Effects of stone topography on abundance of net-building caddisfly larvae and arthropod diversity in an upland stream

We investigated whether small pits on the surfaces of stream stones affected abundances of net-spinning, hydropsychid larvae (Trichoptera) and species diversity in the Acheron River, southeastern Australia. On stream stones, nets occurred more often in small (at least 5 mm width) pits than expected by chance. However, proportionately high numbers of pits were not associated with high abundances of either of two species of hydropsychid larvae (both Asmicridea spp). A colonization experiment, using bricks with 0, 4, 12 or 30 small (diam. 5.5 mm) and large (13 mm) pits drilled into the top surfaces, showed that numbers of nets were related to numbers of pits. Small pits were preferred over large ones and the pits, as a group, were occupied almost entirely by late instars of both species. However, only Asmicridea sp. 1 was more abundant on pitted bricks; Asmicridea sp. 2 showed no response. The differences between the species, and between the stone and brick results, can be explained by different proportions of late instars in the samples. Many I instars probably did not make nets. Hence, higher numbers of larvae on pitted surfaces is expected only when late instars are relatively frequent, as was true for Asmicridea sp. 1 on bricks. There were no effects of pits per se or increased numbers of hydropsychid nets on species diversity or the abundances of other common species. These results contrast with those of other studies, which found stone topography or hydropsychid nets to increase species diversity on stones.     

Synthesis,characterization and absolute configurations of methyl ladderanoates

Methyl esters of [5]-ladderanoic acid and [3]-ladderanoic acid were prepared by esterification of the acids isolated from biomass at a wastewater treatment plant. Optical rotations at six different wavelengths (633, 589, 546, 436, 405 and 365 nm) and vibrational circular dichroism (VCD) spectra in the 1800–900 cm⁻¹ region were measured in CDCl₃ solvent and compared with quantum chemical (QC) predictions using B3LYP functional and 6-311++G(2d,2p) basis set with polarizing continuum model representing the solvent. QC predictions gave negative optical rotations at all six wavelengths for (R)-methyl [5]-ladderanoate and positive optical rotations for (R)-methyl [3]-ladderanoate, the same signs as previously reported for the corresponding acids. The crystal structure of (−)-methyl [5]-ladderanoate independently confirmed (R) configuration. The QC-predicted VCD spectra using Boltzmann population weighted spectra of individual conformers did not provide satisfactory quantitative agreement with the experimental VCD spectra. An improved quantitative agreement for VCD spectra could be obtained when conformer populations were optimized to maximize the similarity between experimental and predicted VCD spectra, but more improvements in VCD predictions are needed.     

Endothelial cell telomere dysfunction induces senescence and results in vascular and metabolic impairments

In advanced age, increases in oxidative stress and inflammation impair endothelial function, which contributes to the development of cardiovascular disease (CVD). One plausible source of this oxidative stress and inflammation is an increase in the abundance of senescent endothelial cells. Cellular senescence is a cell cycle arrest that occurs in response to various damaging stimuli. In the present study, we tested the hypothesis that advanced age results in endothelial cell telomere dysfunction that induces senescence. In both human and mouse endothelial cells, advanced age resulted in an increased abundance of dysfunctional telomeres, characterized by activation of DNA damage signaling at telomeric DNA. To test whether this results in senescence, we selectively reduced the telomere shelterin protein telomere repeat binding factor 2 (Trf2) from endothelial cells of young mice. Trf2 reduction increased endothelial cell telomere dysfunction and resulted in cellular senescence. Furthermore, induction of endothelial cell telomere dysfunction increased inflammatory signaling and oxidative stress, resulting in impairments in endothelial function. Finally, we demonstrate that endothelial cell telomere dysfunction-induced senescence impairs glucose tolerance. This likely occurs through increases in inflammatory signaling in the liver and adipose tissue, as well as reductions in microvascular density and vasodilation to metabolic stimuli. Cumulatively, the findings of the present study identify age-related telomere dysfunction as a mechanism that leads to endothelial cell senescence. Furthermore, these data provide compelling evidence that senescent endothelial cells contribute to age-related increases in oxidative stress and inflammation that impair arterial and metabolic function.     

Removal of the projection domain of microtubule-associated protein 2 alters its interaction with tubulin

Microtubule-associated proteins (MAPs) can promote microtubule assemblyin vitro. One of these MAPs (MAP2) consists of a short promoter domain which binds to the microtubule and promotes assembly and a long projection domain which projects out from the microtubule and may interact wth other cytoskeletal elements. We have previously shown that MAP2 and another MAP, tau, differ in their interactions with tubulin in that tau, but not MAP2, promotes extensive aggregation of tubulin into spiral clusters in the presence of vinblastine and that microtubules formed with MAP2 are more resistant than those formed with tau to the antimitotic drug maytansine [Luduena, R. F.,et al. (1984),J. Biol. Chem. 259, 12890–12898; Fellous, A.,et al. (1985),Cancer Res. 45, 5004–5010]. Here we have used chymotryptic digestion to remove the projection domain of MAP2 and examined the interaction of the digested MAP2 (ctMAP2) with tubulin in the presence of vinblastine and maytansine. We have found that ctMAP2 behaves very much like tau, but not like undigested MAP2, in the presence of vinblastine, in that ctMAP2 causes tubulin to polymerize into large clusters of spirals. In contrast, microtubule assembly in the presence of ctMAP2 is much more resistant to maytansine inhibition than is assembly in the presence of tau or undigested MAP2. Our results suggest that the projection domain of MAP2 may play a role in the interaction of tubulin with MAP2 during microtubule assembly.Abbreviations MAPs microtubule-associated proteins - ctMAP2 MAP2 digested with-chymotrypsin - nMAP2 untreated MAP2 - PMSF phenylmethylsulfonyl fluoride - GMPCPP guanosine-5-(,-methylene)triphosphate     

Abscission responses to moisture stress, auxin transport inhibitors, and ethephon

The three abscission-inducing agents - water stress, Ethephon, and auxin transport inhibitors-acted synergistically to promote leaf fall in cotton (Gossypium hirsutum L.). However, the synergism was primarily between stress and Ethephon. Auxin transport inhibitors did not promote the effect of stress alone, only promoted the effect of Ethephon in well watered plants and gave a very small promotion with stress and Ethephon together. Abscission was rapid in stressed plants treated with Ethephon and an auxin transport inhibitor, while leaves fell more slowly from well watered plants treated with Ethephon alone. This suggests that water stress or auxin transport inhibitors influence initial events in abscission; since an auxin transport inhibitor will replace the effect of stress but not Ethephon, an initial event in stress-induced abscission appears to be inhibition of auxin transport. Ethephon promoted lateral bud release, and auxin transport inhibitors did not duplicate that effect alone or promote it in combination with Ethephon.     

Identification of Beijerinckia in the High Arctic (Devon Island, Northwest Territories)

Although generally considered, with few exceptions, to be restricted to the acidic, tropical soils of the southern hemisphere, Beijerinckia species, resembling B. indica, were found at three sites on Devon Island (75°33′N, 84°40′W) in the Canadian Arctic.     

Inactivation of purine nucleoside phosphorylase by modification of arginine residues.

Treatment of purine nucleoside phosphorylase (EC 2.4.2.1), from either calf spleen or human erythrocytes, with 2,3-butanedione in borate buffer or with phenylglyoxal in Tris buffer markedly decreased the enzyme activity. At pH 8.0 in 60 min, 95% of the catalytic activity was destroyed upon treatment with 33 mM phenylglyoxal and 62% of the activity was lost with 33 mm 2,3-butanedione. Inorganic phosphate, ribose-1-phosphate, arsenate, and inosine when added prior to chemical modification all afforded protection from inactivation. No apparent decrease in enzyme catalytic activity was observed upon treatment with maleic anhydride, a lysine-specific reagent. Inactivation of electrophoretically homogeneous calf-spleen purine nucleoside phosphorylase by butanedione was accompanied by loss of arginine residues and of no other amino acid residues. A statistical analysis of the inactivation data vis-à-vis the fraction of arginines modified suggested that one essential arginine residue was being modified.     

Kinetics of transport of hydrophobic ions through lipid membranes including diffusion polarization in the aqueous phase

Previous interpretations of the kinetics of transport of hydrophobic ions through membranes have been based on one of three limiting assumptions. Either diffusion in the aqueous phase was taken to be rapid, or ionic motion was constrained to the membrane or a steady state was presumed to be established within the membrane. We present a general treatment of the coupled diffusion process through both the aqueous phase and the membrane; our theory contains the previous results as limiting cases. It is applied to voltage jump-current relaxation experiments on black lipid membranes in the presence of dipicrylamine or sodium tetraphenylborate. We have attempted to establish the rate of desorption from the membrane. For the system phosphatidylserine/tetraphenylborate, the rate of desorption and the rate of translocation were found to be comparable.