应用电子探针对植物根际和根内营养元素微区分布的探讨

用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。     

Mitotic gene conversion, reciprocal recombination and gene replacement at the benA, beta-tubulin, locus of Aspergillus nidulans

Summary We have developed a procedure for determining the rates of mitotic recombination of an interrupted duplication created by integration of transforming plasmid sequences at the benA, beta-tubulin, locus of Aspergillus nidulans. Transformation of a strain carrying a benomyl-resistant benA allele with plasmid AIpGM4, which carries the wild-type benA allele and the pyr4 (orotidine-5-phosphate decarboxylase) gene of Neurospora crassa, creates an interrupted duplication with plasmid sequences flanked by two benA alleles, one wild type and one benomyl resdistant. Such transformants will not grow in the presence of high levels of benomyl. Mitotic recombination causes the loss of the wild-type benA allele or conversion of the wild-type to the mutant allele resulting in nuclei carrying only the benomylresistant allele. Conidia containing such nuclei can be selected on media with high benomyl allowing easy quantitation of mitotic recombination. We found that the rate of recombination giving rise to benomyl-resistant conidia was 4.6×10^-4. Reciprocal recombination leading to benomyl-resistant conidia lacking plasmid sequences occurred at a rate of 2.0×10^-4 and gene conversion leading to benomylresistant conidia occurred at a rate of 2.6×10^-4. We selected for reciprocal recombination leading to loss of pyr4 sequences on 5-fluoro-orotic acid and used this selection for two-step gene replacement of a mutant benA allele with the wild-type allele.     

黑腐皮壳属一新种

本文报道发生于我国沈阳地区落叶松枝上的一个新种——大孢黑腐皮壳(Valsa macro-spora sp.nov.)。新种的子囊孢子在15μm以上,属于大型种。其形态特征有汉文和拉丁文描述及其培养性状的记述。     

EVIDENCE FOR CALCIUM-SENSITIVE COMPONENT IN BRAIN ACTOMYOSIN-LIKE PROTEIN (NEUROSTENIN)

Abstract— The isolation of brain actomyosin-like protein (neurostenin) with a Ca²⁺ -sensitive component is described. The addition of 1 m m EGTA results in approximately 50 per cent reduction in MgATPase activity. The inhibition can be released by a free Ca²⁺ concentration of 10⁻⁶ m . Dialysis of the protein complex against low ionic strength medium followed by centrifugation results in a loss of Ca²⁺ sensitivity in the pelleted protein. Ca²⁺ sensitivity can be restored by reprecipitating this desensitized complex in the presence of the 70.000 g supernatant. The protection of sulphhydryl groups during desensitization and reconstitution procedures is essential. This Ca²⁺ regulatory property is similar, in these respects, to other actomyosin-like proteins.     

Soluble Spiroperidol Binding Factors from Bovine Caudate Nucleus

Several properties of soluble spiroperidol binding factors separated from bovine caudate nucleus have been investigated by a previously unreported procedure. Data consistent with high particle weight and rapid binding equilibration are reported for high-affinity (+)butaclamol-sensitive components of a digitonin extract. A slower sedimenting component is found that also exhibits high affinity for spiroperidol but is not sensitive to (+)butaclamol. Centrifugation of a caudate nucleus homogenate yields a supernatant that appears to contain a component that exhibits spiroperidol binding that is more sensitive to displacement by (-) than by (+)butaclamol. The procedure used effects rapid separation of bound from unbound tritiated ligand on short columns of Sephadex G-15 followed by extrusion and sectioning of the Sephadex. The radioactivity remaining with each section is determined. The procedure is very rapid; the addition of active phases or the changing of the ionic environment, which may disturb the equilibrium, is avoided; and recovery of the protein free of bound ligand is easily affected.     

Molecular genetic analysis reveals that a nonribosomal peptide synthetase-like (NRPS-like) gene in Aspergillus nidulans is responsible for microperfuranone biosynthesis

Genome sequencing of Aspergillus species including Aspergillus nidulans has revealed that there are far more secondary metabolite biosynthetic gene clusters than secondary metabolites isolated from these organisms. This implies that these organisms can produce additional secondary metabolites, which have not yet been elucidated. The A. nidulans genome contains 12 nonribosomal peptide synthetase (NRPS), one hybrid polyketide synthase/NRPS, and 14 NRPS-like genes. The only NRPS-like gene in A. nidulans with a known product is tdiA, which is involved in terrequinone A biosynthesis. To attempt to identify the products of these NRPS-like genes, we replaced the native promoters of the NRPS-like genes with the inducible alcohol dehydrogenase (alcA) promoter. Our results demonstrated that induction of the single NRPS-like gene AN3396.4 led to the enhanced production of microperfuranone. Furthermore, heterologous expression of AN3396.4 in Aspergillus niger confirmed that only one NRPS-like gene, AN3396.4, is necessary for the production of microperfuranone.     

A versatile and efficient gene-targeting system for Aspergillus nidulans

Aspergillus nidulans is an important experimental organism, and it is a model organism for the genus Aspergillus that includes serious pathogens as well as commercially important organisms. Gene targeting by homologous recombination during transformation is possible in A. nidulans, but the frequency of correct gene targeting is variable and often low. We have identified the A. nidulans homolog (nkuA) of the human KU70 gene that is essential for nonhomologous end joining of DNA in double-strand break repair. Deletion of nkuA (nkuA delta) greatly reduces the frequency of nonhomologous integration of transforming DNA fragments, leading to dramatically improved gene targeting. We have also developed heterologous markers that are selectable in A. nidulans but do not direct integration at any site in the A. nidulans genome. In combination, nkuA delta and the heterologous selectable markers make up a very efficient gene-targeting system. In experiments involving scores of genes, 90% or more of the transformants carried a single insertion of the transforming DNA at the correct site. The system works with linear and circular transforming molecules and it works for tagging genes with fluorescent moieties, replacing genes, and replacing promoters. This system is efficient enough to make genomewide gene-targeting projects feasible.     

METABOLISM OF [14C]LEUCINE AND [14C]ACETATE IN SENSORIMOTOR CORTEX, THALAMUS, CAUDATE NUCLEUS AND CEREBELLUM OF THE CAT

Abstract— —In the head of the caudate nucleus, the relative specific activity of glutamine (glutamic acid specific activity = 1) was less than 1 with intravenous [¹⁴C]leucine as the tracer metabolite. This is in contrast to observations made in other brain areas (cortex, hippocampus, thalamus, pons, and medulla) where the relative specific activity of glutamine was greater than 1. This is also in contrast to findings when [l-¹⁴C]acetate was utilized as the tracer; under these conditions, in all brain areas, including the head of the caudate nucleus, the relative specific activity of glutamine was greater than 1. It is inferred that the differences in metabolism of [¹⁴C]leucine and [¹⁴C]acetate in the head of the caudate from that in other brain areas reflect differences in compartmentation of the glutamate-glutamine system.     

A colorimetric assay for determination of cell viability in algal cultures

In this work, we propose the determination of cell viability in algal cultures by using a colorimetric assay widely used for estimation of cell proliferation in animal cell cultures. The method is based on in vivo reduction by metabolically active cells of a tetrazolium compound (MTS=3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenil)-2H-tetrazolium, inner salt) to a colored formazan, with maximal absorbance at 490 nm, that is released to the culture medium. For this purpose, we have tested two microalgae with high commercial value (Dunaliella and Spirulina) and two seaweeds with different morphology (Ulva and Gracilaria). Color development in this assay is directly proportional to the number of viable cells, to the incubation time in the presence of the assay solution, and to the incubation temperature. A direct significant correlation was found between algal photosynthesis rate and color development in all species used through this work. Moreover, the intensity of absorbance at 490 nm was significantly lower in stressed cells (e.g. in nutrient-limited cultures, in the presence of toxic substances, and in osmotically-stressed cultures). We conclude that cell viability of algal cultures can be rapidly and easily estimated through colorimetric determination of the reduction of MTS to formazan.