Formation of Phenolic Compounds in Apogeotropic Roots of Cycad Plants

Formation and location of phenolic compounds in apogeotropic roots (coralloid roots) were studied in six cycad species, which belong to the genera Cycas, Encephalartos, and Ceratozamia. Total contents of soluble phenolic compounds in coralloid roots in all species studied varied insignificantly, with except for Ceratozamia mexicana that accumulated three times higher amounts of phenolic compounds. Phenolic compounds were accumulated in cell walls of cortical parenchyma of coralloid roots, in intercellular spaces, and in specialized storage cells, found in all zones of apogeotropic roots. The greatest number of phenol-storing cells was situated in the cortical parenchyma of the central part of coralloid roots, adjacent to a zone where active symbiotic cyanobacteria were localized, and in the coralloid root basal region lacking viable forms of cyanobionts. It was suggested that phenolic compounds affect the formation of symbiosis between cyanobacteria and apogeotropic roots of cycad plants, as well as their metabolism.     

Microbial Complexes Occurring on the Apogeotropic Roots and in the Rhizosphere of Cycad Plants

The microbial complexes of soil, the rhizosphere, and the rhizoplane of the apogeotropic (coralloid) roots of cycad plants were comparatively studied. The aseptically prepared homogenates of the surface-sterilized coralloid roots did not contain bacterial microsymbiont, indicating that in the root tissues the symbiosis is a two-component one (plant–cyanobacteria). At the same time, associated bacteria belonging to different taxonomic groups were detected in increasing amounts in the cycad rhizoplane, rhizosphere, and the surrounding soil. The bacterial communities found in the cycad rhizoplane and the surrounding soil were dominated by bacteria from the genus Bacillus. The saprotrophic bacteria and fungi colonizing the cycad rhizosphere and rhizoplane were dominated by microorganisms capable of degrading the plant cell walls. The local degradation of the cell wall was actually observed on the micrographs of the thin sections of cycad roots in the form of channels through which symbiotic cyanobacterial filaments can penetrate into the cortical parenchyma.     

On the Occurrence of Intracellular Blue-green Algae in Cortical Cells of the Apogeotropic Roots of Macrozamia communis L. Johnson

The occurrence of species of the cyanophytes Nostoc and Anabaenain the cortex near the algal zone is reported for apogeotropicroots of Macrozamia communis L. Johnson. Algae were found tooccur both intercellularly and intracellularly in cells of theinner and outer cortex. This is the first record of intracellularalgae in the cycads and only the second report of this phenomenonin vascular plants. By examination of cells at various stagesof invasion by algae, it is interpreted that algal invasionof cortical cells and intercellular spaces is preceded by mucusapparently secreted by algal zone cells of the host, and depositedin intercellular spaces of cortical parenchyma cells nearby.Also algal penetration of cortical cells is preceded by an algalinvasion front of finely granular mucal material which bypassesmucus already deposited in intercellular spaces and may eitherlyse part of the host cell wall or enter through the plasmo-desmata,filling much of the cell cavity. Subsequently, large numbersof the algal symbionts enter the cell and may be enclosed withinhost wall material. Electron microscopic techniques are nowbeing employed to further clarify these invasion processes.     

Analysis of Lignin-Polysaccharide Complexes Formed during Grass Lignin Degradation by Cultures of Pleurotus Species

A brown material, precipitable with ethanol, was formed during wheat straw and lignin degradation by liquid cultures of different species of Pleurotus. Fourier transform infrared spectroscopy and cross-polarization and magic-angle-spinning (sup13)C nuclear magnetic resonance spectroscopy showed that most of the precipitable material was formed from exopolysaccharide secreted by the fungus but it also contained an aromatic fraction. The results of acid hydrolysis, methylation analysis, and Smith degradation indicated that the major exopolysaccharide produced by these fungi is a (1(symbl)3)-(beta)-glucan branched at C-6 every two or three residues along the main chain. The presence of lignin or straw in the culture medium had little effect on the composition and structure of the extracellular polysaccharide. Cross-polarization and magic-angle-spinning (sup13)C nuclear magnetic resonance spectroscopy provided an estimation of the aromatic content of the lignin-polysaccharide complexes, assigning 20% of the total (sup13)C signal in the material recovered from cultures of Pleurotus eryngii in lignin medium to aromatic carbon. Analytical pyrolysis indicated that the aromatic fractions of the lignin-polysaccharide complexes were derived from lignin, since products characteristic of pyrolytic breakdown of H (p-hydroxyphenylpropane), G (guaiacylpropane), and S (syringylpropane) lignin units were identified. These complexes cannot be fractionated by treatment with polyvinylpyrrolidone or extraction with lignin solvents, suggesting that the two polymers were chemically linked. Moreover, differences in composition with respect to the original lignin indicated that this macromolecule was modified by the fungi during the process of formation of the lignin-polysaccharide complexes.     

植物根系复合共生体研究进展

植物根系与菌根真菌形成的互惠共生体,即菌根(mycorrhizas)是最常见、最广泛分布的共生体之一。自然条件下,一些植物的根系可同时形成由2种类型菌根构成的混合菌根,或菌根与细菌、菌根与放线菌、菌根与其他种类真菌构建的所谓复合共生体。文中从复合共生体的概念入手,简要介绍混合菌根、菌根与细菌、菌根与放线菌、菌根与其他真菌构建的复合共生体的多样性、形态解剖特征、生长发育及其功能等方面的研究概况,旨在为推进该领域的研究提供依据和借鉴的思路。     

Economic Botany of the Cycads

Cycads are used mainly as sources of food starch, particularly during periods of shortage of regular supplies. Aside from the use as food, some species are used as decorative plants, as minor sources of gums, fibers, and possibly oils. This work reviews most of the scattered literature on the uses of seven of the nine genera of the Cycadaceae, excludingZamia andCeratozamia.     

A Natural View of Microbial Biodiversity within Hot Spring Cyanobacterial Mat Communities

This review summarizes a decade of research in which we have used molecular methods, in conjunction with more traditional approaches, to study hot spring cyanobacterial mats as models for understanding principles of microbial community ecology. Molecular methods reveal that the composition of these communities is grossly oversimplified by microscopic and cultivation methods. For example, none of 31 unique 16S rRNA sequences detected in the Octopus Spring mat, Yellowstone National Park, matches that of any prokaryote previously cultivated from geothermal systems; 11 are contributed by genetically diverse cyanobacteria, even though a single cyanobacterial species was suspected based on morphologic and culture analysis. By studying the basis for the incongruity between culture and molecular samplings of community composition, we are beginning to cultivate isolates whose 16S rRNA sequences are readily detected. By placing the genetic diversity detected in context with the well-defined natural environmental gradients typical of hot spring mat systems, the relationship between gene and species diversity is clarified and ecological patterns of species occurrence emerge. By combining these ecological patterns with the evolutionary patterns inherently revealed by phylogenetic analysis of gene sequence data, we find that it may be possible to understand microbial biodiversity within these systems by using principles similar to those developed by evolutionary ecologists to understand biodiversity of larger species. We hope that such an approach guides microbial ecologists to a more realistic and predictive understanding of microbial species occurrence and responsiveness in both natural and disturbed habitats.     

Robust Hydrocarbon Degradation and Dynamics of Bacterial Communities during Nutrient-Enhanced Oil Spill Bioremediation

Degradation of oil on beaches is, in general, limited by the supply of inorganic nutrients. In order to obtain a more systematic understanding of the effects of nutrient addition on oil spill bioremediation, beach sediment microcosms contaminated with oil were treated with different levels of inorganic nutrients. Oil biodegradation was assessed respirometrically and on the basis of changes in oil composition. Bacterial communities were compared by numerical analysis of denaturing gradient gel electrophoresis (DGGE) profiles of PCR-amplified 16S rRNA genes and cloning and sequencing of PCR-amplified 16S rRNA genes. Nutrient amendment over a wide range of concentrations significantly improved oil degradation, confirming that N and P limited degradation over the concentration range tested. However, the extent and rate of oil degradation were similar for all microcosms, indicating that, in this experiment, it was the addition of inorganic nutrients rather than the precise amount that was most important operationally. Very different microbial communities were selected in all of the microcosms. Similarities between DGGE profiles of replicate samples from a single microcosm were high (95% ± 5%), but similarities between DGGE profiles from replicate microcosms receiving the same level of inorganic nutrients (68% ± 5%) were not significantly higher than those between microcosms subjected to different nutrient amendments (63% ± 7%). Therefore, it is apparent that the different communities selected cannot be attributed to the level of inorganic nutrients present in different microcosms. Bioremediation treatments dramatically reduced the diversity of the bacterial community. The decrease in diversity could be accounted for by a strong selection for bacteria belonging to the alkane-degrading Alcanivorax/Fundibacter group. On the basis of Shannon-Weaver indices, rapid recovery of the bacterial community diversity to preoiling levels of diversity occurred. However, although the overall diversity was similar, there were considerable qualitative differences in the community structure before and after the bioremediation treatments.     

Ubiquitin Pool Modulation and Protein Degradation in Wheat Roots during High Temperature Stress

Ubiquitin, a key component in an ATP-dependent proteolytic pathway, participates in the response of various eucaryotic organisms to high temperature stress. Our objective was to determine if ubiquitin serves a similar capacity for metabolizing altered proteins in higher plants during stress. Degradation of total proteins was measured, and ubiquitin pools (free versus conjugated) were extracted with an improved protocol from wheat (Triticum aestivum L. cv Len) roots treated at 22, 27, 32, 37, and 42°C for 1 hour and assayed by western blots and radioimmunoassays. Heat-shock protein synthesis was detected by in vivo labeling and autoradiography. Mean half-life of total root proteins decreased from 51 hours at 22°C to 23 hours at 40°C. Ubiquitin pools were extracted better and proteolysis was slowed more by the improved protocol than by a conventional procedure for plant proteins. Amounts of high molecular mass conjugates were elevated and levels of low molecular mass conjugates and free ubiquitin were depressed when roots were treated at 37 or 42°C than at lower temperatures; the same high temperatures also induced synthesis of heat-shock proteins. We concluded that high temperatures increase breakdown of root proteins, which are degraded via the ubiquitin proteolytic pathway. A conjugate with an apparent molecular mass of 23 kilodaltons was tentatively identified as an ubiquitinated histone.     

Maintenance of Motility Bias during Cyanobacterial Phototaxis

Signal transduction in bacteria is complex, ranging across scales from molecular signal detectors and effectors to cellular and community responses to stimuli. The unicellular, photosynthetic cyanobacterium Synechocystis sp. PCC6803 transduces a light stimulus into directional movement known as phototaxis. This response occurs via a biased random walk toward or away from a directional light source, which is sensed by intracellular photoreceptors and mediated by Type IV pili. It is unknown how quickly cells can respond to changes in the presence or directionality of light, or how photoreceptors affect single-cell motility behavior. In this study, we use time-lapse microscopy coupled with quantitative single-cell tracking to investigate the timescale of the cellular response to various light conditions and to characterize the contribution of the photoreceptor TaxD1 (PixJ1) to phototaxis. We first demonstrate that a community of cells exhibits both spatial and population heterogeneity in its phototactic response. We then show that individual cells respond within minutes to changes in light conditions, and that movement directionality is conferred only by the current light directionality, rather than by a long-term memory of previous conditions. Our measurements indicate that motility bias likely results from the polarization of pilus activity, yielding variable levels of movement in different directions. Experiments with a photoreceptor (taxD1) mutant suggest a supplementary role of TaxD1 in enhancing movement directionality, in addition to its previously identified role in promoting positive phototaxis. Motivated by the behavior of the taxD1 mutant, we demonstrate using a reaction-diffusion model that diffusion anisotropy is sufficient to produce the observed changes in the pattern of collective motility. Taken together, our results establish that single-cell tracking can be used to determine the factors that affect motility bias, which can then be coupled with biophysical simulations to connect changes in motility behaviors at the cellular scale with group dynamics.     

我国某些苏铁类生殖器官化石的发现兼论苏铁类起源

本文对苏铁类化石的系统分类作了概要的介绍。重点报道了笔者在近廿年来所采集的苏铁类生殖器官化石,各别是中晚石炭世的一枚苏铁大孢子叶化石的发现,将苏铁类起源的时间大大地推前了,并指出其起源地应在中国西北的甘肃地区。所有这些生殖器官的发现将推动苏铁化石生殖生物学的发展,对其起源、分布、演化和苏铁植物区系的形成和发展提供了极为重要的材料。     

Determination of Glyceraldehyde Formed in Glucose Degradation and Glycation

Glyceraldehyde (GLA) was determined in glucose degradation and glycation. GLA was detected as a decahydroacridine-1,8-dione derivative on reversed phase HPLC using cyclohexane-1,3-dione derivatizing reagent. The glucose-derived GLA level was higher than the glycation-derived GLA level, because GLA was converted to intermediates and advanced glycation end products (AGE) in glycation. GLA was also generated from 3-deoxyglucosone and glucosone as intermediates of glucose degradation and glycation. This study suggests that glyceraldehyde is generated by hyperglycemia in diabetes, and that it is also formed in medicines such as peritoneal dialysis solution.     

Structural Diversity of Bacterial Communities Associated with Bloom-Forming Freshwater Cyanobacteria Differs According to the Cyanobacterial Genus

The factors and processes driving cyanobacterial blooms in eutrophic freshwater ecosystems have been extensively studied in the past decade. A growing number of these studies concern the direct or indirect interactions between cyanobacteria and heterotrophic bacteria. The presence of bacteria that are directly attached or immediately adjacent to cyanobacterial cells suggests that intense nutrient exchanges occur between these microorganisms. In order to determine if there is a specific association between cyanobacteria and bacteria, we compared the bacterial community composition during two cyanobacteria blooms of Anabaena (filamentous and N₂-fixing) and Microcystis (colonial and non-N₂ fixing) that occurred successively within the same lake. Using high-throughput sequencing, we revealed a clear distinction between associated and free-living communities and between cyanobacterial genera. The interactions between cyanobacteria and bacteria appeared to be based on dissolved organic matter degradation and on N recycling, both for N₂-fixing and non N₂-fixing cyanobacteria. Thus, the genus and potentially the species of cyanobacteria and its metabolic capacities appeared to select for the bacterial community in the phycosphere.     

The Cuticles of Two Fossil Cycads and Epiphytic Fungi

Cuticles of two fossil cycads and seven epiphytic fungi are described in this paper. They are Nilssonia sinensis Yabe et Oishi, Ctenis lyrata Li et Ye; Perisporiacites shaheziensis sp. nov., Notothyrites haizhouensis sp. nov., Microthyriacites pilcatus sp. nov., M. fuxinensis sp. nov., Stigmateacites polymorphus gen. et sp. nov., S. simplex gen. et sp. nov., Liaoningnema multinoda gen. et sp. nov. Materials were collected from the Shahezi Formation of Changtu district and the Haizhou Formation in Haizhou mine-field of Li- aoning Province, China. The age of these tossils is Early Cretaceous.     

Trophic Structure of Amoeba Communities Near Roots of Medicago sativa After Contamination with Fuel Oil No. 6

Root exudation increases microbial activity, selecting bacterial and fungal communities that metabolize organic matter such as hydrocarbons. However, a strong contamination pulse of hydrocarbons around plant roots may reorganize the soil's microbial trophic structure toward amoebae feeding on bacteria. We conducted a microcosm experiment to elucidate the effect of Medicago sativa on the trophic structure of naked amoebae after a strong pulse of pollution (50,000 ppm of fuel oil no. 6, which is a mixture of long chains ranging from C10 to C28). Plants were seeded 24 h after contamination and species of amoebae in the microcosms were identified at 1, 30, and 60 days after pollution. Several species from three trophic groups of naked amoeba were still alive 24 h after the hydrocarbon pulse. Non-planted microcosms harbored three trophic groups after 60 days, while planted ones nourished four groups. The bacterivore group was the most diverse in all microcosms, followed by protist-eaters and omnivores. The quantity of amoebae was significantly higher (3.4×10³ organisms/g soil) in the planted pots than in the non-planted ones (1.3×10³ organisms/g soil after 30 days of pollution (P?≤?0.01). The shortest hydrocarbon chains (C10–C14) disappeared or diminished in all microcosms, and the longest ones increased in the planted ones. M. sativa thus exerted a positive effect on species richness, quantity, and the composition of amoebae trophic groups in contaminated soil. This indirect effect on bacterial predators is another key factor underlying hydrocarbon assimilation by living organisms during phytoremediation.     

Effect of Temperature on the Taxonomic Structure of Soil Bacterial Communities during Litter Decomposition

Microbiology - Effect of temperature on succession changes of the saprotrophic bacterial community of gray forest soil in the course of decomposition of aspen leaves and branches was studied in...     

Acclimation of Cyanobacterial Communities in Rice Fields and Response of Nitrogenase Activity to Light Regime

Abstract The short-term and long-term effects of light regime on nitrogenase activity (NA) and cyanobacterial communities in rice fields (Valencia, Spain) were examined. Daily variation in nitrogen fixation was measured during three periods of the crop cycle: tillering (formation of secondary stems in the rice plants), heading (formation of reproductive structures), and maturity. Two locations were examined over two consecutive years (1994 and 1995). Despite differences in the crop-cycle periods, location, and year, a consistent pattern of nitrogen fixation was observed, with a main activity peak in the morning and another in the late evening. Short-term experiments, performed on two cyanobacterial blooms (Nostoc sp. and Anabaena sp.) exposed to natural light under plant canopy (7% incidence irradiance), and to different light intensities under neutral density screens without plant cover (full sunlight, 43%, 26%, and 13% of incident irradiance), indicated that nitrogenase activity (NA) was dependent on both light intensity and quality. In long-term experiments, where natural communities of cyanobacteria were exposed to one month of different light intensities, changes in the species composition of the three main genera of heterocystous cyanobacteria (Nostoc, Anabaena, and Calothrix) were observed. The light intensity at which communities were exposed for one month became the optimum irradiance for NA for each cyanobacterial community. Assays performed at higher or lower irradiances showed lower NA. Nitrogen fixation followed a pattern of seasonal variation along the crop cycle. Values were low at the beginning of the crop (May), reached a maximum value at the end of the tillering stage (June), and declined thereafter until the end of the cultivation cycle (September). Received: 25 February 1997; Accepted: 8 July 1997