Effects of salt stress on growth, mineral nutrition and proline accumulation in relation to osmotic adjustment in rice (Oryza sativa L) cultivars differing in salinity resistance

Salt-resistant rice cultivars Nona Bokra and IR 4630 exposed at the seedling stage during one or two weeks to 0, 20, 30, 40 or 50 mM NaCl accumulated less Na, Cl, Zn and proline and more K at root and shoot levels than salt-sensitive I Kong Pao and IR 31785. Aiwu, a moderately resistant genotype, exhibited an intermediate behaviour. P transport from root to shoot was inhibited in the most sensitive cultivar IR 31785. Accumulation of Na and Cl and decrease in K content at the shoot level were restricted to the oldest leaves in salt-resistant genotypes while proline accumulated in the youngest leaves in all cultivars. In the presence of NaCl, the osmotic potentials of the roots and of the oldest and youngest leaves were lower in the salt-resistant than in the salt-sensitive genotypes, differences among genotypes increasing with stress intensity. Proline did not appear to be involved in osmotic adjustment in salt-stressed rice plants and the significance of its accumulation is discussed in relation to salinity resistance.