Salinity and Copper-Induced Oxidative Damage and Changes in the Antioxidative Defence Systems of Anabaena doliolum

Summary This study provides first-hand information on the salinity and copper-induced oxidative damage and its protection in Anabaena doliolum by the antioxidant defence system. Oxidative damage measured in terms of lipid peroxidation, electrolyte leakage and H₂O₂ production was induced by different concentrations of NaCl and Cu²⁺. A greater electrolyte leakage by NaCl than Cu²⁺ supported the hypothesis of salinity being more injurious than copper. To explore the survival strategies of A. doliolum under NaCl and Cu stress, enzymatic antioxidant activities e.g. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) and nonenzymatic antioxidant contents such as glutathione reduced (GSH), ascorbate, α-tocopherol, and carotenoid were measured. A general induction in SOD and APX activities as well as ascorbate and α-tocopherol contents was found under NaCl and Cu²⁺ stress. In contrast to this, an appreciable decline in GR activity, GSH pool and carotenoid content under Cu²⁺ and an increase under NaCl stress were observed. CAT activity was completely inhibited at high doses of NaCl but stimulated following Cu²⁺ treatment. The above results suggest the involvement of APX and CAT in the scavenging of H₂O₂ under Cu²⁺ stress. In contrast to this, only APX was involved in H₂O₂ scavenging under salt stress. Our postulate of Cu²⁺-mediated antagonism of salt stress can be explained by a conceivable reversion of Na⁺-induced disturbance of cellular homeostasis by redox active Cu²⁺.     

Accumulation, subcellular localization and ecophysiological responses to copper stress in two Daucus carota L. populations

Copper accumulation, subcellular localization and ecophysiological responses to excess copper were investigated using pot culture experiments with two Daucus carota L. populations, from a copper mine and an uncontaminated field site, respectively. Significant differences of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations and antioxidant enzyme [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)] activities of leaves under Cu treatment were observed between the two populations. At high Cu concentrations (400 and 800 mg kg⁻¹), a significant increase in contents of MDA and H₂O₂ but a significant decrease in activities of SOD, CAT and APX were observed in uncontaminated population. Contrarily, the population from copper mine maintained a lower level of MDA and H₂O₂ but higher activities of SOD, CAT and APX. Copper accumulation in roots and shoots increased significantly with the increase of copper concentrations in soils in the two populations. No significant difference of the total Cu in roots and shoots was found between the two populations at same copper treatment. There were also no striking differences of cell wall-bound Cu and protoplasts Cu of leaves between the two populations. The difference was that Cu concentration in vacuoles of leaves was 1.5-fold higher in contaminated site (CS) population than in uncontaminated site population. Hence, more efficient vacuolar sequestration for Cu and maintaining high activities of SOD, CAT and APX in the CS population played an important role in maintaining high Cu tolerance.     

Studies on nucleic acids. VIII. Changes in the stability of DNA secondary structure by interaction with divalent metal ions

The melting temperature of a natural DNA is decreased in the presence of increasing amounts of copper ions, whereas other divalent metal ions stabilize the DNA secondary structure at low ionic strength. At 1.28 × 10^?4M, Cu²⁺ produces a decrease of T_m depending on base composition. At very low Cu²⁺ concentrations (0.5 Cu²⁺/2 DNA-P) a stabilization of the DNA conformation appears due to an interaction between Cu²⁺ and phosphate groups of the DNA molecule. In this case the normal trend of GC dependence of T_m exists similar to that with Na⁺ and Mg²⁺ as counterions. If copper ions are in excess, the observed destabilization is stronger for DNAs rich in guanine plus cytosine than for those rich in adenine plus thymine. A sharp decrease of T_m occurs between 0.5–0.8 Cu²⁺/2 DNA-P and 1.5 Cu²⁺/2 DNA-P. The breadth of the transition decreases at high Cu²⁺ concentration with further addition of copper ions. Denaturation and renaturation experiments indicate that Cu²⁺ ions exceeding the phosphate equivalents interact with the bases and reduce the forces of the DNA helix conformation. Evidence is presented, that the destabilization effect produced by Cu²⁺ is possibly due to an interaction with guanine sites of the DNA molecule.     

山黧豆根系对H2O2诱导氧化胁迫的生理应答

以水培7d苗龄的山黧豆幼苗为材料,向水培溶液中施加不同浓度H2O2处理山黧豆幼苗24h,分析山黧豆根系受氧化胁迫的程度与抗氧化系统的应答特征,以揭示山黧豆对氧化胁迫的耐受机制。结果显示:(1)随外源H2O2处理浓度的不断增加,山黧豆幼苗侧根的数目无显著变化,而其根的鲜重则显著降低。(2)同时,根系组织的内源H2O2染色范围和程度显著增高,但根尖区域始终保持较低水平的H2O2;相反,O-·2染色范围和程度明显减少,根尖区域却始终保持较高水平的O-·2。(3)同期根系抗坏血酸(ASC)含量及过氧化氢酶(CAT)、过氧化物酶(POD)与抗坏血酸过氧化物酶(APX)的活性均表现出了先升高后降低的趋势,而超氧化物歧化酶(SOD)一直表现为持续上升的趋势。研究表明,在外源H2O2胁迫条件下,山黧豆根系O-·2的积累可能与其生长和活力呈正相关,而根系H2O2的积累则与其受氧化胁迫程度呈正相关;低浓度的H2O2处理可以提高山黧豆抗氧化系统对体内活性氧的清除能力。     

Copper-Ligand Interactions and Physiological free Radical Processes. Part 2. Influence of Cu2+ Ions on Cu+-Driven Oh Generation and Comparison with Their Effects on Fe2+-Driven Oh Production

In our search to establish a reference ·OH production system with respect to which the reactivity of copper(II) complexes could then be tested, the influence of free Cu²⁺ ions on the Cu⁺/H₂O₂ reaction has been investigated.

This influence depends on the C_Cu²⁺/C_Cu⁺ ratio. At low Cu²⁺ concentrations, ·OH damage to various detector molecules decreases with increasing Cu²⁺ concentrations until C_Cu²⁺/C_Cu⁺ reaches unity. Above this value, ·OH damage increases sharply until C_Cu²⁺/C_Cu⁺ becomes equal to 5 with salicylate and 2 with deoxyribose, ratios for which the protective effect of Cu²⁺ cancels. Finally, at higher concentrations, Cu²⁺ ions logically add their own ·OH production to that normally expected from Cu⁺ ions. The possible origin of this unprecedented alternate effect has been discussed. The possible influence of Cu⁺ ions on the generation of ·OH radicals by water gamma radiolysis has also been tested and, as already established for Cu²⁺ in a previous work, shown to be nonexistent. This definitely confirms that either form of ionised copper cannot scavenge ·OH radicals in the absence of a Iigand.     

喷施铜和硼肥对忍冬生理生化及其茎藤指标成分的影响

以4年生忍冬为试验材料，采用盆栽和叶面喷施方式，设置不同质量浓度的铜肥(10，30，50 mg/L Cu²⁺，分别表示为Cu₁₀、Cu₃₀、Cu₅₀)和硼肥(20，40，60 mg/L B₄O^2-₇，分别表示为B₂₀、B₄₀、B₆₀)及其配施组合处理，测定忍冬叶片的光合参数以及茎藤的营养物质、药效成分含量、矿质离子含量，探究施铜和硼肥对忍冬光合生理、营养物质、矿质离子及其茎藤品质的影响，为优化忍冬栽培技术和提高其药材品质提供理论参考。结果表明：(1)喷施一定质量浓度的铜硼肥有助于提高忍冬叶片的净光合速率，尤以B₄₀Cu₅₀配施处理最佳；适宜质量浓度的铜硼肥有利于增加总叶绿素含量，高质量浓度的铜硼肥则起抑制作用。(2)配施铜硼肥对忍冬藤中营养物质及药效成分含量的影响比单施铜、硼肥更显著，其中B₄₀Cu₅₀处理可显著提高忍冬藤中可溶性蛋白、淀粉、还原糖含量，B₂₀Cu₁₀处理可显著提高可溶性糖含量；有利于忍冬藤中绿原酸和马钱苷积累的最佳配施处理分别是B₆₀Cu₅₀和B20Cu₃₀。(3)喷施铜硼肥对忍冬藤矿质离子的含量也具有显著的影响，单施与配施铜硼肥处理忍冬藤矿质离子含量均有增加，且配施铜硼肥比单施铜硼肥增加效果显著，尤以B₂₀Cu₁₀、B₂₀Cu₃₀、B₂₀Cu₅₀处理最佳。综合考虑，B₄₀Cu₅₀配施处理可有效增加忍冬藤的营养与药用指标成分含量，是忍冬叶面喷施铜和硼肥的最佳比例。     

Nitric oxide retards xanthine oxidase-mediated superoxide anion generation in Phalaenopsis flower: an implication of NO in the senescence and oxidative stress regulation

Senescence is a developmentally regulated and highly ordered sequence of events. Senescence leads to abscission of plant organs and eventually leads to death of a plant or part of it. Present study revealed that Phalaenopsis flower undergo senescence due to over activation of O₂ ^·−generating xanthine oxidase (XO), which consequently increases the concentrations of O₂ ^·− leading to enhanced oxidative damage and disturbed cellular redox environment as indicated by increased lipid peroxidation and DHA/AsA + DHA ratio, respectively. While activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and non-specific peroxidase (POD) were enhanced in sepals and petals of old flower, activities of catalase (CAT) and glutathione reductase (GR) were decreased. Exogenous application of nitric oxide (NO) retarded H₂O₂-induced senescence of Phalaenopsis flower by downregulating activity of XO and concentrations of O₂ ^·−, H₂O₂ and malondialdehyde (MDA, an index of lipid peroxidation). Exogenous application of NO also downregulated SOD activity and upregulated antioxidant enzymes involved in the detoxification of H₂O₂ (CAT and APX), and in the regulation of redox couples viz, monodehydroascorbate reductase (MDHAR) and GR, together with the modulation in non-protein thiol status and DHA/AsA + DHA ratio.     

The system modulating ROS content in germinating seeds of two Brazilian savanna tree species exposed to As and Zn

The effects of increasing arsenic (0, 10, 50, 100 mg L^?1) and zinc (0, 50, 80, 120, 200 mg L^?1) doses on germination and oxidative stress markers (H₂O₂, MDA, SOD, CAT, APX, and GR) were examined in two Brazilian savanna tree species (Anadenanthera peregrina and Myracrodruon urundeuva) commonly used to remediate contaminated soils. The deleterious effects of As and Zn on seed germination were due to As- and Zn-induced H₂O₂ accumulation and inhibition of APX and GR activities, which lead to oxidative damage by lipid peroxidation. SOD and CAT did not show any As- and Zn-induced inhibition of their activities as was seen with APX and GR. We investigated the close relationships between seed germination success under As and Zn stress in terms of GR and, especially, APX activities. Increased germination of A. peregrina seeds exposed to 50 mg L^?1 of Zn was related to increased APX activity, and germination in the presence of As (10 mg L^?1) was observed only in M. urundeuva seeds that demonstrated increased APX activity. All the treatments for both species in which germination decreased or was inhibited showed decreases in APX activity. A. peregrina seeds showed higher Zn-tolerance than M. urundeuva, while the reverse was observed with arsenic up to exposures of 10 mg L^?1.     

Physiological and molecular responses of pearl millet seedling to atrazine stress

Pearl millet has been recommended beneficial for several therapeutic purposes. However, little is known of the physiological responses to abiotic stressors, especially of atrazine. In order to elucidate the physiological and molecular responses of pearl millet to atrazine stress, we studied the response of various biomarkers under increasing herbicide concentrations (0, 5, 10, and 50 mg/kg). We also quantified the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂?^?) produced in the leaves to evaluate the extent of oxidative damage. Increasing atrazine concentrations significantly increased ROS and MDA production in the plant leaves. Ascorbate peroxidase (APX) and peroxidase (POD) activities increased, while catalase (CAT) and superoxide dismutase activities reduced with increasing atrazine concentrations. Generally, atrazine applied at 50 mg/kg suppressed chlorophyll contents, whereas, chlorophyll (a/b) ratio was increased. Atrazine applied at 50 mg/kg significantly suppressed antioxidant gene expressions to the lowest. The APX gene showed overall low response to the atrazine treatments. The chloroplastic psbA gene showed highest expression with 10 mg/kg atrazine, whereas atrazine at 50 mg/kg significantly suppressed the gene expression to its lowest. Pearl millet was able to suppress oxidative stress under low atrazine levels, but high atrazine concentration could induce more oxidative damage.     

Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage

Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC₅₀) for most of the tested polyphenols are between 8 and 480 μM for copper-mediated DNA damage prevention. Although most tested polyphenols were antioxidants under these conditions, they generally inhibited Cu^I-mediated DNA damage less effectively than Fe^II-mediated damage, and some polyphenols also displayed prooxidant activity. Because semiquinone radicals and hydroxyl radical adducts were detected by EPR spectroscopy in solutions of polyphenols, Cu^I, and H₂O₂, it is likely that weak polyphenol-Cu^I interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu^I, H₂O₂, and reducing agents) are regenerated. The polyphenol compounds that prevent copper-mediated DNA damage likely follow a radical scavenging pathway as determined by EPR spectroscopy.     

Phytochemical and Gene Expression Reveals the Antioxidant Responses to Copper Ions in Brassica rapa

The toxicity of increasing heavy metal ion in soil has been threatening the food security and environments. In this study, we used Brassica rapa variety Qinggen #1, a leafy and oil vegetable, to investigate the effects of coper ion (Cu²⁺) on adaptive defense to understand regulatory molecular mechanisms. The variety exhibited a high tolerance at high Cu²⁺ concentration (200 mg L⁻¹). More increases in superoxide radical, hydrogen peroxide, malondialdehyde, and proline were observed at higher concentration than low concentrations. Enzyme activities of SOD, GR, CAT, and APX were significantly altered earlier than corresponding expression of coding genes was up-regulated, indicating two distinct regulations at enzyme and gene levels. The CAT activity and expression correlated with the reactive oxygen species levels, indicating a more important role than other enzymes. Taken together, the high tolerance to Cu²⁺ in B. rapa is resulting from changes in biochemistry, enzyme, and gene expression.

     

Effects of copper on expression of methane monooxygenases,trichloroethylene degradation,and community structure in methanotrophic consortia

Copper plays a key role in regulating the expression of enzymes that promote biodegradation of contaminants in methanotrophic consortia (MC). Here, we utilized MC isolated from landfill cover to investigate cometabolic degradation of trichloroethylene (TCE) at nine different copper (Cu²⁺) concentrations. The results demonstrated that an increase in Cu²⁺ concentration from 0 to 15 μM altered the specific first‐order rate constant k_1,TCE, the expression levels of methane monooxygenase (pmoA and mmoX) genes, and the specific activity of soluble methane monooxygenase (sMMO). High efficiency TCE degradation (95%) and the expression levels of methane monooxygenase (MMO) were detected at a Cu²⁺ concentration of 0.03 μM. Notably, sMMO‐specific activity ranged from 74.41 nmol/(mg_cell h) in 15 μM Cu²⁺ to 654.99 nmol/(mg_cell h) in 0.03 μM Cu²⁺, which contrasts with cultures of pure methanotrophs in which sMMO activity is depressed at high Cu²⁺ concentrations, indicating a special regulatory role for Cu²⁺ in MC. The results of MiSeq pyrosequencing indicated that higher Cu²⁺ concentrations stimulated the growth of methanotrophic microorganisms in MC. These findings have important implications for the elucidation of copper‐mediated regulatory mechanisms in MC.     

Inhibitory effects of copper on bacteria related to the free ion concentration

Cu²⁺ ion determinations were carried out in complex and in inorganic salts-glycerol media, to which increasing amounts of Cu(II) had been added, with the ion-specific Cu(II)-Selectrode. Likewise, complexing capacity of bacterial suspensions was estimated by titration with CuSO₄.Copper-sensitive bacteria, e.g.,Klebsiella aerogenes, were inhibited in their growth and survival in the range of 10^–8–10^–6 M Cu²⁺ ion concentrations. In copper-buffered complex media, high copper loads could be tolerated, as growth proceeded with most of the copper bound to medium components. In low-complexing mineral salts media, in which high Cu²⁺ ion concentrations exist at low copper loads, there was competition of Cu²⁺ for binding sites of the cells. Total allowed copper was then determined by the ratio of copper to biomass.Copper-resistant bacteria could be isolated from a stock solution of CuSO₄, containing 100 ppm Cu(II). They were of thePseudomonas type and showed a much higher tolerance towards Cu²⁺, up to 10^–3 M.     

Thermodynamics and kinetics of the interaction of copper (II) ions with native DNA.

Based on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu²⁺ ions with native DNA at low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation at low relative ligand concentrations and at low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu²⁺ ions with atoms N₍₇₎ of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N₍₇₎ and O of C₍₆₎ of the guanine bases, as well as the formation of specific intestrand crosslink complexes at adjacent G°C pairs of the sequence dGpC. CD spectra of the resulting nondenatured complex (DNA–Cu²⁺)_nat may be interpreted in terms of a conformational change of DNA from the B-form to a C-like form on ligand binding. A slow cooperative denaturing complex formation occurs at increased copper concentrations and/or at increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA–Cu²⁺)_denat, indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA. From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu²⁺ ions to atoms N₍₃₎ of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G·C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu²⁺ ions between atoms N₍₇₎ and O of C₍₆₎ of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G·C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence-specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu²⁺, Cd²⁺, and Zn²⁺ ions with DNA. In temperature-jump experiments with the nondenatured complex (DNA–Cu²⁺)_nat, a specific kinetic effect is observed, namely, the appearance of a lag in the response to the perturbation. The resulting sigmoidal shape of the kinetic curves is considered to be a consequence of the necessity of disrupting a certain number of the crosslinks existing in the nondenatured complex before the local unwinding of the binding regions (a main step of denaturing complex formation) may proceed.     

Effect of salinity on antioxidant enzymes in calli of the halophyte <Emphasis Type="Italic">Nitraria tangutorum</Emphasis> Bobr.

Nitraria tangutorum Bobr., a typical desert halophyte, plays an important ecological role because of its superior tolerance to severe drought and high salinity. Very little is known about the physiological adaptative mechanism of this species to environmental stresses. The aim of this study was to investigate the changes of antioxidant enzyme activities and the regulatory mechanism of ascorbate peroxidase (APX) activity in the calli from Nitraria tangutorum Bobr. after treatment with different NaCl concentrations. The activities of superoxide dismutase (SOD) and catalase (CAT) significantly increased in the calli treated with NaCl, while the peroxidase activity decreased. APX activity was also elevated significantly in response to NaCl, but the increase was partly abolished by H₂O₂ scavenger dimethylthiourea (DMTU). Furthermore, the excitatory effect of salinity on APX could be alleviated by the addition of exogenous CAT and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor diphenylene iodonium, indicating that the modulation of the APX activity in Nitraria tangutorum Bobr. calli might be associated with NADPH oxidase-dependent H₂O₂ generation. Measurement and analysis using fluorescent dye 2′,7′-dichlorodihydrofluorescein diacetate showed the increase of H₂O₂ content in salinity-treated calli. The investigation of NADPH-dependent O₂⁻ production in plasma membrane (PM) vesicles isolated from Nitraria tangutorum Bobr. calli revealed that salinity treatment stimulated NADPH oxidase activity. In conclusion, these results suggest that the higher activities of antioxidant enzymes play an important role in the salt tolerance of Nitraria tangutorum Bobr. calli and that the extracellular production of H₂O₂, depending on the excitation of PM NADPH oxidase, is responsible for enhancing the APX activity in Nitraria tangutorum Bobr. calli under salinity stress.     

Impediment to growth and yeast-to-hyphae transition in Candida albicans by copper oxide nanoparticles

Abstract

The effects of two prominent copper oxide nanoparticles (CuO-NP and Cu₂O-NP), with the oxidation state of Cu⁺⁺ (cupric) and Cu⁺ (cuprous), on Candida albicans were evaluated. CuO-NP and Cu₂O-NP were synthesized and characterized by XRD, FESEM, HR-TEM and Zeta potential. At sub-MIC (50?µg ml^?1), both cupric and cuprous oxide NPs prevented yeast-to-hyphae switching and wrinkling behaviour in C. albicans. The mechanism for the antifungal action of the two NPs differed; CuO-NP significantly elicited reactive oxygen species, whereas membrane damage was more pronounced with Cu₂O-NP. Real time PCR analysis revealed that CuO-NP suppressed the morphological switching of yeast-to-hyphae by down-regulating cph1, hst7 and ras1 and by up-regulation of the negative regulator tup1. In comparison, Cu₂O-NP resulted in down-regulation of ras1 and up-regulation of the negative regulators nrg1 and tup1. Between the two NPs, CuO exhibited increased antifungal activity due to its stable oxidation state (Cu⁺⁺) and its smaller dimensions compared with Cu₂O-NP.     

DNA damage in mouse lymphocytes exposed to curcumin and copper

Dietary polyphenolics, such as curcumin, have shown antioxidant and anti-inflammatory effects. Some antioxidants cause DNA strand breaks in excess of transition metal ions, such as copper. The aim of this study was to evaluate thein vitro effect of curcumin in the presence of increasing concentrations of copper to induce DNA damage in murine leukocytes by the comet assay. Balb-C mouse lymphocytes were exposed to 50 μM curcumin and various concentrations of copper (10 μM, 100 μM and 200 μM). Cellular DNA damage was detected by means of the alkaline comet assay. Our results show that 50 μM curcumin in the presence of 100–200 μM copper induced DNA damage in murine lymphocytes. Curcumin did not inhibit the oxidative DNA damage caused by 50 μM H₂O₂ in mouse lymphocytes. Moreover, 50 μM curcumin alone was capable of inducing DNA strand breaks under the tested conditions. The increased DNA damage by 50 μM curcumin was observed in the presence of various concentrations of copper, as detected by the alkaline comet assay.     

MUCILAGINOUS CAPSULE ADSORPTION AND INTRACELLULAR UPTAKE OF COPPER BY KIRCHNERIELLA APERTA (CHLOROCOCCALES)1

The purpose of the present investigation was to evaluate possible ecological and physiological functions of mucilaginous capsules produced by the freshwater algae Kirchneriella aperta Teiling (Chlorococcales) as related to copper ions. All experiments were performed using synthetic media under laboratory‐controlled conditions. Copper interactions were investigated by distinguishing between adsorption onto the mucilaginous material present at the surface of the cells, intracellular uptake, and differentiation between total dissolved copper and free copper ions in the culture medium. Kirchneriella aperta is sensitive to copper, as revealed by a 96‐h EC₅₀ value of 10 ^{? 9.22} M Cu^{2 +} . We demonstrated that the mucilaginous capsules were able to sequester copper ions from the medium through a passive mechanism, thus providing the cell with a mechanism able to postpone the toxic effects of copper. The organic material that diffuses into the test medium as well as the mucilaginous capsules produced by K. aperta both effectively complex copper; thus, toxicity must be related to free copper ions and not the total dissolved copper concentration in the medium.     

Increase of Copper Toxicity to Growth of Chlorella vulgaris with Increase of Light Intensity

Abstract In the absence of inhibitory concentrations of copper, the photoautotrophic growth of Chlorella vulgaris INETI58C at 27°C exhibited a higher specific growth rate and reached a higher maximal concentration of biomass, under irradiance of 150 W m⁻², compared with 100 W m⁻². However, when the mineral growth medium was supplemented with CuSO₄ (range 40–80 μM), algal growth was significantly affected at the higher light intensity. In the presence of Cu²⁺, the increase in dry biomass was uncoupled from the increase in cell concentration since more than 16 autospores gathered together, inside the enlarged mother cell, suggesting that copper arrested the normal bursting of the mother cell wall. At the higher irradiance, growth medium supplementation with 80 μM of CuSO₄ led to bleaching of photosynthetic pigments. No growth was observed, while, under the lower irradiance, growth was only slightly inhibited. Results clearly showed that copper toxicity to growth of C. vulgaris was strongly influenced by light intensity. Higher light intensity elicits lethal or sublethal Cu²⁺ damage at concentrations lower than the threshold level for damage at lower light intensities. Cu²⁺ may elicit lethal or sublethal light damage at irradiances lower than the threshold level for unpolluted aquatic systems. Received: 17 January 1997; Accepted 15 April 1997     

植物色素在24-表油菜素内酯调节油菜耐盐性中的作用

为了探索24表油菜素内酯(24-EBL)对盐胁迫下油菜生长的调节效应和植物色素在油菜耐盐性中的作用,采用盆栽实验,在盐胁迫下外源喷施1 000、10、0.1、0.001 nmol·L-1 24-EBL处理油菜幼苗,测定植株的生物量、电解质渗漏率(ELP)、净光合速率(Pn)、光合色素、酚类、类黄酮、花青素含量以及抗氧化能力(T-AOC).结果显示:(1) 24-EBL可显著缓解盐胁迫对油菜幼苗的氧化伤害,提高盐渍下油菜幼苗Pn和光合色素含量,并以0.1nmol·L-1 24 EBL(EBL3)对生长的调控效应最佳.(2)盐胁迫下,植株不同部位叶片的β-胡萝卜素(β-Car)和叶黄素(Lut)含量均显著下降,EBL3处理可显著提高其上部叶的β-Car含量,以及上部和中部叶的Lut含量;EBL3处理可显著提高盐胁迫下油菜所有叶片和叶柄的酚类含量,以及叶柄中类黄酮含量;EBL3处理可显著提高盐胁迫下油菜幼苗所有器官的花青素含量.(3) EBL3仅能够诱导上部叶和中部叶类胡萝卜素(Car)提取液的抗氧化能力(T-AOC)提高,但可诱导植株所有器官的酚类提取液的T-AOC提高.(4)不同部位的叶片Car、β-Car和Lut含量均与其Car提取液的T-AOC呈极显著正相关;而上部叶的总酚和花青素含量、中部叶和叶柄的花青素含量及茎秆中总酚、类黄酮和花青素含量与各自的酚类提取液的T-AOC呈极显著正相关.研究表明,外源喷施适宜浓度的24-EBL能够显著促进盐渍条件下油菜幼苗的光合能力,提高其抗氧化能力,从而增强其对盐渍胁迫的适应性,而光合色素和花青素水平被24-EBL诱导上升在油菜幼苗抗氧化过程中起着重要的作用.