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Zoospores

Distribution by Scientific Domains

Life Sciences	90%
3 Other Domains	10%

Distribution within Life Sciences

Phycology	36%
Plant Pathology	17%
Plant Science	15%
6 Other Subdomains	32%

Selected Abstracts

Interaction of Zoospores of the Green Alga Ulva with Bioinspired Micro- and Nanostructured Surfaces Prepared by Polyelectrolyte Layer-by-Layer Self-Assembly

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Xinyu Cao
Abstract The interaction of spores of Ulva with bioinspired structured surfaces in the nanometer,micrometer size range is investigated using a series of coatings with systematically varying morphology and chemistry, which allows separation of the contributions of morphology and surface chemistry to settlement (attachment) and adhesion strength. Structured surfaces are prepared by layer-by-layer spray-coating deposition of polyelectrolytes. By changing the pH during application of oppositely charged poly(acrylic acid) and polyethylenimine polyelectrolytes, the surface structures are systematically varied, which allows the influence of morphology on the biological response to be determined. In order to discriminate morphological from chemical effects, surfaces are chemically modified with poly(ethylene glycol) and tridecafluoroctyltriethoxysilane. This chemical modification changes the water contact angles while the influence of the morphology is retained. The lowest level of settlement is observed for structures of the order 2,µm. All surfaces are characterized with respect to their wettability, chemical composition, and morphological properties by contact angle measurement, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. [source]

Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 6 2008
Tatsuya Togashi
Abstract By finding some important culture conditions as below, we succeeded in experimentally controlling the whole life history of a dioecious marine green alga, Bryopsis plumosa (Hudson) C. Agardh. In this study, we focused on the primary and secondary sex ratios (i.e. at inception and maturity) using these culture techniques. Gametogenesis was induced by culturing haploid gametophytes with Provasoli's enriched seawater (PES) medium under a 14:10 h light : dark cycle at 14 °C. Formed zygotes grew into diploid sporophytes, which were cultured for 3 months with PES medium under a 14:10 h light : nbsp;dark cycle at 18 °C. Then they were transferred into Schreiber medium and cultured under a 10:14 h light : dark cycle at 22 °C. Within 1 week, zoosporogenesis was observed. Zoospores were released within a couple of days. Each zoospore soon germinated and grew into a unisexual gametophyte. The primary sex ratio was examined in gametophytes that originated from a single sporophyte. The secondary sex ratio was studied in the field. Both were estimated as 1:1. Synchronized meiotic cell divisions might occur during zoosporogenesis dividing each sex-determining factor evenly among zoospores. Given the equal sex ratio at maturity, there seems to be no environmental factor that differentially affects the survival of male or female gametophytes in nature. [source]

A COMPREHENSIVE STUDY OF THE LIFE CYCLE OF A SOUTH AMERICAN POPULATION OF STIGEOCLONIUM TENUE (CHAETOPHORALES, CHLOROPHYTA),

JOURNAL OF PHYCOLOGY, Issue 5 2010
Karina M. Michetti
The diplobiontic,haplodiplontic life cycle with alternating isomorphic generations in Stigeoclonium tenue (C. Agardh) Kütz. is described for the first time. Sporophytes (2n = 10) arise from tetraflagellate zoospores that are produced by meiosis. Sporic meiosis might be inferred from the cruciform divisions formed during zoosporogenesis and is confirmed through observations of prophase I substages. Zoospores do not germinate directly but produce a haploid cyst that germinates to give rise to a gametophyte (n = 5). Gametophytes produce biflagellate isogametes, which fuse to produce zygotes that germinate by mitosis into the sporophytic stage. Gametophytes and sporophytes reproduce asexually both via mitotic tetraflagellate zoospores and by thallus fragmentation. Results from this study indicate that both the cosmopolitan distribution and dominance of S. tenue in many periphytic communities might be due to its multiple reproductive strategies. [source]

HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA),

JOURNAL OF PHYCOLOGY, Issue 3 2004
Bas W. Ibelings
Some chytrids are host-specific parasiticfungithat may have a considerable impact on phytoplankton dynamics. The phylum Chytridiomycota contains one class, the Chytridiomycetes, and is composed of five different orders. Molecular studies now firmly place the Chytridiomycota within the fungal kingdom. Chytrids are characterized by having zoospores, a motile stage in their life cycle. Zoospores are attracted to the host cell by specific signals. No single physical,chemical factor has been found that fully explains the dynamics of chytrid epidemics in the field. Fungal periodicity was primarily related to host cell density. The absence of aggregated distributions of chytrids on their hosts suggested that their hosts did not vary in their susceptibility to infection. A parasite can only become epidemic when it grows faster than the host. Therefore, it has been suggested that epidemics in phytoplankton populations arise when growth conditions for the host are unfavorable. No support for such a generalization was found, however. Growth of the parasitic fungus Rhizophydium planktonicum Canter emend, parasitic on the diatom Asterionella formosa Hassal, was reduced under stringent nutrient limitation,because production and infectivity of zoospores were affected negatively. A moderate phosphorous or light limitation favored epidemic development, however. Chytrid infections have been shown to affect competition between their algal hosts and in this way altered phytoplankton succession. There is potential for coevolution between Asterionella and the chytrid Zygorhizidium planktonicum Canter based on clear reciprocal fitness costs, absence of overall infective parasite strains, and possibly a genetic basis for host susceptibility and parasite infectivity. [source]

Ultrastructure of Lobocharacium coloradoense, gen. et sp. nov. (Chlorophyta, Characiosiphonaceae), an unusual coenocyte from Colorado

JOURNAL OF PHYCOLOGY, Issue 2 2000
Paul Kugrens
Light and electron microscopic descriptions are provided for Lobocharacium coloradoense, gen. et sp. nov., a unicellular coenocytic green alga isolated from a power plant's retaining pond in north-central Colorado. Vegetative cells range from 120,230 ,m in length and 80,120 ,m in diameter in culture. The large vegetative cells are attached to substrates by small discoid attachment pads. The cells are multinucleate and consist of distinct cytoplasmic lobes, with each lobe containing a chloroplast and a basal nucleus. Chloroplasts are somewhat cone-shaped in profile and stellate or lobed when viewed from the surface, and each has a central, basal pyrenoid. Hundreds of these cytoplasmic lobes occur within a cell, and thin cytoplasmic bridges interconnect the lobes. When a vegetative cell matures, each of the cytoplasmic lobes cleaves to form numerous fusiform zoospores or spherical isogametes. The biflagellate isogametes range in size from 4,10 ,m, they lack a cell wall, they have a cup-shaped chloroplast with a pyrenoid and stigma, and they have a nucleus close to the basal bodies. Isogametes are incapable of forming vegetative cells. Zoospores are biflagellate and fusiform, measuring 8,12 ,m in length and 4,6 ,m in diameter. Each zoospore has a cell wall, a single parietal chloroplast with a prominent pyrenoid in the center of the chloroplast, and a long oval stigma. Gamete and zoospore release involves a dissolution of the entire vegetative wall. Released zoospores usually settle and cluster near the vegetative cell from which they were produced, attach to the substrate with their flagella, and, shortly after losing their flagella, extrude mucilage through the flagellar pores in the wall to form a small discoid attachment pad. The incipient vegetative cell is fusiform and uninucleate, but it becomes more rounded and multinucleate as enlargement occurs. Most vegetative cells in culture become dormant, and the chloroplast becomes orange in color. Some cells form single aplanospores that can withstand desiccation, but occasionally numerous aplanospores may also be formed later in the larger vegetative cells. [source]

Defence Responses of Calli and Seeds of Hevea brasiliensis to Zoospores and the Elicitin of Phytophthora palmivora

JOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2008
Nion Chirapongsatonkul
Abstract The defence responses of calli and seeds of two cultivars (resistant; BPM-24 and susceptible; RRIM600) of the rubber tree, Hevea brasiliensis, against zoospores and elicitin purified from its pathogen, Phytophthora palmivora, were investigated. Both zoospores and elicitin induced the biosynthesis of the phytoalexin, scopoletin (Scp), in Hevea calli ranging from 5 × 105 to 4.5 × 106 zoospores/ml and 0.5 to 2 ,g elicitin/g fresh weight of calli. At the highest concentration of zoospores (4.5 × 106 zoospores/ml) or elicitin (2 ,g/g fresh weight of calli), the rate of Scp production was fastest but then it rapidly decreased and produced lower peak value than detected at the optimum concentration. The decline of Scp level at the highest zoospore/elicitin concentration was correlated to the amount of cell death measured by Evans Blue method. Peroxidase (POD) activities in Hevea calli were also measured using the optimum level of zoospores or elicitin. Induction of Scp preceded the production of Scp POD and o -dianisidine POD then followed by the guaiacol POD. The Scp and POD accumulations were approximately two to three times higher in the resistance cultivar than those in the susceptible one. As the responses of the calli to elicitin were faster than those to the zoospores, it demonstrates that zoospores require more time to act on the host cells. The pattern of Scp and POD activities monitored in elicitin-treated Hevea seeds was similar to that of Hevea calli after treating with zoospores or elicitin. Therefore, the callus cultures could be used as a tool for studying other defence mechanisms in H. brasiliensis. The achieved knowledge will be applied to enhance resistance and led to the protection of Hevea young seedlings from the pathogen in the plantation. [source]

Zoospores of Three Arctic Laminariales Under Different UV Radiation and Temperature Conditions: Exceptional Spectral Absorbance Properties and Lack of Phlorotannin Induction

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009
Ruth Müller
Phlorotannins have often been considered to act as UV-protective compounds in zoospores of brown algae. However, only the absorption characteristics of zoospores under UV exposure have been determined and no data are available on the actual content of phlorotannins or on temperature,UV interactions. Therefore, we determined the absorbance spectra and the phlorotannin contents in zoospore suspensions of three Arctic species (Saccharina latissima, Laminaria digitata, Alaria esculenta), and in the media surrounding zoospores after exposure to different radiation (400,700, 320,700, 295,700 nm) and temperature (2,18°C) conditions for 8 h. Absorption typical of phlorotannins with a maximum at 276 nm was monitored in zoospore suspensions as well as in the media surrounding zoospores, but the results depended strongly on radiation treatments and on zoospore densities. Surprisingly, the content of UV-absorbing phlorotannins subsequent to different exposures did not change in any of the three species. The observed exceptional absorption properties could, therefore, not be related to phlorotannin contents. These findings are discussed in light of a strong phlorotannin investment from sporophytes during spore release and a minor UV-protective role of phlorotannins for zoospores of Arctic kelp species. [source]

Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa

SNOW ALGAE OF THE WINDMILL ISLANDS, CONTINENTAL ANTARCTICA: DESMOTETRA AUREOSPORA, SP.

JOURNAL OF PHYCOLOGY, Issue 1 2001

Two cryophilic Desmotetra species, D. aureospora, sp. nov., and D. antarctica (Fritsch) Ling appear to be unique to the southern hemisphere snow ecosystem, or at least to the Windmill Island region, Antarctica. They have not been encountered in previous extensive studies of the Arctic and northern alpine regions. Also unusual are the higher pH (6.8 and 7.8) and conductivities of 279 ,S·cm,1 and 426 ,S·cm,1 for habitat conditions of D. antarctica that can be attributed to the influence of penguin guano. Both species are characterized by cells enveloped in individual mucilage layers, 1,3 contractile vacuoles, and a cup-shaped chloroplast containing a diffuse pyrenoid. The cells divided in three planes to form cubical loosely aggregated green cell packages embedded in mucilage. Vegetative cells of the two species cannot be distinguished with certainty; however, their zygospores are very different. Desmotetra aureospora has spherical, smooth-walled, golden zygospores, whereas D. antarctica has pale, yellow green, aereolate zygospores. Mucilage stalk morphology of cells in stationary-phase cultures can also be used to separate the two species. Zygospores of D. antarctica have previously been identified as the snow alga Trochiscia antarctica Fritsch. Both species are currently maintained in culture at the Australian Antarctic Division. The cultures did not grow at temperatures above 15° C. The two species are compared with the soil alga D. stigmatica (Deason) Deason et Floyd, the only other species in the genus, and also with Chlorosarcina stigmatica Deason strain T105. Results show that the three Desmotetra species form a natural group and that the absence or presence of a wall on the zoospore is of dubious value in classifications of green algal taxa above the species level. [source]

Ultrastructure of Lobocharacium coloradoense, gen. et sp. nov. (Chlorophyta, Characiosiphonaceae), an unusual coenocyte from Colorado

Specificity in the settlement , modifying response of bacterial biofilms towards zoospores of the marine alga Enteromorpha

ENVIRONMENTAL MICROBIOLOGY, Issue 5 2003
Pratixa Patel
Summary Previous studies have shown that the rate of settlement of zoospores of the green alga Enteromorpha is stimulated by mixed microbial biofilms and that the number of zoospores settling is positively correlated with the number of bacteria in the biofilm. In the present study the specificity of this relationship has been investigated. Ninety-nine strains of marine bacteria were isolated from natural biofilms on rocks and the surface of Enteromorpha plants. Isolates were screened by denaturing gradient gel electrophoresis (DGGE) to eliminate replicates and 16S rDNA sequencing identified a total of 37 unique strains. Phylogenetic analysis revealed that the isolated bacterial strains belonged to three groups ,- Proteobacteria (28 strains), Cytophaga-Flavobacteria-Bacteroid (CFB) group (six strains) and ,- Proteobacteria (one strain). Two strains were unassigned, showing < 93% sequence similarity with the CFB group. The main genera of ,- Proteobacteria were Pseudoalteromonas (14 strains), Vibrio (five strains), Shewanella (five strains), Halomonas (three strains) and Pseudomonas (one strain). Spore settlement experiments were conducted on single-species biofilms, developed for different times on glass slides. The effect of correcting spore settlement values for biofilm density was evaluated. Results showed that the effect of bacterial strains on spore settlement was strain- but not taxon-specific and activity varied with the age of the biofilm. However, most of the strains belonging to genera Vibrio and Shewanella showed stimulation. Pseudoalteromonas strains showed a range of effects including settlement-inhibiting, paralysing and lysing activities. Spatial analysis of bacterial density in the presence and absence of spores revealed a range of different types of association between spores and bacteria. Overall, the spatial association between spores and bacteria appears to be independent of the overall quantitative influence of bacterial cells on spore settlement. [source]

Molecular diagnosis of Phytophthora lateralis in trees, water, and foliage baits using multiplex polymerase chain reaction

FOREST PATHOLOGY, Issue 5 2001
L. M. Winton
A polymerase chain reaction (PCR)-based protocol for detection of Phytophthora lateralis in plant tissues and water is described. Base-pair (bp) deletions in both of the ribosomal DNA internal transcribed spacer (ITS) regions in P. lateralis were used to design complementary PCR primer sequences that amplify a 738 bp fragment only if P. lateralis DNA is present in the sample. Universal control primers based on conserved sequences of the nuclear ribosomal small subunit are included in a multiplexed reaction, providing an internal check on the procedure. The universal primers amplify an approximately 550 bp fragment that is common to plants, protists, and true fungi. The procedure reliably detects P. lateralis in cedar stem tissues and in roots. Positive reactions were obtained with as few as 200 P. lateralis zoospores in water. Diagnostic moléculaire par PCR multiplex pour détecter Phytophthora lateralis dans les arbres, l'eau et le feuillage utilisé comme piège Un protocole basé sur la PCR est décrit pour détecter Phytophthora lateralis dans les tissus végétaux et l'eau. Des délétions de paires de bases dans chacune des régions ITS de l'ADN ribosomal de P. lateralis ont été utilisées pour définir des amorces de PCR qui n'amplifient un fragment de 738 paires de bases que si l'ADN de P. lateralis est présent dans l'échantillon. Des amorces universelles basées sur des régions conservées de la petite sous-unité de l'ADN ribosomal nucléaire ont été incluses dans une réaction de PCR multiplex, fournissant ainsi un témoin interne de la réaction. Ces amorces universelles amplifient un fragment de 550 pb qui est commun aux plantes, aux protistes et aux champignons vrais. Ce protocole permet la détection de P. lateralis dans les tiges et dans les racines du Chamaecyparis. Des réactions positives ont été obtenues avec seulement 200 zoospores de P. lateralis dans l'eau. Molekulare Diagnose von Phytophthora lateralis in Bäumen, Wasser und als Köder benutzten Blättern mittels Multiplex-PCR Eine auf der PCR beruhende Methode zum Nachweis von Phytophthora lateralis in Pflanzengeweben und Wasser wird beschrieben. Deletionen in den beiden ITS Regionen der ribosomalen DNA von P. lateralis wurden zur Synthese von PCR-Primern ausgenutzt, die ein 738 Basenpaare langes Fragment nur dann amplifizieren, wenn P. lateralis in der Probe vorhanden ist. Universelle Primer, die konservierten Sequenzen der kleinen Unterheit der ribosomalen Kern-DNA entsprechen, wurden als interne Kontrollen in die Multiplex-PCR miteinbezogen. Diese Primer amplifizieren ein ungefähr 550 Basenpaare langes Fragment, das sowohl bei Pflanzen als auch bei Protisten und höheren Pilzen vorkommt. Mit der Methode liess sich P. lateralis im Stamm und in den Wurzeln von Lawsons Scheinzypresse verlässlich nachweisen. Für den Nachweis von P. lateralis im Wasser waren mindestens 200 Zoosporen nötig. [source]

A combination of baiting and PCR techniques for the detection of Phytophthora quercina and P. citricola in soil samples from oak stands

FOREST PATHOLOGY, Issue 2 2001
Nechwatal
A description is given of the use of a combination of polymerase chain reaction (PCR) and baiting techniques for the specific detection of Phytophthora quercina and Phytophthora citricola from soil around declining oak trees. The soil was flooded with water and subjected to a specific baiting procedure using Quercus robur leaflets as baits. Single round or nested PCR, respectively, with species-specific primers allowed the detection of P. quercina and P. citricola in infected oak leaflets used as baits and in the water from the same bait tests. PCR detection of both fungi was also possible after soil samples had been thoroughly mixed with water and the floating organic debris had been collected. Phytophthora quercina and P. citricola could be readily detected in almost every case in the water from these tests by PCR but less frequently in the organic debris. The identities of P. quercina and P. citricola were confirmed by restriction digests of the corresponding PCR amplicons. The presence of both fungi was also confirmed in parallel in soil samples tested by baiting with oak leaflets. Nested PCR with the primers used allowed the detection of as few as five zoospores of P. citricola and 300 zoospores of P. quercina in a volume of 100 ,l. The methods presented here allow detection and identification of species of Phytophthora in soil without the need for direct extraction of soil samples, and without specific knowledge of the morphological characteristics of the genus. Détection de Phytophthora quercina et de P. citricola dans le sol de chênaies par une méthode combinant le piégeage et la PCR L'article décrit la détection spécifique de Phytophthora quercina et de P. citricola dans le sol prélevé autour de chênes dépérissants, par une méthode combinant les techniques de piégeage et de PCR. Le sol a été immergé dans l'eau et soumis à la procédure du piégeage avec de très jeunes feuilles de Quercus robur. Une amplification par PCR simple ou par PCR gigogne, respectivement, avec des amorces spécifiques des espèces ont permis de détecter P. quercina et P. citricola dans les feuilles-piège infectées, et dans l'eau de piégeage. La détection des deux champignons par PCR a aussi été possible après que les échantillons de sol aient été soigneusement mélangés à de l'eau et que les débris organiques aient été collectés. Phytophthora quercina et P. citricola ont pu être facilement détectés par PCR dans presque tous les cas dans l'eau de piégeage, mais moins fréquemment dans les débris organiques. L'identité de P. quercina et de P. citricola a été confirmée par les profils de restriction des amplifiats obtenus. La présence des deux champignons a aussi été confirmée en parallèle dans des échantillons de sol par piégeage. L'amplification par PCR gigogne avec les amorces utilisées a permis la détection de seulement 5 zoospores de P. citricola et 300 zoospores de P. quercina, dans un volume de 100 ,l. Les méthodes présentées ici permettent la détection et l'identification des espèces de Phytophthora dans le sol en évitant l'extraction directe d'ADN du sol, et sans connaissances spécifiques sur les caractéristiques morphologiques du genre. Eine Kombination von Köder- und PCR-Techniken zum Nachweis von Phytophthora quercina und P. citricola in Bodenproben von Eichenstandorten Es wird der spezifische Nachweis von Phytophthora quercina und P. citricola in Bodenproben von absterbenden Eichen mit Hilfe einer Kombination von PCR- und Baiting-Methoden beschrieben. Die Bodenproben wurden mit Wasser geflutet und Baiting-Tests unterzogen, bei denen junge Blättchen von Quercus robur als Köder zum Einsatz kamen. Einfache oder nested PCR-Reaktionen mit artspezifischen Primern erlaubten den Nachweis von P. quercina und P. citricola in den infizierten Eichenblättchen aus diesen Tests und im jeweiligen ,Baiting-Wasser'. Der PCR-Nachweis beider Erreger war auch möglich, wenn Bodenproben gründlich mit Wasser gemischt wurden, das aufgeschwemmte organische Material abgesammelt und das Wasser abgenommen wurde. P. quercina und P. citricola wurden dabei in nahezu allen Fällen im Wasser, jedoch weniger regelmäßig im organischen Material nachgewiesen. Die Identität der betreffenden Arten wurde zusätzlich durch Restriktions-Analysen der entsprechenden Amplicons bestätigt. Außerdem wurde die Anwesenheit beider Arten in den untersuchten Bodenproben durch klassische Baiting-Methoden nachgewiesen. Nested PCR mit den verwendeten Primerpaaren erlaubte den Nachweis von nur 5 Zoosporen von P. citricola und 300 Zoosporen von P. quercina in einem Gesamt-Volumen von 100 ,l. Die beschriebenen Methoden ermöglichen Nachweis und Identifizierung von Phytophthora-Arten in Bodenproben, ohne die Notwendigkeit einer direkten Extraktion des Bodens und ohne weitreichende Kenntnis der morphologischen Merkmale der Arten dieser Gattung. [source]

Chytrid infections of Daphnia pulicaria: development, ecology, pathology and phylogeny of Polycaryum laeve

FRESHWATER BIOLOGY, Issue 4 2006
PIETER T. J. JOHNSON
Summary 1. We combined ecological surveys, life table studies, microscopy and molecular sequencing to determine the development, ecology, pathology and phylogeny of Polycaryum laeve, an endoparasite of cladocerans. We report the first records of P. laeve from North America, where we have used a polymerase chain reaction primer and microscopic examination to confirm infections in 14 lakes. Infections are highly pathogenic and caused increased mortality, reduced growth, and reproductive castration in Daphnia pulicaria during life table studies. 2. Biweekly data from Allequash Lake (Wisconsin, U.S.A.) throughout 2003 indicated that fecundity and infection prevalence were inversely correlated. Infection prevalence was highest in late winter and early spring (up to 80%) and lowest during late summer. Epidemics were generally followed by sharp declines in host population density (up to 99%). 3. Within the haemocoel of its host, P. laeve forms thick-walled sporangia, which occur systemically in later stages of infection. Fungal thalli associate closely with muscle fibres and connective tissue, leading to degeneration as the infection becomes advanced. Following death of the host, flagellated zoospores are released through an exit papilla on the sporangium. Based on the infection-induced castration of the host and increases in infection prevalence with Daphnia size, we postulate that transmission is horizontal, but may be indirect through an additional host or free-living stage. 4. Molecular and morphological data clearly indicate that P. laeve belongs in the fungal phylum Chytriodiomycota, order Blastocladiales. Based on ribosomal RNA gene sequences and morphological features, we transfer the genus Polycaryum from the Haplosporidia to the Chytridiomycota, and designate a lectotype and epitype for P. laeve. Considering the high prevalence of P. laeve infection within Daphnia populations, the frequency with which we detected infections among lakes, and the keystone importance of large-bodied Daphnia in aquatic food webs, we suggest that P. laeve may exert a regulatory influence on Daphnia populations in lake ecosystems. [source]

GROWTH OF CRUSTOSE LICHENS: A REVIEW

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2010
RICHARD ARMSTRONG
ABSTRACT. Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (lichenometry). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development; 2) radial growth rates (RGR, mm yr,1); 3) the growth rate,size curve; and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenized fungal hypothallus. Recent data suggest that ,primary' areolae may develop from free-living algal cells on the substratum while ,secondary' areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the ,asymptotic' type of curve recorded in foliose and placodioid species; the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature ,reproductive' areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments. [source]

Functional, genetic and chemical characterization of biosurfactants produced by plant growth-promoting Pseudomonas putida 267

JOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2009
Marco Kruijt
Abstract Aims:, Plant growth-promoting Pseudomonas putida strain 267, originally isolated from the rhizosphere of black pepper, produces biosurfactants that cause lysis of zoospores of the oomycete pathogen Phytophthora capsici. The biosurfactants were characterized, the biosynthesis gene(s) partially identified, and their role in control of Phytophthora damping-off of cucumber evaluated. Methods and Results:, The biosurfactants were shown to lyse zoospores of Phy. capsici and inhibit growth of the fungal pathogens Botrytis cinerea and Rhizoctonia solani. In vitro assays further showed that the biosurfactants of strain 267 are essential in swarming motility and biofilm formation. In spite of the zoosporicidal activity, the biosurfactants did not play a significant role in control of Phytophthora damping-off of cucumber, since both wild type strain 267 and its biosurfactant-deficient mutant were equally effective, and addition of the biosurfactants did not provide control. Genetic characterization revealed that surfactant biosynthesis in strain 267 is governed by homologues of PsoA and PsoB, two nonribosomal peptide synthetases involved in production of the cyclic lipopeptides (CLPs) putisolvin I and II. The structural relatedness of the biosurfactants of strain 267 to putisolvins I and II was supported by LC-MS and MS-MS analyses. Conclusions:, The biosurfactants produced by Ps. putida 267 were identified as putisolvin-like CLPs; they are essential in swarming motility and biofilm formation, and have zoosporicidal and antifungal activities. Strain 267 provides excellent biocontrol activity against Phytophthora damping-off of cucumber, but the lipopeptide surfactants are not involved in disease suppression. Significance and Impact of the Study:,Pseudomonas putida 267 suppresses Phy. capsici damping-off of cucumber and provides a potential supplementary strategy to control this economically important oomycete pathogen. The putisolvin-like biosurfactants exhibit zoosporicidal and antifungal activities, yet they do not contribute to biocontrol of Phy. capsici and colonization of cucumber roots by Ps. putida 267. These results suggest that Ps. putida 267 employs other, yet uncharacterized, mechanisms to suppress Phy. capsici. [source]

Susceptibility of zoospores to UV radiation determines upper depth distribution limit of Arctic kelps: evidence through field experiments

JOURNAL OF ECOLOGY, Issue 2 2006
CHRISTIAN WIENCKE
Summary 1The UV susceptibility of zoospores of the brown seaweeds Saccorhiza dermatodea, Alaria esculenta and Laminaria digitata (Laminariales) was determined in field experiments in June 2004 on Spitsbergen (78°55, N, 11°56, E). 2Freshly released zoospores were exposed for 1 or 2 days at various water depths to ambient solar radiation, ambient solar radiation depleted of UVB radiation (UVBR) and ambient solar radiation depleted of both UVBR and UVAR. Subsequently, germination rates were determined after exposure to favourable light and temperature conditions in the laboratory. 3The radiation regime was monitored at the water surface and in the water column using data loggers attached adjacent to each experimental platform for the duration of the field exposure. 4Under ambient solar radiation, the tolerance of zoospores to UVR was highest in the shallow water species S. dermatodea, intermediate in the upper to mid sublittoral A. esculenta and lowest in the upper to mid sublittoral L. digitata. There was, however, no difference in the susceptibility of the zoospores to ambient solar radiation or to solar radiation depleted of UVBR. 5The water column was relatively UV transparent, especially in the upper water layers. The 1% UVB depth ranged between 5.35 and 6.87 m, although on one stormy day the 1% UVB depth was only 3.57 m, indicating resuspension of sediments. 6Early developmental stages are most susceptible to environmental stress. Tolerance of zoospores to UVR is a major if not one of the most important factors determining the upper distribution limit of different Laminariales on the shore. 7Kelps are very important primary producers in inshore coastal ecosystems, serving as food for herbivores and as habitat for many organisms. Enhanced UVBR due to stratospheric ozone depletion may lead to changes in the depth distribution of kelps and may cause significant ecological domino effects. [source]

Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa

A COMPREHENSIVE STUDY OF THE LIFE CYCLE OF A SOUTH AMERICAN POPULATION OF STIGEOCLONIUM TENUE (CHAETOPHORALES, CHLOROPHYTA),

PSEUDULVELLA AMERICANA BELONGS TO THE ORDER CHAETOPELTIDALES (CLASS CHLOROPHYCEAE), EVIDENCE FROM ULTRASTRUCTURE AND SSU RDNA SEQUENCE DATA,

JOURNAL OF PHYCOLOGY, Issue 4 2006
M. Virginia Sanchez-Puerta
The genus Pseudulvella Wille 1909 includes epiphytic, freshwater, or marine disk-shaped green microalgae that form quadriflagellate zoospores. No ultrastructural or molecular studies have been conducted on the genus, and its evolutionary relationships remain unclear. The purpose of the present study is to describe the life history, ultrastructural features, and phylogenetic affiliations of Pseudulvella americana (Snow) Wille, the type species of the genus. Thalli of this microalga were prostrate and composed of radiating branched filaments that coalesced to form a disk. Vegetative cells had a pyrenoid encircled by starch plates and traversed by one or two convoluted cytoplasmic channels. They had well-defined cell walls without plasmodesmata. Asexual reproduction was by means of tetraflagellate zoospores formed in numbers of two to eight from central cells of the thallus. The flagellar apparatus of zoospores was cruciate, with four basal bodies and four microtubular roots. The paired basal bodies lay directly opposite (DO) one another. The microtubular root system had a 5-2-5-2 alternation pattern, where the "s" roots contained five microtubules in a four-over-one configuration. A tetralobate nonstriated distal fiber connected all four basal bodies. A wedge-shaped proximal sheath subtended each of the basal bodies. The ultrastructural features of the zoospores were those of members of the order Chaetopeltidales. Phylogenetic analyses based on SSU rDNA placed P. americana sister to Chaetopeltis orbicularis in a well-supported Chaetopeltidales clade. Such a combination of features confirmed that this alga is a member of the order Chaetopeltidales. [source]

PRESENCE OF SPOROPHYLLS IN FLOATING KELP RAFTS OF MACROCYSTIS SPP. (PHAEOPHYCEAE) ALONG THE CHILEAN PACIFIC COAST,

JOURNAL OF PHYCOLOGY, Issue 5 2005
Erasmo C. Macaya
Some species of macroalgae continue to live for extended periods of time after detachment and may even maintain reproductive structures, yet very little is known about this process. Here, we describe the presence of sporophylls (with sporogenous tissues) on floating kelp rafts of Macrocystis spp. along the coast of Chile. Surveys were conducted at nine sites (18,50° S) during austral summer 2002, and floating kelp rafts were seen and collected at seven of these nine sites (between 22 and 50° S). Fifteen (26.8%) of the 56 samples had sporophylls, indicating maintenance of sporophylls after detachment. Some of the kelp sporophytes with reproductive blades showed signs of having been afloat for long periods (indicated by the large size of attached stalked barnacles). Additionally, experiments showed that floating kelps released viable zoospores. To understand the reproductive dynamics of floating kelps, we compared these results with information from attached populations of Macrocystis spp. at nearby coastal sites. In general, attached kelp had higher proportions of sporophylls than floating rafts, suggesting that detachment may negatively affect reproductive status. Nevertheless, floating kelps remained functionally reproductive, suggesting that zoospores may be dispersed via floating rafts. Published reports on other macroalgae indicate that some species (Lessoniaceae, Fucaceae, and Sargassaceae) are fertile and probably release zoospores or zygotes while floating or drifting in ocean currents. Because dispersal distances achieved by spores of most macroalgae are relatively short, release of spores from floating algae may be an alternative mechanism of long-distance dispersal. [source]

HOST PARASITE INTERACTIONS BETWEEN FRESHWATER PHYTOPLANKTON AND CHYTRID FUNGI (CHYTRIDIOMYCOTA),

Ultrastructure of Lobocharacium coloradoense, gen. et sp. nov. (Chlorophyta, Characiosiphonaceae), an unusual coenocyte from Colorado

Fungicide Effectiveness during the Various Developmental Stages of Peronophythora litchii In Vitro

JOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2009
Hancheng Wang
Abstract Litchi downy blight caused by Peronophythora litchii is one of the most destructive diseases suffered by litchi in China. This study has evaluated the activities of the fungicides dimethomorph (DMM), azoxystrobin (AZB), famoxadone (FMD), metalaxyl (MTL), cymoxanil (CYX) and mancozeb (MCB) on the mycelial growth, sporulation, zoospores release, and germination of sporangia as well as of cystospores of P. litchii. Dimethomorph and MTL inhibited mycelial growth more effectively than the other fungicides tested. Mycelial growth was affected less by MCB, and only weakly by AZB, FMD and CYX. Sporangia production was more strongly reduced by DMM and MTL than by AZB, FMD, CYX or MCB. Zoospore release from the sporangia was most sensitive to AZB and FMD, less sensitive to MCB and insensitive to DMM, MTL and CYX. Direct germination of sporangia of P. litchii was the most strongly inhibited by AZB and FMD, followed by DMM and MCB, whilst the sensitivity of this life stage to MTL and CYX was relatively low. Germination of encysted zoospores of P. litchii was the most sensitive to AZB and FMD, followed by DMM. Mancozeb was moderately active, while MTL and CYX did not inhibit this development stage. This is the first report on the in vitro response of the litchi pathogen, P. litchii, to fungicides. These findings can be valuable tools in setting up efficient disease management programmes to control litchi downy blight. [source]

Defence Responses of Calli and Seeds of Hevea brasiliensis to Zoospores and the Elicitin of Phytophthora palmivora

Conditions for Infection of Apple by Phytophthora syringae

JOURNAL OF PHYTOPATHOLOGY, Issue 4 2003
D. C. Harris
Abstract The processes leading to Phytophthora fruit rot were divided into two main stages for the purposes of investigating the effects of temperature and duration of wet periods on pathogen development: oospore germination and infection of fruit by zoospores. It was found that the first stage was markedly affected by temperature over the range 10,20°C and required a wet period of 4,7 days. At 18 and 20°C, activation was low regardless of the length of the wet period. Once oospore germination (first stage) had occurred, free water was necessary for only a few hours for fruit infection (second stage) to occur, but the incidence of infection rose rapidly over the first 48 h, regardless of temperature over the range 10,20°C. From the data obtained, mathematical models were produced relating the incidence of Phytophthora fruit rot to the two weather variables. These models can be used to develop a weather-based risk assessment system for the disease. [source]

Effects of hydrostatic pressure, agitation and CO2 stress on Phytophthora nicotianae zoospore survival

PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2010
Monday O Ahonsi
Abstract BACKGROUND:Phytophthora nicotianae Breda de Haan is a common pathogen of ornamental plants in recycled irrigation systems. In a previous study, annual vinca (Catharanthus roseus Don) inoculated with zoospore suspensions using a CO2 -pressurized sprayer had less foliage blight than plants inoculated using a hand sprayer. Here, the impact of hydrostatic pressure, agitation and aeration with CO2 on the survival of P. nicotianae zoospores was examined. RESULTS: Exposure of zoospores to 840 kPa hydrostatic pressure for 8 min or agitation at a mixing intensity (G) of 6483 s,1 for 4 min at 22,23 °C did not kill zoospores, but resulted in viable cysts. Motile and forcefully encysted zoospores of P. nicotianae were equally infectious on vinca or lupine (Lupinus polyphylus Lindl.). Bubbling CO2 into zoospore-infested water at 110.4 mL (0.2 g) min,1 for 5 min caused 81% reduction in the number of germinated zoospores. Pressure at 630 kPa (16.3 g CO2) or 70 kPa (3.85 g CO2) facilitated CO2 injection and shortened the zoospore inactivation time to 30 s. When air was bubbled through the suspension, germination was similar to the control. CONCLUSIONS: Exposure to CO2 killed P. nicotianae zoospores in water. Neither pressure nor agitation had an effect on zoospore viability or infectivity. Based on results of this study, the authors designed a recycling CO2 water treatment system that is currently under evaluation. Copyright © 2010 Society of Chemical Industry [source]

Zoospores of Three Arctic Laminariales Under Different UV Radiation and Temperature Conditions: Exceptional Spectral Absorbance Properties and Lack of Phlorotannin Induction

Zoospore-specific antigen as a useful marker for molecular analysis of net formation in Hydrodictyon reticulatum (Chlorococcales, Chlorophyceae)

PHYCOLOGICAL RESEARCH, Issue 3 2000
Kyoko Hatano
SUMMARY In the green alga Hydrodictyon reticulatum zoospores are arranged in a regular fashion to form an intricate hexagonal network during the asexual reproductive cycle. A monoclonal antibody which was raised against a homogenate of zoospores recognized a single poly-peptide in zoospores with a molecular mass of 31 kDa. The antigenic polypeptide, which was designated Amy1, was localized within the cytoplasm of zoospores. The accumulation of Amy1 occurred concomitantly with the transition from multinuclear vegetative cells to mononuclear zoospores, and the degradation of Amy1 occurred concomitantly with the further development of zoospores. Amy1 was constantly expressed during the period of mononuclear zoospores. Thus, we conclude that Amy1 is a zoospore-specific polypeptide. Using the anti-Amy1 monoclonal antibody, we could easily distinguish between mononuclear zoospores and multinuclear vegetative net-cells. This provides an important tool for analysing the molecular mechanisms involved in the hexagonal net formation by zoospores. [source]

The mode of interaction between Vitis and Plasmopara viticola Berk.

PLANT BIOLOGY, Issue 6 2009
& Curt.
Abstract In order to obtain insight into host responses to grapevine downy mildew (Plasmopara viticola), we compared pathogen development on a panel of Vitis species from North America, Asia and Europe. Leaf discs from different host species were inoculated in parallel, and the colonisation of the mesophyll was visualised by aniline blue staining and quantified with respect to infection incidence and mycelial growth. In parallel, the morphology of guard cells was screened for the presence of an internal cuticular rim after staining with acridine orange and using low-temperature scanning electron microscopy. We observed three response patterns: (i) inhibition of pathogen development early after attachment of zoospores; (ii) successful colonisation of the mesophyll by the pathogen; and (iii) aberrant development, where the pathogen does not attach to guard cells, but produces hyphae on the leaf surface without formation of viable sporangiophores. Inhibition is observed in the North American and Siberian species, successful colonisation prevails in the European hosts, and surface hyphae are found on non-Siberian Asiatic species. We propose that the interaction between host and pathogen is under control of specific signals that have been subject to evolutionary diversification. [source]