Is N‐feedback involved in the regulation of nitrogenase activity in Medicago truncatula?

To determine whether senescing leaves provoke an active nitrogen (N) remobilization that results in the reduction of nitrogenase activity, 60% of Medicago truncatula lower leaves were either darkened or individually excised for two weeks. Although a considerable amount of N was remobilized, N₂ fixation activity was found to be increased to maintain the N source/sink balance, indicating an absence of the negative N‐feedback regulation of nitrogenase activity in the senescing M. truncatula.     

铁皮石斛优良共生菌的抗旱机理

为阐明细胞膜保护酶在菌根提高铁皮石斛抗旱能力过程中的作用,采用模拟自然干旱胁迫的方法,对胁迫过程中菌根化铁皮石斛细胞膜保护酶的活性变化进行研究。结果表明:铁皮石斛菌根真菌(JSAFC003、JSAFC004)能够在一定程度上提高植株的抗旱能力,SOD、POD活性与植株抗旱能力呈正相关,MDA含量与植株抗旱能力呈负相关,表明细胞膜保护酶的调节作用在菌根提高铁皮石斛抗旱能力过程中发挥了一定作用。     

Effects of mycorrhizal fungi on root-hair growth and hormone levels of taproot and lateral roots in trifoliate orange under drought stress

A pot experiment was used to evaluate the effects of an arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae on plant growth performance, root-hair growth, and root hormone levels in trifoliate orange (Poncirus trifoliata) seedlings under well-watered (WW) and drought stress (DS). A 9-week mild DS treatment significantly reduced mycorrhizal colonization of 2nd- and 3rd-order lateral roots. Root mycorrhizal colonization was relatively higher in the 2nd- and 3rd-order lateral roots than in the taproot and the 1st-order lateral root under WW and DS. AMF seedlings exhibited significantly higher root-hair density, length (except for the taproot) and diameter in taproot and 1st-, 2nd-, and 3rd-order lateral roots under WW, and considerably higher root-hair density (except for 1st-order lateral root), length (except for 2nd-order lateral root) and diameter under DS. Mycorrhizal inoculation remarkably increased root abscisic acid (ABA), indole-3-acetic acid (IAA), methyl jasmonate, and brassinosteroids (BRs) concentrations under DS, in company with the decrease in root zeatin riboside and gibberellins levels and root IAA effluxes. Root-hair traits were significantly positively correlated with root colonization and root ABA and BRs levels. It is concluded that mycorrhizal plants possessed better root-hair growth to adapt mild DS, which is associated with mycorrhizal colonization and endogenous hormone changes.     

Effects of nitrogen feeding for extraradical mycelium of Rhizophagus irregularis maize symbiosis incorporated with phosphorus availability

In terrestrial ecosystems, plants are frequently in symbiosis with arbuscular mycorrhizal fungi (AMF) with mineral nutrients and photosynthesis carbon exchanges in between. This research sought to identify the effects of phosphorus (P) levels on the nitrogen (N) uptake via extraradical mycelium (ERM) and the mycorrhizal growth response (MGR) of maize plants within the AMF symbiosis. Pots were separated into root compartments and hyphae compartments (HCs) with two layers of a 30‐μm mesh membrane and an air gap in between, where only hyphae could pass through, to avoid both N diffusion and root growth effects. Maize plants were inoculated with Rhizophagus irregularis with different N fertilization in HCs under two different P fertilization levels. Our results indicated that a strong increase in MGR with low‐P fertilization. The same tendency was not observed with high‐P fertilization, although both had a large increase in P concentration as a potential source of growth in shoot tissue of mycorrhizal plants. Substantial effects (10.5% more N) were observed in the case of high‐P availability for the host plants from ERM fed with N, whereas under low‐P conditions ERM may prioritize P uptake rather than N uptake. The AM fungi increase the uptake of N and P, which are most limiting in the soil with fewer forces from soil resources. In addition, there was still more P accumulated than N due to the high N for ERM with high‐P supply. Low N in HCs corresponded with a lower colonization rate in roots but with high hyphae density in HCs; this result suggest that N and P availability might change the ratio of extraradical to intraradical hyphae length.     

菌根真菌对3种兰花幼苗生长作用研究

菌根真菌在兰科植物生活史中具有重要作用。为获得促进兰科植物生长的共生真菌,阐明菌根真菌对兰科植物的作用,本研究对从野生建兰中分离获得的3株共生真菌进行形态学和系统进化分析,并将3株真菌与建兰、硬叶兰和铁皮石斛幼苗在不同浓度燕麦琼脂培养基(OMA)条件下共培养,进行比较研究。结果表明,3株真菌分属于胶膜菌属(Tsc)、角担菌属(Cej3)和蜡壳菌属(Sec),且菌丝和菌落特征存在明显差异;系统进化分析发现,Tsc菌株与Cej3菌株亲缘关系较近,与Sec菌株亲缘关系较远;与兰科植物共培养结果表明,Tsc菌株可在全部OMA浓度条件下与3种兰科植物幼苗建立共生关系,且定殖率均为100%;Cej3菌株和Sec菌株与3种兰科植物在不同OMA浓度条件下定殖时间及定殖率存在差异,且具有一定的专一性;与对照组相比,与真菌共生的兰科植物幼苗的平均鲜重、干重、苗高、根长增长率均明显提高。本研究结果为深入研究兰科植物与真菌共生的分子机制奠定了一定的理论基础,并为兰花种质资源的保护提供了参考。     

湖南农业旅游名牌发展战略和开发模式及对策

乡村旅游产业链的构建对提升乡村旅游产业竞争力,促进乡村旅游健康发展具有重要的战略意义。本文把乡村旅游产业作为一个共生系统,从共生的视角对乡村旅游产业链概念进行再认识,得出乡村旅游产业链的共生互利性、自组织性、共演化性、协同性等系统特征;在分析乡村旅游产业链共生模式演化阶段及其特征基础上,提出构建山西省乡村旅游产业链共生系统的3种途径:横向产业链共生——寻求共生合作组织、纵向产业链共生——链条一体化、乡村旅游价值链共生——文化共生链。     

人和动物丝虫共生菌——沃尔巴克氏体研究进展

沃尔巴克氏体(Wolbachia,Wb)是在丝虫体内发现的一类共生菌,它诱导的免疫病理引起的炎症反应是丝虫感染后致病的主要原因之一。论文论述了丝虫沃尔巴克氏体的分类、结构与分布、生殖及传播方式、基因组和沃尔巴克氏体与丝虫之间的相互作用关系,重点阐述了沃尔巴克氏体与丝虫致病性和清除沃尔巴克氏体药物在人和动物丝虫病治疗中的作用,为人和动物丝虫病的防治研究提供参考。     

The endophytic fungus Piriformospora indica protects wheat from fusarium crown rot disease in simulated UK autumn conditions

The root endophytic fungus Piriformospora indica (Sebacinacea) forms mutualistic symbioses with a broad range of host plants, increasing their biomass production and resistance to fungal pathogens. This study evaluated the effect of P. indica on fusarium crown rot disease of wheat, under in vitro and glasshouse conditions. Interaction of P. indica and Fusarium isolates under axenic culture conditions indicated no direct antagonistic activity of P. indica against Fusarium isolates. Seedlings of wheat were inoculated with P. indica and pathogenic Fusarium culmorum or F. graminearum and grown in sterilized soil‐free medium or in a non‐sterilized mix of soil and sand. Fusarium alone reduced emergence and led to visible browning and reduced root growth. Roots of seedlings in pots inoculated with both Fusarium isolates and P. indica were free of visible symptoms; seed emergence and root biomass were equivalent to the uninoculated. DNA was quantified by real‐time polymerase chain reaction (qPCR). The ratio of FusariumDNA to wheat DNA rose rapidly in the plants inoculated with Fusarium alone; isolates and species were not significantly different. Piriformospora indica inoculation reduced the ratio of Fusarium to host DNA in the root systems. The reduction increased with time. The ratio of P. indica to wheat DNA initially rose but then declined in root systems without Fusarium. With Fusarium, the ratio rose throughout the experiment. The absolute amount of FusariumDNA in root systems increased in the absence of P. indica but was static in plants co‐inoculated with P. indica.     

An improved method for bright-field imaging of arbuscular mycorrhizal fungi in plant roots

Easy observation methods to assess the colonization levels of arbuscular mycorrhizal (AM) fungi in plant roots are crucial for studying the biology of AM symbiosis and for considering agricultural use. Many AM studies employ Trypan Blue (TB) coupled with lactic acid to stain AM fungal structures as bright-field images; however, TB staining can be difficult to use owing to its noxiousness and high viscosity. Here, we report the development of an easy method for visualizing AM fungal structures as bright-field images using 3,3′-diaminobenzidine (DAB). Wheat germ agglutinin (WGA)-conjugated horseradish peroxidase (HRP), which specifically targets N-acetylglucosamine polymers and detects AM fungal cell walls, penetrated the cortical layers of 10% potassium hydroxide (KOH)-treated soybean roots and stained AM fungal mycelia in the presence of DAB and hydrogen peroxide (H₂O₂). Comparison between DAB and TB staining of soybean (Glycine max L.) roots suggested that the intactness of root systems and image contrast using DAB staining were superior. Background signals in stele observed by DAB staining were negligible as compared with those observed by WGA-fluorescein isothiocyanate staining. DAB staining, which combines the advantages of TB (easy bright-field imaging) and WGA-fluorophore (specific and high-quality) staining, provides a robust imaging method for macro- and micro-level analyses of AM roots and is applicable to at least six crops: soybean, onion (Alium cepa L.), potato (Solanum tuberosum L.), maize (Zea mays L.), rice (Oryza sativa L.), and sunflower (Helianthus annuus L.).