Copyright (c) 2009 University of Wollongong All rights reserved. http://ro.uow.edu.au/scipapers Recent documents in Faculty of Science - Papers en-us Wed, 11 Nov 2009 16:09:25 PST 3600 http://ro.uow.edu.au/scipapers/171 http://ro.uow.edu.au/scipapers/171 Thu, 05 Nov 2009 14:43:18 PST We report a meta-analysis of data from 34 field studies into the effects of UV-B radiation on Arctic and Antarctic bryophytes and angiosperms. The studies measured plant responses to decreases in UV-B radiation under screens, natural fluctuations in UV-B irradiance, or increases in UV-B radiation applied from fluorescent UV lamps. Exposure to UV-B radiation was found to increase the concentrations of UV-B absorbing compounds in leaves or thalli by 7% and 25% (expressed on a mass or area basis, respectively). UV-B exposure also reduced aboveground biomass and plant height by 15% and 10%, respectively, and increased DNA damage by 90%. No effects of UV-B exposure were found on carotenoid or chlorophyll concentrations, net photosynthesis, Fv/Fm or ΦPSII, belowground or total biomass, leaf mass, leaf area or specific leaf area (SLA). The methodology adopted influenced the concentration of UV-B absorbing compounds, with screens and natural fluctuations promoting significant changes in the concentrations of these pigments, but lamps failing to elicit a response. Greater reductions in leaf area and SLA, and greater increases in concentrations of carotenoids, were found in experiments based in Antarctica than in those in the Arctic. Bryophytes typically responded in the same way as angiosperms to UV-B exposure. Regression analyses indicated that the percentage difference in UV-B dose between treatment and control plots was positively associated with concentrations of UV-B absorbing compounds and carotenoids, and negatively so with aboveground biomass and leaf area. We conclude that, despite being dominated by bryophytes, the vegetation of polar regions responds to UV-B exposure in a similar way to higher plant-dominated vegetation at lower latitudes. In broad terms, the exposure of plants in these regions to UV-B radiation elicits the synthesis of UV-B absorbing compounds, reduces aboveground biomass and height, and increases DNA damage. K. K. Newsham http://ro.uow.edu.au/scipapers/170 http://ro.uow.edu.au/scipapers/170 Thu, 29 Oct 2009 18:01:01 PDT This study explores methods of characterising experimental and modelling data to see if trace gas measurements at the Cape Point GAW station could improve our understanding of sources from the continent. Selection criteria have been defined which make it possible to divide the samples into categories with predominant transport to Cape Point from one of four source regions: City (greater Cape Town); close rural (within about 150 km of Cape Point); distant rural (from 150 to about 500 km) and very distant rural covering the rest of southern Africa. For species with fairly uniform source such as radon or CO, this regional selection worked well, but for CO2 the respiration and photosynthesis cycle from very close vegetation usually overwhelmed the input from other sources. It was only in winter that the draw-down by wheat growing in the close rural zone was clearly evident in the Cape Point CO2 data. S. Whittlestone http://ro.uow.edu.au/scipapers/169 http://ro.uow.edu.au/scipapers/169 Thu, 03 Sep 2009 20:01:39 PDT Various mammalian small heat-shock proteins (sHSPs) can interact with one another to form large polydisperse assemblies. In muscle cells, HSPB2/MKBP (myotonic dystrophy protein kinase-binding protein) and HSPB3 have been shown to form an independent complex. To date, the biochemical properties of this complex have not been thoroughly characterized. In this study, we show that recombinant HSPB2 and HSPB3 can be successfully purified from E.coli cells co-expressing both proteins. Nanoelectrospray ionization mass spectrometry and sedimentation velocity analytical ultracentrifugation analysis showed that HSPB2/B3 forms a series of well defined hetero-oligomers, consisting of 4, 8, 12, 16, 20 and 24 subunits, each maintaining a strict 3:1 HSPB2:HSPB3 subunit ratio. These complexes are thermally stable up to 40 °C, as determined by far-UV circular dichroism spectroscopy. Surprisingly, HSPB2/B3 exerted a poor chaperone-like and thermoprotective activity, which is likely related to the low surface hydrophobicity, as revealed by its interaction with the hydrophobic probe 1-anilino-8-naphthalenesulfonic acid. Co-immunoprecipitation experiments demonstrated that the HSPB2/B3 oligomer cannot interact with HSP20, HSP27 or αB-crystallin, whereas the homomeric form of HSPB2, thus not in complex with HSPB3, could efficiently associate with HSP20. Taken altogether, this study brings evidence that despite the high sequence homology within the sHSP family, the biochemical properties of the HSPB2/B3 complex are distinctly different from other sHSPs, indicating that the HSPB2/B3 assembly likely possesses other cellular functions than its family members. J. den Engelsman http://ro.uow.edu.au/scipapers/168 http://ro.uow.edu.au/scipapers/168 Tue, 25 Aug 2009 20:07:40 PDT We report the results of an intercomparison of vertical column amounts of hydrogen chloride (HCl), hydrogen fluoride (HF), nitrous oxide (N2O), nitric acid (HNO3), methane (CH4), ozone (O3), carbon dioxide (CO2) and nitrogen (N2) derived from the spectra recorded by two ground-based Fourier transform infrared (FTIR) spectrometers operated side-by-side using the sun as a source. The procedure used to record spectra and derive vertical column amounts follows the format of previous instrument intercomparisons organised by the Network for Detection of Atmospheric Composition Change (NDACC), formerly known as the Network for Detection of Stratospheric Change (NDSC). For most gases the differences were typically around 3% and in about half of the results the error bars given by the standard deviation of the measurements from each instrument did not overlap. The worst level of agreement was for HF where differences of over 5% were typical. The level of agreement achieved during this intercomparison is a little worse than that achieved in previous intercomparisons between ground-based FTIR spectrometers. C. Paton-Walsh http://ro.uow.edu.au/scipapers/167 http://ro.uow.edu.au/scipapers/167 Mon, 24 Aug 2009 23:56:40 PDT We report the first atmospheric column measurements of methanol made by ground-based solar Fourier transform infrared spectroscopy. The measurements were made through smoke plumes over South Eastern Australia during the Austral summers of 2001/2002 and 2002/2003. There is a strong correlation between the measured column amounts of methanol and simultaneous and co-located measurements of aerosol optical depth. An emission factor for methanol from Australian forest fires of 2.3 ± 0.8 grams per kilogram of dry fuel consumed is estimated by use of the correlations of methanol and carbon monoxide with aerosol optical depth and literature values for the emission factor of carbon monoxide. This agrees well with literature values for emissions measured from extra-tropical forest fires elsewhere in the world. Methanol is clearly an important volatile organic product of forest fires with an emission factor similar to formaldehyde's and approximately half that of methane. C. Paton-Walsh http://ro.uow.edu.au/scipapers/166 http://ro.uow.edu.au/scipapers/166 Tue, 11 Aug 2009 22:35:26 PDT The flesh-eating bacterium group A Streptococcus (GAS) binds and activates human plasminogen, promoting invasive disease. Streptococcal surface enolase (SEN), a glycolytic pathway enzyme, is an identified plasminogen receptor of GAS. Here we used mass spectrometry (MS) to confirm that GAS SEN is octameric, thereby validating in silico modeling based on the crystal structure of S. pneumoniae α-enolase. Site-directed mutagenesis of surface-located lysine residues (SENK252+255A, SENK304A, SEN>sup>K334A, SENK344E, SENK435L and SENΔ434-435) was used to examine their roles in maintaining structural integrity, enzymatic function and plasminogen binding. Structural integrity of the GAS SEN octamer was retained for all mutants except SENK344E, as determined by circular dichroism spectroscopy and MS. However, ion-mobility MS revealed distinct differences in the stability of several mutant octamers in comparison to wild-type. Enzymatic analysis indicated that SENK344E had lost α-enolase activity, which was also reduced in SENK334A and SENΔ434-435. Surface plasmon resonance demonstrated that the capacity to bind human plasminogen was abolished in SENK252+255A, SENK435L and SENΔ434-435. The lysine residues at positions 252, 255, 434 and 435, therefore play a concerted role in plasminogen acquisition. This study demonstrates the ability of combining in silico structural modeling with ion mobility-MS validation for undertaking functional studies on complex protein structures. A. J. Cork http://ro.uow.edu.au/scipapers/165 http://ro.uow.edu.au/scipapers/165 Mon, 27 Jul 2009 18:58:57 PDT Mangroves form important ecosystems in Kenya's coastal areas. They produce goods and services that are of environmental, ecological and economic importance to human society. However, mangroves are under continuing pressure from anthropogenic disturbances. A particular concern has been the clearing of mangrove areas to reclaim land for other uses such as aquaculture, salt manufacture, agriculture and housing. About 10 000 ha of mangrove areas have been cleared for salt manufacture between Ngomeni and Karawa, while in Lamu, close to 100 ha of mangrove forest was killed by dredged-up sediment that was deposited during the construction of the Mokowe sea jet. 100 ha of mangrove area have been converted for aquaculture at Ngomeni. At Gazi Bay, about l00 ha of mangrove forests was cleared for fuelwood and in Makupa Creek, Mombasa, 10 ha of mangroves died due to oil pollution. The total area lost is therefore 10 310 ha which represents about 20% of the total mangrove forest. In this paper, deforestation, conversion of mangrove areas for other land uses and pollution of mangrove swamps on the Kenyan coast are discussed and call for sustainable use, and the government policies that will enable this, is made. P. A. O. Abuodha http://ro.uow.edu.au/scipapers/164 http://ro.uow.edu.au/scipapers/164 Sun, 19 Jul 2009 20:21:28 PDT Since the IPCC Third Assessment Report (TAR), our understanding of the implications of climate change for coastal systems and low-lying areas (henceforth referred to as 'coasts') has increased substantially and six important policy-relevant messages have emerged. Coasts are experiencing the adverse consequences of hazards related to climate and sea level (very high confidence). Coasts are highly vulnerable to extreme events, such as storms, which impose substantial costs on coastal societies [6.2.1, 6.2.2, 6.5.2]. Annually, about 120 million people are exposed to tropical cyclone hazards, which killed 250,000 people from 1980 to 2000 [6.5.2]. Through the 20th century, global rise of sea level contributed to increased coastal inundation, erosion and ecosystem losses, but with considerable local and regional variation due to other factors [6.2.5, 6.4.1]. Late 20th century effects of rising temperature include loss of sea ice, thawing of permafrost and associated coastal retreat, and more frequent coral bleaching and mortality [6.2.5]. Coasts will be exposed to increasing risks, including coastal erosion, over coming decades due to climate change and sea-level rise (very high confidence). Anticipated climate-related changes include: an accelerated rise in sea level of up to 0.6 m or more by 2100; a further rise in sea surface temperatures by up to 3°C; an intensification of tropical and extra-tropical cyclones; larger extreme waves and storm surges; altered precipitation/run-off; and ocean acidification [6.3.2]. These phenomena will vary considerably at regional and local scales, but the impacts are virtually certain to be overwhelmingly negative [6.4, 6.5.3]. R. J. Nicholls http://ro.uow.edu.au/scipapers/163 http://ro.uow.edu.au/scipapers/163 Thu, 16 Jul 2009 19:16:37 PDT Multiwall carbon nanotubes have been grown by catalytic chemical vapour deposition using iron catalyst particles drop cast onto etched silicon wafers. The catalyst used was poly(styrene-vinylferrocene) in toluene solution which has an iron content of 2.1%. The etched silicon wafers have trench regions of varying widths ranging from 0.32 to 1 μm. For trench widths below 0.5 μm the number of "interconnecting" tubes growing from one side of the trench to the other increases sharply. A significant proportion of these "interconnects" are found to be Y-junction and multiple junction MWNTs. A systematic study of the effects of each of the growth conditions (temperature, run time, gas flow, catalyst concentration and trench width) versus interconnect yield was carried out. Densities of ~ 1.6 interconnects per micron of trench are obtained, with junction structures accounting for 38% of these interconnects. Densities can be controlled through modification of chemical vapour deposition conditions. R. W. Leahy http://ro.uow.edu.au/scipapers/162 http://ro.uow.edu.au/scipapers/162 Tue, 14 Jul 2009 17:47:28 PDT A transition in hemoglobin (Hb), involving partial unfolding and aggregation, has been shown previously by various biophysical methods. The correlation between the transition temperature and body temperature for Hb from different species, suggested that it might be significant for biological function. In order to focus on such biologically relevant human Hb dynamics, we studied the protein internal picosecond motions as a response to hydration, by elastic and quasielastic neutron scattering. Rates of fast diffusive motions were found to be significantly enhanced with increasing hydration from fully hydrated powder to concentrated Hb solution. In concentrated protein solution, the data revealed that amino acid side-chains can explore larger volumes above body temperature than expected from normal temperature dependence. The body temperature transition in protein dynamics was absent in fully hydrated powder, indicating that picosecond protein dynamics responsible for the transition is activated only at a sufficient level of hydration. A collateral result from the study is that fully hydrated protein powder samples do not accurately describe all aspects of protein picosecond dynamics that might be necessary for biological function. A. M. Stadler