Species coherence in the face of karyotype diversification in holocentric organisms: the case of a cytogenetically variable sedge (Carex scoparia,Cyperaceae)

Background and Aims

The sedge genus Carex, the most diversified angiosperm genus of the northern temperate zone, is renowned for its holocentric chromosomes and karyotype variability. The genus exhibits high variation in chromosome numbers both among and within species. Despite the possibility that this chromosome evolution may play a role in the high species diversity of Carex, population-level patterns of molecular and cytogenetic differentiation in the genus have not been extensively studied.

Methods

Microsatellite variation (11 loci, 461 individuals) and chromosomal diversity (82 individuals) were investigated in 22 Midwestern populations of the North American sedge Carex scoparia and two Northeastern populations.

Key Results

Among Midwestern populations, geographic distance is the most important predictor of genetic differentiation. Within populations, inbreeding is high and chromosome variation explains a significant component of genetic differentiation. Infrequent dispersal among populations separated by >100 km explains an important component of molecular genetic and cytogenetic diversity within populations. However, karyotype variation and correlation between genetic and chromosomal variation persist within populations even when putative migrants based on genetic data are excluded.

Conclusions

These findings demonstrate dispersal and genetic connectivity among widespread populations that differ in chromosome numbers, explaining the phenomenon of genetic coherence in this karyotypically diverse sedge species. More generally, the study suggests that traditional sedge taxonomic boundaries demarcate good species even when those species encompass a high range of chromosomal diversity. This finding is important evidence as we work to document the limits and drivers of biodiversity in one of the world''s largest angiosperm genera.     

芦苇克隆整合对石油污染湿地土壤微生物群落结构和生物量的影响

克隆植物形体相连的无性个体(分株)之间可以进行水分、养分和光合产物的传递和共享,并且这种克隆整合可以显著提高分株对环境胁迫的耐受能力,从而可能进一步影响分株周围的土壤微生物群落结构和生物量。尽管国内外已经开展了大量有关克隆整合对分株耐受胁迫能力影响的研究,但克隆整合对土壤微生物群落结构和生物量影响的研究却十分缺乏。以黄河三角洲芦苇(Phragmites australis)湿地生态系统为研究对象,将直径60 cm的圆形样方进行三个水平的石油添加处理(不添加石油或每年添加5 mm或10 mm厚的石油),同时通过切断或不切断样方内外芦苇根状茎的连接来控制克隆整合的有无。实验连续开展了两年(2014—2015年),每年8月份在样方内进行土壤样品取样,在实验室内采用磷酸脂肪酸(PLFA)法测定土壤微生物总量及主要微生物类群含量,并测定土壤微生物生物量碳和氮含量。取样时间显著影响土壤微生物PLFA总量、微生物碳和氮含量,这3个变量在2015年均显著高于2014年。石油添加在2015年显著增加了土壤微生物PLFA总量,但在2014年却无显著效应;同时,石油添加在2014年降低了土壤微生物碳和氮含量,而在2015年却增加了其含量。然而,无论在2014年还是2015年,芦苇的克隆整合对土壤微生物PLFA含量、微生物碳和氮含量均没有显著影响。土壤微生物PLFA总量与土壤微生物碳和氮含量呈正相关关系。这些结果表明,石油污染可以显著影响湿地土壤微生物动态,但克隆整合却无显著效应。     

Arbuscular mycorrhizal fungi contribute to phosphorus uptake by wheat grown in a phosphorus-fixing soil even in the absence of positive growth responses

We used 32P to quantify the contribution of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices) to phosphorus (P) uptake by wheat (Triticum aestivum), grown in compartmented pots. The soil was from a major cereal-growing area, the Eyre Peninsula, South Australia; it was highly calcareous and P-fixing. Fertilizer P was added to soil at 20 mg kg(-1), as solid or liquid. Two extraction methods were used to estimate plant-available P. Fungal colonization was well established at harvest (36 d). Application of P decreased both colonization and hyphal length density in soil, with small differences between different P fertilizers. Plants showed large positive responses in terms of growth or total P uptake to all P additions, and showed no positive (or even negative) responses to AM colonization, regardless of P application. 32P was detected only in AM plants, and we calculated that over 50% of P uptake by plants was absorbed via AM fungi, even when P was added. The results add to the growing body of knowledge that 'nonresponsive' AM plants have a functional AM pathway for P transfer to the plant; it should not be ignored in breeding plants for root traits designed to improve P uptake.     

Interactions of liposomes with the reticuloendothelial system: II. Nonspecific and receptor-mediated uptake of liposomes by mouse peritoneal macrophages

Liposomes are taken up as intact vesicles by mouse peritoneal macrophages in a process which is temperature sensitive and is affected by inhibitors of glycolytic metabolism and of microfilament activity. Macrophages take up negatively charged vesicles more readily than positively charged vesicles (2-fold) or neutral vesicles (4-fold). Macrophages take up similar amounts of multilamellar liposomes, reversed phase liposomes and small unilamellar liposomes in terms of lipid, however this corresponds to vastly different numbers of particles and amounts of trapped volume. Coating the liposomes with macromolecular ligands capable of interacting with macrophage surface receptors can markedly promote liposome uptake. Thus, formation of an IgG-antigen complex on the liposome surface results in a 10²-fold enhancement of liposome uptake, while coating the vesicles with fibronectin results in a 10-fold augmentation of uptake. Uptake via IgG-mediated and fibronectin-mediated processes seem to be independent since excess unlabelled, IgG-coated liposomes will inhibit the uptake of radioactively-labelled IgG-coated liposomes much more effectively than the uptake of radioactively-labelled fibronectin-coated liposomes. Cell-bound liposomes can readily be visualized on and inside of the macrophages using fluorescence microscopy techniques.     

Influence of Ca on the plasma membrane potential and electrogenic uptake of glycine by myeloma cells. Involvement of a Ca-activated K channel

The involvement of Ca²⁺-activated K⁺ channels in the regulation of the plasma membrane potential and electrogenic uptake of glycine in SP 2/0-AG14 lymphocytes was investigated using the potentiometric indicator 3,3′-diethylthiodicarbocyanine iodide. The resting membrane potential was estimated to be −57 ± 6 mV (n = 4), a value similar to that of normal lymphocytes. The magnitude of the membrane potential and the electrogenic uptake of glycine were dependent on the extracellular K⁺ concentration, [K⁺]_o, and were significantly enhanced by exogenous calcium. The apparent V_max of Na⁺-dependent glycine uptake was doubled in the presence of calcium, whereas the K_0.5 was not affected. Ouabain had no influence on the membrane potential under the conditions employed. Additional criteria used to demonstrate the presence of Ca²⁺-activated K⁺ channels included the following: (1) addition of EGTA to calcium supplemented cells elicited a rapid depolarization of the membrane potential that was dependent on [K⁺]_o; (2) the calmodulin antagonist, trifluoperazine, depolarized the membrane potential in a dose-dependent and saturable manner with an IC₅₀ of 9.4 μM; and (3) cells treated with the Ca²⁺-activated K⁺ channel antagonist, quinine, demonstrated an elevated membrane potential and depressed electrogenic glycine uptake. Results from the present study provide evidence for Ca²⁺-activated K⁺ channels in SP 2/0-AG14 lymphocytes, and that their involvement regulates the plasma membrane potential and thereby the electrogenic uptake of Na⁺-dependent amino acids.     

Amino acids as a nitrogen source for tomato seedlings: The use of dual-labeled (C, N) glycine to test for direct uptake by tomato seedlings

Direct uptake of organic nitrogen (ON) compounds, rather than inorganic N, by plant roots has been hypothesized to constitute a significant pathway for plant nutrition. The aim of this study was to test whether tomatoes (Solanum lycopersicum cv. Huying932) can take up ON directly from the soil by using ¹⁵NH₄Cl, K¹⁵NO₃, 1, 2-¹³C₂¹⁵N-glycine labeling techniques. The ¹³C and ¹⁵N in the plants increased significantly indicating that a portion of the glycine-N was taken up in the form of intact amino acids by the tomatoes within 48 h after injection into the soil. Regression analysis of excess ¹³C against excess ¹⁵N showed that approximately 21% of the supplied glycine-N was taken up intact by the tomatoes. Atom% excesses of ¹⁵N and ¹³C in the roots were higher than in any shoots. Results also indicated rapid turnover of amino acids (e.g., glycine) by soil microorganisms, and the poor competitive ability of tomatoes in absorbing amino acids from the soil solution. This implies that tomatoes can take up ON in an intact form from the soil despite the rapid turnover of organic N usually found under such conditions. Given the influence of climatic change and N pollution, further studies investigating the functional ecological implications of ON in horticultural ecosystems are warranted.     

High-resolution nuclear magnetic resonance spectroscopy studies of polysaccharides crosslinked by sodium trimetaphosphate: a proposal for the reaction mechanism

An NMR spectroscopy study ((31)P, (1)H, (13)C) of the postulated crosslinking mechanism of sodium trimetaphosphate (STMP) on polysaccharides is reported using methyl alpha-D-glucopyranoside as a model. In a first step, reaction of STMP with Glc-OMe gives grafted sodium tripolyphosphate (STPP(g)). On the one hand, STTP(g) can react with a second alcohol functionality to give a crosslinked monophosphate. On the other hand, a monophosphate (grafted phosphate) could be obtained by alkaline degradation of STPP(g). NMR spectroscopy allows to detect the various species formed and to obtain the crosslinking density of STMP-polysaccharides hydrogels.     

Loss of 3-chlorotyrosine by inflammatory oxidants: implications for the use of 3-chlorotyrosine as a bio-marker in vivo

Activated neutrophils generate the potent oxidant hypochlorous acid (HOCl) from the enzyme myeloperoxidase (MPO). A proposed bio-marker for MPO-derived HOCl in vivo is 3-chlorotyrosine, elevated levels of which have been measured in several human inflammatory pathologies. However, it is unlikely that HOCl is produced as the sole oxidant at sites of chronic inflammation as other reactive species are also produced during the inflammatory response. The work presented shows that free and protein bound 3-chlorotyrosine is lost upon addition of the pro-inflammatory oxidants, HOCl, peroxynitrite, and acidified nitrite. Furthermore, incubation of 3-chlorotyrosine with activated RAW264.7 macrophages or neutrophil-like HL-60 cells resulted in significant loss of 3-chlorotyrosine. Therefore, at sites of chronic inflammation where there is concomitant ONOO⁻ and HOCl formation, it is possible measurement of 3-chlorotyrosine may represent an underestimate of the true extent of tyrosine chlorination. This finding could account for some of the discrepancies reported between 3-chlorotyrosine levels in tissues in the literature.