湛江特呈岛红树植物群落结构特征

2008年6月,采用样方调查法对湛江特呈岛红树植物群落结构及白骨壤(Avicennia marina)的种群特征进行了全面调查.结果表明:该地区红树林是白骨壤纯林以及白骨壤为主,有红海榄(Rhizophora stylosa)、木榄(Bruguieragymnorrhiza)和桐花树(Aegiceras corniculatum)的混交林.白骨壤在潮滩上连续分布,红海榄、木榄和桐花树生长于近陆林缘及潮滩的中部,物种多样性指数由陆缘向海缘呈降低趋势.通过分析白骨壤种群的株高、地径在潮滩上的变化规律得出年幼的个体聚集于近陆林缘,近海林缘较少.白骨壤种群的年龄结构为增长型,但是根据生境条件及白骨壤种群在海滩上的分布格局,分析得出该红树林资源处于退化的状态.     

Uptake kinetics of nitrogen and phosphorus by Zostera marina

Aims Nutrient availability is an external factor that affect the growth of seagrasses. However, the demand for and absorption of different forms of nitrogen and phosphorus by different tissues of seagrasses are unclear. In this study, the uptake of nitrogen and phosphorus by Zostera marina was studied to determine the nutrient uptake kinetics. The objectives of this research are to: 1) investigate the absorption characteristics of ammonia nitrogen, nitrate nitrogen and phosphorus in Z. marina; 2) evaluate the differences in absorption between the different forms of nitrogen; and 3) analyse the differences in absorption between the different tissues of Z. marina.Methods Equipment was used to separate the aboveground and belowground tissues of Z. marina. Six concentration levels of ammonia nitrogen, nitrate nitrogen and phosphorus were established to experimentally test the uptake kinetics of nutrients by Z. marina. The nutrient concentrations in different parts of seawater column were measured to determine the nutrient changes and calculate the kinetic characteristics of nutrient uptake.Important findings 1) The absorption of ammonia nitrogen, nitrate nitrogen and phosphorus by Z. marina was consistent with the characteristics of saturated absorption kinetics. The relationship between the absorption rate and the nutrient concentrations in water could be described by the Michaelis-Menten equation. 2) The maximum absorption rate (V_max) of ammonia nitrogen by Z. marina (52 μmol·g^-1·h^-1) was significantly higher than that of nitrate nitrogen (39 μmol·g^-1·h^-1). 3) Both aboveground and belowground tissues of Z. marina could absorb nutrient, but the V_max of leaves (aboveground tissues) for ammonia nitrogen, nitrate nitrogen and phosphorus absorption were 43.1, 30.5 and 15.6 μmol·g^-1·h^-1, respectively, which were 2.6-fold, 1.2-fold and 6-fold higher than the corresponding V_max of belowground tissues. The results show that the absorption capacity of Z. marina for ammonia nitrogen is higher than that for nitrate nitrogen, and the absorption of nitrogen and phosphorus may depend primarily on the aboveground tissues (leaves). The results provide a theoretical basis for the study of the mechanisms of nitrogen and phosphorus uptake and utilization by Z. marina and the evaluation of marine ecological impacts.     

大叶藻对氮磷营养盐的吸收动力学特征

营养盐是影响海草生长的关键因子, 目前有关海草不同组织对不同形式氮和磷的吸收特征尚不明确。该研究通过利用海草地上和地下组织分隔培养装置, 设置不同的氨态氮、硝态氮和磷酸盐浓度, 探究了大叶藻(Zostera marina)植株及其地上和地下组织对氮磷营养盐的吸收动力学特征。结果显示: (1)大叶藻对氮磷的吸收符合饱和吸收动力学特征, 吸收速率和水体氮磷浓度可用米式方程描述; (2)大叶藻植株对NH₄⁺-N的最大吸收速率(V_max, 52 μmol·g^-1·h^-1)显著高于其对NO₃^--N的V_max (39 μmol·g^-1·h^-1); (3)大叶藻地上组织和地下组织均可吸收氮磷, 但地上组织对氨态氮、硝态氮、磷酸盐的V_max分别为43.1、30.5和15.6 μmol·g^-1·h^-1, 为地下组织的2.6、1.2和6倍。结果表明, 大叶藻对氨态氮的吸收能力高于硝态氮, 且对氮磷的吸收可能主要依赖地上组织(叶片)。结果为查明大叶藻对氮磷的吸收利用机制及评估大叶藻的海洋生态效应提供了理论依据。     

The proteinaceous, gum polysaccharide from Azadirachta indica A. Juss

The gum exuded by Azadirachta indica trees contains 35% of proteinaceous material. The most abundant amino acid is aspartic acid; there are also considerable proportions of serine and threonine, and at least 2% of amino sugars. Attempts to deproteinise the polysaccharide material were unsuccessful. Fractionation of the gum exudate on agarose columns gave a protein-depleted fraction of high molecular weight and a protein-enriched fraction of lower molecular weight. Studies involving molecular-sieve chromatography showed a close correspondence in protein and carbohydrate content, and it appears that the proportion of proteinaceous component that is free or only loosely associated with carbohydrate is small. The carbohydrate component is much more complex than was indicated by earlier investigators. In addition to galactose and arabinose (major components), mannose, xylose, fucose, and rhamnose are also present. The uronic acid content (28%) is higher than previously believed, and a relatively high methoxyl content has been found. The major aldobiouronic acid, previously undetected, is 4-O-(4-O-methyl-- -glucopyranosyluronic acid)- -galactose, with 4-O-(- -glucopyranosyluronic acid)- -galactose also present. The exudate from Azadirachta indica is therefore a complex material having several features that are unusual in gum chemistry.     

Antibiotic-resistantArthrobacter sp. andPseudomonas sp. responses in the rhizosphere of blue grama after herbage removal

Summary Streptomycin-resistant Pseudomonas and Arthrobacter were isolated from semi-arid grassland soil and their relative responses in the rhizosphere of blue grama (Bouteloua gracilis) subjected to herbage removal were evaluated. Using plants grown in normal soil, the two bacteria showed differential responses to herbage removal, which were most marked in the rhizoplane, where the Pseudomonas showed a two-log unit increase over a 60 hour period, while Arthrobacter, in contrast, exhibited a one-log unit decrease in viable counts for at least 48 hours after defoliation, responses which are similar to those observed in root exudate medium experiments by earlier workers. These results suggest that the rhizoplane may be a critical environment for interaction of these two types of microorganisms, and that sequential responses of the root-associated soil microorganisms may occur after herbage removal from this important rangeland plant. These responses are most likely associated with increased exudate release following herbage removal, which has been best documented using blue grama grown under sterile conditions.     

A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina

Photosystem I (PSI) is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin (or cytochrome c₆) and the reduction of ferredoxin. This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor (a special chlorophyll (Chl) pair) and electron acceptors A₀, A₁, and three Fe₄S₄ clusters, F_X, F_A, and F_B. Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3 Å resolution obtained by single-particle cryo-electron microscopy. The A. marina PSI exists as a trimer with three identical monomers. Surprisingly, the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A₀ is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures. A novel subunit Psa27 is observed in the A. marina PSI structure. In addition, 77 Chls, 13 α-carotenes, two phylloquinones, three Fe-S clusters, two phosphatidyl glycerols, and one monogalactosyl-diglyceride were identified in each PSI monomer. Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.     

Species richness in macroalgae and macrofauna assemblages on Fucus serratus L. (Phaeophyceae) and Zostera marina L. (Angiospermae) in Skagerrak, Norway

The macrophytes Fucus serratus and Zostera marina form similar substrates for associated flora and fauna in shallow waters in Norway. While F. serratus forms a more or less continuous belt on rocky substrate along the coast, Z. marina forms disjunct populations on sandy or muddy bottoms. This study focused on the organisms associated with these two macrophytes in two localities in the Skagerrak region. In total, 130 taxa of epiphytic organisms were identified: 22 green algae, 41 red algae, 32 brown algae, eight diatoms and 27 sessile animals. One hundred and twenty-seven taxa of mobile macrofauna were registered. The dominant group was crustaceans, with amphipods as the order containing most species. Many species of both plants and animals preferred one or the other habitat. It is concluded that coastal macrophyte systems have high species diversity.     

Comparison of a current eelgrass disease to the wasting disease in the 1930s

A comparison is made of the wasting disease that struck the whole Atlantic population of Zostera marina L. in the 1930s and a current outbreak of a rather similar disease in Z. marina beds along the north-eastern coasts of the U.S.A. Although the disease phenomena on the plants appear to be very similar, disease-related declines of Z. marina are at present still very local. In Europe, diseased plants have been found, but no declines have been observed.

The wasting disease in the 1930s was not investigated before the epidemic reached a devastating stage. Present observations may indicate that a new widespread die-off may be developing. In order to facilitate the study of the current epidemic, a scenario of disease and related decline, with several variants, has been elaborated, based on the existing knowledge of the epidemic of the 1930s, but also clearly showing the gaps in this knowledge.     

海洋卡盾藻(香港株)溶血毒素的提取和分离

海洋卡盾藻(Chattonella marina)是我国南方沿海主要的鱼毒性赤潮生物,近年来由该藻形成的赤成已造成多起近岸养殖鱼类大量死亡的事件。为了弄清该藻毒素的基本成分特征,本文研究了室内培养条件下海洋卡盾藻(香港株)溶血毒素的提取方法,观察了溶血毒素对红细胞的溶血过程,采用薄层色谱法对溶血成分进行了初步分析。结果表明:海洋卡盾藻藻细胞的超声波破碎最适条件为功率400W,4℃下处理15min;通过显微镜观察,证实提取的毒素对血红细胞膜具破坏作用;海洋卡盾藻合成的溶血毒素至少含有4种组分,其中1种可能为为脂类,3种为糖脂类。该研究成果有助于我国今后进一步开展鱼毒性赤潮生物毒素的研究。     

Effects of inhibitors of serine/threonine protein kinases on <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> root morphology and microtubule organization in its cells

The effect of different types of serine/threonine protein kinase inhibitors (cyclin-dependent, Ca²⁺-calmodulin dependent and protein kinase C) on the microtubule organization in cells of Arabidopsis thaliana main primary root zones were investigated in vivo. It was found that the microtubules in epidermal and cortex cells of transition and elongation zones, as well as microtubules in trichoblasts and atrichoblasts of the differentiation zone, were the most sensitive to the action of the investigated protein kinase inhibitors. It was established that, in these types of cells, microtubules change their initial orientation from transverse (oblique) to chaotic or longitudinal relative to the main primary root axis as a result of serine/threonine protein kinase inhibition. Microtubules in cells of root meristematic zone, as well as in root hairs, were less sensitive to the action of tested protein kinase inhibitors. Changes in the orientation of microtubules in cells of primary root zones under the effect of serine/threonine protein kinase inhibitors led to further disturbances in the growth and differentiation processes. It was assumed that the phosphorylation of microtubule proteins, primarily tubulin, could be involved in the regulation of these processes.     

Drought stress and plant ecotype drive microbiome recruitment in switchgrass rhizosheath

The rhizosheath, a layer of soil grains that adheres firmly to roots, is beneficial for plant growth and adaptation to drought environments. Switchgrass is a perennial C4 grass which can form contact rhizosheath under drought conditions. In this study, we characterized the microbiomes of four different rhizocompartments of two switchgrass ecotypes (Alamo and Kanlow) grown under drought or well-watered conditions via 16S ribosomal RNA amplicon sequencing. These four rhizocompartments, the bulk soil, rhizosheath soil, rhizoplane, and root endosphere, harbored both distinct and overlapping microbial communities. The root compartments (rhizoplane and root endosphere) displayed low-complexity communities dominated by Proteobacteria and Firmicutes. Compared to bulk soil, Cyanobacteria and Bacteroidetes were selectively enriched, while Proteobacteria and Firmicutes were selectively depleted, in rhizosheath soil. Taxa from Proteobacteria or Firmicutes were specifically selected in Alamo or Kanlow rhizosheath soil. Following drought stress, Citrobacter and Acinetobacter were further enriched in rhizosheath soil, suggesting that rhizosheath microbiome assembly is driven by drought stress. Additionally, the ecotype-specific recruitment of rhizosheath microbiome reveals their differences in drought stress responses. Collectively, these results shed light on rhizosheath microbiome recruitment in switchgrass and lay the foundation for the improvement of drought tolerance in switchgrass by regulating the rhizosheath microbiome.     

A 56,000 Mr phosphoseryl protein in PC12 cell lysates strongly associates with protein-A sepharose beads and was observed in immune complex kinase assays for PP60c-src

Using an immune complex kinase assay to measure pp60c-src kinase activity, we have identified a 56,000 M_r protein (p56) from PC12 cell lysates that co-purified with pp60c-src by strong association with protein-A sepharose beads. The p56 protein was strongly phosphorylated on serine but no tyrosine or threonine phosphorylation was evident. However, pp60c-src was strongly phosphorylated on tyrosine, weakly phosphorylated on serine with no observed threonine phosphorylation. P56 was not a proteolytic breakdown product of pp60c-src, since it was neither tyrosine phosphorylated nor was it recognized by anti-src antibody. P56 was also not recognised by other antibodies to 56kD signalling molecules such as p56lck. The identity of p56 awaits further investigation but its appearance in immunoprecipitates of pp60c-src using protein-A sepharose beads is of interest but complicates the interpretation of results from immune complex kinase assays in PC12 cells.     

Inter-specific variation in the concentration of two iridoid glucosides in Avicennia L. (Avicenniaceae Endl.)

Concentrations of two iridoid glucosides (2′-cinnamoyl mussaenosidic acid and 2′-caffeoyl mussaenosidic acid) were measured in different populations of several Avicennia species. The results obtained for 2′-cinnamoyl mussaenosidic acid seem to confirm the recognition of infraspecific taxa in A. marina and also in A. germinans (africana (palaeotropic) and germinans (neotropic)).     

Suitability of Zostera marina populations for transplantation to the Wadden Sea as determined by a mesocosm shading experiment

As part of eelgrass re-establishment efforts in the Wadden Sea, five northwest European eelgrass (Zostera marina L.) populations were studied in a mesocosm filled with Wadden Sea water over a 2-year period. The original habitats of these populations varied with regard to salinity, tidal regime, latitude, substrate type and water nutrient content. The reproductive strategies ranged from semi-annual to perennial. Experimental parameters studied were: planting density (64 and 121 plants m⁻²) and irradiance corresponding to 75%, 89%, 95% and 98% light reduction at the bottom. Three out of five Z. marina populations were successfully transplanted. Planting density, although initially positively correlated, had no effect on final transplantation success. The populations maintained their original reproductive strategy. The reproductive strategy of the donor population did not show a clear correlation with transplantation success. The maximum light reduction tolerated at the bottom was 75%–89%. The populations did not differ in shading tolerance. Assuming a light attenuation coefficient in the Wadden Sea of k=2.0 m⁻¹, this corresponds to a maximum transplantation depth of between 0.45 m and 0.85 m below mean sea level. The differences in transplantation success, and the conservative reproductive strategy of different Z. marina populations, indicate genetic differences and/or low phenotypic plasticity. Moreover, this implies that the characteristics of a donor population must be carefully considered prior to transplantation.     

Light adaptation and the role of autotrophic epiphytes in primary production of the temperate seagrass, Zostera marina L.

Photosynthetic features of Zostera marina L. and its autotrophic epiphyte community were investigated in a population inhabiting a shallow (1.3 m depth) water meadow in Great Harbor, Woods Hole, MA (U.S.A.). Photosynthesis versus irradiance (P-I) relationships were measured with respect to leaf age determined by the leaf position in the shoot bundle and by location of the tissue along the leaf axis. Therefore both age and light intensity gradients along the leaf axis were considered. The maximum photosynthesis (P_max) per dm² typically increased nearly two-fold along the leaf axis from leaf bases to apices. Photosynthetic rate on a chlorophyll (Chl) basis did not increase as dramatically along the leaf axis, and rates were usually lowest in tissues with the highest Chl content. The P-I relationships of leaves of different ages did not reveal photoinhibition even at light intensities > 1400 μE • m⁻² • s ⁻¹. Furthermore, no photoinhibition was observed in tissues from leaf blade bases, which never experienced high light levels (> 500 μE • m ⁻² • s⁻¹) in situ in Great Harbor. The initial slopes of the P-I curves and light compensation and saturation values varied along the leaf axis in relation to in situ light intensity gradients and in relation to leaf or tissue age. It appeared that leaf and/or tissue age was more important than light environment in determining P-I responses. The contribution of the autotrophic epiphyte community on Z. marina leaves to total photosynthesis per dm² was between 27 and 50%, and between 10 and 44% per mg chlorophyll. These levels of epiphyte photosynthesis can double the primary production of Z. marina leaves. No detrimental effects of epiphyte cover were realized in leaf maximal photosynthesis or P-I relationships. Non-epiphytized leaves and leaves from which epiphytes were removed showed essentially identical photosynthetic features. Light intensity and age gradients along the leaf axis control both the photosynthetic performance of the leaves and epiphyte biomass and photosynthesis.     

On the use of antibiotics to reduce rhizoplane microbial populations in root physiology and ecology investigations

No straightforward method exists for separating the proportion of ion exchange and respiration due to rhizoplane microbial organisms from that of root ion exchange and respiration. We examined several antibiotics that might be used for the temporary elimination of rhizoplane bacteria from hydroponically grown wheat roots ( Triticum aestivum cv. Veery 10). Each antibiotic was tested for herbicidal activity and plate counts were used to enumerate bacteria and evaluate antibiotic kinetics. Only -lactam antibiotics (penicillins and cephalosporins) did not reduce wheat growth rates. Aminoglycosides, the pyrimidine trimethoprim, colistin and rifampicin reduced growth rates substantially. Antibiotics acted slowly, with maximum reductions in rhizoplane bacteria occurring after more that 48 h of exposure. Combinations of nonphytotoxic antibiotics reduced platable rhizoplane bacteria by as much as 98%; however, this was generally a reduction from about 10⁹ to 10⁶ colony forming units per gram of dry root mass, so that many viable bacteria remained on root surfaces. We present evidence which suggests that insufficient bacterial biomass exists on root surfaces of nonstressed plants grown under well-aerated conditions to quantitatively interfere with root nitrogen absorption measurements.     

Role of Lectins in Plant-Microorganism Interactions: III. Influence of Rhizosphere/Rhizoplane Culture Conditions on the Soybean Lectin-binding Properties of Rhizobia

The influence of rhizosphere/rhizoplane culture conditions on the ability of various rhizobia to bind soybean seed lectin (SBL) was examined. Eleven strains of the soybean symbiont, Rhizobium japonicum, and six strains of various heterologous Rhizobium species were cultured in root exudate of soybean (Glycine max [L.] Merr.) and in association with roots of soybean seedlings which were growing either hydroponically or in montmorillonite clay soil amendment (Turface). All 11 of the R. japonicum strains developed biochemically specific receptors for the lectin when cultured under these conditions, whereas six of the 11 did not develop such receptors when cultured in synthetic salts medium. Two cowpea strains also developed receptors for SBL. The other four heterologous strains of rhizobia gave no evidence of biochemically specific SBL binding in either synthetic salts media or rhizosphere/rhizoplane cultures. These results demonstrate that the environment provided by plant roots is an important factor in the development of specific lectin receptors on the cell surface of R. japonicum.     

Molecular characterisation of peanut agglutininbinding glycoproteins from Eimeria tenella

A group of glycoproteins, which strongly bind peanut agglutinin (PNA) was found in Eimeria tenella. Two major antigenic glycoproteins, Etl 10gp and Et35gp, were identified in sporulated oocysts and sporozoites. Molecular characterisation of carbohydrate moieties (lectin binding, enzymic hydrolysis and monosaccharide composition) revealed that both glycoproteins are rich in galactose and N-acetylgalactosamine, and appear to be sialylated. Both glycoproteins were susceptible to treatment with neuraminidase followed by O-glycosidase, suggesting that the oligosaccharide chains are attached to the protein by an O-glycosidic linkage to serine and/or threonine. Purified Et35gp contained a large number of serine (14) and threonine (33) residues, and was rich in glycine. This protein aggregated after repetitive lyophilisation and migrated on SDS-PAGE gels as an 85,000 protein. Sera against purified Et35gp raised in chickens and rabbits, and anti-E. tenella immune chicken serum recognised both antigens on blots and on the surface of sporozoites. Chickens immunised with purified Et35gp were not protected against coccidial infection.     

Genomic variation patterns of subspecies defined by phenotypic criteria: Analyses of the mangrove species complex,Avicennia marina

Subspecies is used to designate taxa below species but above geographical populations. What patterns of genomic variation are expected if taxa are designated as subspecies? In this study, we carry out such a survey on the mangrove tree Avicennia marina (Forssk.) Vierh. of the Indo-West Pacific coasts. This species has three subspecies, distinguished by morphological traits and geographical distribution. We collected samples from 16 populations (577 individuals) covering all three subspecies and sequenced 94 nuclear genes. We reveal comprehensive genetic divergence among subspecies, generally higher than among geographical populations within subspecies. The level of genetic diversity differs among the three subspecies, possibly hinting at a degree of separation among their gene pools. We observed that divergence varies from locus to locus across the genome. A small portion of the genome is most informative about subspecies delineation, whereas the rest is undifferentiated or slightly differentiated, hinting at uneven gene flow and incomplete isolation. The three subspecies likely split simultaneously with gene flow among lineages. This reticulate evolution results in some discordance between morphology and genetics in areas of population contact. In short, A. marina subspecies show species-like patterns in some respects and population-like patterns in others. We propose that the subspecies designated in A. marina are informative in predicting genetic divergences and useful in making conservation decisions.