lon Homeostasis in NaCl Stress Environments.

Abstract

Homeostasis can be defined as the tendency of a cell or an organism to maintain interna1 steady state, even in response to any environmental perturbation or stimulus tending to disturb normality, because of the coordinate responses of its constituent components. Typically, ions constantly flux in and out of cells in a controlled fashion with net flux adjusted to accommodate cellular requirements, thus creating an ionic homeostasis. When plant cells are exposed to salinity, mediated by high NaCl concentrations, kinetic steady states of ion transport for Na+ and C1- and other ions, such as Kt and Ca2+, are disturbed (Binzel et al., 1988). High apoplastic levels of Na+ and C1- alter aqueous and ionic thermodynamic equilibria, resulting in hyperosmotic stress, ionic imbalance, and toxicity. Thus, it is vital for the plant to re-establish cellular ion homeostasis for metabolic functioning and growth, that is, to adapt to the saline environment.