Abstract
A theoretical model has been built to bypass the equation of titration of the cell wall. This equation, which is an extension of the Henderson-Hasselbach equation, underlines the importance of the exchange constant, the ionic strength as well as the rate of neutralization. The model is restricted to the case when the ionization degree is equal to the neutralization degree. The shape of the titration curve is shown to be strongly dependent on the valency of the base used.
Experimental results have shown that isolated cell walls bear at least two kinds of sites. The first sites which are titrated after a short time of equilibration are attributed to polyuronic acids (capacity: 0.3 milliequivalents per gram fresh cell walls). The second sites, are obtained after a long time of equilibration (capacity: 1.2 to 1.3 milliequivalents per gram, fresh cell walls). Titrations have been performed with different bases [KOH, NaOH, and Ca(OH)2] and under different ionic strengths.
The results obtained with NaOH and KOH do not exhibit any difference of selectivity. Conversely, the sites have a much bigger affinity for the Ca2+ ions than for the monovalent ones. The apparent pKa of the uronic acids was estimated to lie between 3.0 and 3.4; this is consistent with the values obtained with polyuronic acid solutions.
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Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Burke D., Kaufman P., McNeil M., Albersheim P. The Structure of Plant Cell Walls: VI. A Survey of the Walls of Suspension-cultured Monocots. Plant Physiol. 1974 Jul;54(1):109–115. doi: 10.1104/pp.54.1.109. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Demarty M., Morvan C., Thellier M. Exchange Properties of Isolated Cell Walls of Lemna minor L. Plant Physiol. 1978 Oct;62(4):477–481. doi: 10.1104/pp.62.4.477. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hiatt A. J. Electrostatic association and donnan phenomena as mechanisms of ion accumulation. Plant Physiol. 1968 Jun;43(6):893–901. doi: 10.1104/pp.43.6.893. [DOI] [PMC free article] [PubMed] [Google Scholar]