Improved HPLC method for determination of phytosiderophores in root washings and tissue extracts

Phytosiderophores (PS) of the mugineic acid family can be separated effectively by HPLC on resin‐based anion exchange columns. Using gradient elution with aqueous NaOH, separation of 2'‐deoxymugineic acid (DMA), mugineic acid (MA), 3‐hydroxymugineic acid (HMA), 3‐epi‐hyydroxymugineic acid (epi‐HMA), and nicotianamine was obtained within 16 min with a complete cycle time of 30 min. Fluorimetric detection was performed after post‐column derivatization using sodium hypochlorite (NaOCl) and orthophtaldialdehyde. External standardization revealed a linear range between 0.1–2.5 nmol of each compound applied to the column, with a detection limit of approximately 0.05 nmol. Only minimal sample pre‐treatment by addition of sodium hydroxide (NaOH) was required prior to HPLC‐injection of natural occurring samples such as root exudates, collected from the whole root system or from single apical root zones, xylem sap, and hot water extracts of root material, obtained from iron (Fe)‐deficient maize and barley plants. The method is discussed in comparison with cation exchange HPLC which is conventionally employed for the separation of phytosiderophores.     

Cadmium‐induced changes in glutathione and phenolics of Thlaspi and Noccaea species differing in Cd accumulation

Glutathione (GSH) and phenolics play an important role in plant defense against metal‐ion toxicity. The antioxidant activity and metal‐binding capacity of these compounds can account for the protective effects. In contrast to animal‐cell models, however, the possible interplay among these substances in stress defense of plants is poorly investigated. This study compares the influence of cadmium (Cd) on the profiles of both soluble phenolics and GSH in shoots of different Thlaspi and Noccaea species: two ecotypes of the nonhyperaccumulator T. arvense differing in Cd resistance (ecotype Aigues Vives, Cd‐sensitive, and ecotype Jena, Cd‐resistant) and two Cd‐tolerant Cd‐Zn hyperaccumulators N. praecox and N. caerulescens (formerly Thlaspi praecox and T. caerulescens). To reveal the possible influence of Cd‐induced sulfur (S) shortage on the stress response, plants receiving normal S concentrations (500 μM MgSO₄) and plants treated with surplus S (500 μM MgSO₄ + 500 μM K₂SO₄) were analyzed. Our working hypothesis was that species differences in tolerance to high tissue Cd concentrations should be reflected by differences in endogenous levels of GSH and phenolic compounds. The results reveal clear species‐dependent differences in both the constitutive patterns and the Cd‐ and S‐induced changes in shoot concentrations of GSH and phenolics. However, no simple relationship between these shoot concentrations and Cd accumulation and tolerance can be established.     

Assessment of sediment connectivity from vegetation cover and topography using remotely sensed data in a dryland catchment in the Spanish Pyrenees

Purpose

Many Mediterranean drylands are characterized by strong erosion in headwater catchments, where connectivity processes play an important role in the redistribution of water and sediments. Sediment connectivity describes the ease with which sediment can move through a catchment. The spatial and temporal characterization of connectivity patterns in a catchment enables the estimation of sediment contribution and transfer paths. Apart from topography, vegetation cover is one of the main factors driving sediment connectivity. This is particularly true for the patchy vegetation cover typical of many dryland environments. Several connectivity measures have been developed in the last few years. At the same time, advances in remote sensing have enabled an improved catchment-wide estimation of ground cover at the subpixel level using hyperspectral imagery.

Materials and methods

The objective of this study was to assess the sediment connectivity for two adjacent subcatchments (~70 km²) of the Isábena River in the Spanish Pyrenees in contrasting seasons using a quantitative connectivity index based on fractional vegetation cover and topography data. The fractional cover of green vegetation, non-photosynthetic vegetation, bare soil and rock were derived by applying a multiple endmember spectral mixture analysis approach to the hyperspectral image data. Sediment connectivity was mapped using the index of connectivity, in which the effect of land cover on runoff and sediment fluxes is expressed by a spatially distributed weighting factor. In this study, the cover and management factor (C factor) of the Revised Universal Soil Loss Equation (RUSLE) was used as a weighting factor. Bi-temporal C factor maps were derived by linking the spatially explicit fractional ground cover and vegetation height obtained from the airborne data to the variables of the RUSLE subfactors.

Results and discussion

The resulting connectivity maps show that areas behave very differently with regard to connectivity, depending on the land cover and on the spatial distribution of vegetation abundances and topographic barriers. Most parts of the catchment show higher connectivity values in August as compared to April. The two subcatchments show a slightly different connectivity behaviour that reflects the different land cover proportions and their spatial configuration.

Conclusions

The connectivity estimation can support a better understanding of processes controlling the redistribution of water and sediments from the hillslopes to the channel network at a scale appropriate for land management. It allows hot spot areas of erosion to be identified and the effects of erosion control measures, as well as different land management scenarios, to be studied.     

Titanium oxide nanoparticle effects on composition of soil microbial communities and plant performance

We examined the effect of TiO₂ nanoparticles (NPs) on the growth of maize and soybean plants and associated soil microbial communities. Plants were grown in a greenhouse, and low levels of undoped or nitrogen-doped TiO₂ NPs were applied. Plant growth and nutrient content were determined, and effects of NPs on composition of soil microbial communities were examined using terminal restriction fragment length polymorphism analysis (TRFLP) of rDNA. We found no significant effects of TiO₂ NPs on plant growth, nutrient content, or the composition of bacterial communities within the rhizosphere. However, arbuscular mycorrhizal fungal communities were affected by application of undoped and nitrogen-doped TiO₂ NPs. This observation may be partially attributed to the small but significant TiO₂ NP uptake levels in the root tissues of both plants. Our results suggest that even low concentrations of TiO₂ NPs may influence some important groups of soil microbes, such as mycorrhizal fungi, but changes in the composition of microbial communities may not affect plant growth under conditions of adequate moisture and nutrients.     

Evaluation of the temporal distribution of <Emphasis Type="Italic">Fusarium graminearum</Emphasis> airborne inoculum above the wheat canopy and its relationship with Fusarium head blight and DON concentration

With the aim of unravelling the role of airborne Fusarium graminearum inoculum in the epidemic of Fusarium head blight (FHB) caused by this species in wheat spikes, a network of Burkard air samplers was set up in five wheat fields distributed in Belgium from 2011 to 2013. Each year from April to July, the daily amounts of F. graminearum inoculum above the wheat canopy were quantified using a newly developed TaqMan qPCR assay. The pattern of spore trapping observed was drastically different per year and per location with a frequency of detection between 9 and 66% and a mean daily concentration between 0.8 and 10.2 conidia-equivalent/m³. In one location, air was sampled for a whole year. Inoculum was frequently detected from the wheat stem elongation stage until the end of the harvesting period, but high inoculum levels were also observed during the fall. Using a window-pane analysis, different periods of time around wheat flowering (varying in length and starting date) were investigated for their importance in the relation between airborne inoculum and FHB parameters (FHB severity, frequency of F. graminearum infection and DON). For almost all the combinations of variables, strong and significant correlations were found for multiple window lengths and starting times. Inoculum quantities trapped around flowering were highly correlated with F. graminearum infection (up to R?=?0.84) and DON (up to R?=?0.9). Frequencies of detection were also well correlated with both of these parameters. DON concentrations at harvest could even be significantly associated with the F. graminearum inoculum trapped during periods finishing before the beginning of the anthesis (R?=?0.77). Overall, these results highlight the key role of the airborne inoculum in F. graminearum epidemics and underline the importance of monitoring it for the development of disease forecasting tools.     

Recombinant DNA, gene transfer and the future of animal agriculture

Recombinant deoxyribonucleic acid (DNA) technology and gene transfer are two areas of biotechnology that will have significant impact on animal agriculture. Applications to animal agriculture can be expected in animal health management, improved crops and feeds, manipulation of animal physiology, and genetic improvement of livestock species. Improved diagnostic reagents and vaccines that will improve herd health are currently under development. Yield of crop plants such as corn will be increased and the nutritional value of these feeds improved through applications of recombinant DNA technology. Administration of exogenous hormones synthesized by bacteria holds great promise for increasing the yield of milk and possibly meat. Research on the transfer of cloned genes into animals has progressed rapidly and has recently been accomplished in sheep and swine. Tissue-specific and developmentally regulated expression of transferred genes now seems possible with defined gene promoter sequences. Several applications of these biotechnologies can be expected within 5 to 10 yr, whereas others may require longer periods of research. The 21st century will herald a new era in animal science research and applications, with recombinant DNA and gene transfer playing major roles.     

Ovicidal and larvicidal effectiveness of insecticides applied by dipping apples on the small fruit tortrix Grapholita lobarzewskii

The larvicidal and ovicidal effectiveness of twelve insecticides on Grapholita lobarzewskii Nowicki was tested by dipping apples in different concentrations of the insecticides. Emamectin was the most effective larvicidal product, with an LC(50) of 0.01 mg kg(-1), closely followed by spinosad, methoxyfenozide and chlorpyrifos-methyl, with LC(50) values between 0.2 and 0.7 mg kg(-1). Products like imidacloprid, indoxacarb, phosmet and thiacloprid gave LC(50) values between 1 and 2 mg kg(-1). Lastly, chlorpyrifos-ethyl and phosalone had LC(50) values of around 4 mg kg(-1), whereas tebufenozide and diflubenzuron had almost no larvicidal effect. Most of the products tested had low ovicidal effectiveness, and only fenoxycarb and emamectin gave LC(50) values worthy of note, close to 2 mg kg(-1).