Salt stress effects on growth, ion accumulation and seed oil concentration in an arid zone traditional medicinal plant ajwain (Trachyspermum ammi [L.] Sprague)

A greenhouse experiment was conducted to assess the effect of salt stress on growth, seed yield, and seed oil concentration in a traditional medicinal plant ajwain (Trachyspermum ammi L.). Sixty-seven-day-old plants of T. ammi were subjected for 46 days to sand culture salinized with varying concentrations of NaCl, i.e. 0 (control), 40, 80, and 120 mmol L−1. Increasing salt levels caused a significant reduction in fresh and dry masses of both shoots and roots as well as seed yield. However, the adverse effect of salt was more pronounced on seed yield than biomass production at the vegetative stage. The reduction in shoot dry biomass of T. ammi at the highest salt level (120 mmol L−1) with respect to control was about 27%, whereas that in seed yield was almost 50%. As in most glycophytes, Na+ and Cl− in both shoots and roots increased, whereas K+ and Ca2+ decreased consistently with the progressive increase in salt level of the growth medium. Plants of T. ammi maintained markedly higher K+/Na+ and Ca2+/Na+ ratios in the shoots than those in the roots, and the former ratio was greater than 1 even at the highest external salt level (120 mmol L−1). Proline concentration in the shoots increased markedly at the highest salt level. Seed oil concentration did not change with increase in external salt level. Overall, T. ammi is a moderately salt tolerant crop whose response to salinity is associated with maintenance of high K+/Na+ and Ca2+/Na+ ratios in both shoots and roots.