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  • 1
    ISSN: 1432-2048
    Keywords: Circadian rhythms ; Electric potential ; Leaf movements ; Oscillators ; Pulvini ; Samanea ; Transport (ions, sucrose)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Measurements with microelectrodes implanted into Samanea saman (Jacq.) Merrill leaf pulvini showed that membrane potentials were rhythmically sensitive to the application of sucrose. The magnitude of the electrical depolarizations induced by sucrose were dependent on the concentration of H+ in the medium, yet changes in [H+] alone did not greatly affect the potential. During sucrose-induced electrical depolarization, there was a slight increase in the pH of the bathing medium; both effects were abolished by high levels of K+, Na+ or Ca2+ in the medium. These observations indicate that H+ enter the cells by some cooperative action with sucrose. A model of H+-substrate cotransport is proposed in which a sugar carrier in the membrane is made more permeable by the attachment of a proton. The rhythmic nature of this proposed cotransport may be related to circadian leaf-movements in this plant.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Planta 139 (1978), S. 155-158 
    ISSN: 1432-2048
    Keywords: Avena ; Cell-wall regeneration ; Electrical potential ; Nicotiana ; Protoplast culture ; Turgor pressure ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Four independent kinds of observations indicate that the cell wall regenerated by oat (Avena sativa L.) and corn (Zea mays L.) protoplasts in culture is less well developed than that regenerated by tobacco (Nicotiana tabacum L.) protoplasts. Following wall regeneration the cereal protoplasts remained susceptible to osmotic shock upon transfer to water, showed great enlargement, stained poorly with calcofluor white, and maintained a positive internal electrical potential. The development of a negative membrane potential by tobacco protoplasts in culture often occurred simultaneously with the onset of cell division. Since division was observed only in protoplasts which had regenerated good cell walls and had re-established negative membrane potentials it is suggested that culture conditions which favor these two processes should improve protoplast viability.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1615-6102
    Keywords: Secretion ; Vesicles ; Ultrastructure ; Cultured cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Callus-derived suspension cultures of oats dramatically increase the viscosity of the culture media after one month in culture. Colorimetric assays for sugars and protein, as well as measurements of viscosity, suggest that the released material is a long-chain polysaccharide, probably a pectinaceous substance. These cells grow slowly in liquid culture, yet despite their low cell density, they are able to increase the viscosity of the media several fold within seven days after media transfer. Ultrastructural observations show that oat cells have features common to actively-secreting cells; especially evident are numerous dictyosomes with hypertrophied cisternae. Using a combination of filtering and centrifugation techniques we were able to recover large numbers of intact secretory vesicles. The interior of the vesicles stain with periodic acid-silver hexamine, and colormetric analysis of the vesicle pellet for total sugars confirms the presence of polysaccharides in this vesicle fraction. Because of the uniformity of these cells, the high rate of secretion, and the accessability of a large vesicle population, this culture system is'a useful model for studying the secretory process in plant cells.
    Type of Medium: Electronic Resource
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