bluuebunny/crossref_metadata_2025_split huggingface dataset:
The distribution of planktonic dinoflagellates and their cysts in the eastern and northeastern Atlantic Ocean
Authors: DODGE J. D. , HARLAND R. 
Published: April 2006

summaryData are presented on the distribution of both planktonic dinoflagellates and their cysts from 20° N to 70° N and from the western coasts of Europe and Africa to 25° W in the eastern and northeastern Atlantic Ocean. Although most of the thecate dinoflagellates are widely distributed, sometimes with a discontinuous pattern, the cysts are generally more restricted. There is an increase in the ratio of cyst types to thecate plankton and in cyst diversity from ocean to inshore and from low to high latitudes; in both cases paralleling an increase in diversity of the plankton. Cyst distributions may also be discontinuous, occurring around the British Isles and also in the upwelling area off N.W. Africa. Particular species show similar distribution patterns for cyst and thecae e.g. Polykrikos schwarzii; distribution patterns where the cyst is less widely distributed than the thecae e.g. Spiniferites bentori/Gonyaulax digitalis; and where the cysts are more widespread than the thecae as in the problematical Gonyaulax spinifera‘complex’. Difficulties identified in comparing data sets include the lack of detailed knowledge of dinoflagellate life cycles, the need to know more about environmental parameters affecting encystment, and knowledge of cyst transportation and preservation in sediments. Overall cyst distribution patterns may be compared to the broad coccolithophorid zones recognised in the Atlantic Ocean.
Mechanisms of action of abscisic acid at the cellular level
Authors: HETHERINGTON ALISTAIR M. , QUATRANO RALPH S. 
Published: April 2006

summaryAbscisic acid (ABA) has been implicated in the control of a diverse range of physiological processes in higher plants. In this review, we focus on the events which constitute the cellular responses to ABA. Current evidence suggests that it is possible to classify the responses to ABA on the basis of whether they are rapid, involving ion fluxes (typified by the stomatal response), or slower and requiring alterations to gene expression (for example the response of cereal embryos to ABA). In our consideration of ABA stimulus response coupling pathways, we have chosen to highlight the role of the calcium ion in the rapid responses, while we have concentrated on the contribution of as‐acting elements and trans‐acting factors in the regulation of ABA‐responsive genes. We also draw attention to the possibility that interaction may exist between these pathways.Additionally, we discuss the controls of ABA concentrations during development and in response to environmental stimuli. Factors which contribute to the controls of ABA sensitivity are also reviewed. In our conclusions, we suggest that a general role for ABA may be to prepare tissue for entry into a new and different physiological state, perhaps by resetting the direction of cellular metabolism.

CONTENTS

Summary
9

I.
Introduction
10

II.
Stimulus response coupling
17

Synopsis
27

Acknowledgements
28

References
28
Adaptation of a white clover population to ozone stress
Authors: HEAGLE ALLEN S. , McLUGHLIN MICHAEL R. , MILLER JOSEPH E. , JOYNER RONALD L. , SPRUILL SUSAN E. 
Published: April 2006

summaryWhite clover (Trifolium repens L.) ‘Regal’ and tall fescue (Festuca arundinacea Schreb.) ‘Kentucky 31’ were grown together in a field and exposed for two seasons in open‐top chambers to six ozone (O3) regimes ranging from 0.59 to 1.95 times the ambient O3 concentration. Plants that survived were propagated clonally and used in the present study to determine whether selection for resistance or sensitivity to O3 had occurred. Relative foliar sensitivity of surviving clones to various short‐term O3, exposure regimes was determined with and without infection by several viruses. In tests of all surviving clones with viruses present, higher percentages of clones that survived two seasons at the high O3 levels were resistant to short‐term exposure to O3, than were those that survived exposure to the low O3 treatments. Only one of the 33 clones that survived exposure to charcoal‐filtered air (059 treatment) was O3‐resistant while 19 of the 30 clones surviving the 1.95 treatment were O3‐resistant. Conversely, eight clones that survived the 0.59 treatment were sensitive to O3 while none of those that survived the l.95 treatment were sensitive. The results indicate that selection pressure in the presence of O3 stress was for resistance to O3. Various combinations of five common viruses of clover were present among the surviving clones. Shoot‐rip meristem culture was used to free one O3‐resistant and one O3‐sensitive clone from at) viruses. The relative O3 sensitivity of these two clones was not affected by viruses. Further testing is required to determine the relationships between relative foliar sensitivity to short‐term O3 exposure and relative sensitivity to growth effects caused by long‐term exposure.
Soil nitrogen and chronic ozone stress influence physiology, growth and nutrient status ofPinus taedaL. andLiriodendron tulipiferaL. seedlings
Authors: TJOELKER M. G. , LUXMOORE R. J. 
Published: April 2006

summaryThe effects of soil nitrogen availability and chronic ozone stress on carbon and nutrient economy were investigated in loblolly pine (Pinus. taedaL.) and yellow‐poplar (Liriodendron tulipiferaL.). One‐year‐old seedlings were planted individually in pots in forest soil of low (58 μg g−1), medium (96 μg g−1) or high (172 μg g−1) initial concentrations of soluble nitrogen. The seedlings were exposed to ozone in open‐top field chambers at sub‐ambient (charcoal‐filtered air), ambient, and elevated (ambient + 60 nl 1−1O3) (32, 56, 108 nl 1−1O3,1h seasonal mean, respectively) levels for 18 weeks. At final harvest loblolly pine dry matter increased by 50% at the highest soil K level relative to the low with the largest gains in new needle biomass. Elevated ozone reduced the biomass of current‐year needles by 20% in plants grown at the highest N level. Higher soil N supply increased the concentration of nitrogen in needles, stimulated current‐year needle photosynthesis and increased needle and whole‐plant water‐use efficiencies. Ozone treatment had no significant effect on photosynthesis or water‐use efficiency in either species, although ozone exposure tended to reduce‐ stomatal conductance in loblolly pine. The low N treatment increased the proportion of dry matter allocated to fine roots in yellow‐poplar, but whole‐plant dry weight had not responded to N fertilization at the final harvest, suggesting other limitations on growth. Ozone exposure increased leaf abscission and doubled leaf turnover m yellow‐poplar. Although yellow‐poplar was highly sensitive to ozone‐induced leaf abscission, final whole‐plant dry weights were not affected. The indeterminate growth habit of yellow‐poplar permitted compensatory leaf growth which may have ameliorated effects of chronic ozone stress on biomass gain. Ozone exposure also decreased shoot weight more than root weight, resulting in higher root:leaf ratios in loblolly pine and a similar trend m higher fine roor:leaf ratios in yellow‐poplar. Greater proportional allocation of carbon to roots in response to nutrient deficiency may preclude an increased allocation to shoots often observed in response to air pollution stress. Interspecific differences in growth response to chronic ozone and nutrient stress may be influenced by differences in leaf growth habit.
Utilization of microbial siderophores by mycorrhizal and non‐mycorrhizal pine roots
Authors: LEYVAL C. , REID C. P. P. 
Published: April 2006

summaryIn iron‐deficient conditions, most bacteria and fungi are known to release siderophores, iron‐chelating compounds. Most plants do not produce siderophores, but seem to use microbial siderophores as iron sources. Although ectomycorrhizal fungi have been found to release siderophores in pure culture, little research has addressed production by mycorrhizas and the consequences for plant iron nutrition.The objectives of this study were to determine the effect of an ectomycorrhizal fungus [Pisolithus tinctorius (Pers.) Coker and Couch] on the utilization of siderophore (ferrioxamine B) by slash pine (Pinus elliottii Engelm.) roots grown under iron‐deficient or iron‐sufficient conditions. Experiments were conducted with excised roots and whole seedlings. Uptake of 55Fe from ferrioxamine B was lower by mycorrhizal roots than non‐mycorrhizal roots. Growth under iron‐deficient conditions had little effect on iron uptake by non‐mycorrhizal roots but increased the uptake by mycorrhizal roots. Uptake of iron from a non‐purified siderophore isolated from a pure culture of P. tinctorius was also lower by mycorrhizal roots. The uptake of iron was not dependent on the pH of the uptake solution. Differential responses could be attributed to different mechanisms of iron uptake between fungal cells and root cells. However, the higher iron content of mycorrhizal roots may indicate a negative feedback effect on uptake.
Effect of phosphorus nutrition on morphological characteristics of vesicular‐arbuscular mycorrhizal colonization of maize
Authors: BRAUNBERGER P. G. , Miller M. H. , PETERSON R. L. 
Published: April 2006

summaryThe morphology of the colonization of maize (Zea mays L.) by the vesicular arbuscular mycorrhizal fungus Glomus versiforme (Daniels and Trappe) Berch was determined quantitatively to establish the stage at which colonization was limited in response to increased P nutrition. Harvests were taken 14, 19, 24 and 29 d after planting maize in a calcined clay medium to which nutrient solution containing 0.16, 0.8 or 2.4 mM P was added daily. The fraction of the root length containing arbuscules (FAC) 19 d after planting was 0.4 with 0.16 mM P, 0.3, with 0.8 mM P and 0.17 with 2.4 mM P. Corresponding shoot P concentrations were 1.5, 2.0 and 3.2 mg g−l. Increased shoot P concentration reduced the number of appressoria per unit root length, but this accounted for only a part of the reduction in FAC. Increased root length did not account for the effect of shoot P concentration on FAC. The length of arbuscular colonized root length (total root length × FAC) per appressorium was strongly reduced in response to increased shoot P concentration. It was concluded that the reduction in FAC was mediated primarily through an inhibition of intra‐radical development.
Interactions between three alfalfa nodulation genotypes and two Glomus species
Authors: BRADBURY S. M. , PETERSON R. L. , BOWLEY S. R. 
Published: April 2006

summarySeedlings of a non‐nodulating alfalfa (Medicago sativa L.) genotype (nod−fix−) and an ineffectively nodulating alfalfa genotype (nod+fix−) exhibited resistance to vesiscular‐arbuscular mycorrhizal (VA mycorrhizal) colonization, when grown in pot cultures inoculated with either Glomus versiforme (Daniels and Trappe) Berth or Glomus intraradices Schenck and Smith. Appressoria, showing considerable variation in size and shape, developed on the root surface, but failed to form any internal structures such as arbuscules and vesicies. Wild‐type (nod+fix−) alfalfa seedlings developed normal colonization. This phenomenon will be extremely useful in studying the processes of recognition and compatibility between plant species and VA mycorrhizal fungal species.
The role of ascorbate in drought‐treated Cochlearia atlantica Pobed. and Armeria maritima (Mill.) Willd.
Authors: BUCKLAND SARAH M. , PRICE ADAM H. , HENDRY GEORGE A. F. 
Published: April 2006

summary Cochlearia atlantica is a species rich in ascorbic acid. After 4 days of intermittent drought treatment, there was a large decrease in the concentration of ascorbate and glutathione, functioning probably as radical scavengers (anti‐oxidants). Although there was no increase in lipid peroxidation (a marker of oxygen radical damage), drought treatment did result in the destruction of chlorophyll and a decrease in protein. This species showed little or no change in the activities of five enzymes usually associated with the processing of, and protection from, activated forms of oxygen. Armeria maritima showed similar decreases in relative water content and dry weight after droughting, but a quantitatively smaller decrease in ascorbate with no loss of glutathione. Instead a major response to drought, in this species, was the marked increases in the activities of superoxide dismutasc and peroxidase. Despite these increases in enzymic defences against oxygen radicals, drought treatment resulted in increased lipid peroxidation. in A. maritima. It is concluded that ascorbic acid and glutathione may play a significant role in the response to drought in C. atlantica but protection in A. maritima is largely through enzymic processing of activated farms of oxygen.
Variation in salinity tolerance and ion uptake in accessions of brown beetle grass [Diplachne fusca(L.) Beauv.]
Authors: WARWICK N. W. M. , HALLORAN G. M. 
Published: April 2006

summarySignificant variation in tolerance was found in natural populations ofDiplachne fusca(L.) Beauv, grown under a range of NaCl concentrations, with greatest variation in accessions from different sites and a narrower range of tolerance from those within sites. Significant differences were found between accessions for Na, Cl and K uptake. Ma and Cl concentrations were found to be higher in sheaths than in leaf blades, indicating thatD. fuscahas the capacity to sequester high levels of Na and Cl in the sheath away from the leaf blade as well as maintaining a high selectivity for K. over Na. The salinity level of the site from which an accession was collected did not show any correlation with the salt‐tolerance of that accession. WhileD. fuscawas found generally to be highly tolerant of NaCl (with plants surviving at 400 mol m−3NaCl) there was variation in tolerance in its natural populations, indicating the potential for selecting to increase tolerance further.
Soil salinity modifies SO2 sensitivity in soybean
Authors: QIFU MA , MURRAY FRANK 
Published: April 2006

summarySoybean (Glycine max L. cv. Buchanan) growing in top‐covered chambers was exposed to a factorial combination of three concentrations of SO2, (2, 99 and 189 nl1−1) and three concentrations of soil salinity with electrical conductivities of 0.7, 4.9 and 7.0 dS m−1. Each combination was tested in duplicate chambers. SO2 exposure was for 4 h d−1 for 106 d from planting to final harvest.SO2, increased leaf sulphur concentrations, while high salinity had the opposite effect. Stress interactions were observed late in the season, with leaf sulphur concentrations significantly decreased by simultaneous SO2, and salinity stress when compared with exposure to SO2, alone, SO2 or salinity stress both reduced leaf chlorophyll concentration, leaf area, plant dry weight and seed yields. Although SO2‐salinity interactions on the growth variables were not statistically significant, there were stress interactions on seed yield by affecting the number of pods produced. As SO2‐induced leaf injury developed is became more severe in the nonsaline plants than in the saline plants, indicating a protective function for salinity against SO2 injury. However, salinity‐induced leaf injury occurred earlier and was more severe in the high SO2 and saline‐treated plants than in the low SO2 and non‐fumigated saline‐treated plants.
The mechanisms of arsenate tolerance in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L.
Authors: MEHARG ANDREW A. , MACNAIR MARK R. 
Published: April 2006

summaryArsenate influx isotherms in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L. showed that tolerance to arsenate in these grasses is achieved at least in part by adaptation of the arsenate uptake system, which leads to reduced influx of arsenate in arsenate‐tolerant plants. In D. cespitosa, this reduction in arsenate ioflux was by suppression of the Vmax of the high‐affinity uptake system and by an increase in the Km of the low‐affinity uptake system. In A. capillaris the reduction in arsenate uptake in arsenate‐tolerant plants was by a decrease in the Vmax of both uptake systems and by an increase in the Km of the high‐affinity uptake system. The differences in the rates of arsenate influx between tolerant and non‐tolerant plants was much greater for D. cespitosa than for A. capillaris. The mechanism of arsenate tolerance in D. cespitosa and A. capillaris was the same mechanism of tolerance that had been demonstrated in arsenate‐tolerant Holcus lanatus L. Reduced arsenate influx by adaptation of the arsenate uptake mechanism is a mechanism of tolerance that has evolved in three separate species.
Are seedlings from small seeds always inferior to seedlings from large seeds? Effects of seed biomass on seedling growth in Pastinaca sativa L.
Authors: HENDRIX STEPHEN D. , NIELSEN ERIC , NIELSEN TODD , SCHUTT MARK 
Published: April 2006

summaryPrevious field studies of recruitment in Pastinaca sativa L. indicate that more seedlings from small seeds than from large seeds survive short‐term droughts. To explore this phenomenon, the effects of variation in seed biomass in Pastinaca sativa on embryo size and seedling characteristics 10, 20, 30 and 40 days after emergence were investigated. On the basis of most characteristics, seedlings from large seeds should be superior to seedlings from small seeds. Embryo length and cotyledon area were positively related to seed biomass, as were above ground biomass, total leaf area, and root biomass in all harvests. Total seedling biomass was positively related to seed biomass in the 10, 20, and 30 day harvests, but not the 40 day harvest. However, the ratio of maximum root length/total leaf area was negatively related to seed biomass in the 10 and 20 day harvests, suggesting that, under drought conditions, seedlings from small seeds may transpire less water than those from large seeds relative to their ability to reach water supplies. Although seedlings from larger seeds had greater root biomass, this may be of little advantage under drought conditions since approximately 90% of the root biomass is in the upper 10 cm of soil which dries out quickly. The advantage that seedlings from small seeds have under drought conditions is short‐lived, lasting about 20 days in the glasshouse and an estimated 60–90 days in the field. This advantage is short‐term because the relationship between seed biomass and resource allocation patterns changes during early seedling development.
Population structure and mating system in Marasmius androsaceus Fr.
Authors: HOLMER LILLIAN , STENLID JAN 
Published: April 2006

summaryIsolates of the rhizomorph‐forming fungus Marasmius androsaceus were obtained from four different sites in stands of either Norway spruce or Scots pine of different age. The mating system and the mycelial interactions within each site were studied. The fungus had a bifactorial mating system and genetically different dikaryons were strongly mutually antagonistic in culture. On the basis of such antagonism, up to 18 different individual genets could be found within an area of 2.8 m2. No differences between the four sites could be detected with respect to the size of the genets. Isolates belonging to the same genet were frequently found in close proximity in areas from which other types were excluded. However, the older plots contained genets with a discontinuous distribution in the plots. The likely origin of this distribution is discussed in relation to the pattern of dispersal, establishment and spread of this saprophytic fungus in different woodland habitats.
Experimental studies of lobe growth in the lichen Parmelia conspersa (Ehrh. ex Ach.) Ach.
Authors: ARMSTRONG R. A. 
Published: April 2006

summaryThe radial growth of individual lobes of the foliose lichen, Parmelia conspersa (Ehrh. ex Ach.) Ach., was studied to determine whether (1) adjacent lobes exchange carbohydrate and (2) marginal competition between lobes influences radial growth. In a survey of thalli of different size, the number of marginal lobes was linearly related to thallus circumference. However, the relationship between mean lobe width and thallus circumference was fitted by a second order polynomial. Hence, mean lobe width may reach a maximum in thalli approx. 3 cm in diameter. The interactions between marginal lobes were studied by either painting single lobes with acrylic paint or by removing lobes from the thallus. Painting the whole of a lobe virtually stopped its radial growth while partially painted lobes grew less than control lobes. The radial growth of a lobe was unaffected by either completely painting or removing its neighbour. Removal of both neighbouring lobes did not influence the radial growth of a lobe but severing the lobe from the thallus reduced its radial growth. In addition, lobe width increased significantly when both neighbouring lobes were removed. These results suggest that adjacent lobes have a considerable degree of independence and that there is little exchange of carbohydrate between them. In addition, marginal competition between adjacent lobes may restrict the lateral extension of a lobe and this may maintain a more constant mean lobe width in larger thalli. It is possible that the intensity of marginal competition between adjacent lobes may vary with thallus size and this could be a factor determining the growth curve of a foliose lichen throughout its life.
The control of sucrose synthesis in leaves of Lolium temulentum L., a fructan‐accumulating grass
Authors: COLLIS B. E. , POLLOCK C. J. 
Published: April 2006

summaryThe control of sucrose synthesis was studied in leaves of the fructan‐accumulating species Lolium temulentum L. The cytoplasm it fructose‐1,6‐bisphosphatase (Cyt'F‐1,6‐BPase) was partially purified and its kinetic properties compared with the reported values for the enzyme from spinach leaves. The enzymes from the two species were similar, particularly in their inhibition by fructose‐2,6‐bisphosphate (F‐2,6BP). Leaves were excised and illuminated or whole plants were chilled and illuminated in order to increase the accumulation of sucrose and low‐molecular‐weight fructan, Leaf glucose‐6‐phosphate (G‐6‐P) and fructose‐6‐phosphate (F‐6‐P) contents were estimated. The G‐6‐P/F‐6‐P ratio showed that most of the hexose phosphates were present in the cytoplasm. In excised leaves G‐6‐P concentrations were higher than controls after 4 h of illumination, probably reflecting the release of glucose by fructan synthesis. This extra source of substrate supply may disrupt the coordinated control of sucrose phosphate synthase (SPS) and Cyt'F‐1,6‐BPase. The calculated activity of Cyt'F‐1,6‐BPase in vivo is insufficient to catalyse the observed flux of photo assimilates to sucrose and fructan. The maximum catalytic activity of phosphofructophosphotransferase (PFP) was determined, and was found to be 12–14Ümol hexose g1 f. wt h1 in control leaves. It is proposed that, given suitable metabolite concentrations, PFP could supplement the inhibited Cyt'F‐1,6‐BPase activity and contribute to the flux of photo assimilates to sucrose and fructan.