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.

In vivo studies on toxin accumulation in liver and ultrastructural changes of hepatocytes of the phytoplanktivorous bighead carp i.p.-injected with extracted microcystins

Phytoplanktivorous bighead carp were injected i.p. with extracted microcystins (mainly MC-RR and -LR) at two doses, 200 and 500 MC-LReq. mu g kg(-1) bw, and the changes in extractable MCs in liver and in the ultrastructure of hepatocytes were studied at 1, 3, 12, 24 and 48 h after injection. Quantitative and qualitative determinations of MCs in the liver were conducted by HPLC and LC-MS, respectively. MC concentration in the liver reached the maxima at 12 It (2.89 mu g MCs g(-1) dry weight at the lower dose) or at 3 h (5.43 mu g MCs g(-1) dry weight at the higher dose) post-injection, followed by sharp declines afterwards, whereas the ultrastructural changes of hepatocytes in both dose groups suggest progressive increases in severity toward the directions of apoptosis and necrosis from I to 24 h, respectively. There were two new findings in fish: widening of intercellular spaces was among the early ultrastructural changes induced by MCs and ultrastructural recovery of hepatocytes was evident at 48 h post-injection in both dose groups. Both the present and previous studies suggest that with in vivo or in vitro exposure to microcystins, hepatocyte damage in fish tends to proceed toward the direction of apoptosis at lower MC concentrations but toward the direction of necrosis at high MC concentrations. The temporal dynamics of MCs in the liver suggest that bighead carp may have a mechanism to degrade or bind MC-LR actively after it enters the blood system. (c) 2005 Elsevier Ltd. All rights reserved.

Kinetic studies on the effects of rare earth elements (REES) on the growth of Microcystis and their accumulation by Microcystis

In the paper the kinetic effects of La3+ and Ce4+ on the growth of Microcystis and the accumulation kinetics of Microcystis in the single and combined systems of La3+ and Ce4+ were studied. The mechanism of the effects of La3+ and Ce4+ on the growth of Microcystis and their accumulation kinetics were also discussed. In the single system, La3+ stimulated the growth of Microcystis at initial concentrations below 2 mg / 1, but inhibited it above 2 mg / 1. Ce4+ accelerated the growth of Microcystis at initial concentrations below 0.2 mg / 1 and inhibited at above 0.2 mg /l. Furthermore, the stimulation weakened with the increase of initial concentrations of La3+ and Ce4+. In the combined system, the growth of Microcystis was accelerated in the over all cases. In the single system, the amount of La3+ and Ce4+ uptake was more at higher initial concentrations than at lower ones. At the same initial concentrations, La3+ and Ce4+ uptake in the combined system was less than that in the single system. The kinetic process of La3+ and Ce4+ adsorpted by Microcystis can be explained with the second order kinetics adsorption model.

Distribution, transformation, and long-term accumulation of polychlorinated dibenzo-p-dioxins and dibenzofurans in different tissues of fish and piscivorous birds

The present study monitored 10-year-old fish and piscivorous birds from sites contaminated for many Stars. The data reflected the results of actual, long-term environmental exposures, The results demonstrate that different tissues of fish have quite different concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), The concentration order of PCDD/F within fish is liver congruent to egg congruent to intestines kidney congruent to hearts gill congruent to bladders > muscle > brain. The concentration order of PCDD/F within piscivorous birds was livers egg congruent to hearts muscle congruent to stomachs brain, The results obtained also demonstrate that the accumulation patterns of piscivorous birds and fish are quite different. The tissues of fish and piscivorous birds have different capacities for bioaccumulation and biotransformation of PCDD/F; variable proportions of TEQs were also found throughout their bodies. In fish, toxic equivalency quotient (TEQ): PCDD/F ratios in various tissues ranged from 0.01 to 0.07, whereas in birds the ratios ranged from 0.07 to 0.43. If the concentrations are normalized with lipid content, the results vary less. The effect of different lipid properties is obvious in the case of brain tissue, which is richer in phospholipids. (C) 2000 Academic Press.

Temperature-dependent transport and spin accumulation in a quantum wire with Rashba spin-orbit interaction

We study the theory of temperature-dependent electron transport, spin polarization, and spin accumulation in a Rashba spin-orbit interaction (RSOI) quantum wire connected nonadiabatically to two normal conductor electrode leads. The influence of both the wire-lead connection and the RSOI on the electron transport is treated analytically by means of a scattering matrix technique and by using an effective free-electron approximation. Through analytical analysis and numerical examples, we demonstrate a simple way to design a sensitive spin-transfer switch that operates without applying any external magnetic fields or attaching ferromagnetic contacts. We also demonstrate that the antisymmetry of the spin accumulation can be destroyed slightly by the coupling between the leads and the wire. Moreover, temperature can weaken the polarization and smear out the oscillations in the spin accumulation.

长期施用氮、磷和有机肥对不同种植体系土壤有效硫累积的影响

以22年定位试验为基础,研究了长期施用氮、磷和有机肥(NPM)对不同种植体系土壤有效硫在剖面上分布与累积状况。结果表明,在60—80 cm土层各处理出现第一个累积峰,累积峰值为粮饲轮作31.3,玉米连作29.2,小麦连作27.9,粮豆轮作25.6,苜蓿连作24.0 mg/kg;在140—180 cm土层各处理又出现有效硫的第二个累积峰,累积峰值为粮饲轮作44.7,粮豆轮作43.1,小麦连作41.0,玉米连作39.7,苜蓿连作36.5 mg/kg。第二累积峰值均大于第一累积峰值。0—200 cm土层有效硫总累积量粮饲轮作高达746.3 kg/hm~2,其次为玉米连作640.6,粮豆轮作为638.3,小麦连作为622.4,苜蓿连作最小为557.3 kg/hm~2。长期施用磷肥和有机肥是有效硫在土壤中累积的主要因素,有效硫在土壤剖面上有向深层迁移的趋势。不同作物对硫的吸收利用差异和不同种植方式对有效硫的累积与分布产生影响。