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et al., The draft genome of the moss model, Physcomitrella patens, comprised approximately 2000 unordered scaffolds. In order to enable analyses of genome structure and evolution we generated a chromosome-scale genome assembly using genetic linkage as well as (end) sequencing of long DNA fragments. We find that 57% of the genome comprises transposable elements (TEs), some of which may be actively transposing during the life cycle. Unlike in flowering plant genomes, gene- and TE-rich regions show an overall even distribution along the chromosomes. However, the chromosomes are mono-centric with peaks of a class of Copia elements potentially coinciding with centromeres. Gene body methylation is evident in 5.7% of the protein-coding genes, typically coinciding with low GC and low expression. Some giant virus insertions are transcriptionally active and might protect gametes from viral infection via siRNA mediated silencing. Structure-based detection methods show that the genome evolved via two rounds of whole genome duplications (WGDs), apparently common in mosses but not in liverworts and hornworts. Several hundred genes are present in colinear regions conserved since the last common ancestor of plants. These syntenic regions are enriched for functions related to plant-specific cell growth and tissue organization. The P. patens genome lacks the TE-rich pericentromeric and gene-rich distal regions typical for most flowering plant genomes. More non-seed plant genomes are needed to unravel how plant genomes evolve, and to understand whether the P. patens genome structure is typical for mosses or bryophytes., The work conducted by the US Department of Energy Joint Genome Institute is supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231. Support to RR and SAR by the German Research Foundation (DFG RE 837/10-2), the Excellence Initiative of the German Federal and State Governments (EXC 294), and by the German Federal Ministry of Education and Research (BMBF FRISYS), is highly appreciated. CoGe is supported by the US National Science Foundation under Award Numbers IOS-339156 and IOS-1444490, CyVerse is supported by the U.S. National Science Foundation under Award Numbers DBI-0735191 and DBI-1265383. YK and ACC are grateful for support from the UK Biological Sciences and Biotechnology Research Council (Grant BB/F001797/1). KV acknowledges the Multidisciplinary Research Partnership ‘Bioinformatics: from nucleotides to networks’ Project (no 01MR0410W) of Ghent University. JC is grateful for support from the Spanish Ministerio de Economía y Competitividad (Grant AGL2013-43244-R). RSQ is grateful to Monsanto (St. Louis, MO, USA) for sequencing genomic DNA of P. patens accession Kaskaskia. The 1000 Plants (1 KP) initiative, led by GKSW, is funded by the Alberta Ministry of Innovation and Advanced Education, Alberta Innovates Technology Futures (AITF), Innovates Centres of Research Excellence (iCORE), Musea Ventures, BGI-Shenzhen and China National Genebank (CNGB). TW was supported by EMBO Long-Term Fellowships (ALTF 1166-2011) and by Marie Curie Actions (European Commission EMBOCOFUND2010, GA-2010-267146). The work conducted at PGSB was supported by the German Research Foundation (SFB924) and German Ministry of Education and Research (BMBF, 031A536/de.NBI).

Apple scab, one of the most damaging diseases in apple worldwide is caused by the fungal pathogen Venturia inaequalis. Pathogen-induced gene expression was analyzed in leaves of greenhouse- and field-grown trees of the scab susceptible cultivar Golden Delicious and the resistant cultivar Rewena using the macroarray technique. The results show that the defence of the Vf-resistant cultivar Rewena is based on different mechanisms than the basal defence response of the susceptible Golden Delicious: whereas lignification seems to play an essential role in scab defence of Rewena, a thaumatin-like as well as a flavonoid gene are assumed to be involved in the mostly insufficient defensive response of Golden Delicious. Furthermore, a method was developed for quantification of the V. inaequalis in infected leaves using real-time quantitative reverse transcription-PCR.

The effects of high and low N concentrations on the Solanum tuberosum-Phytophthora infestans interaction were studied in the potato cultivars Bettina, New York 121, Indira and Arkula, which exhibited different levels of resistance. Aboveground biomass and Chl and N content were significantly higher in all cultivars grown in higher N environments, while C:N ratios were lower, confirming successful application of N. High availability of N significantly increased susceptibility of three of the four potato cultivars, and amounts of pathogen within the infected leaflets determined in a quantitative real-time reverse transcriptase-polymerase chain reaction reflected this. Differential gene expression of P. infestans-induced and -repressed genes derived from three subtracted cDNA libraries at 0, 24, 48 and 72 h post-inoculation was studied in parallel. P. infestans attack led to an induction of defense-related and at the same time repression of growth-related potato genes mainly encoding photosynthetic genes. High N supply led to higher transcript abundance of photosynthetic genes such as Chl a/b-binding protein and ribulose bisphosphate carboxylase. N-dependent suppression of defense-related compounds in absence of the pathogen was not observed. Better N nutrition appeared to allow the plants to invest more resources in defense reactions.

The molecular mechanisms underlying the development and progression of sugarcane mosaic virus (SCMV) infection in maize are poorly understood. A transcript profiling study based on maize unigene-microarrays was conducted to identify genes associated with SCMV resistance in the near-isogenic line (NIL) pair F7 + (SCMV resistant) and F7 (susceptible). Altogether, 497 differentially expressed genes were identified in 4 comparisons addressing constitutive genetic differences, inducible genetic differences, compatible reaction, and incompatible reaction. Compared to a suppression subtractive hybridization (SSH) approach on the same materials, expression patterns of microarray-ESTs and SSH-ESTs were consistent for the same comparisons despite technical discrepancies. Pathogen-induced transcripts were underrepresented on the unigene-microarray, consequently fewer microarray-ESTs (45.8%) were classified into pathogenesis-related categories than SSH-ESTs (60.5%). Moreover, fewer microarray-ESTs (4) co-segregated with Scmv QTL than SSH-ESTs (18). However, our results demonstrate that the microarray experiments complement the SSH-macroarray studies. Good candidate genes (CGs) associated with SCMV resistance can be chosen from three classes: (i) positional CGs co-localized with major Scmv QTL, (ii) functional CGs exhibiting the homology to pathogenesis-related genes, or (iii) differentially expressed ESTs showing consistent expression pattern in both approaches.

Recent advances in RNA profiling offer an opportunity to establish functional links between genotype and phenotype for complex traits such as SCMV resistance. The change of RNA profiles was monitored on a macroarray containing SSH (suppression subtractive hybridization) clones. The number of differentially expressed genes (SCMV infected vs. non-infected) in individual lines was 177, 163, 165, 62, 47, 37, and 93, for FAP1360A, D21, D32, Pa405, F7, D145, and D408, respectively. All inbreds were divided into two groups by hierarchical cluster analysis: D32, D21, FAP1360A and D408 formed one; Pa405, D145, and F7 another group. Due to the genetic structure among the seven inbreds, genetic background and resistance response are confounded. With or without the resistant U.S. inbred line Pa405, 22 and 112 genes were identified by t tests between resistant (D21, D32, and FAP1360A) and susceptible (D145, D408, and F7) inbred lines, respectively. The 112 candidate genes were divided into three clusters by K-means clustering and analyzed in more detail, e.g., five genes were in silico mapped surrounding Scmv2 QTLs. These candidate genes provide a better understanding of signal transduction pathway for SCMV resistance and have the potential to develop functional markers to distinguish resistant and susceptible genotypes.

The molecular mechanisms underlying the development and progression of sugarcane mosaic virus (SCMV) infection in maize are poorly understood. A study of differential expression was conducted to identify genes involved in resistance to SCMV. In this study, we combined suppression subtractive hybridization and macroarray hybridization to identify genes that are differently expressed in the near isogenic lines F7+ (SCMV resistant) and F7 (susceptible). Altogether, 302 differentially expressed genes were identified in four comparisons based on constitutively expressed and inducible genes, and on compatible and incompatible plant-virus interactions. Apart from genes related to metabolism, most of the functionally classified genes identified belonged to three pathogenesis-related categories: cell rescue, defense, cell death and ageing, signal transduction, and transcription. The latter three groups accounted for 56-66% of the genes classified. Some 19% (60 of 302) of the identified genes had previously been assigned to 29 bins distributed over all ten maize chromosomes. Among the mapped genes, 31% (18 of 58) were located within the Scmv2 and Scmv1 regions on chromosomes 3 and 6, respectively, which have been associated with resistance to SCMV. Promising candidate genes for Scmv1 have been identified, such as AA661457 (receptor-like kinase Xa21-binding protein 3). The implications of the genomic distribution of differentially expressed genes identified by this isogenic comparison are discussed in the context of breeding for resistance.

SUMMARY To gain deeper understanding of the host-pathogen interaction in the system potato-Phytophthora infestans, subtractive hybridization in combination with cDNA array hybridization was used. Leaflets of a moderately resistant and a susceptible potato cultivar were inoculated with P. infestans. The infection of the potato leaves was quantified by real-time quantitative PCR. Using infected and control tissue, two cDNA libraries highly enriched for P. infestans-induced genes were prepared. Within 531 clones randomly picked and sequenced from the libraries, 285 unigenes were found, from which 182 clones were selected for further analysis by cDNA array hybridization. Sixteen hours post inoculation genes were not induced significantly, whereas 72 h post inoculation induction of gene expression was clearly detectable. In both cultivars, 143 genes were induced moderately (>/= two-fold), and 35 of the selected genes appeared to be strongly induced (>/= seven-fold). Among these clones were mainly genes associated with stress and/or defence mechanisms. The strongest gene induction was found in 4-week-old susceptible plants. In the moderately resistant cultivar, transcripts of a number of genes accumulate with plant age; as a result, induction of gene expression upon infection was less pronounced. Down-regulation of three genes was observed in both cultivars, upon infection. Transcript levels of these three genes increased in uninfected plants within 4 weeks of growth. Other differences in defence responses of the two cultivars could be determined and their effects are discussed.

In the moss Ceratodon purpureus, phytochrome is encoded by two different genes, CpPHY1 and CpPHY2. CpPHY2 represents a conventional type phytochrome characterized by a C-terminus homologous to the catalytic domain of bacterial sensor histidine kinases, whereas CpPHY1 represents an unique phytochrome, which carries a C-terminus homologous to the catalytic domain of eukaryotic serine/threonine/tyrosine kinases. Southern blot analysis revealed that CpPHY1 is present in different Ceratodon cultivars which were collected in Germany and in Finland, implying that CpPHY1 represents a functional and active gene in Ceratodon, but CpPHY1 homologous genes could not be detected in another moss, Physcomitrella patens, or in Arabidopsis thaliana. cDNA analysis of CpPHY1 revealed the presence of a hitherto unnoticed intron within the 3' region. This results in a change of the sequence of the 11 C-terminal amino acids from KLSSHSYLTSK to FSSYQDSYPSTEELS. CpPHY1 and CpPHY2 mRNAs appear to accumulate in a light-independent manner, with CpPHY2 being much more strongly expressed than CpPHY1. Accordingly, in crude protein extracts, CpPHY2 is clearly detectable by Western blot analysis, whereas CpPHY1 is not. Light-dependent expression of CpPHY2 can be detected at the post-transcriptional level; during a 7-day period of dark adaptation, pronounced CpPHY2 accumulation occurs. Upon transfer to white light, dark-accumulated CpPHY2 is depleted within 24 h. That depletion can be completely inhibited by the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), implying that photosynthesis is strongly involved in the adjustment of phytochrome steady-state concentrations in Ceratodon. The presence of an ORF within the 5' UTR region of CpPHY2 (uORF) encoding peptide MKEFSSTSRSLMIVGIY suggests regulation at the translational level. The uORF resides on a short intron which is excised from the 5' leader in a light-dependent manner, resulting in the formation of an alternative uORF encoding peptide MEEEEDCVP.

The transcript accumulation for subunits 2–6 of photosystem I (PSI) was determined after irradiation of 5.5 days old etiolated seedlings of Spinacea oleracea . Homologous gene probes were used for Northern blot and slot blot analysis. For comparison, heterologous probes of a light-regulated ( cab ) and a constitutively expressed ( actin ) gene were included. In dark-grown seedlings, only the PSI-4 transcript was detectable in relatively high amounts apart from the actin transcript; all other transcripts were present only in trace amounts. The kinetic of transcript accumulation was nearly linear during 8 h of continuous irradiation with white light; the increase for PSI-2, −3, −5, −6 and cab transcripts was 7–10-fold within this time. The level of the PSI-4 transcript increased only 2.5-fold in the same experiments. After short (1–5 min) pulses of red light, a lag phase of about 1 h was found for accumulation of all light-regulated transcripts except for accumulation of PSI-4 which occurred immediately without lag phase. The maximum level for PSI-2, −3, −5, −6 and cab transcripts was reached at about 5–6 h after the red light pulse. A far-red light pulse given immediately after the red light pulse decreased the transcript levels to those found after a far-red light pulse alone. We conclude that transcription of the genes coding for PSI subunits 2–6 is regulated by phytochrome.

The polymerase chain reaction was carried out with primers hybridizing to conserved regions of the phytochrome genes. With DNA from the moss Ceratodon purpureus 5 overlapping fragments were obtained resulting in a continuous nucleotide sequence of 1474 bp. The deduced amino acid sequence showed homology of around 60% with all known phytochrome sequences. The sequences contained a conserved chromophore attachment site. In light-grown Ceratodon protonemata the phytochrome mRNA with the size of about 4.5 kb was detected.

The role of boron (B) and carbon (C) additions on the microstructural development of pressureless sintered silicon carbide (SiC) was examined. Green compacts, which have been fired at a rate of 20 K/min up to 1773, 2123, 2223 and 2423 K were analyzed by means of electron microscopy and high-resolution scanning Auger electron spectroscopy. In the first stage of sintering C forms a uniform layer on the SiC grains. B and O are also present in that layer. At higher temperatures C reacts with SiO 2 under formation of SiC. B disappears from the layer of C as well as from the grain boundaries. The final dense material exhibits SiC crystallites and polycrystalline C-inclusions. The results are discussed under microstructural aspects and with respect to the sintering process of SiC.

A systematic molecular analysis of the structure and function of plant genomes will be essential for future developments in plant science and its applied field: agriculture and food processing. This research area, called genomics, is presently of so much interest that in numerous countries special programs are offered, e.g., in Germany the project Genome Analysis in the Biological System Plant (GABI). Genomics can be divided into (1) structural genomics, which means mapping and sequencing (the initial phase of genome analysis) the endpoint of which would be the identification of the complete DNA sequence (Ordon et al., this Vol.), and (2) functional genomics, where the biological function of genes is uncovered. While the first part is still descriptive, though on the most basic level of life, functional analysis integrates available biochemical and physiological knowledge and forms the bridge to the in vivo state.

22 novel members of the Arabidopsis thaliana protein kinase family (AKs) were identified by using degenerate oligonucleotide primers directed to highly conserved amino acid sequences of the protein kinase (PK) catalytic domain. Of these 22 genes, 16 turned out to carry intron sequences. Homologies of AK sequences were detected to S-locus receptor protein kinases (SRKs) from Brassica spp., to SRK-like PKs from maize and A. thaliana and to several other receptor PKs from A. thaliana. Sequence similarity was also detected to Ca(2+)-dependent PKs (CDPKs) from rape and soybean, to SNF1 and to CDC2 homologues. The genomic organization and the accumulation of the mRNAs from these 22 AK genes were investigated.

In the moss Ceratodon purpureus a phytochrome gene encodes a phytochrome type (PhyCer) which has a C-terminal domain homologous to the catalytic domain of eukaryotic protein kinases (PKs). PhyCer exhibits sequence conservation to serine/ threonine as well to tyrosine kinases. Since PhyCer is expressed very weakly in moss cells, to investigate the proposed PK activity of PhyCer, we overexpressed PhyCer transiently in fibroblast cells. For this purpose we made a chimeric receptor, EC-R, which consists of the extracellular, the membrane-spanning and the juxtamembrane domains of the human epidermal growth-factor receptor (EGF-R) linked to the PK catalytic domain of PhyCer (CerKin). The expression of EC-R in transiently transfected cells was confirmed with antibodies directed against the extracellular domain of EGF-R or against CerKin. Both EGF-R and EC-R were immunoprecipitated from lysates of overexpressing cells with antibodies against the extracellular domain of EGF-R. Phosphorylation experiments were performed with the immunoprecipitates and the phosphorylation products were subjected to phosphoamino acid analysis. Phosphorylation products specifically obtained with EC-R-transfected cells exhibit phosphorylation on serine and threonine residues. In EC-R transfected cells the endogenous EGF-R showed enhanced phosphorylation of serine and threonine residues compared to EGF-R immuno-precipitated from control cells. Although CerKin is closest to the catalytic domain of a protein tyrosine kinase from Dictyostelium discoideum, EC-R does not appear to phosphorylate tyrosine residues in vitro. From our data we conclude that PhyCer carries an active PK domain capable of phosphorylating serine and threonine residues.

Absorption of light quanta is the precondition for any photochemical reaction and hence for photobiological phenomena. Starting with white light, one can consider a ‘black body’ the ideal absorber in a physical sense because all wavelengths (i.e. all energy levels) of the light are equally absorbed. However, this situation is not realized in plants. The actual absorbers preferentially absorb certain wavelengths of visible light but are more or less transparent for other wavelengths. After such an absorption, the remaining light looks ‘coloured’ to the human eye. The absorbers are therefore called chromophores (= carriers of colours). Molecules which have the properties of such absorbers are called pigments. These terms are used here in such a sense that the entire molecule is called pigment whereas the particular part of the molecule which absorbs light is called its chromophore.

The phytochrome gene of the moss Ceratodon purpureus (phyCer) codes for a novel phytochrome polypeptide with a predicted molecular mass of 145 kDa that has a COOH-terminal domain which is homologous to the catalytic domain of eukaryotic protein kinases. In this paper we report the first biochemical evidence that in fact, as predicted from the gene sequence, PhyCer represents an active, light-regulated protein kinase. In vitro phosphorylation experiments with protonemata extracts revealed the existence of a 140 kDa protein, phosphorylated in a red/far-red light dependent manner. The binding of a polyclonal antibody directed to the protein kinase catalytic domain of PhyCer enhanced the phosphorylation of a 140 kDa band when assayed in a renaturation-auto-phosphorylation experiment with nitrocellulose bound protein. These findings strongly implicate that the phyCer gene product has protein kinase activity and is capable of auto-phosphorylation. The results of the renaturation-phosphorylation experiments were essentially the same, no matter whether protein extracts from light grown or dark adapted moss protonemata were used. Thus, phyCer expression most likely is not light regulated.

The phytochrome gene (phyCer) of the moss Ceratodon purpureus was isolated and characterized. phyCer is composed of three coding exons: exon I of 2035 bp, exon II of 300 bp and exon III of 1574 bp. The deduced polypeptide encoded by exon I and II exhibits substantial sequence homology to the conserved NH2-terminal chromophore domain of known phytochromes. In contrast, the COOH-terminal polypeptide encoded by exon III shows no sequence homology to any phytochrome molecule. phyCer most likely represents a single-copy gene and is expressed in a light-independent manner. From the DNA sequence analysis it can be deduced that the PhyCer polypeptide is composed of 1303 amino acids (including the starting Met) which predicts a molecular mass for PhyCer of 145 kDa. The polypeptide encoded in exon III exhibits striking homology within the 300 carboxy-terminal amino acids to the catalytic domain of protein kinases. The carboxy terminus of PhyCer was found to be most homologous to protein-tyrosine kinases of Dictyostelium discoideum and to the products of retroviral oncogenes which belong to the Raf-Mos serine/threonine kinase family. From the hydropathy profile PhyCer appears to be a soluble protein. The predicted structure suggests that PhyCer represents a soluble light-sensor protein kinase which is linked with a cellular phosphorylating cascade.

— The possibility of transforming Cerarodon purpureus protoplasts by PEG-mediated direct DNA uptake was tested. Transformation with a plasmid carrying a kanamycin-resistance gene resulted in kanamycin-resistant colonies of C. purpureus protonemata. A full-length cDNA clone coding for oat phyA phytochrome was isolated. The clone HM4.1 which is 3.7-kb long exhibits about 99% nucleotide sequence identity to the known phytochrome clone AP3. The expression of HM4.1 in C. purpureus protonemata was tested. A construct with the 35s-promotor and the structural gene of HM4.1 was cotransformed with the plasmid containing the kanamycin-resitance. Kanamycin-resistant colonies were tested for the presence of HM4.1 sequences in a genomic Southern experiment. Two out of 19 kanamycin-resistant colonies reacted positively with a HM4.1 specific probe. The expression of phyA in the positive colonies was examined with monoclonal antibodies specific for oat phytochrome. The Western blot experiment with protein extracts of the two positive colonies grown in the dark revealed clear signals at 124-kDa which were not detected in control plants. These data demonstrate the possibility of expressing oat phyA-apoprotein in C. purpureus protonemata. The transgenic moss protonemata did not show phenotypical alterations in response to the foreign phytochrome polypeptide; it is not known at the moment if the tetrapyrole chromophore is attached to the oat polypeptide in the protonemata or not.

Chromopeptides were prepared from the Pfr form of phytochrome by pepsin digestion. After separation from colorless peptides and Pr peptides by column chromatography, spectral characteristics of this Pfr peptide were determined (λ1 max = 610nm, λ2 max = 380nm in acid methanol). Irradiation of Pfr peptide produces Pr peptide without liberation of a detectable compound. The Pfr peptide is more sensitive to oxidation and reduction than the Pr peptide. Oxidation with iodine and reduction with dithionite leads to partial chemoconversion of the Pfr peptide to the Pr peptide. The results favor the model of cis-trans isomerization for the Pr ⇌ Pfr transformation.

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

The (4 Z, 10 Z, 15E)-2,3-dihydrobilindione 4, along with the fully unsaturated (E, Z, Z)-analogue 8, has been prepared from the corresponding (Z, Z, Z)-isomer by a variation of Falk's method (Falk et aL, 1980). The photochemical and acid-catalyzed back-reactions have been studied by UV-vis and 1H-NMR spectroscopy.

Using lambda gt11 expression cloning and immunoscreening, cDNA-containing recombinant phages for subunits IV and V of the photosystem I reaction center were isolated, sequenced and used to probe Northern blots of polyadenylated RNA prepared from spinach seedlings. The mRNA sizes for both components are approximately 1000 and 850 nucleotides, respectively. The 968 nucleotide cDNA sequence and derived amino acid sequence for subunit IV predict a single open reading frame of 231 amino acid residues (25.4 kDa). Comparison with a 13-residue N-terminal amino acid sequence determined for subunit IV suggests a mature protein of 17.3 kDa (154 residues) and a transit sequence of 77 amino acids (8.1 kDa). The corresponding data for subunit V are 677 bp (cDNA), 167 residues for the precursor protein (18.2 kDa), 98 residues for the mature polypeptide (10.8 kDa) and 69 residues for the transit peptide (7.4 kDa). Secondary structure predictions indicate that both proteins possess greatly different transit sequences and that none is membrane-spanning.

Chromopeptides which contain linear tetrapyrrole chromophores are prepared by proteolytic digestion of phycocyanin and phytochrome (P r and P fr forms). After the nucleophilic addition of mercaptoethanol to C-10 of the tetrapyrrole, irradiation with white light leads to photoisomerization of the tetrapyrrole ( Z → E ). The products prepared from ( Z )-phycocyanin and P r chromopeptides are similar to P fr chromopeptides with respect to chromatographic properties, electronic spectra and photolability. It is concluded that the linear tetrapyrrole chromophore of P r is all- Z whereas P fr , has the E configuration at one of the bridges.

Property measurements were made in UO2-Mo-eermets. The specific electrical resistivity of UO2 Mo green pellets and UO2Mo sintered pellets decreased with the molybdenum-concentration. Between 30 and 40 wt-% of molybdenum there is a clear change in the shape of the curve. This phenomenon is attributed to the matrix change from one component to the other, which is geometrically limited. A clear discontinuity approximately at 35 wt-% molybdenum is shown in the curve of the thermal conductivity in dependence of the molybdenum-concentration. The thermal conductivity is improved by the additions of molybdenum. The improvment in the present case amounts to 100% at a molybdenum-concentration of 30 wt-%. The thermal conductivity was measured at 200, 400 and 600 °C. The linear thermal coefficient of expansion becomes smaller with increasing molybdenum-concentration. The curve of the linear thermal coefficient of expansion in dependence of the concentration is not linear till approximately 25 wt-% Mo (again because of the matrix change), while at higher molybdenum-concentration the curve becomes a straight line. The rupture stength is bending and the modulus of elasticity in bending of UO2-Mo cermets, in dependence of the concentration, shows a peculiar minimum in the range of the matrix change (30–40 wt-% Mo). In all cases an alternate was made to interpret the course of the curves and — as far as possible — to compare with literature values. Equations were derived for the concentration dependence of the coefficient of the electrical resistivity and of the linear thermal expansion. They agree to a certain extent with the curves. Several experiments were made on the machinability of the UO2/Mo sintered pellets. Reactor irradiation experiments were made of at UO2/Mo sintered pellets and pure UO2 sintered pellets. The mixed pellets were not subject to any greater alterations in properties than the pure oxide pellets.

Phytochrome, the best characterised plant photoreceptor, is encoded by a small multigene family within the plant kingdom. The different phytochrome types are composed of a conserved light-sensing chromophore domain of about 80 kDa and a less-conserved C-terminal domain of about 50 kDa. The C-terminus of phytochrome of the moss Ceratodon purpureus is homologous to the catalytic domain of eukaryotic serine/threonine or tyrosine protein kinases; in contrast, for all other phytochromes (conventional phytochromes) sequence similarities within the C-terminal domain to the catalytic domain of bacterial histidine kinases have been reported. We performed careful sequence comparisons of the putative catalytic domains of phytochrome with each other, with authentic serine/threonine, tyrosine and with histidine kinases. We report that conventional phytochromes exhibit structural elements of the catalytic domains of both histidine and, to a lesser extent, of serine/threonine and tyrosine kinases. The significance of these observations is discussed in the framework of the structure, function and evolution of phytochrome.

In den letzten zwei Jahrzehnten erfolgte eine zunehmend sturmische Entwicklung neuer keramischer Werkstoffe, deren Potential fur Anwendungen im Maschinenbau, Elektronik, Elektrotechnik, Fertigungstechnik und anderen Bereichen von hohem Interesse ist. Die bisher realisierten Eigenschaften dieser neuen Keramiken haben zu sehr grosen Hoffnungen, verschiedenen technischen und wirtschaftlichen Erfolgen, aber auch zu gewissen Ernuchterungen gefuhrt. Da das Potential dieser Werkstoffgruppe aber noch keinesfalls ausgeschopft, d.h. die Werkstoffentwicklung noch in vollem Flus ist, sind weitere positive Ergebnisse und „Durchbruche“ zu erwarten. Im vorliegenden Beitrag werden die wichtigen Aspekte dieser Entwicklung beschrieben. Auf Anwendungen besonders im Maschinenbau wird eingegangen und die Notwendigkeit einer fachubergreifenden Zusammenarbeit zwischen Anwender, Konstrukteur und Werkstoffwissenschaftler aufgezeigt.

Werden die hochsten Anspruche an die Regulierung gestellt, dann mussen wir auch die mit den kleinen Schwingungen des Reglers verbundenen kleinen Geschwindigkeitsschwankungen der Maschine bei konstanter Belastung zu beseitigen suchen. Das einzige Mittel dazu ist das Tanzen des Reglers, wodurch ein Unempfindlichkeitsgrad erreicht wird, der praktisch null ist. Auser durch den Ungleichformigkeitsgrad des Schwungrades kann das Tanzen durch den Ruckdruck der Steuerung verursacht werden. In diesem Falle kann der Unempfindlichkeitsgrad des Reglers bedeutend groser sein, als der Ungleichformigkeitsgrad des Schwungrades, da der Ruckdruck der Steuerung meist von betrachtlicher Grose ist. Isaachsen hat zuerst die gunstige Einwirkung des Reglertanzes auf die Regulierung klar erkannt oder wenigstens ausgesprochen. Er schreibt: „Zwei Eigentumlichkeiten bei Dampfmaschinen, welche allgemein, besonders bei Ventilsteuerungen, nur als Ubelstand bezeichnet werden und deren Beseitigung in einer Anzahl von Regulierungen sogar besonders angestrebt wird, sind es, welche trotz ihrer allgemeinen Verkennung die einzige Rettung fur die feineren Regulierungen bilden. Es sind dies der Ruckdruck vieler Steuerungen auf den Regulator und die Ungleichformigkeit der Drehbewegung aller Dampfmaschinen durch die Ungleichformigkeit der Drehkraft“. —

Wir wollen es als Tatsache hinnehmen, das der schwingungsdampfende Einflus eines sich mit der Geschwindigkeit vergrosernden, auf den Kurbelkreis reduzierten Widerstandes sehr wenig in Frage kommt, wenn wir es mit Regulierungen zu tun haben, an die hohe Anspruche gestellt werden. Die Abhandlung von Isaachsen befast sich etwas eingehender mit den selbstregulierenden Eigenschaften der Kraftmaschinen. Es sei bier nur bemerkt, das die meisten Widerstande, welche die. Kraftmaschinen zu uberwinden haben, mit der Geschwindigkeit wachsen. Es ist leicht einzusehen, das ein mit der Geschwindigkeit zunehmender Widerstand schwingungsdampfend wirken mus, das hingegen ein mit der Geschwindigkeit abnehmender Widerstand die Schwungradschwingungen und somit die relativen Reglerschwingungen vergrosert. Wir konnen unmittelbar die in § 2 uber relative Schwingungen angestellten Untersuchungen auf die relativen Schwingungen des Schwungrades gegen eine mit konstanter mittlerer Winkelgeschwindigkeit rotierende konzentrische Scheibe anwenden. Nach der Auffassung, welche sich an die Darstellung der Bewegung des Reglers im Tolleschen Diagramm anschliest, konnen wir uns auch vorstellen, das zu jeder eingetretenen plotzlichen grosen Belastungsanderung wahrend der Bewegung des Reglers noch weitere kleine Belastungsanderungen im gleichen oder entgegengesetzten Sinne hinzukommen, sodas die den Beharrungszustand storende Ursache etwas vergrosert bezw. zum Teil wieder beseitigt wird. Diese kurze Erklarung ist naturlich unvollkommen; doch um Bekanntes nicht nochmals zu behandeln, sei dieser Punkt hiermit erledigt.

Der Regler soll mit konstanter Geschwindigkeit sich drehen und zunachst ohne Reibung gedacht werden. Wird das Pendel durch einen Anstos in Schwingungen versetzt, die in der Pendelebene vor sich gehen, also relativ sind, so ist uber diese relativen Schwingungen genau dasselbe zu sagen, wie uber die gewohnlichen Federschwingungen gegen einen festen Raum. Betrachten wir den Fliehkraftstrahl, welcher der konstanten Winkelgeschwindigkeit w entspricht, als Abscissenachse, so ist die W-Kurve des Reglers die Kraftkurve der Schwingung. Wir haben gegen Fig. 1 nur den Unterschied, das im Tolleschen Diagramm die Koordinaten schiefwinklig sind. Bewegt sich der Schwungkorper nach ausen, so wird die Arbeit A (Fig.7), welche die Fliehkraft gegen die reduzierten Widerstandskrafte leistet, der Antriebswelle der Reglerspindel entnommen. Ein weiterer, gleich groser Energiebetrag A wird der Antriebswelle entnommen, um die Zunahme der kinetischen Energie des rotierenden Systems infolge der Vergroserung des Tragheitsmomentes beim Aufwartsgang zu bewirken. Beim Abwartsgang des Reglers wird die Arbeitsmenge 2A der Antriebswelle zuruckgegeben. Bei jeder unendlich kleinen Bewegung der Schwungkorper haben wir: Anderung der potentialen Energie: d Ep = C. dx = m.x. ω2. dx Anderung der kinetischen Energie: d E k x = d (1/2 m. x2. ω2) = m. x. ω2. dx.

Die bekanntesten Schwingungen sind die unter dem Einflus elastischer Krafte. Das Kraftediagramm besteht in diesem Falle aus einer geraden Linie. Denken wir uns die Bewegung reibungslos, so bleiben die Schwingungen erbalten. Der Korper behalt seine Energie, die ihm irgendwie mitgeteilt worden ist. Diese besitzt die Grose 1/2 m. v 0 2 , wenn v0 die groste Geschwindigkeit der schwingenden Masse m ist. Treten aber irgendwelche Reibungswiderstande zu den elastischen Kraften hinzu, so mussen die Schwingungen allmahlich kleiner werden und schlieslich ganz aufhoren, wenn die Ebene A (Fig. 4) gegen die Ebene B fest, d. h. wenn die Schwingung des Korpers k gegen die Ebene B eine absolute, nicht nur eine relative ist. Es wird dem Korper k fortwahrend Energie entzogen, die sich in Reibungswarme umsetzt. Tritt z. B. ein kleiner, konstanter Reibungswiderstand W hinzu, so ist die dem Korper k wahrend einer vollen Schwingung entzogene Energie 2. W. L (naturlich etwas kleiner, weil die Schwingungsweite L ein wenig abgenommen hat). In Fig. 5 ist dieser Energieverlust durch die schraffierte, schmale Flache dargestellt, welche von der Kraftkurve eingeschlossen wird. Innerhalb der mit 2r bezeichneten Strecke mus der Korper k schlieslich zur Ruhe kommen. Wollen wir die Schwingungen aufrecht erbalten, so mus die dem Korper durch Reibung entzogene Energie von ausen wieder zugefuhrt werden. Beim Uhrpendel geschieht diese Zufuhr z. B. durch das bekannte Steigrad mit auf der Welle aufgewundenem Gewicht.

Die folgende Rechnung geschieht unter den in § 4 ausfuhrlich gemachten Voraussetzungen. Als schwingungsdampfendes Mittel ist nur ein konstanter, reduzierter Reibungswiderstand vorhanden. Wir nehmen an, das der Regler sich in seiner Beharrungsstellung in relativer Ruhe zur Pendelebene befinde. Tritt jetzt eine plotzliche Belastungsanderung, z. B. eine Entlastung ein, so wird der Regler sich nicht eher in Bewegung setzen, bis die Fliehkraft um den Betrag der konstanten Reibung angewachsen ist, wenn das nicht schon vorher der Fall war. Sobald nun die Bewegung eintritt, ist dieselbe identisch mit der Bewegung des reibungslosen Reglers unter denselben Anfangsbedingungen. Die Identitat reicht aber nur bis zur ersten Bewegungsumkehr, weil dann die Reibungskraft ihr Vorzeichen wechselt. Es dreht sich jetzt alles um den Punkt, wo und wann die Geschwindigkeit dx/dt des Schwungkorpers zum ersten Mal gleich null wird. Geschieht die erste Bewegungsumkehr des Reglers noch vor Erreichung der neuen Beharrungsstellung, so tritt eben das Uberregulieren nicht ein. Geschieht die erste Bewegungsumkehr, die bei genugend groser Reibung nicht stattfindet, gerade in der neuen Gleichgewichtslage, so ist dieselbe mit der Geschwindigkeit null erreicht worden, ein Fall, der fur uns der ideale ware. Es ist dieser Fall nicht nur theoretisch denkbar, sondern auch praktisch erreichbar. Sind jedoch nicht alle fur eine gute Regulierung erforderlichen Bedingungen erfullt, was sehr oft der Fall ist, so tritt das Uberregulieren ein. Der Schwungkorper kommt erst jenseits der neuen Beharrungsstellung zum ersten Mal zur Ruhe, um dann wieder zuruckzuschwingen und so fort. Im Kraftediagramm mus jedenfalls die Kraftkurve von einem zum andern Fliehkraftstrahle aufsteigen, solange die neue Beharrungsstellung noch nicht erreicht ist. Als Beispiel soll eine Eincylinderdampfmaschine dienen, welche vom Verfasser in den Konstruktionsubungen des Geh. Hofrats Prof. L. Lewicki, Dresden, entworfen worden ist. —

Der reduzierte konstante Reibungswiderstand mus so gros sein, das bei einer Bewegungsumkehr des Reglers potentielle Energie nicht mehr vorhanden sein kann. Ist das der Fall, dann wird bei aperiodischer Bewegung (70) eine Umkehr in der Stellbewegung des Reglers uberhaupt nicht zu stande kommen. Ist aber der Ungleichformigkeitsgrad δ 0 des Reglers kleiner als Formel (70) angibt, dann mussen Schwingungen auftreten. Ist nun der reduzierte Reibungswiderstand gerade so gros wie die Kraft P bei der Bewegungsumkehr, dann tritt eine Pause in der Bewegung des Reglers nicht ein; ist aber die Kraft P kleiner als die Reibung, dann mus eine Bewegungspause eintreten, bis die Fliehkraft eine der auseren W-Kurven erreicht hat. Die Grose der Bewegungspause kann nach Formel (47) berechnet werden. Es ist nicht notig, das zur Erzielung einer Schwingungsdampfung alle potentielle Energie bei der Bewegungsumkehr durch die Reibung vernichtet wird; wir wollen es aber als wunschenswert hinstellen, das auch bei grosen Belastungsanderungen von etwa 1/2 der Vollbelastung die Grose des reduzierten Reibungswiderstandes gerade noch hinreicht, um eine potentielle Energie nicht entstehen zu lassen. Die bisher gezeichneten Kraftkurven lehren uns, das die Kraft P bei der ersten Bewegungsumkehr die in der betreffenden Kraftwelle groste Kraft ist.