Survival and growth of alpha-spores of Porphyra schizophylla Hollenberg (Rhodophyta: Bangiophyceae)

Alpha-spores of the intertidal Porphyra schizophylla Hollenberg f. norrisii Mumford appear able to tolerate environmental stress factors associated with intertidal habitats, (viz., drying of water films with salt crystal formation, increased salt concentrations in the surrounding water, exposure to humid air when spores are enclosed in water films), and to produce Conchocelis filaments of normal appearance when subsequently germinated in sea water cultures. Tolerances of lowered salinities were observed down to 17.4%., but little survival at salinities lower than this. Alpha-spore germination on thalli of intertidal macro-algae was observed, with initial penetration in some cases. Penetrations of algal thalli were observed with Conchocelis filaments of α-spores germinated on red algae from low intertidal and subtidal habitats. Cell recognition phenomena would seem to be involved in these growth responses.     

Cytochalasin B Treatment of Apple (<Emphasis Type="Italic">Malus pumila</Emphasis> Mill.) Pollen Tubes Alters the Cytoplasmic Calcium Gradient and Causes Major Changes in the Cell Wall Components

It is well established that the actin cytoskeleton is absolutely essential to pollen germination and tube growth. In this study we investigated the effects of cytochalasin B (CB), which affects actin polymerization by binding to the barbed end of actin filaments, on apple (Malus pumila Mill.) pollen tube growth. Results showed that CB altered the morphology of pollen tubes, which had a larger diameter than control tubes beside inhibiting pollen germination and tube growth. Meantime CB also caused an abnormal distribution of actin filaments in the shank of the treated pollen tubes. Fluo-3/AM labeling indicated that the gradient of cytosolic calcium ([Ca²⁺]c) in the pollen tube tip was abolished by exposure to CB, which induced a much stronger signal in the cytoplasm. Cellulose and callose distribution in the tube apex changed due to the CB treatment. Immunolabeling with different pectin and arabinogalactan protein (AGP) antibodies illustrated that CB induced an accumulation of pectins and AGPs in the tube cytoplasm and apex wall. The above results were further supported by Fourier-transform infrared (FTIR) analysis. The results suggest the disruption of actin can result in abnormal growth by disturbing the [Ca²⁺]c gradient and the distribution of cell wall components at the pollen tube apex.     

Growth aspects of Flustra foliacea(Bryozoa, Cheilostomata) in laboratory culture

Flustra foliacea is a cheilostome marine bryozoan which, after initial horizontal growth during the first year, changes to erect growth thereafter. Appraising this slow-growing species for biotechnological use, required the development of cultivation methods for economical biomass production. Vegetative reproduction via cuttings, as employed in the horticulture of various plants, was tested. Fronds of F. foliacea were cut into pieces (10–150 mg fresh weight) and fixed in longitudinally cut silicon tubes. Bryozoa were fed with a mixture of Isochrysis galbana, Dunaliella tertiolecta and Cryptomonas sp. yielding growth rates of 0.3% ± 0.02 day^?1of the initial fresh weight. Growth of the colony occurred firstly at the original growth margin, but later also at the transections, including the side fixed in the silicon tube, opposite to the growth margin. After three months of growth, the two layers of zooids split at the growth margin, forming two monolayers. This growth feature, not described previously for Flustra foliacea,was observed under experimental and natural conditions, and is interpreted as the beginning of one type of ramification. According to our findings, vegetative reproduction of F. foliacea under laboratory conditions is possible and might be an alternative to natural resources regarding biomass of this species.     

Photosynthetic Reactions in the Marine Alga Codium vermilara: II. Structural Studies

Chloroplasts from Codium vermilara, isolated by relatively crude methods, are able to fix CO₂ at rates comparable to the rates of intact plants. Sections in thalli of Codium vermilara show that the chloroplasts are surrounded by a thin layer of cytoplasm. This surrounding layer of cytoplasm, is retained also in isolated chloroplasts, and presumably preserves the intactness of the chloroplast envelope.     

Effects of the bryozoan Membranipora tuberculata (Bosc.) on the photosynthesis and growth of Gelidium rex Santelices et Abbott

Several species of Membranipora commonly occur on brown and red algae. It is currently believed that these bryozoans could affect growth of the host plant by modifying incident light. In the present study, we report on the changes that occur in both intensity and quality of light passing through colonies of M. tuberculata (Bosc.) and on the effects of bryozoans on growth of the host plant. M. tuberculata decreases photon-flux density by up to 56% of the incident light and slightly affects the quality of the incident light. Although the bryozoan reduces the photosynthetic rate of Gelidium rex Santelices et Abbott, it does not have a net effect on algal growth. It is concluded that the effects of epifauna on algal growth depend on the nature of the algal structure colonized. Therefore, it cannot be predicted a priori that encrusted thalli should grow at a slower rate than nonencrusted thalli.     

Complanate Scytosiphon lomentaria (Lyngbye) J. Agardh (Scytosiphonales: Phaeophyta) from Southern Australia: The effects of season,temperature, and daylength on the life history

Cultures of the complanate form of Scytosiphon lomentaria (Lyngbye) J. Agardh were initiated at different times of year, maintained in several temperature daylength regimes, and grown through at least three generations. The composition of the F₁ generation varied on a seasonal basis, with a greater proportion of complanate individuals in winter and a predominance of ralfsioid and and cylindrical individuals in spring-summer.In culture, complanate thalli were only initiated from zooids derived from thalli (complanate or ralfsioid) grown in short days; ralfsioid progeny developed in long days. Some kinds of ralfsioid thalli and the cylindrical thalli developed and reproduced in long and short day conditions. The effects of temperatures between 11° and 20°C were subtle, and principally related to the rate of growth of cultured plants and not to the determination of particular stages in the life history.The relationship between the seasonal occurrence of complanate S. lomentaria, its seasonal pattern of reproduction, and the effects of daylength on the life history are discussed.     

Developmental pattern of crust into upright thalli of Grateloupia asiatica (Halymeniaceae,Rhodophyta)

Grateloupia asiatica is an edible seaweed and source of carrageenan in Korea. Considering the economic importance of this edible seaweed, mass culturing methods from spores have been conducted. Moreover, it helps prevent natural population depletion. Spores germinate to form crusts, filaments and spherical structures that subsequently differentiate and develop into thalli. The objective of our research was to study the developmental pattern of crust into upright thalli. Vegetative cells of crust divided circularly to expand and coalescence with other crusts, while those cells that divide vertically increase the thickness of the crust. The specific growth rate of the crusts was optimal at 20 °C (8.6 % day^?1) and 42 μmol photons m^?2 s^?1 (10.8 % day^?1). At optimum condition, they grew in regularity that forming pattern of zonation and circular mounds onto the crusts subsequently produce upright thalli. Thalli would be generated if the crusts, generally composed of six cells in thickness, will start to produce cortical and medulla cells to support and generate upright thalli. In the tank culture, the upright thalli grew rapidly during July to October and reached a maximum length of around ±5.2 cm. The thalli matured and contained many carposporangia in the branches after 150 culture days.     

Arabidopsis Villins Promote Actin Turnover at Pollen Tube Tips and Facilitate the Construction of Actin Collars

Apical actin filaments are crucial for pollen tube tip growth. However, the specific dynamic changes and regulatory mechanisms associated with actin filaments in the apical region remain largely unknown. Here, we have investigated the quantitative dynamic parameters that underlie actin filament growth and disappearance in the apical regions of pollen tubes and identified villin as the major player that drives rapid turnover of actin filaments in this region. Downregulation of Arabidopsis thaliana VILLIN2 (VLN2) and VLN5 led to accumulation of actin filaments at the pollen tube apex. Careful analysis of single filament dynamics showed that the severing frequency significantly decreased, and the lifetime significantly increased in vln2 vln5 pollen tubes. These results indicate that villin-mediated severing is critical for turnover and departure of actin filaments originating in the apical region. Consequently, the construction of actin collars was affected in vln2 vln5 pollen tubes. In addition to the decrease in severing frequency, actin filaments also became wavy and buckled in the apical cytoplasm of vln2 vln5 pollen tubes. These results suggest that villin confers rigidity upon actin filaments. Furthermore, an observed decrease in skewness of actin filaments in the subapical region of vln2 vln5 pollen tubes suggests that villin-mediated bundling activity may also play a role in the construction of actin collars. Thus, our data suggest that villins promote actin turnover at pollen tube tips and facilitate the construction of actin collars.     

Ultrastructural correlates of the antidiuretic hormone-dependent and antidiuretic hormone-independent increase of osmotic water permeability in the frog urinary bladder epithelium

Electron and confocal microscopy, using immunocytochemical methods, was employed to assess osmotic water permeability of the frog (Rana temporaria) urinary bladder during transcellular water transport, induced by antidiuretic hormone (ADH) or by wash-out of autacoids from serosal, ADH-free Ringer solution. The increase of osmotic water permeability of the urinary bladder was accompanied by relevant ultrastructural changes, the most remarkable being: (1) the appearance of aggregates of intramembranous particles in the apical membrane of granular cells, and the extent of the membrane area covered by the aggregates proportional to that of the water flow; (2) redistribution of actin filaments in the cytoplasm of granular cells; judging from the anti-actin label density, the number of actin filaments in the apical region of cytoplasm was reduced by 2.5–4 times compared with normal; (3) a decrease in the total electron density of the cytoplasm due to the increased water content of granular cells.     

Multilocus Comparative Phylogeography of Two Aristeid Shrimps of High Commercial Interest (Aristeus antennatus and Aristaeomorpha foliacea) Reveals Different Responses to Past Environmental Changes

Phylogeographical studies can reveal hidden patterns in the evolutionary history of species. Comparative analyses of closely related species can further help disentangle the relative contributions of processes responsible for such patterns. In this work, the phylogeography of two aristeid species, Aristeus antennatus and Aristaeomorpha foliacea, was compared through multiple genetic markers. These marine shrimp species are of high commercial importance, and are exploited in the Mediterranean Sea (MED) and in Mozambique Channel (MOZ) where they occur in partial sympatry. Aristeus antennatus (N = 50) from Western and Eastern Mediterranean (WM and EM, respectively), Atlantic Ocean (AO) and MOZ, and Aristaeomorpha foliacea (N = 40) from WM, EM, MOZ North-Western Australia (AUS) were analyzed with two nuclear genes (PEPCK and NaK) and one mitochondrial (COI) gene. Within the study area differences were found between the two species in their phylogeographical patterns, suggesting distinct responses to environmental changes. Monophyly of Aristeus antennatus was found across its distributional range. This pattern contrasted by a deep evolutionary split within Aristaeomorpha foliacea where genetic diversity followed geography distinguishing MED-MOZ and AUS. We propose that the AUS lineage of A. foliacea warrants consideration as a distinct species, with consequent implications in systematics and resource management.     

The life history of Porphyra endiviifolium from the South Shetland Islands, Antarctica

This paper describes the reproduction and life history of an intertidal species, Porphyra endiviifolium, from Antarctica. Field specimens were examined microscopically, prepared for electron microscopy and used to establish cultures. Wild populations comprised two kinds of leafy thalli, morphologically similar but distinguished by their mode of reproduction, either sexual or asexual. Carpospores from monoecious leafy gametophytes developed into conchocelis filaments in culture, and under “winter-spring” conditions these formed conchospores that germinated to produce leafy thalli. Monospores from asexual leafy thalli developed directly into two different forms of leafy thalli. Only one of the cultured morphotypes became fertile, reproducing asexually by monospores. We conclude that the phases of the life history of P. endiviifolium show different ecological strategies, the conchocelis phase reproducing in response to short days unlike the leafy thalli in which growth and reproduction respond primarily to irradiance. Received: 2 May 1997 / Accepted: 11 October 1997     

Production and application of filaments of <Emphasis Type="BoldItalic">Grateloupia turuturu</Emphasis> (Halymeniaceae,Rhodophyta)

Filaments from Grateloupia turuturu were obtained through germination of spores, regeneration from fragments of discoid crusts and erect thalli. The rates of filament formation through the three ways were 5.3 ± 1.2%, 100%, and 62.3 ± 5.6%, respectively. Discoid crusts were the best materials for the production of filaments. The obtained filaments were cloned in stationary and aerated culture. The differentiations of filaments were observed. When attached to the substrata, filaments differentiated into discoid crusts from which erect thalli grew, whereas for filaments in suspension culture, some cells in the filaments differentiated into spherical structures that also formed new erect thalli. Moreover, fragments of filaments (< 100 μ m) were seeded onto nori-nets. The regenerated plantlets grew into adult thalli in field cultivation.     

Epi-endophytic symbiosis between Laminariocolax aecidioides (Ectocarpales, Phaeophyceae) and Undaria pinnatifida (Laminariales, Phaeophyceae) growing on Argentinian coasts

The present is the first study on epi-endophytic algae on thalli of Undaria pinnatifida growing along Argentinian coasts. The main goal is to describe the nature and the morphology of this symbiosis. Individuals of Laminariocolax aecidioides were detected in both June and December 2004, growing on U. pinnatifida sporophytes. In nature, the epi-endophyte were macroscopically observed as dark zones that partially covered the hosts’ fronds. L. aecidioides vegetative thalli were irregularly branched uniseriate filaments. The life cycle is described from laboratory cultures started from Patagonian populations. Caryology revealed that the sporophytic diploid phase presented 16 chromosomes whereas the gametophytic haploid phase presented 8 chromosomes. Isolates made from thalli growing in the interior of infected hosts developed into filamentous, branched sporophytes that reproduced by both unispores and plurispores that were produced in unilocular and plurilocular sporangia, respectively. The results of this paper also allowed us to conclude that L. aecidioides uses the thalli of U. pinnatifida as a proper substrate. The penetration of endophitic filaments among the host′s cortical cells produced a lateral compression and, finally, their thalli development generated perforations in the host tissues. The effects of the epi-endophytic infection of L. aecidioides on U. pinnatifida are neither severe nor deleterious.     

Meristem clusters in cortical layer of thallus cells of the cultured red alga Palmaria palmata

For the first time somatic spotlike formations of 1.5 mm in diameter and height up to 0.5 mm were revealed in thalli of the red alga Palmaria palmata reared in an aerated stirred culture. It was determined that some cortical cells of the thallus are able to divide in the periclinal and anticlinal directions forming spots. Deep freezing and subsequent thawing of thalli showed that the cortical cells of spots were meristematic cells. In certain conditions they enabled the formation of prolifications, which germinated plantlets. These clusters of meristem tissue in the cortical layer of cells of the thallus of P. palmata, which were formed in the culture as in nature, function as growth cells facilitating growth of thalli in thick and natural “planting material” formed upon thalli fragmenting after their freezing in the winter season.     

The effects of severe carbon limitation on the green seaweed,Ulva conglobata (Chlorophyta)

Low inorganic carbon (Ci) concentrations in seawater are usually an important factor controlling photosynthesis and growth of seaweeds. The green seaweed, Ulva conglobata Kjellm, collected from a rock pool in a middle intertidal zone located at Nanao Island, Shantou, China, were cultured under low Ci level for several days, to examine the effect of severe carbon limitation on photosynthesis. The rather high pH compensation points obtained from the pH-drift experiments indicated that U. conglobata was capable of acquiring HCO₃ ^? from surrounding seawater as its Ci source for photosynthesis. However, thalli of U. conglobata cultured in Ci-starved seawater exhibited a decline of biomass, showing that the realistic photosynthetic carbon gain could not compensate for the respiratory carbon consumption in the thalli under severe Ci limitation during laboratory culture. Compared with ambient Ci conditions, the culture under severe Ci limitation significantly had an increased pigment content, but a lower maximum quantum yield and photosynthetic electron transport rate. Additionally, the maximum carbon-saturating photosynthesis rate and the apparent photosynthetic conductance of U. conglobata thalli increased in cultures with severe Ci limitation compared with ambient Ci in low N-grown thalli. The results suggest that under severe Ci limitation, U. conglobata thalli increased capacities of both light absorption processes and carbon fixation pathways.     

In situ development of the foliicolous lichen Phyllophiale (Trichotheliaceae) from propagule germination to propagule production

The vegetative cycle of the foliicolous lichen Phyllophiale, from propagule germination to propagule production, was studied by light microscope observation of thalli colonizing plastic cover slips placed within a lowland tropical forest. Discoid propagules germinated by growth of radially arranged fungal cells and developed directly into lichen thalli. The young lichen comprised a single disc of closely branched, radiating filaments of the algal symbiont Phycopeltis, covered by a network of fungal hyphae extending onto the substrate as a prothallus. The prothallic hyphae incorporated additional Phycopeltis thalli encountered on the substrate. The phycobiont formed a single layer, with individual algal thalli clearly distinguishable within the lichen. Radial growth ceased at points of contact between adjacent phycobiont thalli. The visible shape of the crustose lichen thallus corresponded to the perimeter of the phycobiont thalli within. Propagules were initiated at points corresponding to the margins of the phycobiont thalli, by vertical reorientation of horizontal algal filaments surrounded by fungal hyphae. The lichenized alga produced intercalary gametangia. Degeneration of propagules unsuccessful in lichen establishment sometimes resulted in free growth of the phycobiont. The alga generally maintained its shape, growth pattern, and reproductive independence within the lichen, while also participating in the formation of unique symbiotic propagules.     

Neuroglia in the corpus callosum of the primate, slow loris (Nycticebus coucang coucang)

The corpus callosum of adult slow loris consists of a mixed population of several cell types, i.e. free subependymal cells, oligodendrocytes, astrocytes and microglia. The free subependymal cell is rather small and slender with a somewhat patchy nucleus. It shows scanty cytoplasm with free ribosomes. Oligodendrocytes vary both in nuclear and cytoplasmic densities and can be divided into three classes: light, medium dense and dark types. Their cytoplasm contains microtubules, rough endoplasmic reticulum and Golgi saccules. Astrocytes are pale cells with large amount of filaments in their cytoplasm. Microglia are small cells with granulated nuclei. The cells often show large cytoplasmic protrusions containing the usual cell organelles and lipofuscin bodies in their cytoplasm. Lastly, cells with typical features of neurons are occasionally encountered among the white matter.     

Ultrastructure of early stages of Rozella allomycis (Cryptomycota) infection of its host, Allomyces macrogynus (Blastocladiomycota)

This study reconstructs early stages of Rozella allomycis endoparasitic infection of its host, Allomyces macrogynus. Young thalli of A. macrogynus were inoculated with suspensions of R. allomycis zoospores and allowed to develop for 120 h. Infected thalli at intervals were fixed for electron microscopy and observed. Zoospores were attracted to host thalli, encysted on their surfaces, and penetrated their walls with an infection tube. The parasite cyst discharged its protoplast through an infection tube, which invaginated the host plasma membrane. The host plasma membrane then surrounded the parasite protoplast and formed a compartment confining it inside host cytoplasm. The earliest host-parasite interface within host cytoplasm consisted of two membranes, the outer layer the host plasma membrane and the inner layer the parasite plasma membrane. At first a wide space separated the two membranes and no material was observed within this space. Later, as the endoparasite thallus expanded within the compartment, the two membranes became closely appressed. As the endoparasite thallus continued to enlarge, the interface developed into three membrane layers. Thus, host plasma membrane surrounded the parasite protoplast initially without the parasite having to pierce the host plasma membrane for entry. Significantly, host-derived membrane was at the interface throughout development.     

Cryo-electron tomography of the magnetotactic vibrio Magnetovibrio blakemorei: Insights into the biomineralization of prismatic magnetosomes

We examined the structure and biomineralization of prismatic magnetosomes in the magnetotactic marine vibrio Magnetovibrio blakemorei strain MV-1 and a non-magnetotactic mutant derived from it, using a combination of cryo-electron tomography and freeze-fracture. The vesicles enveloping the Magnetovibrio magnetosomes were elongated and detached from the cell membrane. Magnetosome crystal formation appeared to be initiated at a nucleation site on the membrane inner surface. Interestingly, while scattered filaments were observed in the surrounding cytoplasm, their association with the magnetosome chains could not be unequivocally established. Our data suggest fundamental differences between prismatic and octahedral magnetosomes in their mechanisms of nucleation and crystal growth as well as in their structural relationships with the cytoplasm and plasma membrane.