Flagellar Swelling Research Articles

Re-examination of the marine 'chrysophyte' Polypodochrysis teissieri (Pinguiophyceae)

SUMMARY A marine ‘chrysophyte’ species Polypodochrysis teissieri Magne having distinctive lorica was re-examined using both light and electron microscopy. Light microscopic observations were basically identical to Magne's descriptions (Magne 1975), except that the aplanospore in that paper was shown to be a distinctive uniflagellate zoospore. General ultrastructure of both chloroplast and mitochondria was typical of the photosynthetic stramenopiles (chromophytes). An embedded pyrenoid was found in the center of chloroplast and was penetrated by the chloroplast envelope. Two Golgi bodies were always located adjacent to the nucleus; they were arranged perpendicularly in vegetative cells, but had a parallel arrangement in zoospores. Thin sections of the lorica resembled siliceous structures such as diatom frustules, but energy dispersive X-ray analysis did not show any significant amount of silicon. Naked zoospores have a single emergent flagellum that lacked mastigonemes; a flagellar swelling and an eyespot were also absent. Zoospores showed gliding motion on the surface of substrate. Two different cytoplasmic extensions (pseudopods) were observed in the zoospore. One lingulate pseudopod originated from the base of the flagellum and was always associated with the flagellum, and the second pseudopod formed only when the cell changed direction. Investigations of the flagellar apparatus showed a single transitional plate in the transitional region of the emergent flagellum, a second basal body closely located to the flagellum-bearing basal body, three microtubular roots and a set of cytoskeletal microtubules, and a small rhizoplast that connected the non-flagellum-bearing basal body and the nucleus. Many features of the zoospore of Polypodochrysis show a similarity with that of Glossomastix chrysoplasta (Pinguiophyceae), suggesting that the single emergent flagellum of Polypodochrysis and Glossomastix is homologous. This single flagellum may correspond to the mature flagellum that is generally recognized as the short posterior flagellum in stramenopiles, and it represents a unique flagellar arrangement within stramenopiles. Based on the morphological features, in addition to the other data (18S rRNA and rbcL genes and biochemical features) published elsewhere, Polypodochrysis was removed from the class Chrysophyceae and transferred to a new class, the Pinguiophyceae.

Glossomastix chrysoplasta n. gen., n. sp. (Pinguiophyceae), a new coccoidal, colony-forming golden alga from southern Australia

SUMMARY Glossomastix chrysoplasta gen. et sp. nov. is described from cultures isolated from sandstone rubble, Sorrento Back Beach, Mornington Peninsula, Victoria, Australia. The alga forms wall-less, coccoidal vegetative cells that congregate in mucilaginous colonies and reproduce by successive bipartition. Plastids have girdle lamellae and partially embedded pyrenoids that are traversed by cytoplasmic channels. Zoospores are uniflagellate and swim poorly; a narrow lingulate pseudopod provides their primary form of motion. The single flagellum, which lacks hairs, a flagellar swelling, and autofluorescence, is the equivalent of the posterior flagellum in other golden algae. The anterior flagellum is absent; the basal body with which it would normally be associated is blind. The flagellar apparatus has two basal bodies, three microtubular roots, and a rhizoplast. The posterior (elder) basal body has a transitional helix that is proximal to the basal plate. Glossomastix chrysoplasta, placed in the Pinguiophyceae on the basis of molecular sequence and biochemical data, shares some ultrastructural features with other members of the class, especially Polypodochrysis teissieri, which has similar zoospores, but it also differs from other pinguiophytes in many respects. Glossomastix chrysoplasta is the pinguiophyte with, on average, the largest cells (exclusive of external materials), and it is the only one with a colonial habit.

Isolation of the Flagellar Swelling and Identification of Retinal in the Phototactic Flagellate, Ochromonas danica (Chrysophyceae)

ABSTRACT Ochromonas danica, a freshwater, planktonic chrysophyte, is capable of sensing the light conditions of its environment. This biflagellate alga has a swelling near the base of the short flagellum and a chloroplastidic stigma in close association with it. A procedure is described for the isolation of this three dimensional flagellar swelling, the presumed photoreceptor. In contrast to an earlier method developed for the isolation of the paraflagellar swelling from Euglena gracilis, the protocol reported here for Ochromonas results in higher yields that should facilitate future biochemical investigations and could open avenues of investigation for the isolation and purification of the presumptive receptor protein. To verify the hypothesis that a rhodopsin‐like protein might be present in this alga, we applied a standard extraction procedure successfully used in the identification of retinal. We here report the purification and identification of all‐trans retinal in Ochromonas cells by column chromatography, HPLC and GC‐MS. Since retinal is the chromophore of rhodopsin‐like proteins, this finding may suggest that in these unicellular algae, too, a rhodopsin‐like protein could be the photoreceptor pigment.

Green flagellar autofluorescence in brown algal swarmers and their phototactic responses

A flavin-like green autofluorescent substance is noticed to occur in one of the flagella of flagellated cells in the Phaeophyceae, Chrysophyceae, Synurophyceae, Xanthophyceae and Prymnesiophyceae. In the phaeophycean swarmers the autofluorescence occurs in the posterior flagellum throughout its length. It is considered to be involved in the photoreception of phototaxis, since it almost always occurs in the swarmers which have a flagellar swelling and stigma and show phototaxis. In the phaeophycean swarmers, the stigma is shown to act as a concave reflector mirror focusing the reflection light onto the flagellar swelling. In the action spectrum studies, phaeophycean swarmers showed phototaxis between 370 and 520 nm, having two major peaks at 420 or 430 nm and 450 or 460 nm. Their responses were true phototactic and not photophobic. Rotation of the swarmer was shown to be essential in the photoreception ofEctocarpus gametes.

REFLECTIVE PROPERTIES OF THE STIGMA IN MALE GAMETES OF ECTOCARPUS SILICULOSUS (PHAEOPHYCEAE) STUDIED BY CONFOCAL LASER SCANNING MICROSCOPY1

ABSTRACTThe reflection properties of the stigma in male gametes of Ectocarpus siliculosus (Dillw.) Lyngbye were investigated using confocal laser scanning microscopy in the epireflection contrast mode. The complex reflection pattern obtained after optical xy (horizontal) and xz (vertical) sectioning was consistent with stigma ultrastructure as revealed by serial thin sections. The intensity and pattern of the reflection signal varied with the orientation of the cell/stigma to the incident laser light. Maximal reflection occurred only in approximately normal orientation of the stigma to the light source. Focusing of reflected light from an elongated concave depression of the stigma on the region of the flagellar swelling was observed in xy and xz sections of living and fixed gametes. The results indicate the importance of mechanisms (focusing) other than quarter‐wave interference reflection in signal amplification by the eyespot of flagellate algae.

Phototactic responses in the gametes of the brown alga, Ectocarpus siliculosus

The action spectrum of phototaxis was determined and the photoreceptive mechanism was studied in Ectocarpus gametes (Ectocarpales, Phaeophyceae) using a computerized cell-tracking system. The fine structures of the stigma and the flagellar swelling were analyzed, and the reflective function of the stigma was demonstrated for the first time. Under monochromatic light stimulation, Ectocarpus gametes show mainly positive phototaxis between 370 nm and 520 nm. The action spectrum has a minor peak near 380 nm, and two major peaks at 430 nm and 450 nm or 460 nm and a shoulder at 470 nm adjoining a remarkable depression near 440 nm. Under unilateral stroboscopic illumination with more than four pulses per second, the gametes show clear phototaxis. However, the response is disturbed at lower frequencies. Addition of methyl cellulose, which increases the viscosity of the medium and slows down gamete rotation, decreases the threshold frequency. These results indicate that rotation of the gamete plays an essential role in the photoreceptive mechanism. Under equal intensities of bilateral illumination at an angle of 90°, most of the gametes swim on the resultant between the two light beams. This response is disturbed when the angle of the two light beams is as large as 120°. Observations by transmission electron microscopy show that the flagellar swelling fits precisely into a concave depression of the chloroplast at the central region of the stigma. Electron-dense material is present in that sector of the flagellar swelling which faces away from the stigma. Epifluorescence microscopy without a barrier filter and epipolarization microscopy reveal that stigmata reflect blue light. A hypothesis is formulated which discusses the possibility that the reflected light is focused onto the flagellar swelling.

A FLAVIN‐LIKE AUTOFLUORESCENT SUBSTANCE IN THE POSTERIOR FLAGELLUM OF GOLDEN AND BROWN ALGAE1

ABSTRACTAn autofluorescent substance occurs in the flagella of flagellate cells of the golden and brown algae. It is localized only in the posterior (short) flagellum and could not be detected in the anterior (long) one. It showed maximum fluorescence emission at 515–520 nm upon excitation of 440 nm; therefore, it is considered to be a flavin. This substance is distributed widely among flagellate cells of golden and brown algae irrespective of their nature (vegetative cells, zoospores, gametes, or sperm). It is absent, however, in some brown algal zoospores and sperm which lack an eyespot and flagellar swelling and are considered to lack phototaxis. Because the flagellar swelling in the posterior flagellum is a presumptive photoreceptor for phototaxis in these groups, it is suggested that the flavin located in the posterior flagellum acts as a photoreceptor pigment in phototaxis.

THE AUTOFLUORESCENT FLAGELLUM: A NEW PHYLOGENETIC ENIGMA1

ABSTRACTEpifluorescence microscopy reveals the presence of fluorescence in the living cells of at least three classes of flagellates. In Ochromonas cells, the fluorescence is blue‐green in color and is found only in the short flagellum, both in the flagellar swelling and throughout the length of the flagellum. As recognized by the locale and color of the flagellar fluorescence, the same fluorescence is observed in only certain other heterokont algal groups but is also found in one of the two isokont flagella of the prymnesiophyte Prymnesium parvum.

FLAGELLUM AUTOFLUORESCENCE and PHOTOACCUMULATION IN HETEROKONT ALGAE

AbstractZoids of various brown algae capable of positive or negative phototaxis show strong autofluorescence of their posterior fiagellum and flagellar swelling when excited with blue light of 450 nm. This effect is lacking in zoids without stigma and phototactic capability. Fluorescence studies on living cells point to a flavin as photoreceptor pigment. The spectral sensitivity curve of photoaccumul‐ation suggests a carotenoid pigment (maximum 430–450 nm) being involved, with no effect below 380 nm and above 540 nm. The results obtained in this study indicate a flavin as photoreceptor pigment, which is periodically shaded by a carotenoid stigma.

Stigma and flagellar swelling in relation to light and carotenoids in Euglena gracilis var. bacillaris

Wild-type Euglena gracilis var. bacillaris, W3BUL (a mutant having lower amounts and a different mix of carotenoids), and W10BSmL (in which colored carotenoids are undetectable) were grown in light and darkness and were serially sectioned to ascertain the form and relations of stigma and flagellar swelling by electron microscopy. The length and width of the flagellar swelling in all organisms in light and darkness was the same within experimental error, and this structure showed the characteristic fine reticulate substructure in all cases. The stigma is absent or is reduced to a few tiny vesicles in W10 and show less staining in W3 compared with wild type. In dark-grown resting wild type and W3 the stigma is rather amorphous and only becomes a group of spheres after prolonged exposure to light. Three-dimensional reconstructions of the reservoir region showing the relations of organelles including the stigma and flagellar swelling have been made. Comparing wild-type B and its mutants, the presence of a normal flagellar swelling is not correlated with the ability to form colored carotenoids. This conclusion is supported by experiments with (4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H) pyridazinone) (SAN 9789) a specific inhibitor of carotenoid biosynthesis in Euglena at the phytoene stage. Growing cells of dark-grown wild type or W3 treated with SAN show a very great reduction in the stigma, but the flagellar swelling is unaffected. We conclude that ability to form stigma material does correlate with the ability to make colored carotenoids but light is required to organize this material into the individual spheres characteristic of the normal stigma.

Fine structure of photo-kinetic systems inDinobryon cylindricumvar.Alpinum(chrysophyceae)

The ultrastructure of the stigma and associated flagellar-microtubular systems in Dinobryon cylindricum var. alpinum is described in detail and compared with observations on comparable photo-kinetic systems in other chrysophycean organisms. The chloroplastidic stigma of D. cylindricum var. alpinum is shown to lie in a particular positional relationship to the flagellar swelling in the anterior furrow and to several other organelles, to consist of a monolayer of c. 40 pigmented granules, each c. 250–500 nm diameter, arranged in a definite pattern, and to be overlain by several membrane systems. Other cytoplasmic pigmented bodies with dense crystalline contents surrounded by a single “unit membrane” aggregate near the anterior furrow on the side opposite the stigma. The swelling on the proximal portion of the smooth flagellum is separated from the plasmalemma of the anterior furrow by a nearly constant distance of 75–100 nm, has a multilamellate substructure that is linked by fine radiating interconnections to the axoneme doublets, and is connected to the plasmalemma by a system of fibrillar interconnections. A transitional helix in the basal body region is described as similar to structures reported in other chrysophycean flagellates. A striated rhizoplast with a periodicity of c. 90 nm extends from basal body I to the nuclear envelope. A seven-stranded microtubular root extends from the same basal body. Other fibrous and microtubular root systems are also described. The inter-relationships and possible functions of the aforementioned structures are discussed.

Isonema papillatum sp. n., a New Colorless Marine Flagellate: A Light‐ and Electronmicroscopic Study

SYNOPSIS. Isonema papillatum sp. n. is described from observations with the light and electron microscope. It has 2 short emergent subapical flagella without appendages, a specialized ingestion apparatus, and a nonrigid naked cell body capable of pronounced changes in shape similar to euglenoid movements. It lacks a stigma and flagellar swelling and does not form paramylon granules. The nucleolus persists throughout nuclear division.

Pseudocharaciopsis TexensisGen. et sp. nov., a new member of the Eustigmatophyceae

A new genus of the Eustigmatophyceae and its type species, Pseudocharaciopsis texensis, are described. The actively growing vegetative cells have a short stalk and an attaching disc. The pyrenoid is spherical and is attached to the typically single, parietal chloroplast. There may be 1–4 or sometimes more pyrenoids and chloroplasts in older cells. Zoospore ultrastructure is similar to that of Ellipsoidion acuminatum Pascher. However, the zoospore of P. texensis is characterised by the presence of two large, conspicuously membrane-bounded osmiophilic vesicles and by the fan-shaped (in transverse section) flagellar swelling instead of the T-shaped one of Ellipsoidion acuminatum.

A NEW ALGAL CLASS — THE EUSTIGMATOPHYCEAE

SummaryA formal description is given of a new class of algae, separated from the Xanthophyceae by several unique features of zoospore organisation, particularly the large size and special construction of the eyespot and the location of the flagellar swelling, and the form of the pyrenoid in the vegetative cell.