Abstract
In order to diversify the production of plants with pharmacological interest, it is important to understand the mechanisms involved in their tolerance to environmental constraints, such as salinity. Basil (Ocimum basilicum), known for its therapeutic uses, has been claimed to be salt tolerant, but physiological aspects of this behavior remain unknown. Since salt tolerance is known to be associated with several characteristics concerning Na+ transport to leaves, we studied this function in hydroponically grown basil. We analyzed the response of 30-day-old seedlings to 25-50 mM NaCl applied for 15 days. Growth was poorly affected, indicating that these concentrations corresponded to the tolerated salinity range. Leaves accumulated Na+ at relatively high concentration, without dehydrating. Potassium concentration in leaf tissues was maintained close to control level, indicating that K+ was 15- to 25-fold preferred over Na+ for ion transport and deposition. Collection of xylem sap on detopped plants revealed that this preference was only 10-fold for ion introduction into root xylem sap. Short-term (24 h) changes in Na+ distribution between organs after stem (steam) girdling suggested that Na+ downward recirculation by phloem occurred. Although modest, this transport might have augmented K+ selectivity of ion deposition in leaves.