Direct Evidence for Changes in the Resistance of Legume Root Nodules to O2 Diffusion

Indirect evidence suggests that legumes can adjust rapidly theresistance of their root nodules to O₂ diffusion. Here we describeexperiments using O₂ specific micro-electrodes and dark fieldmicroscopy to study directly the operation of this diffusionbarrier. The O₂ concentration sensed by the electrode decreasedsharply in the region of the inner cortex and was less than1.0 mmol m^–3 throughout the infected tissue in nodulesof both pea (Pisum sativum) and french bean (Phaseolus vulgaris).In a number of experiments the ambient O₂ concentration wasincreased to 40% while the electrode tip was just inside theinner cortex. In 13 out of 21 cases the O₂ concentration atthis position either remained low and unchanged or increasedirreversibly to near ambient values. In the remaining casesthe O₂ concentration increased after 1 to 2.5 min and then decreasedto its former value. These results are ascribed to an increasein resistance of the barrier in response to increased O₂ fluxinto the nodule. It was shown microscopically that air spacesboth at the boundary between the infected zone and the innercortex, and within the infected zone started to disappear 3min after nodules were exposed to high ambient O₂ concentrationsand had disappeared completely after 8 min. These spaces werenot changed by exposure of the nodule for 10 min to either N₂or air. Key words: Oxygen, root nodules, air spaces     

Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Regulation of mammary epithelial cell function: a role for stromal and basement membrane matrices

Summary Interactions between epithelial cells and their environment are critical for normal function. Mammary epithelial cells require hormonal and extracellular matrix (ECM) signalling for the expression of tissue specific characteristics. With regard to ECM, cultured mammary epithelial cells synthesize and secrete milk proteins on stromal collagen I matrices. The onset of function coincides both with morphogenesis of a polarized epithelium and with deposition of basement membrane ECM basal to the cell layer. Mammary specific morphogenesis and biochemical differentiation is induced if mammary cells are cultured directly on exogenous basement membrane (EHS). Thus ECM may effect function by the concerted effect of permissivity for cell shape changes and the direct biochemical signalling of basement membrane molecules.A model is discussed where initial ECM control of mammary epithelial cell function originates in the interstitial matrix of stroma and subsequently transfers to the basement membrane when the epithelial cells have accumulated and deposited an organized basement membrane matrix.Dedicated to Professor Stuart Patton on the occasion of his 70th birthday.     

S49 lymphoma wild type and variant clones contain normal calcium dependent regulator.

Calcium dependent regulator is present in wild-type S49 lymphoma cells, in the variant that is deficient in adenylate cyclase activity (AC-), and in the uncoupled variant (UNC). The electrophoretic mobility and the ability to stimulate cyclic nucleotide phosphodiesterase of the calcium dependent regulator from each of these three clones are indistinguishable from those of the modulator protein isolated from bovine brain. Calcium dependent regulator does not appear to be involved in the defect responsible for the UNC or AC- variants.     

Studies on 125I-labeled proteins in rat plasma using an air-driven ultracentrifuge: protein-protein interactions and nonideality

The molecular weights of a number of ¹²⁵I-labeled plasma proteins have been determined from an analysis of their sedimentation equilibrium behavior in an air-driven ultracentrifuge. The values obtained agree well with results obtained by other methods. Molecular weights obtained for ¹²⁵I-labeled bovine serum albumin and the rat serum proteins albumin, α₁-acid glycoprotein, and major acute-phase α₁-protein were unaffected by the addition of 7% rat plasma. Direct evidence for protein-protein interactions was obtained for mixtures of ¹²⁵I-labeled rat α₁-acid glycoprotein and the plant lectin concanavalin A and for mixtures of ¹²⁵I-labeled protein A from Staphylococcus aureus and 7% rat plasma. Interactions of a different type were observed when the sedimentation equilibrium profiles of ¹²⁵I-labeled proteins were determined in concentrated solutions of other proteins. Under these conditions the effects of molecular exclusion or nonideality became significant and low estimates were obtained for the molecular weights of the labeled proteins. Analysis of the data obtained for ¹²⁵I-labeled bovine serum albumin in concentrated solutions of bovine serum albumin (20–80 mg/ ml) yielded nonideality coefficients in good agreement with literature values. Analysis of the behavior of ¹²⁵I-labeled rat serum albumin, transferrin, and α₁-acid glycoprotein yielded nonideality coefficients and hence activities of these proteins in undiluted rat plasma.     

Ca2+ -Dependent Release from Rat Brain of Cannabinoid Receptor Binding Activity

As a result of the identification, pharmacological characterization, and localization of the cannabinoid receptor in the CNS, the existence of an endogenous ligand for this receptor can be hypothesized. Following the premise that such a substance could have the properties of a neuromodulator being stored in intracellular vesicles, we tested the ability of increased intracellular Ca2+ levels to stimulate release. We demonstrate here that the Ca2+ ionophore A23187 can induce release of cannabinoid-like binding activity in the presence but not in the absence of Ca2+. The effect of A23187 was maximal at 1.2 microM, consistent with vesicular release. It was necessary to increase the concentration of extracellular free Ca2+ to greater than 60 nM to evoke release. The released cannabinoid-like binding activity displaced [3H]CP-55940 binding to cannabinoid receptors in rat synaptosomal membranes in a concentration-dependent manner. This is the first report of a substance present endogenously in brain that can be released in a Ca(2+)-dependent manner and that binds to the cannabinoid receptor.     

Hereditary spherocytosis of man. Altered binding of cytoskeletal components to the erythrocyte membrane

The endogenous respiration of the rumen ciliate Dasytricha ruminantium maintained under an O2 tension of 2kPa (approximately 0.02 atm) was partially inhibited by KCN (40% inhibition) and NaN3 (58% inhibition). The organisms lack cytochromes, and sensitivity of respiration to KCN, NaN3, chloroquine and quercetin suggest that the operation of flavoprotein-iron-sulphur-mediated electron transport. As in Tritrichomonas foetus, hydrogenosomal respiration can be stimulated by the addition of CoA in the presence of 0.025% Triton X-100; stimulation by ADP was not detected. Stimulation of pyruvate-supported O2 uptake by Pi suggests that acetate is produced via acetyl phosphate.     

Soluble and membrane-bound aspartate-binding activities in Salmonella typhimurium.

The specificities of the soluble and membrane aspartate-binding activities were compared with each other and with the specificity of aspartate chemotaxis and were found to be distinct. The soluble aspartate-binding protein was purified to homogeneity and had a molecular weight of 30,000. The dissociation constant was 10(-6) M for aspartate, and the protein bound glutamate, cysteic acid, and 2-amino-3-phosphonopropionate. Aspartate transport was inhibited by cysteic acid.