Effect of solar ultraviolet radiation on growth in the marine macroalga Dictyota dichotoma (Phaeophyceae) at Helgoland and its ecological consequences

At Helgoland, in the North Sea, growth of the high sublittoral brown macroalga Dictyota dichotoma (Hudson) Lamoroux was examined in October (the time of tetraspore release) in an outdoor tank by exposing 2-day-old germlings to four solar radiation treatments achieved with different filter materials or an additional artificial light source: photosynthetically active radiation (PAR; 395–700 nm), PAR plus ultraviolet (UV)-A (320–700 nm), full solar spectrum, or solar spectrum plus artificial UV radiation (UVR). Based on length measurements over a period of 3 weeks, the growth rate in germlings strongly decreased in conditions with UVR compared to PAR: by 14% under PAR+UV-A, by 31% under the full solar spectrum and by 65% with additional UVR. Although growth rates of germlings under UVR were reduced mainly in the first week, the plants did not regain the size of the untreated plants even after 9 weeks. Regardless of the exposure, no defects in morphology or anatomy including the exposed apical meristem were detected, except for a reduction in cell division rates perhaps due to additional cost for photoprotective or repair mechanisms. Depending on the actual position of D. dichotoma plants in the natural habitat, individuals in high positions receive substantial amounts of the more harmful UV-B while those lower down might only receive UV-A during part of the day, thus the effect of UV-B on the growth of D. dichotoma will depend on its position in the field. The effects of tidal variation of the light climate and the implications of our results for the zonation of D. dichotoma are discussed. Received in revised form: 6 July 2000 Electronic Publication     

Environmental influences on akinete germination and development in Nodularia spumigena (Cyanobacteriaceae), isolated from the Gippsland Lakes, Victoria, Australia

This study was carried out to investigate the genesis of N. spumigena blooms by specifically studying the effects of environmental variables (salinity, nitrogen, phosphorus and light) on the germination of N. spumigena akinetes. Optimal conditions for maximum germination and germling growth were determined by exposing akinetes to a range of salinities and nutrient (nitrogen and phosphorus) concentrations under two different irradiances. At pre-determined time periods, treatments were sampled and the percent germination and length of germlings assessed. The results indicated that akinete germination and germling growth were optimal at salinities from 5 to 25 and significantly reduced outside this range. A positive correlation in germination was observed with increasing nutrient (phosphorus and nitrate) concentration. Similarly, germling growth increased with increasing concentrations of both nutrients. Irradiance significantly influenced both germination and growth during salinity experiments, whereas in nutrient addition experiments, irradiance had no effect on germination; however, growth was significantly influenced during phosphorus addition experiments. Consequently, salinity and light appeared to be most critical in the germination process for N. spumigena akinetes, with phosphorus most important for germling growth. The study showed that N. spumigena may be able to germinate under environmental conditions outside its optimal range, but the growth of the germling is significantly reduced, which in turn suggests that its ability to form a bloom outside its optimal environmental conditions would also be greatly reduced.     

Modeling variation in interaction strength between barnacles and fucoids

The strength by which species interact can vary throughout their ontogeny, as environments vary in space and time, and with the density of their populations. Characterizing strengths of interaction in situ for even a small number of species is logistically difficult and may apply only to those conditions under which the estimates were derived. We sought to combine data from field experiments estimating interaction strength of life stages of the barnacle, Semibalanus balanoides, on germlings of Ascophyllum nodosum, with a model that explored the consequences of variability at per capita and per population levels to the abundance of year-old algal recruits. We further simulated how this interaction affected fucoid germling abundance as the timing of their respective settlements varied relative to one another, as occurs regionally across the Gulf of Maine, USA. Juvenile S. balanoides have a weak estimated per capita effect on germlings. Germling populations are sensitive to variation in per capita effects of juvenile barnacles because of the typically large population sizes of the latter. However, high mortality of juvenile barnacles weakens the population interaction strength over time. Adult barnacles probably weakly facilitate fucoid germlings, but greater survival of adults sustains the strength of that interaction at the population level. Germling abundance is positively associated with densities of adult barnacles and negatively associated with that of juvenile barnacles. Metamorphosing cyprid larvae have the strongest per capita effect on germling abundance, but the interaction between the two stages is so short-lived that germling abundance is altered little. Variation in the timing of barnacle and A. nodosum settlement relative to one another had very little influence on the abundance of yearling germlings. Interactions between barnacles and germlings may influence the demographic structure of A. nodosum populations and the persistence of fucoid-dominated communities on sheltered rocky shores in New England. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Substrate Hydrophobicity and Adhesion of Uromyces Urediospores and Germlings

Terhune, B. T., and Hoch, A. C. 1993. Substrate hydrophobicity and adhesion of Uromyces urediospores and germlings. Experimental Mycology 17, 241-252. Adhesions of urediospores and urediospore germlings of Uromyces appendiculatus, the bean rust pathogen, to various substrata was evaluated with regard to surface wettability. A range of surface wettabilities, or conversely hydrophobicities, was obtained by coating glass or quartz substrates with various organosilanes. Adhesion of urediospores or germlings was evaluated after the spore or germling laden-silanized surfaces were washed. Both urediospores and germlings adhered most tenaciously to surfaces with wettability ratings less than 30. Such surfaces were polystyrene and glass treated with dimethyldichlorosilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichorosilane, and diphenyldichlorosilane. The degree of germling contact to the various surfaces correlated closely with hydrophobicity and with the adhesion of germlings. Induction of appressoria on quartz substrates bearing inductive topographies (0.5-μm-deep grooves) was also closely associated with the degree of hydrophobicity.     

NICHE PARTITIONING AND THE COEXISTENCE OF TWO CRYPTIC DICTYOTA (DICTYOTALES,PHAEOPHYCEAE) SPECIES FROM THE CANARY ISLANDS1

Coexistence in a homogeneous environment requires species to specialize in distinct niches. Sympatry of cryptic species is of special interest to both ecologists and evolutionary biologists because the mechanisms that facilitate their persistent coexistence are obscure. In this study, we report on two sympatric Dictyota species, D. dichotoma (Huds.) J. V. Lamour. and the newly described species D. cymatophila sp. nov., from the Canary Islands. Gene sequence data (rbcL, psbA, nad1, cox1, cox3, and LSU rDNA) demonstrate that D. dichotoma and D. cymatophila do not represent sister species. Rather, D. cymatophila and D. dichotoma have converged on a nearly identical morphology, only to be distinguished with detailed morphometric observations. Both species co‐occur in eulittoral pools and the shallow subtidal in Tenerife. Even though D. cymatophila was more dominant in wave‐exposed places and D. dichotoma in less exposed areas, the spatial distribution of both species overlapped in intermediate habitats. The species display radically different phenologies. D. dichotoma reached its highest density in winter and early spring and disappeared nearly completely in autumn, while D. cymatophila dominated the study site from July until November. The timing of gamete release also differs between both species, D. dichotoma releasing gametes twice every lunar cycle, while the release of gametes in D. cymatophila occurred roughly every other day.     

Early development of germlings of <Emphasis Type="Italic">Sargassum thunbergii</Emphasis> (Fucales,Phaeophyta) under laboratory conditions

Morphology and culture studies on germlings of Sargassum thunbergii (Mertens et Roth) Kuntze were carried out under controlled laboratory conditions. Growth characteristics of these germlings grown under different temperatures (from 10 to 25°C), irradiances (from 9 to 88 μmol photons m⁻² s⁻¹), and under blue and white light conditions are described. The development of embryonic germlings follows the classic “8 nuclei 1 egg” type described for Sargassaceae. Fertilized eggs spent 5–6 h developing into multicellular germlings with abundant rhizoids after fertilization. Under conditions of 20°C, 44 μmol photons m⁻² s⁻¹ and photoperiod of 12 h, young germlings with one or two leaflets reached 2–3 mm in length after 8 weeks. Temperature variations (10, 15, 20, 25°C) under 88 μmol photons m⁻² s⁻¹ significantly influenced the growth rate within the first week, although this effect became less obvious after 8 weeks, especially at 15 and 20°C. Variation in germling growth was highly significant under different irradiances (9, 18, 44, 88 μmol photons m⁻² s⁻¹) at 25°C. Low temperature (10°C) reduced germling growth. Growth of germlings cultured under blue light was lower than in white light. Optimal growth of these germlings occurred at 25°C and 44 μmol photons m⁻² s⁻¹.     

CHLOROPELTA GEN. NOV., AN ULVACEOUS GREEN ALGA WITH A DIFFERENT TYPE.OF DEVELOPMENT1

A diminutive, distromatic ulvaceous green alga was collected in southern California and studied in culture. The initial stages of development resemble those found in the Ulvaceae sensu Bliding. Germlings pass through a uniseriate filamentous stage, a multiseriate stage and a monostromatic saccate stage. At this stage the development departs from the developmental patterns found in the Ulvaceae. Each cell of the monostromatic upright portion of the germling undergoes a single division in a plane parallel to the surface of the germling to form a distromatic saccate germling. Rupture of the apical end of the germling and continued growth eventually results in a peltate distromatic alga superficially resembling Ulva. Based on the developmental pattern, which is unique to the green algae, the new genus Chloropelta gen. nov. and new species Chloropelta caespitosa sp. nov. are proposed for this alga.     

Photosystem 2 activities of hyper-accumulator Dicranopteris dichotoma Bernh from a light rare earth elements mine

The distribution of rare earth elements (REEs) in the fern Dicranopteris dichotoma Bernh plants from a light rare earth elements mine (LRM) and a non-mining (NM) area in Longnan county of Jiangxi province, China were investigated by means of inductively coupled plasma-mass spectrometry, transmission electron microscopy, and energy-dispersive X-ray microanalysis. The photosynthetic characteristics of D. dichotoma were studied by chlorophyll (Chl) a fluorescence kinetics. Contents of REEs in the lamina and the root of D. dichotoma were higher than those in soils, and were mainly distributed in lamina. A part of them was found in the chloroplast. By comparing with D. dichotoma from NM area, the efficiency of photosystem 2 photochemistry and electron transport rate were significantly enhanced in lamina of the plant from LRM because most of REEs deposits were distributed along cell wall, in vacuole, and in chloroplast. High contents of REEs in lamina did not decrease the photosynthetic activities in LRM plants of D. dichotoma. Besides, D. dichotoma could change its β-carotene content to avoid the damaging effect of high REEs content.     

DISAPPEARANCE OF MALE MITOCHONDRIAL DNA AFTER THE FOUR‐CELL STAGE IN SPOROPHYTES OF THE ISOGAMOUS BROWN ALGA SCYTOSIPHON LOMENTARIA (SCYTOSIPHONACEAE,PHAEOPHYCEAE)1

Mitochondrial DNA (mtDNA) of the isogamous brown alga Scytosiphon lomentaria (Lyngb.) Link is inherited maternally. We used molecular biological and morphological analyses to investigate the fate of male mitochondria. Ultrastructural observations showed that the number of 25 mitochondria in a zygote coincided with the number of mitochondria derived from male and female gametes. This number remained almost constant during the first cell division. Strain‐specific PCR in single germlings suggested that mtDNA derived from the female gamete remained in the germling during development, while the male mtDNA gradually and selectively disappeared after the four‐cell stage. One week after fertilization, male mtDNA had disappeared in sporophytic cells. Using bisulfite DNA modification and methylation mapping assays, we found that the degree of methylation on three analyzed sites of mtDNA was not different between male and female gametes, suggesting that maternal inheritance of mtDNA is not defined by its methylation. This study indicates that the mechanism of selective elimination of male mtDNA is present in each cell of a four‐celled sporophyte and that it does not depend on different degrees of DNA methylation between male and female mtDNA.     

Comparing salinity tolerance in early stages of the sporophytes of a non-indigenous kelp (Undaria pinnatifida) and a native kelp (Saccharina latissima)

The short-term effects of low salinities on the survival of germlings of an introduced kelp Undaria pinnatifida and a native kelp Saccharina latissima were assessed under laboratory conditions. This experiment was designed to compare the differential stress tolerance to salinity of the early life history stages of sporophytes of these two kelps that co-occur on European Atlantic coasts. Germlings (young sporophytes) of both species were exposed for 4 days to salinities ranging from 31 (control) to 26, 21, 16, 11, and 6 psu. Afterwards, they were post-cultured in control seawater (31 psu) for another 4 days to corroborate the viability of injured germlings. Results showed that germlings of the introduced kelp were less resistant to low salinity, surviving to as low as 16 psu; whereas the germlings of the native kelp survived in salinities as low as 11 psu. Despite the observed differences, both species are relatively tolerant to low salinity. Our observations also indicated that, at least in a short term, gametophytes of both species were able to survive in salinities as low as 6 psu. The significance of low-salinity tolerance to the distribution of these kelps and for their offshore cultivation is discussed.     

THE HORMESIS OF THE GREEN MACROALGA ULVA FASCIATA WITH LOW‐DOSE 60COBALT GAMMA RADIATION1

Homogenous germlings of the marine macroalga Ulva fasciata D. (synonym, Ulva lactuca L.) were used to study hormesis effects in macroalgae grown under a low dose of ⁶⁰Co γ‐ray radiation. The results of this study are the first to confirm the effects of macroalgal hormesis. Here it was demonstrated that growth of U. fasciata germlings was promoted substantially under 15 Gy of ⁶⁰Co γ‐ray radiation, with an average increase of algal biomass of 47.43%. The levels of polysaccharides and lipids varied among the tested material and showed no effects from the ⁶⁰Co γ‐ray radiation. However, the amount of protein was higher in the irradiated algae than in the control; the highest protein content of the irradiated algae was 3.958% (dry weight), in contrast to 2.318% in nonirradiated samples. This technique was applied to a field algal mass culture, which decreased the harvest time from 90 to 60 d. The mass culture approach may facilitate the production of macroalgae under unstable weather conditions such as typhoons in the summer or strong waves in the winter. The mass‐cultured macroalgae could be used as a source of bioenergy through the fermentation of algal simple sugars that derived from polysaccharides to produce ethanol.     

Electron microscopic examination of ribosome preparations from germinated spores of Aspergillus fumigatus

Ribosomes were isolated from germinated spores (germlings) of Aspergillus fumigatus and electron microscopy was used to determine qualitatively the extent of cellular contamination. After differential centrifugation, the initial crude preparation contained 80S ribosomes and numerous membrane contaminants in the form of membrane sheets, palisade aggregates, and vesicles 0.10–0.18 m in size. Gel filtration chromatography of crude ribosomes in Sepharose CL-4B did not remove all of the membrane contamination. Homogenous ribosome suspensions, morphologically free of other cellular component contamination, were then obtained after gel filtration fractions were centrifuged through a 35% sucrose solution. The total ribosome yield from a germling preparation was approximately four times the yield of ribosomes from a comparable spore preparation. Gel diffusion precipitin patterns of germling ribosomes were identical to those of spore ribosomes with both germling and spore ribosomes antisera.     

侵蚀退化地植被恢复过程中芒萁对土壤可溶性有机碳的影响

林下植被是生态系统的重要组分。通过对比分析红壤侵蚀区植被恢复过程中,林下有无芒萁覆盖地的土壤可溶性有机碳(DOC,Dissolved Organic Carbon)含量及其与地下根系生物量、地上植被淋溶液DOC含量的关系。结果表明:林下植被芒萁覆盖增加了地上叶片和地下根系生物量,土壤DOC含量及储量也显著增加(P0.05),芒萁覆盖对表层土壤(0—20cm)DOC的影响大于深层土壤(20—100cm)(P0.05);相关分析结果表明,林下芒萁覆盖地土壤DOC储量与细根生物量的垂直变化呈显著的正相关关系(P0.05),且随植被恢复年限的增加相关性显著增加,地下根系的垂直分布直接影响各土层DOC储量。不同植被恢复时期,林下芒萁覆盖地土壤DOC与鲜叶(马尾松+芒萁)和枯落物(马尾松+芒萁)淋溶液DOC均呈显著的正相关关系(P0.01),而林下裸露地土壤DOC仅与鲜叶(马尾松)淋溶液DOC呈显著的相关性(P0.01),林下芒萁覆盖地相对于裸露地枯落物淋溶液对土壤DOC储量的影响大于鲜叶。植被恢复过程中芒萁覆盖地土壤微生物生物量碳和微生物熵显著高于林下裸露地。因此,在植被恢复进程中,芒萁能够提供更多底物参与土壤物质与养分循环,对土壤DOC的贡献较大,为侵蚀区马尾松林恢复提供了重要的养分再吸收来源;同时芒萁覆盖增加了微生物活性,促进了微生物对土壤DOC的同化作用,提高了微生物碳源的利用率,对土壤有机碳的积累起着重要的作用。     

Genome Wide Association Identifies Novel Loci Involved in Fungal Communication

Understanding how genomes encode complex cellular and organismal behaviors has become the outstanding challenge of modern genetics. Unlike classical screening methods, analysis of genetic variation that occurs naturally in wild populations can enable rapid, genome-scale mapping of genotype to phenotype with a medium-throughput experimental design. Here we describe the results of the first genome-wide association study (GWAS) used to identify novel loci underlying trait variation in a microbial eukaryote, harnessing wild isolates of the filamentous fungus Neurospora crassa. We genotyped each of a population of wild Louisiana strains at 1 million genetic loci genome-wide, and we used these genotypes to map genetic determinants of microbial communication. In N. crassa, germinated asexual spores (germlings) sense the presence of other germlings, grow toward them in a coordinated fashion, and fuse. We evaluated germlings of each strain for their ability to chemically sense, chemotropically seek, and undergo cell fusion, and we subjected these trait measurements to GWAS. This analysis identified one gene, NCU04379 (cse-1, encoding a homolog of a neuronal calcium sensor), at which inheritance was strongly associated with the efficiency of germling communication. Deletion of cse-1 significantly impaired germling communication and fusion, and two genes encoding predicted interaction partners of CSE1 were also required for the communication trait. Additionally, mining our association results for signaling and secretion genes with a potential role in germling communication, we validated six more previously unknown molecular players, including a secreted protease and two other genes whose deletion conferred a novel phenotype of increased communication and multi-germling fusion. Our results establish protein secretion as a linchpin of germling communication in N. crassa and shed light on the regulation of communication molecules in this fungus. Our study demonstrates the power of population-genetic analyses for the rapid identification of genes contributing to complex traits in microbial species.     

Leucine-lysine synchronization of Allomyces germlings

Summary The leucine-lysine synchronization technique of Dill and Fuller (1970) has been further refined and used to study various biosynthetic events of pre-mitotic germlings of Allomyces neo-moniliformis (the time of DNA replication, RNA synthesis, and protein synthesis), and various morphogenetic changes (germling development, nuclear cap breakdown, and the first mitotic nuclear division). The degree of synchrony induced in a population of germlings appears to be determined by the time when the zoospores are induced to encyst and germinate rather than by the duration of the swimming period of the zoospore. DNA replication, nuclear cap breakdown, early protein synthesis, and morphogenetic development appear to occur prior to messenger RNA synthesis in developing thalli and thus would be under the control of pre-existing messenger RNA. The degree of synchrony of particular morphogenetic or biosynthetic developmental changes induced in a population of A. neo-moniliformis germlings must be determined for each aspect of development which is to be studied.     

Carpospore early development and callus-like tissue induction of <Emphasis Type="Italic">Chrysymenia wrightii</Emphasis> (Rhodymeniaceae,Rhodophyta) under laboratory conditions

Morphological and culture studies of germlings derived from carpospores of Chrysymenia wrightii (Harvey) Yamada were carried out under various treatments combining temperature and irradiance. Basal, main, and tip branches were applied for inducing callus-like tissue. Focus was on how carpospores develop into germlings, how callus-like tissues are induced from explants, and how temperature and irradiance affect carpospore germination and discoid crust growth. Results show that carpospore development can be divided into three stages: division stage, discoid crust stage, and erect juvenile germling stage. Discoid crusts, even more than ten, might coalesce into a big discoid crust, and then developed into germlings. Filamentous fronds, formed on the rims of discoid crusts, exhibited in self-existence or co-existence form with germlings, could form spherical tufts if cultured separately. Filamentous callus-like tissues appeared on the tip branches after 13 days. PES is suitable for filament induction and culture, and filaments have potential use in germplasm preservation and vegetative propagation. Temperature (10, 15, 20, 25°C) and irradiance (8 and 36 μmol photons m⁻² s⁻¹) significantly influenced carpospore germination rate and discoid crust diameter. Carpospores germinated normally under 36 μmol photons m⁻² s⁻¹, 15~25°C, and maximum growth of discoid crusts was at 25°C, 36 μmol photons m⁻² s⁻¹; 10°C and 8 μmol photons m⁻² s⁻¹ did not favor carpospore germination or discoid crust growth.     

Tank cultivation of <Emphasis Type="Italic">Ulva prolifera</Emphasis> in deep seawater using a new “germling cluster” method

A new “germling cluster” method is proposed for tank cultivation of seaweed in a free-floating form. This method was applied to the tank cultivation of Ulva prolifera using deep seawater (DSW) pumped up from over 300 m depth off the cape of Muroto in southwest Japan. Numerous zoids of U. prolifera were induced by cutting thalli into 1–2 mm long pieces. Three days after fragment production, the zoids were released. The zoid suspension was concentrated to a density of more than 10⁴ zoids per mL medium, and placed in a Petri dish for culture. The dense, germinating zoids began to adhere to each other and form aggregations. The germling aggregations were then removed from the bottom of the dish and torn into a large number of small “germling clusters” using an electric mixer. Each cluster contained 10–100 germlings. Once the germling clusters had attained more than 5 mm diameter in culture, they were transplanted as free-floating forms to a 500 L outdoor tank with continuous aeration, to which DSW was supplied at an exchange rate of 3 volumes per day. As a result, the average daily growth rate (DGR) in the tank throughout the year was 37%, though the DGR fluctuated with seasonal temperature changes.     

Zygote-derived seedling production of Sargassum thunbergii: focus on two frequently experienced constraints in tank culture of seaweed

Mass collection of germlings and growth of fouling algae are two main constraints for the seedling production of Sargassum thunbergii. In this study, 65% and 40% of reproductive output (allocation of biomass to sexual reproductive tissue) for farmed and natural populations respectively, were recorded during peak reproduction. In terms of germlings per kilogram wet weight of plants, the farmed population gave a higher yield than the natural population (3.2?×?10⁵ and 1.2?×?10⁵ germlings kg^-1, respectively). These results indicate that farmed populations could be used as parental plants for germling collection in seedling production. During the experiment, fouling was controlled by jet washing and high-density seeding. A germling detachment of less than 10% was observed when, after 48?h of attachment, collectors were jet-washed with an intensity of 1?kg cm^-2. High-density seeding had adverse effects on length mean, size equality, and occurrence of branches of germlings. However, 30–50 individuals cm^-2 are thought to be usable in the seedling production of S. thunbergii because of less density effects. Seedlings of?>?0.5?cm length could be achieved after 1?month of tank culture.     

Combined effects of temperature and salinity on growth rates of germlings of threeFucus species from iceland,helgoland and the north adriatic sea

The growth rate of germlings of threeFucus species (F. distichus subsp.edentatus from Iceland,F. vesiculosus from Helgoland, North Sea, andF. virsoides from the North Adriatic Sea) has been investigated under different temperature and salinity conditions. The highest growth rate and the maximum elongation factor were found at 9° C forF. distichus; in the other two species growth increased with increasing temperature. Growth decreases with dilution in the three species under consideration. A rather low tolerance to dilution was observed inF. vesiculosus germlings. In view of the overall distribution of the latter species the opposite was expected. It seems likely, however, that susceptible strains have developed at Helgoland, where salinity rarely drops below 30.