水芹水浸提液对斜生栅藻的化感效应研究

采用栅藻在不同浓度的水芹水浸提液中纯培养的方法,研究了水芹水浸提液对斜生栅藻细胞数、叶绿素含量及藻细胞超微结构的影响。结果显示,10 g·L^-1水芹水浸提液对斜生栅藻的生长和叶绿素含量的增加具有明显的促进效应;20 g·L^-1水芹水浸提液对藻细胞数和叶绿素含量的增加持续到第3 d,3 d后出现显著的抑制效应;高浓度（30~50 g·L^-1）水芹水浸提液对藻细胞数和叶绿素含量的明显抑制在第2 d始现,随时间延长而加剧,并具有浓度效应;40 g·L^-1水芹水浸提液处理后,斜生栅藻细胞壁断裂甚至消失,细胞中叶绿体片层肿胀甚至解体,核膜破裂,核质外渗。水芹水浸提液对斜生栅藻具有化感效应,低浓度促进生长,高浓度抑制。     

Biosynthesis of chlorophyll b in pigment mutant C-2A' of Scenedesmus obliquus

It is demonstrated that chlorophyll b does not only derive from chlorophyll a , but is also formed separately from an in vivo-occurring chlorophyllide b . The branching point for the latter synthesis is at the level of chlorophyllide, since no protochlorophyllide b was detectable. We have indications that the enzyme oxidizing chlorophyll a to chlorophyll b accepts also non-phytylated 17,18 dihydroporphyrins and is not restricted to chlorophylls. Preparations of chlorophyllide a and chlorophyll a could both be transferred with the same enzyme fraction to chlorophyllide b and chlorophyll b , respectively. Preliminary experiments show this enzyme to be membrane bound and light independent. An updated scheme for chlorophyll b biosynthesis is presented.     

The effect of arsenate and arsenite on photosynthesis in Scenedesmus obliquus. A Potentiometric study in a closed CO2-system

Abstract

A Potentiometric titration method was used to study the adverse effect of arsenate (As(V)) and arsenite (As(III)) on inorganic carbon uptake in suspensions of the green alga Scenedesmus obliquus. The measurements were performed in a closed CO₂-system with diluted synthetic seawater (1‰ salinity) as ionic medium. Usually, the algal chlorophyll concentration was 0.4 mg dm^?3, while the arsenate- and arsenite-concentrations were varied within the limits 0.1 to 200 μmol dm^?3. In some experiments arsenate toxicity was studied in the presence of 1 to 100 μmol dm^?3 of phosphate (P(V)).

With concentrations of arsenate or arsenite less than 0.1 μmol dm^?3 no toxic effects were observed. However, at As-concentrations of 200 μmol dm^?3, the algal carbon uptake was reduced by 41% with arsenate and 29% with arsenite, i.e., arsenate is more toxic to Scenedesmus obliquus than arsenite. The toxicity of arsenate was negligible in the presence of a ten fold excess of phosphate. This is probably due to chemical similarities between arsenate and phosphate causing competition between the ions for the binding sites.

The importance of taking the speciation as well as the buffer capacity of the algal system into account, when calculating the carbon uptake, is also discussed.     

Evidence for the Presence of Chlorophyllide b in the Green Alga Scenedesmus obliquus in vivo

Chlorophyllide b could be extracted from the wild type of Scenedesmus obliquus and its pigment mutant C-2A'. Its identity was proved by absorption and fluorescence spectroscopy and by a positive hydroxylamine test. Chlorophyllide b could be transformed into pheophorbide b and methylpheophorbide b. The formation of chlorophyllide b from chlorophyll b by dephytylation with chlorophyllase could be ruled out. The stimulation of chlorophyllide b biosynthesis with o-phenanthroline, as described in the literature, could not be confirmed under physiological conditions.     

Occurrence of protochlorophyll and its phototransformation to chlorophyll in mutant C-2A' of Scenedesmus obliquus

The pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus accumulates protochlorophyllide and small amounts of protochlorophyll in darkness. Protochlororphyll was isolated and characterized by thin layer chromatography and absorption and fluorescence spectroscopy. The protochlorophyll was photoreduced by light to chlorophyll both in vitro and in vivo.     

Accumulation of uranium at low concentration by the green alga Scenedesmus obliquus 34

Accumulation of UO ₂ ^{2 +} by Scenedesmus obliquus 34 was rapid and energy-independent and the biosorption of UO ₂ ^{2 +} could be described by the Freundlich adsorption isotherm below the maximum adsorption capacity (75 mg g-¹ dry wt). The optimum pH for uranium uptake was between 5.0_8.5.0.1_2.0 M NaCl enhanced uranyl, while Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺ and Mn²⁺ competed slightly with uranyl. Pretreatment had an unexpected effect on biosorption. After being killed by 0.1 M HCl, S. Obliquus 34 showed 45% of the uptake capacity of the control in which fresh cells were suspended directly in uranyl solution, while the pretreatment of cells by 0.1 M NaOH, 2.0 M NaCl, ethanol or heating decreased uptake slightly. Fresh S. obliquus 34 at 1.2_2.4 mg dry wt mL-1 was able to decrease U from 5.0 to 0.05 mg L-1 after 4_6 equilibrium stages with batch adsorption. Deposited U could be desorbed by pH 4.0 buffer. It is suggested that U was captured by effective groups or by capillary action in the cell wall in the form of [UO2OH]+. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monovinyl and divinyl protochlorophyll in different stages of esterification isolated from mutant C-2A'of the unicellular green alga Scenedesmus obliquus

The mutant C-2A'of the unicellular green alga Scenedesmus obliquus accumulates the chlorophyll-precursors protocbloropbyllide and the already eslerified protochlorophyll when grown heterotrophically in the dark. Two derivatives of protochlorophyll. monovinyl protochlorophyll (MV-PChl) and divinyl protochlorophyll (DV-PChl), were isolated from dark-grown cells of mutani C-2A'and characterized by absorption and fluorescence spectroscopy. Their molecular masses were determined by plasma desorption mass spectrometry. Both MV- and DV-PChl were mainly esterified with geranylgeraniol. However, some esterification with the more saturated alcohols dihydrogeranylgeraniol. tetrahydrogeranylgeraniol and phytol could also be detected.     

Effects of temperature and pH on growth and antioxidant content of the microalga Scenedesmus obliquus

Reactive forms of oxygen can damage DNA (among other molecules), thus triggering, e.g., atherogenesis and carcinogenesis. However, such dietary antioxidants as lutein and β-carotene can effectively inactivate them; these compounds were found to high levels in a novel strain (M2-1) of the microalga Scenedesmus obliquus. The independent and combined effects of pH and temperature on its rates of growth and production of antioxidants were experimentally assessed, via a full factorial experimental design; the effects of each parameter independently, and of their interactions were accordingly quantified by ANOVA. Our results indicated that temperature plays a more important role on the maximum specific growth rate than pH; in terms of antioxidant content, pH and, to a lesser extent, temperature also have relevant effects. Consequently, the highest rate of biomass specific growth (0.294 ± 0.013 day(-1)) and biomass productivity (0.837 ± 0.054 mg L(-1) day(-1)) were associated with relatively low pH (6) and relatively high temperature (30°C). Conversely, the antioxidant production rate increased with pH; hence, the highest productivity (0.638 mg L(-1) day(-1)) was attained at pH 8 and 30°C. At the best operating conditions for antioxidant content, the levels of lutein and β-carotene were 203.57 ± 1.41 and 18.20 ± 0.33 mg mL(-1), respectively; the maximum production of either one occurred at the early exponential phase.     

Biotransformation of 1-naphthalenesulfonic acid by the green alga Scenedesmus obliquus

Under sulfate limitation, axenic batch cultures of the green alga Scenedesmus obliquus metabolized 1-naphthalenesulfonic acid and partially used the sulfonate as a source of sulfur. The main metabolite, 1-hydroxy-2-naphthalenesulfonic acid, which was not metabolized further in the algal culture, was formed by hydroxylation of the substrate in position 1 and by migration of the sulfonic acid group to position 2 of the naphthalene ring (NIH shift). A smaller amount of 1-naphthalenesulfonic acid was desulfonated. The resulting 1-naphthol was mostly transformed into 1-naphthyl β-d-glucopyranoside. Received: 27 March 1996 / Revision received: 18 October 1996 / Accepted: 30 October 1996     

Effects of irradiance on diel and seasonal patterns of nutrient uptake by stream periphyton

1. Irradiance strongly affects the abundance of stream periphyton communities that in turn influence patterns of instream nutrient uptake. We examined relationships between irradiance and periphyton nutrient uptake taking into account diel and seasonal variation in ambient irradiance. 2. Uptake of dissolved N, P and C by periphyton as areal uptake (U) and demand (V_f) was determined under 11 irradiance levels (0–100% of ambient conditions) using shallow stream‐side experimental channels. Experiments were conducted once per season over one annual cycle with both day and night uptake rates assessed, together with periphyton biomass and autotrophic production rates. 3. No consistent diel variation in areal uptake or demand was detected for the predominant inorganic or total dissolved nutrients even at the highest irradiances. Lack of variation may indicate nutrient limitation, with photosynthetic sequestration and storage of C during the day for subsequent utilisation at night. Alternatively, oxygen consumption by photoautotrophs at night may stimulate compensatory heterotrophic uptake (e.g. denitrification). 4. In all seasons, release of dissolved organic N was detected during the day but to a lesser extent at night. This was not directly related to irradiance levels, indicating that heterotrophic metabolism (e.g. microbial decomposition) contributes to this phenomenon. 5. Areal uptake and demand for the predominant inorganic and total dissolved nutrients increased in response to increasing irradiance in some or all seasons, but rates were typically higher during the spring and summer. Saturation of areal uptake and demand at elevated irradiances was evident during the spring. demand was also saturated at higher irradiances in the summer and autumn. Maximum demand was comparable during spring and summer, but saturation occurred at lower irradiance in summer (24 h average 135–145 μmol m^?2 s^?1) relative to spring (312–424 μmol m^?2 s^?1), indicating more efficient nutrient uptake in summer. Higher total periphyton biomass in summer, but comparable autotrophic biomass (chlorophyll a), implies that heterotrophic metabolism may contribute to this greater efficiency. In spring, autotrophic biomass peaked at an irradiance level of 225 μmol m^?2 s^?1, also suggesting a role for heterotrophic metabolism in demand at higher irradiances. 6. The results of this study show that irradiance levels exert a strong influence on the nature and quantity of instream nutrient uptake with N demand saturated at elevated irradiance levels during the spring, summer and autumn. Our results also suggest that heterotrophic metabolism makes a measurable contribution to instream nutrient uptake even under higher irradiances that favour autotrophic activity.     

Temperature dependent reduction of protochlorophyllide in darkness followed by the assembly of active photosystems in pigment mutant C-2A' of Scenedesmus obliquus

In the wild type of Scenedesmus obliquus strain D3 grown heterotrophically, the chlorophyll biosynthesis and thus the reduction of protochlorophyllide to chlorophyllide takes place in darkness. However, in pigment mutant C-2A' of Scenedesmus obliquus only traces of protochlorophyllide are reduced under optimal growth conditions in darkness. By lowering the growth temperature from 33° to 15–25°C, protochlorophyllide can be reduced in darkness. At 20°C this process is about 10 times more active than at 33°C, but reaches only about 13% of the light-dependent chlorophyll biosynthesis. The chlorophylls synthesized at the lower temperatures are inserted into the pigment-protein complexes and photosystem I as well as photosys-tem II capacities are developed. The rate of light-independent protochlorophyllide reduction at lower temperatures is not limited by the enzyme PChlide-oxidoreductase itself, but rather by its substrate, being in turn limited by the amount of 5-amino levulinic acid (ALA) available.     

Identification of the aceA gene encoding isocitrate lyase required for the growth of Pseudomonas aeruginosa on acetate, acyclic terpenes and leucine

Pseudomonas aeruginosa PAO1 mutants affected in acyclic monoterpenes, n-octanol, and acetate assimilation were isolated using transposon mutagenesis. The isocitrate lyase gene (aceA) corresponding to ORF PA2634 of the PAO1 strain genome was identified in one of these mutants. The aceA gene encodes a protein that is 72% identical to the isocitrate lyase (ICL) characterized from Colwellia maris, but is less than 30% identical to their homologues from pseudomonads. The genetic arrangement of aceA suggests that it is a monocistronic gene, and no adjacent related genes were found. The ICL protein was detected as a 60-kDa band in sodium dodecyl sulfate polyacrylamide gel electrophoresis from cultures grown on acetate, but not in glucose-grown PAO1 cultures. Genetic complementation further confirmed that the aceA gene encodes the ICL enzyme. The ICL enzyme activity in crude extracts from cultures of the PAO1 strain was induced by acetate, citronellol and leucine, and repressed by growth on glucose or citrate. These results suggest that ICL is involved in the assimilation of acetate, acyclic monoterpenes of the citronellol family, alkanols, and leucine, in which the final intermediary acetyl-coenzyme A may be channelled to the glyoxylate shunt.     

The role of photosynthesis and food uptake for the growth of marine mixotrophic dinoflagellates

Mixotrophy (i.e. combined use of photosynthesis and food uptake for growth) is widespread among marine dinoflagellates. Species with permanent chloroplasts generally display a growth response towards irradiance like an ordinary autotrophic alga. However, some species cannot grow in the light on a standard inorganic nutrient medium, because they require the ingestion of prey for sustained growth. This includes species with various types of chloroplast origin. Only a few species have been shown to be able to grow in the dark if supplied prey. About half of the studied species were primarily phototrophic species, and food uptake marginally increased their growth rates at low irradiances. In the remaining species, food uptake increases to a large degree their growth rate when light is limiting and in some cases even when irradiance is not limiting growth. Some of these species grow relatively fast at high irradiances without food, while other species only grow slowly or cannot even maintain themselves at high irradiances without food. Dinoflagellates, which form symbioses with endo- and ectosymbionts are a very heterogeneous group, which have been studied only sporadically. Some species are clearly primarily phototrophs, while others rely heavily on food uptake for growth.     

The uptake of nitrate and ammonium nitrogen in Chara hispida L.: the contribution of the rhizoid

Abstract The uptake of ammonium and nitrate nitrogen by cultured plants of the green freshwater alga Chara hispida L. has been compared quantitatively with the contribution of its rhizoidal tissue. In the short-term, the rhizoid takes up 7–20% of the ammonium nitrogen, and about 15% of the nitrate that is taken up by whole plants under similar conditions. The uptake was studied over a range of both temperatures and external concentrations. The apparent activation energy for the uptake of NH₄⁺ and NO₃^? by the whole plant was found to be 50 kJ mol^?1 and 30 kJ mol^?1, respectively. For the rhizoid, the values were similar for both nitrogenous ions, 106 kJ mol^?1 and 70–100 kJ mol^?1. The rhizoidal uptake mechanism for ammonium nitrogen operates more efficiently compared to that in the whole plant. Nitrate is taken up by the rhizoid by a mechanism with a substrate affinity higher than in the plant taken as a whole. The possible ecological significance of the results is discussed.     

Effect of culture conditions on the isocitrate dehydrogenase and isocitrate lyase activities in Chlamydomonas reinhardtii

In the green alga Chlamydomonas reinhardtii , nitrogen staravation induced a reversible increase (2-fold) in NAD-isocitrate dehydrogenase (NAD-IDH; EC 1.1.1.41) and NADP-isocitrate dehydrogenase (NADP-IDH; EC 1.1.1.42) activities. Both enzymes were not affected by the concentration of CO₂, the dark or the nature of the nitrogen source (nitrate, nitrite, or ammonium). When cells growing autotrophically were transferred to heterotrophic conditions, a 40% reduction of the NAD-IDH activity was detected, a 2-fold increase of NADP-IDH was observed and isocitrate lyase (ICL; EC 4.1.3.1) activity was induced. The replacement of autotrophic conditions led to the initial activity levels. NAD- and NADP-IDH activities showed markedly different patterns of increase in synchronous cultures of this alga obtained by 12 h light/12 h dark transitions. While NAD-IDH increased in the last 4 h of the dark period, NADP-IDH increased during the last 4 h of the light period, remaining constant for the rest of the cycle.     

Changes in the Carotenoid Pattern During the Synchronous Life Cycle of Scenedesmus

The wild type (WT) of Scenedesmus obliquus and a mutant lacking chlorophyll b and the light-harvesting complexes (WT-LHC₁) were synchronized by a light-dark regime. Both cultures contained the same type of carotenoids. However, concentrations and patterns of carotenoids were different during their synchronous life cycles. The concentration of total carotenoids followed more or less that of chlorophyll. The WT contained more carotenoids per cell mass, but slightly less per chlorophyll. It is discussed that part of the carotenoids of the mutant, lacking the peripheral antenna of PSII, might be located in the chlorophyll b-less apoprotein or in an enlarged core antenna of PSII. During the life cycle of Scenedesmus the carotenes are initially synthesized and most of the α-carotene is immediately oxidized to lutein which is inserted in the antennae systems of PSII and PSI. The further oxidation of lutein to loroxanthin seems to depend on both the change from dark to light, and on stages of the life cycle itself. Although the major part of β-carotene appears to be inserted in the reaction centers, a fraction of the total pool is rapidly converted to violaxanthin, following the onset of illumination. The conversion may serve to protect against photooxidation. Further conversion of violaxanthin to neoxanthin occurs to a greater extent in the mutant, WT-LHC₁. The results demonstrate (1) the close connection between the carotenoid pattern and the modulation of the photosynthetic apparatus during the life cycle of Scenedesmus and (2) the flexibility of the organism in compensating for the absence of the light-harvesting complexes of photosystems II by adjusting the carotenoid distribution.     

Differences in nitrate and ammonium uptake between Scots pine and European larch

In forest soils, ammonium is usually the predominant form of inorganic nitrogen. However, the capacity of trees to utilize both NO₃ ^- and NH₃ ⁺ may provide greater flexibility in responding to changes of nitrogen supply from the environment. Such capacity has been studied in seedlings of Scots pine (Pinus sylvestris L.) and European larch (Larix decidua Mill.) grown in the presence or absence of either nitrate or ammonium. Nitrate-induced plants showed a higher nitrate uptake rate than non-induced plants; this difference was almost negligible after 24 h of exposure to NO₃ ^-. Ammonium uptake in both species was consistently higher than that of nitrate, regardless of prior nitrogen provision. In both nutrient conditions, larch showed a more efficient transport system in comparison with Scots pine, with higher ammonium and nitrate uptake rates in both induced and non-induced plants. This was consistent also with the activity of nitrate reductase, measured in vivo in roots and leaves. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heterotrophic metabolism and regulation of uptake hydrogenase activity in symbiotic cyanobacteria

The H₂ uptake activity of three cyanobionts isolated fromCycas revoluta, C. circinalis andazolla filiculoides was shown to be related primarily to the growth rate and independent of the main mode of carbon nutrition. Significant H₂ uptake was found in the coralloid roots ofCycas revoluta andZamia furfuracea (3 and 22 times higher than the respective C₂H₂ reduction activities). The results attained allow us to conclude that in cyanobacteria, in contrast to most nitrogen-fixing heterotrophs, uptake hydrogenase activity is not repressed by carbon substrates and that cyanobacteria in association seem to be endowed with sufficient H₂ uptake capacity to recover all of the H₂ released during the process of N₂-fixation.     

Regulation of isocitrate lyase in a mutant of Rhodopseudomonas capsulata adapted to growth on acetate

Studies on acetate utilization by Rhodopseudomonas capsulata strain St. Louis indicated that the wild type grew poorly on acetate and made little if any of the glyoxylate cycle enzyme isocitrate lyase. A spontaneous mutant, Ac-l, capable of vigorous and immediate growth on acetate and exhibiting high levels of isocitrate lyase activity, was isolated in the course of those studies.Isocitrate lyase was not formed when the mutant was grown on malate. Addition of malate to cultures of Ac-l growing on acetate resulted in loss of the enzyme by dilution through growth.Starvation of acetate-grown Ac-l for acetate resulted in a rapid and complete loss of isocitrate lyase activity which was shown to be energy dependent. Readdition of acetate to a starved culture previously grown on acetate resulted in a rapid recovery of enzyme activity. The recovery required energy and was sensitive to chloramphenicol inhibition at any time during the recovery phase.