OSMOTIC ADJUSTMENT AND DYNAMIC CHANGES IN DISTRIBUTION OF LOW-MOLECULAR-WEIGHT SOLUTES BETWEEN CELLULAR COMPARTMENTS OF CARROT AND BEET ROOT-CELLS EXPOSED TO SALINITY

Carrot cells (Daucus carota L.) in suspension culture exposed to medium containing 150 mM NaCl plasmolyzed immediately and deplasmolyzed within 35 to 40 hr. Three days after exposure to NaCl the cells resumed proliferation. Accommodation to salinity and renewal of growth was accompanied by absorption of Na+ from the external medium. On completion of deplasmolysis, K+ concentration in the cytosol doubled and Na+ concentration approximated that of K+. The vacuolar K+ concentration was practically unchanged while Na+ accumulated to a concentration double that of K+. Cl- accumulation started later and eventually exceeded that of Na+ plus K+. Malate was redistributed during accommodation to salinity and eventually returned to its initial level. Amino acid content in the cytosol increased fivefold, while in the vacuole it remained unchanged. These results show that: 1) recovery from osmotic shock requires absorption of easily penetrating solute, mainly Na+; 2) distribution of solutes, absorbed or synthesized in cells exposed to salinity, is a dynamic process; 3) cells could grow and proliferate in high NaCl content in the cytosol; 4) red beet root cells grown in the presence of NaCl contain higher cytoplasmic Na+ than K+; and 5) during adjustment to salinity small spherical carrot cells survive the osmotic shock and do not show any detectable damage.