The unexpected long period of elevated CH4 emissions from an inundated fen meadow ended only with the occurrence of cattail (Typha latifolia)

Drainage and agricultural use transform natural peatlands from a net carbon (C) sink to a net C source. Rewetting of peatlands, despite of high methane (CH₄) emissions, holds the potential to mitigate climate change by greatly reducing CO₂ emissions. However, the time span for this transition is unknown because most studies are limited to a few years. Especially, nonpermanent open water areas often created after rewetting, are highly productive. Here, we present 14 consecutive years of CH₄ flux measurements following rewetting of a formerly long-term drained peatland in the Peene valley. Measurements were made at two rewetted sites (non-inundated vs. inundated) using manual chambers. During the study period, significant differences in measured CH₄ emissions occurred. In general, these differences overlapped with stages of ecosystem transition from a cultivated grassland to a polytrophic lake dominated by emergent helophytes, but could also be additionally explained by other variables. This transition started with a rapid vegetation shift from dying cultivated grasses to open water floating and submerged hydrophytes and significantly increased CH₄ emissions. Since 2008, helophytes have gradually spread from the shoreline into the open water area, especially in drier years. This process was periodically delayed by exceptional inundation and eventually resulted in the inundated site being covered by emergent helophytes. While the period between 2009 and 2015 showed exceptionally high CH₄ emissions, these decreased significantly after cattail and other emergent helophytes became dominant at the inundated site. Therefore, CH₄ emissions declined only after 10 years of transition following rewetting, potentially reaching a new steady state. Overall, this study highlights the importance of an integrative approach to understand the shallow lakes CH₄ biogeochemistry, encompassing the entire area with its mosaic of different vegetation forms. This should be ideally done through a study design including proper measurement site allocation as well as long-term measurements.     

Plasma esterase activities in rats fed magnesium-deficient diets

In a study with rats it was determined whether dietary magnesium concentration affects plasma esterase activities. The feeding of a diet with 0.01% (w/w) instead of 0.04% magnesium reduced plasma magnesium concentration by 50%. Plasma total esterase, arylesterase and butyrylcholinesterase activities were significantly decreased in the magnesium-deficient rats. In rats fed a diet containing 0.02% magnesium, plasma magnesium concentration was lowered by 30%, and group mean plasma total esterase activity was decreased, but not the activities of arylesterase and butyrylcholinesterase.     

Organization of the genes necessary for hydrogenase expression in Rhodobacter capsulatus. Sequence analysis and identification of two hyp regulatory mutants

A 25kbp DNA fragment from the chromosome of Rhodobacter capsulatus B10 carrying hydrogenase (hup) determinants was completely sequenced. Coding regions corresponding to 20 open reading frames were identified. The R. capsulatus hydrogenase-specific gene (hup and hyp) products bear significant structural identity to hydrogenase gene products from Escherichia coli (13), from Rhizobium liguminosarum (16), from Azotobacter vinelandii (10) and from Alcaligenes eutrophus (11). The sequential arrangement of the R. capsulatus genes is: hupR2-hupU-hypF -hupS-hupL-hupM-hupD -hupF -hupG -hupH -huoJ -hupK -hypA-hypB-hupR1-hypC -hypD -hypE -ORF19 -ORF20 , all contiguous and transcribed from the same DNA strand. The last two potential genes do not encode products that are related to identified hydrogenase-specific gene products in other species. The sequence of the 12 R. capsulatus genes underlined above is presented. The mutation site in two of the Hup^? mutants used in this study, RS13 and RCC12, was identified in the hypF gene (deletion of one G) and in the hypD qene (deletion of 54 bp), respectively. The hypF gene product shares 45% identity with the product of hydA from E. coli and the product of hypF from R. leguminosarum. Those products present at their N-terminus a Cys arrangement typical of zinc-finger proteins. The G deletion in the C-terminal region of hypF in the RS13 mutant     

Ecological compensation of the impacts of a road. Preliminary method for the A50 road link (Eindhoven-Oss, The Netherlands)

After years of efforts to avoid or reduce the impact of infrastructure projects on nature, the principle of ecological compensation has been incorporated in Dutch governmental policy. Ecological compensation aims to recover those ecological functions and natural values that still remain affected after maximum effort has been made to reduce the impact of the intervention (mitigation). The accepted aim of current policy is thus no-net-loss of area and quality by means of mitigative and compensatory measures. As part of the planning process for construction of a stretch of road in The Netherlands, viz., the A50 road link in the province of North Brabant, a Nature Compensation Plan (NCP) was required to be drawn up. This work has recently been completed by the Regional Directorate of Public Works and Water Management, the initiator of the intervention. The NCP, initially presented as a Draft Plan, was drawn up by the Regional Directorate using a preliminary method designed by the Centre of Environmental Science of Leiden University for deriving compensatory measures. After an opportunity for public comment, the Draft Plan was revised to form a Final NCP. This article describes, firstly, the preliminary method for deriving ecological compensatory measures. The method starts by quantifying the effects of habitat loss, habitat disturbance (by changes in noise emissions, in the water table and in outdoor recreational patterns), barrier action and fauna casualties. Following mitigation of impacts on nature, compensation for non-mitigable effects focuses successively on area size, derived from the impacts on breeding birds, and on area quality, derived from the habitat requirements of the vegetation and fauna groups affected by the road. Guidelines for identifying appropriate locations for compensation are also formulated. Secondly, the compensation method is applied to calculate the mitigative and compensatory measures for the A50 trajectory between Eindhoven and Oss. Thirdly, two comparisons are made: the Draft NCP is compared with the results of the preliminary method, and the Draft and the Final NCP are compared with one another in order to identify the role of the interest groups that played a major role in commenting on the Draft Plan. Finally, realization of the compensatory measures and development of the preliminary method itself are discussed. On the basis of the experience with the A50 case study, a more robust compensation method for road projects is to be developed.     

A third family of allelic hsd genes in Salmonella enterica: sequence comparisons with related proteins identify conserved regions implicated in restriction of DNA

Salmonella enterica serovar blegdam has a restriction and modification system encoded by genes linked to serB . We have cloned these genes, putative alleles of the hsd locus of Escherichia coli  K-12, and confirmed by the sequence similarities of flanking DNA that the hsd genes of S. enterica serovar blegdam have the same chromosomal location as those of E. coli K-12 and Salmonella enterica serovar typhimurium LT2. There is, however, no obvious similarity in their nucleotide sequences, and while the gene order in S. enterica serovar blegdam is serB hsdM , S and R , that in E. coli K-12 and S. enterica serovar typhimurium LT2 is serB hsdR , M and S . The hsd genes of S. enterica serovar blegdam identify a third family of serB -linked hsd genes (type ID). The polypeptide sequence predicted from the three hsd genes show some similarities (18–50% identity) with the polypeptides of known and putative type I restriction and modification systems; the highest levels of identity are with sequences of Haemophilus influenzae Rd. The HsdM polypeptide has the motifs characteristic of adenine methyltransferases. Comparisons of the HsdR sequence with those for three other families of type I systems and three putative HsdR polypeptides identify two highly conserved regions in addition to the seven proposed DEAD-box motifs.     

Minimizing growth regulators in shoot culture of an endangered plant,Hackelia venusta (Boraginaceae)

Summary Hackelia venusta (Boraginaceae) is an endangered perennial herb endemic to the interior northwestern United States. Because of seed scarcity, micropropagation (anex situ conservation strategy) could produce true-to-type plantlets suitable for reintroduction. We hypothesized that clones of predetermined size could be rapidly produced by supplementing multiplication and rooting media with minimal levels of cytokinin and auxin. Microshoots derived from shoot expants were cultured on Murashige and Skoog (1962) media supplemented with 1% (wt/vol) agar and 0.0001 to 10 μM benzyladenine. Inverse regression estimates on 3 genotypes predicted that a target of 2.5 axillary microshoots per explant would require a minimal level of 0.04±0.02 μM benzyladenine. Culture of 25 genotypes with 0.04 μM benzyladenine resulted in an average of 2.3±0.1 axillary microshoots per explant. Elongated microshoots were transferred to media supplemented with 0.1 to 25 μM indoleacetic acid. Clones rooted from 36% to 100% success after 4 wk in 2.0 μM indoleacetic acid. Plantlets transplantedex vitro with three or more roots survived at 84% versus 46% of plantlets with fewer roots. Up to 84% of the plantlets survived in a planting trial. The data suggest that shoot culture ofHackelia venusta, with minimal growth regulators, can produce axillary microshoots for reintroduction.     

Neocentromere-mediated Chromosome Movement in Maize

Neocentromere activity is a classic example of nonkinetochore chromosome movement. In maize, neocentromeres are induced by a gene or genes on Abnormal chromosome 10 (Ab10) which causes heterochromatic knobs to move poleward at meiotic anaphase. Here we describe experiments that test how neocentromere activity affects the function of linked centromere/kinetochores (kinetochores) and whether neocentromeres and kinetochores are mobilized on the spindle by the same mechanism. Using a newly developed system for observing meiotic chromosome congression and segregation in living maize cells, we show that neocentromeres are active from prometaphase through anaphase. During mid-anaphase, normal chromosomes move on the spindle at an average rate of 0.79 μm/min. The presence of Ab10 does not affect the rate of normal chromosome movement but propels neocentromeres poleward at rates as high as 1.4 μm/min. Kinetochore-mediated chromosome movement is only marginally affected by the activity of a linked neocentromere. Combined in situ hybridization/immunocytochemistry is used to demonstrate that unlike kinetochores, neocentromeres associate laterally with microtubules and that neocentromere movement is correlated with knob size. These data suggest that microtubule depolymerization is not required for neocentromere motility. We argue that neocentromeres are mobilized on microtubules by the activity of minus end–directed motor proteins that interact either directly or indirectly with knob DNA sequences. C urrent models suggest that chromosomes move by a combination of forces generated by microtubule disassembly (Inoue and Salmon, 1995; Waters et al., 1996) and the activity of molecular motors (Vernos and Karsenti, 1996; Yen and Schaar, 1996). Microtubule disassembly generates a constant poleward force; while molecular motors can generate force in either poleward or away-from-pole directions, depending on the characteristics of the motor protein. Both plus and minus end–directed microtubule-based motors are localized to kinetochores (Hyman and Mitchison, 1991). Immunolocalization experiments indicate that mammalian kinetochores contain the minus end– directed motor dynein throughout metaphase and anaphase (Pfarr et al., 1990; Steuer et al., 1990). The kinesin-like proteins CENP-E, which has a transient kinetochore localization in animals, and MCAK, which is localized between the kinetochore plates of mammalian chromosomes, are also thought to generate and/or regulate chromosome movement (Yen et al., 1992; Lombillo et al., 1995; Wordeman and Mitchison, 1995).In addition to the molecular motors on kinetochores, several kinesin-like proteins are localized to chromosome arms (Vernos and Karsenti, 1996). Two subfamilies of arm-based motors have been identified in animals: the NOD subfamily (Afshar et al., 1995; Tokai et al., 1996) and the Xklp1/chromokinesin subfamily (Vernos et al., 1995; Wang and Adler, 1995). Both Nod and Xklp1 are required for positioning chromosomes on the metaphase plate, suggesting that they encode plus end–directed motors (Afshar et al., 1995; Vernos et al., 1995). Other evidence suggests that minus end–directed motors interact with chromosome arms. In the plant Haemanthus, a poleward force acts along chromosome arms during metaphase (Khodjakov et al., 1996), and forces propelling chromosome arms poleward have been detected during anaphase in crane fly spermatocytes (Adames and Forer, 1996). Little is known about how poleward arm motility at metaphase–anaphase affects the fidelity or rate of chromosome segregation.The neocentromeres of maize (Rhoades and Vilkomerson, 1942) provide a particularly striking example of poleward chromosome arm motility. In the presence of Abnormal chromosome 10 (Ab10),¹ heterochromatic DNA domains known as knobs are transformed into neocentromeres and mobilized on the spindle (Rhoades and Vilkomerson, 1942; Peacock et al., 1981; Dawe and Cande, 1996). Knobs are primarily composed of a tandem 180-bp repeat (Peacock et al., 1981) which shows homology to a maize B centromere clone (Alfenito and Birchler, 1993). A characteristic feature of neocentromeres is that they arrive at the spindle poles in advance of centromeres; in extreme cases the neocentromere-bearing chromosome arms stretch towards the poles (Rhoades and Vilkomerson, 1942; Rhoades, 1952). A recently identified mutation (smd1) demonstrates that a trans-acting factor(s) encoded on Ab10 is essential for converting the normally quiescent heterochromatic knobs into active neocentromeres (Dawe and Cande, 1996).Here we use neocentromeres as a model for understanding the mechanisms and importance of nonkinetochore chromosome movement. As a part of our analysis, we developed a four-dimensional system for observing chromosome segregation in living meiocytes. Our experiments were designed to determine (a) how poleward arm motility affects the rate and fidelity of chromosome segregation; and (b) whether the mechanism of neocentromere motility is comparable to the mechanism of kinetochore motility.     

Ribosomal DNA and ITS-2 sequence comparisons as a tool for predicting genetic relatedness

The determination of the secondary structure of the internal transcribed spacer (ITS) regions separating nuclear ribosomal RNA genes of Chlorophytes has improved the fidelity of alignment of nuclear ribosomal ITS sequences from related organisms. Application of this information to sequences from green algae and plants suggested that a subset of the ITS-2 positions is relatively conserved. Organisms that can mate are identical at all of these 116 positions, or differ by at most, one nucleotide change. Here we sequenced and compared the ITS-1 and ITS-2 of 40 green flagellates in search of the nearest relative to Chlamydomonas reinhardtii. The analysis clearly revealed one unique candidate, C. incerta. Several ancillary benefits of the analysis included the identification of mislabelled cultures, the resolution of confusion concerning C. smithii, the discovery of misidentified sequences in GenBank derived from a green algal contaminant, and an overview of evolutionary relationships among the Volvocales, which is congruent with that derived from rDNA gene sequence comparisons but improves upon its resolution. The study further delineates the taxonomic level at which ITS sequences, in comparison to ribosomal gene sequences, are most useful in systematic and other studies. Received: 14 February 1997 / Accepted: 28 March 1997     

Evidence for Multiple, Local Functions of Ciliary Neurotrophic Factor (CNTF) in Retinal Development: Expression of CNTF and Its Receptor and In Vitro Effects on Target Cells

Abstract: There is increasing, although largely indirect, evidence that neurotrophic factors not only function as target-derived survival factors for projection neurons, but also act locally to regulate developmental processes. We studied the expression of ciliary neurotrophic factor (CNTF) and the CNTF-specific ligand-binding α-subunit of the CNTF receptor complex (CNTFRα) in the rat retina, a well-defined CNS model system, and CNTF effects on cultured retinal neurons. Both CNTF and CNTFRα (mRNA and protein) are expressed during phases of retinal neurogenesis and differentiation. Retina-specific Müller glia are immunocytochemically identified as the site of CNTF production and CNTFRα-expressing, distinct neuronal cell types as potential CNTF targets. Biological effects on corresponding neurons in culture further support the conclusion that locally supplied CNTF plays a regulatory role in the development of various retinal cell types including ganglion cells and interneurons.     

Changes in organic solutes,volume, energy state,and metabolism associated with osmotic stress in a glial cell line: A multinuclear NMR study

Diffusion-weighted in vivo¹H-NMR spectroscopy of F98 glioma cells embedded in basement membrane gel threads showed that the initial cell swelling to about 180% of the original volume induced under hypotonic stress was followed by a regulatory volume decrease to nearly 100% of the control volume in Dulbecco's modified Eagle's medium (DMEM) but only to 130% in Krebs-Henseleit buffer (KHB, containing only glucose as a substrate) after 7 h. The initial cell shrinkage to approx. 70% induced by the hypertonic stress was compensated by a regulatory volume increase which after 7 h reached almost 100% of the control value in KHB and 75% in DMEM.¹H-,¹³C-and³¹P-NMR spectroscopy of perchloric acid extracts showed that these volume regulatory processes were accompanied by pronounced changes in the content of organic osmolytes. Adaptation of intra- to extracellular osmolarity was preferentially mediated by a decrease in the cytosolic taurine level under hypotonic stress and by an intracellular accumulation of amino acids under hypertonic stress. If these solutes were not available in sufficient quantities (as in KHB), the osmolarity of the cytosol was increasingly modified by biosynthesis of products and intermediates of essential metabolic pathways, such as alanine, glutamate and glycerophosphocholine in addition to ethanolamine. The cellular nucleoside triphosphate level measured by in vivo³¹P-NMR spectroscopy indicated that the energy state of the cells was more easily sustained under hypotonic than hypertonic conditions.To whom to address reprint requests.