Physiological responses of Ocimum basilicum to seawater stress

Basil(Ocimum basilicum) seedlings were subjected to 0,5%,10%,20%,30% and 40% seawater under netting house conditions.Increasing seawater concentration led to considerable reduction in plant growth rate and dry mass accumulation.However,root growth was not affected even by treatment with 30% seawater.High salinity(30% and 40% seawater) caused significant increases of soluble sugar and proline contents as well as leaf water use efficiency,whereas photosynthesis was inhibited mainly due to stomatal restriction.Accumulation of Na+ was correlated with a decline of Ca2+ and K+ in stems,roots or both.However,contents of K+ and Ca2+ in leaves increased or remained relatively unchanged with increasing salt levels.In plants stressed by salinity,Na+ were partitioned mainly in roots(57.1%-64.6% of the total) and more than 50% of the K+ and Ca2+ were stored in leaves.In addition,seawater stress decreased the K+/Na+ and Ca2+/Na+ in this species,although the higher K+/Na+ and Ca2+/Na+ were observed in leaves rather than in roots and stems.The K+/Na+ was greater than three even when subjected to 40% seawater.These results suggest that salt tolerance of basil plants might be associated with the compartmentalisation of Na+ in roots and the balance of K+,Na+ and Ca2+ in leaves as well as the osmotic adjustment with soluble sugar and proline under conditions of high salinity.