| High salinity, especially in the western arid and semiarid regions of China, is a most serious environmental stress that imposes both ionic toxicity and osmotic stress, leading to the reduction of plant growth and crop production. Halophytes widely distribute in these regions, and the research in connection with salt tolerance of these plants provides a theoretical basis for resource exploitation. Limonium aureum (L.) Hill is a typical halophyte in the desert with the strong ability to resist salinity and alkalinity, drought, wind and dust, and it can efficiently fix moving sands and reduce the soil salinity. Seed germination and seedling growth are very complex physiological processes that can be regulated by stress environment. The aim of this study was to investigate the mechanism of salt negative effects on seed germination and seedling growth and the physiological and biochemical responses of L. aureum (L.) Hill with different NaCl concentrations treatment. The results showed that:1.25and50mmol·L-1NaCl had no effect on seed germination and seedling growth in L. aureum (L.) Hill, and even significantly elevated root growth was observed in the seedlings exposed to25mmol·L-1NaCl treatment, while100and150mmol·L-1NaCl inhibited these parameters.2. Analysis using fluorescent dye2’,7’-dichlorofluorescein diacetate (DCFH-DA) and3-amino,4-aminomethyl-2’,7’-difluorescein, diacetate (DAF-FM DA) showed significantly increased levels of hydrogen peroxide (H2O2) and nitric oxide (NO) in the root tissue after treatment with different NaCl concentrations. Additionally, electrolyte leakage was determined, and cell morphology was investigated by using a laser scanning confocal microscopy and a fluorescent dye propidium iodide (PI), the results indicated that higher NaCl concentrations resulted in the inhibition of straight growth of the elongation zone cell and the enhanced permeability of cell membrane associated with cell impairment in the root tips.3. In comparison with the control, there were significant increased of the content of malondialdehyde (MDA), praline, the concentration of soluble carbohydratein, the content of H2O2and the production rate of O2in seedlings of L. aureum with the increasing of NaCl concentration. The amount of soluble protein was somewhat decreased under lower NaCl concentiation treatment, but had a significant increase under higher.4. Different concentration NaCl treatment enhanced the activities of superoxide dismutase (SOD) and the APX than that in control. However, the activities of catalase (CAT) was fell firstly then improved and was all obvirously lower than that in control. Peroxidase (POD) activities increased at the lower concentrations and then decreased at the higher concentrations.In conclusion, these results suggested that L. aureum (L.) Hill had a certain tolerance to lower salt stress while high NaCl concentration inhibited seed germination and seedling growth, and the enhancements of H2O2generation and membrane permeability in the root tissue cells, and the reduction of straight growth of root elongation region were responsible for the inhibition of root growth in L. aureum (L.) Hill seedlings exposed to higher salt treatment. Here it was also indicated that strong oxidative damage in seedling leaves might be associated with NaCl-induced negative effect on the growth of seedling shoots. That L. aureum could enhance the contents of osmolytes and antioxidase activities under the salt stress and thus stronger anrioxidant and osmoregulation capacity contribute to the salt tolerance. |
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