title: The thermodynamic activity of proline in ternary solutions of different water potentials.
abstract: The particular colligative properties of proline caused us to investigate the thermodynamic activity of this amino acid in detail. The dependence of the activity coefficients γ of proline (γ = thermodynamic activity/molality) on the pH of the solutions, the composition of the solution and the water potential has been measured. The results show that the activity coefficient of proline varies according to the solute milieu. The most pronounced alterations of the activity coefficient could be observed in polyethylene glycol solutions in contrast to KCl- and saccharose solutions where the effect was less distinct. The results described provide a basis for discussing water stress induced metabolic alterations in terms of thermodynamic entities. Changed rates of proline metabolizing sequences and changed ratios of the vacuole/extravacuole distribution of this amino acid in stressed and un-stressed plants may partially be explained by thermodynamic causes.
authors.affiliation: Institut für Allgemeine Botanik und Pflanzenphysiologie der Justus-Liebig-Universität, Heinrich-Buff-Ring 54-62, D-6300 Gießen.
authors.forename: E
authors.initials: E
authors.lastname: Pahlich
authors.forename: T
authors.initials: T
authors.lastname: Stadermann