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Title: ELECTRICAL POTENTIALS OF PLANT CELL WALLS IN RESPONSE TO THE IONIC ENVIRONMENT

Author
item SHOMER, ILAN - ARO/THE VOLCANI CTR
item NOVACKY, ANTON - UNIV OF MO
item PIKE, SHARON - UNIV OF MO
item YERMIYAHU, URI - ARO/GILAT RESEARCH CENTER
item Kinraide, Thomas

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2003
Publication Date: 9/20/2003
Citation: SHOMER, I., NOVACKY, A., PIKE, S., YERMIYAHU, U., KINRAIDE, T.B. ELECTRICAL POTENTIALS OF PLANT CELL WALLS IN RESPONSE TO THE IONIC ENVIRONMENT. JOURNAL OF PLANT PHYSIOLOGY. 2003. v. 133. p. 411-422.

Interpretive Summary: Food plants are sometimes bred, selected, or managed with the intention of enhancing the uptake of desired nutrients (such as calcium or phosphorus) and reducing the uptake of dangerous toxicants (such as heavy metals). In contrast, high accumulation of toxicants is desired in plants used in phytoremediation (the cleansing of soils or waters with plants). Investigations to date have concerned plant cell membranes but not cell walls despite the fact that cell walls are the major repository of many charged solutes (ions), especially heavy metals. Because the surfaces of plant cells (cell membranes and cell walls) are electrically charged, ions are attracted or repelled. Different conditions in the rooting medium, either in nature or in experiments, cause the electrical charge of cell surfaces to change. This study determines the characteristics of metal binding to cell walls in accordance with electrical theory and quantitative models for the theory. We are now approaching a comprehensive theory for plant wall-membrane-ion interactions that will help predict plant responses to management practices and guide more rational selection, breeding, and engineering of plants.

Technical Abstract: Electrical potentials in cell walls (yWall) and at plasma membrane surfaces (yPM) are determinants of ion activities in these phases. The yPM plays a demonstrated role in ion uptake and intoxication, but a comprehensive theory of plant-ion interactions will require further understanding of yWall. yWall from potato tubers (Solanum tuberosum L.) and wheat roots (Triticum aestivum L. cv. Scout 66) was monitored in response to changes in ion type and concentration. Measurements were taken by placing glass microelectrodes against the outer cell surfaces of heat-killed tissues. Cations reduced the negativity of yWall of wheat-root cells (and, generally, potato cells) with effectiveness in the order Al3+ > La3+ > H+ > Cu2+ > Ni2+ > Ca2+ > Co2+ > Cd2+ > Mg2+ > Zn2+ > hexamethonium2+ > Rb+ > K+ > Cs+ > Na+. The electrical measurements were considered in terms of a model composed of Donnan theory and ion binding. Measured and model-computed values for yWall in response to monovalent and divalent cations agree closely, but the models accommodated the effects of Al3+ and La3+ only partially. Our measurements of yWall agree with most of the few published measurements, which we consider to be at least proportional to the actual Donnan potentials. yWall and yPM are similar, but yWall resisted conversion to positive values more than yPM, indicating greater ion binding to neutral sites in PMs. Ion activities at plant cell surfaces can now be computed with some assurance that the values are at least proportional to actual values.