Fifty-one species belonging to 16 families of halophytes have been collected in salty areas surrounding the Seyfe Lake in Central Anatolia (Turkey). Their plant/sodicity relationships and the involvement of nitrogenous solutes in their osmotic adjustment have been more specifically investigated in order to compare adaptative traits involved in their salt tolerance with those well-known occurring in halophytes from marine salt marshes. The internal molecular ratio between [K+](int) and [K+ + Na+](int) was found to be low in the shoots of dicots due to important abilities to accumulate Na+. In contrast this ratio was higher in the monocots, this being due to low contents of Ne not to high ones of K+. This suggests specific traits which allow the dicots to absorb, accumulate and compartmentalize Na+ in order to provide cheap osmotic particles for osmotic adjustment. In terms of putative compatible solutes derived from primary nitrogen metabolism the study has been restricted to free proline and glycine betaine. It reveals that the 51 species investigated could be discriminated according to their capacity to accumulate, under natural saline conditions, either proline or glycine betaine or both of these compounds. It was also shown that species that behaved as glycine betaine accumulators behaved as poor proline accumulators and vice versa. This might suggest that in a number of species exhibiting attributes for glycine betaine production the level of free proline could be under the negative control of that of glycine betaine. A number of other nitrogenous osmolytes, such as Delta(1)-acetylornithine, beta-alanine betaine and choline-O-sulfate were also found in certain species. Plantago maritima previously found to accumulate sorbitol in response to saline conditions was shown here to coaccumulate proline and glycine betaine in addition to sorbitol which was also found to be abundant. Phenetic analysis of the set of data obtained allow to discriminate two main clusters of halophytic species refering mainly to the traits associated with proline and (or) glycine betaine accumulation. As expected, the majority of the Chenopodiaceae, exhibited a distinct behavior within cluster II, based on their dual ability to store Na+ and glycine betaine. Some species of this family did not conform with this model. Thus, it becomes clear that salt tolerance in halophytic plants which might partly result from the cooperativity of a number of well-conserved mechanisms could also result from specific processes that could be modulated by the saline environment. (c) 2005 Elsevier B.V. All rights reserved.