bluuebunny/crossref_metadata_2025 huggingface dataset:
Camptothecin production in Camptotheca acuminata seedlings in response to shading and flooding
Authors: Liu Zhijun , Carpenter Stanley B. , Constantin Roysell J.
Published: April 2011

One-year-old Camptotheca acuminata seedlings were grown under heavy shade (27% full sunlight), slight shade (67% full sunlight), or full sunlight for 2 weeks, then subjected to flooding for 4 weeks under continued shading schemes. Growth, chlorophyll fluorescence, and camptothecin concentrations were determined. Flooding led to significant decreases in leaf biomass, while shading significantly increased stem biomass. Under full sunlight or slight shade conditions, lateral root biomass was significantly decreased by flooding, whereas under heavy shade, it was not significantly reduced by flooding. Shaded leaves displayed significantly higher chlorophyll fluorescence than the non-shaded leaves throughout the 6-week period. Onset of flooding caused immediate decline of chlorophyll fluorescence of nonshaded and slight-shaded seedlings, but the effect of flooding quickly diminished. Heavy shade led to elevated camptothecin concentrations in leaves, whereas flooding had no effect. Camptothecin concentrations in stems were not altered by either flooding or shading; however, they were substantially lowered in lateral roots under heavy shade compared with those grown in full sunlight. Flooding induced an additional camptothecin accumulation in lateral roots under slight shade, but it failed to do so under either heavy shade or full sunlight conditions. Key words: anti-tumor compounds, camptothecin, chlorophyll fluorescence, flooding, secondary metabolites, shading.
Regulation of extracellular proteases in Achlya ambisexualis
Authors: Hill Terry W. , Pott Markus P.
Published: April 2011

The use of proteins as a nutrient source by Achlya ambisexualis was investigated, using media containing defined and undefined sources of carbon, nitrogen, and (or) sulfur. Release of extracellular proteases occurred during growth on all proteins and protein hydrolysates tested, but not during growth on yeast extract or in defined medium. In gelatin-containing media, three major bands of extracellular protease activity were detected by electrophoresis, with estimated molecular mass of 26, 48, and 58 kDa. Growth on gelatin was stimulated to a much greater degree by the addition of glucose to the medium than by additions of glutamic acid or methionine. This and the release of ammonia during growth indicate that gelatin is less effective in meeting metabolic needs for carbon than it is in meeting the needs for nitrogen and sulfur. Protease secretion is only partially regulated by glucose, whereas glucose, methionine, and glutamic acid in combination cause almost complete repression. The pattern of regulation indicated by these results is most consistent with one of induction + derepression. Key words: oomycetes, proteinases, regulation, secreted enzymes.
Effect of sexual systems and dichogamy on levels of abortion and biomass allocation in plant reproductive structures
Authors: Ramirez Nelson , Berry Paul E.
Published: April 2011

The levels of abortion at three stages (ovule, seed, and flower–fruit) and biomass allocation to flowers, seeds, and fruits were determined in 231 species from five Venezuelan plant communities. These values were analyzed as a function of the sexual systems of the plants and the presence of dichogamy. In this study, the only significant difference between sexual systems was in the level of ovule abortion, which was greater in dioecious and hermaphroditic species than in monoecious and andromonoecious species. Species with protandrous or protogynous flowers had higher seed set and lower levels of aborted ovules and aborted flowers and fruits than species with adichogamous flowers. These results indicate that hermaphroditic plants do not compensate for their inability to independently control the number of male and female flowers by producing an excess of flowers that function mainly as pollen donors. On the other hand, the temporal separation of male and female functions in hermaphroditic and monoecious species may contribute to increased seed and fruit set by enhancing reallocation of assimilates from floral organs or flowers to fruit formation in time, and by reducing pollen–stigma interference within plants. Key words: fruit abortion, ovule abortion, dichogamy, sexuality, biomass allocation.
Relationship of soil properties and soil amendments to response of Glomus intraradices and soybeans
Authors: Frey J. E. , Ellis J. R.
Published: April 2011

Knowledge of the role of soil properties on mycorrhizal relationships with host plants may contribute to the ecological understanding of the fungus and its effectiveness in indigenous or introduced soil conditions. This study examined the response of Glomus intraradices, an arbuscular mycorrhizal (AM) fungus, and soybean host in five benchmark soils. Glomus intraradices increased, with a few exceptions, shoot dry weight, root length, shoot phosphorus, and shoot zinc in all soils. Soil amendments (nitrogen, phosphorus, and pH adjustments) affected mycorrhizal hyphal length per plant and hyphal to root length ratio, as well as shoot Zn. Interactions among soil properties, soybean plant, and this mycorrhizal isolate suggested that soil properties, such as pH, pore diameter, and silt and organic matter, may have difficulties predicting arbuscular mycorrhizal fungal response. However, before soil amendment, regression models were accurate in predicting shoot dry weight, mycorrhizal colonization, and hyphal development of this mycorrhizal isolate on plants. When soil amendments were added to the soil property regression model, the predictive ability of the model was greatly reduced or nonexistent. The observations in this study indicate the effects of soil properties on root colonization and external hyphal production are important in examining AM fungal – plant interaction. An understanding of soil properties will be essential to understand mycorrhizal fungal ecology and to effectively use mycorrhiza in biological systems. Key words: mycorrhiza, soil properties, soybean growth, mycorrhizal hyphae, benchmark soils.
The impact of eucalypt on the leaf-associated aquatic hyphomycetes in Spanish streams
Authors: Chauvet Eric , Fabre Eric , Elósegui Arturo , Pozo Jesús
Published: April 2011

Aquatic hyphomycete assemblages on decomposing leaf litter of the exotic species Eucalyptus globulus Labill. were compared with those on the native riparian species Alnus glutinosa (L.) Gaertn. in three low-order streams of the Agüera watershed (Basque Country – Cantabria, Spain). These streams contrast by the importance of eucalypt in the riparian vegetation and by the nutrient contents in the water. Neither the total conidial production nor the number of fungal species differed between the two leaf species in any of the streams. Fungal colonization of eucalypt leaves appeared to be delayed by about 2 weeks, probably owing to their high content in inhibitory constituents. While Flagellospora curvula Ingold largely dominated pioneer assemblages on both leaf species, the second most important species, Lunulospora curvula Ingold, exhibited a preference for eucalypt. In the stream surrounded by eucalypt, the fungal diversity was surprisingly lower on eucalypt than on alder. In the stream with higher orthophosphate concentrations, the conidial production was similarly increased on both leaf species. The present data together with recent results from a similar investigation in Portugal suggest a minor impact of eucalypt on the activity and diversity of aquatic hyphomycete leaf-associated assemblages in southern European streams. Key words: aquatic hyphomycetes, eucalypt, alder, leaf litter, stream.
Epiphytic growth and survival of Tilletiopsis pallescens, a potential biological control agent of Sphaerotheca fuliginea, on cucumber leawes
Authors: Urquhart E. J. , Punja Z. K.
Published: April 2011

The influence of low (70%) and high (90%) relative humidity on epiphytic growth, development, and survival of Tilletiopsis pallescens, a ballistospore-forming yeast-like fungus, on cucumber leaves was investigated. In addition, survival of the fungus in the presence or absence of powdery mildew (Sphaerotheca fuliginea) colonies was determined. Growth and development were visualized by scanning electron microscopy of the leaf surface, and survival was quantified as colony-forming units recovered on a semiselective medium. Development of T. pallescens from blastospores that were applied to healthy leaves at 70% relative humidity was limited to small colonies that grew adjacent to leaf veins 7 days after application. At 90% relative humidity, extensive hyphal networks had developed within 3 days of blastospore germination, and ballistospores were produced within 7 days. Growth and sporulation of T. pallescens were most extensive at the base and on the surface of leaf trichomas. In the presence of S. fuliginea, T. pallescens mycelium developed adjacent to hyphae and conidiophores of the pathogen within 3 days at both 70 and 90% relative humidity. However, at 90% relative humidity, growth of T. pallescens was more extensive and ballistospores were produced within 5 days, and there was visible collapse of mildew hyphae. There was no evidence of penetration of the leaf or mildew hyphae by T. pallescens. Survival of T. pallescens was significantly (P = 0.05) increased at 1 and 5 days postapplication at 70% relative humidity when blastospores were amended with 1% (v/v) canola oil – lecithin. Survival at 90% relative humidity was also significantly increased with canola oil – lecithin and by the presence of S. fuliginea. The addition of liquid paraffin – lecithin or liquid paraffin – Tween had no effect on survival when compared to the control. The results from this study indicate that growth and survival of T. pallescens are enhanced by high relative humidity and by the presence of powdery mildew, and canola oil – lecithin amendment improved survival on the leaf surface at reduced ambient humidity. Key words: antagonism, biological control, powdery mildew, yeast.
Retarded embryo growth and early degeneration of sporophytic tissue are associated with embryo abortion in the interspecific cross Alstroemeria pelegrina × Alstroemeria aurea
Authors: Jeu Marjo J. De , Calderé Francesc Garriga
Published: April 2011

Histological studies on crosses between distantly related Alstroemeria species revealed post-fertilization crossing barriers. Developmental events between normal developing seeds (after self-fertilization) and aborting seeds (after cross-fertilization) during 0–32 days after pollination were compared. In both cases the pollen tube remained as a swollen structure inside the micropyle during eight days, and thereafter degenerated. The first division of the zygote occurred within four days after pollination and resulted in a polar two-celled proembryo with a large basal cell and a small apical cell. The self-fertilized embryos developed a polar structure with suspensor and a globular embryo eight days after pollination according to the monocotyledonous type. The cross-fertilized zygotes showed retardation and deviation in plane of the cell plate in the second and third divisions, resulting respectively in linear three-celled and eight-celled proembryos 4–6 days after pollination. Differentiation in suspensor and globular stage embryos proper was not found in the cross-fertilized ovules but in stead aberrant undifferentiated embryos were observed, which formed two groups of cells in later stages. Endosperm development was quite similar in both cases till 12 days after pollination, when the coenocytic endosperm of the self-fertilized ovules formed cell walls around the nuclei, whereas cell wall formation was completely absent in the cross-fertilized ovules. The chalazal nucellus of the cross-fertilized ovules started to degenerate six days after pollination, and presumably restricted the flow of carbohydrates to the developing embryo and endosperm. Subsequently, a loss of contact between the endospermic transfer wall and the chalazal nucellus occurred after twelve days of development. Finally the cross-fertilized embryos aborted after they had lost their contact with the micropylar side of the former embryo sac. Thus, a number of events occurred from the second division of the hybrid zygote onwards, all leading to the abortion of the embryo 18–22 days after pollination. It seemed that during the early cell divisions of the zygote the fate of the embryo was already determined. Embryo abortion was associated with retarded embryo growth and early degeneration of sporophytic tissue. Key words: Alstroemeria spp., interspecific hybridization, embryogenesis, embryo abortion, endosperm degeneration, chalazal nucellus degeneration.
Changes in the wall potential ofScutellospora calosporaassociated with colonization ofAllium porrumroots are not accompanied by equivalent changes in the host
Authors: Ayling S M , Smith S E , Reid R J , Smith F A
Published: April 2011

Cell wall electrical potentials were recorded from external hyphae, appressoria, and associated hyphae of the vesicular-arbuscular (VA) mycorrhizal fungus Scutellospora calospora (Nicolson & Gerdemann) Walker & Sanders colonizing leek (Allium porrum L.) roots. As colonization progressed the hyphal walls became more polarized with similar values to the walls of the leek root. These changes, which may reflect changes in fungal wall composition, have important implications for nutrient uptake by the fungus. There were no differences in wall or intracellular potentials between leek roots colonized by either S. calospora orGlomus sp. ("City Beach") and non-mycorrhizal roots. These results are further evidence of the close compatibility between roots and VA mycorrhizal fungi. Key words: vesicular-arbuscular mycorrhiza, cell wall, electrical potential difference, leek, Allium porrum, Scutellospora calospora.
Ectomycorrhizas of lodgepole pine (Pinus contorta) seedlings originating from seed in southwestern Alberta cut blocks
Authors: Bradbury S M
Published: April 2011

Lodgepole pine (Pinus contorta Dougl. ex Loud.) seedlings, originating from seed in three southwestern Alberta cut blocks, were sampled to identify their ectomycorrhizal associates. Fourteen ectomycorrhizal taxa were identified, 10 were common to all three cut blocks, and 12 to two cut blocks. Individual seedlings were colonized by two fungal associates on average and never had more than six fungal associates at one sampling time. Total percent colonization of seedling roots was greater than 50% one year after seed germination and greater than 90% two years after seed germination. Species richness increased throughout the course of the study; however, all but two ectomycorrhizal taxa were found in mature forests nearby. Typical late-stage ectomycorrhizal fungi colonized regenerating lodgepole pine seedlings in the absence of refuge host plants; therefore, either these fungi remained viable in situ between harvesting and regeneration or they migrated back into the cut block once revegetation was initiated.Key words: lodgepole pine seedlings, ectomycorrhiza, percent relative abundance, Alberta cut blocks.
Epilithic diatoms of the St. Lawrence River and their relationships to water quality
Authors: Reavie Euan D , Smol John P
Published: April 2011

Epilithic diatoms were sampled at 48 sites along the St. Lawrence River, from Salaberry de Valleyfield to Québec City, in an attempt to determine how diatom assemblages were related to measured water quality variables. Canonical correspondence analysis was used to explore the relationships between environmental variables and patterns in the epilithic diatom assemblages. "Distance downstream from Cornwall" was determined to be the strongest variable influencing the structure of epilithic diatom assemblages, likely due to the effect of tides (favouring aerophilic species) closer to the river outlet. Variables related to pollution (suspended solids, fecal coliforms, chlorophyll a) also explained significant (P < 0.05) amounts of variance in the diatom assemblages. The optima of common diatom species to suspended solids were explored further. Reconstructive models using weighted-averaging calibration and regression illustrated that "distance from Cornwall" and concentrations of suspended solids, fecal coliforms, and chlorophyll a, the most influential variables, could be inferred from the diatom assemblages. When compared with the inference models developed for pollution variables using epiphytic diatom assemblages (attached to macrophytes or Cladophora), the epilithon model appears to perform better.Key words: diatoms, rocks, epilithic, St. Lawrence River, water quality, calibration.
Dispersal of white spruce seed in mature aspen stands
Authors: Stewart James D , Hogg Edward H , Hurdle Patrick A , Stadt Kenneth J , Tollestrup Peter , Lieffers Victor J
Published: April 2011

The dispersal of white spruce (Picea glauca (Moench) Voss) seed through trembling aspen (Populus tremuloides Michx.) forests was investigated by releasing artificial seed (confetti) from different heights on a meteorological tower, and, secondly, by observing the distribution of spruce regeneration along transects radiating out from small isolated patches of mature spruce seed trees. Mean dispersal distance of confetti increased with height of release. Before leaf fall of the aspen canopy, most confetti landed close to and in all directions around the tower. After leaf fall, no confetti was observed upwind from the tower and the mean dispersal distance increased, with peak densities occurring at a distance of 15 m in the downwind direction. The rate of decrease in regeneration density with distance from patches of mature, seed-bearing white spruce was much less than that observed during confetti release experiments. Furthermore, regeneration densities were significantly greater in the prevailing downwind direction (toward the east). The results indicate that stronger than average winds, primarily from the northwest, west, and southwest, play a major role in the dispersal of white spruce seed. Simulation modelling of the observed distribution of regeneration suggests that long-distance (>250 m) dispersal may be an important mechanism for the persistence of white spruce in the fire-prone boreal forest of western Canada.Key words: seed dispersal, boreal forest, mixedwood, wind dispersal, artificial seed.
Predictability of the combined effects of sulphur dioxide and nitrate on the green-algal lichen Ramalina farinacea
Authors: Balaguer Luis , Manrique Esteban , Ascaso Carmen
Published: April 2011

The interactive effects of SO2 and NO3− on the green-algal lichen Ramalina farinacea (L.) Ach. were investigated using the degree of chlorophyll phaeophytinization and ultrastructural damage to the Trebouxia photobiont. Thalli were submitted to several factorial design experiments in which they were exposed to mean SO2 concentrations ranging from 118 to 140 nmol∙mol−1 plus or minus aqueous solutions of NO3− at either 50 or 1000 μmol∙L−1, for 6–14 days. Interactive effects of SO2 and NO3− were synergistic when the effects of each individual pollutant were slight. However, this pattern reverted to additive effects, and sequentially to antagonistic effects as the detrimental impact of SO2 alone became more severe. Despite this transition, neutralization of the damaging impact of SO2 by simultaneous treatment with NO3− was not observed. The results show that interactions between SO2 and NO3− were variable, but predictable on the basis of the expected effects following exposure to each pollutant alone. The coincidence of this empirical pattern with those observed in previous studies suggests involvement of unspecific causes. The wider ecological significance of interactions between SO2 and NO3− is discussed in the light of other findings with respect to the effects of air pollution on lichens in the field. Key words: air pollution, sulphur dioxide, nitrate, interactive effects, lichens, pigments, ultrastructure.
Trade-offs between reproduction and growth influence time of reproduction in Oenothera biennis
Authors: Reekie Edward , Parmiter Dale , Zebian Kassim , Reekie Julia
Published: April 2011

Size at which reproduction occurs was examined in two populations of Oenothera biennis occupying contrasting habitats: (1) a gravel embankment without complete canopy closure, and (2) a second-year successional field with a closed canopy. One hundred plants were randomly harvested from each site and weighed. A greater proportion of plants reproduced in the closed versus open canopy site (83 versus 61%). There was no difference in mean size at reproduction between the two sites; however, variation in size at reproduction was greater in the closed site where both the smallest and largest plants were found. In the smallest size category, more plants reproduced in the closed than in the open site, indicating that the minimum size required for reproduction is smaller in the closed site. We suggest that plants reproduce at a smaller size in the closed site because of the marked stem elongation associated with reproduction in this species, which increases the ability of plants to compete for light. This question was addressed in a garden experiment in which seedlings were transplanted into either weeded plots (i.e., an open canopy) or a successional field (i.e., a closed canopy). Half the plants at each site were left as vegetative controls and the other half treated with gibberellic acid to induce bolting. Bolting had no effect on growth in the open canopy but increased growth in the closed canopy as predicted. Key words: time of reproduction, Oenothera biennis, life history variation, stem elongation, bolting, size at reproduction, phenotypic plasticity.
Foliar venation characteristics ofVacciniumsect.Macropelmaand sect.Myrtillus(Ericaceae): a comparative analysis
Authors: Powell E. Ann , Kloet S. P. Vander
Published: April 2011

A suite of eight foliar venation characteristics from two closely related sections of Vaccinium L., sect. Macropelma Klotzsch and sect. Myrtillus Dumortier, were analyzed to assess the level of similarity between these sister sections, address the questionable classification of Vaccinium cereum (L.f) Forster, and assess the diagnostic ability of venation characteristics. Our analysis revealed no significant differences in foliar venation characteristics between V. cereum and the Hawaiian species from sect. Macropelma. In addition, all the leaves of V. cereum examined contained the attenuated extended bundle sheath system as found in other representatives from sect. Macropelma. Taximetric analysis showed that these quantitative foliar venation characters were diagnostic at the sectional level but not at the species level. A cluster analysis of 108 operational taxonomic units did separate the two sections but did not discriminate among the 12 individual species. However, a similar taximetric analysis using the character means for each species (for the eight foliar characters), which "smoothed out" the variation due to environmental plasticity, produced a dendrogram which closely resembled the currently accepted Vaccinium classification. Although further investigations into the constancy and reliability of foliar venation characters in the remaining sections of Vaccinium are desirable, our results clearly show that these quantitative vegetative foliar characters do have diagnostic value and can be utilized in taximetric analyses. Key words: Vaccinium, venation, leaf, systematics.
Mycoflora of peach bark: population dynamics and composition
Authors: Buck James W , Lachance Marc-André , Traquair James A
Published: April 2011

Yeasts and filamentous fungi associated with smooth (non-lenticel) and lenticel bark of young and scaffold branches of peach (Prunus persica (L.) Batsch) were monitored using bark washing and direct or impression plating techniques and scanning electron microscopy during potential Cystospora canker infection periods. Total populations of fungi were high in the fall but dropped in the winter and increased during the spring. Yeasts and yeast-like fungi predominated in the spring and fall samples. The principal yeasts were Basidiomycetes in the form genera Cryptococcus, Rhodotorula, and Sporobolomyces. The yeast-like fungi were Aureobasidium and Taphrina. The principal filamentous fungi were in the form genera Alternaria, Epicoccum, Cladosporium, Coniothyrium, and Libertella. The canker pathogens, Leucostoma persoonii (Nits.) Höhn. and Leucostoma cincta (Pers. & Fr.) Höhn., were observed mainly in the spring sampling. Lenticels supported greater fungal populations than smooth (non-lenticel) bark surfaces. The impact of fungal epiphytes, particularly the yeasts, on the potential biological control of peach canker is discussed.Key words: Cytospora canker, mycoflora, yeast, bark, biological control, fungal epiphyte.
Palmoxylon hebbertii, from the Lower Oligocene Goldens Ranch Formation of central Utah, U.S.A., with an analysis of some characteristics previously used in the classification of Palmoxylon
Authors: Nambudiri EMV , Tidwell William D
Published: April 2011

The new species, Palmoxylon hebbertii, described here was collected from the Lower Oligocene Goldens Ranch Formation southwest of Nephi, Utah, U.S.A. In cross section, the collateral vascular bundles are generally reniform in shape with a well-developed fibrous bundle sheath and a median sinus that is very shallow or absent. They are bivascular and, in the subdermal zone, surrounded by radiating parenchyma. The phloem is well differentiated into protophloem and metaphloem elements with oblique sieve plates. The metaxylem and protoxylem vessel elements show a gradual change in the morphology of their end plates as well as in their wall thickenings. An analysis of 41 well preserved Palmoxylon species from India suggests that Stenzel's grouping of the species based on the nature of the bundle sheath is artificial and that several characteristics including the nature of the vascular tissues, used in classification of extant species, should be used.Key words: palm, Goldens Ranch Formation, Utah, Oligocene, Stenzel's grouping, Jaccard's method.
Growth and virulence of mountain pine beetle associated blue-stain fungi, Ophiostoma clavigerum and Ophiostoma montium
Authors: Solheim Halvor , Krokene Paal
Published: April 2011

The mountain pine beetle (Dendroctonus ponderosae) is commonly associated with the blue-stain fungi Ophiostoma clavigerum and Ophiostoma montium. Ophiostoma clavigerum is the primary invader of sapwood after beetle infestation and is thought to be the most virulent of the two fungi. Growth of these fungi was studied under oxygen-deficient conditions on malt agar in test tubes and Petri dishes. In addition, growth was studied in phloem and sapwood of young living shore pines (Pinus contorta var. contorta) and western white pines (Pinus monticola) inoculated with fungus in low densities (eight inoculations per tree). In test tubes with limited oxygen O. clavigerum grew for a longer time than O. montium. Both fungi are fast growing on malt agar (maximum growth 4.4-9.0 mm/day), but O. clavigerum grew better at temperatures below 25°C. The rapid growth and the ability to tolerate low oxygen levels may be important adaptations for O. clavigerum as the primary invader of fresh sapwood. However, although O. clavigerum grew better in the phloem of both tree species, there were no differences between the two fungi in their ability to colonize the sapwood of the inoculated trees.Key words: blue-stain fungi, Dendroctonus ponderosae, growth rate, oxygen deficiency, virulence.
Influences foliaires dans le contrôle du développement des « bourgeons anticipés » chez Vitis vinifera
Authors: Fournioux Jean-Claude
Published: April 2011

In grapevines, the young leaves play an important role in the control of the growth of anticipated buds. Through a basipetal inhibition, which these young leaves exercise over subjacent buds, they contribute to apical dominance. This inhibitory influence persists as long as the duration of laminar growth of the leaf; it is neither sector-based nor cumulative; it is perceived even by buds very far from young leaves. This foliar inhibition is also one of the causes of the acrotonic character of lateral ramification that develops, in the apical part of the shoot, after shoot tip removal. In the older part of the shoot, this acrotony, consecutive to a shoot section, is mainly determined by correlations between the buds. All these results are analysed and discussed in regard to morphogenesis elements previously established in other species. The contribution of young leaves to apical dominance has been demonstrated previously in many other plants. On the other hand, in grapevine, this morphogenetic character was unknown. The fact that young leaves contribute to the acrotonic development of the lateral ramifications growing after decapitation of the main shoot constitutes a much more original result because it has rarely been described in previous studies relative to other species. Earlier works also lead us to expect that both correlative inhibitions and competitive process are involved in the correlations between anticipated buds released from apical dominance. Concerning the growth correlations between grapevine buds, only thuse correlations relative to latent buds had been, until now, very much studied. New and precise knowledge on correlations that control the development of anticipated buds are supplied by this work. It appears then that correlations between these two sorts of buds have two common features: inhibition of their growth by young leaves and sectorial character of the inhibitions between the buds. A hypothesis on the mechanisms through which young leaves control the growth of anticipated buds is suggested. These mechanisms probably change in relation with the developmental stage of a bud; before the bud develops, the young leaves exercise on it a basipetal polarized inhibition. As soon as the bud begins to grow, nonpolarized competitive relations become established between the lateral ramification and the upper young leaves.Key words: Vitis vinifera, apical dominance, acrotony, leaves, buds, correlations.
Viability and wall permeability of the extramatrical hyphae of the ectomycorrhizal fungus Hebeloma cylindrosporum
Authors: Taylor Jeff H , Peterson Carol A
Published: April 2011

The extramatrical hyphae of ectomycorrhizae are known to absorb ions from the soil for the symbiotic association, but the fraction of hyphae involved in this activity has not been studied. For hyphae to potentially absorb ions, they must have permeable walls and be viable. In the present study, the proportion of living, extramatrical hyphae of Hebeloma cylindrosporum (Romagnesi) was measured by a grid-intersect method after staining with fluorescein diacetate, disodium fluorescein, or ethidium bromide. Results with ethidium bromide indicated that 89% of the hyphae were alive when the association was 2 weeks old and that this value declined to 76% at 26 weeks. In contrast, both fluorescein treatments resulted in staining of only 25% of the hyphae at 2 weeks and 7% at 26 weeks. The difference in measured viability was ascribed to wall permeability. Ethidium bromide was applied following an ethanol pretreatment, which apparently increased the permeability of the hyphal wall as well as that of its membranes. Our results indicate that only a fraction of hyphae are likely involved in ion uptake (as indicated by the fluorescein tests), a fraction that declines as the association ages. Further, parts of the hyphal mass are alive but encased in impermeable walls; these parts may act as conduits for the ions that were absorbed by the younger regions.Key words: Hebeloma cylindrosporum, ectomycorrhizae, ion uptake, permeability, viability.
Carbon isotope fractionation by photosynthetic aquatic microorganisms: experiments with Synechococcus PCC7942, and a simple carbon flux model
Authors: Erez Jonathan , Bouevitch Anne , Kaplan Aaron
Published: April 2011

Stable carbon isotopes (12C and 13C) are widely used to trace biogeochemical processes in the global carbon cycle. Natural fractionation of carbon isotopes is mainly due to the discrimination of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) against 13C during photosynthesis. In marine and other aquatic microorganisms, this fractionation is lowered when the dissolved CO2 (CO2(aq)) is decreasing, but the underlying mechanisms are poorly understood. Cultured Synechococcus PCC7942 showed maximum isotopic fractionations of -33omicron (in delta 13C units) relative to the total inorganic carbon (Ci) when CO2(aq) is above 30 m M. As the culture grew, pH increased, CO2(aq) was lower than 1 m M, and the Ci concentrating mechanism was induced although the Ci was above 3 mM. The isotopic fractionation was drastically reduced to values of -1 to -3 omicron relative to Ci. A simple carbon isotope flux model suggests that during the first stages of the experiment the total uptake (F1) was roughly three- to four-fold greater than the photosynthetic net accumulation (F2). When the Ci concentrating mechanism was induced, the leakage of CO2 from the cells declined, the cells started to utilize HCO3- and the F1/F2 ratio decreased to values close to 1. Based on this model the isotopic variability of oceanic phytoplankton suggests that the F1/F2 ratio may be above 3 in high latitudes and ~1.1 in equatorial waters, where the Ci concentrating mechanism is probably induced. Attempts to reconstruct past atmospheric CO2 levels and paleoproductivity should take into account the effects of the Ci concentrating mechanism on the isotopic fractionation of aquatic primary producers.Key words: carbon concentrating mechanism, carbon isotope fractionation, CO2, photosynthesis.
CO2 uptake mechanism in Eremosphaera viridis
Authors: Deveau Jason ST , Khosravani Houman , Lew Roger R , Colman Brian
Published: April 2011

Electrophysiological measurements of the acidophilic alga Eremosphaera viridis De Bary explored the effects of low CO2 levels on both membrane potential and resistance. This procedure incorporates a double-barreled microelectrode and suction pipette system, coupled with an approximately CO2-free environment. A key requirement is an artificial pond water perfusion media that has been purged of dissolved inorganic carbon by being boiled and bubbled with nitrogen gas. Both membrane potential and resistance were measured at pH5 in both low-CO2 conditions (2µM) and high-CO2 conditions (14µM) in both light, where CO2 transport is known to be active, and dark, where CO2 transport is not active. To avoid dissolved inorganic carbon contamination of the perfusion media, a special chamber was constructed, featuring a laminar flow of nitrogen gas over the solution, which allowed for the manipulation of cells while preventing any contamination by CO2 from the air. Results indicate that the uptake of CO2 by the alga is electrically silent and, therefore, not the result of a symport or antiport cotransport system that would "drive" CO2 uptake by coupling it to the electrochemical gradient of ions such as protons or sodium. The uptake is most likely facilitated by a transporter directly coupled with ATP hydrolysis.Key words: Eremosphaera viridis, dissolved inorganic carbon, CO2-ATPase, electrophysiology.
The use of mutants in the analysis of the CO2-concentrating mechanism in cyanobacteria
Authors: Ohkawa Hiroshi , Sonoda Masatoshi , Katoh Hirokazu , Ogawa Teruo
Published: April 2011

Mutants of cyanobacteria defective in parts of the CO2-concentrating mechanism are classified into three types. (i) Mutants defective in inorganic carbon transporters. One of these mutants was constructed by inactivating cmpA encoding 42 kDa protein in the cytoplasmic membrane. (ii) Mutants defective in NAD(P)H dehydrogenase(s). There are five ndhD genes in Synechocystis PCC6803, two of them expressed constitutively and three inducible by low CO2. Two kinds of NAD(P)H dehydrogenase appear to be involved in energizing and inducing the high affinity inorganic carbon transport system. (iii) Mutants defective in carboxysome with impaired ccm or icfA genes. New type of mutants with impaired cotA (renamed as pxcA) have also been isolated. These mutants did not show light-induced proton extrusion and were unable to grow at acidic pHs. A mutant constructed by inactivating cotA (pxcA) in the wild-type Synechocystis was unable to transport CO2 at pH 6.5. We concluded that cotA (pxcA) has a role in light-induced proton extrusion that is essential at acidic pHs to extrude protons produced during CO2 transport.Key words: CO2-concentrating mechanism (CCM), CO2 transport, NAD(P)H dehydrogenase, proton extrusion, carboxysome, mutant.
Bicarbonate utilization and pH polarity. The response of photosynthetic electron transport to carbon limitation in Potamogeton lucens leaves
Authors: van Ginkel Lucina C , Prins Hidde BA
Published: April 2011

By the process of pH polarity, several submersed angiosperms can use bicarbonate as carbon source for photosynthesis. Under conditions of relatively high light intensity and low CO2 availability, the pH of the apoplast and unstirred layer becomes acid at one side of the leaf and alkaline at the other. In the acid region, bicarbonate is converted into CO2, which diffuses into the leaf where it is fixed. Previous experiments on the light-dependent reduction of extracellular electron acceptors led to the hypothesis of redox regulation. Under conditions of high light and low CO2, excess reducing power in the chloroplast was supposed to be shuttled to the cytoplasm where it can upregulate the plasma membrane proton pump, leading to activation of polarity. Chlorophyll a fluorescence is an indicator for photosynthetic electron transport, the energization of thylakoids, and the reoxidation of chloroplast NADPH. It was used therefore to test redox regulation in vivo in Potamogeton lucens L. leaves. The fluoresence parameter, qP, an indicator for photochemical quenching and NADPH reoxidation, appeared to be rather insensitive to the inorganic carbon concentration and to the presence or absence of polarity. In contrast, qN, an indicator for non-photochemical quenching related to thylakoid energization, photoinhibition, and state transitions, increased under conditions of low CO2 - high light and polarity. Taken together the data show polarity to be an effective mechanism to make bicarbonate accessible as carbon source and seem to agree with the idea of redox regulation of pH polarity.Key words: bicarbonate utilization, chlorophyll a fluoresence, pH polarity, redox regulation, Potamogeton lucens, submerged aquatic macrophyte.
Carbonic anhydrase in eukaryotic algae: characterization, regulation, and possible function during photosynthesis
Authors: Sültemeyer Dieter
Published: April 2011

Carbonic anhydrase (CA) speeds up the equilibrium between CO2and HCO3-at physiological pH values and has been detected in almost every species of the animal and plant kingdoms. Among eucaryotic micro- and macro-algae the enzyme is widely distributed and plays an important role in photosynthetic CO2fixation. In some cases, different forms of carbonic anhydrases located extracellularly and intracellularly have been found to occur in the same cell. The expression of the genes encoding these CA isoforms are under the control of the inorganic carbon concentration in the medium, as the activities increase with decreasing the inorganic carbon content. Considerable progress has been made in recent years in isolating and characterizing the various forms of carbonic anhydrases on a biochemical and molecular level. Most of the data have been collected for microalgae like Chlamydomonas reinhardtii (Dangeard), while the situation in macroalgae is still descriptive. Therefore, this review summarizes the recent development with an emphasis on microalgae carbonic anhydrases.Key words: carbonic anhydrase, CO2concentrating mechanism, macroalgae, microalgae, photosynthesis.
A molecular phylogenetic reappraisal of theGraphiumcomplex based on 18S rDNA sequences
Authors: Okada Gen , Seifert Keith A , Takematsu Akiko , Yamaoka Yuichi , Miyazaki Satoru , Tubaki Keisuke
Published: April 2011

Based on nuclear encoded small subunit (18S) rDNA sequences, a taxonomic reappraisal of Graphium (anamorphic fungi) was undertaken using neighbour-joining (NJ) and fast DNA maximum likelihood (fastDNAml) methods and compared with traditional classifications. In common with Graphium putredinis, Graphium penicillioides (the lectotype species) was found to be related to the Microascales, not the Ophiostomatales as previously believed. Both species might be heterogenous and should be treated as species aggregates. The representative mode of conidiogenesis for these two species was nodular-annellidic, rather than the dense-annellidic mode characteristic of the synnematous ophiostomatalean anamorphs. Graphium is emended to be restricted to G. penicillioides, G. putredinis, and related synnematous anamorphs of Petriella and Pseudallescheria, and a nomenclator for the nine species presently accepted in Graphium is presented. Pesotum, originally characterized mainly by sympodial conidiogenesis, is emended to include synnematous anamorphs of Ophiostoma species formerly included in a variety of genera with sympodial to dense-annellidic conidiogenesis. Eight new combinations in Pesotum are included in a nomenclator for the 26 species currently known. Three new combinations from Ceratocystis to Ophiostoma are proposed for species with Pesotum anamorphs. The holomorph of Graphium calicioides has affinities to the black yeasts and should be classified in the Chaetothyriales. However, the critical morphological, loculoascomycetous characters of the teleomorph are not completely documented. Interpreted from the molecular context, the morphological similarities between these three groups of anamorphs are homoplasies and examples of convergent evolution.Key words: Chaetothyriales, Graphium, Microascales, Ophiostomatales, Pesotum, 18S (SSU) rDNA sequences.
The function of multiple flowers of a spring ephemeral, Gagea lutea (Liliaceae), with reference to blooming order
Authors: Nishikawa Yoko
Published: April 2011

Flowering pattern, seed-set success, and allocation to male and female functions of a spring ephemeral lily, Gagea lutea, were compared within individual inflorescences. Although the number of flowers increased with plant size and anthesis was extended as the number of flowers increased from one to four, the total number of seeds produced per plant did not increase with the number of flowers under natural conditions. The later-blooming flowers were smaller in size than the earlier ones within an inflorescence, and the ratio of stamen dry weight to pistil dry weight in the later flowers was higher than that in the earlier ones. Although the ovule fertilization rate was increased by artificial pollination, it was lower in the later flowers than in the earlier ones within an inflorescence. Neither nutrient addition to the soil nor removal of earlier flowers increased the seed production of the later flowers. These results indicated that the later flowers had a lower potential for female function than did the earlier ones and that this was probably due to variation inherent in inflorescence architecture. Seed production of the later flowers was also limited by the time needed for seed maturation because the aboveground part of G. lutea died soon after canopy closure in early summer. Furthermore, the later flowers probably contributed to the reproductive success of a plant as pollen donors.Key words: flowering order, Gagea lutea, resource allocation, seed production, short growing season.
Mechanisms of recolonization of the clonal intertidal alga Mazzaella cornucopiae (Rhodophyta, Gigartinaceae) after disturbances
Authors: Scrosati Ricardo
Published: April 2011

The recolonization of the clonal intertidal alga Mazzaella cornucopiae (Postels et Ruprecht) Hommersand is considered here, as part of a larger project on its population ecology. Recolonization in Barkley Sound, Pacific Canada, started a few months after completely clearing experimental 100-cm2 quadrats in late spring and occurred both by vegetative growth of perennating holdfasts bordering disturbed quadrats and by recruitment from spores. In terms of percent cover, both mechanisms contributed similarly to recolonization during the first 2 years, although vegetative recolonization was highly variable among quadrats. Great spatial variability prevented the detection of a temporal pattern for recruit density on statistical grounds. However, cohort demography showed some degree of seasonality. Turnover rates of recruits were high; they lived 2.6 months on average. Recruitment was highest between fall or winter and midspring (as might be expected, given that reproductive structures appeared in fall and winter) and null in the first two summer seasons. The highest mortality was recorded in summer, when desiccation and irradiance are highest on an annual basis. Frond density was very variable on a spatial scale and did not follow a clear temporal pattern. The average number of fronds per recruit apparently increased between winter and summer, paralleling frond dynamics in mature stands. By monitoring recolonization in quadrats of the same size cleared previously by other researchers, the time of full recovery of M. cornucopiae was estimated to be 2.7-3.5 years.Key words: demography, disturbance, Gigartinaceae, Mazzaella cornucopiae, mortality, recolonization, recruitment.
The role of specific plant organs and polar auxin transport in correlative inhibition of leafy spurge (Euphorbia esula) root buds
Authors: Horvath David P
Published: April 2011

Localization of the source of the signal(s) controlling correlative inhibition of leafy spurge root buds (underground adventitious shoot buds located on the lateral roots) was studied by sequential removal of various plant organs. It was determined that full correlative inhibition of root buds was lost only after excision of all aerial tissue from the plant, or after excision of all aerial tissue except the stem. If mature leaves or growing axillary buds (or both) were left intact, no growth of root buds was observed. The synthetic auxin, alpha-NAA, prevented release of apical dominance and subsequent outgrowth of stem and crown buds when applied to the cut end of the stem or crown. Exogenous application of NAA to either the stem or the crown had little effect on root bud growth. Application of the auxin transport inhibitor NPA around the base of the crown had no effect on root bud quiescence. These data are not consistent with the previous studies (Weed Sci. 35: 155-159 (1987)) that indicate a role for auxin in maintenance of correlative inhibition of root bud growth in leafy spurge. The results of auxin transport inhibitor studies presented here suggest that correlative inhibition of root bud growth does not rely on the classic polar auxin transport system.Nomenclature: leafy spurge, Euphorbia esula L. #3 EPHES; NAA, naphthalene acetic acid; NPA, N-1-naphthylphthalamic acid; TIBA, 2,3,5-triiodobenzoic acid.Key words: root buds, apical dominance, auxin, NPA.