PHOTOPHYSIOLOGY OF A TURF ALGAL COMMUNITY: INTEGRATED RESPONSES TO AMBIENT LIGHT AND STANDING BIOMASS1

This study investigated the variation in the relationship between photosynthesis and ambient light (P‐E curves) for turf algal communities on a temperate reef off the coast of South Australia, analyzing the integrated effects of ambient light and standing biomass. The photophysiology of turfs was studied in situ on a seasonal basis, examining algal communities growing on artificial substrate (plates) at depths of 4 m and 10 m. P‐E curves and estimates for the photokinetic parameters (P_m, R_d, α, E_k, and E_c) were obtained through oxygen evolution methods, using an automated underwater respirometer. Photoacclimation responses to changes in ambient light were strongly affected by the biomass of the community. P_m showed an inverse relationship to standing biomass, irrespective of depth and season, which was considered to be a response to self‐shading and boundary layer effects. Biomass effects imposed a high variance on estimates for all photosynthetic parameters, overshadowing differences observed for season and depth. Biomass also affected photoinhibition on turf communities, where significant afternoon depression of photosynthesis was observed in sparse turf patches when compared to denser patches. High areal productivity rates were maintained across all seasons with a significant decrease only being observed during winter.     

Test of an antifouling treatment on tuna fish-cages in Boston Bay, Port Lincoln, South Australia

A test of the antifouling properties of Wattyl NetClear was conducted on fish farms containing southern bluefin tuna (Thunnus maccoyii) during a 6-month period (February-July 2002). Wattyl NetClear is a water-based synthetic latex-based coating where the active antifouling agent is a mixture of two isothiazolinones likely to affect both biochemical conditioning and bacterial colonisation. The development of fouling was monitored using underwater stereo-photogrammetry on 3 treated and 3 untreated net cages with the main factors treatment, depth and cage nested within treatment. A significant treatment and depth effect was found but variable through time and in some instances with significant cage effects. By the end of the study, the difference in fouling load between treated and untreated nets was 14.7%. In total 72% of all free-space data points were on treated nets. The dominating fouling organisms were Enteromorpha sp. and sponges with low settlement of blue mussel and paper oysters. Passive deposition of tuna faeces contributed significantly to the cover. The largest cover of fouling was observed in April-May with a dominance of sponges in June-July. Enteromorpha sp. dominated shallow depths while sponges dominated at deeper levels. Tuna faeces were distributed independent of depth but varied with time. The results showed that fouling of fish cages consisted of both active settlement and passive deposition, the latter independent on antifouling treatment.     

Fluid structure interaction of patient specific abdominal aortic aneurysms: a comparison with solid stress models

Background  

Abdominal aortic aneurysm (AAA) is a dilatation of the aortic wall, which can rupture, if left untreated. Previous work has shown that, maximum diameter is not a reliable determinant of AAA rupture. However, it is currently the most widely accepted indicator. Wall stress may be a better indicator and promising patient specific results from structural models using static pressure, have been published. Since flow and pressure inside AAA are non-uniform, the dynamic interaction between the pulsatile flow and wall may influence the predicted wall stress. The purpose of the present study was to compare static and dynamic wall stress analysis of patient specific AAAs.     

Leptin prevents obesity induced by a high-fat diet after diet-induced weight loss in the marsupial S. crassicaudata

The aims of this study were to determine in the marsupial Sminthopsis crassicaudata, the effects of leptin on food intake, body weight, tail width (a reflection of fat stores), and leptin mRNA, after caloric restriction followed by refeeding ad libitum with either a standard or high-fat preferred diet. S. crassicaudata (n = 32), were fed standard laboratory diet (LabD; 1.01 kcal/g, 20% fat) ad libitum fo 3 days. On days 4-10, animals received LabD at 75% of basal intake and then (days 11-25) were fed either LabD or a choice of LabD and mealworms (MW; 2.99 kcal/g, 30% fat); during this time, half the animals (n = 8) in each group received either leptin (2.5 mg/kg) or PBS intraperitoneally two times daily. On day 26, animals were killed and fat was removed for assay of leptin mRNA. At baseline, body weight, tail width, and food intake were similar in each group. After caloric restriction, body weight (P < 0.001) and tail width (P < 0.001) decreased. On return to ad libitum feeding in the PBS-treated animals, body weight and tail width returned to baseline in the LabD-fed animals (P < 0.001) and increased above baseline in the MW-fed animals (P < 0.001). In the LabD groups, tail width (P < 0.001) and body weight (P < 0.001) decreased after leptin compared with PBS. In the MW groups, the increase in tail width (P < 0.001) and body weight (P = 0.001) were attenuated after leptin compared with PBS. The expression of leptin mRNA in groups fed MW were greater in PBS than in leptin-treated animals (P < 0.05). Therefore, after diet-induced weight loss, leptin prevents a gain in fat mass in S. crassicaudata; this has potential implications for the therapeutic use of leptin.     

Automated classification of peripheral distal by-pass geometries reconstructed from medical data

Abnormal haemodynamic conditions are implicated in the development of anastomotic myointimal hyperplasia (MIH). However, these conditions are difficult to determine in vivo, prompting research using ex vivo idealised models. To relate the understanding gained in idealised geometries to anatomically correct conditions we have investigated a reproducible approach to classify in vivo distal graft anastomoses and their inter-patient variability. In vivo distal anastomotic geometries were acquired by magnetic resonance (MR) angiography from 13 patients who had undergone infrageniculate autologous venous by-pass surgery. On average, the images were acquired 2 weeks post-operatively. Five patients also underwent repeat examinations 2 to 7 weeks later. For each geometry, the surface of the arterial lumen is represented by the zero level set of an implicit function constructed from radial basis functions that minimise curvature. The three-dimensional binary image created from the interpolated surface is processed using a skeletonisation algorithm to obtain the centreline of each branch in the geometry. This allows for the measurement of the branching angles between straight line approximations of the centrelines of each vessel, averaging them over a characteristic length of each anastomosis. The main finding in the application of the proposed classification methodology to this set of patients is that the spectrum of anastomoses can be reduced to a small subset of cases characterised by two angles: the angle between the graft and the plane of the host artery and the angle between the graft and the proximal branch of the artery.     

Anderson Fabry disease,a close linkage with highly polymorphic DNA markers DXS17, DXS87 and DXS88

Summary Anderson Fabry disease is an X-linked lysosomal storage disorder caused by α-galactosidase A deficiency. Hemizygous males and some heterozygous females develop renal failure and cardiovacular complications in early adult life. We have investigated six large UK families to assess the possible linkage of five polymorphic DNA probes to the Anderson Fabry locus, previously localised to Xq21-24. No recombination was found between Anderson Fabry disease and DXS87, DXS88 and DXS17, which gave lod_max=6.4,6.4 and 5.8 respectively at θ=0.00, (upper confidence limit 0.10). DXS3 gave lod_max 2.9 at θ=0.10 (upper confidence limit 0.25). DXYS1 was excluded from linkage. The best fit map (DXYS1/DXS3) θ=0.192 (DXS17/DXS87/DXS88/Anderson Fabry locus) provided no information about the order of loci in parentheses due to the absence of recombinants. The close linkage of DXS17, DXS87 and DXS88, together with α-galactosidade A estimation, can be used for antenatal diagnosis and carrier detection until the application of a gene specific probe has been evaluated.     

Uncoupling of Chlamydomonas flagellar gene expression and outgrowth from flagellar excision by manipulation of Ca2+

Chlamydomonas cells respond to certain environmental stimuli by shedding their flagella. Flagellar loss induces a rapid, transient increase in expression of a specific set of genes encoding flagellar proteins, and assembly of a new flagellar pair. While flagellar gene expression and initiation of flagellar outgrowth are normally tightly coupled to flagellar excision, our results demonstrate that these processes can be uncoupled by manipulating Ca2+ levels or calmodulin activity. In our experiments, wild-type cells were stimulated to excise their flagella using mechanical shearing, and at times after deflagellation, flagellar lengths were measured and flagellar mRNA abundance changes were determined by S1 nuclease protection analysis. When extracellular Ca2+ was lowered by addition of EGTA to cultures before excision, flagellar mRNA abundance changes and flagellar outgrowth were temporally uncoupled from flagellar excision. When extracellular Ca2+ was lowered immediately after excision or when calmodulin activity was inhibited with W-7, flagellar outgrowth was uncoupled from flagellar excision and flagellar mRNA abundance changes. Whenever events in the process of flagellar regeneration were temporally uncoupled, the magnitude of the flagellar mRNA abundance change was reduced. These results suggest that flagellar gene expression may be regulated by multiple signals generated from these events, and implicate Ca2+ as a factor in the mechanisms controlling flagellar regeneration.