Showing papers by "Leibniz Association published in 2002"

DNA methylation controls histone H3 lysine 9 methylation and heterochromatin assembly in Arabidopsis

Abstract: We propose a model for heterochromatin assembly that links DNA methylation with histone methylation and DNA replication. The hypomethylated Arabidopsis mutants ddm1 and met1 were used to investigate the relationship between DNA methylation and chromatin organization. Both mutants show a reduction of heterochromatin due to dispersion of pericentromeric low‐copy sequences away from heterochromatic chromocenters. DDM1 and MET1 control heterochromatin assembly at chromocenters by their influence on DNA maintenance (CpG) methylation and subsequent methylation of histone H3 lysine 9. In addition, DDM1 is required for deacetylation of histone H4 lysine 16. Analysis of F 1 hybrids between wild‐type and hypomethylated mutants revealed that DNA methylation is epigenetically inherited and represents the genomic imprint that is required to maintain pericentromeric heterochromatin.

Jasmonates and octadecanoids: signals in plant stress responses and development.

Abstract: Plants are sessile organisms. Consequently they have to adapt constantly to fluctuations in the environment. Some of these changes involve essential factors such as nutrients, light, and water. Plants have evolved independent systems to sense nutrients such as phosphate and nitrogen. However, many of the environmental factors may reach levels which represent stress for the plant. The fluctuations can range between moderate and unfavorable, and the factors can be of biotic or abiotic origin. Among the biotic factors influencing plant life are pathogens and herbivores. In case of bacteria and fungi, symbiotic interactions such as nitrogen-fixating nodules and mycorrhiza, respectively, may be established. In case of insects, a tritrophic interaction of herbivores, carnivores, and plants may occur mutualistically or parasitically. Among the numerous abiotic factors are low temperature, frost, heat, high light conditions, ultraviolet light, darkness, oxidation stress, hypoxia, wind, touch, nutrient imbalance, salt stress, osmotic adjustment, water deficit, and desiccation. In the last decade jasmonates were recognized as being signals in plant responses to most of these biotic and abiotic factors. Signaling via jasmonates was found to occur intracellularly, intercellularly, and systemically as well as interorganismically. Jasmonates are a group of ubiquitously occurring plant growth regulators originally found as the major constituents in the etheric oil of jasmine, and were first suggested to play a role in senescence due to a strong senescence-promoting effect. Subsequently, numerous developmental processes were described in which jasmonates exhibited hormone-like properties. Recent knowledge is reviewed here on jasmonates and their precursors, the octadecanoids. After discussing occurrence and biosynthesis, emphasis is placed upon the signal transduction pathways in plant stress responses in which jasmonates act as a signal. Finally, examples are described on the role of jasmonates in developmental processes.

The tomato fer gene encoding a bHLH protein controls iron-uptake responses in roots.

Abstract: Iron deficiency is among the most common nutritional disorders in plants. To cope with low iron supply, plants with the exception of the Gramineae increase the solubility and uptake of iron by inducing physiological and developmental alterations including iron reduction, soil acidification, Fe(II) transport and root-hair proliferation (strategy I). The chlorotic tomato fer mutant fails to activate the strategy I. It was shown previously that the fer gene is required in the root. Here, we show that fer plants exhibit root developmental phenotypes after low and sufficient iron nutrition indicating that FER acts irrespective of iron supply. Mutant fer roots displayed lower Leirt1 expression than wild-type roots. We isolated the fer gene by map-based cloning and demonstrate that it encodes a protein containing a basic helix–loop–helix domain. fer is expressed in a cell-specific pattern at the root tip independently from iron supply. Our results suggest that FER may control root physiology and development at a transcriptional level in response to iron supply and thus may be the first identified regulator for iron nutrition in plants.

In silico analysis on frequency and distribution of microsatellites in ESTs of some cereal species.

Abstract: During the last decade microsatellites or SSRs (simple sequence repeats) have been proven to be the markers of choice in plant genetics research and for breeding purposes because of their hypervariability and ease of detection. However, development of these markers is expensive, labour intensive and time consuming, in particular, if they are being developed from genomic libraries. In the context of large-scale sequencing and genomics programmes in various cereal species at different laboratories, a large set of expressed sequence tags (ESTs) is being generated, which can be used to search for microsatellites. Keeping in view the importance of such type of SSRs, available ESTs of some cereal species like barley, maize, oats, rice, rye and wheat were investigated for a study of abundance, frequency and distribution of various types of microsatellites. SSRs were present in about 7% to 10% of the total ESTs in the investigated cereal genomes. On the basis of surveying EST sequences amounting to 75.2 Mb in barley, 54.7 Mb in maize, 43.9 Mb in rice, 3.7 Mb in rye, 41.6 Mb in sorghum and 37.5 Mb in wheat, the frequency of SSRs was 1/7.5 kb in barley, 1/7.5 kb in maize, 1/6.2 kb in wheat, 1/5.5 kb in rye and sorghum and 1/3.9 kb in rice. The overall average SSR frequency for these species is 1/6.0 kb. Trimeric repeats are the most abundant (54% to 78%) class of microsatellit es followed by dimeric repeats (17% to 40%). Among the trimeric repeats the motifs CCG are the most common in all the cases ranging from 32% in wheat to 49% in sorghum. When all these SSRs were analysed for assessing their potential to develop new markers, unique primer pairs could be designed for 30% to 70% of the total non-redundant microsatellites which are up to 3% of total ESTs in the studied species.

Reconciling traditional inland fisheries management and sustainability in industrialized countries, with emphasis on Europe

Abstract: In northern industrialized countries, the inland fisheries sector has long been dominated by recreational fisheries, which normally exploit fish for leisure or subsistence and provide many (poorly investigated) benefits to society. Various factors constrain the development and existence of inland fisheries, such as local user conflicts, low social priority and inadequate research and funding. In many cases, however, degradation of the environment and loss of aquatic habitat are the predominant concerns for the sustainability of inland fisheries. The need for concerted effort to prevent and reduce environmental degradation, as well as conservation of freshwater fish and fisheries as renewable common pool resources or entities in their own right is the greatest challenge facing sustainable development of inland waters. In inland fisheries management, the declining quality of the aquatic environment coupled with long-term inadequate and often inappropriate fisheries management has led to an emphasis on enhancement practices, such as stocking, to mitigate anthropogenic stress. However, this is not always the most appropriate management approach. Therefore, there is an urgent need to alter many traditional inland fisheries management practices and systems to focus on sustainable development. This paper reviews the literature regarding the inputs needed for sustainability of inland fisheries in industrialized countries. To understand better the problems facing sustainable inland fisheries management, the inland fisheries environment, its benefits, negative impacts and constraints, as well as historical management, paradigms, trends and current practices are described. Major philosophical shifts, challenges and promising integrated management approaches are envisaged in a holistic framework. The following are considered key elements for sustainable development of inland fisheries: communication, information dissemination, education, institutional restructuring, marketing outreach, management plans, decision analysis, socioeconomic evaluation and research into the human dimension, in addition to traditional biological and ecological sciences. If these inputs are integrated with traditional fisheries management practices, the prospects for sustainability in the inland fisheries will be enhanced.

Characterisation of interphase nanoscale property variations in glass fibre reinforced polypropylene and epoxy resin composites

Abstract: The local microstructure can be altered significantly by various fibre surface modifications, causing property differences between the interphase region and the bulk matrix. By using tapping mode phase imaging and nanoindentation tests based on the atomic force microscope (AFM), a comparative study of the sized fibre surface topography and modulus as well as the local mechanical property variation in the interphase of E-glass fibre reinforced epoxy resin and E-glass fibre reinforced modified polypropylene (PPm) matrix composites was conducted. The phase imaging AFM was found a highly useful tool for probing the interphase with much detailed information. Nanoindentation experiments indicated the chemical interaction during processing caused by a gradient profile in the modulus across the interphase region of γ-aminopropyltriethoxy silane (γ-APS) and polyurethane (PU)-sized glass fibre reinforced epoxy composite. The interphase with γ-APS/PU sizing is much softer than the PPm matrix, while the interphase with the γ-APS/PP sizing is apparently harder than the matrix, in which the modulus was constant and independent of distance away from the fibre surface. The interphase thickness varied between less than 100 and ≈300 nm depending on the type of sizing and matrix materials. Based on a careful analysis of ‘boundary effect’, nanoindentation with sufficient small indentation force was found to enable measuring of actual interphase properties within 100 nm region close to the fibre surface. Special emphasis is placed on the effects of interphase modulus on mechanical properties and fracture behaviour. The interphase with higher modulus and transcrystalline microstructure provided simultaneous increase in the tensile strength and the impact toughness of the composites.

Allelopathic growth inhibition of selected phytoplankton species by submerged macrophytes1

Abstract: Allelopathic effects of submerged macrophytes on the growth and photosynthesis of different unialgal cultures of planktonic cyanobacteria, a diatom, and a green alga were tested in coexistence experiments using dialysis cultures. The method applied allowed measurements under conditions similar to that in lakes but without nutrient and light limitation. Growth and photosynthesis were measured with a pulse amplitude modulated fluorometer as an increase of chl a fluorescence and activity of PSII, respectively. Eurasian water milfoil Myriophyllum spicatum L. and rigid hornwort Ceratophyllum demersum L. proved to inhibit the PSII activity and then growth of the investigated phytoplankton species, whereas sago pondweed Potamogeton pectinatus L. showed no effect. Growth inhibition was dependent on biomass of M. spicatum. Considerable differences between phytoplankton groups and among species of cyanobacteria were found regarding their response to M. spicatum. Members of the Oscillatoriales and Microcystis aeruginosa Kutz. emend. Elenkin were more sensitive than the cyanobacterium Aphanizomenon fios-aquae Ralfs ex Born. et Flah., the diatom Stephanodiscus minutulus (Kutz) Cleve et Moller, and the green alga Scenedesmus armatus Chodat. A possible contribution of this result to changes in the phytoplankton succession of lakes after loss of macrophytes is discussed.

Long term measurements of submicrometer urban aerosols: statistical analysis for correlations with meteorological conditions and trace gases

Abstract: Long-term measurements (over 4 years) of par- ticle number size distributions (submicrometer particles, 3- 800 nm in diameter), trace gases (NO, NO2, and O3), and meteorological parameters (global radiation, wind speed and direction, atmospheric pressure, etc.) were taken in a mod- erately polluted site in the city of Leipzig (Germany). The resulting complex data set was analyzed with respect to sea- sonal, weekly, and diurnal variation of the submicrometer aerosol. Car traffic produced a peak in the number size dis- tribution at around 20 nm particle diameter during morning rush hour on weekdays. A second peak at 10-15 nm particle diameter occurred around noon during summer, confirmed by high correlation between concentration of particles less than 20 nm and the global radiation. This new-particle for- mation at noon was correlated with the amount of global radi- ation. A high concentration of accumulation mode particles (between 100 and 800 nm), which are associated with large particle-surface area, might prevent this formation. Such high particle concentration in the ultrafine region (particles smaller than 20 nm in diameter) was not detected in the parti- cle mass, and thus, particle mass concentration is not suitable for determining the diurnal patterns of particles. In summer, statistical time series analysis showed a cyclic pattern of ul- trafine particles with a period of one day and confirmed the correlation with global radiation. Principal component anal- ysis (PCA) revealed a strong correlation between the parti- cle concentration for 20-800 nm particles and the NO- and NO2-concentrations, indicating the influence of combustion processes on this broad size range, in particular during win- ter. In addition, PCA also revealed that particle concentration depended on meteorological conditions such as wind speed and wind direction, although the dependence differed with particle size class.

The origin of aluminum flocs in polluted streams.

Abstract: About 240,000 square kilometers of Earth9s surface is disrupted by mining, which creates watersheds that are polluted by acidity, aluminum, and heavy metals. Mixing of acidic effluent from old mines and acidic soils into waters with a higher pH causes precipitation of amorphous aluminum oxyhydroxide flocs that move in streams as suspended solids and transport adsorbed contaminants. On the basis of samples from nine streams, we show that these flocs probably form from aggregation of the ɛ-Keggin polyoxocation AlO4Al12(OH)24(H2O)127+(aq) (Al13), because all of the flocs contain distinct Al(O)4 centers similar to that of the Al13nanocluster.

Possible allelopathic effects of cyanotoxins, with reference to microcystin-LR, in aquatic ecosystems.

Abstract: During recent years a shift from macrophyte-dominated to more phytoplankton-dominated lakes has been correlated to the process of eutrophication. The existence of numerous substances exhibiting allelopathic effects on the growth of algae has been shown in different aquatic macrophytes (e.g., Myriophyllum spicatum) and is thought to be an important mechanism in stabilizing the macrophyte-dominated clear-water state of a lake. A few recent studies have shown that algae themselves can produce special substances inhibiting growth or photosynthetic processes in other algae. A well-known cyanobacterial secondary metabolite, microcystin-LR, was tested for its allelopathic power on aquatic macrophytes such as Ceratophyllum demersum and Myriophyllum spicatum, resulting in growth inhibition, reduction in photosynthetic oxygen production, and changes in pigment pattern. This shows that microcystin-LR has a possible role as an allelopathic infochemical.

The Hohenpeissenberg aerosol formation experiment (HAFEX): a long-term study including size-resolved aerosol, H 2 SO 4 , OH, and monoterpenes measurements

Abstract: . Ambient aerosol size distributions (>3 nm) and OH, H 2 SO 4 , and terpene concentrations were measured from April 1998 to August 2000 at a rural continental site in southern Germany. New particle formation (NPF) events were detected on 18% of all days, typically during midday hours under sunny and dry conditions. The number of newly formed particles correlated significantly with solar irradiance and ambient levels of H 2 SO 4 . A pronounced anti-correlatation of NPF events with the pre-existing particle surface area was identified in the cold season, often associated with the advection of dry and relatively clean air masses from southerly directions (Alps). Estimates of the particle formation rate based on observations were around 1 cm -3 s -1 , being in agreement with the predictions of ternary homogeneous H 2 SO 4 -NH 3 -H 2 O nucleation within a few orders of magnitude. The experimentally determined nucleation mode particle growth rates were on average 2.6 nm h -1 , with a fraction of 0.7 nm h -1 being attributed to the co-condensation of H 2 SO 4 -H 2 O-NH 3 . The magnitude of nucleation mode particle growth was neither significantly correlated to H 2 SO 4 , nor to the observed particle formation rate. Turn-over rate calculations of measured monoterpenes and aromatic hydrocarbons suggest that especially the oxidation products of monoterpenes have the capacity to contribute to the growth of nucleation mode particles. Although a large number of precursor gases, aerosol and meteorological parameters were measured, the ultimate key factors controlling the occurence of NPF events could not be identified.

Biomanipulation of lake ecosystems: successful applications and expanding complexity in the underlying science

Abstract: 1. To illustrate advances made in biomanipulation research during the last decade, seven main topics that emerged after the first biomanipulation conference in 1989 are discussed in relation to the papers included in this special issue and the general literature. 2. The substantially higher success rates of biomanipulations in shallow as opposed to stratified lakes can be attributed to several positive feedback mechanisms relating mainly to the recovery of submerged macrophytes. 3. The role of both nutrient loading and in-lake concentrations in predicting the success of biomanipulations is emphasised and supported by empirically defined threshold values. Nutrient recycling by aquatic organisms (such as fish) can contribute to the bottom-up effects on lake food webs, although the degree can vary greatly among lakes. 4. Ontogenetic niche shifts and size-structured interactions particularly of fish populations add to the complexity of lake food webs and make scientifically sound predictions of biomanipulation success more difficult than was previously envisaged. 5. Consideration of appropriate temporal and spatial scales in biomanipulation research is crucial to understanding food web effects induced by changes in fish communities. This topic needs to be further developed. 6. An appropriate balance between piscivorous, planktivorous and benthivorous fishes is required for long-lasting success of biomanipulations. Recommended proportions and absolute densities of piscivorous fish are currently based on data from only a few biomanipulation experiments and need to be corroborated by additional and quantitative assessments of energy flow through lake food webs. 7. Biomanipulation effects in stratified lakes can be sustained in the long term only by continued interventions. Alternate stable states of food web composition probably exist only in shallow lakes, but even here repeated interventions may be needed as long as nutrient inputs remain high. 8. Biomanipulation is increasingly used as a lake restoration technique by considering the needs of all lake users (sustainability approach). The combination of water quality management and fisheries management for piscivores with positive effects for both appears to be particularly promising. 9. Biomanipulation research has contributed substantially to progress in understanding complex lake food webs, which should in turn promote a higher success rate of future whole-lake biomanipulations.

Small‐scale temperature variations in the vicinity of NLC: Experimental and model results

Abstract: [1] Gravity waves (GWs) are a ubiquitious dynamical feature of the polar summer mesopause region During three summer campaigns, in 1991, 1993 and 1994, we launched seven sounding rockets from the north Norwegian island Andoya Each of these payloads carried an ionization gauge capable of measuring the total atmospheric density at a high spatial resolution From these measurements, temperature profiles were determined for altitudes between 70 and 110 km, with an altitude resolution of 200 m The temperature profiles reveal significant rms variations that are as large as 6 K at 80 km, 10 K at 85 km, and even 20 K at 95 km During three out of the seven launches a bright noctilucent cloud (NLC) was simultaneously detected by our ground-based lidar and by rocket-borne in situ experiments During these flights, the NLC is located close to a local temperature minimum below the mesopause We then estimated gravity wave parameters from accompanying falling sphere and chaff wind observations and found signatures that the wave periods during the NLC cases were on the order of 7–9 hours, with corresponding horizontal wavelengths of 600–1000 km Motivated by these observations, we used a microphysical model of NLC generation and growth to study the interaction between GWs and NLC Based on recently measured and modeled temperatures and water vapor mixing ratios, and our gravity wave parameter estimates, we find that the NLC layer indeed follows the motion of the cold phase of the wave by means of a complex interplay between ice crystal sedimentation, transport by the vertical wind, and simultaneous growth It turns out that the history of individual particles significantly influences the observed properties of NLC Furthermore, we find that GWs with periods longer than 65 hours amplify NLC while waves with shorter periods tend to destroy NLC In addition, we can only find a correlation between local temperature minima and the location of the NLC provided that the wave periods are longer than ∼6 hours, which is consistent with our wave parameter estimates

Multiple Lenders and Corporate Distress: Evidence on Debt Restructuring

Abstract: In the recent theoretical literature on lending risk, the common pool problem in multi-bank relationships has been analyzed extensively. In this paper we address this topic empirically, relying on a unique panel data set that includes detailed credit-file information on distressed lending relationships in Germany. In particular, it includes information on bank pools, a legal institution aimed at coordinating lender interests in borrower distress. We find that the existence of small bank pools increases the probability of workout success and that coordination costs are positively related to pool size. We identify major determinants of pool formation, in particular the distribution of lending shares among banks, the number of banks, and the severity of the distress shock to the borrower.

Amphibians as a model for the study of endocrine disruptors.

Abstract: Evidence shows that environmental compounds can interfere with the endocrine systems of wildlife and humans The main sink of such substances, called endocrine disruptors (EDs), which are mainly of anthropogenic origin, is surface water; thus, aquatic vertebrates such as fishes and amphibians are most endangered Despite numerous reports on EDs in fishes, information about EDs in amphibians is scarce, and this paucity of information is of particular concern in view of the worldwide decline of amphibians EDs could contribute to changes of amphibian populations via adverse effects on reproduction and the thyroid system In amphibians, EDs can affect reproduction by (anti)estrogenic and (anti)androgenic modes of action that produce severe effects including abnormal sexual differentiation ED actions on the thyroid system cause acceleration or retardation of metamorphosis, which may also affect population levels Our broad knowledge of amphibian biology and endocrinology indicates that amphibians are very suitable models for the study of EDs In particular, effects of EDs on the thyroid system triggering metamorphosis can be determined easily and most sensitively in amphibians compared to other vertebrates A new classification of EDs according to their biological modes of action is proposed because EDs have quite heterogeneous chemical structures, which do not allow prediction of their biological effects Methods and strategies are proposed for identification and risk assessment of EDs, whether as pure test substances or as mixtures from environmental samples Effects of EDs on the thyroid system of amphibians can be assessed by a single animal model (Xenopus laevis), whereas the various types of reproduction need comparative studies to investigate whether general endocrine principles do exist among several species of anurans and urodeles Thus, at least one anuran and one urodelean model are needed to determine ED interference with reproduction

Nunatak survival of the high Alpine plant Eritrichium nanum (L.) Gaudin in the central Alps during the ice ages.

Abstract: Polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLPs) and sequence analysis of noncoding regions of chloroplast DNA were used to investigate 37 populations of Eritrichium nanum covering its total distribution area, the European Alps. There was no haplotypic variation within the populations, and most haplotypes were restricted to single sites or to neighbouring populations, suggesting low levels of long distance gene flow via seeds. The present geographical distribution of haplotypes probably reflects an ancient geographical pattern within two regions in the intensely glaciated western and eastern central Alps identified as genetic hotspot areas. These two regions contained seven of the total of 11 haplotypes, including many of the most derived ones. The divergent haplotypes formed closely related groups, which supported a separate evolution of these haplotypes in these two regions and, more importantly, gave strong evidence for the in situ survival of these populations on nunataks within the western and eastern central Alps during Pleistocene glaciation. This result is in concordance with a previous study on E. nanum using nuclear markers. Only one haplotype was common and widespread throughout the distributional range of E. nanum. At the same time, it was the evolutionarily basal-most and all other haplotypes were best described as its descendants. This haplotype is hypothesized to be genetically identical to a Tertiary Alpine colonizing ancestor, whose distribution was secondarily fragmented and infiltrated by derived haplotypes originating through local mutations.

When the American sea sturgeon swam east

Abstract: A colder Baltic Sea greeted this fish from across the Atantic Ocean in the Middle Ages. The two species of Atlantic sea sturgeon on either shore of the North Atlantic, Acipenser sturio in Europe and A. oxyrinchus in North America, probably diverged with the closure of the Tethys Sea and the onset of the North Atlantic Gyre 15–20 million years ago, and contact between them was then presumably precluded by geographic distance. Here we present genetic, morphological and archaeological evidence indicating that the North American sturgeon colonized the Baltic during the Middle Ages and replaced the native sturgeon there, before recently becoming extinct itself in Europe as a result of human activities. In addition to representing a unique transatlantic colonization event by a fish that swims upriver to spawn, our findings have important implications for projects aimed at restocking Baltic waters with the European sturgeon.

Differential retention and utilization of dissolved organic carbon by bacteria in river sediments

Abstract: The differential ability of natural sediment biofilms to store and metabolize specific dissolved organic carbon (DOC) fractions was studied with a set of perfusion experiments that combined a chromatographic method for the analysis of several DOC fractions with the measurement of bacterial abundance and activity. High proportions of low-molecular-weight substances and polysaccharides and low but significant proportions of humic substances were retained in sediment cores after perfusion. Bacterial abundance and production in these cores were high (1.7‐3.0 3 10 9 cells cm 23 and 0.7‐12.0 m gCc m 23 h 21 , respectively). Bacterial abundance, production, and turnover times were correlated with the retention of various DOC fractions, especially polysaccharides, indicating a differential microbial utilization of DOC. Temperature as well as the quantity and quality of retained organic matter were the major factors that influenced bacterial production. However, particulate organic carbon represented the main energy source for sediment bacteria. It is concluded that certain fractions of DOC may be readily utilized for bacterial growth, irrespective of molecular size. Instead, the presence and abundance of specific chemical groups might be decisive. Hence, the processing of organic substrates by the microbial biofilm may largely influence the biogeochemistry of DOC in river waters.

Investigating surface magnetism by means of photoexcitation electron emission microscopy

Abstract: The imaging of surfaces by means of photoexcitation electron emission microscopy (PEEM) has recently received considerable interest. This is mainly due to the extended use and availability of brilliant synchrotron radiation in the soft x-ray regime which generally facilitates studies with surface specificity and chemical selectivity. The most popular application of the x-ray PEEM (XPEEM) technique concerns studies of magnetic systems and phenomena. By exploiting the high degree of circular or linear polarization of the synchrotron light, the magnetic microstructure in both ferromagnets and antiferromagnets can be visualized. In this contribution we demonstrate the unique potential and the versatility of the PEEM approach, and review the current status with a certain emphasis on experiments with soft x-ray excitation. In some cases, the high-energy excitation studies can be complemented by laboratory experiments employing threshold photoemission with ultraviolet light (UV-PEEM). Current limitations and future developments and perspectives of the PEEM technique applied to magnetic systems are discussed.

Molecular and biochemical analysis of the enzymes of cysteine biosynthesis in the plant Arabidopsis thaliana.

Abstract: Among the amino acids produced by plants cysteine plays a special role as a mediator between assimilatory sulfate reduction and provision of reduced sulfur for cell metabolism. Part of this characteristic feature is the presence of cysteine synthesis in plastids, mitochondria and cytosol. Plants are the major source of reduced sulfur for human and animal nutrition. Cysteine biosynthesis deserves special attention, since reduced sulfur is channelled from cysteine into many sulfur-containing compounds in food and feed. Recent investigations are reviewed that focus on structure and regulation of cysteine synthesis in the model plant Arabidopsis thaliana. These data indicate that cysteine synthesis is not just an intermediate reaction step but that it is part of a regulatory network that mediates between inorganic sulfur supply and the demand for reduced sulfur during plant growth and in response to environmental changes.

Golgi Vesicle Proteins Are Linked to the Assembly of an Actin Complex Defined by mAbp1

Abstract: Recent studies indicate that regulation of the actin cytoskeleton is important for protein trafficking, but its precise role is unclear. We have characterized the ARF1-dependent assembly of actin on the Golgi apparatus. Actin recruitment involves Cdc42/Rac and requires the activation of the Arp2/3 complex. Although the actin-binding proteins mAbp1 (SH3p7) and drebrin share sequence homology, they are differentially segregated into two distinct ARF-dependent actin complexes. The binding of Cdc42 and mAbp1, which localize to the Golgi apparatus, but not drebrin, is blocked by occupation of the p23 cargo-protein-binding site on coatomer. Exogenously expressed mAbp1 is mislocalized and inhibits Golgi transport in whole cells. The ability of ARF, vesicle-coat proteins, and cargo to direct the assembly of cytoskeletal structures helps explain how only a handful of vesicle types can mediate the numerous trafficking steps in the cell.

The effect of fasting and refeeding on temperature preference, activity and growth of roach, Rutilus rutilus.

Abstract: Most fish species are regularly subjected to periods of starvation during which a reduction of energy turnover might be favourable for the animal. This reduction of energy flux may be achieved by changes in thermal behaviour and/or swimming activity. We investigated such behavioural changes during starvation and subsequent refeeding in roach, Rutilus rutilus, with respect to energetic benefits and growth maximisation. Roach, acclimated to a wide range of temperatures (4, 12, 20, 24, 27 and 30 °C), were fed to excess, subjected to 3 weeks of starvation and subsequently refed in order to determine the temperature dependence of feeding rates, growth rates and conversion efficiency (K1) under control conditions and during compensatory growth. When exposed to a thermal gradient, control animals preferentially selected a temperature of 26.8±0.9 °C, which is in the range of the optimal temperatures for feeding, growth and conversion efficiency. Starving fish showed a distinct circadian pattern of the mean selected temperature (MST). They migrated to cooler water in the dark (MSTdark=22.8±1.1 °C) but returned to warmer water during daytime. This behaviour may be regarded as a trade-off between the potentially higher food density in warmer water areas and the energetic benefit of selecting cooler water patches. The circadian pattern of MST was gradually abandoned upon refeeding and control values were reached again after 3 weeks. Energetically more effective than behavioural hypothermia was the reduction of swimming activity. During starvation, activity peaks were slightly lower than under control conditions and mean daily activity decreased by about 50%. Swimming velocity, however, was not affected by feeding regime. After a period of starvation fish showed compensatory growth at all temperatures, even below 12 °C, where these animals normally do not grow. This suggests that after a period of starvation the critical temperature for growth shifts to lower values.