Suppression of fungal β-glucan-induced plant defence in soybean (Glycine max L.) by cyclic 1,3-1,6-β-glucans from the symbiont Bradyrhizobium japonicum

The production of antimicrobial phytoalexins is one of the best-known inducible defence responses following microbial infection of plants or treatment with elicitors. In the legume soybean (Glycine max L.), 1,3-1,6--glucans derived from the fungal pathogen Phytophthora sojae have been identified as potent elicitors of the synthesis of the phytoalexin, glyceollin. Recently it has been reported that during symbiotic interaction between soybean and the nitrogen-fixing bacterium Bradyrhizobium japonicum USDA 110 the bacteria synthesize cyclic 1,3-1,6--glucans. Here we demonstrate that both the fungal and the bacterial -glucans are ligands of -glucan-binding sites which are putative receptors for the elicitor signal compounds in soybean roots. Whereas the fungal -glucans stimulate phytoalexin synthesis at low concentrations, the bacterial cyclic 1,3-1,6--glucans appear to be inactive even at relatively high concentrations. Competition studies indicate that increasing concentrations of the bacterial 1,3-1,6--glucans progressively inhibit stimulation of phytoalexin synthesis in a bioassay induced by the fungal 1,3-1,6--glucans. Another type of cyclic -glucan, a 1,2--glucan from Rhizobium meliloti, that does not nodulate on soybean, seems to be inactive as elicitor and as ligand of the -glucan-binding sites. These results may indicate a novel mechanism for a successful plant-symbiont interaction by suppressing the plant's defence response.Abbreviations HG-APEA 1-[2-(4-aminophenyl)ethyl]amino-l-[hexaglucosyl]deoxyglucitol - HG-AzPEA l-[2-(4-azidophenyl)-ethyl]amino-l-[hexaglucosyl]deoxyglucitol - IC₅₀ concentration for half-maximal displacement We thank Ines Arlt for excellent technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 369), the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, Fonds der Chemischen Industrie (J.E.), and USDA CSRS NRI Competitive Research grant 93373059233 (A.A.B.).     

Arachidonic acid-induced hypersensitive cell death as an assay of downy mildew resistance in pearl millet

Arachidonic acid (AA) induces hypersensitive response (HR) on coleoptile/root regions of two-day-old pearl millet seedlings. The response is comparable to the HR induced by the downy mildew pathogen, Sclerospora graminicola. A time gap in the appearance of cell necrosis among genotypes of pearl millet was related to the degree of resistance to downy mildew. Based on the time required for the development of necrotic spots induced by AA, the pearl millet genotypes were categorised as highly resistant/resistant (HR in 3–6 h), susceptible (HR in 7–12 h) and highly susceptible (HR in 13 h and above). The percentage disease incidence in each genotype was compared with the time required for the development of AA-induced HR. The appearance of hypersensitive cell necrosis was rapid in genotypes having high resistance to downy mildew and was slow in genotypes with high susceptibility. This simple method of screening various pearl millet genotypes in the absence of the pathogen aids in identifying the downy mildew resistant/susceptible host cultivars without the risk of introducing the virulent race of the pathogen.     

膜融合的分子机制:线粒体呼吸链不同偶联部位质子泵活性与膜融合程度之间的定量相关性(英文)

我们测定了鼠肝线粒体呼吸链不同偶联部位的质子系活性并通过荧光能量共振转移 法分析了鼠肝线粒体膜与脂质体（二油酰磷脂乙醇胺／心磷脂＝８／２）的膜融合程度。根据测量呼吸链第一段及第二段偶联部位的Ｈ＋／偶联部位的化学计量比值,观察到线粒体呼吸链质子泵的质子（Ｈ＋）泵活性及 Ｈ＋泵出量与膜融合程度呈现线性的定量相关性。这些实验结果进一步支持了我们提出的质子泵诱导膜融合的理论模型（刘树森等,１９８７、１９８９）。     

人鼻咽癌细胞基因组中瘤基因Ha－ras－1的Dnase Ⅰ超敏感位点的初步研究

ＤＮａｓｅⅠ超敏感位点的研究能够发现潜在的调控基因转录活化的位点,比较正常人外周血有核细胞,淋巴瘤细胞株Ｐ３ＨＲ１和人鼻咽癌低分化磷癌细胞株ＨＯｎＥ１和ＨＮＥ２中Ｈａ－ｒａｓ－１瘤基因的ＤＮａｓｅⅠ超敏感位点发现,只有ＨＯＮＥ１和ＨＮＥ２细胞基因组中存在一个ＤＮａｓｅⅠ超敏感位点,位于第一个外显子上游０．３７ｋｂ处,上述结果提示正常白细胞和Ｐ３ＨＲ１细胞中Ｈａ－ｒａｓ－１基因处于失活状态,而在鼻咽癌细胞基因组中则处于活化状态,它的活化可能与０．３７ｋｂ处的ＤＮＡ序列有密切的关系。     

Nucleotide Sequence Surrounding the Locus Marker D21S246 on Human Chromosome 21

Most ofthe human Not I linking clones identified to date areconsidered to be derived from CpG islands because ofthe recognitionsequence of this enzyme, and CpG islands have been reportedto be located around the 5' regions of genes. As a pilot study,we determined the complete nucleotide sequence (41,924 bp) ofa human cosmid clone (LL21NC02Q7A10) containing the marker D21S246originating from a Not I linking clone. As a result of sequenceanalysis, we successfully mapped and revealed the genomic genestructure for KIAA0002 previously reported as a cDNA clone.This gene consists of 15 exons and was shown to exist at theD21S246 locus on human chromosome 21q21.3–q22.1. Theseresults demonstrated that genomic marker-anchored DNA sequencingis a useful approach for the human genome project.     

Restriction endonucleases from Selenomonas ruminantium which recognize and cleave 5′-AT/TAAT-3′

Two natural isolates from fallow-deer rumen identified as Selenomonas ruminantium were found to produce a restriction endonuclease which we called Sru4DI. This enzyme was isolated from cell extracts by phosphocellulose chromatography. Analysis of the Sru4DI recognition site showed that Sru4DI recognizes the hexanucleotide sequence 5-AT/TAAT-3 generating 5 dinucleotide protruding ends upon cleavage and thus is a true isoschizomer of VspI, a restriction enzyme isolated from Vibrio sp.     

Biochemical genetics of methylglyoxal dehydrogenases in the laboratory rat (Rattus norvegicus)

A genetic locus controlling the electrophoretic mobility of a methylglyoxal dehydrogenase (EC 1.2.1.23) in the rat is described. The locus, designatedMgd1, is expressed in liver and kidney. Inbred rat strains have fixed either alleleMgd1 ^a or alleleMgd1 ^b . Codominant expression is observed in heterozygotes, providing evidence for a tetrameric enzyme structure. Backcross progenies showed the expected 1:1 segregation ratio, and there is evidence thatMgd1 is linked toPep3 andFh1 on chromosome 13. There is also evidence for two additional methylglyoxal dehydrogenases:Mgd2, present in liver and kidney, andMgd3, present only in heart.Supported by the Deutsche Forschungsgemeinschaft (Grant Be 352/18-1).     

Chemically modified cardiac Na+ channels and their sensitivity to antiarrhythmics: Is there a hidden drug receptor?

Elementary Na⁺ currents were recorded at 19°C in inside-out patches from cultured neonatal rat cardiocytes. In analyzing the sensitivity of chemically modified Na⁺ channels to several class 1 antiarrhythmic drugs, the hypothesis was tested that removal of Na⁺ inactivation may be accompanied by a distinct responsiveness to these drugs, open channel blockade.Iodate-modified and trypsin-modified cardiac Na⁺ channels are noninactivating but strikingly differ from each other by their open state kinetics, a O₁–O₂ reaction (_open(1) 1.4±0.3 msec; _open(2) 5.4±1.1 msec; at –40 mV) in the former and a single open state (_{open 3.0±0.5} msec; at –40 mV) in the latter. Lidocaine (150 mol/liter) like propafenone (10 mol/liter), diprafenone (10 mol/liter) and quinidine (20 mol/liter) in cytoplasmic concentrations effective to depress NP _o significantly can interact with both types of noninactivating Na⁺ channels to reduce the dwell time in the conducting configuration. lodate-modified Na⁺ channels became drug sensitive during the O₂ state. At –40 mV, for example, lidocaine reduced _open(2) to 62±5% of the control without detectable changes in _open(1). No evidence could be obtained that these inhibitory molecules would flicker-block the open Na⁺ pore. Drug-induced shortening of the open state, thus, is indicative for a distinct mode of drug action, namely interference with the gating process. Lidocaine proved less effective to reduce _open(2) when compared with the action of diprafenone. Both drugs apparently interacted with individual association rate constants, a_lidocaine was 0.64×10⁶ mol^–1 sec^–1 and a_diprafenone 13.6×10⁶ mol^–1 sec^–1. Trypsin-modified Na⁺ channels also appear capable of discriminating among these antiarrhythmics, the ratio a_diprafenone/a_lidocaine even exceeded the value in iodate-modified Na⁺ channels. Obviously, this antiarrhythmic drug interaction with chemically modified Na⁺ channels is receptor mediated: drug occupation of such a hypothetical hidden receptor that is not available in normal Na⁺ channels may facilitate the exit from the open state.This work was supported by a grant of the Deutsche Forschungsgemeinschaft (Ko 778/2-4), Bonn.