盐胁迫对盐生植物黄花补血草种子萌发和幼苗生长的影响

盐生植物黄花补血草广泛分布于我国西北地区、东北西部以及华北北部,对改良盐碱土壤具有重要的生态作用。以黄花补血草(Limonium aureum(L.)Hill)为材料,研究分析了不同浓度NaCl胁迫对其种子萌发和幼苗生长产生的抑制效应及作用机制。结果表明:低浓度NaCl(25 mmol/L和50 mmol/L)处理不影响黄花补血草种子萌发和幼苗生长,25 mmol/L NaCl甚至促进了根生长,而高浓度NaCl(100 mmol/L和150 mmol/L)处理明显抑制种子萌发及幼苗生长。利用荧光探针的检测结果表明,NaCl处理的幼苗根中过氧化氢(H2O2)和一氧化氮(NO)含量明显高于对照水平。碘化丙啶(PI)染色结合激光共聚焦显微镜观察及检测相对电导率结果显示,高浓度NaCl处理抑制了幼苗根尖伸长区细胞的伸长生长,增加了细胞膜的通透性,对根细胞造成了明显的伤害。此外,高浓度NaCl处理诱导叶片丙二醛(MDA)含量显著升高。以上结果说明,黄花补血草对低浓度的盐具有一定的耐盐性,但高浓度盐降低了种子的萌发率,使幼苗根中H2O2产生增加,抑制根尖伸长区细胞的伸长生长,对根、叶造成明显氧化损伤,从而抑制黄花补血草幼苗的生长。

Effects of salinity on seed germination and seedling growth in halophyte Limonium aureum (L.) Hill

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. Additionally, this species owns potential economic values as a source of medicinal compounds. 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 in L. aureum (L.) Hill cultured on 1/4 Hoagland's solid medium supplemented with different NaCl concentrations. After surface-sterilized with 0.1% Javel water for 10 min, the plump and excellent seeds were treated with 0, 25, 50, 100 and 150 mmol/L NaCl and germinated for 7 days. For root and shoot growth experiments, seedlings were also cultivated for 7 days. All assays were replicated at least three times to minimize experimental errors. The results showed that: 25 and 50 mmol/L NaCl 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 to 25 mmol/L NaCl treatment, while 100 and 150 mmol/L NaCl inhibited these parameters. Analysis using fluorescent dye 2',7'-dichlorofluorescein diacetate (DCFH-DA) and 3-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. Malondialdehyde (MDA) is a product of lipid peroxidation and a most prominent indicator of oxidative stress in plants exposed to stress conditions. In comparison with the control, MDA content had no significant change in the leaves of L. aureum (L.) Hill seedlings under lower salt treatment, but markedly elevation in the amount of MDA was observed in response to 100 and 150 mmol/L NaCl, suggesting that higher salt stress led to significant oxidative damage in the leaves of L. aureum (L.) Hill seedlings. 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 H2O2 generation 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.