Some physiological responses of Chinese iris to salt stress

Chinese iris (Iris lactea Pall. var. chinensis (Fisch) Koidz.), a robust iridaceous plant, is widespread in and and semiarid regions with high salinity. However, the mechanism of its salt tolerance is not well understood. In this study, plant growth, water status, content and distribution of inorganic ions, cell membrane permeability, and proline content of I. lactea under salt stress were investigated using nutrient solutions with six NaCl concentrations ranging from 0 to 350 mmol L-1. The results indicated that the biomass, height, fresh weight, K+ content, and K+/Na+ and Ca2+/Na+ ratios decreased with increasing NaCl stress, whereas plant water deficit and contents of Na+ and Cl- increased with increasing NaCl stress. In all salt treatments, water deficit of shoots was found to be higher than that of roots and had a positive correlation with salt concentration. When the NaCl concentration was less than 280 mmol L-1, the ion absorption selectivity ratio and the transportation selectivity ratio sharply increased with increasing NaCl stress. Under medium salt stress, I. lactea exhibited a strong K+ selective absorption and the transportation of K+ from roots to shoots increased, whereas Na+ was not transported and was mostly retained in roots. The plants were able to maintain osmotic adjustment through the accumulation of Na+, Cl-, and proline. On the basis of its biomass production under salt stress, I. lactea could be considered as a facultative halophyte.