Hydroponic Seedling Bioassay for the Bioherbicides Colletotrichum truncatum and Alternaria cassiae

A rapid bioassay was developed to measure the bioherbicidal efficacy of spore preparations of the pathogens Colletotrichum truncatum (Schwein.) Andrus and W. D. Moore and Alternaria cassiae Jurair and Khan on hemp sesbania (Sesbania exaltata) and sicklepod (Cassia obtusifolia), respectively. The system uses 4-day-old dark-grown seedlings (grown hydroponically in paper towel cylinders) which were sprayed with spore suspensions. Shoot lengths were monitored non-destructively, and recorded over time under conditions of dark growth, 90-100% relative humidity and 25 C. Shoot growth inhibition and stem collapse (mortality) were directly related to the spore concentration applied. Generally, at 10 3 - 10 4 spores ml-1, these pathogens caused significant shoot growth inhibition within 25-30 h and seedling death within 40-50 h. This bioassay has been used to study herbicide-pathogen interactions, and may be extended to determine the bioherbicidal efficacy of different pathogen isolates, pathovars or spore formulations. This technique is more rapid, uses a lower inoculum volume, requires less space and is performed under more controlled conditions than conventional greenhouse bioassay methods. The data obtained are more quantitative than those obtained from bioassays relying on visual rating systems.     

A new method for evaluating defense of microalgae against protozoan grazing

Body-size spectrum has proved to be a highly informative indicator to summarize the functional structure of a community at taxon-free resolution. In this study, an approach based on body-size spectrum of protozoan communities was used to detect the defense of microalgae against protozoan grazing. The biofilm-dwelling protozoan communities were used as a test predator system, and two algal species, Chlorella sp. and Nannochloropsis oceanica, were employed as test microalgae. A nine-day bioassay test was carried out by exposing biofilm-dwelling protozoan communities to a gradient of concentrations 10⁰ (control), 10⁴, 10⁵, 10⁶, and 10⁷ cell ml⁻¹ of both microalgae, respectively. Results showed that both algal species represented strong defense effects on the test predator system at different levels of concentration. The body-size distinctness of the protozoan assemblages showed a sharp decrease at high concentration level more than 10⁶ cell ml⁻¹ in both algal treatments. Based on the paired body-size distinctness indices of the protozoa, ellipse tests demonstrated that the body-size spectrum showed an increasing trend of departure from the expected pattern with increasing concentrations of both test algae. Thus, it is suggested that the body-size spectrum of protozoa may be used as a useful indicator to identify the defense of microalgae against protozoan grazing.     

The effects of soluble-Al on root growth and radicle elongation

Summary In order to determine the effects of concentration on plant growth, aluminium (Al) was extracted (10^–3 M CaCl₂) from 4 acid brown hill soils which had been treated with superphosphate at rates equivalent to 0 to 300 kg P ha^–1. The soils ranged in pH (CaCl₂) from 3.5 to 4.9, and Al concentration from 0 to 0.6 mM. The effects of Al on ryegrass growth in the 4 soils in a glasshouse was compared with its effect on radicle elongation of seeds germinated in contact with CaCl₂ extracts from the same soils.Ryegrass root growth in the glasshouse, and radicle elongation in the bioassay test were both unaffected by Al concentrations below 0.1 mM. Root growth was substantially reduced when Al concentration exceeded 0.1 mM and above 0.2 mM growth was almost completely inhibited. Radicle elongation rate was also reduced when the concentration of Al was greater than 0.2 mM agreeing well with the observation from the pot experiment.It is concluded that because of its speed and convenience the bioassay method offers a useful method of establishing critical levels of Al for crop plants.     

三种转基因酵母法筛选类雌激素活性物质方法的比较

利用转基因酵母菌株 ,分别采用摇瓶法、96孔板法和单板法筛选类雌激素活性化学品 ,并对实验参数进行了优化。通过对工作光密度及 β 半乳糖苷酶反应时间的优化 ,使改进后的转基因酵母筛选法筛选一批样品的时间从原来需要的几天缩短为半天。并且在时间缩短的同时 ,仍保留原来检测的高灵敏度和准确性 ,也节省了大量的试验耗材 ,达到了能应用于环境样品中类雌激素活性物质的快速测定的目的。     

外来杂草加拿大一枝黄花对入侵地植物的化感效应

采用人工气候箱培养试验,初步研究了入侵杂草加拿大一枝黄花对本地植物的化感作用.测定了根系和根状茎的不同浓度浸提液对白三叶发芽率和幼苗生长的影响;不同播种密度下根系1∶60提取浓度对白三叶种子萌发和幼苗生长的影响;根状茎1∶60提取浓度对白三叶、红三叶、天蓝苜蓿、黑麦草、北美车前、鸡眼草、苇状羊茅、胜红蓟、马齿苋、碱蓬和刺苋的种子萌发和幼苗生长的影响.结果表明,加拿大一枝黄花根系和根状茎的化感抑制作用均随浓度的升高而增强,且根状茎提取物的抑制效应高于根系提取物的效应;在1∶60低浓度根系浸提液作用下,不同密度的白三叶幼苗萌发率和幼根、幼芽长度差异不显著;1∶60低浓度根状茎提取物对11个物种的种子萌发均有显著抑制作用,但对不同物种的抑制程度有差异,对禾本科植物的抑制作用大于非禾本科和豆科;1∶60低浓度根状茎提取物对10个物种的幼根影响与对萌发率的影响相似,但在对幼芽的影响上,仅对鸡眼草、刺苋和苇状羊茅起抑制作用,而对其他植物无显著抑制(黑麦草、北美车前、胜红蓟、马齿苋和刺苋)或起促进作用(白三叶、红三叶、天蓝苜蓿).     

The toxicity of Irgarol 1051 and Sea-Nine 211 to the non-target macroalga Fucus serratus Linnaeus, with the aid of an image capture and analysis system

A programme of research was initiated to provide information on the efficacy of the antifouling agents Irgarol 1051™ and Sea-Nine 211™ to zygotes of the fucoid alga Fucus serratus Linnaeus. The development of methodologies that incorporated the use of image capture and analysis, which minimised the problems of subjectivity and bias that can be typical, are also described. The generation of macro-instructions allowed rapid generation and interpretation of accurate quantitative data. Emphasis was placed on the use of methodologies that did not rely on the subjective determination of spore germination. Consequently, affects due to the biocides were determined that, otherwise, would not have been realised through normal analytical routines.Zygotes were exposed, in static non-renewal systems, for 3 days, to a range of concentrations of biocide dissolved in seawater. Data for seven zygote parameters were recorded daily and values of percentage germination were calculated. From these data, NOEC values of 8 μg l⁻¹ were calculated for both Sea-Nine 211 and Irgarol 1051. An EC₅₀ of 19.4 μg l⁻¹ was also determined for Sea-Nine 211. It is, therefore, suggested that F. serratus zygote germination and early development is unaffected by published environmental concentrations of these biocides. Additionally, it has been demonstrated that the image capture and analysis methodologies developed provide an invaluable tool for use in future bioassays.     

Development of permethrin resistance in Culex quinquefasciatus Say in Kuala Lumpur,Malaysia

The resistance status towards permethrin among the laboratory strain, the permethrin-selected strain and four field strains of Culex quinquefasciatus collected in Kuala Lumpur, Malaysia was determined using three standard laboratory methods: WHO larval bioassay, WHO adult bioassay and biochemical microplate assay. Cx. quinquefasciatus permethrin-selected strain larvae were the least susceptible to permethrin with a resistance ratio of 47.28-folds, whereas all field strain larvae of the same species were tolerant to permethrin with resistance ratios of more than 3-folds. In contrast, in adult stage, the permethrin exposed permethrin-selected strain (resistance ratio = 1.27) was found to be more susceptible to permethrin than all permethrin-exposed field strains (resistance ratios = 2.23–2.48). Complete mortalities for all strains of Cx. quinquefasciatus adults proved the effectiveness of the synergist; piperonyl butoxide (PBO). For the biochemical microplate assay, the reduction of the mean optical density of elevated oxidase activity of three field strains upon exposure to PBO confirmed the association between oxidase activity and permethrin tolerance. On the other hand, irregular patterns of the mean optical density of elevated oxidase activity in the laboratory strain, permethrin-selected strain and Jalan Fletcher strain illustrated the gene variation within these mosquito colonies as well as the involvement of other enzyme activities in the permethrin resistance occurred.     

Phytoremediation and natural attenuation of sulfentrazone: mineralogy influence of three highly weathered soils

Abstract

This study evaluated remediation of the herbicide sulfentrazone in soils with three different mineralogies (kaolinite, hematite, and gibbsite) and three remediation sulfentrazone treatments (Canavalia ensiformis L., Crotalaria juncea L., and natural attenuation). This study was conducted in a factorial scheme, in triplicate with randomized block design. Sulfentrazone was applied at 0 and 400?g ha^?1. We analyzed sulfentrazone residue in the soils by high-performance liquid chromatography and confirmed the results with bioassays of Pennisetum glaucum. Herbicide movement was greater in the kaolinitic soil without plant species. The retention of herbicide in the kaolinitic soil occurred in larger quantities in the 0–12?cm layer, with higher levels found in the treatments with plants. In the hematitic soil with C. juncea, all applied herbicides were concentrated in the 0–12?cm layer. In the other hematitic soil treatments, sulfentrazone was not detected by chemical analysis at any soil depth, although in many treatments, it was detected in the bioassay. Phytoremediation was more efficient with C. ensiformis grown in gibbsitic soil, reducing the sulfentrazone load by approximately 27%. Natural attenuation was more efficient than phytoremediation in oxidic soils due to soil pH and texture soils favored microbial degradation of the compound.

• Highlights

• The influence of soil mineralogy of herbicide sulfentrazone retention was evaluated.

• Canavalia ensiformis and Crotalaria juncea were evaluated as phytoremediation plants.

• Kaolinite soils presented great movement of sulfentrazone in the soil.

• Natural attenuation is more efficient in oxide soils than phytoremediation.

     

The molecular basis for the inhibition of phosphodiesterase-4D by three natural resveratrol analogs. Isolation,molecular docking,molecular dynamics simulations,binding free energy,and bioassay

The phosphodiesterase-4 (PDE4) enzyme is a promising therapeutic target for several diseases. Our previous studies found resveratrol and moracin M to be natural PDE4 inhibitors. In the present study, three natural resveratrol analogs [pterostilbene, (E)-2′,3,5′,5-tetrahydroxystilbene (THSB), and oxyresveratrol] are structurally related to resveratrol and moracin M, but their inhibition and mechanism against PDE4 are still unclear. A combined method consisting of molecular docking, molecular dynamics (MD) simulations, binding free energy, and bioassay was performed to better understand their inhibitory mechanism. The binding pattern of pterostilbene demonstrates that it involves hydrophobic/aromatic interactions with Phe340 and Phe372, and forms hydrogen bond(s) with His160 and Gln369 in the active site pocket. The present work also reveals that oxyresveratrol and THSB can bind to PDE4D and exhibits less negative predicted binding free energies than pterostilbene, which was qualitatively validated by bioassay (IC₅₀ = 96.6, 36.1, and 27.0 μM, respectively). Additionally, a linear correlation (R² = 0.953) is achieved for five PDE4D/ligand complexes between the predicted binding free energies and the experimental counterparts approximately estimated from their IC₅₀ values (≈RT ln IC₅₀). Our results imply that hydrophobic/aromatic forces are the primary factors in explaining the mechanism of inhibition by the three products. Results of the study help to understand the inhibitory mechanism of the three natural products, and thus help the discovery of novel PDE4 inhibitors from resveratrol, moracin M, and other natural products.     

A yeast bioassay for T-2 toxin

A disk diffusion type bioassay was developed for T-2 toxin using the yeast Kluyveromyces fragilis. The lower limit of detection for this in 0.2 μg of T-2 toxin. The growth of this yeast was sensitive to other trichothecenes such as verrucarin A (0.01 μg). Aflatoxin B₁ (50 μg) and zearalanone (20 μg) did not inhibit the growth of this yeast.