不同pH条件下CdCl2对紫花苜蓿种子萌发的胁迫效应

采用培养皿滤纸萌发试验,研究在3种pH(4.0、6.0和8.0)条件下,不同质量浓度(0、5、10、20、40和80mg/L)的CdCl₂溶液对紫花苜蓿种子萌发的胁迫效应. 结果表明,低质量浓度的CdCl₂(≤20mg/L)显著提高了紫花苜蓿种子的发芽率、发芽势、发芽指数和活力指数,ρ(CdCl₂)为20mg/L、pH为6.0时活力指数与对照组相比明显增加,达到177.52±16.61；随着ρ(CdCl₂)的提高,CdCl₂对苜蓿幼苗生长的促进效应不断增强,ρ(CdCl₂)为20mg/L时,3种pH条件下的芽鲜质量分别为(6.60±0.11)、(6.68±0.20)和(9.51±0.16)mg,根鲜质量分别为(6.71±0.10)、(7.09±0.08)和(9.10±0.08)mg,达到最大； 当ρ(CdCl₂)达到40和80mg/L时,紫花苜蓿种子萌发和幼苗生长则受到显著抑制,ρ(CdCl₂)为80mg/L时发芽率和活力指数分别仅为对照组的14.8%和46.5%；ρ(CdCl₂)为80mg/L时芽鲜质量最低,3种pH条件下分别为(3.48±0.15)、(4.03±0.19)和(7.00±0.22)mg. 研究还发现,紫花苜蓿种子发芽率和活力指数随pH降低而降低,弱碱(pH=8.0)条件下紫花苜蓿在ρ(CdCl₂)为80mg/L时的发芽率为66.40%±3.19%,大于酸性条件(pH=4.0、6.0)下的发芽率(11.20%±3.61%、9.20%±4.22%),而活力指数(93.90±10.71)也高于酸性条件(pH=4.0、6.0)下的活力指数(49.77±3.25、56.67±3.48),表明pH由酸性到碱性的变化过程能够缓解CdCl₂对紫花苜蓿种子萌发和幼苗生长的毒性. 

Effects of CdCl2Stress under Different pH to Seed Germination in Alfalfa

To understand the effects of CdCl_2stress to seed germination in alfalfa (Medicago sativa) is important for its bioremediation of heavy metal. Using the petri dish germination method, the effects of different concentrations of CdCl₂(0,5, 10,0, 40and 80mg/L) treated with alfalfa seed germination were studied under three conditions of pH (4.0,6.0and 8.0). The results showed that the treatments with low concentrations of CdCl₂(≤20mg/L) significantly improved the seed germination rate, germination potential, germination index and vigor index. Compared to the control group, the vigor index greatly increased up to 177.52±16.61under the treatments of concentration of CdCl_2was 20mg/L (pH 6.0). The promotion for root length, shoot length, root fresh weight and shoot fresh weight were also strengthened with the increasing concentration under 20mg/L CdCl₂.Treated with concentration of CdCl_2was 20mg/L under pH 4.0, pH 6.0and pH 8.0, the shoot fresh weight was (6.60±0.11), (6.68±0.20) and (9.51±0.16) mg, while root fresh weight was (6.71±0.10), (7.09±0.08) and (9.10±0.08) mg, up to the maximum respectively. The seed germination and seedling growth of alfalfa were significantly inhibited as CdCl_{2concentration} increased (40and 80mg/L). Under 80mg/L, the germination rate and vigor index of alfalfa seed were only 14.8% and 46.5% of those of controls, and shoot fresh weight decreased to (3.48±0.15), (4.03±0.19) and (7.00±0.22) mg under pH 4.0, pH 6.0and pH 8.0, all down to the minimum respectively. The germination rate and vigor index of alfalfa seed decreased with the decrease of pH. Treated with concentration of CdCl_2was 80mg/L under weak base (pH 8.0) condition, the germination rate (66.40%±3.19%) was higher than those treated with strong acid (pH 4.0) (11.20%±3.61%) and weak acid (pH 6.0) (9.20%±4.22%), while the vigor index (93.90±10.71) was also higher than those under pH 4.0(49.77±3.25) and pH 6.0(56.67±3.48), respectively. The results indicated that adjust of the environment from acid to alkaline could alleviate CdCl_2toxicity to seed germination and seedling growth in alfalfa.