Associate-Professor Walker is distinguished for his original biophysical contributions to understanding the electrical and iontransporting properties of plant cells. In 1955, he made an important advance by being first to distinguish the electrical characteristics of the cell-surface membrane (plasmalemma) from those of the vacuolar membrane (tonoplast). He has combined rigorous experimental and theoretical approaches to explain both the resting and the active (chemiosmotic) potentials of the plasmalemma, to discover various transport systems (Cl-, H+ , NH+4 and HC0-3), the circulation of electric current between different areas of the cell surface and the transport of solutes in the plasmodesmata between cells. His imaginative approach to plant cell biophysics has had wide international influence.
