Glyphosate uncouples gas exchange and chlorophyll fluorescence

BACKGROUND: Changes in chlorophyll fluorescence have often been advocated as a sensitive biomarker of plant stress, assuming that any kind of plant stress serious enough to affect plant growth will also affect photosynthesis. Glyphosate affects photosynthetic electron transport indirectly by inhibiting sink processes. The question is how fast this inhibition can be observed on CO₂ assimilation and ultimately on chlorophyll fluorescence? RESULTS: Experiments measuring CO₂ assimilation, conductance and chlorophyll fluorescence using four Kautsky curve parameters on barley (Hordeum vulgare L.) exposed to increasing doses of glyphosate showed a total cessation of CO₂ fixation and conductance without significant changes in chlorophyll fluorescence. The decrease in CO₂ fixation and conductance was significant 1 day after spraying and corresponded well to the decrease in biomass 5–7 days after spraying. CONCLUSION: A total cessation of CO₂ assimilation can take place without affecting chlorophyll fluorescence. Hypotheses concerning what happens to the energy from the photosynthetic apparatus that is not used for CO₂ assimilation are discussed. The results question the use of chlorophyll fluorescence as a universal indicator of stress on photosynthetic processes. Also, they demonstrate that changes in gas‐exchange parameters are more sensitive biomarkers for glyphosate toxicity compared with chlorophyll fluorescence. Copyright © 2010 Society of Chemical Industry     

Incorporation and remobilization of ¹³C within the fine-root systems of individual Abies alba trees in a temperate coniferous stand

Forest ecosystems have a large carbon (C) storage capacity, which depends on their productivity and the residence time of C. Therefore, the time interval between C assimilation and its return to the atmosphere is an important parameter for determining C storage. Especially fine roots (≤2 mm in diameter) undergo constant replacement and provide a large biomass input to the soil. In this study, we aimed to determine the residence time of C in living fine roots and the decomposition rates of dead fine roots. Therefore, we pulse-labelled nine 20-year-old individual silver fir trees (Abies alba Miller; ～70 cm tall) with 13CO? in situ to trace the assimilated C over time into the fine-root systems. Whole trees were harvested at different time points after labelling in autumn, biomass was determined and cellulose and starch of fine roots were extracted. Moreover, soil cores were taken and ingrowth cores installed, in which fine roots were genetically identified, to assess incorporation and remobilization of 13C in the fine roots of silver fir trees; litterbags were used to determine fine-root decomposition rates. The 13C label was incorporated in the fine-root system as cellulose within 3 days, with highest values after 30 days, before reaching background levels after 1 year. The highest δ13C values were found in starch throughout the experiment. 13C recovery and carbon mean residence times did not differ significantly among fine-root diameter classes, indicating size-independent C turnover times in fine roots of A. alba trees of ～219 days. Furthermore, carbon was remobilized from starch into newly grown fine roots in the next spring after our autumn labelling. One year after installation, litterbags with fine roots revealed a decrease of biomass of ～40% with relative 13C content in fine-root bulk biomass and cellulose of ～50%, indicating a faster loss of 13C-labelled compounds compared with bulk biomass. Our results also suggest that genetic analysis of fine-root fragments found in soil and ingrowth cores is advisable when working in mixed forest stands with trees of similar fine-root morphology. Only then can one avoid dilution of the labelling signal by mistake, due to analysis of non-labelled non-target species roots.     

Early recurrence of thoracolumbar intervertebral disc extrusion after surgical decompression: a report of three cases

Thoracolumbar disc extrusions were diagnosed in three chondrodystrophic dogs with paraparesis of up to three days duration. All cases were managed by hemilaminectomy and removal of extruded disc material. In one dog, fenestration of the herniated disc space was also performed. Initially neurological function improved or was unchanged, but from two to ten days postoperatively clinical signs of deterioration became apparent. In all the dogs, recurrence of disc extrusion at the same location as the initial extrusion was diagnosed by computer tomography and at a second surgery abundant disc material was found at the hemilaminectomy site between the dura and an implanted graft of autogenous fat.     

噻虫嗪对B型烟粉虱抗性种群取食行为的影响

<正>烟粉虱Bemisia tabaci(Gennadius)是一类全球广泛分布的农业害虫,由至少24个生物型组成,其中B和Q型烟粉虱入侵性最强、为害最重。目前,化学防治仍是防治烟粉虱的主要手段,吡虫啉、噻虫嗪等新烟碱类药剂因杀虫效果好、持效期长而成为防治该虫的重要药剂。但是大量持续使用药剂易导     

Marinopyrrole derivatives as potential antibiotic agents against methicillin-resistant Staphylococcus aureus (I)

Infections caused by drug-resistant pathogens are on the rise. The ongoing spread of methicillin-resistant Staphylococcus aureus (MRSA) strains exemplifies the urgent need for new antibiotics. The marine natural product, marinopyrrole A, was previously shown to have potent antibiotic activity against Gram-positive pathogens, including MRSA. However, its minimum inhibitory concentration (MIC) against MRSA was increased by >500 fold in the presence of 20% human serum, thus greatly limiting therapeutic potential. Here we report our discovery of a novel derivative of marinopyrrole A, designated 1a, featuring a 2-4 fold improved MIC against MRSA and significantly less susceptibility to serum inhibition. Importantly, compound 1a displayed rapid and concentration-dependent killing of MRSA. Compared to the natural product counterpart, compound 1a provides an important natural product based scaffold for further Structure Activity Relationship (SAR) and optimization.     

银杏细胞微管免疫荧光观察体系的优化

以银杏(Ginkgo biloba L.)雄株为材料,对银杏小孢子母细胞微管的免疫荧光观察体系进行了优化,并以优化后的方法对其减数分裂时期的微管骨架变化情况进行了研究.研究发现:利用PEG包埋可将银杏样本保存1 a以上,经蛋清粘合制片可获细胞数较多的样片,且无需酶解处理即可观察到清晰、完整的银杏小孢子母细胞微管结构.此...     

Dangerous Relations in the Arctic Marine Food Web: Interactions between Toxin Producing Pseudo-nitzschia Diatoms and Calanus Copepodites

Diatoms of the genus Pseudo-nitzschia produce domoic acid (DA), a toxin that is vectored in the marine food web, thus causing serious problems for marine organisms and humans. In spite of this, knowledge of interactions between grazing zooplankton and diatoms is restricted. In this study, we examined the interactions between Calanus copepodites and toxin producing Pseudo-nitzschia. The copepodites were fed with different concentrations of toxic P. seriata and a strain of P. obtusa that previously was tested to be non-toxic. The ingestion rates did not differ among the diets (P. seriata, P. obtusa, a mixture of both species), and they accumulated 6%–16% of ingested DA (up to 420 µg per dry weight copepodite). When P. seriata was exposed to the copepodites, either through physical contact with the grazers or separated by a membrane, the toxicity of P. seriata increased (up to 3300%) suggesting the response to be chemically mediated. The induced response was also triggered when copepodites grazed on another diatom, supporting the hypothesis that the cues originate from the copepodite. Neither pH nor nutrient concentrations explained the induced DA production. Unexpectedly, P. obtusa also produced DA when exposed to grazing copepodites, thus representing the second reported toxic polar diatom.     

Pulse-labelling trees to study carbon allocation dynamics: a review of methods, current knowledge and future prospects

Pulse-labelling of trees with stable or radioactive carbon (C) isotopes offers the unique opportunity to trace the fate of labelled CO(2) into the tree and its release to the soil and the atmosphere. Thus, pulse-labelling enables the quantification of C partitioning in forests and the assessment of the role of partitioning in tree growth, resource acquisition and C sequestration. However, this is associated with challenges as regards the choice of a tracer, the methods of tracing labelled C in tree and soil compartments and the quantitative analysis of C dynamics. Based on data from 47 studies, the rate of transfer differs between broadleaved and coniferous species and decreases as temperature and soil water content decrease. Labelled C is rapidly transferred belowground-within a few days or less-and this transfer is slowed down by drought. Half-lives of labelled C in phloem sap (transfer pool) and in mature leaves (source organs) are short, while those of sink organs (growing tissues, seasonal storage) are longer. (13)C measurements in respiratory efflux at high temporal resolution provide the best estimate of the mean residence times of C in respiratory substrate pools, and the best basis for compartmental modelling. Seasonal C dynamics and allocation patterns indicate that sink strength variations are important drivers for C fluxes. We propose a conceptual model for temperate and boreal trees, which considers the use of recently assimilated C versus stored C. We recommend best practices for designing and analysing pulse-labelling experiments, and identify several topics which we consider of prime importance for future research on C allocation in trees: (i) whole-tree C source-sink relations, (ii) C allocation to secondary metabolism, (iii) responses to environmental change, (iv) effects of seasonality versus phenology in and across biomes, and (v) carbon-nitrogen interactions. Substantial progress is expected from emerging technologies, but the largest challenge remains to carry out in situ whole-tree labelling experiments on mature trees to improve our understanding of the environmental and physiological controls on C allocation.     

Agroforestry systems reduce invasive species richness and diversity in the surroundings of protected areas

The Serra do Brigadeiro State Park (PESB) is one of the largest fragments of Brazilian Atlantic Rainforest, and it is relevant for native species conservation. However, monocultures settled around the Park resulted in extensive open areas that facilitate the establishment of alien species on the PESB perimeter, which may threaten native species conservation therein, since biological invasion is the second main cause of global biodiversity loss. In this region, there are also farmers planting agroforestry systems (AFS), characterized by tree-based intercropping, which are structurally more similar to the Atlantic Rainforest reminiscent fragments present in the region and may limit local occurrence of potentially invasive exotic weeds for several reasons, such as the high levels of shade provided by trees, the groundcover that result from loss of tree leaves and the increased competition for belowground resources. This study aimed to test whether AFS limit exotic species establishment when compared to monoculture systems. Accordingly, three coffee monocultures and three agroforestry coffee plantations around the PESB were studied. In each of the six study areas, 30 plots of 1 m² were established between the lines of coffee plantation, where all species present were surveyed. In both treatments, rarefaction curves were constructed to evaluate native and exotic richness, and diversity of these two categories was estimated through Simpson index inverse (1/D). All 13 sampled exotic species were present in monocultures, but only three of them occurred in AFS. Besides, alien diversity in monocultures (\(1/D\) = 2.173 ± 0.011) was significantly higher than in AFS (\(1/D\) = 1.031 ± 0.001). Such changes in alien plant community between land-use show that AFSs limit invasive species establishment. Therefore, when planted around protected areas, AFS may contribute to the control of biological invasions and to biodiversity conservation.     

How is agroforestry perceived in Europe? An assessment of positive and negative aspects by stakeholders

Whilst the benefits of agroforestry are widely recognised in tropical latitudes few studies have assessed how agroforestry is perceived in temperate latitudes. This study evaluates how stakeholders and key actors including farmers, landowners, agricultural advisors, researchers and environmentalists perceive the implementation and expansion of agroforestry in Europe. Meetings were held with 30 stakeholder groups covering different agroforestry systems in 2014 in eleven EU countries (Denmark, France, Germany, Greece, Hungary, Italy, Netherlands, Portugal, Spain, Sweden and the United Kingdom). In total 344 valid responses were received to a questionnaire where stakeholders were asked to rank the positive and negative aspects of implementing agroforestry in their region. Improved biodiversity and wildlife habitats, animal health and welfare, and landscape aesthetics were seen as the main positive aspects of agroforestry. By contrast, increased labour, complexity of work, management costs and administrative burden were seen as the most important negative aspects. Overall, improving the environmental value of agriculture was seen as the main benefit of agroforestry, whilst management and socio-economic issues were seen as the greatest barriers. The great variability in the opportunities and barriers of the systems suggests enhanced adoption of agroforestry across Europe will be most likely to occur with specific initiatives for each type of system.