Bioaccumulation, subcellular, and molecular localization and damage to physiology and ultrastructure in Nymphoides peltata (Gmel.) O. Kuntze exposed to yttrium.

Bioaccumulation, subcellular distribution, and acute toxicity of yttrium (Y) were evaluated in Nymphoides peltata. The effects of Y concentrations of 1-5 mg L(-1) applied for 4 days were assessed by measuring changes in photosynthetic pigments, nutrient contents, enzymatic and non-enzymatic antioxidants, and ultrastructure. The accumulation of Y in subcellular fractions decreased in the order of cell wall > organelle > soluble fraction. Much more Y was located in cellulose and pectin than in other biomacromolecules. The content of some mineral elements (Mg, Ca, Fe, Mn, and Mo) increased in N. peltata, but there was an opposite effect for P and K. Meanwhile, ascorbate, and catalase activity decreased significantly for all Y concentrations. In contrast, peroxidase activity was induced, while initial rises in superoxide dismutase activity and glutathione content were followed by subsequent declines. Morphological symptoms of senescence, such as chlorosis and damage to chloroplasts and mitochondria, were observed even at the lowest Y concentration. Pigment content decreased as the Y concentration rose and the calculated EC50 and MPC of Y for N. peltata were 2 and 0.2 mg L(-1) after 4 days of exposure, respectively. The results showed that exogenous Y was highly available in water and that its high concentration in water bodies might produce harmful effects on aquatic organisms. N. peltata is proposed as a biomonitor for the assessment of metal pollution in aquatic ecosystems.

Responses of Hydrilla verticillata (L.f.) Royle to zinc: in situ localization, subcellular distribution and physiological and ultrastructural modifications.

Hydrilla verticillata (L.f.) Royle exposed to 15-150 µM Zn for 7 days were analyzed with reference to the ultrastructural localization, subcellular distribution of metal and its influence on photosynthetic efficiency, malondialdehyde (MDA), adenosine triphosphate (ATP) and ultrastructure. Zn grains were found in the cell walls and within nuclei and chloroplasts using the autometallographic technique. Subcellular fractionation of Zn-containing tissues indicated 43-54% of the element was located in the cell wall fraction, followed by cell organelles (24-31%) and the soluble fraction (21-29%). A significant reduction in photosynthetic efficiency was observed in a concentration dependent manner, as indicated by the reduced efficiency of the PS II photochemical system (Fv/Fm). MDA content showed a sharp increase at all Zn concentrations, which indicated oxidative stress. Zn-exposed plants displayed a significant decrease in ATP content. Zn exposure also caused the chloroplasts and nuclei to disintegrate and the vacuolization of mitochondria, all of which suggested that Zn hastened plant senescence.

Copper ultrastructural localization, subcellular distribution, and phytotoxicity in Hydrilla verticillata (L.f.) Royle.

Laboratory experiments were conducted to investigate copper (Cu) subcellular distribution and toxicity in Hydrilla verticillata. Fronds were subjected to different concentrations (15, 75, and 150 µM) of Cu for 7 days. Cu grains were found in cell walls, plasmodesmata, and within the nuclei and chloroplasts using the autometallographic technique. Subcellular fractionation of Cu-containing tissues indicated that in leaves subjected to high Cu concentrations, 59-65 % of the element was located in the cell wall fraction, followed by cell organelles (21-30 %) and the soluble fraction (10-14 %). The levels of K, P, Zn, and Mg declined under all Cu concentrations, but Ca, Mn, and Fe contents reached their peak at 15 µM Cu and decreased thereafter. F v/F m, F 0, and F m fell significantly in line with the decrease in pigment content. Cu exposure also caused significant damage to the chloroplasts, mitochondria, and nuclei, including disintegration of the chloroplasts and vacuolization of the mitochondria and nuclei, all of which suggested that Cu hastened plant senescence. The Cu maximum permissible concentration for H. verticillata was 10 µM, which was less than the existing general water quality standard. This suggested that H. verticillata could be used to assess Cu phytotoxicity.

Laboratory assessment of uptake and toxicity of lanthanum (La) in the leaves of Hydrocharis dubia (Bl.) Backer.

Increasing amounts of lanthanum (La) is released into aquatic environments. However, little information is available on the influence of La on aquatic plants. In this study, physiological and ultrastructural responses of Hydrocharis dubia (Bl.) Backer leaves to elevated concentrations of La (up to 160 µM) were investigated. The accumulation of La was found to be increased in a concentration-dependent manner. La disturbed the intrinsic balance of nutrient elements (P, Mg, Ca, Fe, K, and Zn). Pigment content decreased with the rise of the La concentrations and the EC(50) value for chlorophyll was 20 µM on day 7. The antioxidants (superoxide dismutase, peroxidase, catalase, reduced ascorbate, and reduced glutathione) exhibited varied response to the La treatments. Malondialdehyde content enhanced gradually at all La concentrations. The enhancement in proline content was found in a concentration-dependent manner. The amounts of three polypeptides with apparent molecular weights of 61.9, 51.5, and 16.7 kDa, respectively, were gradually diminished, as well as one existing polypeptides with apparent molecular weight of 22.3 kDa, elevating in response to increasing La concentrations. Significant damage to the chloroplast, mitochondrion, and nucleus was imposed by La indicated a general disarray in the cellular functions. The negative effects of La on H. dubia unequivocally indicate that La could exert an adverse influence on aquatic ecosystem and should lead to a more careful discharge of such elements into water environment.

Subcellular distribution and toxicity of cadmium in Potamogeton crispus L.

The submerged macrophyte Potamogeton crispus L. was subjected to varying doses of cadmium (0, 20, 40, 60 and 80 µM) for 7 d, and the plants were analyzed for subcellular distribution of Cd, accumulation of mineral nutrients, photosynthesis, oxidative stress, protein content, and ultrastructural distribution of calcium (Ca). Leaf fractionation by differential centrifugation indicated that 48-69% of Cd was accumulated in the cell wall. At all doses of Cd, the levels of Ca and B rose and the level of Mn fell; the levels of Fe, Mg, Zn, Cu, Mo, and P rose initially only to decline later. Exposure to Cd caused oxidative stress as evident by increased content of malondialdehyde and decreased contents of chlorophyll and protein. Photosynthetic efficiency, as indicated by the quenching of chlorophyll a fluorescence (Fv/Fm, Fo and Fm), decreased significantly, the extent of decrease being directly proportional to the concentration of Cd. Increased amounts of precipitates of calcium were noticed in the treated plants, located either outside the cell membrane or in chloroplasts, mitochondria, the nucleus, and the cytoplasm whereas control plants showed small deposits of the precipitates around surface of the vacuole membrane and in the intercellular space but rarely in the cytoplasm. Photosynthetic efficiency and oxidative stress could be used as indicators of physiological end-points in determining the extent of Cd phytotoxicity.