Al3+-Ca2+ interactions in aluminum rhizotoxicity

Several mineral rhizotoxicities, including those induced by Al³⁺, H⁺, and Na⁺, can be relieved by elevated Ca²⁺ in the rooting medium. This leads to the hypothesis that the toxic cations displace Ca²⁺ from transport channels or surface ligands that must be occupied by Ca²⁺ in order for root elongation to occur. In this study with wheat (Triticum aestivum L.) seedlings, we have determined, in the case of Al³⁺, that (i) Ca²⁺, Mg²⁺, and Sr²⁺ are equally ameliorative, (ii) that root elongation does not increase as Ca²⁺ replaces Mg²⁺ or Sr²⁺ in the rooting media, and (iii) that rhizotoxicity is a function solely of Al³⁺ activity at the root-cell membrane surface as computed by a Gouy-Chapman-Stern model. The rhizotoxicity was indifferent to the computed membrane-surface Ca²⁺ activity. The rhizotoxicity induced by high levels of tris(ethylenediamine)cobaltic ion (TEC³⁺), in contrast to Al³⁺, was specifically relieved by Ca²⁺ at the membrane surface. The rhizotoxicity induced by H⁺ exhibited a weak specific response to Ca²⁺ at the membrane surface. We conclude that the Ca²⁺-displacement hypothesis fails in the case of Al³⁺ rhizotoxicity and that amelioration by cations (including monovalent cations) occurs because of decreased membrane-surface negativity and the consequent decrease in the membrane-surface activity of Al³⁺. However, TEC³⁺, but not Al³⁺, may be toxic because it inhibits Ca²⁺ uptake. The nature of the specific H⁺-Ca²⁺ interaction is uncertain.Abbreviations {Al³⁺ }₀ chemical activity of Al³⁺ at the root-cell membrane surface - {Al³⁺ }_E chemical activity of Al³⁺ in the external rooting medium - E₀ electrical potential at the root-cell membrane surface - HXM²⁺ hexamethonium ion - TEC³⁺ tris(ethylenediamine)cobaltic ion     

Repetitive DNA of grapevine: classes present and sequences suitable for cultivar identification

Summary Repetitive DNA sequences present in the grapevine genome were investigated as probes for distinguishing species and cultivars. Microsatellite sequences, minisatellite sequences, tandemly arrayed genes and highly repetitive grapevine sequences were studied. The relative abundance of microsatellite and minisatellite DNA in the genome varied with the repeat sequence and determined their usefulness in detecting RFLPs. Cloned Vitis ribosomal repeat units were characterised and showed length heterogeneity (9.14–12.15 kb) between and within species. A highly repetitive DNA sequence isolated from V. vinifera was found to be specific only to those species classified as Euvitis. DNA polymorphisms were found between Vitis species and between cultivars of V. vinifera with all classes of repeat DNA sequences studied. DNA sequences suitable for DNA fingerprinting gave genotype-specific patterns for all of the cultivars and species examined. The DNA polymorphisms detected indicates a moderate to high level of heterozygosity in grapevine cultivars.On leave from the Biochemical Research Institute, Nippon Menard Cosmetic Co, Ltd, Ogaki Gifuken, 503 Japan     

Different propensity for spontaneous differentiation of cell clones isolated from the human ovarian surface epithelial cell line HOC-7

Abstract. Limiting dilution culture of cell fractions obtained by discontinuous density gradient centrifugation was used to establish six different cell clones from HOC-7 ovarian adenocarcinoma cells (D1-D3, N1-N3). Clones D1-D3 revealed a phenotype similar to that seen in parental cells exposed to differentiation inducers such as dimethyl sulfoxide (DMSO, 0.8% [v/v]). They were flattened, slowly growing cells (doubling times: 42–46 h). The cells developed long cytoplasmic extensions and adopted a complicated growth pattern. Fixed-cell enzyme-linked immunosorbent assay (ELISA) and Western blotting demonstrated that these cells contained high levels of epidermal growth factor-receptor (EGF-R), carbohydrate antigen 125 (CA 125), fibronectin and desmoplakin, but low levels of myc oncoproteins. However, untreated parental cells and clones N1–N3 were fastgrowing (doubling times: 23–28 h), regularly shaped, polygonal cells ("cobblestone'monolayer) with low levels of EGF-R, CA 125, fibronectin and desmoplakin, but relatively higher amounts of myc oncoproteins. The similarity of the sublines to either untreated or inducertreated parental cells indicated that clones D1–D3 represented spontaneously differentiated HOC-7 cells, whereas clones N1–N3 originated from less-differentiated cells. The features examined in this model cell system proved to be closely related to ovarian cancer cell proliferation and differentiation. The observation of a tumorinherent propensity for spontaneous differentiation suggests that exogenous stimulation of existing differentiation pathways may represent an alternative approach for tackling the problem of growth control and differentiation in malignant tissues.     

Cardiovascular and metabolic responses to noradrenaline in men acclimatized to cold baths

The purpose of this study was to see whether artificial acclimatization to cold would reduce the pressor response to noradrenaline (NA) as natural acclimatization has been shown to do, and whether it would induce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 g·kg^–1·min^–1 (2–23 g·min^–1), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatization was induced by ten daily cold (15°Q baths of 30–60 min followed by rapid rewarming in hot (38–42°C) water, and was confirmed by tests of the subjects responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Acclimatization substantially reduced the pressor response to NA at 0.150 and 0.300 g·kg^–1·min^–1, confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P<0.05 for both changes). Acclimatization did not change the response to NA of heart rate, subjective impressions, skin temperature of finger and toe, pulmonary ventilation, or plasma free fatty acids and ketone bodies. At no time did NA increase oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show that acclimatization to cold reduces sensitivity to the pressor effect of NA but does not induce nonshivering thermogenesis, and that the reduced sensitivity is replaced by a hypersensitivity to NA when acclimatization decays.     

Cholinesterases regulate neurite growth of chick nerve cells in vitro by means of a non-enzymatic mechanism

Cholinesterases present homologies with some cell adhesion molecules; however, it is unclear whether and how they perform adhesive functions. Here, we provide the first direct evidence showing that neurite growth in vitro from various neuronal tissues of the chick embryo can be modified by some, but not all, anticholinesterase agents. By quantifying the neuritic G4 antigen in tectal cell cultures, the effect of anticholinesterases on neurite growth is directly compared with their cholinesterase inhibitory action. BW 284C51 and ethopropazine, inhibiting acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively, strongly decrease neurite growth in a dose-dependent manner. However, echothiophate which inhibits both cholinesterases, does not change neuritic growth. These quantitative data are supplemented by morphological observations in retinal explant cultures grown on striped laminin carpets, viz., defasciculation of neurite bundles by BW 284C51 and Bambuterol occurs, indicating that these drugs disturb adhesive mechanisms. These data strongly suggest that a) cholinesterases can participate in regulating axonal growth, b) both AChE and BChE can perform such a nonsynaptic function, and c) this function is not the result of the enzyme activity per se, since at least one drug was found that inhibits all cholinesterase activities but not neurite growth. Thus, a secondary site on cholinesterase molecules must be responsible for adhesive functions.     

Salt tolerance and methionine biosynthesis in Saccharomyces cerevisiae involve a putative phosphatase gene.

The progressive salinization of irrigated land poses a threat to the future of agriculture in arid regions. The identification of crucial metabolic steps in salt tolerance is important for the understanding of stress physiology and may provide the tools for its genetic engineering. In the yeast Saccharomyces cerevisiae we have isolated a gene, HAL2, which upon increase in gene dosage improves growth under NaCl and LiCl stresses. The HAL2 protein is homologous to inositol phosphatases, enzymes known to be inhibited by lithium salts. Complementation analysis demonstrated that HAL2 is identical to MET22, a gene involved in methionine biosynthesis. Accordingly, methionine supplementation improves the tolerance of yeast to NaCl and LiCl. These results demonstrate an unsuspected interplay between methionine biosynthesis and salt tolerance.     

Synthetic glycosylation of peptides using unprotected saccharide β-glycosylamines

Glycopeptides can be valuable tools in determining the influence of carbohydrate moieties on the intrinsic properties of glycoproteins. However, glycopeptides of sufficient quantity and purity are as yet not readily available from biological sources. The chemical coupling of a -glycosylamino group of an unprotected carbohydrate with an activated aspartic acid residue of an unprotected peptide is a simple method for synthesizing asparagine-linked glycopeptides. In this report we demonstrate that the use of this method is not restricted to -glycosylamines of simple monosaccharides or short aspartic acid-containing pentapeptides. This is illustrated by the syntheses of several glycopentapeptides containingN,N-diacetylchitobiose, a glutamine-linked glycopentapeptide containing a biantennary complex oligosaccharide, and glycosylated variants of two analogs of a polypeptide hormone, atriopeptin, containingN,N-diacetylchitobiose.Abbreviations Ac acetyl - Bzl benzyl - DMF dimethylformamide - Fmoc 9-fluorenylmethoxycarbonyl - Fuc fucose - Gal galactose - GlcNAc N-acetylglucosamine - HBTU O-benzotriazol-1-yl-N,N,N,N-tetramethyluroniumhexa-fluorophosphate - HOBt 1-hydroxybenzotriazole - Man mannose - m/z mass/charge - NMR nuclear magnetic resonance - Xyl xylose - Z benzyloxycarbonyl; unless otherwise specified, amino acids are abbreviated using their one-letter codes.     

Gluconeogenesis from pyruvate in the hyperthermophilic archaeon Pyrococcus furiosus: involvement of reactions of the Embden-Meyerhof pathway

The hyperthermophilic archaeon Pyrococcus furiosus was grown on pyruvate as carbon and energy source. The enzymes involved in gluconeogenesis were investigated. The following findings indicate that glucose-6-phosphate formation from pyruvate involves phosphoenolpyruvate synthetase, enzymes of the Embden-Meyerhof pathway and fructose-1,6-bisphosphate phosphatase.Cell extracts of pyruvate-grown P.furiosus contained the following enzyme activities: phosphoenolpyruvate synthetase (0.025 U/mg, 50 °C), enolase (0.9 U/mg, 80 °C), phosphoglycerate mutase (0.13 U/mg, 55 °C), phosphoglycerate kinase (0.01 U/mg, 50 °C), glyceraldehyde-3-phosphate dehydrogenase reducing either NADP⁺ or NAD⁺ (NADP⁺: 0.019 U/mg, NAD⁺: 0.009 U/mg; 50 °C), triosephosphate isomerase (1.4 U/mg, 50 °C), fructose-1,6-bisphosphate aldolase (0.0045 U/mg, 55 °C), fructose-1,6-bisphosphate phosphatase (0.026 U/mg, 75 °C), and glucose-6-phosphate isomerase (0.22 U/mg, 50 °C). Kinetic properties (V _max values and apparent K _m values) of the enzymes indicate that they operate in the direction of sugar synthesis. The specific enzyme activities of phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase (NADP⁺-reducing) and fructose-1,6-bisphosphate phosphatase in pyruvate-grown P. furiosus were by a factor of 3, 10 and 4, respectively, higher as compared to maltose-grown cells suggesting that these enzymes are induced under conditions of gluconeogenesis. Furthermore, cell extracts contained ferredoxin: NADP⁺ oxidoreductase (0.023 U/mg, 60 °C); phosphoenolpyruvate carboxylase (0.018 U/mg, 50 °C) acts as an anaplerotic enzyme.Thus, in P. furiosus sugar formation from pyruvate involves reactions of the Embden-Meyerhof pathway, whereas sugar degradation to pyruvate proceeds via a modified non-phosphorylated Entner-Doudoroff pathway.     

Demonstration of Z-d(5BrCGAT5BrCG) and B-d(CGCGATCGCG) form crystal structures in DNA-cobalt hexammine complexes by Kr 647.1 nm excitation of Raman spectra.

Cobalt hexammine [Co(NH3)6(3+)] is an efficient DNA complexing agent which significantly perturbs nucleic acid secondary structure. We have employed red excitation (647.1 nm) from a krypton laser to obtain Raman spectra of the highly colored complexes formed between cobalt hexammine and crystals of the DNA oligomers, d(5BrCGAT5BrCG) and d(CGCGATCGCG), both of which incorporate out-of-alternation pyrimidine/purine sequences. The Co(NH3)6(3+) complex of d(5BrCGAT5BrCG) exhibits a typical Z-form Raman signature, similar to that reported previously for the alternating d(CGCGCG) sequence. Comparison of the Raman bands of d(5BrCGAT5BrCG) with those of other oligonucleotide and polynucleotide structures suggests that C3'-endo/syn and C3'-endo/anti thymidines may exhibit distinctive nucleoside conformation markers, and tentative assignments are proposed. The Raman markers for C2'-endo/anti adenosine in this Z-DNA are consistent with those reported previously for B-DNA crystals containing C2'-endo/anti dA. Raman bands of the cobalt hexammine complex of d(CGCGATCGCG) are those of B-DNA, but with significant differences from the previously characterized B-DNA dodecamer, d(CGCAAATTTGCG). The observed differences suggest an unusual deoxyguanosine conformer, possibly related to a previously characterized structural intermediate in the B-->Z transition. The present results show that crystallization of d(CGCGATCGCG) in the presence of cobalt hexammine is not alone sufficient to induce the left-handed Z-DNA conformation. This investigation represents the first application of off-resonance Raman spectroscopy for characterization of highly chromophoric DNA and illustrates the feasibility of the Raman method for investigating other structurally perturbed states of DNA-cobalt hexammine complexes.