Abstract: Soil salinity severely limited crop production worldwide. Breeding and planting salt-tolerant species were the most effective and economic way for utilizing saline soils. However, lacking of reliable, convenient, inexpensive and quick screening techniques was the limiting factor for salt-tolerant breeding program. It has been shown that coleoptile elongation under drought condition could be used as a useful index to screen drought-tolerant wheat cultivars. In the present study, a salt-tolerant wheat (Triticum aestivum L.) cultivar DK961 and a salt-sensitive one LM15 treated with 100 mmol L^-1 NaCl for two days were used to examine the response of coleoptile elongation to NaCl stress. Several indexes including radicle and coleoptile length, relative elongation rate (RER), fresh and dry weight, osmotic potential and osmotic adjustment ability, and contents of solutes such as proline, soluble sugars, Na⁺, and K⁺ were determined. The results showed that NaCl stress inhibited the radicle, coleoptile elongations and 100 mmol L^-1 NaCl was the optimal concentration to show the difference between the two cultivars. NaCl postponed the maximal elongation date. Interestingly, compared with controls, NaCl stress did not affect the final coleoptile length of both cultivars. Fresh and dry weights of coleoptile were both decreased and the decrease degree of LM15 was more than that of DK961. Osmotic potentials of coleoptile of both cultivars were decreased by NaCl stress and osmotic adjustment ability of DK961 was stronger than that of LM15; proline, soluble sugar and Na+ contents in coleoptile of both cultivars were increased by NaCl stress, and the increase degrees of DK961 were more than those of LM15. However, K+ content in coleoptile of both cultivars was decreased, and the decrease degree of LM15 was more than that of DK961. These results indicate that the coleoptile of salt-tolerant wheat cultivar (DK961) has a higher ability to maintain K⁺ in its cells than that of salt-sensitive one (LM15). Coleoptile elongation of salt-tolerant wheat cultivar (DK961) was significantly higher than that of salt-sensitive one (LM15) under the same NaCl stress, which was partly due to having a stronger osmotic adjustment ability in the former than in the latter. Conclusively, the coleoptile length under a certain NaCl stress might be used to screen salt-tolerant wheat cultivars.

Key words: Wheat, Coleoptile, NaCl stress, Osmotic adjustment, Salt tolerance