水淹条件下秋华柳亚细胞中镉的分配特征

选取秋华柳(Salix variegata)扦插苗为研究对象,通过设置0、0.5、2、10 mg/kg 4个镉胁迫浓度,研究了水淹条件下秋华柳根、枝、叶亚细胞中镉的分配特征。结果表明:(1)试验各处理组秋华柳存活率均为100%,表现出良好的镉和水淹耐受能力。(2)与对照相比,在水淹条件下,各处理组秋华柳根、枝和叶的细胞壁仍是镉最主要的富集部位。各处理组植株细胞壁中的镉含量显著高于其他组分,质体中镉含量次之,细胞核和线粒体组分中的镉含量始终处于较低水平。(3)水淹显著提高了秋华柳根细胞壁中的镉含量,显著降低了高浓度镉处理(10 mg/kg)下萌枝细胞壁中的镉含量,但对叶细胞壁中的镉含量没有显著影响。(4)水淹显著提高了秋华柳根细胞中质体中的镉含量,对萌枝、叶细胞质体中的镉含量没有显著影响。研究证明,水淹条件下,秋华柳根枝叶细胞壁仍然是镉积累富集的最主要部位,从而减少了重金属对植物细胞的伤害。秋华柳适用于三峡消落带镉污染区域的植物修复。

Cadmium distribution in the subcellular fractions of Salix variegata under flooding conditions

The altered water regime of the Three Gorges reservoir in the Yangtze River in China has formed a hydro-fluctuation zone that has caused many serious environmental problems, such as vegetation degradation, soil erosion, and landscape deterioration. After water impoundment, heavy metals in the soil can dissolve into the water, thereby increasing the risk of water pollution. Cadmium (Cd) contamination is one of the most serious heavy metal pollutions in the Three Gorges reservoir area. Cd shows high biological activity; it can easily enter the food chain via absorption by plants and affect the ecosystem health. Revegetation is an eco-friendly measure in restoring ecological integrity of the hydro-fluctuation zone. However, it is a great challenge to successfully revegetate the degraded hydro-fluctuation zone because the plants need to exhibit tolerance to the altered water regime and Cd contamination. Salix variegata, a native species in the Three Gorges reservoir, exhibits tolerance to both long-term flooding and heavy metal stress and therefore, is a promising candidate for revegetation in this area. However, the ability of this species to tolerate and accumulate Cd under flooding conditions is still unclear. To explore the effect of flooding on Cd distribution in subcellular fractions of S. variegata, 60-d long factorial experimental treatments including two water regimes and four Cd concentrations were designed. The water treatments included ambient water supply (CK) and light flooding (FL), whereas the Cd treatments included control and low, middle, and high concentrations (0, 0.5, 2, and 10 mg/kg, respectively). Each treatment involved a group of planted S. variegata shoots. Plant cells were separated into subcellular fractions of cell walls, plastids, cell nuclei, and mitochondria and soluble fractions, by differential centrifugation. All subcellular fractions were digested using microwave digestion and the Cd content in different subcellular fractions was determined using an inductively coupled plasma-atomic emission spectrometer. The results showed that:(1) The survival rate of S. variegata in all treatments was 100%, which indicated high tolerance of this species to flooding and Cd stress. (2) Most of the accumulated Cd was more highly enriched in the cell walls of plant cells under FL than under CK. In contrast, the Cd content in the nucleus and mitochondria was always lower under FL than under CK. (3) Under FL, the Cd content significantly increased in root cell wall, decreased in stem cell wall under high Cd concentration, and showed no significant difference in leaf cell wall. (4) Flooding significantly increased Cd content in plastids of root cells; however, it did not affect the Cd content in plastids of stem and leaf cells. In conclusion, in S. variegata under flooding conditions, cell wall was still the main subcellular component enriched with Cd, which reduced the harmful effects of Cd stress on plants. These results indicated that there was no significant difference in the allocation strategy of Cd in subcellular fractions under flooding and ambient water supply for S. variegata, and that S. variegata could be suitable for phytoremediation of Cd in the hydro-fluctuation zone of the Three Gorges reservoir.