大豆根瘤的超微结构特征

用透射电镜研究了中国丰收11号大豆根瘤(Glycine max L.)的超微结构。它主要由外部的皮层及内部的中心组织组成。在其发育过程中,除～般的细微结构变化外,还具有以下一些特征：(1)早期侵染细胞具有核仁联合体;(2)有一种大而长并包围着造粉体的特殊类型的线粒体;(3)在幼龄侵染细胞中有一种染色很深,圆形或近似圆形的内含体;(4)细菌中含有大量的多聚磷酸盐颗粒。本文详细地描述了上述各种变化,同时讨论了这些变化的意义与根瘤发育的关系。     

大豆根瘤中根瘤菌的电镜观察(简报)

在研究大豆根瘤的超微结构时,也常常描述一些有关细菌结构的变化,但一般比较简单,且多指寄主细胞中的幼龄细菌和成熟细菌,而对于侵入线中的细菌和寄主细胞中衰老细菌却很少有详细报道,即使在其他根瘤,特别是球形根瘤也是如此。显然这对研究根瘤中细菌的发育和衰老是很不够的。丰收11号大豆产量高,抗干旱,其根瘤在超微结构方面有许多特点。为了了解这种     

豇豆根瘤菌NGR234和紫云英根瘤菌109感染紫云英的比较研究

利用光学和电子显微镜对紫云英根瘤菌菌株109和广宿主的快生型根瘤菌菌株NGR234感染温带型豆科植物紫云英进行了研究,结果表明根瘤菌感染紫云英是通过在根毛中形成侵染线的途径。电子显微镜研究揭示了固氮根瘤中细胞内侵染线的存在。接种二天后,首先可观察到根毛的卷曲或分枝。接种四至五天后,在每株植物卷曲的根毛中可看到侵染线。接种八至十天后的植株出现肉眼可见的根瘤。菌株NGR234能够在紫云英上诱导根毛的卷曲,侵染线和根瘤的形成,但所形成的根瘤却未能固氮,根瘤中无明显的类菌体区,但有少数包有细菌的侵染线。NGR234抗抗菌素的衍生菌均未能使紫云英结瘤。将NGR234的共生质粒转移至三叶草、苜蓿、豌豆、快生型大豆根瘤菌和农杆菌,亦未能使这些细菌获得紫云英上结瘤的能力。     

豌豆根瘤侵染细胞衰老过程的电镜观察

用透射电镜观察了豌豆根瘤侵染细胞在衰老过程中的超微结构变化,结果表明,侵染细胞和拟菌体的衰老有一定的规律和特征,首先是一些包裹拟菌体的包囊变得疏松,包囊和拟菌体之间出现较大间隙,间隙中常有一些纤维状和泡状物质。然后,细胞质失去正常结构,逐渐凝聚为染色很深的团块,进而完全泡状化,伴随着拟菌体的衰老,寄主细胞质染色由深变浅,细胞器逐渐减少,最后,液泡和质膜相继破裂,细胞完全瓦解,有时在衰老细胞的胞间隙,或在衰老的细胞质中有一定年轻的细菌,甚至在一片崩溃的拟菌体中还有侵染丝,有的还正在向寄主细胞质释放细菌。     

豌豆根瘤侵染细胞衰老过程的电镜观察

用透射电镜观察了豌豆根瘤侵染细胞在衰老过程中的超微结构变化,结果表明,侵染细胞和拟菌体的衰老有一定的规律和特征,首先是一些包裹拟菌体的包囊变得疏松,包囊和拟菌体之间出现较大间隙,间隙中常有一些纤维状和泡状物质。然后,细胞质失去正常结构,逐渐凝聚为染色很深的团块,进而完全泡状化,伴随着拟菌体的衰老,寄主细胞质染色由深变浅,细胞器逐渐减少,最后,液泡和质膜相继破裂,细胞完全瓦解,有时在衰老细胞的胞间隙,或在衰老的细胞质中有一定年轻的细菌,甚至在一片崩溃的拟菌体中还有侵染丝,有的还正在向寄主细胞质释放细菌。     

豆科根瘤的超微结构研究

Bergerson等于1958年开创了豆科根瘤超微结构的研究,并逐渐形成一门崭新的学科和科研领域。根瘤超微结构研究是指运用各种电镜技术(包括超薄切片、扫描、冰冻蚀刻、放射自显影、细胞化学和免疫电镜等),在亚细胞水平上研究根瘤在发育过程中的结构变化以及这些变化与根瘤发育和固氮的关系。归纳起     

白车轴草和紫花苜蓿根瘤的显微及超微结构

通过对白车轴草(Trifolium repens Linn.)和紫花苜蓿(Medicago sativa Linn.)根瘤的显微及超微结构进行观察,发现其根瘤显微结构都由4部分组成,由外向内依次为：保护层、皮层、鞘细胞层和中心组织(侵染组织)。在中心组织的侵染细胞中,分布有大量的线粒体、高尔基体、核糖体及内质网,白车轴草根瘤侵染细胞中的细菌圆形或椭圆形,有明显的周膜、细菌细胞壁和质膜,在细菌发育过程中,周膜活动旺盛,有时相邻细菌的周膜发生融合,在周膜附近常分布有大量的内质网、高尔基体以及高尔基体小泡,似与周膜融合有关。紫花苜蓿细菌椭圆形、长棒形,甚至有的细菌呈分枝状。二者细菌细胞质中分布着大量的核糖体和纤维状的核物质。在白车轴草中还有染色很深的多聚磷酸盐颗粒。     

豌豆根瘤脂质体的分布及形态特征

豌豆根瘤中有大量的脂质体,广泛分布于非侵染细胞和侵染细胞内,它既可以存在细胞质中,也可位于液泡里面。有时单个存在,有时又多个聚集在一起。非侵染细胞与侵染细胞相比,前者中的脂质体明显多于后者。这些脂质体近似圆形或椭圆形,表面无膜,电子密度较高,内部无固定的结构,常有一些细胞器位于它的附近。讨论了脂质体的细胞发育及细胞种类的关系。     

箭舌豌豆根瘤液泡中细菌周膜来源的研究

电镜观察结果表明,幼龄箭舌豌豆根瘤侵染细胞的细胞质较少,中央是一些体积较大的液泡。细胞质中侵入线经常可见,由侵入线释放出来的细菌均有细菌周膜。这些细菌只位于细胞质中,不出现在液泡里面。成熟根瘤中的侵染细胞与此不同,它们中有大量的成熟侵染细胞,细胞质丰富,里面充满大量细菌,中央常有一个大液泡。当中央液泡发育到一定程度时,位于其附近的细菌可通过液泡膜内吞、液泡膜与细菌周膜融合及液泡膜破裂3种途径进入液泡,后一种途径常伴有寄主细胞质。液泡中的细菌绝大部分裸露在外,只有个别细菌具有细菌周膜且多位于液泡膜的破损处附近,因此细菌周膜可能是原来就有的。     

翅果油树根瘤超微结构及其内生菌的观察

作者用光学显微镜,透射电镜和扫描电镜对翅果油树(Eldaeagnus mollis D.)根瘤侵染细胞的超微结构及其内生菌的形态进行了观察研究。翅果油树根瘤中的内生菌具有五种不同的发育形态:菌丝、固氮泡囊、孢囊、孢囊孢子和拟类菌体。内生菌的这些不同形态以及它们在共生固氮中的作用,本文也作了讨论。     

The effect of inoculation with Rhizobium leguminosarum on the contents of cytoplasmic protein and free amino acids in the roots of pea seedlings

The changes in the contents of protein and free amino acids in pea plants inoculated with Rhizobium leguminosarum were studied taking into account the susceptibility of roots to root nodule bacteria. The content of cytoplasmic protein during infection increased in the actively growing root region (0-5 mm) and decreased in the root regions susceptible to rhizobia (5-20 mm from the root tip). The quantitative composition of free amino acids changed essentially upon inoculation of pea seedlings with R. leguminosarum.     

Effect of Root Agglutinin on Microbial Activities in the Rhizosphere

A total of 220 bacterial isolates were obtained from pea rhizosphere and nonrhizosphere samples. Of these samples, 100 isolates were chosen randomly to test for their agglutinative reaction against pea root exudate. The percentage of positive agglutination of bacteria isolated from the nonrhizosphere sample was significantly lower than that of bacteria isolated from the rhizosphere sample. Moreover, this agglutinative reaction could not be blocked either by treating the bacterial cells or root exudate with different carbohydrates before they were mixed or by boiling the root exudate first. Bacteria that could be agglutinated by pea root exudate followed the downward growth of the pea root through the soil profile. The greater abilities of such bacteria to colonize the pea rhizosphere were indicated by their higher rhizosphere-colonizing (rhizosphere/nonrhizosphere) ratios, whether the bacteria were added alone or together with nonagglutinating bacteria. However, bacteria did show different agglutinative reactions toward root exudates obtained from different plants.     

Lipopolysaccharide epitope expression of Rhizobium bacteroids as revealed by in situ immunolabelling of pea root nodule sections.

To investigate the in situ expression of lipopolysaccharide (LPS) epitopes on nodule bacteria of Rhizobium leguminosarum, monoclonal antibodies recognizing LPS macromolecules were used for immunocytochemical staining of pea nodule tissue. Many LPS epitopes were constitutively expressed, and the corresponding antibodies reacted in nodule sections with bacteria at all stages of tissue infection and cell invasion. Some antibodies, however, recognized epitopes that were only expressed in particular regions of the nodule. Two general patterns of regulated LPS epitope expression could be distinguished on longitudinal sections of nodules. A radial pattern probably reflected the local physiological conditions experienced by endosymbiotic bacteria as a result of oxygen diffusion into the nodule tissue. The other pattern of expression, which followed a linear axis of symmetry along a longitudinal section of the pea nodule, was apparently associated with the differentiation of nodule bacteria and the development of the nitrogen-fixing capacity in bacteroids. Basically similar patterns of LPS epitope expression were observed for pea nodules harboring either of two immunologically distinct strains of R. leguminosarum bv. viciae, although these epitopes were recognized by different sets of strain-specific monoclonal antibodies. Furthermore, LPS epitope expression of rhizobia in pea nodules was compared with that of equivalent strains in nodules of French bean (Phaseolus vulgaris). From these observations, it is suggested that structural modifications of Rhizobium LPS may play an important role in the adaptation of endosymbiotic rhizobia to the surrounding microenvironment.     

Diversity and geographic variation of endosymbiotic bacteria in natural populations of the pea aphid (Acyrthosiphon pisum) in China

Bacterial symbionts in aphids are known to benefit the insect host and associated with aphid’s ecological adaptation. The pea aphid (Acyrthosiphon pisum), an important legume pest worldwide, carries at least eight endosymbionts, providing a model system to study insect–bacteria interactions. However, species diversity and geographic variations of endosymbionts are unknown in Chinese populations; therefore, we characterized symbiont communities and diversity of 27 pea aphid samples from 13 geographic populations of China. Via amplicon high-throughput sequencing and diagnostic PCR, we found that bacterial communities of Chinese populations were dominated by Proteobacteria and Firmicutes. Among eight known endosymbionts, five (Buchnera, Serratia, Hamiltonella, Regiella, and Rickettsia) were detected by both methods, with a specific geographical distribution. The obligate symbiont, Buchnera, was present in all aphid samples, while the four facultative symbionts showed a significant geographic variation. Each population was randomly infected with distinct endosymbionts, ranging from three to five species. Serratia and Rickettsia showed relatively higher abundance in central regions of China, Regiella was predominant in eastern and western China, whereas Hamiltonella showed an extremely low abundance and was absent in four populations. Samples grouped by altitudes showed a significant diversity difference, whereas there was no significant difference between red and green body colors. Bacterial community structures of the Chinese pea aphid populations were mainly influenced by environmental factors, other than body colors. These data can guide the development of potential biocontrol techniques against this aphid.     

Control of Pythium damping-off of sugar beet by seed treatment with crop straw powders and a biocontrol agent

Seed treatment with non-sterilized powdered straws from 39 crops was tested for the control of Pythium damping-off of sugar beet. Four straws, including flax, coriander, pea, and lentil were effective in controlling the disease in soil artificially infested with Pythium sp. “group G.” Sterilizing flax and pea straws eliminated the efficacy of these straws. Wheat straw powder coated on sugar beet seeds increased the incidence of Pythium damping-off but this effect was reversed by the co-inoculation of wheat straws with the biocontrol agent Pseudomonas fluorescens 708. Coating sugar beet seeds with P. fluorescens 708 and flax or pea straws also increased the efficiency of the bacterial strain for the control of Pythium damping-off. Pea straws and to a lesser extent lentil straws produced volatile substances that affected mycelial growth of Pythium sp. “group G” on potato dextrose agar in Petri plates when the straws were mixed with water and left to ferment for two days. Fermentation of pea straws led to the accumulation of volatile ammonia, which was produced by the reduction of the large amount of nitrate stored in the straw. Reduction of nitrate and therefore the release of volatile ammonia did not occur in sterilized pea straws. However, fermenting sterile pea straws with bacteria from different genera restored nitrate reduction and the release of volatile ammonia, suggesting that microorganisms associated with pea straws are responsible for the conversion of nitrate into volatile ammonia which in turn control Pythium damping-off disease in sugar beet.     

Plants secrete substances that mimic bacterial N-acyl homoserine lactone signal activities and affect population density-dependent behaviors in associated bacteria

In gram-negative bacteria, many important changes in gene expression and behavior are regulated in a population density-dependent fashion by N-acyl homoserine lactone (AHL) signal molecules. Exudates from pea (Pisum sativum) seedlings were found to contain several separable activities that mimicked AHL signals in well-characterized bacterial reporter strains, stimulating AHL-regulated behaviors in some strains while inhibiting such behaviors in others. The chemical nature of the active mimic compounds is currently unknown, but all extracted differently into organic solvents than common bacterial AHLs. Various species of higher plants in addition to pea were found to secrete AHL mimic activities. The AHL signal-mimic compounds could prove to be important in determining the outcome of interactions between higher plants and a diversity of pathogenic, symbiotic, and saprophytic bacteria.     

Immunological Studies on Glutamine Synthetase using Antisera Raised to the Two Plant Forms of the Enzyme from PhaseolusRoot Nodules

Antisera specific for glutamine synthetase (GS) have been raisedto the two forms of the enzyme from the plant fraction of rootnodules of Phaseolus vulgaris. The two antisera recognized bothforms of plant nodule GS and also the enzyme from some otherhigher plant tissues. However, the antiserum did not cross-reactwith GS from free-living or bacteroid Rhizobium Phaseolinorwith the enzyme from representatives of green algae, fungi,mammals and bacteria. Results are presented which suggest thatone of the forms of nodule GS is closely related to the rootenzyme whereas the other, the 'nodule specific' form, has someantigenic differences Key words: Phaseolus Vulgaris, Legume/Rhizobium symbosis, Glutamine synthetase, Immunology     

The effect of inoculation with <Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis> on the contents of cytoplasmic protein and free amino acids in the roots of pea seedlings

The changes in the contents of protein and free amino acids in pea plants inoculated with Rhizobium leguminosarum were studied taking into account the susceptibility of roots to root nodule bacteria. The content of cytoplasmic protein during infection increased in the actively growing root zone (0–5 mm) and decreased in the root zones susceptible to rhizobia (5–20 mm from the root tip). The quantitative composition of free amino acids changed essentially upon inoculation of pea seedlings with R. leguminosarum.     

Nod factors stimulate seed germination and promote growth and nodulation of pea and vetch under competitive conditions

Nod factors are lipochitooligosaccharide (LCO) produced by soil bacteria commonly known as rhizobia acting as signals for the legume plants to initiate symbiosis. Nod factors trigger early symbiotic responses in plant roots and initiate the development of specialized plant organs called nodules, where biological nitrogen fixation takes place. Here, the effect of specific LCO originating from flavonoid induced Rhizobium leguminosarum bv. viciae GR09 culture was studied on germination, plant growth and nodulation of pea and vetch. A crude preparation of GR09 LCO significantly enhanced symbiotic performance of pea and vetch grown under laboratory conditions and in the soil. Moreover, the effect of GR09 LCOs seed treatments on the genetic diversity of rhizobia recovered from vetch and pea nodules was presented.     

Differential reactions of wheat and pea genotypes to root inoculation with growth-affecting rhizosphere bacteria

Spring wheat (Triticum aestivum L.) and pea (Pisum spp.) genotypes were tested for reaction to root inoculation with rhizosphere bacteria affecting plant growth. Plant response was studied in greenhouse experiments after treatment of seedlings with bacteria suspended in nutrient broth. Significant genotype variation was found in both wheat and pea in terms of shoot dry weight and severity of bacteria-induced leaf symptoms. For most bacterial isolates tested, there was good correlation between ratings of leaf symptoms 7 to 14 days after inoculation and growth inhibition measured after four weeks. Interactions between isolates and plant genotypes were significant in both wheat and pea (P=0.0024 and 0.0001, respectively), but genotypes with sensitivity or tolerance to most isolates could be distinguished. In an outdoor pot experiment, two of the bacterial isolates caused delayed plant development and differential decreases in grain yield of wheat genotypes. The hypothesis that the reaction of wheat genotypes to the tested becteria was related to their influence on bacterial establishment in the rhizosphere could not be substantiated.