The Glycine-Alanine Dipeptide Repeat from C9orf72 Hexanucleotide Expansions Forms Toxic Amyloids Possessing Cell-to-Cell Transmission Properties

Hexanucleotide expansions, GGGGCC, in the non-coding regions of the C9orf72 gene were found in major frontotemporal lobar dementia and amyotrophic lateral sclerosis patients (C9FTD/ALS). In addition to possible RNA toxicity, several dipeptide repeats (DPRs) are translated through repeat-associated non-ATG-initiated translation. The DPRs, including poly(GA), poly(GR), poly(GP), poly(PR), and poly(PA), were found in the brains and spinal cords of C9FTD/ALS patients. Among the DPRs, poly(GA) is highly susceptible to form cytoplasmic inclusions, which is a characteristic of C9FTD/ALS. To elucidate DPR aggregation, we used synthetic (GA)₁₅ DPR as a model system to examine the aggregation and structural properties in vitro. We found that (GA)₁₅ with 15 repeats fibrillates rapidly and ultimately forms flat, ribbon-type fibrils evidenced by transmission electron microscopy and atomic force microscopy. The fibrils are capable of amyloid dye binding and contain a characteristic cross-β sheet structure, as revealed by x-ray scattering. Furthermore, using neuroblastoma cells, we demonstrated the neurotoxicity and cell-to-cell transmission property of (GA)₁₅ DPR. Overall, our results show the structural and toxicity properties of GA DPR to facilitate future DPR-related therapeutic development.     

Antifeedant and toxic activity of Trichilia americana extract against the larvae of Spodoptera litura

The biological activity of a crude methanolic extract of Trichilia americana (Sesse and Mocino) Pennington (Meliaceae) was assessed using the Asian armyworm, Spodoptera litura (Fabr.) (Lepidoptera: Noctuidae). The extract exhibited strong antifeedant activity in a choice leaf disc bioassay with 0.18 g cm^–2 extract deterring feeding by 50%. In nutritional assays, the crude extract reduced growth, consumption and the utilisation of ingested and digested food in a dose-dependent manner when fed to larvae, suggesting both antifeedant and toxic activities. When relative growth rates were plotted against relative consumption rates, the growth efficiency of the S. litura fed on diet containing T. americana crude extract was significantly less than that of control larvae. This result further indicates that the extract acts as both an antifeedant and chronic toxin. Toxicity is only seen following ingestion and was not observed following topical application or injection into the hemocoel. Larvae reared initially on extract-containing diet then transferred to control diet showed nutritional indices comparable to those of larvae fed continuously on control diet. This suggests that the extract is not permanently damaging the insect's digestive tract. The mode-of-action of the extract as a chronic toxin remains unknown.     

Cadmium-induced oxidative damage in rice leaves is reduced by polyamines

The protective effect of polyamines against Cd toxicity of rice (Oryza sativa) leaves was investigated. Cd toxicity to rice leaves was determined by the decrease in protein content. CdCl₂ treatment results in (1) increased Cd content, (2) induction of Cd toxicity, (3) increase in H₂O₂ and malondialdehyde (MDA) contents, (4) decrease in ascorbic acid (ASC) and reduced glutathione (GSH) contents, and (5) increase in the activities of antioxidative enzymes (superoxide dismutase, glutathione reductase, ascorbate peroxidase, catalase, and peroxidase). Spermidine (Spd) and spermine (Spm), but not putrescine (Put), were effective in reducing CdCl₂-induced toxicity. Spd and Spm prevented CdCl₂-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of ASC and GSH, and increase in the activities of antioxidative enzymes. Spd and Spm pretreatments resulted in a decrease in Cd content when compared with H₂O pretreatment, indicating that Spd and Spm may reduce the uptake of Cd. Results of the present study suggest that Spd and Spm are able to protect Cd-induced oxidative damage and this protection is most likely related to the avoidance of H₂O₂ generation and the reduction of Cd uptake.     

A chemically induced new pea (Pisum sativum) mutant SGECdt with increased tolerance to, and accumulation of, cadmium

BACKGROUND AND AIMS: To date, there are no crop mutants described in the literature that display both Cd accumulation and tolerance. In the present study a unique pea (Pisum sativum) mutant SGECd(t) with increased Cd tolerance and accumulation was isolated and characterized. METHODS: Ethylmethane sulfonate mutagenesis of the pea line SGE was used to obtain the mutant. Screening for Cd-tolerant seedlings in the M2 generation was performed using hydroponics in the presence of 6 microm CdCl2. Hybridological analysis was used to identify the inheritance of the mutant phenotype. Several physiological and biochemical characteristics of SGECd(t) were studied in hydroponic experiments in the presence of 3 microm CdCl2, and elemental analysis was conducted. KEY RESULTS: The mutant SGECd(t) was characterized as having a monogenic inheritance and a recessive phenotype. It showed increased Cd concentrations in roots and shoots but no obvious morphological defects, demonstrating its capability to cope well with increased Cd levels in its tissues. The enhanced Cd accumulation in the mutant was accompanied by maintenance of homeostasis of shoot Ca, Mg, Zn and Mn contents, and root Ca and Mg contents. Through the application of La(+3) and the exclusion of Ca from the nutrient solution, maintenance of nutrient homeostasis in Cd-stressed SGECd(t) was shown to contribute to the increased Cd tolerance. Control plants of the mutant (i.e. no Cd treatment) had elevated concentrations of glutathione (GSH) in the roots. Through measurements of chitinase and guaiacol-dependent peroxidase activities, as well as proline and non-protein thiol (NPT) levels, it was shown that there were lower levels of Cd stress both in roots and shoots of SGECd(t). Accumulation of phytochelatins [(PCcalculated) = (NPT)-(GSH)] could be excluded as a cause of the increased Cd tolerance in the mutant. CONCLUSIONS: The SGECd(t) mutant represents a novel and unique model to study adaptation of plants to toxic heavy metal concentrations.     

Toxicity versus avoidance response of golden shiner, Notemigonus crysoleucas, to five metals

Avoidance thresholds and 96-h LC50 values were determined for golden shiners, Noiemigonus crysoleucas , for five individual elements: chromium, Cr; copper, Cu; cadmium, Cd; arsenic, As; selenium, Se. The avoidance concentrations were 73, 26 and 28 μgl^-1 for Cr-VI, Cu and As-III, respectively. Cadmium and Se were not avoided at experimental concentrations up to 68 and 3489 μg1^-1, respectively. Acute flow-through 96-h LC50 values were Cr-VI 55·0, Cu 84·6, and As-III 12·5 mg 1^-1, which were more than two orders of magnitude above avoidance concentrations. The acute flow-through 96-h LC50 values for Cd and Se were 2·8 and 11·2 mg 1^-1, respectively. These concentrations are 31 and 2·2 times the highest concentration employed in the avoidance tests, neither of which were avoided by the test organisms. Thus, simple toxicity tests do not identify the environmental hazard of some elements, and the most toxic elements may not elicit a behavioural response. When used in concert with tests of organism function, more realistic indicators of environmental hazard or safety may be determined.     

Effects of cadmium on antioxidant enzyme and photosynthetic activities in leaves of two maize cultivars

Effects of cadmium (Cd(2+)) on photosynthetic and antioxidant activities of maize (Zea mays L.) cultivars (3223 and 32D99) were investigated. Fourteen-day-old cultivar seedlings were exposed to different Cd concentrations [0, 0.3, 0.6 and 0.9mM Cd(NO(3))(2).4H(2)O] for 8 days. The results of chlorophyll fluorescence indicated that different levels of Cd affected photochemical efficiency in 3223 much more than that in 32D99. In parallel, the level of Cd at 0.9mM caused oxidative damage but did not indicate cessation of PSII activity of the cultivars; plant death was not observed at highly toxic Cd levels. Additionally, the increase in Cd concentration caused loss of chlorophylls and carotenoid and membrane damage in both cultivars, but greater membrane damage was observed in 3223 than in 32D99. Depending on Cd accumulation, a significant reduction in dry biomass was observed in both cultivars at all Cd concentrations. The accumulation of Cd was higher in roots than in leaves for both cultivars. Nevertheless, cultivar 3223 transferred more Cd from roots to leaves than did 32D99. On the other hand, our results suggest that there were similar responses in SOD, APX and GR activities with increasing Cd concentrations for both cultivars. However, POD activity significantly increased at highly toxic Cd levels in 32D99. This result may be regarded as an indication of better tolerance of the Z. mays L. cultivar 32D99 to Cd contamination.     

Hexavalent chromium reduction in <Emphasis Type="Italic">Desulfovibrio vulgaris</Emphasis> Hildenborough causes transitory inhibition of sulfate reduction and cell growth

Desulfovibrio vulgaris Hildenborough is a well-studied sulfate reducer that can reduce heavy metals and radionuclides [e.g., Cr(VI) and U(VI)]. Cultures grown in a defined medium had a lag period of approximately 30 h when exposed to 0.05 mM Cr(VI). Substrate analyses revealed that although Cr(VI) was reduced within the first 5 h, growth was not observed for an additional 20 h. The growth lag could be explained by a decline in cell viability; however, during this time small amounts of lactate were still utilized without sulfate reduction or acetate formation. Approximately 40 h after Cr exposure (0.05 mM), sulfate reduction occurred concurrently with the accumulation of acetate. Similar amounts of hydrogen were produced by Cr-exposed cells compared to control cells, and lactate was not converted to glycogen during non-growth conditions. D. vulgaris cells treated with a reducing agent and then exposed to Cr(VI) still experienced a growth lag, but the addition of ascorbate at the time of Cr(VI) addition prevented the lag period. In addition, cells grown on pyruvate displayed more tolerance to Cr(VI) compared to lactate-grown cells. These results indicated that D. vulgaris utilized lactate during Cr(VI) exposure without the reduction of sulfate or production of acetate, and that ascorbate and pyruvate could protect D. vulgaris cells from Cr(VI)/Cr(III) toxicity. J.D. Wall and M.W. Fields are both affiliated to the Virtual Institute of Microbial Stress and Survival (). M.E. Clark and S.B. Thieman contributed equally to this work.     

八种植物提取物对蔬菜害虫的室内毒力研究

研究了巴豆 (Croton tiglium L.)等八种植物的提取物对几种常见蔬菜害虫的非选择性拒食和毒杀作用。研究结果表明 :巴豆、青蒿、米仔兰等三种植物提取物在 0 .5 %浓度时对菜粉蝶 5龄幼虫的拒食率分别达到96 .36 %、82 .4 2 %和 86 .30 % ,对菜粉蝶 3龄幼虫的毒杀死亡率分别为 5 9.38%、2 8.1 3%和 4 3.75 % ;对黄曲条跳甲成虫的毒杀死亡率为 77.5 0 %、5 6 .2 5 %和 4 8.75 % ;对美洲斑潜蝇幼虫的毒杀死亡率分别为 83.33%、5 6 .6 7%和 73.33%。     

Variations in plant metallothioneins: the heavy metal hyperaccumulator <Emphasis Type="Italic">Thlaspi caerulescens</Emphasis> as a study case

Plant metallothioneins (MTs) are extremely diverse and are thought to be involved in metal homeostasis or detoxification. Thlaspi caerulescens is a model Zn/Cd hyperaccumulator and thus constitutes an ideal system to study the variability of these MTs. Two T. caerulescens cDNAs (accession: 665511; accession: 665515), that are highly homologous to type 1 and type 2 Arabidopsis thaliana MTs, have been isolated using a functional screen for plant cDNAs that confer Cd tolerance to yeast. However, TcMT1 has a much shorter N-terminal domain than that of A. thaliana and so lacks Cys motifs conserved through all the plant MTs classified as type 1. A systematic search in plant databases allowed the detection of MT-related sequences. Sixty-four percent fulfil the criteria for MT classification described in Cobbett and Goldsbrough (2002) and further extend our knowledge about other conserved residues that might play an important role in plant MT structure. In addition, 34% of the total MT-related sequences cannot be classified strictly as they display modifications in the conserved residues according to the current plant MTs’ classification. The significance of this variability in plant MT sequences is discussed. Functional complementation in yeast was used to assess whether these variations may alter the MTs’ function in T. caerulescens. Regulation of the expression of MTs in T. caerulescens was also investigated. TcMT1 and TcMT2 display higher expression in T. caerulescens than in A. thaliana. Moreover, their differential expression patterns in organs and in response to metal exposure, suggest that the two types of MTs may have diverse roles and functions in T. caerulescens.     

原油和消油剂对鱼类毒性的研究进展

原油对鱼类的毒性主要来自其水溶性成分,可导致鱼卵死亡或发育畸形,并造成鱼类麻痹、发炎、粘膜受损和死亡。消油剂的使用在分散了油膜的同时也带来二次污染,其活性剂对鱼类产生新的毒性影响。消油剂将原油分散为乳化颗粒并能进入鱼体内,加大了原油的毒性并延长其作用时间。综述了原油和消油剂对鱼类毒性的研究进展,展望了鱼类在相关毒性试验领域的应用及发展方向。