水华束丝藻对磷的生理响应研究

束丝藻(Aphanizomenon Morr. ex Born. et Flah.)是我国淡水水体常见的水华蓝藻之一, 由其引发的水华已产生了严重的环境及生态安全问题。然而, 目前对束丝藻的研究仍相对较少。为了揭示环境因子对束丝藻的影响, 研究从淡水水体限制因子?磷入手, 探讨其对束丝藻的生理生态效应, 研究了不同磷浓度(0.00、0.02、0.05、0.50、1.00 mg/L)对水华束丝藻的生长、光合作用及碱性磷酸酶变化的影响。结果表明: 水华束丝藻在磷浓度低于0.50 mg/L 条件下, 其比生长速率()、最大光合反应(Pm)、饱和光强(Ik)、PSⅡ光化学效率(Fv/Fm)和最大电子传递速率(ETRmax)均下降, 而暗呼吸(Rd)显著增加, 这表明培养基磷浓度低于0.50 mg/L 时,水华束丝藻产生磷营养胁迫, 导致其光合作用受到抑制, 呼吸作用增强, 进而抑制其生长。为了应对这种胁迫, 束丝藻显著增加了其碱性磷酸酶活性(APA), APA 的增加, 使得水华束丝藻能够分解有机形态磷物质转化为其可利用无机磷来缓解磷胁迫。当磷浓度高于0.50 mg/L 时, 水华束丝藻各种参数并没显著性差异, 表明磷浓度高于0.50 mg/L 能够保证水华束丝藻的正常生理特征。这些结果揭示了在低磷条件下, 水华束丝藻能通过调节光合作用和APA 等生理响应, 使其保持生存和竞争优势。       

我国淡水水华蓝藻-束丝藻属新记录种

由于束丝藻属(Aphanizomenon Mort.ex Born.et Flah.)的藻丝、营养细胞、藻丝末端细胞(Terminal cells)、异型胞(Heterocysts)、厚壁休眠孢子(Akinetes)的形态和大小等特征易变,对鉴定工作造成许多闲难.所以该属的分类一直以来是藻类学者面临的长期难题.基于当今束丝藻属的分类研究,对我国淡水水体束丝藻属进行了研究,比较了该属的藻丝、营养细胞、异形胞、厚壁孢子及末端细胞的特征,发现了我困淡水水体的2个新记录种:柔细束丝藻(Aphanizomenon gracile Lemmermann)和依沙束丝藻(A.issatschenkoi(Usacev)Progkina-Lavrenko),并对其形态特征进行了详细描述.     

微囊藻对柔细束丝藻生长及土臭素合成与释放的影响

文章选择两种特征不同的微囊藻——产毒的铜绿微囊藻(Microcystis aeruginosa)和无毒的惠氏微囊藻(Microcystis wesenbergii),分别以不同的接种比例(1﹕2、1﹕1和2﹕1)与产土臭素(Geosmin)的柔细束丝藻(Aphanizomenon gracile)混合培养,以探索种间相互作用对藻类生长和束丝藻土臭素合成与释放的影响。结果表明,在共培养条件下,两种微囊藻均抑制了柔细束丝藻的生长,而柔细束丝藻却促进了两种微囊藻的生长。惠氏微囊藻促进了柔细束丝藻土臭素的释放(接种比例为1﹕1时,束丝藻胞外土臭素的细胞份额达到269.43 fg/cell),仅在生长早期与生长受到抑制阶段促进了土臭素的合成;铜绿微囊藻在共培养早期促进了束丝藻土臭素的合成,但共培养却抑制了土臭素的释放,而且在共培养的中后期已检测不到土臭素。研究结果表明,在自然水体中束丝藻与微囊藻的季节演替过程中,微囊藻在与束丝藻的竞争中处于优势,且微囊藻对束丝藻的竞争压力促使后者合成异味物质,随着束丝藻的消亡可能伴随大量异味物质的释放,增加异味事件发生风险。     

不同盐度下水华束丝藻对CO2浓度倍增的生理响应

本文研究了在盐度分别为2‰和4‰的条件下,CO2浓度倍增对水华束丝藻(Aphanizomenon flos-aquae)生长速率、光合活性及光合色素比例与丙二醛含量的影响。结果表明随着盐度的增加水华束丝藻的生长速率和光合活性受到显著抑制,叶绿素a与藻蓝素比例大幅降低,丙二醛含量明显提高。在实验盐度范围内,CO2浓度倍增显著促进水华束丝藻的生长速率和最大光合电子传递速率(ETRmax)与色素比例,而且盐度越高促进效果越明显。此外CO2浓度倍增能显著降低丙二醛(MDA)含量。从而减少膜脂过氧化,缓解盐度胁迫。     

氮磷对水华束丝藻生长及生理特性的影响

从滇池分离得到水华束丝藻藻株,以BG11为基础培养基,在(25±1)℃,光照强度20μE/m2.s,光/暗周期为16h:8h的培养条件下,水华束丝藻的生长周期约为28d,以光密度(OD665)为指标的生长曲线符合典型的"S"型;在实验浓度范围内,N、P的浓度变化均对水华束丝藻的生长产生影响,在一定范围内([NO3--N]:1.6—245.1 mg/L;[PO43--P]:0.3—1.4 mg/L),高浓度的N、P有利于水华束丝藻的生长,但浓度过高([NO3--N]>245.1 mg/L;[PO43--P]>6.9 mg/L)时,则对其生长产生抑制作用;N、P在缺乏和浓度很低时可对水华束丝藻光系统Ⅱ活性(Fv/Fm)产生显著影响(p<0.01);本实验结果还表明,N、P浓度的改变可影响水华束丝藻硝酸还原酶、酸性磷酸酶和碱性磷酸酶的活性;在低N、P浓度下,水华束丝藻的硝酸还原酶和酸性磷酸酶活性升高,显著高于正常BG11培养时的活性(p<0.05)。这一结果表明,在低N、P营养环境中,水华束丝藻可通过调节自身的酶系统来提高对营养的吸收和利用,从而满足自身生长和细胞增殖的需要。     

四种浮游生物的碎屑形成过程

本文就不同学者的观点,讨论了有机碎屑的具体定义问题。从有机碎屑产生的具体途径来看,细菌侵入已死亡的有机体这一时刻,就是碎屑形成的开始。根据Golterman的藻类矿化概念,以细菌侵入藻细胞这一时相作为有机碎屑的开始期;作者将隆线溞,水华束丝藻、螺旋鱼腥藻和铜绿微囊藻的碎屑开始期分别定为:心跳停止和细菌入侵(枝角类)、藻丝体断裂期(水华束丝藻及螺旋鱼腥藻)、灰蓝色细胞质显现期(铜绿微囊藻)。碎屑开始期及其后的各种形态均属碎屑范畴。       

四种浮游生物的碎屑形成过程

本文就不同学者的观点,讨论了有机碎屑的具体定义问题。从有机碎屑产生的具体途径来看,细菌侵入已死亡的有机体这一时刻,就是碎屑形成的开始。根据Golterman的藻类矿化概念,以细菌侵入藻细胞这一时相作为有机碎屑的开始期;作者将隆线溞,水华束丝藻、螺旋鱼腥藻和铜绿微囊藻的碎屑开始期分别定为：心跳停止和细菌入侵(枝角类)、藻丝体断裂期(水华束丝藻及螺旋鱼腥藻)、灰蓝色细胞质显现期(铜绿微囊藻)。碎屑开始期及其后的各种形态均属碎屑范畴。     

东湖蓝藻水华毒性的研究 Ⅱ.季节变化及微囊藻的毒性

1984年至1986年间武汉东湖(包括湖边池塘)的水华有7种,即铜绿微囊藻、大型铜绿微囊藻、边缘微囊藻、水华鱼腥藻、卷曲鱼腥藻、美丽颤藻和束丝藻。经生物测定,除束丝藻未测、卷曲鱼腥藻和美丽颤藻未测出毒性外,其余4种皆为有毒水华。东湖的水华随着季节变化而有不同类型的更迭,其出现格局为:卷曲鱼腥藻、微囊藻、颤藻、微囊藻。微囊藻水华的毒性在不同季节也有较大差异,毒性最低在8—9月份,最高在12月份(LD_(50)=24mg/kg鼠重),随着温度的降低而提高。讨论了某些环境参数与微囊藻水华形成及其毒性变化的关系。此外,还用脑内注射和腹腔注射方法,研究了微囊藻毒素的毒性表现。     

生长素吲哚乙酸对铜绿微囊藻生理生化及产毒特性的影响

为了探究生长素吲哚乙酸(IAA)对产毒铜绿微囊藻(Microcystis aeruginosa)的影响, 从生长、光合色素含量、叶绿素光诱导荧光特征、脂质氧化和微囊藻毒素合成特性等方面, 研究了IAA对M. aeruginosa CHAB6301生理生化及产毒的影响。结果表明, 在低浓度IAA(0.04和0.2 mg/L)条件下, 铜绿微囊藻生长、叶绿素含量、光合系统(PSⅡ)电子传递效率及藻毒素含量均无明显变化, 藻蓝蛋白、别藻蓝蛋白和丙二醛(MDA)含量均低于对照。高浓度IAA(1和5 mg/L)能够促进细胞生长, 提高叶绿素含量, 但是抑制藻蓝蛋白和别藻蓝蛋白含量, 降低膜脂过氧化程度和细胞内藻毒素合成。综合各指标测定结果, 低浓度IAA对M. aeruginosa CHAB6301生长和光合作用影响不明显, 而高浓度IAA可促进藻细胞生长和光合作用, 增加微囊藻水华形成几率。     

檫木叶片性状沿海拔梯度的响应特征

植物叶片性状是植物与环境长期互作的结果,对环境变化具有敏锐的捕捉力,而且植物叶片性状影响植物的"投资-收益"关系。本文以天目山不同海拔的檫木叶片为材料,分析檫木叶面积、叶长宽比、叶片干重和比叶面积等叶片形态性状以及叶绿素含量和叶氮含量(N_(area))等叶片生理性状对海拔的响应。结果表明,不同海拔亚群体间叶面积具有显著差异,比叶面积、叶长宽比和叶片干重存在极显著差异;叶长宽比和叶片干重在亚群体内的变异系数小于叶面积和比叶面积,说明檫木叶片形态性状在亚群体间存在着不同程度的变异。比叶面积与叶面积和叶长宽比具有显著正相关,与叶片干重呈显著负相关;叶绿素含量与N_(area)呈显著正相关;通过檫木叶片性状与温度的线性回归表明,叶面积、比叶面积、叶绿素含量和N_(area)随着温度下降而下降,与之相反,叶片干重和叶长宽比则逐渐增加。     

Morphological variability in selected heterocystous cyanobacterial strains as a response to varied temperature, light intensity and medium composition

The effect of temperature, light and nutrient composition on morphological traits was determined in seven nostocacean cyanobacteria (Anabaena planctonica, A. sphaerica var. conoidea, A. spiroides, Aphanizomenon gracile, Nostoc sp., Scytonema sp., and Tolypothrix sp.). Their morphological variability was high but only some of the features showed changes reflecting varied growth conditions. The frequency of heterocyst occurrence decreased with increasing nitrogen concentration. Within the range studied, the effect of temperature on heterocyst frequency of Tolypothrix sp. and planktonic Anabaena strains could be fitted by a normal curve with a clear optimum while linear correlation was found in Aphanizomenon gracile. T-and S-type branching was observed in both Scytonema sp. and Tolypothrix sp. strains. T-type branching was found to be markedly dependent on nitrogen concentration. The abundance of necridic cells of Tolypothrix sp. increased linearly with temperature and light intensity. Regularity of trichome coiling of A. spiroides depended on culture medium, suggesting that nutrient composition may be the main controlling factor. In contrast, the effect of the experimental conditions on the dimensions of vegetative cells and heterocysts was weak. Their variability was markedly higher within each experimental treatment than between treatments.     

Massive multiplication of genome and ribosomes in dormant cells (akinetes) of Aphanizomenon ovalisporum (Cyanobacteria)

Akinetes are dormancy cells commonly found among filamentous cyanobacteria, many of which are toxic and/or nuisance, bloom-forming species. Development of akinetes from vegetative cells is a process that involves morphological and biochemical modifications. Here, we applied a single-cell approach to quantify genome and ribosome content of akinetes and vegetative cells in Aphanizomenon ovalisporum (Cyanobacteria). Vegetative cells of A. ovalisporum were naturally polyploid and contained, on average, eight genome copies per cell. However, the chromosomal content of akinetes increased up to 450 copies, with an average value of 119 genome copies per akinete, 15-fold higher than that in vegetative cells. On the basis of fluorescence in situ hybridization, with a probe targeting 16S rRNA, and detection with confocal laser scanning microscopy, we conclude that ribosomes accumulated in akinetes to a higher level than that found in vegetative cells. We further present evidence that this massive accumulation of nucleic acids in akinetes is likely supported by phosphate supplied from inorganic polyphosphate bodies that were abundantly present in vegetative cells, but notably absent from akinetes. These results are interpreted in the context of cellular investments for proliferation following a long-term dormancy, as the high nucleic acid content would provide the basis for extended survival, rapid resumption of metabolic activity and cell division upon germination.     

DEVELOPMENT AND GERMINATION OF AKINETES OF APHANIZOMENON FLOS-AQUAE1

Flakes of Aphanizomenon flos-aquae collected from an ice-covered lake were found to contain all developmental stages from vegetative cells to mature akinetes. Changes during development include increase in cell size, gradual disappearance of gas vacuoles (clusters of gas vesicles), narrowing of intrathylakoidal spaces, and increase in cytoplasmic density. Development of akinetes is accompanied by proliferation of ribosomes, including polyribosomes, cyanophycin granules (structured, granules), and glycogen granules. The lipid bodies of vegetative cells are reduced in size and number in mature akinetes. Akinetes may occur singly or as multiples in sequence in a filament, either terminal or intercalary. Loss of flotation by increase in cytoplasmic density permits filaments to sink and overwinter in bottom sediments. The sequence was found to be reversed during germination of akinetes. Cyanophycin granules are reduced in size and staining density in the sporelings, and very few glycogen granules are seen. Gas vesicles reappear and increase in number, and intrathylakoidal spaces become wider. These changes then would permit the sporelings to rise from the bottom and begin another season's bloom.     

A CARD-FISH protocol for the identification and enumeration of cyanobacterial akinetes in lake sediments

Akinetes are the dormant cells of Nostocales (cyanobacteria) that enable the organisms to survive harsh environmental conditions while resting in bottom sediments. The germination of akinetes assists the dispersal and persistence of the species. The assessment of the akinete pool in lake sediments is essential to predict the bloom formation of the Nostocales population. We present here the implementation of an improved catalysed reporter deposition (CARD)-fluorescence in situ hybridization (FISH) protocol to assist the identification and quantification of akinetes in sediment samples. Several 16S rRNA gene oligonucleotide probes were evaluated for labelling akinetes of various species of Anabaena, Aphanizomenon and Cylindrospermopsis. Akinetes of all the taxa studied were successfully labelled and could be easily detected by their bright fluorescence signal. The probes' specificity was tested with 32 strains of different taxa. All six Cylindrospermopsis raciborskii strains were labelled with a specific probe for its 16S rRNA gene. A more general probe labelled 73% of the Anabaena and Aphanizomenon strains. The counting data of field samples obtained with CARD-FISH and the regular light microscopy approach did not differ significantly, confirming the suitability of both methods. The CARD-FISH approach was found to be less time-consuming because of better visibility of akinetes.     

Seasonal changes in particulate and dissolved lipids in a eutrophic prairie lake

1. Critical periods of lipid energy transfer from phyto- to zooplankton were inferred by comparing seasonal patterns of particulate and dissolved lipid fractions in lake water with temporal changes in lipid energy reserves of the zooplankton in a hypereutrophic lake.
2. The midsummer phytoplankton community was dominated by the bloom-forming cyanobacterium Aphanizomenon flos-aquae. The collapse of the bloom was accompanied by a 2-week period of severe nitrogen deficiency after which there was a marked increase in the concentration of lipid energy reserves in the particulate (algal) fraction.
3. Areal lipid energy reserves of the dominant herbivorous zooplankton responded positively to changes in the tri-and diacylglycerol content of the particulate fraction of lake water in a species-specific manner.
4. Bacterial numbers also peaked in September concomitant with a large increase in free fatty acids in the dissolved lipid fraction probably produced by the decay of the
A. flos-aquae bloom.
5. The association between periods of nitrogen deficiency and increased energy reserve lipids in the particulate fraction supports observations made with laboratory algal cultures that periods of nutrient deficiency may intensify lipid synthesis in some algal species, thereby enhancing the rate of lipid energy transfer from phytoplankton to zooplankton.     

PHOTOSYNTHETIC CHARACTERIZATION OF DEVELOPING AND MATURE AKINETES OF APHANIZOMENON OVALISPORUM (CYANOPROKARYOTA)1

Akinetes, differentiated resting cells produced by many species of filamentous, heterocystous cyanobacteria, enable the organism to survive adverse conditions, such as cold winters and dry seasons, and to maintain germination capabilities until the onset of suitable conditions for vegetative growth. Mature akinetes maintain a limited level of metabolic activities, including photosynthesis. In the present study, we have characterized changes in the photosynthetic apparatus of vegetative cells and akinetes of the cyanobacterium Aphanizomenon ovalisporum Forti (Nostocales) during their development and maturation. Photosynthetic variable fluorescence was measured by microscope‐PAM (pulse‐amplitude‐modulated) fluorometry, and the fundamental composition of the photosynthetic apparatus was evaluated by fluorescence and immunological techniques. Vegetative cells and akinetes from samples of Aphanizomenon trichomes from akinete‐induced cultures at various ages demonstrated a gradual reduction, with age, in the maximal photosynthetic quantum yield in both cell types. However, the maximal quantum yield of akinetes declined slightly faster than that of their adjacent vegetative cells. Mature akinetes isolated from 6‐ to 8‐week‐old akinete‐induced cultures maintained only residual photosynthetic activity, as indicated by very low values of maximal photosynthetic quantum yields. Based on 77 K fluorescence emission data and immunodetection of PSI and PSII polypeptides, we concluded that the ratio of PSI to PSII reaction centers in mature akinetes is slightly higher than the ratio estimated for exponentially grown vegetative cells. Furthermore, the cellular abundance of these protein complexes substantially increased in akinetes relative to exponentially grown vegetative cells, presumably due to considerable increase in the biovolume of akinetes.