Chapter 2 - Ion Uptake Mechanisms of Individual Cells and Roots: Short-distance Transport

Abstract

Publisher Summary This chapter focuses on the ion uptake mechanisms of individual cells and roots. Cell walls interact with solutes and thus facilitate or restrict passage across the root and the uptake across the plasma membrane of individual cells. The lipid bilayer of the plasma membrane prevents the indiscriminate movement of ions and large polar molecules from the apoplasm into the cytoplasm (influx) and from the cytoplasm into the apoplasm (efflux), which demonstrates that the plasma membrane is a selective barrier to the uptake of ions. The pH of the external solution influences the uptake of nutrients by plant roots and their effects can be classified into three broad categories, which include effects of solution pH on the chemical species present in solution, effects of apoplasmic pH on the concentrations of ions present in the apoplasm, and the effect of rhizosphere pH in the proton electrochemical gradient and the driving force for proton-coupled solute transport. The pH of the soil solution influences the availability of cations and anions for root uptake, whereas the pH of the rhizosphere solution affects ion uptake by altering both substrate (H+) concentration and the electrochemical driving force for proton-coupled solute transport. Generally, there is a tendency for the rate of ion uptake per unit root length to decrease with distance from the root apex, which strongly depends on the identity of the ion, plant nutritional status and plant species. Water uptake can also affect ion uptake both directly, through effects on the rate of radial transport of ions through the apoplasm, and indirectly, by influencing the supply of ions to the plasma membrane of root cells.