Response of primary plant metabolism to the N-source

Even when plant growth was not visibly affected, ammonium versus nitrate nutrition had distinct effects on some parts of plant metabolism. Barley seedlings growing on 3 mM ammonium rapidly accumulated ammonium up to 20 mM in the roots. In leaves, ammonium accumulation was observed only when the pH of the nutrient medium was very low (pH 4). Yet even under the most extreme conditions there was no indication that plants were suffering from uncoupling of ATP synthesis or from a lack of carbohydrates. Especially dramatic was the response of the organic acid content of pea and barley leaves: it decreased strongly within a few days upon transfer of plants from nitrate to ammonium-media, and this was apparently not due to an inhibition of PEPcarboxylase, which was rather activated under ammonium nutrition. As malate dispappeared from leaves even when pea plants were transferred to an N-free medium, malate degradation was not necessarily connected to increased amino acid synthesis, but eventually to a more rapid decarboxylation by malic enzyme. Also, malate degradation was not a response to ammonium, but rather to (the absence of) nitrate.     

Long-Range Atmospheric Transport and Local Pollution Sources on PAH Concentrations in a South European Urban Area. Fulfilling of the European Directive

A 12 months study on urban atmospheric concentrations of polycyclic aromatic hydrocarbons (PAH) contained in the particulate matter with an aerodynamic diameter less than or equal to 10 microns (PM10) was carried out in Zaragoza (Spain) from July 12th, 2001 to July 26th, 2002 by using a high-volume air sampler able to collect the PAH supported on a Teflon-coated fibre glass filter. Samples were analysed by using Gas Chromatography Mass Spectrometry (GC-MS/MS). PAH of high molecular weight, indeno[1,2,3-cd]pyrene (IcdP), benzo[g,h,i]perylene (BghiP) and coronene (Co) were the most abundant compounds. The concentrations of benz[a]pyrene equivalent carcinogenic power (BaP-eq) showed a mean value of 0.7 ng/m³ with 22.5% of the samples exceeding the 1.0 ng/m³ guide value established by the European Directive. These episodes were mainly produced during cold season. Regarding meteorological variables, a positive effect of the prevalent wind “cierzo” (NW direction) over the Zaragoza city was confirmed from the environmental point of view. The NE, E and S directions, corresponding to highway and industrial areas were the directions showing the high PAH atmospheric concentrations. Despite the proximity of a high-level traffic highway, stationary sources related to industry were the dominant source of PAH in the sampled area. Vehicular emissions and natural gas home heating also contributed to PAH concentrations. The predominance of local pollution sources versus long-range transport on PAH concentrations was shown. However, the contribution of long-range transport of anthropogenic origin from other European areas was reflected for specific dates on PAH concentrations and PM10 levels.     

Seasonal water relations in four co-existing native shrub species from Northeastern Mexico

Seasonal xylem water potentials (Ψ, MPa) and their relationship to soil water content and evaporative demand components were studied in the shrub species Acacia amentacea, Celtis ehrenbergiana, Forestiera angustifolia, and Parkinsonia texana var. macra. Predawn (Ψpd) and midday (Ψmd) water potentials were estimated at 15 days intervals, between January 15 and October 30, 2009 using a Scholander pressure bomb at 06:00 h (predawn) and 14:00 h (midday), respectively. During the humid period, Ψpd ranged from ?0.30 MPa (C. ehrenbergiana), to ?0.90 MPa (P. texana). In contrast, over the driest period, Ψpd varied between ?2.18 (P. texana) and ?3.94 MPa (F. angustifolia). At midday, P. texana and F. angustifolia showed the highest (?1.14 MPa) and lowest (?3.38 MPa) Ψ values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn Ψ. Furthermore, both Ψ reflected the environmental conditions, as indicated by typical correlations observed. The studied shrub species exhibited what seem to be different strategies to avoid damage caused by drought. Thus, P. texana behaved rather as an isohydric plant able to deal well with severe, but short periods of drought. Under exceptionally dry environmental conditions, Ψpd undercut Ψmd values. Similar observations have been made by researchers studying plants in dry ecosystems. All studied native species are recommended for reforestation of the Tamaulipan shrublands, although C. ehrenbergiana and F. angustifolia seem to have limited tolerances for extreme water stress.     

Antiparasitic efficacy of dietary administration of trichlorfon (Masoten®) in the control of Neoechinorhynchus buttnerae (Neochinorhynchidae) in Colossoma macropomum (Serrasalmidae)

Aquaculture International - This study investigated the efficacy of trichlorfon against Neoechinorhynchus buttnerae, as well as its palatability, residue analysis, and the blood parameters of...     

Serotypes and virulence markers of Shiga toxin-producing Escherichia coli (STEC) isolated from dairy cattle in São Paulo State, Brazil

In order to determine the occurrence, serotypes and virulence markers of Shiga toxin-producing Escherichia coli (STEC) strains, 153 fecal samples of cattle randomly selected from six dairy farms in Sao Paulo State, Brazil, were examined for Shiga toxin (Stx) production by the Vero cell assay. Feces were directly streaked onto MacConkey Sorbitol Agar and incubated at 37 degrees C overnight. Sorbitol-negative colonies (maximum 20) and up to 10 sorbitol-positive colonies from each plate were subcultured onto presumptive diagnostic medium IAL. Sorbitol-negative isolates were screened with O157 antiserum for identification of O157:H7 E. coli. Isolates presenting cytotoxic activity were submitted to colony hybridization assays with specific DNA probes for stx1, stx2, eae, Ehly and astA genes. The isolation rate of STEC ranged from 3.8 to 84.6% depending on the farm analysed. STEC was identified in 25.5% of the animals, and most of them (64.1%) carried a single STEC serotype. A total of 202 STEC isolates were recovered from the animals, and except for the 2 O157:H7 isolates all the others expressed cytotoxic activity. The great majority of the STEC isolates carried both stx1 and stx2 genes (114/202, 56.4%) or stx2 (82/202, 40.6%); and whereas the Ehly sequence occurred in most of them (88%) eae was only observed in O157:H7 and O111:HNM isolates. Serotypes O113:H21, O178:H19 and O79:H14 were the most frequent STEC serotypes identified and widely distributed among animals from different farms, while others such as O77:H18, O88:H25 and O98:H17 occurred only in particular farms. This is the first report on the occurrence of STEC in dairy cattle in Sao Paulo State, and the results point to substantial differences in rate of isolation, serotypes and genetic profile of STEC that has been previously described among beef cattle in our community. Moreover, to our knowledge O79:H14 and O98:H17 represent new STEC serotypes, while O178:H19 has only been recently reported in Spain.