On the occurrence of a high content of cytokinins in rice callus tissues

Rice callus tissues contained at least three active cytokinincompounds: zeatin, its riboside and N⁶-(²-isopentenyl) adenosine.These butanol-extractable cytokinins were identified by theirchromatographic mobilities in Sephadex LH-20, paper and gaschromatography. Zeatin, the apparent major cytokinin, was presentat concentrations of 0.7 to 1.0 µg/g fresh tissue and1.3 to 1.7 µg/g fresh tissue in 10^–7 M and 10^–55M 2,4-D callus, respectively. On the basis of these and earlierresults, the induction and growth of rice callus tissue is discussedin relation to the occurrence of cytokinins in the tissue. (Received December 27, 1978; )     

Relationship between hormone content and autonomy in various autonomous tobacco cells cultured in suspension

Various autonomous cultured tobacco cells including crown gallwere examined for their contents of growth regulators by meansof Avena curvature test, cell-division induction test, and tobaccopith callus test. The crown gall cells derived from cv. Hicks produced auxin andcytokinin in the high levels of 300–500 µg IAA equivalentsand 40–80 µg kinetin equivalents per kg, respectively.The major auxin was identified as indole-3-acetic acid basedon mass spectrometry and gas chromatography. These cells alsoproduced methyl indole-3-acetate as a minor component. One ofthe cytokinins was identified as ribosyl-trans-zeatin by meansof both gas chromatography-mass spectrometry and high performanceliquid chromatography. Auxin and cytokinin activities were not detected in the followingthree suspension cultured tobacco cells: cells requiring neithercytokinin nor auxin derived from the callus of N. tabacum cv.Bright Yellow and cells requiring auxin but not cytokinin derivedfrom the calluses of cv. Bright Yellow and cv. Hicks. Theirauxin and cytokinin contents per kg were less than 1 µgIAA equivalent and less than 0.1 µg kinetin equivalent,respectively. The results obtained in this study indicate that enhanced hormonalcontent is not the only reason for autonomous growth. (Received August 16, 1979; )     

Distribution of growth regulators in relation to the light-induced geotropic responsiveness in Zea roots

Growth regulators were measured in extracts from the upper and lower halves of 7-mm apical segments of horizontally oriented, red-light-irradiated and non-irradiated roots of Zea mays L. cv. Golden Cross Bantam 70 which exhibit a georesponse only after an exposure to light. Abscisic acid (ABA) was measured by gas-liquid chromatography, auxin (indole-3-acetic acid, IAA) by the Avena straight-growth assay, and an unidentified growth inhibitor by a Zea root-growth assay. The ratio of ABA in the upper and lower halves was 1.6 in the irradiated roots and 1.0 in the non-irradiated ones. The total amount of ABA after irradiation was increased by a factor of ca. 1.8. The ratio of IAA in the upper and lower halves of irradiated and non-irradiated roots was 1:3.4 and 1:2.9, respectively. The content (or activity) of an unidentified growth inhibitor was highest in the lower halves of horizontally oriented roots which had been irradiated with red light. The unidentified growth inhibitor, rather than IAA or ABA, may be the major factor in the light-induced geotropic responsiveness in Zea roots.     

A self-organizing neural network model for the development of complex cells

On the basis of recent neurophysiological findings on the mammalian visual cortex, a selforganizing neural network model is proposed for the understanding of the development of complex cells. The model is composed of two kinds of connections from LGN cells to a complex cell. One is direct excitatory connections and the other is indirect inhibitory connections via simple cells. Inhibitory synapses between simple cells and complex cells are assumed to be modifiable. The model was simulated on a computer to confirm its behavior.     

Cellular and molecular aspects of immune system aging

Summary We begin with a brief discussion of the importance and advantages of immune studies to the problem of aging. This is followed by a short over-view of immune system aging at the systemic level. The major portion of the article is a review of observations, both at the cellular and molecular level, of changes in aging immune cells, with sections on intercellular communication, membrane phenomena, cyclic nucleotides, and molecular genetic changes. Publication number 043 from Wadsworth GRECC.     

Detection of the changes in protein distribution of rat plasma induced by carbon tetrachloride administration by means of two-dimensional electrophoresis

The changes in rat plasma protein distribution after carbon tetrachloride administration were examined using two-dimensional electrophoresis, utilizing isoelectric focusing in polyacrylamide gel in the first dimension and pore gradient polyacrylamide gel electrophoresis in the second dimension. Drastic changes in amount of protein were observed at more than 20 spot positions including those of transferrin, Gc-globulin and low-density lipoprotein. The time course of the changes was examined, and the most drastic changes were observed at 2 days after carbon tetrachloride administration.     

Replication of Fpoh+ plasmid in mafA mutants of Escherichia coli defective in plasmid maintenance

Summary A class of F plasmids, designated Fpoh ⁺, was previously shown to be able to replicate extrachromosomally on Hfr strains by virtue of carrying the specific site or region poh ⁺ (permissive on Hfr) of the E. coli chromosome (Hiraga, 1975, 1976a). These plasmids were now found to replicate on E. coli mafA mutants (mafA1 and mafA23) that cannot support vegetative replication of F and some other F-like plasmids. The derivatives of Fpoh ⁺ that have lost the poh ⁺ site, on the other hand, failed to replicate on mafA mutants. These mutants harboring Fpoh ⁺ (but not Poh^- derivatives thereof) exhibit abnormal cell division and form elongated cells, presumably due to competition between Fpoh ⁺ and the host chromosome for some factor(s) essential for the initiation of DNA replication of the both replicons. It is tentatively concluded that the poh ⁺ site is required for F plasmids to replicate on mafA mutants as well as on Hfr strains. In view of the fact that the mechanism of inhibition of autonomous F DNA replication in mafA mutants and in Hfr strains are clearly different, the present data seem to provide strong support to the notion that the poh ⁺ region contains the replication origin of the E. coli chromosome.     

Stipe elongation during basidiocarp maturation in Coprinus macrorhizus: Mechanical properties of stipe cell wall

Stipe elongation during basidiocarp maturation in the wild-type,#5026+5132, and the elongationless mutant, NG0398, of Coprinusmacrorhizus was studied, and the following results were obtained.

1. In the wild-type the middle zone of the stipe elongated 8.4times in 15 hr during maturation, while in the mutant it elongatedoaiy 2.2 times.
2. Component cells of the stipe elongated inparallel with thestipe elongation in both the wild-type andthe mutant. The widthof stipe cells was almost constant duringelongation in thewild-type, while it increased 2 times in themutant. Cell volumeincreased ca. 8 times in both stocks.
3. Theosmotic value of stipe cells was almost constant (0.45–0.50M) throughout elongation of both the wild-type and the elongationlessstipes.
4. Mechanical properties of the cell wall were examinedby measuringshrinkage, extensibility and minimum stress-relaxationtime(To) of the stipe during maturation. These parameters weredirectlyproportional to the elongation rate to follow.
5. Whenthe wild-type stipes were incubated in various concentrationsof mannitol solution and then in plain buffer solution, theextensibility of the stipe after the incubation in mannitolsolutions changed proportionally with the stipe length afterthe mannitol treatment, and To with the elongation capacityin plain buffer solution.

(Received March 3, 1977; )     

Effect of auxins on the formation of ubiquinone by tobacco plant cells in suspension culture

Ubiquinone (UQ) formation in BY-2 tobacco cells was especially promoted by a high concentration of 2,4-D. 2,4,5-T, MCP and NAA also promoted UQ formation in these cells. The UQ content in the cells cultured at high concentrations of 2,4-D was higher than that of controls throughout the culture period. The addition of 2,4-D at an early period in cell growth was very effective in promoting UQ formation, but addition at the stationary phase was ineffective. Cell growth was improved by adding phosphate to the medium but UQ content was decreased. UQ content decreased slowly during subculturing, whereas cell growth recovered gradually.