Ultrastructural Evidence for the Presence of Bacteria,Viral-like Particles,and Mycoplasma-like Organisms Associated with Giardia spp.1

ABSTRACT. Giardia trophozoites and cysts, isolated from mammalian and avian hosts, were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and by fluorescent light microscopy for the presence of microbial symbionts. Mycoplasma-like organisms were observed on the surfaces of trophozoites isolated from the prairie vole, laboratory rat, and beaver. Intracellular bacteria were observed by TEM in the trophozoites and cysts of G. microti and by fluorescence microscopy in trophozoites and cysts of Giardia spp. isolated from beaver, muskrat, great-blue heron, and the green heron. Trophozoites of G. muris from rat small intestine contained viral-like particles measuring 60 nm in diameter. These observations suggest that biological associations between Giardia spp. and diverse microbes may be more common than formerly appreciated. It also raises the possibility of transmission of these apparent symbionts, via the Giardia cyst, to other mammalian hosts including man.     

PHYLOGENETIC ANALYSIS OF THE GENUS EUGLENA (EUGLENOPHYCEAE) WITH PARTICULAR REFERENCE TO THE TYPE SPECIES EUGLENA VIRIDIS1

Euglena viridis (subgenus Euglena) serves as the type species for the genus Euglena. In this study, molecular phylogenetic analyses using a small subunit (SSU) and a combined SSU–partial large subunit rDNA data set for members of the genus Euglena showed that strains identified as E. viridis on the basis of morphology are distributed between two separate nonsister clades. Although all the E. viridis strains examined were morphologically indistinguishable and possessed spherical mucocysts and stellate chloroplasts with one paramylon center, there was a high degree of sequence divergence between the E. viridis strains in different clades, making this a cryptic species. Like E. viridis, all taxa from the subgenus Euglena are characterized by having one or more stellate chloroplasts with paramylon grains clustered around the center of the chloroplast. These additional taxa were divided into four clades in all the molecular analyses. Strains of Euglena stellata formed two nonsister clades whose members had a single aggregate chloroplast with paramylon center and spindle‐shaped mucocysts. A geniculata clade included species with one or two stellate chloroplasts with paramylon centers and spherical mucocysts, and the cantabrica clade had members with one stellate chloroplast with paramylon center and spherical mucocysts often arranged in spiral rows. Interspersed among these were three additional clades bearing taxa from the subgenus Calliglena that contains members with discoid plastids and pyrenoids that may or may not be capped with paramylon. These taxa formed a laciniata clade, mutabilis clade, and gracilis clade. This study demonstrates that E. viridis and E. stellata are cryptic species that can only be distinguished at the molecular level. Because E. viridis is the designated type species for the genus Euglena, we designated an epitype for E. viridis.     

MORPHOLOGICAL AND ULTRASTRUCTURAL FEATURES OF A STRAIN OF BOTRYOCOCCUS TERRIBILIS (TREBOUXIOPHYCEAE) FROM BRAZIL1

The genus Botryococcus comprises a group of cosmopolitan species of freshwater colonial green algae, some of which synthesize and accumulate an unusually high level (15–76%) of liquid hydrocarbons. This characteristic suggests the possibility of exploiting species from this group as renewable sources for jet fuel. An oil‐rich strain of Botryococcus (Trebouxiophyceae) was isolated from a freshwater pond in the state of Bahia, Brazil, and is presently maintained under standard conditions at the Culture Collection of the Institute of Biology, Federal University of Bahia. The taxonomic classification of the species was based on light microscopy (LM); and TEM and SEM were used to better characterize its features, which have never before been described at this level. The LM characterization included the size of the colonies (35.7–157 μm) and cells (8–10 × 5–9 μm) and their connection in sub‐colonies by mucilaginous strands, as well as the presence of mucilaginous processes on the periphery of some of the colonies, with most of the cells included inside the colony. Reproduction occurred through divisions into two to four autospores. These features characterized the species as Botryococcus terribilis Komárek and Marvan. The TEM study showed, in addition to the presence of starch grains, pyrenoids that are penetrated by thick thylakoids. The pyrenoid bodies appear as electron‐dense protein inclusions located in the chloroplast and surrounded by a starch sheath. These structures, which contain most if not all of the Ribulose‐1,5‐bisphosphate carboxylase oxygenase in several algal species that have been studied closely, are newly discovered for this species.     

Studies on woloszynskioid dinoflagellates VI: description of Tovellia aveirensis sp. nov. (Dinophyceae), a new species of Tovelliaceae with spiny cysts

A new species of Tovellia, T. aveirensis, is described on the basis of light (LM) and scanning electron microscopy (SEM) of motile cells and resting cysts, complemented with transmission electron microscopy (TEM) of flagellate cells and phylogenetic analysis of partial sequences of the large subunit ribosomal rRNA gene. Both vegetative cells and several stages of a life cycle involving sexual reproduction and the production of resting cysts were examined in cultures established from a tank in the University of Aveiro campus. Vegetative cells were round and little compressed dorsoventrally; planozygotes were longer and had a proportionally larger epicone. Chloroplast lobes were shown by TEM to radiate from a central, branched pyrenoid, although this was difficult to ascertain in LM. The amphiesma of flagellate cells had mainly 5 or 6-sided vesicles with thin plates, arranged in 5–7 latitudinal series on the epicone, 3–5 on the hypocone. The cingulum had 2 rows of plates, the posterior row extending into the hypocone and crossed by a series of small projecting knobs along the lower edge of the cingulum. A line of narrow amphiesmal plates extended over the cell apex, from near the cingulum on the ventral side to the middle of the dorsal side of the epicone. Eight or 9 narrow amphiesmal plates lined each side of this apical line of plates (ALP). Resting cysts differed from any described before in having numerous long, tapering spines with branched tips distributed over most of the surface. Most mature cysts showed an equatorial constriction. Neither cysts nor motile cells were seen to accumulate red cytoplasmic bodies in any stage of the cultures. The phylogenetic analysis placed, with high statistical support, the new species within the genus Tovellia; it formed a clade, with moderate support, with T. sanguinea, a species notable for its reddening cells.     

Phylogenetic Relationships and Morphological Character Evolution of Photosynthetic Euglenids (Excavata) Inferred from Taxon‐rich Analyses of Five Genes

Photosynthetic euglenids acquired chloroplasts by secondary endosymbiosis, which resulted in changes to their mode of nutrition and affected the evolution of their morphological characters. Mapping morphological characters onto a reliable molecular tree could elucidate major trends of those changes. We analyzed nucleotide sequence data from regions of three nuclear‐encoded genes (nSSU, nLSU, hsp90), one chloroplast‐encoded gene (cpSSU) and one nuclear‐encoded chloroplast gene (psbO) to estimate phylogenetic relationships among 59 photosynthetic euglenid species. Our results were consistent with previous works; most genera were monophyletic, except for the polyphyletic genus Euglena, and the paraphyletic genus Phacus. We also analyzed character evolution in photosynthetic euglenids using our phylogenetic tree and eight morphological traits commonly used for generic and species diagnoses, including: characters corresponding to well‐defined clades, apomorphies like presence of lorica and mucilaginous stalks, and homoplastic characters like rigid cells and presence of large paramylon grains. This research indicated that pyrenoids were lost twice during the evolution of phototrophic euglenids, and that mucocysts, which only occur in the genus Euglena, evolved independently at least twice. In contrast, the evolution of cell shape and chloroplast morphology was difficult to elucidate, and could not be unambiguously reconstructed in our analyses.     

Grazing impact of heterotrophic dinoflagellates and ciliates on common red-tide euglenophyte Eutreptiella gymnastica in Masan Bay, Korea

The euglenophyte Eutreptiella gymnastica is a common red tide causative species. However, there have been no studies on the grazing impact of heterotrophic protists on this species. To investigate the grazing impact of heterotrophic protists on E. gymnastica, we measured daily the abundances of E. gymnastica and co-occurring potential heterotrophic protistan grazers in Masan Bay, Korea, in August 2004 when an E. gymnastica red tide occurred. In addition, we tested whether the common heterotrophic dinoflagellates Gyrodinium dominans, Oxyrrhis marina, Pfiesteria piscicida, Polykrikos kofoidii, Protoperidinium bipes, and Stoeckeria algicida and the naked ciliates Strobilidium sp. (30–40 μm in cell length) and Strombidinopsis sp. (70–100 μm in cell length) were able to feed on E. gymnastica. We also measured their growth and ingestion rates on E. gymnastica as a function of prey concentration. Finally, we calculated the grazing coefficients by combining field data on the abundance of the heterotrophic dinoflagellate and ciliate grazers and co-occurring E. gymnastica with laboratory data on ingestion rates obtained in this study. The maximum abundance of E. gymnastica in Masan Bay in August, 2004 was 7575 cells ml⁻¹, while those of Gyrodinium spp., P. kofoidii, P. bipes, the naked ciliates (≤50 μm in cell length), and naked ciliates (>50 μm in cell length) were 50, 9, 58, 32, and 3 cells ml⁻¹, respectively. The maximum growth rate of G. dominans on E. gymnastica (1.13 d⁻¹) was higher than that of O. marina (0.81 d⁻¹) or P. bipes (0.77 d⁻¹). However, E. gymnastica did not support positive growth of P. kofoidii, Strobilidium sp., and Strombidinopsis sp. (−0.04 ∼ −2.8 d⁻¹). The maximum ingestion rates of G. dominans, P. kofoidii, P. bipes, O. marina, and Strobilidium sp. on E. gymnastica (2.1–2.7 ng C predator⁻¹ d⁻¹) were similar, but they were much lower than that of Strombidinopsis sp. (156 ng C predator⁻¹ d⁻¹). The calculated grazing coefficients for P. bipes, small heterotrophic Gyrodinium spp. (25–35 μm in cell length), naked ciliates (≤50 μm in cell length), P. kofoidii, and naked ciliates (>50 μm in cell length) on E. gymnastica were up to 0.77, 0.61, 0.22, 0.07 and 0.03 d⁻¹, respectively (i.e., up to 54%, 46%, 20%, 7%, and 3% of E. gymnastica populations were removed by the population of each of these heterotrophic protistan grazers in 1 d, respectively). The results of the present study suggest that P. bipes, small heterotrophic Gyrodinium spp., and naked ciliates (≤50 μm in cell length) sometimes have considerable potential grazing impact on the populations of E. gymnastica.     

Identification and characterization of cytosolic fructose-1,6-bisphosphatase in Euglena gracilis

Euglena gracilis has the ability to accumulate a storage polysaccharide, a β-1,3-glucan known as paramylon, under aerobic conditions. Under anaerobic conditions, E. gracilis cells degrade paramylon and synthesize wax esters. Cytosolic fructose-1,6-bisphosphatase (FBPase) appears to be a key enzyme in gluconeogenesis and position branch point of carbon partitioning between paramylon and wax ester biosynthesis. We herein identified and characterized cytosolic FBPase from E. gracilis. The K_m and V_max values of EgFBPaseIII were 16.5 ± 1.6 μM and 30.4 ± 7.2 μmol min^?1 mg protein^?1, respectively. The activity of EgFBPaseIII was not regulated by AMP or reversible redox modulation. No significant differences were observed in the production of paramylon in transiently suppressed EgFBPaseIII gene expression cells by RNAi (KD-EgFBPaseIII); nevertheless, FBPase activity was markedly decreased in KD-EgFBPaseIII cells. On the other hand, the growth of KD-EgFBPaseIII cells was slightly higher than that of control cells.     

Generic concept in Chlorella‐related coccoid green algae (Chlorophyta,Trebouxiophyceae)

Using a combined set of sequences of SSU and ITS regions of nuclear‐encoded ribosomal DNA, the concept of the experimental algal genus Chlorella was evaluated. Conventionally in the genus Chlorella, only coccoid, solitary algae with spherical morphology that do not possess any mucilaginous envelope were included. All Chlorella species reproduce asexually by autospores. However, phylogenetic analyses showed that within the clade of ‘true’Chlorella species (Chlorella vulgaris, C. lobophora, and C. sorokiniana), taxa with a mucilaginous envelope and colonial lifeform have also evolved. These algae, formerly designated as Dictyosphaerium, are considered as members of the genus Chlorella. In close relationship to Chlorella, five different genera were supported by the phylogenetic analyses: Micractinium (spherical cells, colonial, with bristles), Didymogenes (ellipsoidal cells, two‐celled coenobia, with or without two spines per cell), Actinastrum (ellipsoidal cells within star‐shaped coenobia), Meyerella (spherical cells, solitary, without pyrenoids), and Hegewaldia (spherical cells, colonial, with or without bristles, oogamous propagation). Based on the secondary structures of SSU and ITS rDNA sequences, molecular signatures are provided for each genus of the Chlorella clade.     

Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts

Leaf extracts of two plants, Magnolia kobus and Diopyros kaki, were used for ecofriendly extracellular synthesis of metallic gold nanoparticles. Stable gold nanoparticles were formed by treating an aqueous HAuCl₄ solution using the plant leaf extracts as reducing agents. UV–visible spectroscopy was used for quantification of gold nanoparticle synthesis. Only a few minutes were required for >90% conversion to gold nanoparticles at a reaction temperature of 95 °C, suggesting reaction rates higher or comparable to those of nanoparticle synthesis by chemical methods. The synthesized gold nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and particle analysis using a particle analyzer. SEM and TEM images showed that a mixture of plate (triangles, pentagons, and hexagons) and spherical structures (size, 5–300 nm) were formed at lower temperatures and leaf broth concentrations, while smaller spherical shapes were obtained at higher temperatures and leaf broth concentrations.     

Role of Sophorolipid Biosurfactant in Degradation of Diesel Oil by Candida tropicalis

The yeast Candida tropicalis, isolated from petroleum-contaminated soil in India, was found to be the potent producer of biosurfactant in mineral salt media containing diesel oil as the carbon source and found to be an efficient degrader of diesel oil (98%) over a period of 10 days. The crude biosurfactant decreased the surface tension of cell-free broth, 78 to 30 mN/m, with a large oil displacement area and highly positive drop collapse test. The crude biosurfactant was purified using silica gel column chromatography followed by dialysis. With the use of Fourier transform infrared (FT-IR) spectroscopy, in combination with gas chromatography–mass spectrometry (GC-MS) analysis, chemical structures of the purified biosurfactant was identified as sophorolipid species. Involvement of biosurfactant in physiological mechanism of diesel adsorption on yeast cell surface was characterized based on zeta potential. When diesel oil was emulsified with biosurfactant, the surface charge of the diesel was modified, resulting in more adsorption of diesel on yeast cell surface. Biosurfactant production by yeast species was monitored using scanning electron microscopy (SEM) analysis and found that yeast species could form thick mat of mucilaginous biosurfactant that could interconnect the individual cells. Uptake of diesel oil by C. tropicalis was elucidated through transmission electron microscopy (TEM) analysis. Interestingly, it was observed that internalization of diesel oil droplet was taking place, suggesting a mechanism similar in appearance to active pinocytosis.     

The ependymal surface of the fourth ventricle of the rat: a combined scanning and transmission electron microscopic study.

The morphological features of the ependymal surface and supraependymal elements of the fourth ventricle of the rat were examined by scanning electron microscopy (SEM) and by the transmission electron microscopy (TEM). The results confirm the following aspects: 1) The presence of supraependymal elements and microvilli in the ependymal territories, including the sites where the cilia completely cover the ependymal surface; 2) The existence of cilia with oval or spherical thickenings together with supraependymal bulbs similar in size to those of the larger ciliary swellings; 3) Identification of the long supraependymal fibres with intermittent fusiform dilations observed under the SEM with the nerve fibres seen under the TEM; 4) The existence of intraventricular axodendritic synapses.     

成都地区19个木芙蓉品种的孢粉学研究及其分类学意义

为了解成都地区木芙蓉(Hibiscus mutabilis)品种间的亲缘关系,采用扫描电镜观察了19个木芙蓉品种的花粉显微结构,并探讨其分类学意义.结果表明,19个木芙蓉品种的花粉均为大粒,主要为圆球形,具散孔,外壁纹饰均为刺状纹饰,表面具有颗粒状突起.木芙蓉品种间在花粉粒大小、外壁纹饰上具有一定差异,可以作为品种分类...     

Evolution of carboxylating enzymes involved in paramylon synthesis (phosphoenolpyruvate carboxylase and carboxykinase) in heterotrophically grown Euglena gracilis

Heterotrophically grown Euglena synthesize grains of paramylon, its reserve carbohydrate, in a vesicular complex of mitochondrial origin. A CO₂ fixation activity in dark grown Euglena was demonstrated in the mitochondria via paramylon. At the beginning of the exponential phase of growth, the activity of phosphoenolpyruvate carboxykinase increases before the augmentation of paramylon.At the end of the exponential phase, the activity of this enzyme decreases, and low residual levels persist in the transition and stationary phases of growth. The activity of phosphoenolpyruvate carboxylase evolves inversely during the heterotrophic growth of the algae in succinate- or a lactate-containing medium. A compartmentalized scheme of carbon metabolism in mitochondria is presented.Abbreviations PEP phosphoenolpyruvate - OAA oxaloacetate - PGA phosphoglyceric acid     

DESCRIPTION OF VIRIDILOBUS MARINUS (GEN. ET SP. NOV.), A NEW RAPHIDOPHYTE FROM DELAWARE'S INLAND BAYS

Delaware's Inland Bays (DIB), USA, are subject to blooms of potentially harmful raphidophytes, including Heterosigma akashiwo. In 2004, a dense bloom was observed in a low salinity tributary of the DIB. Light microscopy initially suggested that the species was H. akashiwo; however, the cells were smaller than anticipated. 18S rDNA sequences of isolated cultures differed substantially from all raphidophyte sequences in GenBank. Phylogenetic analysis placed it approximately equidistant from Chattonella and Heterosigma with only ~96% sequence homology with either group. Here, we describe this marine raphidophyte as a novel genus and species, Viridilobus marinus (gen. et sp. nov.). We also compared this species with H. akashiwo, because both species are superficially similar with respect to morphology and their ecological niches overlap. V. marinus cells are ovoid to spherical (11.4 × 9.4 μm), and the average number of chloroplasts (4 per cell) is lower than in H. akashiwo (15 per cell). Pigment analysis of V. marinus revealed the presence of fucoxanthin, violaxanthin, and zeaxanthin, which are characteristic of marine raphidophytes within the family Chattonellaceae of the Raphidophyceae. TEM and confocal microscopy, however, revealed diagnostic microscopic and ultrastructural characteristics that distinguish it from other raphidophytes. Chloroplasts were in close association with the nucleus and thylakoids were arranged either parallel or perpendicular to the cell surface. Putative mucocysts were identified, but trichocysts were not observed. These features, along with DNA sequence data, distinguish this species from all other raphidophyte genera within the family Chattonellaceae of the Raphidophyceae.     

Stress resistance induced by paramylon treatment in Artemia sp.

A study was undertaken to investigate the effectiveness of paramylon extracted from the non-photosynthetic WZSL mutant of Euglena gracilis in potentiating the resistance of the brine shrimp Artemia sp. to stress conditions resulting from poor growth medium quality and daily handling. The experimental design incorporated four different treatments: I) paramylon addition/no growth medium replacement; II) no paramylon addition/no growth medium replacement; III) paramylon addition/growth medium replacement; IV) noparamylon addition/growth medium replacement. As shown by the survival curves of Artemia sp., the addition of paramylon significantly reduced susceptibility of animals to the stressors. Paramylon effectively increased also the ability of offspring to withstand poor water quality and handling damages. Without paramylon almost all offspring died before adulthood, whereas addition of paramylon allowed the animals to moult to the adult stage. Moreover, reproductive success (higher number of living offspring) was enhanced considerably in animals treated with paramylon treated under both stress conditions. These results show that paramylon extracted from Euglena represents a promising biologically active compound for aquaculture purposes. It could be used as a purified product or as component of whole cells, since the Euglena mutant, because of the high intracellular amount of paramylon it can accumulate, could be added to the feed or to water in tanks and ponds without prior processing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Exine morphology and ultrastructure of Duplicisporites from the Triassic of Italy

A morphological study of dispersed Circumpolles pollen grains from the Upper Triassic of the Southern Alps has been initiated with the genus Duplicisporites. Individual pollen grains were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Seen with SEM the pollen surface is finely verrucate with low verrucae of different sizes. A sub‐equatorial continuous rimula is clearly visible. The proximal trilete scar is small and indistinct. TEM images reveal a bi‐layered exine. The ectexine is formed by numerous small, closely packed, granulae subdivided by irregularly‐spaced cavities. In the region of the subequatorial canal, the ectexine becomes thinner, about 1/3 of the usual thickness. At places, the ectexine is slightly separated from the underlying endexine. The endexine is prominent and significantly darker than the ectexine. It is homogeneous and of constant thickness. On the basis of its older age, with respect to Classopollis, the present ultrastructural dataset provides information on the possible origin of cheirolepidiaceous‐type morphology.     

An ultrastructural study of the melanophages in the cerebrospinal fluid of the tadpoles of Xenopus

Melanin deposits in the brain ventricles of Xenopus tadpoles were studied with light and electron microscopy (TEM and SEM). They appeared to be aggregations of melanophages which accumulated free pigment granules excreted by ependymal cells into the cerebrospinal fluid. Whereas the meningeal melanophores contained oval melanosomes of various sizes, the melanosomes in the scavenger cells were all spherical, large (0.6–1.1 μm) and fairly uniform in size. Moreover, they were arranged in spherical groups which were never seen in the cytoplasm of the melanophores. The melanosomes within the cells were identical to the free melanosomes found in the cerebrospinal fluid and those which occurred within the ependymal cells in the young larva, suggesting a common origin from the egg cytoplasm. The number of the melanosomes in the melanophages increased with age. Fine cytoplasmic projections were involved in catching and engulfing the melanosomes. Some other features of the cytoplasm, e.g., large deposits of cell detritus, also indicated that the cells were macrophages. In the later stages, (48, 49) no projections were observed, but the cells were totally filled with melanosomes.     

A comparison of the morpho-cytology and chemical composition of the two forms of the cyanobacterium, <Emphasis Type="Italic">Nostoc commune</Emphasis> Vauch., from the Philippines and Japan

Nostoc commune Vauch. is one of the few freshwater cyanobacteria that has been used as human food. But its commercial production has been elusive. This prompted us to investigate further on the chemical composition and morpho-cytological characteristics of the discoid and spherical forms of the alga from the Philippines and Japan. Light microscopy of the two forms revealed that they consisted of irregularly coiled, unbranched, heterocystous filaments. Transmission electron microscopy showed that a trichome was enclosed by a 14 μm  thick mucilaginous sheath (extracellular polysaccharide, EPS). A colonial sheath enveloped a spherical colony that was made up of a blue-green outer core that enclosed an inner, whitish, fleshy core, while the discoid form was a deflated or desiccated form of the spherical form. Cytologically, the outer core of the spherical colony (PS) had significantly (p < 0.01) shorter filaments and higher heterocyst frequency than the discoid colony while the discoid type had greater number of detached heterocysts than the other type. Chemical analyses revealed that the cyanobacterium had 34–45% oxalate-oxalic acid soluble substances (OOSS), a dietary fiber that was found to be in higher concentration among the discoid forms than the spherical forms. The major components of OOSS were identified as glucuronic and galacturonic acids that may play a role in modulating water flow in the glycans of the mucilaginous sheath. There were 17 amino acids identified. Philippine spherical (PS) colonies yielded generally higher concentration for each of these amino acids than the discoid types (PD and JD) except for phenylalanine, aspartic acid, and proline. There were six soluble proteins identified in the samples with the following molecular weights in kDa: 73, 55, 39, 36, 29, and 14.4. A protein band of 55 kDa was common to all types of colonies while 73 kDa was identified in the spherical form (PS) and faintly in the discoid form (JD). The protein bands of 39, 36, 29, and 14.4 kDa were found distinctly among the discoid forms (desiccated types) regardless of origin but absent in the spherical forms. In vitro protein digestion was improved, by as much as 30%, when the pigments were extracted. However, the presence of phenolic compounds could also affect protein digestion. Morpho-cytological studies and chemical analyses showed that N. commune of the same colony form generally had the same characteristics regardless of their origin. Although the common traits were more obviously observed among the discoid colonies. However, protein, crude lipid, and chlorophyll a concentrations were found to be more dependent on the age and culture condition of the cyanobacterium than on colony form or origin. Presented at the 6th Meeting of the Asia Pacific Society of Applied Phycology, Manila, Philippines.     

POLLEN MORPHOLOGY IN THE GENUS ERYTHRONIUM (LILIACEAE) AND ITS SYSTEMATIC IMPLICATIONS

Pollen morphology was examined in 40 samples from 19 species in the genus Erythronium (Liliaceae) using scanning (SEM) and transmission electron microscopy (TEM). Pollen grains are monosulcate monads, except for a plant of E. oregonum which has dyad grains. North American and European species are characterized by reticulate exine sculpture composed of various degrees of wavy muri and variably-sized lumina. The most distinctive feature of exine sculpture in the genus is exhibited by the Asian species E. japonicum, which has a unique reticulate pattern composed of striate muri and a distinctive exine structure without columellae. The distinctness of E. japonicum pollen suggests that it has specialized in isolation from species in North America and Europe.     

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF AËTOXYLON,AMYXA, AND GONYSTYLUS TO THE THYMELAEACEAE

The pollen of three closely related genera, Aëtoxylon, Amyxa, and Gonystylus is compared in SEM and TEM with that of Thymelaeaceae, s. s. The Thymelaeaceae have spherical, pantoporate grains with a crotonoid tectum in which the basic subunit is triangular in shape and forms a continuous triangular array. Thin section (TEM) and fractures (SEM) revealed that these subunits are attached to a ringlike network of horizontal rods. Within the Thymelaeaceae, the triangular subunits vary in the number of subdivisions and degree of fusion and form a morphological continuum. Aëtoxylon, Amyxa, and Gonystylus also have spherical, pantoporate pollen but with a tectum in which almost all of the distinction of the subunits appears to have been lost. The structure of the exine in Aëtoxylon, Amyxa, and Gonystylus, however, is unique thus far within the angiosperms. Thin section revealed a thick tectum with a layer of short or even granular columellae, then a thin, discontinuous layer from which larger columellae appear to hang. There is no evidence of an endexine even in the region of the apertures. The distinctive exine structure would support the treatment of Aëtoxylon, Amyxa, and Gonystylus as a separate family, Gonystylaceae, allied to the Thymelaeaceae.