Heterocyst Frequency Research Articles

Effects of Cycloheximide and Maleic Hydrazide on a Nitrogen-fixing Cyanophyte

Cycloheximide showed growth-promoting effect on Anabaena doliolum B haradwaja in low concentrations but inhibited fixation in all tested concentrations. Maleic hydrazide in increasing concentration retarded growth, fixation, heterocyst frequency, and formation of various forms of chlorophyll a.

The effect of cadmium ion on the growth, photosynthesis, and nitrogenase activity of [formula omitted][formula omitted

The growth of Anabaena inaequalis was significantly inhibited by Cd 2+ concentrations greater than 0.02 ppm (μg/ml) and completely inhibited at 0.06 ppm (Day 12). Cadmium had no significant effect upon the lag phase of growth or the culture doubling time, but caused the retardation phase to arrive sooner. One ppm Cd 2+ significantly inhibited the rates of both photosynthesis and acetylene reduction, by A . inaequalis , with complete inhibition at 4 and 20 ppm respectively. Cell sensitivity increased directly with exposure time. Cadmium caused some cell lysis of A . inaequalis and induced an increase in filament length, heterocyst frequency, and a loss of cellular contents from filament apical cells. The cellular abnormalities observed and the fact that toxicity increased with longer exposure times, suggested that metal toxicity resulted from effects of Cd 2+ taken up by cells rather than Cd 2+ at the cell surface.

Control of heterocyst and nitrogenase synthesis in cyanobacteria.

The development of the heterocyst by filamentous nitrogen-fixing cyanobacteria provides an attractive model system for studying cellular differentiation. Heterocyst synthesis is repressed by the presence of exogenous combined nitrogen. In this report, it is shown that the tryptophan analog, D,L-7-azatryptophan (Aza-T), is capable of relieving the repressive effect of exogenous NH4NO3 on heterocyst and nitrogenase synthesis. In nitrogen-fixing cultures, the presence of 20 micron Aza-T increases the heterocyst frequency twofold. The glutamate analog, L-methionine-D,L-sulfoximine (MSX), has also been shown to cause a derepression in the synthesis of heterocysts and nitrogenase. However, unlike MSX, Aza-T does not appear to exert its effects by inhibiting the activity of glutamine synthetase. Therefore, glutamine synthetase may not be the sole key to the derepression of heterocyst and nitrogenase development in the cyanobacteria. It is hoped that a study of Aza-T action may lead to the elucidation of a novel control mechanism.

Nitrogenase activity associated withCodiumspecies from New Zealand marine habitats

Abstract Nitrogenase activity, measured as acetylene reduction, was recorded at rates up to 1028 nmol.h−1 .g−1 dry weight for Codium adhaerens (Cabr.) Ag. var. convolutum Dellow and Codium fragile (Sur.) Hariot subsp. tomentosoides (Van Goor) Silva collected from New Zealand habitats. In both species the ability to reduce acetylene is invariably associated with the presence of a heterocystous blue‐green alga, Calothrix sp., epiphytic or embedded in the Codium thallus. A highly significant (P < 0.001) correlation between heterocyst frequency and nitrogenase activity was found. Nitrogenase and net photosynthesis of the Codium‐Calothrix system have different steady‐state responses to light intensity, and the kinetics of the two processes also differ in that nitrogenase is slow to respond to illumination or darkening. Glucose additions to Codium did not significantly increase nitrogenase activity. Nitrogenase is relatively insensitive to oxygen tension over the range 0–1.0 atm (0–1.033 kgf.cm−2) and still occurs at 1.5 atm (1.55 kgf.cm−2); this condition is unique in all nitrogenase systems thus far reported. Collectively these facts suggest that Calothrix is the agent primarily responsible for nitrogenase activity in these Codium species.

Mutants of the Blue-green Alga Anabaena ambigua

Mutants of the blue-green alga Anabaena ambigua Rao, resistant to ultraviolet, chloramphenicol and 5-fluorouracil were isolated. Seven such strains isolated on the basis of their increased resistance to the above agents were characterized in terms of morphological changes and pigment (chlorophyll a and carotenoids) synthesis. Comparatively, ultraviolet and 5-fluorouracil resulted in enhanced level of pigments which decreased in the case of chloramphenicol. The average filament length and heterocyst frequency were the other paramenters for comparison.

Effect of External cAMP on Growth, Cell Differentiation and Nitrogenase Activity of Nostoc linckia

Summary Three strains of Nostoc linckia (Roth Born et Flah., i.e., the wild type, a mutant producing heterocysts but lacking nitrogenase (Het+ Nif−) and a mutant displaying reduced heterocyst frequency and nitrogenase activity (Hetrf Nifra), were used in this study. In the parent strain, external cAMP suppresses heterocyst formation and nitrogenase activity, and supports less growth than that measured in the presence of nitrate or in the absence of any source of combined nitrogen. In both mutant strains the supply of cAMP stimulates growth and concurrently inhibits heterocyst differentiation and nitrogenase synthesis. The results do not indicate a regulatory function of external cAMP in nitrogen fixation by N. linckia but suggest that exogenous cAMP is utilized by this alga as an alternative source of combined nitrogen.

The Physiology of the Lichen Peltigera aphthosa, with Special Reference to the Blue‐green Phycobiont (Nostoc sp.)

AbstractVariations in the morphology and physiology were noted when parts of the Peltigera aphthosa Willd. thallus differing in age were examined. The many small cephalodia on the growing apex of the lichen showed a lower heterocyst frequency (14%) than those on the rest of the thallus (21–22%), which was reflected in the nitrogenase activity. In contrast, highest levels of photosynthesis (14CO2 uptake and O2 evolution) were noted at the growing apex. while respiration rates were fairly stable over the thallus. The water‐holding capacity was greatest in the midparts.Cephalodial biomass represented an average of 2.6% of total thallus biomass. while the number and size of these structures varied considerably. A minor part of the total carbon fixation (14CO2) and net oxygen evolution (O2 electrode) was performed by the blue‐green phycobiont (Nostoc) in light. A rapid excretion of ammonia from isolated cephalodia was noticed, which together with a comparatively constant C:N ratio throughout the thallus indicated a rapid transport of metabolites facilitated by close physical contact (electron microscopy).

Effect of metabolic inhibitors on growth, heterocyst frequency and spore formation in a blue-green alga,Westiellopsis iyengarii

The effects of metabolic inhibitors, thiourea, sodium bisulphite 2, 4-dinitrophenol, 2, 4-dinitrophenyl hydrazine, actinomycin-D, cycloheximide and 8-azaguanine on the nitrogen fixing heterocystous, heterotrichous stigonematalean blue-green algaWestiellopsis iyengarii were studied. In general three types of responses were discernible: an inhibition of growth in higher concentrations, partial suppression of heterocyst, and total inhibition of sporulation.

A CYTOLOGICAL ANALYSIS OF THE NOSTOC‐BRYOPHYTE RELATIONSHIP

SUMMARYA comparative light and electron microscope study has been made of the Nostoc colonies within the thalli of Blasia pusilla and the three British species of Anthoceros, and also of the Nostoc isolated from each bryophyte. From their morphology in culture two taxa of Nostoc have been identified; N. sphaericum from Anthoceros punctatus, A. husnotii and A. laevis, and N. calcicola from other gatherings of Anthoceros laevis and Blasia. These findings support the notion that the algal‐bryophyte associations are none specific.Within bryophyte thalli, the Nostoc trichomes are closely packed and specific features cannot be recognized. Mucilaginous sheaths are much less extensive and there is no evidence that the alga thrive in mucilage produced by the adjacent bryophyte cells. Heterocyst frequencies as high as 50% in the bryophytic Nostoc spp. strikingly recall the Azolla, Gunnera and cycad‐blue‐green algal symbioses. Akinetes, readily produced in culture were only seen in the Nostoc from dormant Anthoceros. The absence of phycobilisomes and high heterocyst frequencies in the bryophytic Nostoc spp. corroborates physiological data that the algae receive organic carbon from their hosts which enable them to fix nitrogen heterotrophically.The Nostoc colonies in both Blasia and Anthoceros are extensively penetrated by multi‐cellular bryophytic filaments. Whereas in Anthoceros these comprise highly vacuolate, thin‐walled cells, which sometimes contain intracellular Nostoc trichomes, in Blasia the filaments are thick‐walled and often develop labyrinthine wall ingrowths. This transfer cell morphology may be interpreted as an adaptation facilitating interchange of metabolites between Blasia and Nostoc. Its absence in Anthoceros perhaps indicates a far less harmonious relationship or may be related to the higher nutrient status of the habitats where the Anthoceros spp. were collected.

THE CYANOPHYTE‐HEPATIC SYMBIOSIS I. MORPHOLOGY AND PHYSIOLOGY

SUMMARYThe Anthoceros punctatus‐Nostoc and Blasia pusilla‐Nostoc symbioses were investigated. In both associations the Nostoc colonies develop in mucilaginous cavities on the undersurface of the gametophyte. The sporophytes of Anthoceros have no Nostoc colonies; no sporophytes of Blasia were found. The symbiotic algae have been identified as Nostoc sphaericum ex. Born et Flah. The heterocyst frequency of the free‐living isolates is 3–6% but this increases to 30% (Blasia) and 43% (Anthoceros) when the algae are growing symbiotically. On infecting alga‐free gametophytes of Blasia pusilla with Nostoc, algal colonies develop in the cavities within 72 h. The developing Nostoc colonies stretch the cells of the cavity wall and there also arise from a point on the host cavity wall, usually opposite the cavity pore, septate, branched, filamentous protrusions, which increase the surface area of contact between phycobiont and host by about 30% within 4 weeks of colony formation. Such outgrowths may facilitate interchange of metabolites between the alga and liverwort. The Nostoc phycobiont of Anthoceros may infect Blasia and vice‐versa. A strain of Nostoc punctiforme isolated from Gunnera also infects Blasia, but four other Nostoc isolates, including one from cycad root nodules, do not. Five other heterocystous algae, five non‐heterocystous filamentous algae and one unicellular alga tested do not infect Blasia. The nitrogen contents of thalli with Nostoc colonies are significantly higher than those treated with algae which do not develop colonies. The symbiotic algae differ physiologically and biochemically from free‐living algae. They show higher rates of nitrogenase activity (acetylene reduction assay), are depleted of nitrogen‐storing phycobilin pigments and structured granules and although metabolically active do not evolve O2 or fix CO2 photosynthetically, but do have polyhedral bodies which contain the key CO2‐fixing enzyme ribulose‐l,5‐diphosphate carboxylase. The Blasia symbiosis grows well and remains established in the pH range 4–8, at low levels of combined nitrogen (&lt;100 mg I−1 of nitrate‐nitrogen) but not at high levels (100–1000 mg I−1), in the temperature range 10–25°C, and under moist but not waterlogged or desiccated conditions.

Growth Characteristics of Anabaena ambigua Rao and its Strains

Summary A filamentous, heterocystous and nitrogen-fixing blue-green alga, Anabaena ambigua Rao has been used for the isolation of strains. The agents, hydroxylamine hydrochloride and N-methyl-N′-nitro-N-nitrosoguanidine were tried. The strains, Ha- and Lh-forms able to grow in simple mineral nutrient solution with or without combined nitrogen have been isolated. These forms have been noted for the alteration in their growth characteristics like, average filament length, heterocyst frequency, heterocyst dimension and growth rate. The abnormalities observed with NTG treatment could not be maintained in serial cultures in the basal medium with or without combined nitrogen.

Some characteristics of two morphological mutants of Nostoc linckia induced by nitrosoguanidine

AbstractThe blue‐green alga Nostoc linckia was treated with nitrosoguanidine and two classes of morphological mutant clones were isolated. One class shows certain abnormal phenotypic features of vegetative cells, spores, and heterocysts. It has increased heterocyst frequency and impaired growth rate. The other class exhibits an altered heterocyst spacing pattern. Both classes of mutants have reduced nitrogenase activity.

Some characteristics of two morphological mutants ofNostoc linckia induced by nitrosoguanidine

The blue-green alga Nostoc linckia was treated with nitrosoguanidine and two classes of morphological mutant clones were isolated. One class shows certain abnormal phenotypic features of vegetative cells, spores, and heterocysts. It has increased heterocyst frequency and impaired growth rate. The other class exhibits an altered heterocyst spacing pattern. Both classes of mutants have reduced nitrogenase activity.

THE INFECTION PROCESS AND ULTRASTRUCTURE OF THE GUNNERA‐NOSTOC SYMBIOSIS

SUMMARYThe two components of the Gunnera–Nostoc symbiosis were isolated, grown separately in culture and the association resynthesized in vitro. Both components develop normally when grown independently and Nostoc retains its ability to fix atmospheric nitrogen in symbiosis.Infection by Nostoc is initiated when the alga grows on mucilage produced by an apical papillate gland. The alga develops rapidly, growing between the papillae and finally penetrating thin‐walled meristematic cells at the base of the gland. Resulting nodules contain intracellular algal cells within a host membrane envelope. The algae are considerably modified in thylakoid distribution and shape, and have a very high heterocyst frequency. At later stages, the algae are enclosed in a thickened wall continuous with that of the host cell.

Growth and nitrogen fixation of mutants defective in heterocyst differentiation in the blue‐green alga Cylindrospermum sp.

AbstractThree classes of spontaneous and N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (NTG)‐induced mutants of the blue‐green alga Cylindrospermum sp. were isolated in the presence of combined nitrogen. Mutants with complete loss of heterocyst differentiation formed longer filaments than the parent alga and were unable to grow in nitrogen‐free medium and to fix nitrogen. The second type of mutants formed long filaments with terminal heterocysts. In the third type of mutants, paired proheterocyst differentiation occurred at regular intervals in long filaments and these were defective in their further development into mature heterocysts. Mutants with decreased heterocyst frequency due to defective differentiation and development showed less growth and nitrogen fixation in nitrogen‐free medium than the parent alga.

Growth and nitrogen fixation of mutants defective in heterocyst differentiation in the blue-green alga Cylindrospermum sp.

Three classes of spontaneous and N-methyl-N'-nitro-N-nitrosoguanidine (NTG)-induced mutants of the blue-green alga Cylindrospermum sp. were isolated in the presence of combined nitrogen. Mutants with complete loss of heterocyst differentiation formed longer filaments than the parent alga and were unable to grow in nitrogen-free medium and to fix nitrogen. The second type of mutants formed long filaments with terminal heterocysts. In the third type of mutants, paired proheterocyst differentiation occurred at regular intervals in long filaments and these were defective in their further development into mature heterocysts. Mutants with decreased heterocyst frequency due to defective differentiation and development showed less growth and nitrogen fixation in nitrogen-free medium than the parent alga.

NITROGEN METABOLISM IN LICHENS

SUMMARYThe blue‐green algal population and heterocyst frequency in Peltigera aphthosa, P. canina and P. polydactyla have been estimated by means of a chromium trioxide maceration technique followed by visual and photographic observation. Populations of the order of 107 cells/sq cm thallus in P. canina and P. polydactyla, and 106/sq cm in P. aphthosa have been found. These figures are some threefold greater than previously reported; the earlier results are explained by unexpectedly high fragility of the algal cells.A heterocyst frequency of c. 3.5% in P. canina confirms previous estimates obtained by another technique; P. polydactyla is similar but P. aphthosa has a very high heterocyst frequency, c. 22% of the total cells. These findings are reflected in the nitrogenase activity and support the concept that the enzyme is only active in heterocysts.

The pattern of development of Anabaena in the Azolla-Anabaena symbiosis

The development of Anabaena in the leaf cavities of Azolla (probably A. filiculoides) was studied. After the alga is installed in the cavity, heterocyst frequency rises to a maximum (20-30%) about 12 leaves from the apex, then remains constant until the leaf senesces. The size of vegetative cells of the alga increases with cell width apparently increasing linearly with increasing leaf age.

A study of two populations of Anabaena planctonica Brunnth. (Cyanophyta) from Minnesota

Abstract Filaments of Anabaena planctonica Brunnth. from two lakes in Minnesota were examined to determine the seasonal changes in cell composition of filaments. The relationship of heterocysts to akinetes was studied to determine if field data support the thesis that heterocysts induce akinete formation. The average number of cells per filament was highest in early June, decreased markedly in late June, remained constant until late September and then decreased. Initially the population contained filaments composed of vegetative cells only. The heterocyst frequency reached a peak in late August, and the akinete frequency reached a peak in late November. No fixed number of vegetative cells existed between an akinete and a heterocyst.

Ascorbic Acid and Heterocyst Development in the Blue–Green Alga Amabaema ambigua

AbstractThe nitrogen–fixing blue–green alga Anabaena ambigua was grown in a medium which contained either ammonium chloride as nitrogen source or molecular nitrogen. In the latter case the alga produced heterocysts. The material was analysed for ascorbic acid, dehydro‐ascorbic acid and diketogulonic acid. The amount of a,scorbic acid was found always to he higher in the alga grown with molecular nitrogen. When the alga grown with combined nitrogen was transferred to the medium lacking it, there was an increase in the ascorbic acid content. Conversely, when material cultured on the nitrogen–free medium was suspended in the medium containing ammonium chloride, there was a decrease in the cellular ascorbic acid. Esogenously added ascorbic acid, up to 0.5 mg per ml, increased the heterocyst frequency to nearly three times that of the control. D–isoascorbic acid, an analogue of ascorbic acid, also showed an enhancement of heterocyst production.Algal extracts were fractionated by poiyacrylamide electro–phoresis, and the presence of ascorbic acid oxidase was detected on the gels. Two bands, with Rf values 0.34 and 1.0, were found to give positive test: for the enzyme. The total enzyme activity was 16.7 % higher in cells grown with molecular nitrogen than in those grown with combined nitrogen. The exact location of the enzyme in the alga ist not known although the heterocysts were earlier shown to contain ascorbic acid. Cytochemical tests, however, indicated strong per–oxidase activity in the heterocysts.