A contractile ring and cortical changes found in the dividing Tetrahymena pyriformis

A contractile ring consisting mainly of microfilaments was found in the fission zone of dividing Tetrahymena pyriformis. Diameters of the microfilaments were widely distributed from 2.5 to 15 nm. Ring-associated structures such as lateral stripes, linkers and beads with siender tails were recognized. Lateral stripes arranged at regular intervals of about 84 nm on some parts of microfilament bundles were found in both tangential and transverse sections, suggesting that they correspond to bands fastening the contractile ring microfilaments. Linkers that connect individual lateral stripes to the epiplasmic layer were present. Beads or beads with slender tails were found to be arranged on some microfilaments.The results of the present paper also indicate that drastic morphological changes occur in the cortex of the fission zone, especially in the epiplasmic layer, accompanying contraction of the division furrow. The epiplasmic layer which was proved to be a compact filamentous network in this study has been known to exist at the periphery of cytoplasm in immediate contact with one of the cell surface membranes, the inner alveolar membrane; however, in the fission zone of the dividing ceil, it was frequently separated from the membrane and subsided into the cytoplasm. The subsided epiplasmic layer was then loosened and dispersed. The subsidence of the epipiasmic layer appears to be caused by the force generated by the contraction of the contractile ring and transmitted with the linkers to the epiplasmic layer. The changes observed in the epiplasmic layer are presumably indispensable for the rigid cortical layer contraction involved in cytokinesis of Tetrahymena.     

Regulatory mechanism of reagin production in mice at the T cell level. I. Suggestive evidence for the generation of class specific PPD-reactive helper T cell population in Mycobacterium-primed cells.

Helper T cell activities specific for purified protein derivative (PPD) generated by immunization with Mycobacterium tuberculosis (Tbc) or PPD were investigated concerning adoptive IgE and IgG antibody responses. It is interesting that preferential triggering activity of IgG antibody response was observed when PPD-reactive cells from mice immunized with Tbc were used as a helper cell source. The selective triggering of IgG B cells by Tbc-primed cells was consistently observed using DNP-primed B cell populations from mice immunized with DNP-carrier conjugate in either ICFA or alum. T cell dependency of helper activity was demonstrated by the fact that treatment of Tbc-primed cells with anti-Thy 1 antiserum plus complement abolished their helper activity. We also demonstrated that purified T cell populations selectively triggerred IgG B cells. Selective triggering of IgG B lymphocytes by Tbc-primed T cells may not be due to the influence of suppressor T cells supposedly present in Tbc-primed cells since this selectivity was not affected by X-irradiation of Tbc-primed T cell populations which may inactivate suppressor T cells. Furthermore, passive transfer of Tbc-primed cells into normal recipient mice, the condition which may detect the suppressor T cell effect much more sensitively in IgE production, or preimmunization with Tbc 2 weeks before, did not suppress primary anti-DNP IgE antibody response to DNP-PPD. Thus, the observations presented here are favorable to the concept of the presence of IgG class-specific helper T lymphocytes. Furthermore, PPD-reactive T cells from mice immunized with PPD itself exerted their helper function for triggering B cells of both IgE and IgG classes. This may also indicate that some of the components associated with Tbc other than PPD might negatively affect the development of PPD-reactive helper T cells specific to the IgE class. The generation of such IgG-specific T cell activity in the presence of Tbc will be discussed in the light of the T cell population involved in the regulation of antibody responses of different immunoglobulin classes.     

The synthesis of 1,6-anhydro-β-d-glucopyranose and d-glucosyl oligosaccharides from maltose by a fungal glucosyltransferase

The formation of 1,6-anhydro-β-d-glucopyranose and several d-glucosyl oligosaccharides has been observed during the action of a purified, fungal glucosyltransferase (EC 2.4.1.24) on maltose. Such products are synthesized by a transglucosylation mechanism involving the formation of a d-glucosyl-enzyme complex and the displacement of the d-glucosyl group by appropriate acceptor-substrates. The formation of the 1,6-anhydro bond is a novel type of transfer reaction and occurs by displacement of the enzyme from the d-glucosyl-enzyme complex by the proton of the primary hydroxyl group of the same glucosyl group. This reaction is characterized by inversion of configuration at the position of glucosidic bond-cleavage of the substrate. Synthesis of the d-glucosyl oligosaccharides occurs by displacement of the d-glucosyl groups from the enzyme by suitable acceptor-substrates. In these cases, the reactions are characterized by retention of configuration of the d-glucosidic bonds of the substrate. The list of oligosaccharides produced from maltose includes nigerose, kojibiose, isomaltose, maltotriose, panose, isomaltotriose, and 6-O-d-glucosyl-panose. The identity of these compounds has been established by methylation analysis and enzymic hydrolysis. d-Glucose is also a product of the reaction and arises from both the reducing and the non-reducing groups of maltose.     

Plant growth-promoting activities of alkoxycarbonylisoureas in relation to their chemical structures

A number of alkoxycarbonylisourea derivatives were synthesized and their plant growth-promoting activities examined by the rice (Oryza sativa) seedling test. Isourea compounds with an appropriate substituent such as a halogen atom or a methyl, ethyl or methoxy group at the para-position on a benzene ring in 1-alkoxycarbonyl-2-alkyl-3-phenylcarbamoylisoureas promoted the growth of rice seedlings and acted as a highly active gibberellic acid-synergist when used in combination with gibberellic acid. The common structural requirements of isourea derivatives applied well for a growth promoter and a gibberellic acid-synergist.     

Regulation of lettuce hypocotyl elongation by gibberellic acid. Correlation between cell elongation, stress-relaxation properties of the cell wall and wall polysaccharide content

Lettuce hypocotyl elongation caused by gibberellic acid wasstrongly inhibited by coumarin and dichlobenil, known inhibitorsof cellulose biosyndiesis. Stress-relaxation analysis of thecell wall revealed that gibberellic acid induces a decreasein both minimum relaxation time (To) and relaxation rate (b)and an increase in maximum relaxation time (Tm), when gibberellicacid stimulates hypocotyl elongation. Both coumarin and dichlobenilnullified the effect of gibberellic acid on changes in To, Tmand b values. The content of pectic, hemicellulosic and cellulosic substancesin the cell wall increased per hypocotyl but decreased per unithypocotyl length, in response to gibberellic acid treatment.Particularly, gibberellic acid caused a substantial increasein cellulose content per hypocotyl but a decrease per unit length.A good correlation existed between the decrease in To and thedecrease in hemicellulose content per unit lengdi of the cellwall. The increase in Tm was correlated with the decrease incellulose content per unit length of the cell wall. The decreasein b was correlated with the decrease in the content of bothcellulose and hemicellulose per unit length. Based on these results, we discuss the role of polysaccharidemetabolism of the cell wall in gibberellic acid-induced lettucehypocotyl elongation and the nature of gibberellic acid-inducedbiochemical modifications of the cell wall, which are representedby changes in stress-relaxation properties of the cell wall. ¹Present address: Department of Anatomy, Aichi Medical University,Nagakutecho, Aichigun, Aichi 480-11, Japan. (Received September 22, 1975; )     

The location of ribosomal cistrons (rDNA) in chromosomes of the rat

In situ hybridization of ³H-labelled ribosomal RNA to the chromosomes of rat bone marrow cells revealed that clusters of ribosomal cistrons (rDNA) are located in the secondary constrictions of chromosomes No. 3 and 12 and near the centromere of chromosome No. 11, both associated with the late DNA-replicating regions. They were not found in Nos. 1, 2, 13, 19, 20, and the Y chromosome.     

Two new iridoid glucosides from Ixora chinensis

From leaves and twigs of Ixora chinensis, two new iridoid glucosides, ixoroside (1) and ixoside (7,8-dehydroforsythide) (2) along with known geniposidic acid (3) have been isolated and their structures have been established.     

Proline in the Osmoregulation of Brevibacterium lactofermentum

Osmoregulation in Brevibacterium lactofermentum was studied. Proline was accumulated up to approximately 35mg/g dry cell weight in the cells of a wild strain of the bacterium grown under osmotic stress. The osmotic tolerance of a proline auxotroph mutant obtained from the bacterium was lower than that in the wild strain. The activity of pyrroline-5-carboxylate reductase, one of the enzymes in the proline biosynthetic pathway, increased about 3-fold when the cells of B. lactofermentum were grown under osmotic stress. These data indicated that proline is important in osmoregulation in the bacterium.