Conformational Transitions and Modifications in Ionic Exchange Properties Induced by Alkaline Ions in the Nitella flexilis Cell Wall

• Main Authors: Gillet, C., Voué, M., Cambier, P.
• Format: Text
• Language: English
• Published: Oxford University Press 1994
• Subjects: research-article; Nitella flexilis
• Online Access: http://pcp.oxfordjournals.org/cgi/content/short/35/1/79

The decrease in the cationic exchange capacity (CEC) concomitant to the replacement in the Nitella wall of adsorbed Mn2+ ions was measured in different mixtures of alkaline ions. At low external concentrations, the loss of CEC is enhanced in presence of Li+ ions but is weaker when Na+ ions are present in the exchange mixtures. The relative affinity of the wall exchange sites for alkaline ions was Na+>K+>Rb+≥Cs+>Li+. As the CEC is progressively reduced, the wall discrimination between the different alkaline ions tends to cancel out except for the Na+-K+ pair. The wall preference for K+ is then increased. A diminution of the effective pK of the polygalacturonic acids constitutive of the wall is also observed, while increasing the CEC loss. The simple disruption of divalent cation crosslinks cannot fully explain the CEC leakage at low monovalent concentrations. It is suggested that the alkaline ions also cleave H bonds or solvatation-like bonds between the cell wall polyuronides and then cause a concomitant unfolding of the short pectic chains which involves their solubilization.