| In the present study, we selected the widely distributed aquatic plant Lemna minor as the experimental material, the mercury as the stress factor, investigated the stress effects of Hg in L. minor by applying technology of plant physiology and biochemistry, random amplified polymorphic DNA (RAPD), and western-blot technology. The results as follows:1. Using different concentrations of (0, 10, 20, 30 ?mol·L-1) Hg to deal with duckweed for 2 and 6 d, measure their Hg uptake, morphological changes, root length, photosynthetic pigments, starch and soluble protein contents, lipid peroxidation and cell death. Results indicated that the accumulation of Hg increased in a concentration- and duration-dependent manner, reached 7.4 mg·g-1 dry weight when exposed to 30 ?mol·L-1 Hg for 6 d.Photosynthetic pigments decreased as the concentration of Hg increased at all times of exposure. The maximum reduction in the contents of chlorophyll a (52% reduction),chlorophyll b (40% reduction), and carotenoid (26% reduction) were observed in fronds exposed to 30 ?M Hg of 6 d. Pictorial diagram showed that the damage degree of leaf and root become more serious with the increasing concentration of Hg. LOX activity exhibited a bell-shaped curve, but the content in highest concentration group is still higher than the controls. Soluble protein content increased up to 20 ?mol·L-1 Hg, and then decreased sharply at 2 d; and for 6 d, it was gradual declined with increasing Hg concentrations. Hg exposure increased MDA content and cell death in L. minor, in a concentration- and time-dependent manner. These results suggest that L. minor massively accumulated Hg, this accumulation was accompanied by oxidative damage and cell death.2. After exposing L. minor to various concentrations of Hg (0, 10, 20, 30 ?mol·L-1) for 2 and 6 days, the effects on antioxidant mechanisms and osmolytes was investigated. After treatment of Hg, the activities of peroxidase (POD), catalase (CAT) and ascorbate peroxidase(APX) were increased significantly, and the superoxide dismutase (SOD) and glutathione reductase (GR) activities were inhibited apparently. The contents of ascorbate (AsA) and glutathione (GSH) showed increasing trend, nonprotein SH (NP-SH) content was offered upgrade firstly than descending latter tendency. Glutathione synthetase (GS) activity was induced slightly and the activity of phenylalanine ammonia lyase (PAL) increased slightly at 10 ?mol·L-1 Hg and then decreased sharply. The contents of proline and soluble sugar were observed to be a dropping trend after the first rise, but the contents in highest concentration group is still higher than the controls. These results suggest that anti-oxidative enzymes such as POD, CAT and APX, and small molecule antioxidant, eliminate low Hg stress at a certain extent, but cannot relieve high Hg stress disruption.3. The isoenzyme analyses, Hsp70 expression and DNA damage in L. minor after 2 and 6 d of exposure to various concentrations of (0, 10, 20, 30 ?mol·L-1) Hg were determined. LOX and CAT isoforms expression quantity offered upgrade firstly than descending latter tendency,and in highest concentration group were lower than the controls. APX expression quantity presented a trend of escalation along with Hg concentration increasing at 2 d, and decreased at higher Hg concentrations at 6 d, but remained higher than the unexposed controls. The SOD and GR isozymes expression quantity reduced generally. All of the above isozymes only APX was induced a new isozyme by Hg exposure. Western-blot analysis showed that exposure to Hg induced the accumulation of Hsp70, despite the decrease in Hsp70 at higher Hg concentrations and longer period, its level remained higher than the controls. The amplification of new bands and the absence of normal DNA amplicons in treated plants in the random amplified polymorphic DNA (RAPD) profile indicated that genomic template stability (GTS) was affected by Hg treatment. |
PDF Full Text Request