Water and Solute Transport

Abstract

Movement of water and solutes from soil solution to the seed tissue is one of the first processes occurring during seed germination in soil. Mature seeds contain less than 10% water and imbibition leads to hydration of its cells and tissues. With the exception of oxygen and carbon, which are readily available to plants from air, terrestrial plants generally take up water and dissolved nutrient elements from the soil through the root system. Molecular and ionic movements from one site to another are known as transport. Long-distance transport of solutes from one tissue system to another is referred to as translocation. Intracellular and intercellular distribution of water, ions, and organic molecules is crucial for plant growth, cell signaling, nutrition, and cellular homeostasis. To fulfill these essential functions, plants have evolved various transport mechanisms through apoplast and symplast. Membranes act as barriers which separate cells from the environment. The hydrophobic nature of the lipid bilayer of cell membranes ensures that hydrophilic compounds, including most metabolites, are sequestered in one or the other organelles or in the cytosol. Development of endomembrane system in the cells has facilitated homeostatic functions of membranes through compartmentalization of solutes. The major advantage of the compartmentalization of solutes and macromolecules within the membrane-bound organelles is that it concentrates the reactants and catalysts. It also segregates incompatible processes taking place in a cell. Recent advancements in our understanding of the membrane transport process have benefitted significantly from the isolation and characterization of a variety of mutants. Electrophysiological analysis, using techniques like patch clamp, has provided useful information on the modulation of the activity of a number of membrane transport proteins. In this chapter, we will discuss the physical and chemical principles which govern movement of water and ions into and across the plant cells. Attention is further being paid to understand the molecular mechanisms of various transport processes taking place across cells, which are mediated by the large variety of transport proteins, and also about the intracellular distribution of proteins required for maintaining the required ionic balance.