Magnetic microstructure of magnetotactic bacteria by electron holography

Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrystals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains. Shape anisotropy was found to dominate magnetocrystalline anisotropy in elongated crystals. A coercive field between 300 and 450 oersted was determined for one chain.     

Effect of dietary cowpea trypsin inhibitor (CpTI) on the growth and development of the tomato moth Lacanobia oleracea (Lepidoptera: Noctuidae) and on the success of the gregarious ectoparasitoid Eulophus pennicornis (Hymenoptera: Eulophidae)

Cowpea trypsin inhibitor (CpTI) was shown to have a deleterious effect on the growth and development of larvae of the tomato moth, Lacanobia oleracea, when incorporated in artificial diet (2.0 % of soluble protein) and expressed in transgenic potato leaf (up to 1.0 % of soluble protein). The effect of CpTI on parasitism of L oleracea by the ectoparasitoid Eulophus pennicornis was investigated. The parasitic success of the wasp was reduced by the presence of CpTI in the diet of the host and, in the case of transgenic potato leaves expressing the transgene protein, was collated with the length of time the host fed on the diet prior to parasitism. In all cases the proportion of hosts parasitised when fed CpTI‐containing diets was reduced when compared with controls, although these differences were only significant when hosts were fed from the third instar on the transgenic potato leaves. Parasitoid progeny that developed on L oleracea reared on CpTI‐containing diets, however, were not adversely affected. These results show that, whilst expression of CpTI in transgenic potato plants confers resistance to the lepidopterous pest L oleracea, adverse effects on the ability of the ectoparasitoid E pennicornis to parasitise this moth species successfully may also occur. These results are discussed in relation to the potential impact of transgenic crops on beneficial biological control agents. © Crown copyright 2001. Reproduced with the permission of Her Majesty's Stationery Office. Published for SCI by John Wiley & Sons, Ltd.     

Diversity and assembly of weed communities: contrasting responses across cropping systems

Diversity and weed community composition of mid-season plant stands and autumn seedbanks were examined in spring barley–red clover cropping systems that varied according to crop rotation, tillage and weed management. Weed plant and seed density data collected over 4 years were used in the calculation of species richness (number of species), evenness (Shannon's E) and diversity (Shannon's H′), and in multivariate analysis (canonical discriminant analysis) of weed communities. Weed diversity indices were low (H′ < 2.0) but sensitive to management practices. Evenness had intermediate values (E = 0.4–0.8), suggesting little evidence of truly dominant species, particularly in the seedbanks. The difference in the number of species between treatments was never large (approximately two to four species). Overall, diversity indices were highest in the low disturbance treatments, particularly those with minimum weed management. Factors affecting ordination were somewhat different from those affecting diversity. Tillage had little effect on weed diversity indices but had a more major role in determining weed community composition. Seedbanks in no-till and monoculture-chisel plough treatments appeared to have more distinctive species composition compared with other treatments. Weed species assembly in seedbanks showed little discrimination across treatments and over time, confirming the ability of seedbanks to buffer disturbances across a variety of cropping systems. The use of diversity indices revealed part of the complexity of weed communities associated with disturbance in cropping systems, whereas ordination singled out species–cropping systems associations, which may be more meaningful to weed management.     

Development of a PCR-based diagnostic test for Spongospora subterranea f.sp. nasturtii, the causal agent of crook root of watercress (Rorippa nasturtium-aquaticum)

The polymerase chain reaction (PCR) technique was utilized to obtain internal transcribed spacer ribosomal DNA (ITS rDNA) and small-subunit (18S) rDNA sequences from UK isolates of Spongospora subterranea f.sp. nasturtii , a plasmodiophorid pathogen of watercress ( Rorippa nasturtium-aquaticum ). ITS sequence data obtained from S. subterranea isolated from a range of UK sites were found to be identical. PCR primers were designed using these sequences and were shown to be capable of specific amplification of S. subterranea f.sp. nasturtii DNA from plant tissue and from water samples containing zoospores of the pathogen. As little as 5 ng total genomic DNA from infected plant material, or 1000 zoospores, was required for consistently successful amplification of DNA. A filtration-based method for obtaining pathogen DNA for PCR from watercress-bed water was developed.     

巴旦杏砧木组织培养及植株再生

以新疆南疆咯什、和田地区的巴旦杏砧木品种桃巴旦、石头巴旦树上当年结的种子为试材,先用赤霉素打破休眠,消毒后接种子诱导生长及分化的培养基上。生长约一个月后,将由试管中种子培养长成的小植株剪切成长约1cm的单芽茎段,接入增殖培养基,20d后将增殖伸长的嫩茎用于生根,再将生根后的巴旦杏苗移栽到珍珠岩基质中培养,进行有效的移栽驯化管理,获得了较理想的移栽成活率。成功地进行了离体组织培养及植株再生。     

林业病虫害防治工作中的问题及对策

林业有害生物防治是国家减灾工程的重要组成部分,通过对乌拉特前旗林业有害生物防治工作存在问题的分析,提出了解决这类问题切实可行的对策措施。     

Validation of a cranial injection technique of the medial femorotibial joint in the horse

A cranial technique for entry of the medial femorotibial (MFT) joint in the horse was validated. It was hypothesised that the frequency of correct placement into the MFT joint using the described cranial technique would be similar to using a standard medial approach. Twenty‐four limbs from 15 horses were injected with a latex mixture. Limbs with stifle joint effusion and/or known stifle pathology were grouped separately to those without. When effusion/pathology was not present the medial technique (93%) was almost twice as successful as the cranial technique (53%), including when extremes of size were removed from the population. With the presence of femoropatellar or medial femorotibial effusion, the cranial technique (20%) was 5 times less successful than using the medial technique (100%). When extremes of size were removed from the population of horses with effusion, the success of the cranial technique was marginally improved (33%). When an ‘average size’ of horse is used with or without joint effusion, the cranial technique is successful in entering the MFT joint in approximately 50% of cases, and may hence be of use in a fractious animal without sedation, a stallion, or in the presence of a wound/skin infection at the site of the medial needle entrance.     

Laser-Doppler Measurements of Spinal Cord Blood Flow Changes During Hemilaminectomy in Chondrodystrophic Dogs with Disk Extrusion

Objectives— (1) To assess spinal cord blood flow (SCBF) during surgical treatment of disk extrusion in dogs and (2) to investigate associations between SCBF, clinical signs, presurgical MRI images, and 24-hour surgical outcome.
Study Design— Cohort study.
Animals— Chondrodystrophic dogs with thoracolumbar disk extrusion (n=12).
Methods— Diagnosis was based on clinical signs and MRI findings, and confirmed at surgery. Regional SCBF was measured intraoperatively by laser-Doppler flowmetry before, immediately after surgical spinal cord decompression, and after 15 minutes of lavaging the lesion. Care was taken to ensure a standardized surgical procedure to minimize factors that could influence measurement readings.
Results— A significant increase in intraoperative SCBF was found in all dogs (Wilcoxon's signed-rank test; P =.05) immediately after spinal cord decompression and after 15 minutes. Changes in SCBF were not associated with duration of clinical signs; initial or 24-hour neurologic status; or degree of spinal cord compression assessed by MRI.
Conclusion— SCBF increases immediately after spinal cord decompression in dogs with disk herniation; however, increased SCBF was not associated with a diminished 24-hour neurologic status.
Clinical Relevance— An increase in SCBF does not appear to be either associated with the degree of spinal cord compression or of a magnitude sufficient to outweigh the benefit of surgical decompression by resulting in clinically relevant changes in 24-hour outcome.     

Biomechanical Analysis of Torsion and Shear Forces in Lumbar and Lumbosacral Spine Segments of Nonchondrodystrophic Dogs

Objective— To determine stiffness and load–displacement curves as a biomechanical response to applied torsion and shear forces in cadaveric canine lumbar and lumbosacral specimens.
Study Design— Biomechanical study.
Animals— Caudal lumbar and lumbosacral functional spine units (FSU) of nonchondrodystrophic large-breed dogs (n=31) with radiographically normal spines.
Methods— FSU from dogs without musculoskeletal disease were tested in torsion in a custom-built spine loading simulator with 6 degrees of freedom, which uses orthogonally mounted electric motors to apply pure axial rotation. For shear tests, specimens were mounted to a custom-made shear-testing device, driven by a servo hydraulic testing machine. Load–displacement curves were recorded for torsion and shear.
Results— Left and right torsion stiffness was not different within each FSU level; however, torsional stiffness of L7-S1 was significantly smaller compared with lumbar FSU (L4-5–L6-7).
Ventral/dorsal stiffness was significantly different from lateral stiffness within an individual FSU level for L5-6, L6-7, and L7-S1 but not for L4-5. When the data from 4 tested shear directions from the same specimen were pooled, level L5-6 was significantly stiffer than L7-S1.
Conclusions— Increased range of motion of the lumbosacral joint is reflected by an overall decreased shear and rotational stiffness at the lumbosacral FSU.
Clinical Relevance— Data from dogs with disc degeneration have to be collected, analyzed, and compared with results from our chondrodystrophic large-breed dogs with radiographically normal spines.