Bioremoval of lead from water using Lemna minor

This study examined the ability of duckweed (Lemna minor) to remove soluble lead from water. The duckweed was obtained from the Devils Lake wastewater treatment plant in North Dakota. The viable aquatic plants were exposed to a single dose of lead (from Pb(NO₃)₂) at a concentration of 5.0 mg/l for a time period of 21 days. Lead concentrations were measured in the water daily and in the biomass at the conclusion of the experiment. All measurements were done in triplicate and performed in accordance with standard methods. These data were used to calculate the removal efficiency with respect to time, and to provide the necessary empirical constants to model the removal behavior. Viable biomass removed 85–90% of the lead, viable duckweed previously exposed to lead removed 70–80% of the lead, non-viable biomass (control group) removed 60–75% of the lead, and there was no removal in the ‘no-biomass' control group. Based on these results we conclude that the viable biomass is effective in removing lead present at sub-lethal levels.     

Old-Culture Flowering of Lemna paucicostata 6746 in Aged Hutner's Medium

Lemna paucicostata 6746, a short-day plant, flowers in agedHutner's medium even under continuous light, when the endogenousnitrogen level decreases to below 1.6 µmg fr wt. At thesenitrogen levels, daylength-independent flowering of the plantcan be induced even in fresh Hutner's medium. Thus, old-cultureflowering in Hutner's medium is due to nitrogen deficiency inthe plants. ¹Present address: Biological Institute, Faculty of Science,Shizuoka University, Shizuoka 422, Japan. (Received February 12, 1987; Accepted August 28, 1987)     

Selection and characterization of somatic hybrids between Lycopersicon esculentum and Lycopersicon peruvianum

Somatic hybrids of the cultivated tomato, Lycopersicon esculentum, and a wild species, L. peruvianum, were obtained by fusion of leaf protoplasts from both species in the presence of poly-ethylene-glycol (PEG) or in an electric field. The somatic hybrids were selected on the basis of kanamycin resistance of L. esculentum and the plant regeneration capacity of L. peruvainum. Chromosome counts in root tips and the determination of the number of chloroplasts in guard cell pairs revealed that the majority of these hybrids was tetraploid (2n = 4x = 48). The remaining hybrids were at the hexaploid level with chromosome numbers between 64 and 72. The hybrid nature of the regenerated plants was confirmed by analysis of isozyme markers and by their morphology. Most hybrids did flower and set fruits and seeds after selfing. According to RFLP analysis 6 out of the 10 hexaploid hybrids contained two genomes of L. esculentum and four genomes of L. peruvianum. One of these hexaploids had genomes of two different L. peruvianum genotypes and was therefore considered to be derived from a triple protoplast fusion. The hexaploid plants were less fertile than the tetraploids and more resembled L. peruvianum.     

大鹅观草与蛇河披碱草属间杂种的细胞遗传学研究

为探讨大鹅观草(Roegneria grandis,2n=4x=28)的染色体组组成,为其正确的分类处理提供细胞学依据。该研究通过人工远缘杂交,成功获得3株大鹅观草与蛇河披碱草(Elymus wawawaiensis,2n=4x=28)属间杂种F1植株。杂种植株形态介于两亲本之间,不育。亲本及杂种经I2-IK溶液染色后进行花粉育性检测,结果显示Roegneria grandis和Elymus wawawaiensis的花粉可育,育性高达94.6%和90.5%;杂种F1不育。花粉母细胞减数分裂中期I染色体配对结果显示,亲本花粉母细胞配对正常,均形成14个二价体,以环状二价体为主,Roegneria grandis有频率很低(0.04/细胞)的单价体出现;杂种F1平均每个花粉母细胞形成6.46个二价体,变化范围为5~8;在观察的83个花粉母细胞中,有35.2%的花粉母细胞形成了7个二价体,形成6个二价体的细胞占42.59%,较少细胞形成8个二价体;平均每个细胞形成14.66个单价体,变化范围为10~18;平均每细胞观察到0.14个三价体;杂种花粉母细胞染色体构型为14.66 I+6.46 II+0.14 III;平均每细胞交叉数为9.83,C值为0.35。结果表明:(1)R.grandis与Elymus wawawaiensis有一组染色体组同源的St染色体组,另外一组染色体组不是St或者H染色体组,Roegneria grandis的染色体组组成不是St Stg;(2)较低频率的三价体(平均0.14个/细胞),可能是由于R.grandis的St和Y染色体组间具有一定的同源性,也可能是染色体易位等原因导致,对于Y染色体组的起源还需深入地研究;(3)在不同地理来源的披碱草属和鹅观草属物种中St染色体组同源性不同,R.grandis与来自于北美的Elymus lanceolatus与E.wawawaiensis的St染色体组较与分布于亚洲的E.sibiricus和E.caninus的St染色体组同源性反而更高,其原因还需要进一步地研究。     

Light-induced chloroplast movements in Lemna trisulca. Identification of the motile system

In mesophyll cells of the water plant Lemna trisulca L. chloroplasts redistribute in response to blue light. In the present study it is shown that an actin depolymerizing agent cytochalasin D, a crosslinker of actin subunits in F-actin m-maleimidobenzoic acid N-hydroxysuccinimide ester (MBS) as well as N-ethylmaleimide (NEM)—a sulfhydryl group reagent, are potent inhibitors of these blue light-induced chloroplast movements in Lemna. Extraction with cold, buffered glycerol solution preserves light-induced chloroplast arrangements within cells producing permeabilized cell models. ‘Reactivation’ of these cell models by Mg-ATP results in remarkable movements which can be inhibited by treatment with NEM and cytochalasin D. Immunofluorescence microscopy demonstrates that a component which is associated with isolated Lemna chloroplasts cross-reacts with antibodies directed against bovine myosin. These results indicate that a contractile actomyosin system is involved in blue light-induced chloroplast movements in Lemna and a putative motor protein, similar to myosin, is associated with the surface of Lemna chloroplasts.     

Epinephrine, Propranolol, and the Sucrose-Ammonium Inhibition of Flowering in Lemna paucicostata 6746

The sucrose-ammonium inhibition of flowering Lemna paucicostata 6746 in continuous blue light or in short days was partially overcome by epinephrine. This reversal was prevented by propranolol, an antagonist of epinephrine in animals. In ammonium-free medium, propranolol inhibited flowering, and this inhibition was completely overcome by epinephrine. Increased levels of Ca²⁺, Pi and nitrate partially reversed the inhibition by propranolol. Concentrations of cAMP, adenine, and adenosine that partially overcame the sucrose-ammonium inhibition did not affect flowering in cultures treated with propranolol. The possibility is discussed that the effects on flowering of sucrose-ammonium, propranolol, and epinephrine were due to altered intracellular levels of cAMP or of a cAMP-like compound.     

Flowering response of Lemna perpusilla 6746 to a single dark period

Lemna perpusilla 6746 is induced to flower by a single longdark period, but the floral buds once formed disappear afterseveral days under 5000 lux/25?C. Such regression of floralbuds is prevented by lowering the light intensity or temperature,but if the light intensity and/or temperature are lowered beyondcritical levels, new floral buds form. If the cultures are subjectedto 100 lux/20?C, neither regression nor new formation of floralbuds occurs. Under such conditions, the number of floral frondsreaches maximum about 6 days after the inductive dark periodand reamins unchanged for at least 10 days, while the percentageof floral fronds rapidly decreases thereafter, owing to thedilution by newly developed vegetative fronds. When the cultures are subjected to various lengths of a singledark period (25?C) followed by 100 lux/20?C, flowering responsesrepresented by the number of floral fronds per flask show rhythmicfluctuation with a cycle length of about 24 hr. Similar rhythmicresponse is observed when a brief light interruption is givenat different times during a single long dark period. (Received December 2, 1974; )     

Influence of Short Term Inhibitor Treatment on the Flowering of Lemna perpusilla 6746

Short term inhibitor treatment can be used to examine the processes that occur during an inductive dark period in the short day plant Lemna perpusilla Torr., strain 6746. Several inhibitors of protein biosynthesis are most effective in reducing per cent flowering when treatment occurs over the 2-hour intervals beginning at the 12th hour or the 14th hour of a 8 (16) photoperiodic cycle. The antimetabolite, 5-fluorouracil, is most effective when treatment occurs early in the dark period. Evidence is cited suggesting that distilled water incubation inhibits flowering by interfering with protein biosynthesis.     

Phytoaccumulation of zinc by the aquatic plant, Lemna gibba L.

The uptake of zinc (Zn) by the duckweed Lemna gibba L., native to the north-east region of Algeria, was investigated in quarter Coïc solutions enriched with 6.0, 10.0, 14.0 and 18.0 mg l⁻¹ of Zn supplied as zinc sulphate (ZnSO₄). Zinc concentrations were measured in the water daily and in duckweed biomass at the end of the experiments. These results showed that under experimental conditions (pH = 6.0 ± 0.1, T = 21 ± 1 °C, photoperiod = 12 h/j), L. gibba was able to accumulate in its biomass 4.23; 15.62; 23.88 and 25.81 mg g⁻¹ DM, respectively for the four initial concentrations selected. At these concentrations, the metal removed percentages were 61–71%. The mass balance performed on the system showed that about 49–68% of Zn (depending on the initial concentration in water) was removed by precipitation as zinc phosphate. The results showed that this aquatic plant can be successfully used for Zn removal.     

Species hybrids ofDigitalis

Ohne Zusammenfassung

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Species hybrids ofDigitalis

     

铁破锣花序的开花特性与昆虫传粉的相互关系研究

为了揭示植物花的空间布局与开花动态的调节机制以及避免同株异花传粉的生态学策略,该研究对铁破锣［Beesia calthifolia (Maxim.) Ulbr.］花序形态结构、开花动态和传粉生物学进行了观察分析。结果表明：（1）铁破锣花序结构设计巧妙,由3朵花组成一个聚伞花序单元并依次排列在主花序轴上,且花序轴上聚伞花序之间距离较远。（2）铁破锣通过单个聚伞花序顶花先开,通常只有6～8朵聚伞花序的顶花同时开放,而且总状花序从基部到顶部逐次开放,从而使得大量聚集单花的花序达到尽量少开花。（3）铁破锣花白色,花粉是访花昆虫的仅有诱物,纤细巴蚜蝇（Baccha maculata）是铁破锣的主要传粉昆虫,这种昆虫能够以花丝为着力点取食花粉,通常在一个花序上取食一朵单花后很快飞向另外一个花序的花。研究认为,铁破锣花序的空间设计和开花的时间序列动态减少了昆虫访问同株异花的可能性。     

Specific relations between some strains of diazotrophs and corn hybrids

Summary We tested the effect of a large number of diazotrophic strains from the genera Azotobacter, Klebsiella, Escherichia, Derxia, Beijerinckia, and Azospirillum, on nitrogen concentration in four corn hybrids. The range obtained, from highly significant positive to highly significant negative effects, indicates that the strains studied differed in their characters, including the capacity to form useful associations with certain hybrids. The forming of positive associations depended on the specificity of diazotrophic strains and corn hybrids.     

Electrophoretic profile of hybrids between cryotolerant and non-cryotolerant Saccharomyces strains

Escherichia coli O157 : H7 (O157) has unusual acid tolerance. The influence of heat shock on acid tolerance of O157 was studied. Seven strains of O157 and E. coli K-12 were tested for their ability to survive in minimum glucose medium (pH 2·5) at 37 °C. The survival of heat-shocked (10 min at 48 °C) cells was about 10–100 times greater compared with untreated cells depending on the strain. No significant difference ( P > 0·05) for O157 strain 932 was observed between heat shock-induced and acid adaptation-induced (pH 5·0) acid tolerance. Chloramphenicol prevented heat shock-induced acid tolerance, indicating the requirement of newly synthesized protein(s). Two outer membrane proteins (OMP) (22 and 15 kDa) were synthesized within 10 min of heat shock and were expressed for at least 6 h by cells held at 37 °C. N-terminal amino acid sequence analysis suggested that the 22 kDa OMP is a component of an alkyl hydroperoxide reductase. This protein contains a redox active disulphide, which is probably involved in H⁺ transport. Results indicate that sublethal heat treatment of O157 cells substantially increases their tolerance to acidic conditions. This could have practical implications for foods that receive a mild heat treatment and rely on acid as a preservative.     

Influence of Temperature on the Flowering of Lemna perpusilla 6746 Grown under Skeleton Photoperiods

The flowering of Lemna perpusilla Torr. strain 6746 grown under 24-hour skeleton photoperiods consisting of 13- and 10.5-hour dark periods separated by 0.25-hr light pulses is strongly dependent on temperature. When plants are cultured in 50-ml Erlenmeyer flasks containing 20 ml of half-strength Hutner's medium supplemented with 1% (w/v) sucrose maximum, per cent, flowering occurs at 23 C. At temperatures above and below 23 C a marked decline in per cent flowering is seen.     

Production and electrophoretic verification of F1 hybrids between the sibling speciesRhagoletis pomonella andR. cornivora

To investigate the potential for natural interspecific hybridization in theRhagoletis pomonella group of sibling fruit fly species, an attempt was made to hybridizeR. pomonella, the apple maggot fly, withR. cornivora, a non-pest feeding on dogwoods. Laboratory hybridization was difficult, with only five F₁ hybrids produced. Electrophoretic analysis of the hybrids confirmed their hybrid origin. Allele frequency data for three diagnostic loci in up to 5,596 individuals of the parental species, gathered from published and unpublished studies, indicate that the two sibling species hybridize in nature very infrequently, if at all.     

Fertile asymmetric somatic hybrids between Lycopersicon esculentum Mill. and Lycopersicon peruvianum var. dentatum Dun.

Summary Thirteen nuclear asymmetric hybrids were regenerated under selective conditions following fusion of chlorophyll-deficient protoplasts from cultivated tomato (Lycopersicon esculentum Mill.) and -(-irradiated protoplasts from the wild species Lycopersicon peruvianum var. dentatum Dun. All hybrid plants were classified as being asymmetric based on morphological traits, chromosome numbers and isozyme patterns. The majority of the hybrids inherited Lycopersicon peruvianum var. dentatum chloroplasts. Mitochondrial DNA analysis revealed mixed mitochondria populations deriving from both parents in some of the hybrids and rearranged mitochondrial DNA in others. The asymmetric hybrids express some morphological traits that are not found in either of the parental species. Fertile F₁ plants were obtained after self-pollination of the asymmetric hybrids in four cases. The results obtained confirm the potential of asymmetric hybridization as a new source of genetic variation, and as a method for transferring of a part of genetic material from donor to recipient, and demonstrate that it is possible to produce fertile somatic hybrids by this technique.     

Interspecific hybrids between kenaf ( Hibiscus cannabinus ) and roselle ( H. sabdariffa )

The successful interspecific cross is reported for the first time between kenaf (Hibiscus cannabinus L.), a diploid species (2n=36) and roselle (Hibiscus sabdariffa L.), a tetraploid species (2n=72). Kenaf, grown for its bast fiber and also under investigation as a source of paper pulp, is fast-growing and well adapted to mechanical harvesting, but susceptible to root-knot nematodes. Roselle, also grown for its bast fiber, is slower growing, not well adapted to mechanical harvesting, but certain varieties are resistant to root-knot nematodes. Five hybrid plants were produced from the pollination of 4,445 flowers of kenaf with pollen from roselle; no hybrid plants were produced from 2,655 pollinations made in the reciprocal direction. One line of roselle was the parent of 3 of the 5 hybrids; one line of kenaf was the parent of 2 of these 3. The F₁ hybrids were triploid, and varied in vigor, growth habit and vegetative morphology, but had similar flowers. Two of the F₁ hybrids showed high pollen fertility, apparently as a result of restitution at first meiotic division leading to unreduced spores. These two hybrids each produced a small amount of seed, which gave rise to an F₂ population of 22 plants. The F₂ plants vary in vigor but are morphologically uniform, have thick leaves with mosaic sectors, and are presumably spontaneous allohexaploids. The theoretical possibilities of increasing the percentage of recovery of the F₁ interspecific hybrids and of developing a synthesized hybrid variety useful for bast fiber and paper pulp are discussed. Research done cooperatively by Crops Research Division and Agricultural Engineering Research Division, Agricultural Research Service, U.S. Department of Agriculture (USDA), and the University of Florida Agricultural Experiment Station. Cytological investigations were carried out at the Department of Biological Sciences, Florida State University. Thanks are extended to the many individuals and organizations who supplied material for this study, and to M. Griffin Bell and E. Otho Richey, Agricultural Research Technicians, for their enthusiastic assistance.     

Antioxidative response of Lemna minor plants exposed to thallium(I)-acetate

The physiological effects of thallium(I)-acetate on the duckweed Lemna minor after 1-, 4-, 7- and 14-d exposure were analyzed. High bioaccumulation of Tl (221 mg kg⁻¹ dry wt at 2.0 μM Tl-acetate) caused an inhibition of plant growth. After 14-d exposure, 0.2, 0.5, 1.0 and 2.0 μM Tl-acetate reduced the frond-number growth rate by 21.1%, 39.4%, 66% and 83.1%, respectively. Tl-acetate also induced a modulation of the antioxidative response by depleting the ascorbate content and affecting the antioxidative enzymes activities. Superoxide dismutase showed a continuous increase of activity (31–67%) after Tl-acetate exposure. Other antioxidative enzymes displayed a biphasic response to both the concentration and the exposure period. Exposure up to 7 d decreased the catalase activity (up to 40%) in plants treated with higher Tl-acetate concentrations. In contrast, 14-d exposure increased the activity of the enzyme (≥90%). Short-term exposure increased ascorbate peroxidase activity (13–41%), except in plants exposed to the highest Tl-acetate concentration. However, 14-d exposure decreased the enzyme activity at all concentrations tested (38–60%). Although pyrogallol peroxidase activity increased (up to 26%) during 4-d exposure, longer exposures to the highest two concentrations decreased the activity of the enzyme (25–48%). In general, short-term exposure to Tl-acetate activated the antioxidant capacity, which resulted in recovery of the frond-number growth rates in Tl-treated plants. In spite of the activation of the antioxidative response during short-term exposure, higher Tl-acetate concentrations increased the hydrogen peroxide level (up to 45%) and induced marked oxidative damage to lipids, proteins and DNA. Longer exposure induced a decline of the antioxidative response, and plants showed the symptoms of oxidative damage even at lower Tl-acetate concentrations. The genotoxic effect was evaluated by an alkaline version of the cellular and acellular Comet assay, which revealed an indirect genotoxic effect of Tl-acetate, suggesting oxidatively induced damage to DNA.     

ECT 6和ECT 7调控拟南芥开花时间的研究北大核心CSCD

m^(6)A修饰是mRNA上含量最丰富的一种修饰,调控mRNA的命运决定。YT521-B同源性(YTH)结构域蛋白是一类典型的m^(6)A“阅读器”,能识别并结合m^(6)A,完成基因的转录后调控。为了探究拟南芥YTH结构域蛋白ECT6和ECT7的功能及其分子机制,该研究对ect 6、ect 7和ect 6 ect 7双突变体进行基因型和半定量PCR鉴定及开花表型观察,通过细胞学观察分析ECT6和ECT7的亚细胞定位,并采用qRT-PCR检测开花关键基因的表达量。结果显示:(1)ECT 6基因组包含5个外显子和4个内含子,ect 6突变体分别插入在ECT 6基因的第3和第5外显子;ECT 7基因组包含6个外显子和5个内含子,ect 7突变体分别插入在ECT 7基因的第4和第6外显子。(2)突变体ect 6和ect 7均为完全敲除的功能缺失突变体,在长日照下二者均表现出开花提前和叶片数减少。(3)在长日照和短日照下ect6 ect7双突变体均表现出开花提前和叶片数减少。(4)开花抑制基因FLC和成花素基因FT是关键的开花调控因子,qRT-PCR分析结果显示,在ect 6 ect 7双突变体中,FLC的表达水平降低,FT的表达水平升高,且春化通路基因VIN 3、VRN 2、VRN 5和自主通路基因FVE的表达水平也显著升高。(5)ECT6和ECT7均定位于细胞核和细胞质中。