Genetic and biochemical characterization of D-arabinose dehydrogenase from Neurospora crassa.

D-Arabinose dehydrogenase has been purified to homogeneity from wild-type Neurospora crassa 74-A (FGSC 262) and from two colonial mutants, col-15a (FGSC 1391) and col-16a (FGSC 1349), found to contain more of the enzyme. The enzymes were characterized by measurement of several kinetic and physicochemical parameters. The enzymes were the same in all characteristics studied thus far. Immunological studied performed with enzyme preparations from the three strains showed antigenic identity and indicated that those colonial strains contain more normal enzyme, rather than the usual amount of an altered "improved" enzyme. Quantitation of the enzyme in crude extracts, performed by single radial immunodiffusion, showed that the colonial strains have twice the level of enzyme as the wild-type strain. Genetic characterization, performed by analysis of meiotic products, heterokaryosis, and reversions, indicated that the difference in D-arabinose dehydrogenase activity detected among the three strains is probably determined by one gene. The genetic control, structural or regulatory of this enzyme activity is different from that determining the morphological alterations exhibited by mutant strains carrying the col-15 or col-16 gene.     

Hexokinase-coupled radioassays: Glyceraldehyde-3-phosphate dehydrogenase and enolase

A general method for the assay of enzymes which produce ATP, or are susceptible to be coupled to ATP-producing enzymes, is described. We have applied it to the assay of glyceraldehyde-3-phosphate dehydrogenase and enolase. For these enzymes, the product of the reaction, 1,3-bisphosphoglycerate or phosphoenolpyruvate, were coupled to ADP and either phosphoglycerate kinase or pyruvate kinase, respectively. The ATP formed in both cases is used by hexokinase plus labeled glucose to produce labeled glucose 6-phosphate which is quantitatively separated in small Dowex 1 columns and measured by liquid scintillation spectrometry. The conditions described permitted the detection of 0.1 mU of glyceraldehyde-3-phosphate dehydrogenase or enolase. As a further example of the sensitivity of the radioassay, effluents of a CM-cellulose column charged with an extract prepared from one single frog oocyte were analyzed and shown to contain a single enolase and two glyceraldehyde-3-phosphate dehydrogenase fractions.     

Identification of three genes encoding P(II)-like proteins in Gluconacetobacter diazotrophicus: studies of their role(s) in the control of nitrogen fixation

In our studies on the regulation of nitrogen metabolism in Gluconacetobacter diazotrophicus, an endophytic diazotroph of sugarcane, three glnB-like genes were identified and their role(s) in the control of nitrogen fixation was studied. Sequence analysis revealed that one P(II) protein-encoding gene, glnB, was adjacent to a glnA gene (encoding glutamine synthetase) and that two other P(II) protein-encoding genes, identified as glnK1 and glnK2, were located upstream of amtB1 and amtB2, respectively, genes which in other organisms encode ammonium (or methylammonium) transporters. Single and double mutants and a triple mutant with respect to the three P(II) protein-encoding genes were constructed, and the effects of the mutations on nitrogenase expression and activity in the presence of either ammonium starvation or ammonium sufficiency were studied. Based on the results presented here, it is suggested that none of the three P(II) homologs is required for nif gene expression, that the GlnK2 protein acts primarily as an inhibitor of nif gene expression, and that GlnB and GlnK1 control the expression of nif genes in response to ammonium availability, both directly and by relieving the inhibition by GlnK2. This model includes novel regulatory features of P(II) proteins.     

Propolis from Chilean matorral hives

Viscidone (0.5%), vanillin, 3',4'-(methylendioxy)acetophenone, 3-ethoxy-4-methoxybenzaldehyde, cinnamic acid, 3-methoxy-4-hydroxymethyl ester were isolated from propolis of hives from Cuncumen. This is the first report on propolis composition of an arid and a Mediterranean type climate area.     

Sexual and apomictic reproduction in Hieracium subgenus pilosella are closely interrelated developmental pathways

Seed formation in flowering plants requires meiosis of the megaspore mother cell (MMC) inside the ovule, selection of a megaspore that undergoes mitosis to form an embryo sac, and double fertilization to initiate embryo and endosperm formation. During apomixis, or asexual seed formation, in Hieracium ovules, a somatic aposporous initial (AI) cell divides to form a structurally variable aposporous embryo sac and embryo. This entire process, including endosperm development, is fertilization independent. Introduction of reproductive tissue marker genes into sexual and apomictic Hieracium showed that AI cells do not express a MMC marker. Spatial and temporal gene expression patterns of other introduced genes were conserved commencing with the first nuclear division of the AI cell in apomicts and the mitotic initiation of embryo sac formation in sexual plants. Conservation in expression patterns also occurred during embryo and endosperm development, indicating that sexuality and apomixis are interrelated pathways that share regulatory components. The induction of a modified sexual reproduction program in AI cells may enable the manifestation of apomixis in HIERACIUM:     

An unusual variant of chromosome 16

Summary Two new cases of an unusual chromosome 1y variant, 16p+, in non-related normal carriers are reported.     

Migration pattern suggested by terrestrial proximity as possible origin of wild annual <Emphasis Type="Italic">Helianthus</Emphasis> populations in central Argentina

There is a high interest to understand and recreate the invasive process of successful non-native plant invaders. The genetic tools provide scanty information when the invasion is recent and there is gene flow among the invader and its crop relative. The concern about the government and private companies’ responsibilities in the diffusion process and the risk of occupancy of new areas motivated the interest in two wild annual Helianthus species naturalized in the central agricultural lands of Argentina. We used multivariate techniques and random tests to estimate the successive steps accomplished by the plant invaders across transportation routes, following an environmental and ecological gradient. A minimum connection tree through road distances was created considering dispersal from a unique dispersal point for each species. The proposed tree minimized, at the same time, the environmental and the ecological distances calculated by Euclidean and Gower indexes with abiotic and biotic habitat variables, being significantly different from random (P ≤ 0.05). Our methodology allowed the development of an approach for the best estimation of the invasion route. This could be used to clarify the role of different agents involved in the diffusion process and to develop management strategies to prevent the plant invasion. The migration pattern suggests that after their historical introduction, both wild species moved in successive steps across a biotic and abiotic gradient, aided by anthropogenic activity along the road connection infrastructure. There were no evidences of escapes from sunflower breeding stations.