The first study on the effects of microcystin-RR on gene expression profiles of antioxidant enzymes and heat shock protein-70 in Synechocystis sp PCC6803

Microcystins are heptapeptide toxins produced by cyanobacteria. Microcystin-RR(MC-RR) is a common variant among the 80 variants identified so far. There have been many investigations documenting the toxic effects of microcystins on animals and higher plants, but little is known on the toxic effects of microcystins on algae, especially at molecular level. We studied the effects of MC-RR on gene expression profile of a few antioxidant enzymes and heat shock protein-70 (Hsp70) in Synechocystis sp. PCC6803. After two days post-exposure, a high dose toxin (5 mg/l, about 4.8 x 10(-3) mM) significantly increased expression levels of the genes gpx1, sodB, katG, acnB, gamma-TMTand dnaK2, while a relatively low dose toxin (1 mg/l, about 9.63 x 10(-4) mM) induced a moderate and slow increase of gene expression. Our results indicate that MC-RR could induce the oxidative stress in Synechocystis sp. PCC6803 and the increase in gene expression of antioxidant enzymes and Hsp70 might protect the organism from the oxidative damage. in addition, cell aggregation was observed during the early period of exposure, which might be a specific oxidative stress reaction to MC-RR. (C) 2008 Elsevier Ltd. All rights reserved.

Trends of Superoxide Dismutase and Soluble Protein of Aquatic Plants in Lakes of Different Trophic Levels in the Middle and Lower Reaches of the Yangtze River, China

A limnological study was carried out to determine the responses of superoxide dismutase (SOD) activities and soluble protein (SP) contents of 11 common aquatic plants to eutrophication stress. Field investigation in 12 lakes in the middle and lower reaches of the Yangtze River was carried out from March to September 2004. Our results indicated that non-submersed (emergent and floating-leafed) plants and submersed plants showed different responses to eutrophication stress. Both SOD activities of the non-submersed and submersed plants were negatively correlated with their SP contents (P < 0.000 1). SP contents of non-submersed plants were significantly correlated with all nitrogen variables in the water (P < 0.05), whereas SP contents of submersed plants were only significantly correlated with carbon variables as well as ammonium and Secchi depth (SD) in water (P < 0.05). Only SOD activities of submersed plants were decreased with decline of SD in water (P < 0.001). Our results indicate that the decline of SOD activities of submersed plants were mainly caused by light limitation, this showed a coincidence with the decline of macrophytes in eutrophic lakes, which might imply that the antioxidant system of the submersed plants were impaired under eutrophication stress.

The accumulation of alkylphenols in submersed plants in spring in urban lake, China

The concentrations of alkylphenols (APs) were investigated in water, sediments and submersed macrophytes from the Moon Lake, Wuhan city, China. The water samples contained APs, ranging up to 26.4 mu g l(-1) for nonylphenol (NP) and 0.68 mu g l(-1) for octylphenol (OP). APs were found in the sediment samples with concentrations ranging from 4.08 to 14.8 for NP and from 0.22 to 1.25 mu g l(-1) dry weight for OP. The samples from the site near former sewage inlet showed the highest concentrations of APs in both water and sediments. The results of distribution pattern and dynamics of NP and OP in submersed macrophytes of the Moon Lake showed that the two pollutants were all found in Myriophyllum verticillatum, Elodea nuttallii, Ceratophyllum oryzetorum, and Potamageton crispus collected from the Moon Lake. For NP, M. verticillatum had the highest capacity of accumulation, followed by E. nuttallii, C. oryzetorum and P. crispus. However the distribution pattern of OP differed from that of NP, and the highest amount of accumulation was observed in E. nuttallii, followed by M. verticillatum, P. crispus, and C. oryzetorum. The temporal pattern of APs was also observed in submersed macrophytes from March to May, and the highest accumulation period was in May. (c) 2008 Elsevier Ltd. All rights reserved.

Growth and antioxidant system of Escherichia coli in response to microcystin-RR

Microcystins are a kind of cyclic hepatoxins produced by many species of cyanobacteria. The toxic effects of microcystins on animals and plants have been well studied. However, the reports about the effects of microcystins on microbial cells are very limited. In present paper, Escherichia coli was undertaken to determine the effect of microcystin-RR. These results suggested that microcystin-RR could prolong the growth of E. coli when exposed to high concentrations of microcystin-RR and cause the accumulation of ROS and induce the oxidant stress for a short time. The antioxidant system protects E. coli from oxidative damage.

Responses of antioxidant system in Arabidopsis thaliana suspension cells to the toxicity of microcystin-RR

Microcystins are cyclic heptapeptide hepatoxins produced by many species of cyanobacteria. The toxic effects and mechanism of microcystins on animals have been well studied both in vivo and in vitro. It was also reported that microcystins had adverse effects on plants. However, to our knowledge, there is no information about the toxic effects and mechanism of microcystins on plant suspension cells. In this study, Arabidopsis thaliana suspension cells were exposed to a range dose of microcystin-RR. Lipid peroxidation, a main manifestation of oxidative damage, was studied and a time- and dose-dependent increase in malondiadehyde was observed. In contrast, glutathione (GSH) levels in the cells decreased after 48 h treatment with 1 and 5 mg/L of microcystin-RR. The activities of superoxide dismutase (SOD) and catalase (CAT) increased significantly after 48 h exposure to I and 5 mg/L of microcystin-RR, but glutathione S-transferase (GST) activity showed no difference compared with the control. These results clearly indicate that microcystin-RR is able to cause oxidative damage in A. thaliana suspension cells. Decrease of GSH content and increases of SOD and CAT activities reveal that the antioxidant system may play an important role in eliminating or alleviating the toxicity of microcystin-RR. The possible toxicity mechanism of microcystin-RR on the A. thaliana suspension cells is also discussed in this paper. (C) 2005 Elsevier Ltd. All rights reserved.

Microcystin-RR-induced accumulation of reactive oxygen species and alteration of antioxidant systems in tobacco BY-2 cells

Microcystins are cyclic heptapeptide hepatoxins produced by cyanobacteria. It has been shown that microcystins have adverse effects on animals and on plants as well. Previous researches also indicated that microcystins were capable of inducing oxidative damage in animals both in vivo and in vitro. In this study, tobacco BY-2 suspension cell line was applied to examine the effects of microcystin-RR on plant cells. Cell viability and five biochemical parameters including reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), glutathione peroxide (GPX) and peroxide dismutase (POD) were investigated when cells were exposed to 50 mg/L microcystin-RR. Results showed that microcystin-RR evoked decline of the cell viability to approximately 80% after treating for 144 h. ROS levels, POD and GPX activities of the treated cells were gradually increased with a time dependent manner. Changes of SOD and CAT activities were also detected in BY-2 cells. After 168 h recovery, ROS contents, POD, GPX and CAT activities returned to normal levels. These results suggest that the microcystin-RR can cause the increase of ROS contents in plant cells and these changes led to oxidant stress, at the same time, the plant cells would improve their antioxidant abilities to combat mirocystin-RR induced oxidative injury. (c) 2005 Elsevier Ltd. All rights reserved.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Effects of microcystins on the growth and the activity of superoxide dismutase and peroxidase of rape (Brassica napus L.) and rice (Oryza sativa L.)

Microcystins are naturally occurring hepatotoxic cyclic heptapeptides produced by some toxic freshwater cyanobacterial species. In this study, crude extract of toxic cyanobacterial blooms from Dianchi Lake in southwestern China was used to determine the effects of microcystins on rape (Brassica napus L.) and rice (Oryza sativa L.). Experiments were carried out on a range of doses of the extract (equivalent to 0, 0.024, 0.12, 0.6 and 3 mug MC-LR/ml). Investigations showed that exposure to microcystins inhibited the growth and development of both rice and rape seedlings, however, microcystins had more powerful inhibition effect on rape than rice in germination percentage of seeds and seedling height. Microcystins significantly inhibited the elongation of primary roots of rape and rice seedlings. Determination of the activities of peroxidase and superoxide dismutase demonstrated that microcystin stress was manifested as an oxidative stress. Using ELISA, microcystins were examined from the extract of exposed rape and rice seedlings, indicating that consumption of edible plants exposed to microcystins via irrigation route may have health risks. Significantly different levels of recovered microcystins between exposed rice and rape seedlings Suggested that there might be different tolerant mechanisms toward microcystins. (C) 2004 Elsevier Ltd. All rights reserved.