MEMBRANES AND TRANSPORT-SYSTEMS IN PLANTS - AN OVERVIEW

Membranes define the outer boundary of the living protoplast and the i nternal compartmentation of plant cells. From a structural point of vi ew, membranes consist of a lipid bilayer and proteins essential for fu nctions such as solute transport, signal transduction, and numerous me tabolic reactions. While membranes can represent a significant barrier to the free movement of many solutes, those with sufficient lipid sol ubility may move across membranes by dissolving into the lipid bilayer . However, selective membrane transport is generally observed for hydr ophilic solutes such as mineral nutrients and cell metabolites. Such s elective transport requires an input of metabolic energy, and in plant s this occurs via the production of proton electrochemical gradients a cross the membrane by substrate- (ex. ATP, PPi) driven proton pumps. S elective solute transport is then mediated by membrane-associated seco ndary transport systems which utilize the proton electrochemical gradi ent to drive the transport process. This review of membrane structure and transport system function provides a background for a further exam ination of herbicide interactions with plant membranes.