Abstract
Effects of salts at low concentrations on growth were studied from the aspects of controlling factors for cell growth. When germinated lettuce (Lactuca sativa cv. Grand rapids) seeds were incubated in NaCl and KCl solutions for 4 days in the dark, each salt at concentrations lower than 50 mM stimulated hypocotyl elongation. Kinetic studies revealed that both salts (20 mM) stimulated elongation at similar extent until 4 days, then growth rate of NaCl-treated seedlings decreased as compared with KCl-treated ones. Osmotic pressure of cell sap increased in NaCl and KCl treatments, resulting in an increased-delta-osmotic pressure. Extensibilities of hypocotyl cell wall also increased, the effect being much larger in KCl treatment. These suggest that NaCl and KCl at low concentrations stimulate hypocotyl growth by affecting not only osmotic properties but also cell wall properties in etiolated lettuce seedlings, although effectiveness on cell wall properties is different from kind of salts.
