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  • 1
    Electronic Resource
    Electronic Resource
    Environmental Factors Controlling N2 Fixation in Mediterranean Rice Fields (1997)
    Springer
    Microbial ecology 34 (1997), S. 39 -48 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The objectives of this study were to analyze the environmental controls on N2 fixation in Spanish rice fields. Nitrogenase activity, measured as the acetylene-reducing activity (ARA), was estimated in situ during different intervals of the cropping period. At the same time, physical and chemical variables and cyanobacterial occurrence were determined in water and soil. Nitrogen fixation was measurable at all sampling sites, being higher in July and lower in June after a short dry period. The ARA values ranged from 0.23 to 75.5 kg N Na−1 year−1. Because blooms or other conspicuous cyanobacterial forms were not included in the measurements, maximum rates of nitrogen fixation may have been higher. Environmental variables that correlated with ARA varied on a seasonal basis. Water properties such as calcium, hardness, or conductivity, and soil properties such as conductivity and sodium correlated positively with N2 fixation; however, nutrient parameters such as dissolved inorganic nitrogen or soluble reactive phosphorus were negatively correlated. Cyanobacterial abundance, in general, did not correlate with ARA. The overall conclusion is that nitrogen fixation may be an important N input in the N cycle of rice fields, and could lessen pollution problems by lowering the demand for chemical fertilizers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002489900032
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  • 2
    Electronic Resource
    Electronic Resource
    Acclimation of Cyanobacterial Communities in Rice Fields and Response of Nitrogenase Activity to Light Regime (1998)
    Springer
    Microbial ecology 35 (1998), S. 147-155 
    Details
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The short-term and long-term effects of light regime on nitrogenase activity (NA) and cyanobacterial communities in rice fields (Valencia, Spain) were examined. Daily variation in nitrogen fixation was measured during three periods of the crop cycle: tillering (formation of secondary stems in the rice plants), heading (formation of reproductive structures), and maturity. Two locations were examined over two consecutive years (1994 and 1995). Despite differences in the crop-cycle periods, location, and year, a consistent pattern of nitrogen fixation was observed, with a main activity peak in the morning and another in the late evening. Short-term experiments, performed on two cyanobacterial blooms (Nostoc sp. and Anabaena sp.) exposed to natural light under plant canopy (7% incidence irradiance), and to different light intensities under neutral density screens without plant cover (full sunlight, 43%, 26%, and 13% of incident irradiance), indicated that nitrogenase activity (NA) was dependent on both light intensity and quality. In long-term experiments, where natural communities of cyanobacteria were exposed to one month of different light intensities, changes in the species composition of the three main genera of heterocystous cyanobacteria (Nostoc, Anabaena, and Calothrix) were observed. The light intensity at which communities were exposed for one month became the optimum irradiance for NA for each cyanobacterial community. Assays performed at higher or lower irradiances showed lower NA. Nitrogen fixation followed a pattern of seasonal variation along the crop cycle. Values were low at the beginning of the crop (May), reached a maximum value at the end of the tillering stage (June), and declined thereafter until the end of the cultivation cycle (September).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002489900069
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  • 3
    Electronic Resource
    Electronic Resource
    Short- and long-term effects of ammonium on photodependent nitrogen fixation in wetland rice fields of Spain (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 353-357 
    Details
    ISSN: 1432-0789
    Keywords: Key words Acetylene reduction assay ; Anabaena sp. ; Ammonium ; Cyanobacteria ; Nitrogen fixation ; Wetland rice fields ; Nitrogenase activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Short- and long-term experiments were conducted in the rice fields of Valencia, Spain, to determine the ecological significance of ammonium on nitrogen fixation. A significant inhibition of nitrogenase activity by ammonium, at concentrations higher than 0.5mM, was observed after 8h of incubation in short-term experiments done with a bloom of the N2-fixing cyanobacterium Anabaena sp. In a second set of short-term experiments for in situ assays of nitrogenase activity in the field, a significant correlation between nitrogenase activity and the number of N2-fixing cyanobacteria in soil was found. No significant inhibition of nitrogenase activity by ammonium at concentrations up to 2mM was observed in these assays after 24h of incubation. This lack of inhibition was probably due to the rapid decrease in ammonium content in the flood water. Only 5% of the ammonium initially added remained in the water 24h later. In the long-term experiments, nitrogenase activity was assayed in plots fertilized with 0, 70 and 140kgNha–1, over the cultivation cycle, for 5 years. A partial inhibition of nitrogenase activity by deep-placed N fertilizers was observed. Differences were only significant in 2 years. Mean results from 5 years only showed significant differences between plots fertilized with 0 and 140kgNha–1. The partial inhibition of nitrogenase activity by ammonium increased over the cultivation cycle. Inhibition was only significant in September, at the end of the cultivation cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050257
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic evidence that hepA gene is involved in the normal deposition of the envelope of both heterocysts and akinetes in Anabaena variabilis ATCC 29413 (1994)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 123 (1994), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The hepA gene in Anabaena sp. strain PCC 7120 is required for normal formation of the polysaccharide layer of the heterocyst envelope. A plasmid bearing hepA, interrupted by a neomycin-resistance cassette, was transferred by conjugation to wild type Anabaena variabilis ATCC 29413, so that the interrupted hepA gene replaced a homologous sequence. In the recombinant exconjugants, the envelopes of akinetes as well as of heterocysts were altered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1994.tb07202.x
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  • 5
    Electronic Resource
    Electronic Resource
    Light-to-dark transitions trigger a transient increase in intracellular Ca2+ modulated by the redox state of the photosynthetic electron transport chain in the cyanobacterium Anabaena sp. PCC7120 (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Light-to-dark transitions represent one of the most crucial environmental stresses that photosynthetic organisms must cope with, since substantial metabolism adaptations are required in order to utilize alternative energy and carbon sources. Although signal transduction systems for changing light regimes are not sufficiently understood, calcium has been implicated in plants as a second messenger in light-on and light-off events. Much less is known about light signalling in cyanobacteria, but it has been shown that calcium probably performs similar signalling roles in these organisms and other prokaryotes. Herein it is reported that light-to-dark transitions trigger a calcium transient in aequorin expressing Anabaena sp. PCC7120. The magnitude of this transient depends on the fluence rate previously irradiated and can reach a peak height over 2 µm free calcium when the fluence rate of light is around 400 µmol photons s−1 m−2. The use of increasing calcium concentration, ethylene glycol-bis (β-aminoethylether) N,N,N′,N′-tetraacetic acid (EGTA), verapamil and trifluoperazine indicated that these transients are originated by a calcium influx probably through verapamil-sensitive Ca2+ channels and are probably modulated by calcium-binding proteins. Experiments with different light spectral qualities and the photosynthetic inhibitors 3-(3,4 dichlorophenyl)1,1,dimelthylurea (DCMU) and 3,5-dibromo-3-methyl-b-isopropyl-p-benzoquinone (DBMIB) indicate that the calcium transient triggered by the light-to-dark transition is not coupled to a specific photoreceptor but rather to changes in the redox state of photosynthetic electron transport chain components other than the plastoquinone pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01187.x
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  • 6
    Electronic Resource
    Electronic Resource
    Calcium transients in response to salinity and osmotic stress in the nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, expressing cytosolic apoaequorin (2001)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 24 (2001), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We show here that both salinity and osmotic stress trigger transient increases in intracellular free Ca2+ concentration ([Ca2+]i) in cells of the nitrogen-fixing filamentous cyanobacterium Anabaena sp. PCC7120, which constitutively expresses apoaequorin. Isoosmolar concentrations of salt (NaCl) and osmoticum (sucrose) induced calcium transients of similar magnitude and shape, suggesting that cells sense, via Ca2+ signalling, mostly osmotic stress. The Ca2+ transients induced by NaCl and sucrose were completely blocked by the calcium chelator ethylene glycol-bis(b-aminoethylether)N,N,N¢,N¢-tetraacetic acid (EGTA) and were partially inhibited by the calcium channel blocker verapamil. Increased external Ca2+ and the Ca2+ ionophore calcimycin (compound A23187) enhanced Ca2+ influx further, suggesting the involvement of extracellular Ca2+ in the observed response to salinity and osmotic stress. However, the plant hormone abscisic acid (ABA) did not provoke any effect on the Ca2+ transients induced by both stresses, indicating that it may not be acting upstream of Ca2+ in the signalling of salinity and/or osmotic stress in Anabaena sp. PCC7120.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2001.00708.x
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  • 7
    Electronic Resource
    Electronic Resource
    Two mutations that block heterocyst differentiation have different effects on akinete differentiation in Nostoc ellipsosporum (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 12 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Evident differentiation of vegetative cells into hetero-cysts in Anabaena sp. strain PCC 7120 is prevented by Insertions in genes hetR and hetP. Nostoc ellipsosporum possesses single copies of genes that hybridize with hetR and hetP. In mutant NE2 of N. ellipsosporum, in which hetR is interrupted by an insert, and in a double recombinant of wild-type N. ellipsosporum with a plasmid that bears an interrupted copy of hetR, neither heterocysts nor akinetes are formed. When an intact copy of hetR from Anabaena sp. strain PCC 7120 was added to NE2 the ability to form both heterocysts and akinetes was restored, in contrast to the hetR mutant, a hetP mutant of N. ellipsosporum could form akinetes, but heterocyst formation was blocked. Use of luxAB, encoding luciferase, as a reporter, and use of luxC, luxD and luxE to generate aldehyde (a substrate for the luciferase reaction), permitted visualization of the expression of hetR at the level of single cells; hetR was expressed in akinetes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb01055.x
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of phenoxy acetic herbicides on growth, photosynthesis, and nitrogenase activity in cyanobacteria from rice fields (1992)
    Springer
    Archives of environmental contamination and toxicology 22 (1992), S. 130-134 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract The effects of the phenoxy acetic herbicides 2,4-dichlorophenoxy acetic acid (2,4D) and methylchloro-phenoxy acetic acid (MCPA) on growth, photosynthesis, and nitrogenase activity of cyanobacteria has been investigated. Concentrations ranging from 10−9 to 10−3 M did not change significantly the parameters of Anabaena UAM 202. Concentrations higher than 10−3 M of both herbicides were toxic. The primary toxic action of these herbicides in Anabaena UAM 202 was on photosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213311
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  • 9
    Electronic Resource
    Electronic Resource
    Contribution of N2 fixing cyanobacteria to rice production: availability of nitrogen from 15N-labelled cyanobacteria and ammonium sulphate to rice (2000)
    Springer
    Plant and soil 221 (2000), S. 107-112 
    Details
    ISSN: 1573-5036
    Keywords: Cyanobacteria ; `in situ' N2 fixation ; N fertilizer ; 15N balance ; rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This study investigate the potential contribution of nitrogen fixation by indigenous cyanobacteria to rice production in the rice fields of Valencia (Spain). N2-fixing cyanobacteria abundance and N2 fixation decreased with increasing amounts of fertilizers. Grain yield increased with increasing amounts of fertilizers up to 70 kg N ha-1. No further increase was observed with 140 kg N ha-1. Soil N was the main source of N for rice, only 8–14% of the total N incorporated by plants derived from 15N fertilizer. Recovery of applied 15N-ammonium sulphate by the soil–plant system was lower than 50%. Losses were attributed to ammonia volatilization, since only 0.3–1% of applied N was lost by denitrification. Recovery of 15N from labeled cyanobacteria by the soil–plant system was higher than that from chemical fertilizers. Cyanobacterial N was available to rice plant even at the tillering stage, 20 days after N application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004737422842
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