几种非豆科植物根瘤内生菌侵染特征的研究

自不同科、属、种的非豆科植物根瘤分离内生菌,对其寄主植物进行了交叉侵染,结果表明,这些Frankia菌对不同寄主的侵染没有明显的专一性,供试菌可以进行跨越科、属、种的侵染,但有的菌株对于某些植物的侵染,可能存在一些特殊情况,相同菌株对不同植物的侵染能力,以及不同菌株对同一寄主的侵染能力是有差异的。从同一种植物根瘤中分离的不同菌株,侵染能力也有高低之分,供试菌随寄主植物的改变,侵染能力及所建立的共生系统固氮活性有所降低,侵染原寄主植物所形成的根瘤固氮活性较高的菌株,在改变寄主后所形成的根瘤固氮活性也比较高,在一定条件下,寄主植物的结瘤量与根瘤固氮活性呈正相关,而侵染不同寄主后,根瘤中菌体孢子的表面结构也发生了一定变化。     

豆科植物早期共生信号转导的研究进展

豆科植物与根瘤菌建立特异的共生关系,在寄主根部产生固氮根瘤。此过程包含了共生信号识别与传递、根瘤菌侵染、根瘤形成以及固氮功能实现等生物学事件。研究人员已经从2种豆科模式植物蒺藜苜蓿（Medicago truncatula）和百脉根（Lotus japonicus）的共生固氮体系中,筛选到许多与根瘤菌共生相关的突变体及其相对应的功能基因,建立起包含结瘤因子识别、共生信号传递和转录响应在内的早期共生信号途径。该文对豆科植物早期共生信号途径的新进展进行了综述。     

几种非豆科植物根瘤内生菌侵染特征的研究

自不同科、属、种的非豆科植物根瘤分离内生菌,对其寄主植物进行了交叉侵染,结果表明,这些Frankia菌对不同寄主的侵染没有明显的专一性,供试菌可以进行跨越科、属、种的侵染,但有的菌株对于某些植物的侵染,可能存在一些特殊情况,相同菌株对不同植物的侵染能力,以及不同菌株对同一寄主的侵染能力是有差异的。从同一种植物根瘤中分离的不同菌株,侵染能力也有高低之分,供试菌随寄主植物的改变,侵染能力及所建立的共生系统固氮活性有所降低,侵染原寄主植物所形成的根瘤固氮活性较高的菌株,在改变寄主后所形成的根瘤固氮活性也比较高,在一定条件下,寄主植物的结瘤量与根瘤固氮活性呈正相关,而侵染不同寄主后,根瘤中菌体孢子的表面结构也发生了一定变化。     

豆科植物早期共生信号转导的研究进展北大核心CSCD

豆科植物与根瘤菌建立特异的共生关系,在寄主根部产生固氮根瘤。此过程包含了共生信号识别与传递、根瘤菌侵染、根瘤形成以及固氮功能实现等生物学事件。研究人员已经从2种豆科模式植物蒺藜苜蓿(Medicago truncatula)和百脉根(Lotus japonicus)的共生固氮体系中,筛选到许多与根瘤菌共生相关的突变体及其相对应的功能基因,建立起包含结瘤因子识别、共生信号传递和转录响应在内的早期共生信号途径。该文对豆科植物早期共生信号途径的新进展进行了综述。     

SHR-SCR模块通过决定皮层细胞的命运调控豆科植物根瘤起始

\"为什么豆科植物能与根瘤菌共生固氮\"是一个有待阐述的重要科学问题,一直困扰着该领域的学者。2020年12月10日,中国科学院分子植物科学卓越创新中心王二涛团队在Nature发表了题为An SHR-SCR module specifies legume cortical cell fate to enable nodulation的研究论文。该研究发现,豆科植物皮层细胞获得了SHR-SCR分子模块,其通过决定皮层细胞的命运调控豆科植物根瘤起始,使其有别于非豆科植物。这可能是豆科植物共生结瘤固氮的前提事件,回答了\"为什么豆科植物能结瘤固氮\"这一科学问题。该项工作发现了控制豆科植物根瘤共生固氮的关键分子模块,不仅加深了人们对共生固氮的理解,也为非豆科植物皮层细胞命运的改造奠定了基础,为今后减少作物对氮肥的依赖,实现农业生产的可持续发展提供了新的思路。本文特邀山东大学丁兆军教授对这一成果进行点评。     

豆科植物根瘤中非共生的内生菌遗传多样性研究进展

在豆科植物与根瘤菌之间结合形成的固氮共生体中,其典型的特征是由特定的微共生体诱导形成的根瘤或茎瘤,除了根瘤菌外,在根瘤中同样也分离出多种与根瘤菌共生固氮无关的内生菌类群,而且根瘤菌与内生菌通常可以共存于同一个根瘤内是普遍存在的客观现象,这些非共生的内生菌生活史的一部分存在于根瘤内且不会引起植物发病,但有关它们的生态学作用还知之甚少,由于其生态上的重要性,近年来对该现象的研究不断深入.就近年来根瘤中隶属于变形菌门,放线菌门、后壁菌门的非共生的内生菌遗传多样性所取得的最新研究结果进行了总结,并介绍了根瘤中相关内生菌多样性研究的新进展.同时,指出了该研究领域存在的问题,并对未来相关研究方向做了展望.     

固氮细菌找到新伙伴——研究人员已使固氮根瘤菌在水稻等非豆科植物上形成根瘤

固氮根瘤菌有强的选择性,除少数外它们只在大豆、苜蓿和合欢等豆科植物上结根瘤,使其生长生气勃勃。细菌使空气中不能利用的氮气转化成氨和为植物滋养所需的其他化合物。事实上,细菌给植物提供了氮肥工厂。     

银合欢根瘤细胞的光学显微镜和电子显微镜研究

银合欢接种根瘤菌形成根瘤后,应用光镜和电镜技术观察。银合欢根瘤由分生组织细胞、皮层组织细胞、维管束系统和侵染细胞区域四个不同部分组成。根瘤菌借助于侵染线侵染细胞,释放进入宿主细胞质中,转变成固氮类菌体。最初每个包被膜内只含单独的类菌体,随后较老的侵染细胞中,每个包被膜内含有一个以上的类菌体。因此,成熟根瘤的侵染细胞可见有2~5个类菌体群集包被膜里,并且明显地累积PHB物质,显示电子染色透明颗粒。本文还讨论了上述变化的意义与银合欢根瘤细胞结构和功能的关系。     

根瘤菌-豆科植物共生的分子生物学

<正> 一、引言地球上最大的氮源是空气中的分子氮。所有生物都靠结合态氮生存,其中最主要的是氨或氨基酸。动、植物都不能直接利用分子态氮,只能利用从空气中固定的氨态氮。营养链中的重要环节是微生物把分子态氮转化为代谢上可利用的化合物。某些细菌和蓝藻有还原分子     

固氮基因转移的研究进展

生物学家特别是微生物学家、生物化学家、分子遗传学家十分注视生物固氮和固氮基因转移问题。目标是。如何把原核生物系统的固氮基因转移到高等植物特别是粮食作物中去,使它们能自主地进行共生固氮作用。实现这个目标还不是眼前的事,有的科学家认为,需要10年左右的时间才能达到这一目标。美国哈佛大学(F.M.Ausubel)、Cornell大学(A.A.Szalay)等已成功地将固氮基因(来自土壤中能够固氮的Klebsiella)     

Phloem‐derived γ‐aminobutyric acid (GABA) is involved in upregulating nodule N2 fixation efficiency in the model legume Medicago truncatula

Nitrogen fixation in legumes is downregulated through a whole plant N feedback mechanism, for example, when under stress. This mechanism is probably triggered by the impact of shoot‐borne, phloem‐delivered compounds. However, little is known about any whole‐plant mechanism that might upregulate nitrogen fixation, for example, under N deficiency. We induced emerging N‐deficiency through partial excision of nodules from Medicago truncatula plants. Subsequently, the activity and composition of the remaining nodules and shifts in concentration of free amides/amino acids in the phloem were monitored. Furthermore, we mimicked these shifts through artificial feeding of γ‐aminobutyric acid (GABA) into the phloem of undisturbed plants. As a result of increased specific activity of nodules, N₂ fixation per plant recovered almost completely 4–5 d after excision. The concentration of amino acids, sugars and organic acids increased strongly in the upregulated nodules. A concomitant analysis of the phloem revealed a significant increase in GABA concentration. Comparable with the effect of nodule excision, artificial GABA feeding into the phloem resulted in an increased activity and higher concentration of amino acids and organic acids in nodules. It is concluded that GABA might be involved in upregulating nodule activity, possibly because of its constituting part of a putative amino acid cycle between bacteroids and the cytosol.     

Cytochemistry of proteolytic activity and pH status of vacuoles in Medicago truncatula root nodules

The vacuole development in root nodules of Medicago truncatula was analyzed by light and electron microscopy. Histochemistry of protease activity in root nodules was studied using fluorogenic substrates for proteolytic enzymes, 7-amino-4-methylcoumarin, CBZ-L-phenylalanyl-L-arginine amide, hydrochloride (AMC), and rhodamine 110, bis-(CBZ-L-phenylalanyl-L-arginine amide) dihydrochloride (RPA). Furthermore, the topology of acidification of the central vacuoles in infected and noninfected cells in root nodules of Medicago truncatula was analyzed with the fluorescent pH-sensitive acidotropic dye Neutral Red. It was shown that vacuoles were acidic, lytic organelles in noninfected cells and young infected cells of the nodule where they displayed protease activity. Mature vacuoles of infected cells had high pH and did not show any substantial protease activity. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 1, pp. 31–38. The text was submitted by the authors in English.     

Medicago-Sinorhizobium symbiotic specificity evolution and the geographic expansion of Medicago

The legume genus Medicago interacts with soil bacteria commonly referred to as rhizobia, in a nitrogen fixing symbiosis. We analysed the diversity of symbiotic association specificity among the two organisms, and its evolution in the plant genus. Nitrogen fixation tests and molecular phylogenetic reconstructions revealed that the genus Medicago includes more symbiotic specificity groups than previously suggested and that plant specificity is highly unstable and has repeatedly switched along the diversification of this genus. A phylogenetic analysis including geographical data shows that bacterial geographical diversity distribution has a strong influence on the geographic distribution of plant species and their ability to colonize new areas. Multiple other modifications of specificity occurred along the diversification of the genus, presumably due to selection for specialization to a single bacterial biovar. Codivergence between plants and bacteria may also have taken place.