| Soil salinity severely limited crop production in the world. Breeding and planting salt-tolerant species was the most effective and economic way to remediate and use saline soil. However, lacking of reliable, convenient, inexpensive and quick screening techniques has been the limiting factor for salt-tolerant breeding program. Coleoptile was a protect organ whose length and elongation rate affect growth of crops in the early stage. The effects of environment factors on coleoptile length had been studied widely in recent years, and coleoptile length had been used as a reliable index of evaluating drought-resistance in wheat. In this study, a salt-tolerant wheat cultivar (DK961) and a salt-sensitive one (LM15) were used to determine several indexes including radicel and coleoptile length, relative elongation rate (RER), fresh and dry weight, osmotic potential and osmotic adjustment abilities, and solute contents including proline, soluble sugars under 100 mmol/L NaCl to analyze the effect on the elongation of coleoptile of differently salt-tolerant wheat cultivars to NaCl treatments and its possible reasons. The main results were as follows:1. Effects of NaCl treatments on morphological indexesNaCl treatments inhibited the radicel and coleoptile elongation and the inhibition degree increased with the increase of NaCl concentration. All NaCl treatments led to a marked decrease in radicel length and coleoptile length compared with controls,but there was no significant difference between the two cultivars。So, radicel length could not be used as an index of screening salt-resistance in wheat.However, the decrease degree of coleoptile length of DK961 was significantly lower than that of LM15. It was believed that coleoptile length of wheat under a certain NaCl concentration might be a useful index to screening salt-resistant cultivars.2. Effects of NaCl treatment on coleoptile RERThe RER of two wheat cultivars were both decreased under 100 mmol/L NaCl treatment, and the RER of DK961 was always higher than that of salt-sensitive wheat LM15 in 48h. NaCl stress postponed the maximal elongation date, the period of development prolonged slightly. Interestingly, compared with controls, NaCl stress did not affect the final coleoptile length of both cultivars.3. Effects of NaCl treatment on the growth of coleoptileTreated by 100 mmol/L NaCl for 2 d , fresh and dry weight of coleoptile were both decreased compared with controls(P<0.01)and the decrease degree of LM15 was higher than that of DK961(P<0.01). Water contents of coleoptile were both decreased compared with controls (P<0.01)and the decrease degree of LM15 was higher than that of DK961(P<0.01).4. Effects of NaCl treatment on osmotic potential of coleoptileIn a saline environment, halophytes regulate osmotic potential mainly by accumulating inorganic ions and small organic solutes to adapt osmotic stress.Osmotic potentials of coleoptile of both cultivars were decreased by 100 mmol/L 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 degree of DK961 was higher than that LM15. These results indicated that the coleoptile of salt-tolerant wheat cultivar (DK961) had 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 is partly due to having a stronger osmotic adjustment ability of the former than the latter. But K+ contents in coleoptile of both cultivars were decreased and the decrease degree of LM15 was higher than that of DK961.5. Effects of NaCl treatment on K+ leakage from different organs100 mmol/LNaCl treatment caused K+ leaking from the roots, germ and coleoptile. By correlation analysis, we found that K+leakage from different organs was positively correlated with time but negatively with salt tolerance of cultivars. Measuring K~+ flux rate of different zones of root in detail, we found the difference of K~+ flux rate was mainly caused by mature zone. The results showed strong negative correlation between K~+ leaking from the root and the salt tolerance of different wheat cultivars. The cell membrane of the salt-sensitive wheat cultivar (LM15) was damaged sevrely by NaCl stress than that of DK961. The damage making more K~+ leaking was the reason for K~+ nutrition deficiency of LM15. What was more important, the net K~+ leaking of young root under a certain NaCl stress might be used to screen salt-tolerant wheat cultivar.6. Effects of NaCl treatment onα- andβ-amylase activity in seeds100 mmol/LNaCl treatment inhibited theа-amylase andβ- amylase activity and the inhibition degree of DK961 was significantly lower than that of LM15. Fig. 9 showed that100 mmol/LNaCl treatment for 48 h significantly decreased theα- and β-amylase isoenzymes and the isoenzyme pattern differs between the two cultivars( the amount ofβ-amylase isoenzyme expression of DK961 was much higher under control and100 mmol/L NaCl treatment ). During the germination, amylase hydrolyzed starch to provide energy to coleoptile elongation. So, besides the difference inα- andβ-amylase activity, the isoenzyme expression contributed to coleoptile elongation difference of the two cultivars .In conclusion, 100 mmol/L NaCl treatment inhibited the coleoptile elongation of differently salt-tolerant wheats, decreased their RER, Fresh and dry weight, postponed the maximal elongation date, prolonged the period of development slightly. Interestingly, compared with controls, NaCl stress did not affect the final coleoptile length of both cultivars. The decrease degree of coleoptile length of DK961 was significantly lower than that of LM15,the reasons were: the salt-tolerant wheat cultivar (DK961) had a stronger osmotic adjustment ability; the cell membrane of the salt-sensitive wheat cultivar (LM15) was more damaged than that of DK961 under 100 mmol/L NaCl treatment, which leading to more K~+ leaking of LM15;а-amylase activity in seeds of LM15 was more dacreased, that could not provide enough energy to coleoptile elongation. Coleoptile length of wheat under a certain NaCl concentration might be a useful index to screening salt-resistant cultivars. |
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