Photoinhibition in differently coloured juvenile leaves of Syzygium species

Photoinhibition, as measured by the dark-adapted chlorophyll a fluorescence ratio Fv/Fm, was assessed in Syzygium moorei, a species with dark green juvenile leaves, Syzygium corynanthum, which has light green juvenile leaves, and two species with pink-red juvenile leaves (Syzygium wilsonii and Syzygium luehmannii). All plants were glasshouse-grown (maximum PPFD 1500 mol m^-2 s^-1) under optimum nutrition and water.When measured at midday, dark-adapted Fv/Fm ratios of juvenile leaves gradually increased in all species as percentage of full leaf expansion (% FLE) increased. Fluorescence measurement 3h after sunset or pre-dawn also showed a developmental effect on Fv/Fm, with juvenile leaves of S. luehmannii and S. wilsonii showing much lower Fv/Fm at all stages of development. Dark-adapted Fv/Fm, values in both juvenile and mature leaves generally never exceeded 0.8 at any stage in any of the species.Courses of Fv/Fm on sunny days showed greater diurnal photoinhibition in green juvenile (c. 50% FLE) leaves of S. moorei (24%) and S. corynanthum (36%) than in mature leaves of the previous flush in these species (<10%). Diurnal photoinhibition was statistically similar (18-24%) in pink-red juvenile and green mature leaves of S. luehmannii and S. wilsonii. Re-positioning juvenile leaves of S. wilsonii horizontally increased diurnal photoinhibition.Exposure of leaves to a standard mild photoinhibitory light treatment (30 min at 1000 mol m^-2s^-1) showed that juvenile leaves of all species had a lower percentage of high energy state quenching (qE) and a higher percentage of photoinhibitory quenching (qI) than mature leaves.     

The role of different arbuscular mycorrhizal fungi in the growth of Calamagrostis villosa and Deschampsia flexuosa, in experiments with simulated acid rain

A series of microcosm experiments was established to investigate the effects of simulated acid rain on the capacity of three arbuscular mycorrhizal fungi (AMF) to germinate and colonize two grasses, Calamagrostis villosa and Deschampsia flexuosa. These two grasses are normally found in degraded Norway spruce forests in the Northern Czech Republic where acid rain pollution exists and C. villosa initially outcompetes D. flexuosa for the same niche. An AM fungus isolated from acid soils (Acaulospora tuberculata BEG41) was more tolerant of acidification than two species of Glomus (isolated from agricultural soils of neutral pH) in microcosm studies. Different effects of simulated acid rain (SAR) were found at all stages of the development of three AMF studied in model systems, including spore germination, colonization of host roots, and alkaline phosphatase (ALP) and NADH diaphorase activity of the extraradical mycelium. No ALP activity was found in hyphae germinating from the spores without plants whereas it was detected in all hyphae linked to a functioning intraradical mycelium.Simulated acid rain also affected the mycorrhizal growth response and belowground competition of the two grasses. Disturbance of the ERM between the two plant species significantly reduced the growth of C. villosa but not D. flexuosa. Disturbance also decreased root colonization by AMF of both plants, the total length of ERM and the total length of extraradical hyphae with ALP and NADH diaphorase activity adjacent to both plants. D. flexuosa appeared less dependent on the mycorrhizal state, for shoot and root growth, than C. villosa under the experimental conditions. The ability, therefore, of C. villosa to thrive in forest stands suffering from acid rain pollution may be related to this dependence on its mycorrhizal hyphal links to D. flexuosa under the environmental conditions produced by the pollution including higher light levels.     

A comparison of the development and metabolic activity of mycorrhizas formed by arbuscular mycorrhizal fungi from different genera on two tropical forage legumes

 Two glasshouse experiments were done to assess the development and metabolic activity of mycorrhizas formed by isolates of arbuscular mycorrhizal fungi (AMF) from three different genera, Acaulospora, Gigaspora and Glomus on either Pueraria phaseoloides L. or Desmodium ovalifolium L. plants. The second of the two experiments included three levels of a localised phosphate source in the pots. Alkaline phosphatase (ALP), stained histochemically in the intra-radical mycelium (IRM) of AMF over sequential harvests, did not provide a direct marker for the efficiency of AMF in mobilising phosphorus (P) for plant growth and development. The ability of the extra-radical mycelium (ERM) to scavenge a localised phosphate source, determined by its extraction from buried 35-μm mesh pouches, was dependent on the species of AMF tested. This work indicates that AMF from different genera have unique patterns of mycelial development when forming mycorrhizas with tropical hosts in the presence of a localised phosphate source. AMF also appear to have different mechanisms for the control of P transfer, within the mycelium, to the host. The significance of the architecture of the ERM is discussed as well as the localisation of ALP in the IRM in determining the efficiency of AMF in terms of P accumulation in planta and subsequent growth of plants. Accepted: 19 August 1998     

Hydrodynamic properties of mucins secreted by primary cultures of Guinea-pig tracheal epithelial cells: determination of diffusion coefficients by analytical ultracentrifugation and kinetic analysis of mucus gel hydration and dissolution

We have used two different approaches to determine hydrodynamic parameters for mucins secreted by guinea-pig tracheal epithelial cells in primary culture. Cells were cultured under conditions that promote mucous cell differentiation. Secreted mucins were isolated as the excluded fraction from a Sepharose CL-4B gel filtration column run under strongly dissociating conditions. Biochemical analysis confirmed the identity of the high molecular weight material as mucins. Analytical ultracentrifugation was used to study the physical properties of the purified mucins. The weight average molecular mass (M _w ) for three different preparations ranged from 3.3×10⁶ to 4.7×10⁶ g/mol (corresponding to an average structure of 1 – 2 subunits), and the sedimentation coefficient from 25.5 to 35 S. Diffusion coefficients ranging from 4.5×10^–8 to 6.4×10^–8 cm²/s were calculated using the Svedberg equation. A polydispersity index (M _z /M _w ) of ∼1.4 was obtained. Diffusivity values were also determined by image analysis of mucin granule exocytosis captured by videomicroscopy. The time course of hydration and dissolution of mucin was measured and a relationship is presented which models both phases, each with first order kinetics, in terms of a maximum radius and rate constants for hydration and dissolution. A median diffusivity value of 8.05×10^–8 cm²/s (inter-quartile range = 1.11×10^–7 to 6.08×10^–8 cm²/sec) was determined for the hydration phase. For the dissolution phase, a median diffusivity value of 6.98×10^–9 cm²/s (inter-quartile range = 1.47×10^–8 to 3.25×10^–9 cm²/sec) was determined. These values were compared with the macromolecular diffusion coefficients (D _20,w ) obtained by analytical ultracentrifugation. When differences in temperature and viscosity were taken into account, the resulting D _37,g was within the range of diffusivity values for dissolution. Our findings show that the physicochemical properties of mucins secreted by cultured guinea-pig tracheal epithelial cells are similar to those of mucins of the single or double subunit type purified from respiratory mucus or sputum. These data also suggest that measurement of the diffusivity of dissolution may be a useful means to estimate the diffusion coefficient of mucins in mucus gel at the time of exocytosis from a secretory cell. Received: 10 March 1998 / Accepted: 27 March 1998     

Tuberculosis Prevention in South Africa

Background

South Africa has one of the highest per capita rates of tuberculosis (TB) incidence in the world. In 2012, the South African government produced a National Strategic Plan (NSP) to control the spread of TB with the ambitious aim of zero new TB infections and deaths by 2032, and a halving of the 2012 rates by 2016.

Methods

We used a transmission model to investigate whether the NSP targets could be reached if immediate scale up of control methods had happened in 2014. We explored the potential impact of four intervention portfolios; 1) “NSP” represents the NSP strategy, 2) “WHO” investigates increasing antiretroviral therapy eligibility, 3) “Novel Strategies” considers new isoniazid preventive therapy strategies and HIV “Universal Test and Treat” and 4) “Optimised” contains the most effective interventions.

Findings

We find that even with this scale-up, the NSP targets are unlikely to be achieved. The portfolio that achieved the greatest impact was “Optimised”, followed closely by “NSP”. The “WHO” and “Novel Strategies” had little impact on TB incidence by 2050. Of the individual interventions explored, the most effective were active case finding and reductions in pre-treatment loss to follow up which would have a large impact on TB burden.

Conclusion

Use of existing control strategies has the potential to have a large impact on TB disease burden in South Africa. However, our results suggest that the South African TB targets are unlikely to be reached without new technologies. Despite this, TB incidence could be dramatically reduced by finding and starting more TB cases on treatment.     

Ecophysiology of neuronal metabolism in transiently oxygen-depleted environments: Evidence that GABA is accumulated pre-synaptically in the cerebellum

Interactions between coral reef topography, tide cycles, and photoperiod provided selection pressure for adaptive physiological changes in sheltered hypoxic niches to be exploited by specialized tropical reef fish. The epaulette shark Hemiscyllium ocellatum withstands cyclic hypoxia in its natural environment, many hours of experimental hypoxia, and anoxia for up to 5 h. It shows neuronal hypometabolism in response to 5% oxygen saturation. Northern-hemisphere hypoxia- and anoxia-tolerant vertebrates that over-winter under ice alter their inhibitory to excitatory neurotransmitter balance to forestall brain ATP depletion in the absence of oxidative phosphorylation. GABA immunochemistry, HPLC analysis and receptor binding studies in H. ocellatum cerebellum revealed a heterogeneous regional accumulation of neuronal GABA despite no change in its overall concentration, and a significant increase in GABA_A receptor density without altered binding affinity. Increased GABA_A receptor density would protect the cerebellum during reoxygenation when transmitter release resumes. While all hypoxia- and anoxia-tolerant teleosts examined to date respond to low oxygen levels by elevating brain GABA, the phylogenetically older epaulette shark did not, suggesting that it uses an alternative neuroprotective mechanism for energy conservation. This may reflect an inherent phylogenetic difference, or represent a novel ecophysiological adaptation to cyclic variations in the availability of oxygen.     

Differential expression level of cytokeratin 8 in cells of the bovine nucleus pulposus complicates the search for specific intervertebral disc cell markers

Introduction  

Development of cell therapies for repairing the intervertebral disc is limited by the lack of a source of healthy human disc cells. Stem cells, particularly mesenchymal stem cells, are seen as a potential source but differentiation strategies are limited by the lack of specific markers that can distinguish disc cells from articular chondrocytes.     

Applications of computational fluid dynamics (CFD) in the modelling and design of ventilation systems in the agricultural industry: a review

The application of computational fluid dynamics (CFD) in the agricultural industry is becoming ever more important. Over the years, the versatility, accuracy and user-friendliness offered by CFD has led to its increased take-up by the agricultural engineering community. Now CFD is regularly employed to solve environmental problems of greenhouses and animal production facilities. However, due to a combination of increased computer efficacy and advanced numerical techniques, the realism of these simulations has only been enhanced in recent years. This study provides a state-of-the-art review of CFD, its current applications in the design of ventilation systems for agricultural production systems, and the outstanding challenging issues that confront CFD modellers. The current status of greenhouse CFD modelling was found to be at a higher standard than that of animal housing, owing to the incorporation of user-defined routines that simulate crop biological responses as a function of local environmental conditions. Nevertheless, the most recent animal housing simulations have addressed this issue and in turn have become more physically realistic.