CHARACTERIZATION OF HYDRATION-DEPENDENT WALL-EXTENSIBLE PROPERTIES OF RYE COLEOPTILES - EVIDENCE FOR AUXIN-INDUCED CHANGES OF HYDROGEN-BONDING

The magnitude of changes of wall-extensible properties due to changes of the composition or concentration of wall solutions may reflect changes in polymer interactions relevant for growth regulation. Employing this approach, the present study demonstrates that in rye coleoptiles (Secale cereale L.) turgor-mediated wall stress can, in principle, be borne by non-covalent polymer interactions. Transfer of turgid coleoptile segments to methanol fixed the immediate tension-stressed wall length dimensions despite turgor elimination. Length dimensions of methanol-incubated, previously turgid walls of coleoptile segments could reversibly be fixed or relaxed to defined extension states depending on wall water content. Previously auxin-incubated segments exhibited an increased stress relaxation by this method, i.e. they exhibited stronger shrinkage in dependence of defined hydration conditions as compared with control. Methanol-mediated fixation of wall length dimensions, inclusive therein conserved wall stresses, is due to removal of the water from the walls and thereby increased hydrogen bonding between wall polymers. Auxin-incubated segments therefore are characterized by a decrease of hydrogen bonding. Denaturation of wall protein by boiling segments in water, depectination or extraction of non-covalently bound (glyco)protein did not impair methanol-induced fixability of wall lengths tension-stressed in the extensiometer. Regulation of auxin-induced growth, therefore, in principle may also depend on polymer interactions as the ones affected by changes of hydration conditions due to methanol treatment, i.e. changes in hydrogen bonding.