Reorientation of Cortical Microtubules in the Sub-Apical Region during Tuberization in Single-Node Stem Segments of Potato in Culture

The initial events in tuberization were examined in single-nodestem segments of potato, in which the tuberization was easilyregulated in culture. The addition of 8% sucrose to the culturemedium caused the cessation of elongation of lateral shootsand the swelling of the sub-apical region of each shoot. Swellingwas first induced by lateral cell expansion, which was followedby periclinal cell division. The divided cells then expandedlaterally. The alteration in the direction of growth was accompaniedby the reorientation of arrays of cortical microtubules (MTs),which was monitored by immunofluorescence microscopy. Cellsin the sub-apical region of elongating shoots had prominenttransverse arrays of MTs. The MTs in swelling cells were orientedlongitudinally with respect to the axis of the shoot. Finally,the arrays of MTs became completely disorganized. By contrast,the elongation of lateral shoots continued in GA₃-treated segmentsand the cells in the sub-apical region of such shoots retainedconspicuous transverse arrays of MTs during culture, even inthe presence of a high concentration (8%) of sucrose. (Received July 2, 1994; Accepted May 19, 1995)     

Differential Localization of the γ3 and γ12 Subunits of G Proteins in the Mammalian Brain

Abstract: The localization of two forms of the γ subunit of G proteins, γ₃ and γ₁₂, was examined in the mammalian brain. Concentrations of these two γ subunits increased markedly, as did those of glial fibrillary acidic protein, during postnatal development in the rat cerebral cortex. In aged human brains, by contrast, the concentration of γ₃ tended to decrease with age, whereas that of γ₁₂ in the temporal cortex increased slightly. An immunohistochemical study of human brains revealed that γ₃ was abundant in the neuropil, whereas γ₁₂ was localized in glial cells. In the hippocampal formation of aged human brains, levels of γ₁₂-positive cells, as well as levels of glial fibrillary acidic protein- and vimentin-positive astrocytes, increased, in particular in the CA1 subfield and the prosubiculum, in which there was a decrease in the number of pyramidal cells. The appearance of γ₁₂-positive cells associated with the loss of pyramidal cells was also observed in the hippocampus of rats that had been treated with kainic acid. These results indicate that γ₁₂ is strongly expressed in reactive astrocytes. In a study of cultured neural cells, we found that γ₁₂ was predominant in glioma cells, such as C6 and GA-1 cells, in contrast with the specific localization of γ₃ in PC12 pheochromocytoma cells, which are neuron-like cells. Taken together, the results indicate that γ₃ and γ₁₂ are selectively expressed in neuronal and glial cells, respectively, and that concentrations of γ₃ and γ₁₂ in the brain are related to the numbers and/or extent of maturation of these cells.     

Nucleotide sequence of the genes for β and ε subunits of proton-translocating ATPase from Escherichia coli

The 1855-nucleotide long DNA sequence of part of the gene cluster for the proton-translocating ATPase from $\text{E. coli}$ was determined by the method of Maxam-Gilbert. The sequence covers the genes for the β and ε subunits of F₁ along with the flanking region. The amino acid sequence of these subunits deduced from the nucleotide sequence indicates that the β and ε subunits have 459 and 138 amino acids, respectively. The possible secondary structure of the both subunits was estimated from the deduced primary structures. A possible nucleotide binding site in the β subunit is also discussed on the basis of the primary and secondary structures. The codons used in the genes for all the components of F₁F₀ were different in different genes, suggesting that the amount of each subunit in the F₁F₀ is determined to some extent on a translational level.     

Requirement of the core structure of a complex-type glycopeptide for the binding to immobilized lentil- and pea-lectins

Structural requirements for the binding of oligosaccharides and glycopeptides to immobilized lentil- and pea-lectins were investigated by use of radioactively-labeled glycopeptides and oligosaccharides. The results indicate that an intact 2- acetamido-2-deoxy-β-d-glucopyranosyl residue at the reducing end of a complex-type oligosaccharide is essential for high-affinity binding to lentil lectin-Sepharose but not to concanavalin A-Sepharose and that an asparagine residue is required for the binding of a complex-type glycopeptide to pea lectin-Sepharose. In addition, interaction of a complex-type oligosaccharide with lentil lectin-Sepharose was enhanced by exposure of nonreducing, terminal 2-acetamido-2-deoxy-β-d-glucopyranosyl groups, whereas interaction with pea lectin-Sepharose was enhanced only after exposure of nonreducing, terminal α-d-mannopyranosyl groups.     

Antiallergic mechanisms of beta-adrenergic stimulants in rats.

Antiallergic mechanisms of beta-adrenergic stimulants were investigated in rats. Isoproterenol administered intravenously inhibited IgE antibody-mediated homologous passive cutaneous anaphylaxis (PCA) and histamine-induced cutaneous reaction (HCR) elicited at the same time in the same rats significantly. The inhibition of PCA was more potent than that of HCR, suggesting that PCA is inhibited by at least 2 mechanisms. One is the inhibition of vascular permeability increase. In vivo histamine release in the rat peritoneal cavity caused by intravenous antigen was inhibited by the intravenous administration of isoproterenol or salbutamol dose-dependently. On the contrary, when the histamine release in the peritoneal cavity was caused by intraperitoneal antigen, isoproterenol or salbutamol administered simultaneously with antigen failed to inhibit the reaction. Furthermore, antigen-induced histamine release from sensitized peritoneal exudate cells in vitro was not inhibited by isoproterenol or salbutamol. These results indicate that the primary target of beta-adrenergic stimulants is the vascular endothelium, and that the direct inhibition of chemical mediator release from mast cells does not play an important role for the inhibition of PCA and in vivo histamine release in the peritoneal cavity in rats. Beta-adrenergic stimulants therefore may prevent intravenously administered antigen from activating sensitized mast cells through affecting endothelial cells.     

Protective mechanism of sodium molybdate against the acute toxicity of cadmium in rats. II. Prevention of cytoplasmic acidification

In order to clarify the protective mechanism of sodium molybdate against the acute toxicity of cadmium chloride in rat, the effect of in vivo sodium molybdate pretreatment on the cytotoxic action of cadmium in isolated hepatocytes was studied. The cytosolic pH of hepatocytes isolated from untreated rats immediately decreased with incubation in either neutral Hank's balanced salt solution (HBS), pH 7.4, containing 5 µM cadmium chloride minimum or acidic HBS (pH 7.1, 6.8, 6.5, and 6.2). The presence of 5 µM cadmium in HBS adjusted to pH 7.1 aggravated cytosalic acidification induced by the acidic medium alone. Cell viability of hepatocytes incubated in HBS at pH 6.2 was significantly reduced as compared to that of control cells in HBS at pH 7.4, but the presence of cadmium in the acidic HBS had no aggravating action against such a toxic action of the acidic medium although cellular uptake of the metal in the medium increased, as compared to that in HBS at pH 7.4. Molybdenum pretreatment alleviated cytoplasmic acidification induced by the treatment with HBS at pH 7.4 or 7.1 containing cadmium or by extracellular acid load wothout cadmium. This pretreatment also prevented the loss of cell viability induced by the treatment with HBS at pH 6.2 but could not attenuate that when cadmium was present in the medium.These facts suggest that molybdenum pretreatment alleviated the acute toxicity of cadmium in rat by preventing cytoplasmic acidification caused by the harmful metal.     

Angeloylcumambrin-B,an antimicrobial sesquiterpene lactone from Chrysanthemum ornatum var. Spontaneum

Angeloylcumambrin-B, a new antimicrobial guaianolide sesquiterpene lactone, was isolated from Chrysanthemum ornatum and the structure was determined by a combination of chemical and physical methods.     

Distribution of ferritin-conjugated lectins on sialidase-treated membranes of human erythrocytes

The labeling of sialidase-treated, human erythrocyte membranes with ferritin-conjugates of four plant lectinss, concanavalin A, Ricinus communis hemagglutinin, Bauhinia purpurea hemagglutinin and Arachis hypogoea hemagglutinin, is reported. Among these ferritin-conjugated lectins, ferritin-conjugated concanavalin A and ferritin-conjugated R. communis hemagglutinin were found in clusters on the sialidase-treated membranes, whereas ferritin-conjugated B. pupurea hemagglutinin and ferritin-conjugated A. hypogoea hemagglutinin were found in a random distribution on the membranes. Furthermore, when the membranes were labeled with a mixture of concanavalin A and ferritin-conjugated B. purpurea hemagglutinin, ferritin particles were found in clusters, indicating that the membrane receptors for B. purpurea hemagglutinin were forced to move together with those for concanavalin A. A method for thentitative estimation of the clustering of ferritin particles on the membranes was also devised and applied to the labeling of sialidase-treated, human erythrocyte membranes with the above four ferritin-conjugated lectins.