A device for single leaf labelling with CO<Subscript>2</Subscript> isotopes to study carbon allocation and partitioning in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Background

Plant biomass consists primarily of carbohydrates derived from photosynthesis. Monitoring the assimilation of carbon via the Calvin-Benson cycle and its subsequent utilisation is fundamental to understanding plant growth. The use of stable and radioactive carbon isotopes, supplied to plants as CO₂, allows the measurement of fluxes through the intermediates of primary photosynthetic metabolism, long-distance transport of sugars in the vasculature, and the synthesis of structural and storage components.

Results

Here we describe the design of a system for supplying isotopically labelled CO₂ to single leaves of Arabidopsis thaliana. We demonstrate that the system works well using short pulses of ¹⁴CO₂ and that it can be used to produce robust qualitative and quantitative data about carbon export from source leaves to the sink tissues, such as the developing leaves and the roots. Time course experiments show the dynamics of carbon partitioning between storage as starch, local production of biomass, and export of carbon to sink tissues.

Conclusion

This isotope labelling method is relatively simple to establish and inexpensive to perform. Our use of ¹⁴CO₂ helps establish the temporal and spatial allocation of assimilated carbon during plant growth, delivering data complementary to those obtained in recent studies using ¹³CO₂ and MS-based metabolomics techniques. However, we emphasise that this labelling device could also be used effectively in combination with ¹³CO₂ and MS-based techniques.

     

Identification of enterodiol as a masker for caffeine bitterness by using a pharmacophore model based on structural analogues of homoeriodictyol

Starting from previous structure-activity relationship studies of taste modifiers based on homoeriodictyol, dihydrochalcones, deoxybenzoins, and trans-3-hydroxyflavones as obvious analogues were investigated for their masking effect against caffeine. The most active compounds of the newly investigated taste modifiers were phloretin, the related dihydrochalcones 3-methoxy-2',4,4'-trihydroxydihydrochalcone and 2',4-dihydroxy-3-methoxydihydrochalcone, and the deoxybenzoin 2-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)ethanone. Starting with the whole set of compounds showing activity >22%, a (Q)SAR pharmacophore model for maskers of caffeine bitterness was calculated to explain the structural requirements. After docking of the pharmacophore into a structural model of the broadly tuned bitter receptor hTAS2R10 and docking of enterolactone and enterodiol as only very weakly related structures, it was possible to predict qualitatively their modulating activity. Enterodiol (25 mg L(-1)) reduced the bitterness of the 500 mg L(-1) caffeine solution by about 30%, whereas enterolactone showed no masking but a slight bitter-enhancing effect.     

Evaluating the influence of surface soil moisture and soil surface roughness on optical directional reflectance factors

Fine‐scale information on soil surface roughness (SSR) is needed for calculating heat budgets, monitoring soil degradation and parameterizing surface runoff and sediment transfer models. Previous work has demonstrated the potential of using hyperspectral, hemispherical conical reflectance factors (HCRFs) to retrieve the SSR of different soil crusting states. However, this was achieved by using dry soil surfaces, generated in controlled laboratory conditions. The primary aim of this study was therefore to test the impact that in situ variations in surface soil moisture (SSM) content had on the ability of directional reflectance factors to characterize SSR conditions. Five soil plots (20 cm × 20 cm in area) representing different agricultural conditions were subjected to different durations of natural rainfall to produce a range of different levels of SSR. The values of SSM varied from 8.7 to 20.1% across all soil plots. Point laser data (4‐mm sample spacing) were geostatistically analysed to give a spatially‐distributed measure of SSR, giving sill variance values from 3.2 to 23.0. The HCRFs from each soil state were measured using a ground‐based hyperspectral spectroradiometer for a range of viewing zenith angles from extreme forward‐scatter (θ_r = ?60°) to extreme back‐scatter (θ_r = +60°) at a 10° sampling resolution in the solar principal plane. The results showed that despite a large range of SSM values, forward‐scattered reflectance factors exhibited a very strong relationship with SSR (R² = 0.84 at θ_r = ?60°). Our findings demonstrate the operational potential of HCRFs for providing spatially‐distributed SSR measurements, across spatial extents containing spatio‐temporal variations in SSM content.     

Analysis of Flavan-3-ols and procyanidins in food samples by reversed phase high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (RP-HPLC-ESI-MS/MS)

Concentrations of the main dimeric and trimeric procyanidins (PC) and their monomeric constitutive units catechin (CT) and epicatechin (EC) were determined in food samples by using reversed phase high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (RP-HPLC-ESI-MS/MS). In a first step, 12 PCs (PC B1, B2, B3, B4, B5, B6, B7, B8, C1, C2, and A2 and cinnamtannin B1), of which most are not commercially available, were isolated from plant materials or synthesized and purified by a combination of column chromatographic separation techniques with different stationary phases. These PCs in combination with CT and EC were used as standard substances for identification and quantification during the following screening of food samples by RP-HPLC-ESI-MS/MS analysis. The main focus of the newly developed RP-HPLC-ESI-MS/MS method is the compensation of matrix effects by using the echo-peak technique simulating internal standard injection. The suitability of this new method was demonstrated by the determination of recovery rates being 90% or higher. Use of this method allowed the determination of patterns and concentrations of PCs in 55 food samples.     

Effect of variety and harvest date on tuber sugars and chip color

The major tuber sugars—glucose, fructose and sucrose — in tubers of the Red Pontiac, Kennebec and Monona potato varieties harvested five times during the 1970 growing season were determined quantitatively by a gas-liquid Chromatographic technique. Also, chips were made from tubers and chip color was measured objectively and reported as Rd values. Red Pontiac tubers produced the darkest-colored chips (Rd-15.5), and its tubers tended to accumulate the highest levels of the three sugars. The major difference between Monona, which produced chips with the lightest color (Rd-21.1), and Kennebec (Rd-19.5) was the very low level of glucose found in the tubers of Monona. Varieties produced chips lightest in color at the second (8/31) or third (9/15) harvest dates. Conversely, darkest-colored chips were obtained from each variety at the fourth harvest date (9/28). This was attributed to the cool, wet weather. Sugar content also varied during the harvesting schedule. Glucose content changed little until late in the season when an increase occurred. Fructose tended to decline until the final harvest when a distinct increase was obtained. Sucrose declined significantly through the third harvest, but changed little thereafter.     

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Detection of antibiotic residues and association of cefquinome residues with the occurrence of Extended-Spectrum β-Lactamase (ESBL)-producing bacteria in waste milk samples from dairy farms in England and Wales in 2011

Waste milk samples from 103 farms in England and Wales were examined for the presence of β-lactam antibiotics and ESBL-producing Enterobacteriaceae. Approximately 10 months after the initial sampling, further waste milk, environmental and faecal samples from farms shown to be positive for CTX-M Escherichia coli were investigated further. Isolates with an ESBL phenotype were tested by PCR for the presence of bla_CTX-M, bla_OXA, bla_SHV and bla_TEM genes. Isolates positive for bla_CTX-M were sequenced to determine CTX-M type. Representative isolates were further examined by PFGE, plasmid replicon typing and serotyping. Of particular interest, 21.4% of waste milk samples contained residues of the cephalosporin cefquinome, which was significantly associated with CTX-M bacteria. Such bacteria occurred in 5.8% of the waste milk samples (including 3.9% CTX-M E. coli). CTX-M types identified were 1, 14, 14b and 15, but none of the E. coli were serotype O25, the serotype of the human pandemic strain.