Transport

The transport of K+ ion against its concentration gradient through isolated periderm (PM) and cuticular (PFCM) membranes at different pH and salt concentrations was investigated. The mean transport rate and transport fraction were calculated, and a tentative transport mechanism due to fixed charges was proposed. The transport system depends on the concentration gradient of K+ ions and H+ ions and the pH gradient was the main driving force. This system is characterised by asymmetry of binding on both compartments of the membrane for the formation and dissociation of carrier carboxyl groups in the membrane matrix. These carrier groups are dissociated at high pH ranges. The studies were then extended to examine the selective transport of alkali cations by using K-Na and K-Li binary systems with various pH gradients. In the transport of metal ions, the selectivity depends on both the hydrated ionic size and the interaction between the carboxyl groups in the membrane and the metal ions.