RESUMEN
The 45-days-old seedlings of drought resistant (N-22, CR143-2-2) and susceptible rice (Oryza sativa L.) genotypes (Panidhan, Pusa-169) were subjected to osmotic stress in PEG-6000 solution of -10 and -16 bar and the relative water content (RWC), proline content, and pyrroline-5-carboxylate synthetase (P5CS) activity and its P5CS expression were studied. A gradual decrease in RWC was observed in tolerant genotypes, whereas the decrease was drastic in susceptible ones. Proline content and P5CS activity increased both in susceptible and tolerant genotypes; the increase was higher in tolerant genotypes. Higher proline levels in tolerant genotypes were due to increased P5CS activity. The EcoRI, BamHI and XbaI restricted DNA of N-22 and Panidhan genotypes were hybridized with Arabidopsis P5CS sequence and a single band (approx 2.4 kb) was observed, however, P5CS expression was more in N-22 as compared to Panidhan.