丛枝菌根真菌改善镉胁迫下植物根系和土壤微环境的效应

为探究Cd胁迫下丛枝菌根真菌(AMF)对植物根系和土壤微环境的影响,以黑麦草为供试植物、变形球囊霉(Glomus versiforme)为供试AMF,以Cd浓度(0、10、20、30 mg·kg^-1)和是否对黑麦草接种AMF为双因素,设计8个处理,开展盆栽试验。结果显示:随着Cd浓度增加,AMF侵染率和孢子数量显著(P<0.05)降低。相同Cd浓度下,接种AMF显著(P<0.05)改善了黑麦草的根系构型(根系总长度、根系总投影面积、根系总体积、根尖数、根分叉数)。在相同Cd浓度下,接种AMF显著(P<0.05)增加了土壤中真菌、细菌和放线菌的数量,土壤微生物生物量碳、微生物生物量氮含量,以及土壤多酚氧化酶活性,和土壤易提取球囊霉素相关土壤蛋白和总球囊霉素相关土壤蛋白含量。这说明,接种AMF能够通过改善植物根系和微生物环境、提高土壤相关酶活性和球囊霉素含量等,增加植物抗性。     

AMF根外菌丝对重金属铅的吸收与转运

【目的】探讨丛枝菌根真菌（arbuscular mycorrhiza fungi,AMF）异形根孢囊霉（Rhizophagus irregularis,Ri）和摩西斗管囊霉（Funneliformis mosseae,Fm）根外菌丝对重金属铅的吸收及转运能力,为明确AMF根外菌丝的铅转运能力提供依据。【方法】以菌根植物蒺藜苜蓿（Medicago truncatula,寄主）和非菌根植物油菜（Brassica napus）为试验材料,采用三室培养系统（菌根室-施铅室-非菌根室）进行研究,其中菌根室种植蒺藜苜蓿并进行AMF处理,包括接种Ri、Fm和未接种对照（CK）3个处理;施铅室（中间隔室）设置0和800 mg/kg 2个铅处理;非菌根室种植油菜,试验共设CK、Ri、Fm、Pb、Ri×Pb、Fm×Pb 6个处理,研究铅胁迫下2种AMF根外菌丝对植物生长及铅离子富集的影响。【结果】（1）与CK处理比,Ri和Fm处理蒺藜苜蓿总生物量分别提高了43.55%和256.98%,铅胁迫对Ri和Fm处理蒺藜苜蓿的生物量无显著影响。（2）0 mg/kg 铅胁迫下,2种AMF均能够与蒺藜苜蓿形成良好共生关系,Fm和Ri处理菌根侵染率达到90%以上。Fm和Fm×Pb处理侵染根段丛枝丰度分别是Ri和Ri×Pb处理的8.75和2.51倍。（3）与Ri处理比,Ri×Pb处理菌根室培养基质中菌丝密度显著提高231.57%,施铅室培养基质中菌丝密度显著降低49.56%;与Fm处理比,Fm×Pb处理菌根室培养基质中菌丝密度提高314.09%,施铅室培养基质中菌丝密度降低21.09%。（4）Ri×Pb、Fm×Pb处理蒺藜苜蓿地上部铅含量分别是CK处理的3.60和8.45倍,根系铅含量分别是CK处理的7.45和217.87倍;Fm×Pb处理油菜根系铅含量是CK处理的62.15倍。【结论】AMF根外菌丝能够直接吸收并转运铅至寄主植物根部,并可能借由“外排”效应将铅运输至非菌根植物根系,且Fm促进植物生长及根外菌丝吸收转运铅的能力显著高于Ri。     

具毒死蜱降解功能的水稻内生菌降解特性及应用

为挖掘毒死蜱降解内生菌资源、强化功能内生菌在农业生产中的应用,通过微生物梯度驯化技术,从农药池周边生长的水稻根组织中分离纯化获得一株能以毒死蜱为唯一碳源的降解内生菌CP40,研究了该菌株的毒死蜱降解特性及对作物中残留毒死蜱降解的影响。基于16S rRNA和细菌形态学特征,将菌株CP40鉴定为芽孢杆菌（Bacillus sp.CP40）。菌株CP40含有机磷降解酶基因opd,异源表达该基因后毒死蜱的降解率达58.4%。降解条件优化实验表明,毒死蜱初始浓度为10 mg·L^-1、温度为30℃、pH为7时,菌株CP40对毒死蜱的降解效果最佳。此外,发现菌株CP40具有促生能力,接种菌株CP40可显著促进水稻生长,并能将水稻体内毒死蜱含量降低30.9%。研究表明,功能内生菌在调控水稻体内毒死蜱的降解过程中可发挥重要作用。     

Effect of different levels of black cumin (Nigella sativa L.) on performance,intestinal Escherichia coli colonization and jejunal morphology in laying hens

This study was conducted to investigate the effects of different levels of black cumin seeds (Nigella sativa L.) on performance, intestinal Escherichia coli count and morphology of jejunal epithelial cells in laying hens. A total of 100 Leghorn laying hens (Hy‐Line W‐36) of 49 weeks old were randomly distributed among five cage replicates of five birds each. Experimental diets consisted of different levels (0%, 1%, 2% and 3% of diet) of dietary black cumin inclusion. The experimental period lasted for a total of 10 weeks, and egg quality indexes and laying hens' performance were measured as two 35‐day trial periods. At the final day, two hens per replicate were slaughtered to investigate the influence of dietary treatments on intestinal E. coli colonization and morphology of jejunal cells. Although dietary black cumin in all supplementation levels decreased (p < 0.05) the enumeration of ileal E. coli, the morphological and histological alterations in small intestine such as enhancement of villus height to crypt depth ratio, increased goblet cell numbers and proliferation of lamina propria lymphatic follicles were observed after dietary supplementation with at least 2% black cumin. Dietary treatments decreased (p < 0.05) the concentration of serum cholesterol and triglycerides and increased (p < 0.05) serum HDL concentration and relative weight of pancreas; however, the egg yolk cholesterol was not influenced by dietary treatments. In addition, dietary supplementation with black cumin improved (p < 0.05) eggshell quality and Haugh unit. The best feed conversion ratio was obtained when diets were supplemented with 2% black cumin. This improvement was due to the increase (p < 0.05) in egg mass and contemporaneous decrease (p < 0.01) in feed consumption. The present results indicated that regardless of supplementation level, dietary inclusion of black cumin decreased E. coli enumeration in ileal digesta and improved serum lipid profile and eggshell quality, whereas the best intestinal health indices and haying hens' performance were obtained by at least 2% black cumin seeds.     

致仔猪水肿病大肠杆菌减毒株的毒力测定及其在仔猪肠道内增殖的分析

在已构建致仔猪水肿病大肠杆菌S451521菌株的2个毒素敲除菌株（F1、F2）基础上,进一步测定了其毒力及在仔猪肠道内的繁殖能力。选择30日龄的ICR小鼠并随机分成4组,A、B、C试验组分别灌胃接种不同浓度的野生菌株S451521及其毒素敲除菌株F1、F2,D组以灭菌生理盐水作阴性对照;结果表明减毒菌株F1和F2毒力均比野生菌株弱,其中F1株减弱了60.73%、F2株减弱了84.38%。选择24日龄未经仔猪水肿病疫苗免疫过的仔猪共14头,并随机分为2组;第1组口服接种减毒菌株F2,第2组以灭菌生理盐水作阴性对照,定期采集仔猪粪样并进行细菌监测;结果显示,仔猪排出减毒菌株F2的数量随时间不断增多,在接种后28d可达到每克粪样含目的菌约70 000cfu。这说明减毒菌株F2能够在仔猪体内定植并大量繁殖。     

烟草青枯病拮抗芽孢杆菌的筛选、鉴定及其抑菌活性初探

【目的】从不同烟区健康烟草的根际土壤样品中筛选对烟草青枯病具有较强拮抗作用的芽孢杆菌,为防治烟草青枯病提供生防资源。【方法】随机从福建龙岩、四川德昌、陕西汉中等地健康烟草根际土壤中采集30份土壤样品,采用平板稀释法从中分离芽孢杆菌,以烟草青枯病菌为靶标菌筛选拮抗芽孢杆菌,并通过培养特性、菌体形态、生理生化特征分析及16SrDNA序列分析,对筛选的拮抗芽孢杆菌菌株进行鉴定;采用温室盆栽试验,测定拮抗芽孢杆菌的促生作用、定殖能力和抑菌活性。【结果】从健康烟草根际土壤中分离得到1株抗烟草青枯病菌活性较好的菌株LW-4,经鉴定其为甲基营养型芽孢杆菌Bacillus methylotrophicus。LW-4菌悬液对烟草青枯病菌的防治效果为70.37%,其可定殖于烟草根际土壤,具有良好的定殖能力。LW-4对烟草有明显的促生作用;用饱和度为25%的硫酸铵获得的LW-4抑菌物质对烟草青枯病菌的抑菌活性较高,抑菌圈直径达37.82mm。【结论】菌株LW-4在烟草青枯病防治中具有潜在的利用价值。     

丛枝菌根真菌对鸢尾的促进作用研究

为高效利用水陆两栖植物鸢尾修复污染水体,本研究通过测定不同的丛枝菌根真菌(AMF)与鸢尾构建共生体系的生长指标、土壤理化性质及植物光合作用指标,探讨不同AMF对水生植物鸢尾的促进作用。结果表明:AMF对鸢尾的促进作用主要体现在地上及地下两部分,其中地下部分通过利用其庞大的菌丝网络吸收土壤中的营养物质,进而促进了鸢尾的生长,其中对比无菌剂侵染的空白植物,摩西球囊霉作用的鸢尾对氮元素的吸收率提高71.75%,磷元素的吸收率提高8.36%,而根内球囊霉作用的鸢尾对氮元素的吸收率提高42.55%,磷元素的吸收率提高9.5%;而地上部分则是通过加强叶片气孔导度的开启来调控植物净光合速率与蒸腾速率之间的平衡,进而提高了鸢尾的最优水资源利用率,加快植物的新陈代谢,最终促进植物的生长发育。其中对于鸢尾光合作用的调节摩西球囊霉的促进效果显著好于(P<0.05)根内球囊霉。     

Plant pathogen protection by arbuscular mycorrhizas: A role for fungal diversity?

Arbuscular mycorrhizal (AM) fungi can confer protection to host plants against some root pathogens, and several mechanisms for these phenomena have been proposed. If AM fungal taxa vary in the ways that they limit the negative effects of pathogens on host plants, additive and/or synergistic interactions among members of diverse AM fungal assemblages and communities may result in a greater pathogen protection than is currently predicted. However, in a review of the literature on interactions between AM and pathogenic fungi, we found few examples that compared the effectiveness of single- and multi-species AM fungal assemblages. Here, we briefly recount the generally recognized mechanisms of pathogen protection by AM fungi and present evidence, where appropriate, for functional diversity among AM fungal taxa with regard to these mechanisms. We propose that functional complementarity of AM fungal taxa in interactions with pathogens could mimic, or even be the cause of, previously observed relationships between AM fungal diversity and plant productivity.     

Plant growth-promoting bacteria in the rhizo- and endosphere of plants: Their role, colonization, mechanisms involved and prospects for utilization

In both managed and natural ecosystems, beneficial plant-associated bacteria play a key role in supporting and/or increasing plant health and growth. Plant growth-promoting bacteria (PGPB) can be applied in agricultural production or for the phytoremediation of pollutants. However, because of their capacity to confer plant beneficial effects, efficient colonization of the plant environment is of utmost importance. The majority of plant-associated bacteria derives from the soil environment. They may migrate to the rhizosphere and subsequently the rhizoplane of their hosts before they are able to show beneficial effects. Some rhizoplane colonizing bacteria can also penetrate plant roots, and some strains may move to aerial plant parts, with a decreasing bacterial density in comparison to rhizosphere or root colonizing populations. A better understanding on colonization processes has been obtained mostly by microscopic visualisation as well as by analysing the characteristics of mutants carrying disfunctional genes potentially involved in colonization. In this review we describe the individual steps of plant colonization and survey the known mechanisms responsible for rhizosphere and endophytic competence. The understanding of colonization processes is important to better predict how bacteria interact with plants and whether they are likely to establish themselves in the plant environment after field application as biofertilisers or biocontrol agents.     

Pseudomonas putida BP25 alters root phenotype and triggers salicylic acid signaling as a feedback loop in regulating endophytic colonization in Arabidopsis thaliana

Endophytic Pseudomonas putida BP25 (PpBP25) triggered density dependent alterations on Arabidopsis thaliana Col-0 growth. Endogenous colonization of PpBP25 was found regulated within Arabidopsis that caused induction and repression of 131 and 74 plant genes, respectively. Induced genes like WRKY33, AtRLP19, ATL2, ATEXO70B2, pEARLI, RPS2, CBP60G, PLA2, CRK18, ATFBS1, DREB2A, TIR, RAP2.4, and MOS1 were components of defense and salicylic acid (SA) signaling. Development associated genes were found significantly repressed. Biased activation of phytohormone signaling with their associated fitness costs on plant growth was observed. The data suggests that PpBP25 colonization triggered expression of defense genes that restricted its own population in a feedback loop besides causing altered root phenotype.