An ultrastructural re-examination of putative multilayered structures inTrentepohlia aurea

Summary Due to recent interest in the significance of multilayered structures (MLSs) and MLS-like structures in green algal and land plant systematics and evolution, the putative MLSs ofTrentepohlia aurea swarmers were re-examined using conventional TEM of serial thin sections, and high-voltage electron microscopy (HVEM) of thick sections. Features not previously reported to occur in trentepohlialean algae include a structure connecting MLSs to adjacent basal bodies, the lamellar nature of the sub-microtubular layer of the MLS, and the presence of appendages on microtubules overlying the lamellar strip. Reasons are given for concluding that the MLSs ofTrentepohlia and other members of theTrentepohliales are possibly homologous to MLSs ofGlaucophyceae and the MLS-like structures ofFriedmannia. It is proposed that increased attention to the details of MLS structure may be crucial to an understanding of the divergence of main lines of green algal evolution.     

Mucilage secretion and the movements of blue-green algae

Summary Recent discoveries of ultrastructures which might be involved in the gliding movements of blue-green algae have been reviewed, and in the light of these discoveries the role of mucilage secretion in movement has been reconsidered. The formation and behaviour of mucilage rings in filaments ofAnabaena cylindrica is described. The behaviour of the mucilage rings indicates that each cell has an autonomous gliding mechanism which is capable of immediate reversal, and that the gliding mechanism is probably located over the whole surface, rather than at the ends, of the cells. It follows that if mucilage secretion is the cause of movement it must take place over the whole surface of the cell: but if the ends of the cell are the sites of mucilage secretion, as seems likely, then gliding movement must be performed by some other process.A rather remarkable clumping phenomenon is described which takes place in dense suspensions ofAnabaena. It results from the gliding movements of randomly orientated filaments made mutually adhesive by the mucilage which surrounds them.     

Temperature dependence of filament length of Anabaena spiroides Klebahn var. crassa Lemm.

Temperature dependence of filament length ofAnabaena spiroides Klebahn var.crassa Lemm. was examined for a strain isolated from Lake Kasumigaura, Japan. The length of the algal filaments is shown to have good correspondence with the thermal master reaction of cell multiplication.     

Morphology,biology, and systematics ofCryptochlora perforans (Chlorarachniophyta), a phagotrophic marine alga

The life cycle ofCryptochlora perforans is described under culture conditions, including the following stages: Naked and walled amoebae, cysts, coccoid, palmelloid and flagellate stages. Phagotrophy of living diatoms, movement and reproduction are documented. Amoebae ofCryptochlora are chemotactically attracted by damaged algal filaments, perforate and penetrate such filaments, and subsequently engulf part of their contents. A comparison is made with a culture ofChlorarachnion reptans Geitler, according to earlier and own observations. Chloroplast structure as well as zoospore morphology confirm close affinities betweenCryptochlora andChlorarachnion. Generic characters as well as possible phylogenetic affinities with amoeboidXanthophyta andProtozoa are discussed.     

Wood anatomy ofTrimeniaceae

Four collections of three species ofTrimenia and one collection ofPiptocalyx were studied; early-formed and later-formed wood was analyzed for oneTrimenia. Liquid-preserved material permitted analysis of mucilage and starch storage in wood ofT. neocaledonica andP. moorei. BecausePiptocalyx is scandent whereasTrimenia is arborescent, wood differences relative to evolution of a climbing habit could be examined.Piptocalyx contrasts withTrimenia in having wider vessels, more numerous per mm², resulting in a conductive area five times greater per unit area than that of theTrimenia woods averaged.Piptocalyx has appreciably fewer bars per perforation plate and thus much greater conductive area per perforation plate than have the species ofTrimenia. Rays inPiptocalyx are much taller and wider than those ofTrimenia. Wood ofTrimeniaceae is highly primitive in its scalariform perforation plates, scalariform lateral wall pitting on vessels, relatively long vessels elements, and heterocellular rays. Imperforate tracheary elements are septate nucleate fibertracheids (or even libriform fibers) rather than tracheids, but loss of borders on pits (and thus lowered conductive function of the imperforate tracheary elements) can be explained by the development of these elements into starchstoring cells. Some fiber-tracheids inT. neocaledonica are enlarged mucilagecontaining cells. Details of vessel structure inTrimeniaceae are similar to those ofMonimiaceae (s. s.), but similarity to some other lauralean (annonalean) families may be found: in mucilage presence,Trimeniaceae resembleLauraceae rather thanMonimiaceae. Wood ofTrimeniaceae may be regarded as highly mesomorphic, corresponding to the moist habitats in which all of the species occur.     

Chemotaxis of free-living nitrogen-fixing bacteria towards maize mucilage

Summary A method for collecting sterile mucilage from maize root tips growing in sterile conditions has been devised.Enterobacter andAzospirillum strains were isolated from the rhizosphere of maize and rice using the spermosphere model method. To evaluate chemotaxis of these strains, a modification of Adler's microcapillary method was used. Under these conditions, the number of attracted bacteria was proportional to the concentration of mucilage. When comparing the chemotaxis ofA. lipoferum andE. cloacae from the rhizosphere of maize and from the rhizosphere of rice, it appeared that the strains isolated from maize were strongly attracted by maize mucilage whereas strains isolated from rice were not more attracted than the control (E. coli K12). Thus, bacteria of the same species are not equivalent in their chemotactic behaviour. This could imply that some degree of specificity exists in the establishment of plant-bacteria associations.     

Evidence for intergeneric incompatibility in ferns

The archegonial mucilage ofAthyrium filix-femina andA. distentifolium paralyses spermatozoids ofDryopteris filix-mas (and in one caseD. inaequalis) before they penetrate the archegonial venter. The archegonial mucilage ofDryopteris filix-mas has a weak positive chemotactic influence on the spermatozoids of the twoAthyrium species. The spermatozoids ofDryopteris were never observed in the archegonia ofAthyrium. Incompatibility was not observed within and between the twoAthyrium species, withinDryopteris filix-mas or betweenAthyrium filix-femina and twoAsplenium species.Contribution No. 327.     

The development of the mucilage gland of two Japanese species ofAlaria

The genusAlaria possesses a structure known as the mucilage gland which appears mainly on the frond. This is also true ofUndaria. The mucilage gland ofUndaria usually originates from some of the epidermal cells. However, observations of plants ofAlaria at various stages indicate that glands originate not only in the surface layer. There are still other glands which are initiated by some cortical cells situated directly beneath the epidermis. In both, a refractive substance is gradually accumulated as these cells enlarge. The mucilage glands starting in the surface (the primary mucilage glands) resemble those ofUndaria in their development, whereas those in the cortex (the secondary mucilage glands) are quite analogous to the secretory cells ofLaminaria, etc., which secrete mucilage into a mucilage canal in the first stage. Thus,Alaria seems to constitute a link betweenUndaria andLaminaria, etc.     

Bestimmung des Schleimgehaltes myxospermer Diasporen verschiedener Angiospermenfamilien

The mucilage content of structurally differing myxospermatic diaspores from 49 species belonging to 19 families ofAngiospermae has been determined by applying various extraction procedures. The results demonstrate no obvious relationship between the size, mucilage quantity, and the swelling factor of the diaspores studied. Furthermore, mucilage producing structures and structural peculiarities of the mucilages themselves are elaborated.

     

Lichen-like colonies of pure Trentepohlia on limestone monuments

Biofilms were collected on discoloured limestone samples and on adhesive tape from historic buildings at the Mayan site of Edzna, in Campeche, Mexico. Grey, brown, and black areas were colonised predominantly by coccoid and colonial cyanobacteria, also detected as endoliths. The major biomass on the pink stone surface was Trentepohlia. At low power, surface micropits containing crustose-lichen-like black colonies were seen within these pink areas. These were apparently pure colonies of T. umbrina; no filamentous fungi were detected here. The black colour was produced by dense, amorphous pigment deposits in the colony centres. Insolation levels were high (400 μmphotons m⁻² s⁻¹) and the moisture content of the stone was 0.7%. The high carotenoid:chlorophyll-α ratio of Trentepohlia biofilms (3.9:1) is an adaptation protecting against environmental stress. Trentepohlia caused severe local erosion (pitting) and, when present as a more uniform biofilm, the well-known pink surface discoloration.     

HEAVILY LICHENIZED PHYSOLINUM (CHLOROPHYTA) FROM A DIMLY LIT CAVE IN MISSOURI1

Heavily lichenized Physolinum monile (De Wildem.) Printz from damp limestone walls in a dimly lit cave located in Missouri was studied from fresh collections and specimens fixed in situ, and from cultures. The narrow (7-13 μm wide thallus), profusely branched plant consisted of filaments of the alga P. monile ensheathed by clear fungal cells (5-8 in a single layer) that adhered tightly to each other and completely covered the algal cells. Cells of P. monile filaments were uninucleate, each containing a single massive chloroplast with numerous tightly packed thylakoids and lipid droplets and surrounded by a thin layer of cytoplasm. No plasmodesmata occurred in the cellulosic crosswalls between adjacent cells. The ensheathing fungal cells contained concentric bodies, produced haustoria that penetrated the algal cells, and developed hyphae (the tips of which formed clusters of conidia). Ensheathing fungal cells were well situated and constructed to concentrate light on the algal cells. Colonies of blue-green algae were firmly attached to the surface of the fungal cells. The association was slow growing but frequently produced and released aplanospores from the algal cells. Aplanospores were single (not attached to each other) with smooth walls or united in groups of two or more. Structures resembling lichen soredia, composed of aplanospore-like cells attached to one or more comdia-like cells, commonly occurred among the lichenized Physolinum filaments. The single chloroplast that occupies most of the cell's volume, the numerous, tightly packed thylakoids, and light focusing by ensheathing fungus cells may enable the organism to survive in a dimly lit environment. Because the filamentous alga reproduces only by aplanospores, we propose resurrection of the genus Physolinum. The lichenized Physolinum somewhat resembles the lichens Coenogonium moniliforme Tuck. and Cystocoleus Thwaites.     

CELLULAR MOVEMENT IN THE CENTRIC DIATOM ODONTELLA SINENIS1

Cultured, actively growing cells of Odentella sinensis secrete mucilage, forming gelatinous masses; the mucilage can be visualised with Alcian Blue. When examined live with the light microscope, many cells exhibited continuous small shuffing and rocking movements that could last for long periods (30-40 min); the cells, however, were not translocated and remained relatively fixed in position with respect to their neighbours. Ultrastructural examination of these cells showed prominent aggregations of mucilage vesicles, derived from the Golgi bodies, at the base of the labiate processes, each of which is close to an elevation bearing an ocellus. In Ditylum brightwellii, similar aggreations of these vesides were also located at teh labiate processes; this diatom, too, secretes mucilage but does not have ocelli. We conclude that the movements observed in O. sinenisis are an indirect result of active muilage secretion through the labiate process. It has been suggested that the raphe may have evolved from the labiate process; our conclusion, therefore, has phylogenetic implications, suggesting a functional as well as a morphological relationship between the two valve structures.     

The use ofXenopus oocytes and embryos as a route towards cell replacement

When nuclei of somatic cells are transplanted to enucleated eggs ofXenopus, a complete reprogramming of nuclear function can take place. To identify mechanisms of nuclear reprogramming, somatic nuclei can be transplanted to growing meiotic oocytes ofXenopus, and stem cell genes activated without DNA replication. The combination of somatic cell nuclear transfer with morphogen signalling and the community effect may lead towards the possibility of cell replacement therapy. When mechanisms of nuclear reprogramming are understood, it may eventually be possible to directly reprogramme human somatic cell nuclei without the use of eggs.     

Occurrence of cell-associated mucilage and soluble extracellular polysaccharides in Rostherne Mere and their possible significance

The cell-associated mucilage and soluble extracellular polysaccharides (EPS) were investigated in a eutrophic freshwater lake (Rostherne Mere, Cheshire, U.K.) over up to 2 year annual cycles. Five particular lake algae (Anabaena spiroides Klebahn, Anabaena flos-aquae Brébisson ex Bornet & Flahault,Anabaena circinalis Rabenhorst, Microcystis aeruginosa Kützing emend. Elenkin and Eudorina elegans Ehrenberg) were found to be the major contributors to cell-associated mucilage, particularly M. aeruginosa. Calculation of the total amount of cell-associated mucilage in the phytoplankton samples showed that it occupied 0.0001–0.007% (the latter during a bloom of Microcystis) of lake water volume within the epilimnion. Seasonal changes in the total volume of associated mucilage reflected the succession of mucilage-producing algal species in Rostherne Mere, which was closely correlated with the physico-chemical (temperature, oxygen, pH, nutrients) and biological (Secchi depth, phytoplankton) parameters within the lake. High levels of cell-associated mucilage present in the lake may have potential for binding metals or other ions in the aquatic environment. Colourimetric determination of the concentration of soluble EPS revealed concentrations of between 2.5 and 60 mg l^–1, with peak levels during the bacillariophyceaen bloom and late clear water phase. The second phase did not appear to relate directly to changes in algal population, and may result from bacterial activity, algal lysis or zooplankton activity. As soluble EPS forms a major component of the total amount of dissolved carbon in lakes, the study of the soluble EPS is important to understand the carbon cycle in freshwaters. No direct correlation occurred between algal-associated mucilage and soluble EPS over a single annual cycle.     

Extreme isotopic depletion of nitrogen in New Zealand lithophytes and epiphytes; the result of diffusive uptake of atmospheric ammonia?

Several lichens and the terrestrial alga Trentepohlia were found to have extremely depleted ¹⁵N signatures at two sites near the Rotorua geothermal area, New Zealand. Values, typically −20‰, with several extreme cases of −24‰, are more isotopically depleted than any previously quoted δ¹⁵N signature for vegetation growing in natural environments. For Trentepohlia, distance from a geothermal source did not affect isotopic signature. A 100-km transect showed that the phenomenon is widespread and the discrimination is not related to substrate N, or to elevation. Rainfall NHx and atmospheric gaseous NH₃ (NH_3(g)) were shown to be isotopically depleted in the range −1‰ to −8‰ and could not, of themselves, be responsible for the plant values obtained. A simulation of Trentepohlia thallus was created using an acidified fiberglass mat and was allowed to absorb NH_3(g) from the atmosphere. Mats exposed at the geothermal sites and on farmland showed a significant further depletion of ¹⁵N to −17‰. We hypothesize that the extreme isotopic depletion is due to dual fractionation: firstly by the volatilization of NH_3(g) from aqueous sources into the atmosphere; secondly by the diffusive assimilation of that NH_3(g) into vegetation. We further hypothesize that lithophytes, epiphytes, and higher plants, growing on strongly N-limited substrates, will show this phenomenon more or less, depending on the proportion of diffusively assimilated NH_3(g) utilized as a N source. Many of the isotopically depleted δ¹⁵N signatures in vegetation, previously reported in the literature, especially epiphytes, may be due to this form of uptake depending on the concentration of atmospheric NH_3(g), and the degree of reliance on that form of N.     

Laboratory culture and taxonomy of two species ofPedobesia (Bryopsidales,Chlorophyceae) in Japan

The morphology ofPedobesia lamourouxii andDerbesia ryukyuensis, both collected in Shimoda and the adjacent areas in central Japan, was studied from field specimens and laboratory cultures. Specimens which had the same morphology as EuropeanP. lamourouxii produced stephanokont zoospores which developed into either prostrate filaments or expanded discoidal thalli similar to those described by Feldmann and Codomier (1974) and Feldmannet al. (1975). Erect filament identical with the thallus found in nature developed directly from prostrate filaments. The specimens which had morphology similar to that ofDerbesia ryukyuensis described by Yamada and Tanaka (1938) also produced stephanokont zoospores which developed similarly to those ofP. lamourouxii. This species is, therefore, a member ofPedobesia, and it is made a new combinationP. ryukyuensis (Yamada et Tanaka) Kobara et Chihara, comb. nov.     

Ingestion of live filamentous diatoms by the Great Lakes amphipod,Diporeia sp.: a case study of the limited value of gut contents analysis

Individuals of the Great Lakes amphipod, Diporeia sp. (formerly named Pontoporeia hoyi) were collected from a 45-m deep station in southeastern Lake Michigan and isolated in small laboratory feeding vessels at 4 °C, after the animals had voided their guts over a 24-hour period. Over a 20-day period, following introduction of a single ration of live cells of the filamentous diatom, Melosira varians, 9 of 10 animals had ingested this material, and 7 of these 9 individuals had deposited fecal pellets. Subsequent examination of gut contents and fecal pellets showed that although animals had ingested whole algal cells/filaments, little of the material in gut contents or fecal pellets bore any identifiable structural similarity to cells/filaments prior to ingestion. The results suggest that earlier studies of pontoporeiid gut contents may seriously underestimate the importance of algal components in the amphipod's diet and imply that Diporeia sp. growth and production may be more closely linked to primary production than previously thought.     

Soil stabilization by a prokaryotic desert crust: Implications for Precambrian land biota

A cyanophyte dominated mat, desert crust, forms the ground cover in areas measuring hundreds of square meters in Utah and smaller patches in Colorado. The algal mat shows stromatolitic features such as sediment trapping and accretion, a convoluted surface, and polygonal cracking. Sand and clay particles are immobilized by a dense network of filaments of the two dominating cyanophyte species,Microcoleus vaginatus andM. chthonoplastes, which secrete sheaths to which particles adhere. These microorganisms can tolerate long periods of desiccation and are capable of instant reactivation and migration following wetting. Migration occurs in two events: 1. immediately following wetting of dry mat, trichomes are mechanically expelled from the sheath as it swells during rehydration, and 2. subsequently, trichomes begin a self-propelled gliding motility which is accompanied by further production of sheath. The maximum distance traveled on solid agar by trichomes ofMicrocoleus vaginatus during a 12 hour period of light was 4.8 cm. This corresponds to approximately 500 times the length of the fastest trichome, and provides a measure of the potential for spreading of the mat in nature via the motility of the trichomes.Dehydration resistence of the sheath modifies the extracellular environment of the trichomes and enables their transition to dormancy. Following prolonged wetting and evaporative drying of the mat in the laboratory, a smooth wafer-like crust is formed by the sheaths ofMicrocleus trichomes that have migrated to the surface. Calcium carbonate precipitates among the algal filaments under experimental conditions, indicating a potential for mat lithification and fossilization in the form of a caliche crust. It is suggested that limestones containing tubular microfossils may, in part, be of such an origin.The formation of mature Precambrian soils may be attributable to soil accretion, stabilization, and biogenic modification by blue-green algal land mats similar to desert crust.     

A METHOD OF OBTAINING AXENIC CULTURES OF TRENTEPOHLIA SPP. (CHLOROPHYTA)1

Axenic cultures of Trentepohlia species are necessary for the study of growth and hysiological characters of the algae. We describe the use of a Sherman micromanipulator to isolate filaments from samples of T. aurea and T. odorata collected from their natural habitats. These filaments were then used as inocula for the establishment of axenic cultures. In the case of T. aurea, further treatment with lactic acid was necessary.     

Localization to the rhizoid tip implicates a<Emphasis Type="Italic"> Fucus distichus</Emphasis> Rho family GTPase in a conserved cell polarity pathway

Generation and expression of cell polarity in brown algal zygotes of the Fucales involve regulation of the actin cytoskeleton and localized secretion. We used degenerate PCR to isolate cDNAs that encode two small GTPases, FdRac1 and FdRab8, from zygotes of Fucus distichus (L.) Powell. Sequence analysis placed FdRac1 in the Rho family, which regulates actin, and FdRab8 in the Rab family, which regulates vesicle transport. As expected, bacterially expressed forms of both proteins bound GTP in vitro. When expressed in budding yeast, FdRac1 showed some functional overlap with CDC42, the Saccharomyces cerevisiae Rho family gene required for yeast cell polarity. Immunolocalization revealed an asymmetric distribution of FdRac1 in polarized zygotes and embryos, with FdRac1 concentrated at or near the growing tip of the algal rhizoid. Our data support the hypothesis that FdRac1 regulates algal cell polarity, possibly via the actin cytoskeleton. Because brown algae belong to the heterokont group, which diverged from other groups early in eukaryotic evolution, we argue that the Rho family function of regulating cell polarity is ancient and may extend throughout the eukaryotes.Electronic Supplementary Material Supplementary material is available in the online version of this article at Abbreviations AF After fertilization - GST Glutathione-S-transferase - MBP Maltose-binding protein