PHOTOINDUCTION AND PHOTOREVERSAL OF THE NOSTOCACEAN DEVELOPMENTAL CYCLE1

The developmental cycle of Nostoc muscorum, a nitrogen-fixing blue-green alga, is controlled by the spectral quality of illumination. Red light with peak activity at 650 mμ induces development of filaments from a nonfilamentous (aseriate) stage of the life cycle. Red-light photoinduction is reversed by simultaneous or subsequent exposure to light from a broad band in the green region of the spectrum. Photoreversibility of the red-light induction, by green light, decays very slowly, remaining at an appreciable level for over 24 hr after the primary stimulus. Allophycocyanin is indicated to be the photoreceptor for red-light induction. One or more phycoeythrins may operate as photoreceptors for reversal of induction. The dosage response and wavelength dependence of developmental photocontrol in Nostoc muscorum A indicate that a nonphotosynthetic mechanism is involved in both developmental photoinduction and its photoreversal.     

Photomophogenesis in the Blue-green Alga Nostoc commune 584

The blue-green alga Nostoc commune 584 displays a photocontrolled developmental cycle similar to that described for N. muscorum A by Lazaroff and Vishniac (1961). In both species white fluorescent light acts at the same stage, ragulating the development of motile trichomes from sheathed aseriate colonies. However white light blocks this step in N. commune 584, whereas the formation of motile trichomes is promoted by white light in N. muscorum A. Light-grown (aseriate) cultures in N. commune 584 were used to determine the action spectra for photomorphogenesis. Green light (max 520 nm) inhbited aseriate colony breakage, and red light (max 640 nm) promoted colony breakage and the differentiation of motile trichomes. On a quantum basis green light was about 3 times more effective than red light. The morphogenetic effects of either red or green light were reversible by irradiation with the other color of light. Repeated photoreversibility was observed, and the algal culutres responded only to the color of the last irradiation in a sequence. An unidentified substance is excreted into the media of motile cultures of both N. commune 584 and N. muscorum A which promotes motility in non-motile cultures. The motility-promoting substances from both species are reciprocally active. Activity is lost when the media are autoclaved.     

Studies on the hormonal relationships of algae in pure culture

Summary Indole-3-acetic acid (IAA) stimulated the growth (increase in dry weight) of the blue-green algae Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum, Anabaena cylindrica, and Tolypothrix tenuis and the green algae Chlorella pyrenoidosa, Ankistrodesmus falcatus and Scenedesmus obliquus growing under as sterile conditions as possible. The optimum concentration varied from species to species; in the blue-green algae it ranged from 10^-5 to 10^-9 M and in the green algae it was 10^-3 M. These results are discussed in the light of present studies in this field.     

Photochromic Pigments from Blue-Green Algae: Phycochromes a, b, and c

Aqueous extracts of blue-green algae were fractionated by electrofocusing. In all algae investigated, fractions with iso-electric points at or near 4.6 showed photochromic behaviour analogous to that of phytochrome, although they were sensitive to light of shorter wavelength. Three main types of photochromic pigments were found: Phycochrome a (in Tolypothrix distorta, Phormidium luridum, Nostoc muscorum 1453/12, and Anacystis nidulans) has one form absorbing maximally at about 590 nm (formed under red light) and one absorbing maximally at about 630 nm (formed under green light). Phycochrome b (in Tolypothrix distorta) has one form absorbing maximally near 510 nm and one form absorbing maximally at 570 nm (formed in yellow-green and blue-green light, respectively). Phycochrome c (in Nostoc muscorum A and probably in Tolypothrix tenuis) has one form absorbing maximally at 650 nm (formed under green light) and one absorbing very weakly in the green region (formed under red light). The conversion of Phormidium phycochrome a from its red-absorbing form to its green-absorbing form causes the same spectral change as if an f-chromophore of phycocyanin were transformed into an s-chromophore. The quantum yield for this conversion is estimated to be 0.1, while the quantum yield for the reversion is estimated to be 0.4 on the assumption that the absorption coefficients are those of f- and s-chromophores. Phycochrome c is less light-sensitive than phycochromes a and b.     

Studies on the hormonal relationships of algae in pure culture

Summary The effect of potential precursors of Indole-3-acetic acid (IAA) on the growth (increase in dry weight) of Anacystis nidulans, Chlorogloea fritschii, Phormidium foveolarum, Nostoc muscorum and Tolypothrix tenuis have been investigated under as sterile conditions as possible.Tryptamine showed a marked stimulation of growth indicating its possible conversion to IAA. Tryptophan at a hormonal concentration promoted growth in only 1 species, Chlorogloea fritschii. Indole stimulated the growth of Chlorogloea fritschii, Nostoc muscorum and Tolypothrix tenuis. Anthranilic acid promoted the growth of Nostoc muscorum, it failed to stimulate the growth of Chlorogloea fritschii. Anthranilonitrile promoted the growth of Nostoc muscorum and Chlorogloea fritschii. -Alanine promoted the growth of Nostoc muscorum, Tolypothrix tenuis and Chlorogloea fritschii at hormonal concentrations.     

Evidence for a role for L-proline as a salinity protectant in the cyanobacterium Nostoc muscorum

Nostoc muscorum required an active proline oxidase in order to assimilate exogenous proline as a source of fixed nitrogen. A mutant strain (Ac^r) resistant to growth inhibition by L-azetidine-2-carboxylate (AC) was found to be deficient in proline oxidase activity, and to be a proline overaccumulator. Proline overaccumulation, resulting either from mutational acquisition of the Ac^r phenotype or from salinity-inducible uptake of exogenous proline, conferred enhanced salinity tolerance in this cyanobacterium.     

COMPETITIVE EXCLUSION AMONG THREE PLANKTONIC BLUE-GREEN ALGAL SPECIES1,2

Although domination of 1 species in an algal community has often been attributed to toxic effects, nutrient exhaustion can also lead to competitive exclusion among algal species. The bacteria-associated blue-green algae Microcystis aeruginosa, Nostoc muscorum, and Phormidium foveolarum were cultivated in Zehnder-Gorham's medium No. 11 individually and in their combinations. The growth rates of Microcystis and of Nostoc were reduced by the presence of Phormidium. This detrimental effect was apparently not due to formation of any toxic or allelopathic matter. It was caused by the reduction of iron and trace metal concentrations in the medium by Phormidium to levels too low for normal growth of Microcystis and Nostoc. Work with the axenic forms of the 3 algal species also indicated a lowering of iron and trace element concentrations by Phormidium to levels not sufficient for sustained growth of Microcystis and Nostoc. Thus, bacteria played no significant role in this example of competitive exclusion.     

Nutritional regulation of organelle biogenesis inEuglena: Photo- and metabolite induction of mitochondria

Exposure of dark-grown restingEuglena gracilis Klebs var.bacillaris Cori to light, ethanol, or malate produced an increase in the specific activity of fumarase (EC. 4.2.1.2) and succinate dehydrogenase (EC. 1.3.99.1) during the first 8–12 h of exposure to inducer, followed by a decrease in the specific activity of both mitochondrial enzymes between 12 and 72 h. The increased specific activity represented a net increase in the level of active enzyme, and it was dependent upon cytoplasmic protein synthesis. The photoinduction of fumarase required continuous illumination while the subsequent decrease in fumarase specific activity was independent of light. Light had little effect on the ethanol and malate induction of fumarase and succinate dehydrogenase. In the mutant W₃BUL, which has no detectable protochlorophyll(ide) and chloroplast DNA, light induced both mitochondrial enzymes and the kinetics of enzyme induction were similar to the induction kinetics in wild-type cells. The induction of mitochondrial enzymes appears to be controlled by a non-chloroplast photoreceptor. Dark-grown resting cells of the plastidless mutant W₁₀SmL have lost the ability to regulate fumarase levels. In this mutant, the specific activity of fumarase fluctuated and light had little effect on these fluctuations, indicating that fumarase synthesis was uncoupled from the nonchloroplast photoreceptor. Ethanol addition produced transient changes in fumarase specific activity in W₁₀SmL indicating that in this mutant, mitochondrial enzymes are still inductible by metabolites. Fumarase synthesis in wild-type cells was not induced in the dark by levulinic acid, a chemical inducer of the breakdown ofEuglena storage carbohydrates. Taken together, our results indicate that the photoinduction of mitochondrial enzyme synthesis is not a result of the photoinduction of carbohydrate breakdown. The mechanisms by which light and organic carbon induce the synthesis ofEuglena mitochondria may differ.     

Nitrogenase activity of the antarctic cyanobacteriumNostoc commune: Influence of temperature

Nitrogenase activity (C₂H₂ reduction) ofNostoc commune isolated from Schirmacher Oasis (Antarctica) was compared withNostoc muscorum, N. calcicola, Anabaena doliolum andGloeocapsa sp. The temperature profile of acetylene reduction (5–30 °C) forN. commune revealed (a) that the highest rate of nitrogenase activity was at 25±1 °C, (b) that it was low (69 %) in comparison withN. muscorum, and (c) that nitrogenase activity continued at lower temperatures, which was not evident for other cyanobacteria. The results suggest thatN. commune is adapted to lower temperatures in terms of nitrogen fixation.     

Regulation of Nostoc sp. phycobilisome structure by light and temperature.

Nostoc sp. strain MAC cyanobacteria were green in color when grown in white light at 30 degrees C and contained phycobilisomes that had phycoerythrin and phycocyanin in a molar ratio of 1:1. Cells grown for 4 to 5 days in green light at 30 degrees C or white light at 39 degrees C turned brown and contained phycoerythrin and phycocyanin in a molar ratio of greater than 2:1. In addition to the change in pigment composition, phycobilisomes from brown cells were missing a 34.5-kilodalton, rod-associated peptide that was present in green cells. The green light-induced changes were typical of the chromatic adaptation response in cyanobacteria, but the induction of a similar response by growth at 39 degrees C was a new observation. Phycobilisomes isolated in 0.65 M phosphate buffer (pH 7) dissociate when the ionic strength or pH is decreased. Analysis of the dissociation products from Nostoc sp. phycobilisomes suggested that the cells contained two types of rod structures: a phycocyanin-rich structure that contained the 34.5-kilodalton peptide and a larger phycoerythrin-rich complex. Brown Nostoc sp. cells that lacked the 34.5-kilodalton peptide also lacked the phycocyanin-rich rod structures in their phycobilisomes. These changes in phycobilisome structure were indistinguishable between cells cultured at 39 degrees C in white light and those cultured at 30 degrees C in green light. A potential role is discussed for rod heterogeneity in the chromatic adaptation response.     

UV-A/B radiation rapidly activates photoprotective mechanisms in Chlamydomonas reinhardtii

Conversion of light energy into chemical energy through photosynthesis in the chloroplasts of photosynthetic organisms is essential for photoautotrophic growth, and non-photochemical quenching (NPQ) of excess light energy prevents the generation of reactive oxygen species and maintains efficient photosynthesis under high light. In the unicellular green alga Chlamydomonas reinhardtii, NPQ is activated as a photoprotective mechanism through wavelength-specific light signaling pathways mediated by the phototropin (blue light) and ultra-violet (UV) light photoreceptors, but the biological significance of photoprotection activation by light with different qualities remains poorly understood. Here, we demonstrate that NPQ-dependent photoprotection is activated more rapidly by UV than by visible light. We found that induction of gene expression and protein accumulation related to photoprotection was significantly faster and greater in magnitude under UV treatment compared with that under blue- or red-light treatment. Furthermore, the action spectrum of UV-dependent induction of photoprotective factors implied that C. reinhardtii senses relatively long-wavelength UV (including UV-A/B), whereas the model dicot plant Arabidopsis (Arabidopsis thaliana) preferentially senses relatively short-wavelength UV (mainly UV-B/C) for induction of photoprotective responses. Therefore, we hypothesize that C. reinhardtii developed a UV response distinct from that of land plants.

In contrast to land plants, which sense short-wave UV light, the unicellular green alga Chlamydomonas reinhardtii senses long-wavelength UV light for photoprotective responses.     

Quantitative and structural characteristics of lipids in Chlorobium and Chloroflexus

Exposure of dark grown resting Euglena to light induced the synthesis of chloroplast valyl-tRNA synthetase. Ethanol, a specific inhibitor of Euglena chloroplast development had little effect on chloroplast valyl-tRNA synthetase induction during the first 12 h of light exposure. Ethanol, however, completely inhibited enzyme synthesis between 12–72 h of light exposure. Malate, an alternative carbon source, had little effect on the photoinduction of valyl-tRNA synthetase. When dark grown resting cells were exposed to 2 h of light and returned to the dark, chloroplast valyl-tRNA synthetase continued to accumulate for 8–12 h at a rate which was less than the rate in cells maintained continuously in the light. The mutant strain W₃BUL lacks detectable chloroplast DNA and phototransformable protochlorophyllide, but retains a plastid remnant. Exposure of strain W₃BUL to light induced the synthesis of chloroplast valyl-tRNA synthetase and enzyme induction was not inhibited by ethanol. After 72 h of light exposure in the presence or absence of ethanol, enzyme levels in strain W₃BUL were comparable to the levels found in the wildtype strain after 8–14 h of light exposure. These results suggest that the nonchloroplast photoreceptor regulates the initial phase of enzyme synthesis. Mutant strain W₁₀BSmL differs from strain W₃BUL in that the plastid remnant if present, is greatly reduced. Chloroplast valyl-tRNA synthetase was undetectable in the strain W₁₀BSmL suggesting that the levels of active, cytoplasmically synthesized, chloroplast localized enzymes may be related to the developmental status of the chloroplast through the extent to which the enzyme precursor can be accumulated and or posttranslationally processed into an active enzyme within the chloroplast or chloroplast remnant.This research was supported by National Institutes of Health Grant GM26994, Biomedical support grant RR-0755 and funds from the Research Council, University of Nebraska     

Regulatory effect of hydrogen on nitrogenase activity of the blue-green alga (cyanobacterium) Nostoc muscorum.

Preincubation of the blue-green alga (cyanobacterium) Nostoc muscorum under an atmosphere of argon plus acetylene in the light led to a greater than fourfold increase of light-induced hydrogen evolution and to a 50% increase of acetylene reduction, as compared to cells that had not been preconditioned. The basic and the increased hydrogen evolution were both due to nitrogenase activity. Furthermore, after preincubation the hydrogen uptake, usually observed with unconditional cells, was abolished. Nostoc preincubated under acetylene evolved hydrogen in the light even in the presence of nitrogen for at least 2 h, with a 15-fold increase as compared to the unconditioned cells. These acetylene effects could be completely abolished by the presence of hydrogen during acetylene preincubation. These findings indicate that the hydrogen concentration in N. muscorum cells plays a role in regulation of nitrogenase activity.     

NONEQUILIBRIUM RATES OF PHOTOSYNTHESIS AND RESPIRATION UNDER DYNAMIC LIGHT SUPPLY1

To identify processes that might account for differences in growth rates of rhodophytes under constant and dynamic light supply, we examined nonequilibrium gas exchange by measuring time courses of photoinduction, loss of photoinduction, and respiration rates immediately after the light–dark transition. Using the rhodophyte species Palmaria palmata (Huds.) Lamour and Lomentaria articulata (Huds.) Lyngb., we compared the effects of growth-saturating constant photon flux density (PFD) (95 μmol photons · m^?2· s^?1) to those of a dynamic light supply modeled on canopy movements in the intertidal zone (25 μmol photons · m^?2· s^?1 background PFD plus light flecks of 350 μmol photons · m^?2· s^?1, 0.1 Hz). The time required for P. palmata and L. articulata to be fully photoinduced was not affected by the dynamics of light supply. L. articulata required only 6 min of illumination with either fluctuating or constant light to be completely induced compared to 20 min for P. palmata. The latter species also lost photoinduction more rapidly than did L. articulata in the dark. There was no significant decline in photoinduction state for either species at the background PFD. The time courses of respiration after illumination with constant and fluctuating light were significantly different for P. palmata but not for L. articulata when the total photon dose was equal. In general, gas exchange of P. palmata appeared to be particularly sensitive to the temporal distribution of light supply whereas that of L. articulata was sensitive to the amplitude of variations, being photoinhibited at high PFD. These results are discussed in terms of the different mechanisms of inorganic carbon acquisition in the two species.     

Photoperiodic regulation of receptacle induction in Sargassum horneri (Phaeophyceae) using clonal thalli

We developed a clonal culture of Sargassum horneri to investigate the effect of photoperiod on reproduction in this species. Regenerated vegetative thalli were obtained using lateral branches excised from a thallus grown from a single embryo under short‐day conditions (SD = 10:14 h light : dark cycle). Lateral branches excised from the SD‐regenerated thallus became vegetative thalli that remained in that phase as long as they were cultured under SD. When an excised lateral branch was cultured under long‐day conditions (LD = 14:10 h light : dark cycle), it began to enter the reproductive phase while still less than 50 mm long. Induction of the reproductive phase was accompanied by a distinctive morphological change – suppression of blade formation at the apical region of the branch; elongation of branches without blades was then followed by differentiation of receptacles bearing conceptacles on their surface. Apices of receptacles were able to interconvert between reproductive and vegetative phases, as blades resprouted upon transfer from LD to SD. The critical day length for induction of receptacle formation was between 13 and 14 h; receptacle formation was also induced under SD conditions with night breaks (NBs). These results strongly suggest that reproductive regulation of S. horneri is a photoperiodic long‐day response. NBs with blue and green light were effective for reproductive induction but not with red light. This suggests that blue‐ and/or green‐light photoreceptors are involved in the photoperiodic reproductive response of S. horneri.     

Photoregulated or Energy Dependent Process of Hormogonia Differentiation in Nostoc sphaeroides Kutzing （Cyanobacterium）

Abstract: Hormogonium, which was thought to play an important role in the dispersal and survival of these microorganisms in their natural habitats, is a distinguishable developmental stage of heterocystous cyanobacteria. The present study examined the effects of different light conditions and sugars on the differentiation of Nostoc sphaeroides Kützing to the hormogonia stage. Results showed that differentiation of hormogonia was light dependent in the absence of sugar, but that close to 100% of cyanobacteria differentiated to hormogonia in the presence of glucose or sucrose, irrespective of the light conditions. This differentiation was inhibited, even in the presence of sugars, upon application of an inhibitor of respiration. Following the testing of different sugars, the effects of different lights were examined. It was found that 5–10 umol‐nT2‐s‐1 photon flux density was optimal for hormogonia differentiation. One hundred percent differentiation was obtained with white light irradiation, in contrast with irradiation with green light (80% differentiation) and red light (0–10% differentiation). Although they showed different efficiencies in inducing hormogonia differentiation in N. sphaeroides, the green and red radiation did not display antagonistic effects. When the additional aspect of time dependence was investigated through the application of different light radiations and an inhibitor of protein synthesis, it was found that the initial 6 h of the differentiation process was crucial for hormogonia differentiation. Taken together, these results show that hormogonia differentiation in N. sphaeroides is either a photoregulated or an energy dependent process. (Managing editor: Ping HE)     

Hydrogenases in Nostoc sp. Strain PCC 73102, a Strain Lacking a Bidirectional Enzyme

The present study was carried out in order to examine and characterize the bidirectional hydrogenase in the cyanobacterium Nostoc sp. strain PCC 73102. Southern hybridizations with the probes Av1 and Av3 (hoxY and hoxH, bidirectional hydrogenase small and large subunits, respectively) revealed the occurrence of corresponding sequences in Anabaena variabilis (control), Anabaena sp. strain PCC 7120, and Nostoc muscorum but not in Nostoc sp. strain PCC 73102. As a control, hybridizations with the probe hup2 (hupL, uptake hydrogenase large subunit) demonstrated the presence of a corresponding gene in all the cyanobacteria tested, including Nostoc sp. strain PCC 73102. Moreover, with three different growth media, a bidirectional enzyme that was functional in vivo was observed in N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis, whereas Nostoc sp. strain PCC 73102 consistently lacked any detectable in vivo activity. Similar results were obtained when assaying for the presence of an enzyme that is functional in vitro. Native polyacrylamide gel electrophoresis followed by in situ hydrogenase activity staining was used to demonstrate the presence or absence of a functional enzyme. Again, bands corresponding to hydrogenase activity were observed for N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis but not for Nostoc sp. strain PCC 73102. In conclusion, we were unable to detect a bidirectional hydrogenase in Nostoc sp. strain PCC 73102 with specific physiological and molecular techniques. The same techniques clearly showed the presence of an inducible bidirectional enzyme and corresponding structural genes in N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis. Hence, Nostoc sp. strain PCC 73102 seems to be an unusual cyanobacterium and an interesting candidate for future biotechnological applications.     

Fractionation of phycobilisomes from the blue-green alga Nostoc muscorum

Phycobilisomes (PBS) isolated from Nostoc muscorum contain eight spectral forms of phycobiliproteins. PBS partially dissociated by osmotic or temperature shock, were separated into 42S and 34S particles by centrifugation in sucrose density gradient. The 42S particles are enriched with phycocyanin, the 34S ones--with allophycocyanin. The 42S particles dissociate to free pigments by repeated osmotic or temperature shock and the 34S ones dissociate to subparticles I and II having the constant pigments composition. The integrity of PBS and isolated substructures is controlled by the yield of energy transfer between pigment molecules. PBS from Nostoc muscorum was found to contain the rods of three different types. The model PBS containing different spectral forms of biliproteins is proposed.     

Screening for acetylcholinesterase inhibitory activity in cyanobacteria of the genus Nostoc

Fifty-four cyanobacterial strains of the genus Nostoc from different habitats were screened for acetylcholinesterase inhibitory activity. Water-methanolic extracts from freeze-dried biomasses were tested for inhibitory activity using Ellman's spectrophotometric method. Acetylcholinesterase inhibitory activity higher than 90% was found in the crude extracts of Nostoc sp. str. Lukesova 27/97 and Nostoc ellipsosporum Rabenh. str. Lukesova 51/91. Extracts from Nostoc ellipsosporum str. Lukesova 52/91 and Nostoc linckia f. muscorum (Ag.) Elenk. str. Gromov, 1988, CALU-980 inhibited AChE activity by 84.9% and 65.3% respectively. Moderate AChE inhibitory activity (29.1-37.5%) was found in extracts of Nostoc linckia Roth. str. Gromov, 1962/10, CALU-129, Nostoc muscorum Ag. str. Lukesova 127/97, Nostoc sp. str. Lhotsky, CALU-327 and Nostoc sp. str. Gromov, CALU-998. Extracts from another seven strains showed weak anti-AChE activities. The active component responsible for acetylcholinesterase inhibition was identified in a crude extract of Nostoc sp. str. Lukesova 27/97 using HPLC and found to occur in one single peak.     

Phycobiliprotein fluorescence of Nostoc punctiforme changes during the life cycle and chromatic adaptation: characterization by spectral confocal laser scanning microscopy and spectral unmixing

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analyse in vivo the fluorescence spectra of the photosynthetic pigments chlorophyll a (Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of two Nostoc punctiforme strains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein composition in vivo.