Salinity tolerance in Spergularia marina

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Abstract
Attributes of the coastal halophyte S. marina (L.) Griseb. that make it useful for studies of the physiological basis for salt tolerance in fully autotrophic higher plants are discussed. Growth, morphological, and ion-content characteristics are presented to serve as a background for subsequent studies of transport physiology. Plants were grown in solution culture on dilutions of artificial seawater or on the same solution without NaCl ("fresh water") from the time at which they could be conveniently transferred as seedlings (about 2 weeks old) to the onset of flowering about 5 weeks later. Eighteen days after transfer, plants growing on 0.2 .times. seawater were larger, being nearly twice the size of plants on fresh water. A Na+ specific effect was indicated, as the major part of the growth stimulation (54%) resulted from a 1 mM NaCl supplementation of "fresh water." Succulence was not a consideration in the growth response: root length was directly proportional to weight as was leaf surface area and neither was affected by salinity. Total Na+ plus K+ per gram root or shoot showed little variation with salinity from 1 to 180 mM Na+ levels. In roots, the relative Na+ and K+ contents were also little affected by salinity, but in the shoots, increasing salinity resulted in higher Na+ and lower K+ contents. Distribution within the shoots of 0.2 .times. plants showed no regions either free of or exceptionally high in Na+. The ion content and distribution patterns are compared with those in a number of other halophytes.