Excitation in Plant Membrane Biology

Very few substances can waltz right through cell membranes-indeed, could they do so, cells would lose their integrity rapidly. The control of ion and macromolecule passage through both plasma membranes and organellar membranes falls to various channel, pump, and carrier proteins, which are diagrammed in Figure 1. Not onlydo these proteins allow ions and other macromolecules to pass from one side of the membrane to the other, they also establish and maintain ion gradients that are essential for the control of metabolic processes, involved in storage processes, signal, and energy transduction, and, in some cases, render cells electrically excitable. The properties of these proteins alter in response to environmental and intracellular cues, allowing for controlled ion and macromolecule fluxes. These fluxes in turn initiate many of the cell’s responses to environmental stimuli as diverse as hormones, touch, and light. With the development of the patch clamp technique, along with methods to isolate high quality plant protoplasts, it has become possible to analyze in exquisite detail the currents that pass across plant cell membranes. These and other technical advances have also paved the way for the characterization of other membranemediated processes, such as sugar and amino acid transport. The ninth of the triennial lnternational Workshops on Plant Membrane Biology, which was held from July 19 to 24, 1992, in Monterey, California, bore witness to the dramatic progress that has seized the field of plant membrane biology in the last year or two. Many of the more than 300 participants at this year’s meeting, which was organized by Lincoln Taiz, together with Frances Dupont, Russell Jones, Rob Leonard, Bill