Effects of salt stress in hydroponic media on clover plants inoculated with Rhizobium

The application of salt stress in hydroponic conditions on clover seedlings ( Trifolium alexandrinum L.) inoculated with Rhizobium affected the nodulation starting from 2 g NaCl . l(-1), whereas the growth began to be reduced only from 4 g . l(-1). The growth of shoots was reduced by about 20% at 4 g . l(-1) and 44% at 6 g . l(-1). The development of the root system was less sensitive. This depressive effect on the growth was accompanied by biochemical and ultrastructural modifications. The soluble protein content of the leaves fell by about 75% at 6 g . l(-1) of NaCl. Proline and soluble sugars accumulated mainly in leaves, where they probably contributed to the osmotic adjustment phenomena. The transport and/or the utilization of starch was affected, so it accumulated in the chloroplasts. Salt stress also caused disorganization of the thylakoid membranes and an accumulation of lipidic globules inside the chloroplasts.