1d2 and cyt-G1 lines. No reproducible differences in total leaf, embryonic, and chloroplast protein profiles and plastid DNAs could be correlated with the mutations that induced chlorophyll retention.     

Molecular phylogeny and divergence times of drosophilid species

The phylogenetic relationships and divergence times of 39 drosophilid species were studied by using the coding region of the Adh gene. Four genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and Sophophora--were included. After conducting statistical analyses of the nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila as the outgroup. The phylogenetic tree obtained showed that the first major division of drosophilid species occurs between subgenus Sophophora (genus Drosophila) and the group including subgenera Drosophila and Engiscaptomyza plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then divided into D. willistoni and the clade of D. obscura and D. melanogaster species groups. In the other major drosophilid group, Zaprionus first separates from the other species, and then D. immigrans leaves the remaining group of species. This remaining group then splits into the D. repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila, Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups is monophyletic. The splitting of subgenera Drosophila and Sophophora apparently occurred about 40 Mya, whereas the D. repleta group and the Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya, suggesting that Scaptomyza experienced a rapid morphological evolution. The D. obscura and D. melanogaster groups apparently diverged about 25 Mya. Many of the D. repleta group species studied here have two functional Adh genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two duplication events.      

Effects of parathyroid hormone and calcitonin on adenylate cyclase in murine mononuclear phagocytes

Peritoneal mononuclear phagocytes elicited by thioglycollate demonstrate responsiveness to parathyroid hormone (PTH) and calcitonin (CT) which differs from that seen in the normal resident population. PTH causes a twofold stimulation of adenylate cyclase activity in elicited cells but inhibits this activity in resident cells. CT causes a greater stimulation of adenylate cyclase in elicited than in resident cells. Both CT and PTH cause an increase in cyclic AMP accumulation in cultures of elicited mononuclear phagocytes. These results indicate that cells of the mononuclear phagocyte lineage have functional receptors for both PTH and CT. This is the first biochemical evidence to support the hypothesis that mononuclear phagocytes are precursors of the bone resorbing osteoclast.     

Large scale, analytical method for isolating basal lateral plasma membranes from rat duodenum.

A procedure is described for obtaining large amounts of basal lateral plasma membranes from the rat duodenal epithelium. The yield is approximately 50%, and the purification factor is 18; preparations from 25 rats routinely contain 100 mg of protein. The procedure depends on mild homogenization with a nitrogen cavitation bomb, followed by removal of brush borders by sedimentation in a weak centrifugal field. Basal lateral membranes in the resulting supernatant are partially purified by differential centrifugation in a medium which approximates their equilibrium density, and then further purified by equilibrium density gradient centrifugation in a high capacity zonal rotor. Brush border membranes may be isolated from the 450 x g pellet. Since both brush border and basal lateral membranes may be isolated from the same homogenate, this preparative procedure is suitable for such analytical purposes as determinations of distribution of enzyme activities between the two surfaces of the epithelium. The large scale of the isolation procedure makes it an appropriate starting point for purification of specific basal lateral membrane components.     

Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

Perturbation of pulmonary immune functions by carbon nanotubes and susceptibility to microbial infection

Occupational and environmental pulmonary exposure to carbon nanotubes (CNT) is considered to be a health risk with a very low threshold of tolerance as determined by the United States Center for Disease Control. Immortalized airway epithelial cells exposed to CNTs show a diverse range of effects including reduced viability, impaired proliferation, and elevated reactive oxygen species generation. Additionally, CNTs inhibit internalization of targets in multiple macrophage cell lines. Mice and rats exposed to CNTs often develop pulmonary granulomas and fibrosis. Furthermore, CNTs have immunomodulatory properties in these animal models. CNTs themselves are proinflammatory and can exacerbate the allergic response. However, CNTs may also be immunosuppressive, both locally and systemically. Studies that examined the relationship of CNT exposure prior to pulmonary infection have reached different conclusions. In some cases, pre-exposure either had no effect or enhanced clearance of infections while other studies showed CNTs inhibited clearance. Interestingly, most studies exploring this relationship use pathogens which are not considered primary pulmonary pathogens. Moreover, harmony across studies is difficult as different types of CNTs have dissimilar biological effects. We used Pseudomonas aeruginosa as model pathogen to study how helical multi-walled carbon nanotubes (HCNTs) affected internalization and clearance of the pulmonary pathogen. The results showed that, although HCNTs can inhibit internalization through multiple processes, bacterial clearance was not altered, which was attributed to an enhanced inflammatory response caused by pre-exposure to HCNTs. We compare and contrast our findings in relation to other studies to gauge the modulation of pulmonary immune response by CNTs.