Studies On The Physiological Response And Resistant Mechanisms Of Athyrium Niponicum Hance Under Pb And As Pollution

Lead (Pb) and arsenic (As) are two main elements of soil heavy metal pollution, and their combined contamination is a common phenomenon. Because of its low cost and environmental friendliness, phytoremediation has become a green and effective approach for remediation of heavy metal contaminated soils. Finding special hyperaccumulators is the foundation of phytoremediation. To elucidate systematically the toxicity and tolerance mechanisms of Athyrium niponicum Hance to heavy metal stress at tissue and subcellular level, pot experiments were conducted to investigate effects of Pb and As single and combined pollution on the membrane lipid peroxidation and antioxidant enzymes systems, leaf ultra-structure, accumulation, transportation and enrichment characteristics of Athyrium niponicum with electron microscopy technique, ICP-MS and other physiological measurement methods. The major results were summarized as follows:1. With the increasing of treatment concentration and the prolonging stress days of Pb and As, the total chlorophyll, chlorophyll a and chlorophyll b decreased compared with control, and chlorophyll a decreased more significantly than chlorophyll b. The single and combined Pb and As stress caused A. niponicum frond membrane lipid peroxidation, coupling the malondialdehyde (MDA) and soluble protein (SP) contents increased. The superoxide dismutase (SOD) and peroxidase (POD) activities were induced to first increase and last decline obviously, respectively. Single As stress injured A. niponicum more severely than single Pb on the same concentration, indicated that A. niponicum has stronger tolerance to Pb stress. Compared with single stress, the interactions of Pb and As combined stress on the physiological injure were the trend of synergistic effect, but on the high concentration (Pb400As400), it showed slight antagonism.2. Accumulation of Pb in frond, stipe and root of A. niponicum increased signficantly with the increasing of the concentrations single of Pb and combined stress. A. niponicum uptake Pb mainly in stipe, following in root and frond, respectively. A. niponicum showed strong accumulation and transfer ability to Pb. The bioaccumulation factor (BF) and transfer factor (TF) of A. niponicum to Pb were increase as the Pb treatment concentration increased, and both peak values were greater than 1. The results were consistented with McGrah et al (2003) on the definitions of the hyperaccumulators, indicating that A.niponicum was a Pb hyperaccumulator. Compared with Pb, As was accumulated by A.niponicum mainly in root, following in stipe and frond. The BF and TF of A.niponicum to As were less than 1, which indicated that A.niponicum was not a As hyperaccumulator. On the subcellular level, whether in root, stipe or frond of A.niponicum, cell wall was the main part of Pb and As accumulation, accounting for more than 50 percent, reducing damage to A.niponicum. 3. Ultra-structure of A. niponicum fronds were damaged by lead and arsenic stress to some extent. The chloroplast was the most sensitive organelles among which were affected by heavy metals stress, such as thylakiods of chloroplast swelled, chloroplast membrane disappeared, osmilphilic granule increased obviously, and chloroplast which was wounded serious disintegrated. The symptoms of wounded nucleus were nuclear membrane disrupted, agglomeration of chromatin and nucleoplasm of nucleus. The damaged mitochondria expressed the symptoms of disruption of mitochondria membrane and vacuolation. The damage of single arsenic on A. niponicum.was more severe the damage of single lead in the same concentration and the interactions of lead and arsenic combined stress on the chloroplast, mitochondria and nuleus were synergistic effects.