Author
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Kinraide, Thomas |
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Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/16/2004 Publication Date: 11/12/2004 Citation: Kinraide, T.B. 2004. Possible influence of cell walls upon ion concentrations at plasma membrane surfaces. Toward a comprehensive view of cell-surface electrical effects upon ion uptake, intoxication, and amelioration. Plant Physiology, 136:3804-3813. Interpretive Summary: Plant cells are bounded by a membrane and a semirigid wall outside of the membrane. The wall provides support for the plant, and plants have no other skeleton, as do most animals. The membrane is the regulatory barrier between the external environment (e.g., the rooting medium) and the cell interior. It has the function of admitting needed nutrients, expelling waste products, and secreting substances needed outside the cell for normal function. Cell walls carry negative charges, which attract or repel charged solutes from the rooting medium. Some of the solutes are needed nutrients and some are toxic. A long-standing question in plant physiology is the influence of the cell wall upon the cell membrane. Does the wall increase or decrease the concentration of solutes at the surface of the cell membrane? This study has determined that the presence of the wall enhances slightly the concentration of positively charged solutes and reduces slightly the concentration of negatively charged solutes at the cell membrane, but generally, the wall has little effect on the uptake or exclusion of solutes. These analyses have been enabled by electrostatic models developed in our laboratory. Technical Abstract: Plant uptake of ions, intoxication by ions, and the alleviation of intoxication by other ions, often correlate poorly with ion concentrations in the rooting medium. In contrast, uptake, intoxication, and alleviation correlate well with ion concentrations at the plasma membrane (PM) surface computed as though the PM were bathed directly in the rooting medium with no effect from the cell wall (CW). According to two separate lines of analysis, a close association of CWs and PMs results in a slight increase in cation concentrations and a slight decrease in anion concentrations at the PM surface compared with concentrations when the CW is separated or has no effect. Although slightly different, the ion concentrations at the PM surface computed with and without close association with the CW are highly correlated. Altogether, the CW would appear to have a small effect upon ion uptake by the PM or upon intoxication or alleviation of intoxication originating at the PM surface. These analyses have been enabled by the recent evaluation of parameters required for the electrostatic models (Gouy-Chapman-Stern and Donnan-plus-binding) used to compute electrical potentials and ion concentrations in CWs and at PM surfaces. |
