土壤重金属镉胁迫对石竹幼苗生长的影响及其机理

为了揭示土壤重金属镉(Cd)对植物的毒害机理,采用温室盆栽试验方法,研究了不同浓度(0, 0.3, 1, 3, 10, 30和50 mg/kg)Cd污染土壤对石竹幼苗生长以及对抗坏血酸-谷胱甘肽(AsA-GSH)循环的影响。结果表明,石竹幼苗的分蘖数、株高和生物量表现出显著的“低促高抑”的现象,这缘于土壤Cd低浓度(≤1 mg/kg)胁迫和胁迫的初期,石竹叶片的超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDAR)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)等抗氧化酶活性提高,以抵抗体内逐渐增多的活性氧(ROS);随着Cd浓度的增加和镉胁迫时间的延长,石竹叶片中的超氧阴离子(O₂^-·)和过氧化氢(H₂O₂) 等ROS爆发,SOD、APX、MDAR、DHAR和GR等抗氧化酶活性迅速降低,抗坏血酸(AsA)和谷胱甘肽(GSH)含量减少,过多的ROS不能被石竹自身的抗氧化系统有效地清除,最终导致膜脂过氧化受到逆境伤害。另外,试验结果验证了APX是清除H₂O₂的重要酶,GR是生成GSH的重要酶,MDAR还原MDHAR是AsA-GSH循环中再生AsA的主要途径。

Effect and mechanisms of soil cadmium stress on Dianthus chinensis seedling growth

The toxicity mechanisms of soil heavy metal cadmium (Cd) were investigated on seedling growth of Dianthus chinensis and its ascorbic acid-glutathione (AsA-GSH) cycle using concentrations of (0, 0.3, 1, 3, 10, 30 and 50 mg/kg Cd) in the soil in a greenhouse pot experiment. Seedling tiller number, height and biomass exhibited significantly ‘low promoting/suppression’ phenomena. This was because the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and some other antioxidant enzymes increased gradually against increased reactive oxygen species in seedling leaves at low concentrations of soil Cd and at the beginning of the stress. With an increase in Cd concentration and prolonged stress time, the activities of SOD, APX, MDAR, DHAR and GR decreased. This led to the accumulation of excessive reactive oxygen species that could not be removed in an effective way, thus resulting in an outbreak of the superoxide anion (O₂^-·), hydrogen peroxide (H₂O₂), and some other reactive oxygen species, eventually causing membrane lipid peroxidation and stress damage. This work also demonstrated that APX was an important enzyme for H₂O₂ removal, and GR was an important enzyme to generate GSH. It was the main way to renew AsA in the AsA-GSH cycle and restore MDAR to MDHAR.