Sodium and proline accumulation as osmoregulators in tolerance of sugar beet genotypes to salinity.

Twenty eight sugar beet genotypes were analysed for their tolerance at 3 NaCl levels (0, 3000 and 6000 mg NaCl kg(-1) soil) and Na+, K+, Na+/K+ and free proline were measured from the leaf samples. Results showed that increasing salinity level caused an increase in Na+, Na+/K+ and proline, but a decrease in K+ content of leaf samples (p < or = 0.01). As compared to non-tolerant genotypes, tolerant ones accumulated more Na+ and Na+/K+ and proline and less K+. It seems that Na+ and proline accumulation in shoots are effective mechanisms for osmotic pressure adjustment and plant tolerance to salinity, a mechanism commonly seen in sugar beet ancestors.