Ginzberg, I., Department of Botany, Tel-Aviv University, Tel-Aviv 69978, Israel, Institute of Field and Garden Crops, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Stein, H., Department of Botany, Tel-Aviv University, Tel-Aviv 69978, Israel
Kapulnik, Y., Institute of Field and Garden Crops, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Szabados, L., Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, 6701 Szeged, Hungary
Strizhov, N., Max-Planck Institute, 50829 Köln, Germany
Schell, J., Max-Planck Institute, 50829 Köln, Germany
Koncz, C., Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, 6701 Szeged, Hungary, Max-Planck Institute, 50829 Köln, Germany
Zilberstein, A., Department of Botany, Tel-Aviv University, Tel-Aviv 69978, Israel

Two different cDNA clones, MsP5CS-1 and MsP5CS-2, encoding Δ1-pyrroline-5-carboxylate synthase (P5CS), the first enzyme of the proline biosynthetic pathway, were isolated from a λZap-cDNA library constructed from salt stressed Medicago sativa roots. MsP5CS-1 (2.6 kb) has an open reading frame of 717 amino acids, as well as a non-spliced intron at a position corresponding to the evolutionary fusion point of the bacterial proA and proB genes. MsP5CS-2 (1.25 kb) is a partial clone. The clones share 65% identity in nucleotide sequences, 74% homology in deduced amino acid sequences, and both show a high similarity to Vigna aconitifolia and Arabidopsis thaliana P5CS cDNA clones. Southern blot analysis confirmed the presence of two different P5CS genes. The effect of salinity on the transcription of MsP5CS-1 and MsP5CS-2 in roots was studied, using northern blot analysis and a RT-PCR approach. A rapid increase in the steady-state transcript level of both genes in roots was observed by RT-PCR upon exposure of hydroponically grown 6-day old seedlings to 90 mM NaCl, suggesting that both ate salt-inducible genes, yet a higher response was observed for MsP5CS-2.