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  • 1
    Electronic Resource
    Electronic Resource
    An investigation of the role of solutes in the xylem sap and in the xylem parenchyma as the source of root pressure (2000)
    Springer
    Protoplasma 211 (2000), S. 183-197 
    Details
    ISSN: 1615-6102
    Keywords: Cell turgor ; Guttation ; Osmotic potentials ; Root pressure ; Xylem sap ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Solute osmotic potentials (Ψx) in the vessels of hydroponically grown maize roots were measured to assess the osmotic-xylem-sap mechanism for generating root pressure (indicated by guttation). Solutes in vessels were measured in situ by X-ray microanalysis of plants frozen intact while guttating. Osmotic potentials outside the roots (Ψo) were changed by adding polyethylene glycol to the nutrient solution. Guttation rate fell when Ψo was decreased, but recovered towards the control value during 3–5 days when Ψo was greater than or equal to −0.3 MPa, but not when Ψo was equal to −0.4 MPa. In roots stressed to Ψo = −0.3 MPa, Ψx, was always more positive than Ψo, and Ψx changed only slightly (ca. 0.05 MPa). Thus the adjustment in the roots which increased root pressure cannot be ascribed to Ψx, contradicting the osmotic-xylem-sap mechanism. An alternative driving force was sought in the osmotic potentials of the vacuoles of the living cells (Ψv), which were analysed by microanalysis and estimated by plasmolysis. Ψv showed larger responses to osmotic stress (0.1 MPa). Some plants were pretreated with abundant KNO3 in the nutrient solution. These plants showed very large adjustments in Ψv (0.4 MPa) but little change in Ψx (0.08 MPa). They guttated by 4 h after Ψo was lowered to −0.4 MPa. It is argued that turgor pressure of the living cells is a likely alternative source of root pressure. Published evidence for high solute concentrations in the xylem sap is critically assessed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01304486
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  • 2
    Electronic Resource
    Electronic Resource
    Breakdown of cytoplasmic vacuoles (1990)
    Springer
    Protoplasma 155 (1990), S. 144-152 
    Details
    ISSN: 1615-6102
    Keywords: Motile vacuoles ; Vesiculation ; Mathematical model ; Fixation ; Osmotic conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plant cells possess an extensive motile vacuolar system (MVS) easily observed with dark field, Nomarski or phase contrast optics. The elements of the MVS are long cylindrical vacuoles, 1–6 μm in diameter, but are transformed into spherical vesicle upon fixation with non-coagulant fixatives (e.g., glutaraldehyde). A mathematical model is developed to describe the vesiculation event, taking into account osmotic properties of the fixing solution. A computer simulation is prepared, using the model equations, to examine response of vesicle radius and number under weak to strong osmotic conditions. Vesicle radius is strictly dependent upon initial vacuolar radius, while vesicle number is found to depend upon initial vacuole length as well as radius. However, vesicle number is more dependent upon initial vacuolar radius as osmotic influences increase. The model points out important basic properties of membrane cylinders and spheres that can be scaled up or down to include similar structures at various magnitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01322624
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