Effects Of Cadmium,Zinc And Their Interactions On Accumulation,Translocation And Subcellular Distribution Of Cadmium And Zinc In Spartina Alterniflor

Heavy metals are typical refractory cumulative pollutants, which can be accumulated in the ecosystem through the food chain. And they can be transformed into more toxic metal compounds under some conditions, causing direct or potential hazards to wetland ecosystem and coastal estuaries. Phytoremediation is an emerging technology that uses plants to clean up pollutants from the environment. Compared with physical-chemical methods, phytoremediation has been highlighted as an effective remediation technique repairing heavy metal polluted soil, for their advantages of low-cost and environmentally friendly.Spartina alterniflora is a rhizomatous perennial grass native to the temperate Atlantic and Gulf coast of North America. This species occupies low intertidal mudflats or the river beach affected by tide. In1979, S. alterniflora was introduced to China. At present, from North Sea in Guangxi of southern China to Tanggu in Tianjin and Panjin in Liaoning of Northern China, S. alterniflora has formed the dominant population of the salt marsh habitat. Although it leads to a certain amount of competitive pressure to some native coastal species in southern China, causing some negative effect, it plays an important role in repairing and cleaning pollutants in northern China. Because it can not only promote the silt land reclamation and protect embankment, but also change the beach environment. In order to provide scientific evidence for the accumulation and translocation pattern of Cd and Zn in S. alterniflora, we studied the accumulation, translocation and subcellular distribution of Cd and Zn in S. alterniflora under different treatments of Cd, Zn and their interactions. Our results in this study may provide important theory basis for the protection and sustainable utilization of wetland ecosystems. The results are summarized as follows:(1) Under Cd stress, S. alterniflora could also grow normally under the highconcentration of Cd treatment(200μg·g-1), without obvious external poisoning symptom, which suggested the high Cd tolerance of S. alterniflora. The transport coefficient of Cd in S. alterniflora was low under Cd treatments, which showed that S. alterniflora retained high amounts of Cd in roots, limiting its transfer to the shoots. The great amount of Zn presented in cell wall fraction, followed by cytoplasmic supernatant. In all, the subcellular distribution of Zn presented the following order: cell wall>cytoplasmic supernatant>cell organelle, and the sesults suggested that the chelating ability of the cell wall was the main mechanism of Cd tolerance for S. alterniflora.(2) Under Zn stress, low concentration of Zn promoted the growth of S. alterniflora, while the high concentration of Zn restrained its growth. The highest content of Zn could be finded in the fine roots of S. alterniflora, while the highest accumulation in the leaves. The transport coefficient of Zn in S. alterniflora was high under Zn treatments, which indicated the strong translocation ability of S. alterniflora. The subcellular distribution of Zn presented the following order:cell wall≥cytoplasmic supernatant> cell organelle and the results suggested that Zn mainly distributed in cell wall and vacuole, and the chelating ability of cell wall and the compartmentalization of vacuole were the main mechanism of Zn tolerance for S. alterniflora.(3) Cd-Zn interaction had more severe impact on the growth of S. alterniflora than Cd or Zn treatment singly. The growth of S. alterniflora could be significantly inhibited under Cd-Zn interaction. Zn increased Cd uptake of S. alterniflora, while Cd reduced Zn uptake. Zn had significant impact on the subcellular distribution of Cd in different organs of S. alterniflora, causing the transfer of Cd from cell wall to vacole, while the presence of Cd had no obvious effect on Zn distribution in plant cell. The main chemical forms of Cd and Zn in the leaves of S. alterniflora were the NaCl-extractable Cd and NaCl-extractable Zn.