saltexclusion

Salt exclusion is a plant physiological mechanism by which an organism limits the uptake and/or movement of salt ions, especially sodium (Na+) and chloride (Cl−), from the soil into the roots and toward the shoots. The goal is to prevent ion toxicity, preserve cellular ion balance, and maintain growth under saline conditions. Exclusion can operate at multiple stages, including uptake at the root surface, loading into the xylem, and long-distance transport to aerial tissues.

Key mechanisms include structural barriers and selective transport. The endodermis and its suberin lamellae restrict apoplastic flow of ions, forcing more control over what enters the vascular system. Root epidermal and cortical cells employ selective transporters to limit Na+ entry. Transport proteins such as HKT transporters reduce Na+ loading into the xylem, while SOS1-type Na+/H+ exchangers remove Na+ from root cells to the soil. In addition, sequestration of Na+ into vacuoles by NHX transporters in root or shoot tissues helps lower cytosolic Na+ concentrations. Some species also combine exclusion with reduced transpiration or limited shoot ion transport to further mitigate damage.

Relevance and variation are large across species. Salt exclusion is a major component of salinity tolerance in many glycophytic crops and is assessed alongside exclusion versus exclusion-related traits in breeding programs. It is often discussed together with salt excretion and sequestration as overlapping strategies that contribute to overall salt tolerance.

Measurement typically involves assessing tissue Na+ and K+ concentrations and the Na+/K+ ratio, alongside hydroponic or soil-based experiments to evaluate ion movement from roots to shoots.