ONTOGENY OF SODIUM-CHLORIDE TOLERANCE OF THE SOYBEAN - COMPARISON OF SALT RESPONSES AT 2 STAGES OF DEVELOPMENT AND IN THE CORRESPONDING CALLUSES

The ontogenic evolution of tolerance to NaCl was demonstrated for soya: plantlet biomass, 6 days after germinations ,was already reduced in the presence of 25 mM NaCl, whereas adult plants (after 28 days of culture) were barely affected in the presence of 100 mM NaCl. Calluses from embryos showed the same level of sensitivity as plantlets; in contrast, calluses from roots showed a higher sensitivity than those obtained from stems or leaves. The soja response to salt (at the plantlet stage, at the adult plant stage and in undifferentiated callus cells) is not dependent on the concentrations of Cl, Na, or on the osmolarity due to (in)organic solutions; it is the expression of cellular mechanisms (the degradation of soluble proteins, as well as peroxydase and invertase potentials, are indicative of salt sensitivity) and of the requirement of tissue organization. This organization promotes the regulation of some enzymes (nitrate reductase, glutamine synthetase, and glutamate synthase, among others) and the evolution of nonenzymatic functions: the phosphoenolpyruvic carboxylase seems to be more related to the control of amino acid synthesis in adult plants and to the heterotrophic use of carbon by plantlets as well as by calluses. Therefore, amino acids and sugars play a major role in the adaptative mechanisms at these ontogenetic stages.