Toxicity and mutual interactions of cadmium and zinc ions in normal and carcinogen-transformed mouse cells

The toxicity of chloride salts of physiological (zinc, manganese, nickel) and non physiological (cadmium) bivalent metal ions was studied in normal or carcinogen-transformed mouse embryo fibroblast cells. The dose response curves for toxicity to both types of cells exhibited similar shapes. The transformed cells, however, were about twice as sensitive to zinc toxicity as normal cells. When normal and transformed cells were grown together and incubated for several hours with an appropriate concentration of zinc, the malignant cells were selectively killed. Cadmium was much more toxic than the three other metal ions in both types of cells. Its toxic effect was reversed by simultaneous addition of zinc at nontoxic concentrations.Abbrevications CFA colony forming ability - MCA 3-methylcholanthrene     

Copper uptake by free and immobilized cyanobacterium

Abstract Copper uptake in free and immobilized cells of the cyanobacterium Nostoc calcicola has been examined. The immobilized cells invariably maintained a higher profile of Cu intake rate (12.7 nmol mg⁻¹ protein min⁻¹) over the free cells (6.0 nmol mg⁻¹ protein min⁻¹). The total Cu uptake in immobilized cells was almost two and a half-times more than their free cell counterpart under identical experimental conditions. Also, the immobilized cells showed a stronger positive correlation between Cu adsorption and uptake. The results have been discussed in terms of improved metabolic efficiency of immobilized cells.     

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.     

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.     

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。     

Expression of a moderately anionic peroxidase is induced by aluminum treatment in tobacco cells: Possible involvement of peroxidase isozymes in aluminum ion stress

To clarify the mechanism of aluminum (Al) toxicity and Al tolerance, we isolated a new clone (pAL201) from a tobacco cDNA library. Northern blot hybridization analysis indicated that the expression of pAL201 is induced by Al treatment and phosphate (P₁) starvation. The complete cDNA sequence suggested that this clone encodes a moderately anionic peroxidase (EC 1.11.1.7). Analysis by isoelectric focussing indicated that a moderately anionic peroxidase (approximately pI 6.7) and two cationic peroxidases (pI 9.2 and 9.7) in the soluble fraction are activated by Al treatment and P₁ starvation, while two moderately anionic isozymes are repressed by these stresses. We suppose that Al ion stress can control the activity of some peroxidase isozymes, one of which is probably induced by enhanced gene expression of pAL201. There is a possibility that some of these isozymes have some functions in Al ion stress.     

Interspecific hybridization of cultivated rice, Oryza sativa L. with the wild rice, O. minuta Presl.

Crosses were made between four varieties (Mahsuri, Setanjung, MR84 and MR103) of Oryza sativa L. (2n=24, AA) and one accession of O. minuta (2n= 8, BBCC). The seed set obtained ranged between 9.5% and 25.1% depending on the rice variety used. By rescuing 14-day-old embryos and culturing them on 25%-strength MS medium we obtained a total of 414 F₁ hybrids. The F₁s were vigorous, tillered profusely, were perennial and male-sterile. The hybrids were triploid (ABC) with 36 chromosomes and showed irregular meiosis. The average frequency and range of chromosome associations at metaphase I or early anaphase I pollen mother cells of F₁ plants were 29.31(16–36) Is +3.32(0–10) IIs+0.016(0–1) IIIs+0.002(0–1) IVs. Upon backcrossing the original triploid hybrids and colchicine-treated hybrids to their respective recurrent parents, and further embryo rescue, 17 backcross-1 (BC₁) plants were obtained. Of all the crosses using MR84, no BC₁ plant was obtained even after pollinating 13 894 spikelets of the triploid hybrid. The BC₁s were similar in appearence to the F₁s and were male-sterile, their chromosome number ranged from 44 to 48. By backcrossing these BC₁s and nurturing them through embryo rescue, we obtained 32 BC₂ plants. Of these, however, only 18 plants grew vigorously. One of these plants has 24 chromosomes and the other 17 have chromosome numbers ranging between 30 and 37. The 24-chromosome plant was morphologically similar to the O. sativa parent and was partially fertile with a pollen and spikelet fertility of 58.8% and 12.5% respectively. All of the F₁ and BC₁ plants were found to be resistant to five Malaysian isolates (XO66, XO99, XO100, XO257 and XO319) of Xanthomonas campestris pv oryzae. Amongst the BC₂s, the reaction varied from resistant to moderately susceptible. The 24-chromosome BC₂ plant was resistant to the four isolates and moderately resistant to isolate XO100 to which the O. sativa parent was susceptible.Part of PhD thesis submitted by first author to Universiti Kebangsaan Malaysia, Bangi     

Organogenesis andin vitro flowering ofEchinochloa colona. Effect of growth regulators and explant types

Echinochloa colona regeneration via organogenesis in callus cultures derived from leaf base and mesocotyl expiants andin vitro flowering were achived. Shoot bud regeneration was achieved on Murashige and Skoog’s (MS) basal medium supplemented with 6.66 μM 6-benzylaminopurine (BAP), 2.68 μM 1-naphthalene acetic acid (NAA) and 3 % (m/v) saccharose. Regenerated shoots were rooted on half strength basal MS medium with 2 % (m/v) saccharose devoid of growth regulators. About 90 -95 % of rooted plantlets survived in the greenhouse.In vitro flowering was induced in the regenerated shoots derived from callus on half strength MS medium supplemented with 4.4 μM BAP, 74.07 μM adeninesulphate, 0.72 μM gibberellic acid, and 3 % (m/v) saccharose. The frequency ofin vitro flowering was 80 – 90 % in three repeated experiments. Fertile seeds were recovered fromin vitro grown plantlets which were subsequently germinated into plants. Acknowledgement: The authors wish to thank to the Department of Environment and Forests, Government of India for financial assistance to undertake this investigation.     

Rapid transfer of low copy-number episomal plasmids fromSaccharomyces cerevisiae to Escherichia coli by electroporation

A simple and reproducible method for transferring low copy-number episomal plasmids from yeast toEscherichia coli has been developed. Although slightly more time-consuming than direct transfer methods, which are effective with high copy number plasmids, the method is significantly faster than methods that require purification of yeast DNA. Plasmid DNA is released from yeast cells during brief treatments involving grinding with glass beads and heating. The treated yeast are cooled, electrocompetentE. coli is added, the mixture is electroporated, and transformants are selected using standard conditions forE. coli electrotransformation. The procedure typically yields sufficient transformants for most applications.     

Mercury (Hg2+) and zinc (Zn2+): Two divalent cations with different actions on voltage-activated calcium channel currents

Summary 1. We examined the actions of mercury (Hg²⁺) and zinc (Zn²⁺) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg²⁺ and Zn²⁺. The threshold concentration for Hg²⁺ effects was 0.1 µM and that for Zn²⁺ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg²⁺ or 200µM Zn²⁺. The peak calcium current was reduced to 50% (IC₅₀) by 1.1µM Hg²⁺ or 69µM Zn²⁺. While Zn²⁺ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg²⁺ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn²⁺ was not dependent on an open channel state, Hg²⁺ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg²⁺ and with higher concentrations (>100µM) of Zn²⁺.5. As Zn²⁺ in the concentration range used had no influence on resting membrane currents, Hg²⁺ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects.