Abstract
The osmoregulatory role of amino acids and inorganic ions was studied in Plantago japonica Franch. et Sav., Which was grown on vermiculite irrigated with increasing salinity, as well as in samples collected from sandy beaches along the Sea of Japan. The amino acid contents increased with increasing salinity. In particular, arginine, which is originally present at high levels in the crowns, together with asparagine and glutamine, increased considerably, but the proline content in the plant was low and did not seem to function to regulate turgor pressure. Increasing the salinity of the medium revealed the capacity of the plant to increase chloride, potassium, and sodium ions in the tissues, and to a lesser extent, magnesium, calcium, and phosphate contents. The solute levels in leaves, calculated as the sum of the content found in the extract, matched closely the external osmolarity in the medium. Other ions or compounds may also be involved in the osmoregulation in this plant, particularly in the roots. Sugars, glycerol, citric acid (and other common organic acids) and putrescine did not seem to be involved in the osmoregulation.
