Plant interactions for pollinator visits: a test of the magnet species effect

Summary From 1985–1987, patterns of fruit and seed set were studied in a population of mayapple (Podophyllum peltatum), a clonal, self-incompatible herb found in deciduous woods in eastern North America. Mayapple flowers do not produce nectar, but depend on infrequent visits by nectar-seeking queen bumble bees for pollination. In all years female reproductive success in mayapple colonies was influenced by colony size (number of flowers), by the distance to neighbouring colonies and by proximity to lousewort plants (Pedicularis canadensis), a prolific nectar producer heavily visited by bumble bees. In all years fruit and seed set were greater in mayapple colonies <25 m from lousewort flowers than in matched colonies which were >50 m from lousewort. In 1985 and 1987 the frequency of queen bumble bee visits to flowers in colonies close to lousewort was about four times greater than to distant colonies. In 1986 I removed about 80% of lousewort flowers to test whether the enhanced fruit and seed set in mayapples close to lousewort was pollinator mediated. Mayapple colonies close to flowerless lousewort patches did not differ in fruit or seed set from matched colonies >50 m from lousewort. In contrast, mayapples close to flowering lousewort patches had greater fruit and seed set compared with distant colonies. Over all years, a larger proportion of mayapples close to flowering lousewort patches had enhanced fruit and seed set compared with colonies close to louseworts without flowers. Though rarely documented, this type of facilitative interaction between plants that are highly attractive to pollinators (magnet species), and co-flowering species that are rarely visited by pollinators, may be widespread in plant communities.     

Cloning and characterization of SK2 channel from chicken short hair cells

In the inner ear of birds, as in mammals, reptiles and amphibians, acetylcholine released from efferent neurons inhibits hair cells via activation of an apamin-sensitive, calcium-dependent potassium current. The particular potassium channel involved in avian hair cell inhibition is unknown. In this study, we cloned a small-conductance, calcium-sensitive potassium channel (gSK2) from a chicken cochlear library. Using RT-PCR, we demonstrated the presence of gSK2 mRNA in cochlear hair cells. Electrophysiological studies on transfected HEK293 cells showed that gSK2 channels have a conductance of approximately 16 pS and a half-maximal calcium activation concentration of 0.74±0.17 M. The expressed channels were blocked by apamin (IC₅₀=73.3±5.0 pM) and d-tubocurarine (IC₅₀=7.6±1.0 M), but were insensitive to charybdotoxin. These characteristics are consistent with those reported for acetylcholine-induced potassium currents of isolated chicken hair cells, suggesting that gSK2 is involved in efferent inhibition of chicken inner ear. These findings imply that the molecular mechanisms of inhibition are conserved in hair cells of all vertebrates.     

The identification of intestinal scavenger receptor class B, type I (SR-BI) by expression cloning and its role in cholesterol absorption

The molecular mechanisms of cholesterol absorption in the intestine are poorly understood. With the goal of defining candidate genes involved in these processes a fluorescence-activated cell sorter-based, retroviral-mediated expression cloning strategy has been devised. SCH354909, a fluorescent derivative of ezetimibe, a compound which blocks intestinal cholesterol absorption but whose mechanism of action is unknown, was synthesized and shown to block intestinal cholesterol absorption in rats. Pools of cDNAs prepared from rat intestinal cells enriched in enterocytes were introduced into BW5147 cells and screened for SCH354909 binding. Several independent clones were isolated and all found to encode the scavenger receptor class B, type I (SR-BI), a protein suggested by others to play a role in cholesterol absorption. SCH354909 bound to Chinese hamster ovary (CHO) cells expressing SR-BI in specific and saturable fashion and with high affinity (K(d) approximately 18 nM). Overexpression of SR-BI in CHO cells resulted in increased cholesterol uptake that was blocked by micromolar concentrations of ezetimibe. Analysis of rat intestinal sections by in situ hybridization demonstrated that SR-BI expression was restricted to enterocytes. Cholesterol absorption was determined in SR-B1 knockout mice using both an acute, 2-h, assay and a more chronic fecal dual isotope ratio method. The level of intestinal cholesterol uptake and absorption was similar to that seen in wild-type mice. When assayed in the SR-B1 knockout mice, the dose of ezetimibe required to inhibit hepatic cholesterol accumulation induced by a cholesterol-containing 'western' diet was similar to wild-type mice. Thus, the binding of ezetimibe to cells expressing SR-B1 and the functional blockade of SR-B1-mediated cholesterol absorption in vitro suggest that SR-B1 plays a role in intestinal cholesterol metabolism and the inhibitory activity of ezetimibe. In contrast studies with SR-B1 knockout mice suggest that SR-B1 is not essential for intestinal cholesterol absorption or the activity of ezetimibe.     

Bumble bee (Hymenoptera: Apidae) activity and pollination levels in commercial tomato greenhouses

Commercial greenhouse studies were conducted to assess levels of pollination of tomato (Lycopersicon esculentum Mill.) flowers in relation to bumble bee (Bombus impatiens Cresson) colony activity and colony densities. For the assessment of pollination levels of tomato flowers, five categories were defined based on bruising levels caused by bumble bee pollination. Colony activity was measured as bee trips per ha/d using electric powered photodiode monitors inserted into the hive entrance. Levels of pollination were positively correlated with bee activity levels, up to a mean of approximately 400 pollen grains per stigma per day, after which greater activity did not result in further increases in daily pollination levels. Densities of colonies in the commercial greenhouses studied ranged from 7.6 to 19.8 colonies per hectare with a mean of 11.6 +/- 0.9. We found that an average activity of 2,000 bee trips per hectare per day was more than adequate to ensure sufficient pollination, and that this level of activity could be achieved with 7-15 colonies per hectare, depending on greenhouse conditions. Greenhouses requiring >15 colonies per hectare to achieve this level of pollination may be able to increase bee activity through alteration of greenhouse conditions. Across 50-m rows of tomato plants, levels of pollination decreased with increasing distance from bee colonies, suggesting that colonies should be evenly distributed throughout the greenhouses.     

Impact of a COPD Discharge Care Bundle on Readmissions following Admission with Acute Exacerbation: Interrupted Time Series Analysis

ObjectivesWe evaluated the impact of a COPD discharge care bundle on readmission rates following hospitalisation with an acute exacerbation.DesignInterrupted time series analysis, comparing readmission rates for COPD exacerbations at nine trusts that introduced the bundle, to two comparison groups; (1) other NHS trusts in London and (2) all other NHS trusts in England. Care bundles were implemented at different times for different NHS trusts, ranging from October 2009 to April 2011.SettingNine NHS acute trusts in the London, England.ParticipantsPatients aged 45 years and older admitted to an NHS acute hospital in England for acute exacerbation of COPD. Data come from Hospital Episode Statistics, April 2002 to March 2012.ResultsIn hospitals introducing the bundle readmission rates were rising before implementation and falling afterwards (e.g. readmissions within 28 days +2.13% per annum (pa) pre and -5.32% pa post (p for difference in trends = 0.012)). Following implementation, readmission rates within 7 and 28 day were falling faster than among other trusts in London, although this was not statistically significant (e.g. readmissions within 28 days -4.6% pa vs. -3.2% pa, p = 0.44). Comparisons with a national control group were similar.ConclusionsThe COPD discharge care bundle appeared to be associated with a reduction in readmission rate among hospitals using it. The significance of this is unclear because of changes to background trends in London and nationally.     

Vitamin C transport and SVCT1 transporter expression in chick renal proximal tubule cells in culture

The characteristics of vitamin C (ascorbic acid, ASC) transport were studied in polarized cultured monolayers of the chick (Gallus gallus) renal proximal tubule in Ussing chambers. Under voltage clamp conditions, monolayers responded to apical addition of ASC in a dose-dependent manner, with positive short circuit currents (I(SC)), ranging from 3 microA/cm(2) at 5 microM ASC to a maximal response of 27 microA/cm(2) at 200 microM, and a half-maximal response at 40 microM. There was no effect of basolateral addition of ASC, indicating a polarized transport process. The oxidized form of ASC, dehydroascorbic acid had negligible effects. The I(SC) response to ASC was completely eliminated with Na(+) ion replacement, and was also eliminated by bilateral reduction of bath Cl(-), from 137 to 2.6 mM. There was significant inhibition of the I(SC) responses to 30 microM ASC by the flavanoid quercetin (50 microM) and by 100 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 5-ethylisopropylamiloride (EIPA), blockers of anion exchangers and sodium-proton exchangers, respectively. There was no inhibition, however, by the chloride channel blocker 5-nitro-2(3-phenylpropylamino)benzoic acid (NPPB). Phorbol 12-myristate 13 acetate (PMA), the phorbol ester activator of protein kinase C, caused a 37% decrease in the I(SC) response to ASC. Chicken-specific primers to an EST homolog of the human vitamin C transporter SVCT1 (SLC23A1) were designed and used to probe transporter expression in these cells. RT-PCR analysis demonstrated the presence of chicken SVCT1 in both cultured cells and in freshly isolated proximal tubule fragments. These data indicate the presence of an electrogenic, sodium-dependent vitamin C transporter (SVCT1) in the chick renal proximal tubule. Vitamin C transport and conservation by the kidney is likely to be especially critical in birds, due to high plasma glucose levels and resulting high levels of reactive oxygen species.     

Impacts of a national strategy to reduce population salt intake in England: serial cross sectional study

Background

The UK introduced an ambitious national strategy to reduce population levels of salt intake in 2003. The aim of this study was to evaluate the impact of this strategy on salt intake in England, including potential effects on health inequalities.

Methods

Secondary analysis of data from the Health Survey for England. Our main outcome measure was trends in estimated daily salt intake from 2003–2007, as measured by spot urine. Secondary outcome measures were knowledge of government guidance and voluntary use of salt in food preparation over this time period.

Results

There were significant reductions in salt intake between 2003 and 2007 (−0.175grams per day per year, p<0.001). Intake decreased uniformly across all other groups but remained significantly higher in younger persons, men, ethnic minorities and lower social class groups and those without hypertension in 2007. Awareness of government guidance on salt use was lowest in those groups with the highest intake (semi-skilled manual v professional; 64.9% v 71.0% AOR 0.76 95% CI 0.58–0.99). Self reported use of salt added at the table reduced significantly during the study period (56.5% to 40.2% p<0.001). Respondents from ethnic minority groups remained significantly more likely to add salt during cooking (white 42.8%, black 74.1%, south Asian 88.3%) and those from lower social class groups (unskilled manual 46.6%, professional 35.2%) were more likely to add salt at the table.

Conclusions

The introduction a national salt reduction strategy was associated with uniform but modest reductions in salt intake in England, although it is not clear precisely which aspects of the strategy contributed to this. Knowledge of government guidance was lower and voluntary salt use and total salt intake was higher among occupational and ethnic groups at greatest risk of cardiovascular disease.     

Survival of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> in Wilted and Additive-Treated Grass Silage

Grass was field-dried to 3 different dry matter (DM) levels (200, 430 and 540 g/kg) and inoculated with 10⁶–10⁷ cfu/g of a Listeria monocytogenes strain sharing a phagovar occasionally involved in food-borne outbreaks of listeriosis. Formic acid (3 ml/kg) or lactic acid bacteria (8·10⁵/g) with cellulolytic enzymes were applied only to forages with low and intermediate DM levels. Forages were ensiled in laboratory silos (1700 ml) and were stored at 25°C for 30 or 90 days. After 90 days of storage, L. monocytogenes could not be detected in any silo, except one with the high dry matter grass without additive. After 30 days of storage, between 10² and 10⁶ cfu L. monocytogenes/g silage were isolated from the untreated silages. Increasing the DM content from 200 to 540 g/kg did not reduce listeria counts possibly because of the lower production of fermentation acids (higher pH). In silages treated with additives, counts of L. monocytogenes were always lower than in silages without additive. In wet silages (DM 200 g/kg) both additives were effective, but in the wilted silages (DM 430 g/kg) only the bacterial additive reduced listeria counts below detection level. Listeria counts were highly correlated to silage pH (r = 0.92), the concentration of lactic acid (r = -0.80) and the pooled amount of undissociated acids (r = -0.83).