Filamentous Green Alga Mougeotia Research Articles

A review of the enigmatic microalga Tetranguladinium Yu et al. 1983 ex Chen et al. 1988; palaeoecology, stratigraphy and palaeogeographical distribution

The probable zygnematacean zygospore Tetranguladinium is recorded in Mesozoic strata from southern Scandinavia for the first time. Tetranguladinium, which exhibits morphological similarities to the extant filamentous green alga Mougeotia, occurs in Jurassic–Cretaceous (J/K) boundary (latest Tithonian–Early Berriasian) assemblages from the Vomb Trough, southern Sweden and on the Danish island of Bornholm. The J/K boundary strata of southern Scandinavia were deposited in marginal marine settings, varying from freshwater marshes, lakes and flood plains, to lagoons, shoreface, and shallow marine to fully marine environments. The assemblages containing Tetranguladinium are diverse, consisting of spores and pollen, the colonial green alga Botryococcus, various other zygnematacean zygospores e.g. Ovoidites, Schizosporis and Tetraporina, and rare marine dinoflagellate cysts. A review of published fossil occurrences of Tetranguladinium reveals that its stratigraphical range extends at least from the Late Guadalupian (Mid Permian) to the Holocene. It has been recorded from Africa (Tanzania), Asia (China, Korea), Australia, northwest Europe (Denmark, Great Britain, Sweden), North America (Canada, USA), and South America (Argentina). Depositional and palaeoclimatological data for the known localities of Tetranguladinium confirm a preference for freshwater settings in a humid warm temperate to subtropical–tropical climate, often with a pronounced dry season. The palaeogeographical positions of all the known Tetranguladinium localities indicate that it is has stayed restricted within narrow belts between 30–40 south and 30–60 north of the palaeoequator since the Late Jurassic.

Physiological ecology of a species of the filamentous green alga Mougeotia under acidic conditions: Light and temperature effects on photosynthesis and respiration

One of the earliest and most reliable indications of acid precipitation affecting freshwater systems is the development of littoral blooms of the filamentous green alga Mougeotia (Zygnematales, Charophyceae). Field observations of depth distribution and seasonal abundance in Little Rock Lake, an experimentally acidified seepage lake in north‐central Wisconsin, suggest that Mougeotia might prefer warmer temperatures and carry out net photosynthesis at fairly low light levels. To test these hypotheses, we measured net photosynthesis and respiration at 56 combinations of irradiance and temperature in a controlled environment facility. Optimum conditions were 25°C and 300‐2,300 µmol quanta m−2 s− 1. Over this range, net photosynthesis averaged 40.4 mg O2 g−1 h−1. Respiration rates increased with both temperature and prior irradiance. Light‐enhanced respiration rates were significantly greater than dark respiration rates following irradiance ≥ 164 µmol quanta m−2 s−1. Mougeotia's photosynthetic response to temperature and irradiance explains aspects of its growth and distribution in acidified lakes but it does not by itself explain the magnitude of this alga's growth at low pH.

Effects of pH and selected metals on growth of the filamentous green alga Mougeotia under acidic conditions

When acid precipitation impacts freshwater systems, littoral blooms of the filamentous green alga Mougeotia (Zygnematales, Charophyceae) frequently develop. Field observations of its development in Little Rock Lake, an experimentally acidified seepage lake in north‐central Wisconsin, indicated that the species of Mougeotia present there may have an optimum pH for growth of ~5.2. Because a number of metals increase in concentration in acidified waters, we also proposed that this species of Mougeotia may be particularly tolerant of metals. To test these hypotheses, we grew Mougeotia from Little Rock Lake in culture at eight levels of pH (3 through 10) and measured net photosynthesis and respiration at each level. We also grew this isolate over a range of Zn concentrations from 10 to 2,400 µg liter−1 and Al concentrations from 10 to 3,600 µg liter−1. Little Rock Lake Mougeotia grew over a broad range of pH levels from 3 to 9 with an optimum at 8, in contrast to our expectation. Mougeotia, however, was tolerant to levels of Zn and Al considerably higher than the elevated levels to which it had been exposed in the acidified basin of the lake. Mougeotia may grow luxuriously in acidified waters because of an efficient uptake of CO2 and dissolved organic C and a lack of grazing pressure.

Dynamic changes in the actin cytoskeleton during the high-fluence rate response of theMougeotia chloroplast

Since photo-induced orientation movement of a single, ribbon-shaped chloroplast in each cell of the filamentous green algaMougeotia is inhibited in the presence of cytochalasin B, actin is thought to be involved in the process of chloroplast movements. However, this possibility remains to be proved. A specific class of cytoplasmic filaments, which emerge from the advancing front of the moving chloroplast, can be seen by differential interference contrast (DIC) microscopy. However, no one has yet succeeded in defining the nature of these filaments. We have been able to stain the actin filaments (AFs) associated with the moving chloroplast with fluorescein-conjugated phalloidin (FP) after pre-treatment withm-maleimidobenzoyl N-hydroxysuccinimide ester (MBS). No filamentous structures were observed in cells that had been pre-irradiated with low-fluence rate red light. However, transversely oriented fluorescent filaments appeared at the front edge of the moving chloroplast when it began to rotate under irradiation with high-fluence rate white light. These filaments disappeared after completion of the orientation movement, suggesting the simultaneous appearance of AFs and the orientation movement of the chloroplast. Thick cytoplasmic strands connecting the edge of the chloroplast with the parietal cytoplasm were often seen by DIC microscopy before and after completion of the high-fluence rate orientation movement. These thick cytoplasmic strands could not be stained by FP, but were often stained by 3,3′-dihexyloxacarbocyanine iodide (DiOC6(3)), suggesting that they are transvacuolar strands that include endoplasmic reticulum.

Capacity for microtubule reorganization and cell wall synthesis in cytoplasts of the green algaMougeotia

Sunnnary. A small proportion of nucleate subprotoplasts (karyoplasts) and enucleate subprotoptasts (cytoplasts) are formed during the preparation ofprotoplasts from the filamentous green alga Mougeotia. Regeneration of Mougeotia protoplasts is an orderly process known to involve reorganisation of cortical microtubules into polar arrays centered upon two opposing foci, synthesis of new cell walls and elongation to reform cylindrical cells. The ability of cytoplasts to carry out microtubule reorganisation and cell wall synthesis was investigated by combining Hoechst staining, to distinguish cytoplasts from karyoplasts and protoplasts, with immunofluorescent of microtubules and Calcofiuor or Tinopal staining of cell walls. Cytoplasts survived at least 20 h in culture, but did not elongate. However, cytoplasts did participate in the first steps of protoplast regeneration. The majority of cytoplasts synthesized some cell wall material, while a small proportion was able to form ordered arrays of cortical microtubules indistinguishable from those in regenerating nucleate protoplasts. These results demonstrate the ability of plant microtubules to form new, orderly arrays in the absence of a nucleus, and suggest that the reestablishment of axiality in the protoplasts does not require a nucleus or nuclear DNA transcription.

Inferences concerning climatic change from a deeply frozen lake on Rundfjeld, Ellesmere Island, Arctic Canada

A small lake on top of Rundfjeld, central Ellesmere Island, at an elevation of approximately 830 m, is frozen to the bottom, and the thickness of lake ice present is at least 5.45 m. Under present climatic conditions the lake does not thaw to the bottom, even during the warmest summers; i.e., 3 to 4 m of ice still floored the deepest part of the lake in mid-August 1987. A radiocarbon age determination via accelerator mass spectrometry (AMS) on a sample of the filamentous green alga Mougeotia sp., recovered from the lake ice at a depth below 4 m, gave 5730±70 BP (TO-530). The date indicates that the lake was probably completely open for an unspecified period of time during the warmest part of the Hypsithermal Interval. This situation is in agreement with data derived from a variety of other sources in Ellesmere Island and adjacent Greenland.

Effects of nutrient (N, P, C) enrichment upon periphyton standing crop, species composition and primary production in an oligotrophic softwater lake

SUMMARY. 1. The effects of nutrient addition upon algal periphyton standing crop and benthic community metabolism were investigated in Lake Lacawac, Pennsylvania. Nutrient‐diffusing flower pot substrates were filled with combinations of P (0.015 mol Na2HPO4), N (0.15molNaNO3) and carbon as glucose (0.015mol (LG) or 0.15mol (HG)) or 0.58 mol NaHCO3 (C). Fifty‐two pots representing ten treatments were placed in the lake on 5 May 1985 and sampled after 32‐38 days.2. Maximum chlorophyll‐a values of 23.82μgcm−2 and 29.72μgcm−2 were obtained on NPC and NPHG pots respectively, compared to 0.82μgcm−2 on control pots. Algal growth was not enhanced unless N and either organic or inorganic carbon were supplied. Ash Free Dry Mass was especially high on NPHG pots.3. Gross production, net production and community respiration were assessed with light‐dark chambers affixed to the pots using microwinkler measurements of dissolved oxygen. Highest production rates were obtained on NC and NPC pots. Pots with NPLG and NPHG also showed significant increases in gross production compared to control levels (P < 0.01). Specific production (=gross production/chlorophyll‐a) was significantly related to standing crop as chlorophylls (P < 0.001), alkalinity in the chambers (P < 0.00l) and light (P < 0. 05), but not to N or P supplied by the pots.4. The periphyton community was dominated by Chlorophyta, which averaged 86.1% of total algal biovolume. Enrichment with NC and NPC significantly enhanced the growth of three Chlorophyceae (Stigeoclonium, Scenedesmus and an unidentified coccoid) and two Cryptophyceae (Cryptomonas. Rhodomonas) (all P < 0.05). In contrast, the filamentous green alga Mougeotia dominated other treatments, but declined significantly with NPC enrichment (P < 0.05). Addition of NPHG stimulated an 8‐fold increase in total biovolume and significant increases in growth of Cryptomonas, Rhodomonas and Euglena (all P < 0.05).

Spindle function in the green alga Mougeotia: Absence of anaphase A correlates with postmitotic nuclear migration

AbstractIn the filamentous green alga Mougeotia, each daughter nucleus formed by mitosis is then rapidly moved along the recently divided daughter cell to the central cleavage developing in the chloroplast. This movement is brought about by a cone‐shaped array of microtubules (MTs) that ensheath the daughter nucleus and are focused upon a small region, presumably a microtubule‐organising center (MTOC). Movement is completed when the MTOC locates and then resides in the chloroplast cleavage, drawing the nucleus into this position.The mitotic spindle is open with initially broad, ill‐defined poles. Anaphase A contributes minimally, if at all, to chromosome separation since the half spindles remain about the same length during anaphase and telophase. Thus, anaphase is accommodated and probably achieved by spindle elongation; the interzonal MTs also generate a rudimentary phragmoplast at the ingrowing cleavage furrow. The persistent polar MTs become directly transformed into the cone‐shaped array and initiate nuclear movement during early telophase. Various closely or distantly related green algae show this trait of persistent polar MTs. We conclude that this trait has allowed some species to evolve a motility system based directly on the capabilities of astral MTs, for generating the postmitotic nuclear movement essential for the restoration of the interphase cell organization.

Microtubule reorganization, cell wall synthesis and establishment of the axis of elongation in regenerating protoplasts of the algaMougeotia

Microtubule reorganization and cell wall deposition have been monitored during the first 30 hours of regeneration of protoplasts of the filamentous green algaMougeotia, using immunofluorescence microscopy to detect microtubules, and the cell-wall stain Tinopal LPW to detect the orientation of cell wall microfibrils. In the cylindrical cells of the alga, cortical microtubules lie in an ordered array, transverse to the long axis of the cells. In newly formed protoplasts, cortical microtubules exhibit some localized order, but within 1 hour microtubules become disordered. However, within 3 to 4 hours, microtubules are reorganized into a highly ordered, symmetrical array centered on two cortical foci. Cell wall synthesis is first detected during early microtubule reorganization. Oriented cell wall microfibrils, co-aligned with the microtubule array, appear subsequent to microtubule reorganization but before cell elongation begins. Most cells elongate in the period between 20 to 30 hours. Elongation is preceded by the aggregation of microtubules into a band intersecting both foci, and transverse to the incipient axis of elongation. The foci subsequently disappear, the microtubule band widens, and microfibrils are deposited in a band which is co-aligned with the band of microtubules. It is proposed that this band of microfibrils restricts lateral expansion of the cells and promotes elongation. Throughout the entire regeneration process inMougeotia, changes in microtubule organization precede and are paralleled by changes in cell wall organization. Protoplast regeneration inMougeotia is therefore a highly ordered process in which the orientation of the rapidly reorganized array of cortical microtubules establishes the future axis of elongation.

Mechanism of chloroplast movement inMougeotia

The single, ribbon-shaped chloroplast in the filamentous green algaMougeotia performs orientational movements with respect to light. The chain of reaction involves phytochrome as the photoreceptor pigment to perceive the light signal differentiated by wavelength and direction, calcium probably to convert the light signal into a chemical message and actomyosin to respond to this message and to move the chloroplast accordingly.Precise reorientation of the chloroplast is proposed to be brought about by a dual function of phytochrome: regulation of the cellular level of calciumand regulation of membrane anchorage sites to actin.

The role of microtubules and cell-wall deposition in elongation of regenerating protoplasts of Mougeotia

Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils areoobserved within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented.

DIFFERENTIAL EFFECT OF CALCIUM ON CHLOROPLAST MOVEMENT IN MOUGEOTIA

AbstractThe flat, ribbon‐shaped chloroplast in the filamentous green alga Mougeotia sp. undergoes light‐induced orientational movement controlled by an intracellular tetrapolar gradient of the active form of phytochrome, Pfr. Some substructural and physiological aspects of this reaction were studied. An intracellular pattern of microfilaments (diameter: 5–10nm), presumably related to chloroplast movement, was identified in situ. In addition, it could be shown that chloroplast movement decreases parallel to a nitric acid soluble fraction of intracellular calcium. These results might indicate that phytochrome governs chloroplast movement in Mougeotia via control of the binding state of calcium.

Light-dependent Fluxes and Compartmentation of Calcium in the Green Alga Mougeotia

Summary Fluxes and compartmentation of calcium in the filamentous green alga Mougeotia sp. were analyzed using 45Ca2+ and chemical analysis. Efflux data of 45Ca2+ revealled two rate constants: kw and ki, respectively. Corresponding measurements on dead cells and isolated cell walls enabled the identification of kw as the rate constant describing the release of 45Ca2+ from the cell wall; ki probably reflects the 45Ca2+-release from the inner space of Mougeotia. Photosynthetically saturating irradiances of continuous white light enhance the active and passive fluxes of Ca2+ across the plasmalemma by a factor of two. Furthermore, the amount of «HNO3-extractable» Ca2+ in Mougeotia is light-dependent, too, whereas the amount of «H2O-extractable» Ca2+ was found to be constant. Two mechanisms regulating the intracellular level of H2O-extractable Ca2+ are discussed: 1. Transport of Ca2+ across the plasmalemma, 2. Intracellular storage of Ca2+ in a H2O-insoluble form.

Fluxes and compartmentation of potassium and chloride in the green alga Mougeotia

Some ionic relations of the filamentous green alga Mougeotia sp. have been analyzed under different light conditions. Data from influx and efflux measurements using (86)Rb(+) and (36)Cl(-) fit the model of three cellular compartments (cell wall, cytoplasm, vacuole) in series. This result is remarkable, since in a Mougeotia cell at least two thirds of the cytoplasmic compartment are occupied by the cell-filling, flat and nearly rectangular chloroplast which is axially oriented. The chloroplast is concluded to be part of the cytoplasmic flux compartment.Photosynthetically saturating irradiances of continuous white light enhance the active and passive fluxes of K(+) and Cl(-) at the plasmalemma by a factor of 3. Photosystem II is responsible for the light-dependent increase of the uptake of Cl(-) ((36)Cl(-)) whereas the uptake of K(+) ((86)Rb(+)) depends additionally on energy from photosystem I.Ion flux measurements performed after irradiations with red and far-red, respectively, show that the fluxes of K(+) and Cl(-) across the plasmalemma are not affected by the state of phytochrome.