Poly(γ-glutamylcysteinyl)glycines or phytochelatins and their role in cadmium tolerance of Silene vulgaris

Abstract. The effect of cadmium on growth of Cd-tolerant and -sensitive plants of Silene vulgaris and on the production of metal-binding compounds in both types of plants was studied. The Cd-content of the roots and the Cd-root/shoot ratio was higher in Cd-tolerant plants. A Cd-binding compound (Cd-BC) with an apparent molecular mass of 14.5 kD was isolated from the roots of Cd-tolerant and -sensitive plants, grown in 40 mmol m⁻³ Cd for 21 d. More than 60% of the total Cd in the roots was associated with this compound. Determination of the amino-acid content of the purified Cd-containing compound from both types of plants showed that they possessed a similar amino-acid composition to that of phytochelatins. Only the bis- and tris-forms were present. The amount of Cd and sulphide associated with phytochelatin was greater in tolerant plants than in sensitive ones suggesting that an increased sulphide content of complexes containing peptide, sulphide and Cd may form the basis of evolved Cd-tolerance in Silence vulgaris.     

Continuous stereospecific Δ-3-keto-steroid reduction by PAAH bead-entrapped Clostridium paraputrificum cells

The development of a continuous anaerobic process for stereospecific Δ⁴-3-keto-steroid reduction by immobilized Clostridium paraputrificum cells cells is described. Following a study on conditions for cell growth and sporulation, spores of C. paraputrificum were aseptically immobilized in PAAH beads. Conditions for cell growth and induction in the immobilized state were determined, as well as the medium composition required to maintain a stabilized immobilized cell population. The effect of the concentration of ethylene glycol added as selected cosolvent on reaction kinetics, substrate solubility, specific activity, and cell growth, was investigated. A 10% (v/v) cosolvent input provided maximal activity along with enhanced solubility of the steroidal substrate. It was shown that cell growth was enhanced in the presence of the added cosolvent in addition to its effect on substrate solubility and enzymic activity. The immobilized cells readily performed Δ⁴, as well as 3-keto steroid reduction of several steroids, including ADD, AD, 16-dehydroprogesterone, progesterone, and hydrocortisone. It was shown that repeated batch-wise reduction cycle—in the presence of the cosolvent—resulted in rapid loss of activity, while the continuous uninterrupted process permitted the attaining of full bioconversion level, maintained stable for at least the period of 5 days of continuous operation tested.     

Effects of metals on enzyme activity in plants

Abstract. Uptake of phytotoxic amounts of metal by higher plants or algae can result in inhibition of several enzymes, and in increase in activity (= induction) of others. Two mechanisms of enzyme inhibition predominate: (1) binding of the metal to sulphydryl groups, involved in the catalytic actionor structural integrity of enzymes, and (2) deficiency of an essential metal in metalloproteins or metal-protein complexes, eventually combined with substitution of the toxic metal for the deficient element. Metal accumulation in the cellular compartment of the enzyme is a prerequisite for enzyme inhibition in vivo. The induction of some enzymes is considered to play a significant role in the stress metabolism, induced by metal phytotoxicity. Peroxidase induction is likely to be related to oxidative reactions at the biomembrane; several enzymes of the intermediary metabolism might be stimulated to compensate for metal-sensitive photosynthetic reactions. The induction of enzymes and metal-specific changes in isoperoxidase pattern can be used as diagnostic criteria to evaluate the phytotoxicity of soils, contaminated by several metals. Lines for future research on metal phytotoxicity are proposed, involving the study of inhibition and induction of enzymes at the different cell membranes (especially the plasmamembrane) in vivo.     

Lithium in drinking water and the incidences of crimes,suicides, and arrests related to drug addictions

Using data for 27 Texas counties from 1978-1987, it is shown that the incidence rates of suicide, homicide, and rape are significantly higher in counties whose drinking water supplies contain little or no lithium than in counties with water lithium levels ranging from 70-170 micrograms/L; the differences remain statistically significant (p less than 0.01) after corrections for population density. The corresponding associations with the incidence rates of robbery, burglary, and theft were statistically significant with p less than 0.05. These results suggest that lithium has moderating effects on suicidal and violent criminal behavior at levels that may be encountered in municipal water supplies. Comparisons of drinking water lithium levels, in the respective Texas counties, with the incidences of arrests for possession of opium, cocaine, and their derivatives (morphine, heroin, and codeine) from 1981-1986 also produced statistically significant inverse associations, whereas no significant or consistent associations were observed with the reported arrest rates for possession of marijuana, driving under the influence of alcohol, and drunkenness. These results suggest that lithium at low dosage levels has a generally beneficial effect on human behavior, which may be associated with the functions of lithium as a nutritionally-essential trace element. Subject to confirmation by controlled experiments with high-risk populations, increasing the human lithium intakes by supplementation, or the lithiation of drinking water is suggested as a possible means of crime, suicide, and drug-dependency reduction at the individual and community level.     

Establishment of anaerobic,reducing conditions in lake sediment after deposition of acidic,aerobic sediment by a major storm

Hurricane Danny resulted in the rapid deposition of 10cm of oxidized, acidic sediment in the Contrary Creek arm of Lake Anna, Virginia. Several biological and geochemical parameters were monitored with time to ascertain how long it took the newly-deposited lake sediments to attain the anaerobic, circumneutral, actively sulfate-reducing state normally observed in this portion of the lake. The sediment platinum-electrode potential dropped from 350 mV to 100 mV within the first week after the storm. The pH of the pore water increased from 4.5 to 5.8 within three weeks, and titratable alkalinity was detected within two weeks and three weeks at 3 cm and 1 cm depths, respectively. Accumulation of reduced products of sulfate reduction (acid volatile sulfide) began by three to four weeks after the storm event. Both methanogens and sulfate reducers were present in high and approximately equal numbers in the freshly deposited material. The rapid neutralization of the acidity in the fresh sediment prior to the onset of sulfate reduction suggests that reactions other than sulfate reduction caused the initial increase in pH and alkalinity in this system.     

试论云阳县人口激增与土地锐减的矛盾及对策

土地是人们赖以生存的物质基础,是其它任何东西不可代替的生产资料。离开了土地,人就不能生存下去,这是众所周知的真理。但是,目前人口的激增与土地锐减的矛盾越来越尖锐。据有关统计资料表明,1978—1988年全国耕地面积减少3.66×10~6ha,与此同时全国人口又猛增1.33亿,给农业粮食生产、     

双胸蚓纤溶酶的纯化及性质

 用硫酸铵分段盐析、超滤膜分级分离及DEAE-纤维素、Sephadex A-25和Sephadex G-50三种柱层析方法从双胸蚓组织的粗提取液中分离纯化出一种纤溶酶,分子量为29kD,由一条肽链组成。此晦具有强烈的溶解纤维蛋白的作用,对家兎实验性血凝块也具有明显的溶解作用。此酶的最适pH为8.0,在pH7.6～8.4之间活力相差不到2％;酶在PH4.7—11.0范围内稳定;酶作用的最适温度为57℃;此酶热稳定性较好,于25～50℃保温3小时,酶活力基本不变,60℃时,活力保留65％。金属离子Na~(+)、K~(+)、Mg~(2+)等可提高此酶的活力,而Hg~(2+)、Ca~(2+)等金属离子对此酶有不同程度的抑制作用。     

The effect of sulfate reduction on the thermophilic (55°C) methane fermentation process

Summary The continuously operated suspended growth anaerobic contact system was utilized to estimate the effect of sulfate reduction on the thermophilic (55°C) methane fermentation process. Results indicated that reduction in methanogenesis in the presence of sulfate was due to two separate, but related, processes;i.e. competitive and sulfide inhibition. Although prevention of competitive inhibition would be difficult under normal fermenter operation, sulfide inhibition could be minimized by environmental selection of sulfide tolerant microbial populations through biomass recycle and pH control. Stable fermenter operation was achieved at soluble sulfide concentrations as high as 330 mg/l soluble sulfide. Using batch fermenters, a maximum thermophilic sulfate reduction rate of 3.7 mg SO₄ ^2––S/g volatile solids (VS)-day was estimated. The importance of reporting sulfate reduction rates on a biomass basis is demonstrated by a simple population adjustment kinetic model.This research study was conducted at the Department of Agricultural Engineering, Cornell University, Riley Robb Hall, Ithaca, NY 14853, U.S.A.     

The role of the genesnrf EFG andccmFH in cytochromec biosynthesis inEscherichia coli

It has been suggested that two groups ofEscherichia coli genes, theccm genes located in the 47-min region and thenrfEFG genes in the 92-min region of the chromosome, are involved in cytochromec biosynthesis during anaerobic growth. The involvement of the products of these genes in cytochromec synthesis, assembly and secretion has now been investigated. Despite their similarity to other bacterial cytochromec assembly proteins, NrfE, F and G were found not to be required for the biosynthesis of any of thec-type cytochromes inE. coli. Furthermore, these proteins were not required for the secretion of the periplasmic cytochromes, cytochromec ₅₅₀ and cytochromec ₅₅₂, or for the correct targeting of the NapC and NrfB cytochromes to the cytoplasmic membrane. NrfE and NrfG are required for formate-dependent nitrite reduction (the Nrf pathway), which involves at least twoc-type cytochromes, cytochromec ₅₅₂ and NrfB, but NrfF is not essential for this pathway. Genes similar tonrfE, nrfF andnrfG are present in theE. coli nap-ccm locus at minute 47. CcmF is similar to NrfE, the N-terminal region of CcmH is similar to NrfF and the C-terminal portion of CcmH is similar to NrfG. In contrast to NrfF, the N-terminal, NrfF-like portion of CcmH is essential for the synthesis of allc-type cytochromes. Conversely, the NrfG-like C-terminal region of CcmH is not essential for cytochromec biosynthesis. The data are consistent with proposals from this and other laboratories that CcmF and CcmH form part of a haem lyase complex required to attach haemc to C-X-X-C-H haem-binding domains. In contrast, NrfE and NrfG are proposed to fulfill a more specialised role in the assembly of the formate-dependent nitrite reductase.     

细胞培养生产人参寡糖素降低成本的途径

在人参（Ｐａｎａｘｇｉｎｓｅｎｇ）细胞悬浮培养中,以无离子水代替重蒸馏水,细胞生长速率和寡糖素产率分别降低２．３％和２．９％。用白糖代替蔗糖,细胞生长速率和寡糖素产生率分别降低１．７４％和１．２３％。综合上述两方面结果,以无离子水和白糖分别替代原培养基中的重蒸馏水和蔗糖组成替代培养基,用替代培养基培养人参培养细胞,其生长速率可达０．５０９ｇＤＷ／Ｌ．ｄ．寡糖素产率可达１．４４３ｇ／Ｌ,和原培养基相