bluuebunny/crossref_metadata_2025_split huggingface dataset:
GLUTAMINE SYNTHETASE ISOFORMS IN ALGAE
Authors: CASSELTON P. J. , CHANDLER G. , SHAH N. , STEWART G. R. , SUMAR N. 
Published: May 2006

SUMMARYThe occurrence of glutamine synthetase isoforms in algae, from seven different phyla, has been investigated, using ion‐exchange chromatography. The algae have been classified into three groups according to their glutamine synthetase isoform content. The first group is characterized by having only the cytosolic glutamine synthetase, whereas the second group is distinguished by having only the chloroplastic glutamine synthetase. The third group is characterized by having both the isoenzymes. Stability studies were used along with the elution profiles from ion‐exchange chromatography to designate the isoforms to the cytosolic or the chloroplastic isoform. Immunoprecipitation studies, for specific identification of the cytosolic and chloroplastic isoforms showed varied results and indicated that the two forms from the lower algae have very similar antigenic sites.
THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS VI. THE RELATIONSHIP BETWEEN DEVELOPMENT OF INFECTION, AND INTENSITY OF INFECTION IN YOUNG LEEK ROOTS
Authors: AMIJEE F. , STRIBLEY D. P. , TINKER P. B. 
Published: May 2006

SUMMARYLeek plants (Allium porrum L.) were grown on gamma‐irradiated soil in tall pots with two layers of inoculum of the vesicular‐arbuscular mycorrhizal fungus Glomus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe, at depths of 6 and 9 cm respectively. The main axes of primary and adventitious roots extended linearly with time. However, the total root length and infected root length both increased exponentially, as did total root numbers. The fractional infection had a lag phase, a phase of rapid increase, and then a steady value.The density of internal hyphae rapidly increased in the main axis of infected primary roots while the infected segments extended at a constant rate, with sharply demarcated fronts each progressing at approx. 0.2 cm d−1. Where internal hyphae from the two infected segments met there was no resulting increase in hyphal density. This coalescence formed a single infection segment of uniform hyphal density. On these main axes, the total number of entry points increased exponentially with time after initial infection, but after 20 d the rate of increase declined sharply. At sites of initial infection there were high concentrations of unusually small entry points, but away from these the numbers per unit length of root diminished.At a higher concentration of soil phosphorus, results were similar for hyphal density and numbers of entry points, but fractional infection was less, because of increased root growth. We conclude that the length of infected root closely reflects hyphal biomass at moderate levels of soil phosphorus.
GROWTH, NUTRITION AND GAS EXCHANGE OF BROMUS INERMIS INOCULATED WITH GLOMUS FASCICULA TUM
Authors: BILDUSAS I. J. , DIXON R. K. , PFLEGER F. L. , STEWART E. L. 
Published: May 2006

SUMMARYPlants of Bromus inermis Leyss. inoculated or not with the mycorrhizal fungus Glomus fasciculatum (Thaxter sensu. Gerd.) Gerd. and Trappe, were pre‐conditioned at two soil moisture levels (Φs− 0.03 or − 0.8 MPa) for 17 weeks, then subjected to a drying cycle. Stomatal conductance (g1), soil‐plant liquid flow resistance (Rs−p), and photosynthesis rates (Ps) were measured before, during, and after the drying cycle. Soil water stress and mycorrhizal inoculation significantly reduced plant top dry weight during the 18 week study. Chlamydospore production by the mycorrhizal symbiont G. fasciculatum was significantly increased by soil water stress of −0.8 MPa. Foliar Ca and Mg concentrations were significantly greater in mycorrhizal plants. Foliar concentrations of P, K, N, Mn, Zn and Cu were significantly greater in drought stressed plants whereas Ca and Mg concentrations were significantly greater in well‐watered plants.Mycorrhizal plants pre‐conditioned at Φs−0.8 MPa had 36 and 34% lower Rs−p values than nonmycorrhizal plants at pre and peak drought sampling times, respectively. Following re‐irrigation, g1 was 64% greater in mycorrhizal plants when compared to nonmycorrhizal plants. Inoculation with G. fasciculatum increased photosynthesis rates by 20, 52, and 22 % over the noninoculated plants before, during, and after the drying cycle respectively. Despite increased rates of photosynthesis, top dry weight of mycorrhizal plants was 15 % less than that of noninoculated plants.Regardless of inoculation treatment, plants pre‐conditioned at ΦS−0.8 MPa exhibited greater g1 and Ps values during and after the drying cycle. Bromus inermis demonstrated the ability to adapt to water deficits. Mycorrhizal symbiosis may play a role in the adaptation of B. inermis to dry sites.
THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA
Authors: SCOTT MARTHA G. , LARSON DOUGLAS W. 
Published: May 2006

SUMMARY Umbilicaria vellea (L.) Ach. and U. deusta (L.) Baum. have distribution patterns that are mutually exclusive. U. vellea occurs in vertically inclined microsites that are permanently snow‐free. In contrast, U. deusta occurs on flat or gently sloping surfaces that receive a substantial snow cover. Earlier field work had suggested that this distribution pattern was maintained, at least in part, by the inability of U. vellea to store photosynthetic products and thereby maintain a positive carbon balance when growing in areas receiving a significant snow‐cover. We report controlled laboratory experiments conducted in order to determine which aspect of the subnivean environment interfered with U. vellea, but not with U. deusta. The four experiments investigated effects of long‐term continuous subzero temperatures, alternating periods of freeze and thaw, exposure to slightly above‐zero conditions (in the dark), and lastly, a combination of freezethaw and slightly‐above‐zero treatments.Only the slightly above‐zero treatment in the dark interfered significantly with CO2 exchange in U. vellea. None of the treatments reduced significantly CO2 exchange in U. deusta. The decline in productivity of U. vellea in the current experiments was identical to that found in material reciprocally transplanted in the field.We conclude that U. vellea is excluded from snow‐covered habitats because of an inability to store or mobilize stored respiratory substrate in the subnivean environment. In contrast, U. deusta which stores such products in great number, is able to survive long periods of time without a flux of photosynthates. It would appear that one of the costs of such an ability, is the allocation of very few reserves to growth.
PATHWAYS OF AMMONIUM ASSIMILATION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS NAEG.
Authors: AHMAD IFTIKHAR , HELLEBUST JOHAN A. 
Published: May 2006

SUMMARYGlutamine synthetase (GS) and NADPH‐glutamate dehydrogenase (GDH) are key enzymes for ammonium assimilation in Stichococcus bacillaris Naeg. (UTEX 314). Cells growing with different concentrations of nitrate and ammonium contain activities of both GS and NADPH‐GDH in excess of required nitrogen assimilation rates under autotrophic as well as heterotrophic conditions. The activity of GS increases 2 to 3 fold, and NADPH‐GDH 10 to 15 fold when the concentration of ammonium in the medium is lowered from 2 to 0–2 mM, or when nitrate is present as the nitrogen source. The activity of ferredoxin‐dependent glutamate synthase (GOGAT) is similar to, or high than that of GS. In this alga. NADPH‐GDH has a low Km for ammonium (1–6 mM), and is capable of functioning effectively over the pH range occurring in the chloroplast stroma. A possible role of NADPH‐GDH in nitrogen assimilation by S. bacillaris is supported by the observation that the alga grows normally in the presence of methionine sulphoximine (MSX), when high levels of this enzyme are present, while GS is almost completely inhibited. Stichococcus bacillaris also contains high activities of NADH‐GDH, but the Km for ammonium of this GDH (33 mM) appears too high for it to function effectively in nitrogen assimilation. The activity of NADH‐GDH increases 3 to 5 fold when cells growing photoautotrophically are transferred to heterotrophic conditions, suggesting a catabolic role for this enzyme.
THE STRUCTURE AND FUNCTION OF THE VEGETATIVE MYCELIUM OF ECTOMYCORRHIZAL PLANTS
Authors: FINLAY R. D. , READ D. J. 
Published: May 2006

SUMMARYIt is increasingly evident that in natural plant communities the vegetative mycelia of ectomy‐corrhizal fungi can form networks of hyphal interconnections which link the root systems of their host plants in both intra‐ and inter‐specific combinations. Root observation chambers have been used to examine the development of these mycelial networks and to assess their functional significance as pathways for the transfer of assimilate between individuals in a range of host‐fungus associations. Carbon transfer between plants of Pinus spp. is significantly increased by the presence of mycelial connections and preliminary evidence suggests that such transfer may be enhanced where concentration gradients are induced by shading. The significance of these experimental results is discussed in relation to nutrient cycling processes in natural ecosystems.
ANATOMY OF BRANCH ABSCISSION INLAGERSTROEMIA MICROCARPAWIGHT
Authors: BHAT K. V. , SURENDRAN T. , SWARUPANANDAN K. 
Published: May 2006

SUMMARYSome anatomical details of branch abscission inLagerstroemia microcarpaWight (Lythraceae) are discussed. Repeated abscission of numerous annual twigs and subsequent healing of their scars produce irregular growth of the subjacent branch portions to give gall‐like structures. In the abscission zone, secondary xylem fibres are thin walled and poorly lignified, with dense protoplasmic contents and closely spaced septa. Disintegration of pith parenchyma cells and shrinkage of bark and wood tissues contribute towards weakening of abscission zone. The protective zone situated proximal to the abscission zone is strongly lignified and rich in extractives. Detachment occurs immediately above the protective zone leaving the encircling dormant buds intact. Abscission scars are healed centripetally by the usual method of callus formation from the cambial tissue. It appears that branch abscission inL. microcarpais a mechanism to withstand drought by reducing the transpiring surface.
THE CONTRASTING RESPONSE TO SIMULATED ACID RAIN OF LEAVES AND COTYLEDONS OF CABBAGE (BRASSICA OLERACEA L.)
Authors: CAPORN SIMON J. M. , HUTCHINSON THOMAS C. 
Published: May 2006

SUMMARY Brassica oleracea L. (cabbage) was grown in glasshouse and controlled environments and exposed to simulated rains delivered as sprays at pH 5.6‐2.8. A single rain treatment of pH 3.0 given to 10 d old plants elicited a marked downward curvature in the cotyledons, occurring within the duration of the 30‐min spray. Subsequent to this initial response, the cotyledon surface was extensively damaged. In contrast, the older‘true’leaves showed little or no injury after similar treatments. Estimates of the contact angles between rain droplets and leaf surfaces, and SEM studies of adaxial surfaces, indicated that the contrasting morphology of the epicuticular wax on cotyledons and leaves was a major factor determining the extent of acid rain damage. Simulated rain treatments of pH 3.2 and 2.8, starting at the cotyledons stage, reduced plant growth by 17 and 15% respectively over a 20 d period. However, the same treatments given at later stages in development when the‘true’leaves were predominant, had no significant effect on growth. In the natural environment the occurrence of rate, highly acidic rain events during different stages of plant development may be an important determinant of the impact of rainfall on vegetation. The young, seedling stage of species, such as B. oleracea, in which cotyledons show poor development of surface wax, may be particularly vulnerable.
EFFECTS OF PHOSPHATE SUPPLY AND INOCULATION WITH A VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGUS ON THE DEATH OF THE ROOT CORTEX OF WHEAT, RAPE AND SUBTERRANEAN CLOVER
Authors: MacLEOD W.J. , ROBSON A. D. , ABBOTT L. K. 
Published: May 2006

SUMMARYThe effect of phosphorus supply and mycorrhizal infection on the death of the cortex of roots (RCD) was examined in two glasshouse experiments. RCD was observed in both Australian and English cultivars of wheat (Triticum aestivum L.), and in rape (Brassica napus L.), but not in subterranean clover (Trifolium subterraneum L.). It occurred most rapidly in wheat plants moderately deficient in phosphorus (i.e. in plants producing approx. 60% of shoot weight with phosphorus not limiting growth) but was delayed both in plants severely deficient in phosphorus and in plants with adequate and luxury supplies of phosphorus compared to those which were moderately deficient. Although inoculation with a vesicular‐arbuscular mycorrhizal fungus did not markedly affect plant growth, it delayed RCD in phosphorus‐deficient plants and accelerated RCD in phosphorus‐adequate plants. The effects of phosphorus supply and mycorrhizal infection on RCD cannot be readily explained by effects of these treatments on plant growth or phosphorus concentrations within plants. Moreover, it is unlikely that effects of these treatments on RCD are related to effects on the availability of assimilates required to maintain the cortex.
SITES OF FLAVONE ACCUMULATION IN SOME GENOTYPES OF SILENE PRA TENSIS (RAFN.) GODRON ET GREN. (CARYOPHYLLACEAE)
Authors: VAN GENDEREN H. H. , VAN HEMERT J. 
Published: May 2006

SUMMARYPetal laminae in Silene pratensis (Rafn.) Godron et Gren, contain 60 to 80% of the flower flavonoids. The flavone content of the petal lamina on a fresh weight basis is about 10 times that of the petal claw and at least five times that of the calyx. The ratios between the different glycosides found in the stigmata or in the stamen usually differ from those in the rest of the flower. The highest flavone concentration is always found in the vacuoles of the epidermal cells in the most exposed parts of both leaves and the flower. The total flavone distribution pattern is not influenced by the type of glycosylation.
ENDOGENOUS ETHYLENE AFFECTS THE BEHAVIOUR OF STOMATA IN EPIDERMIS ISOLATED FROM RUST INFECTED FABA BEAN (VICIA FABA L.)
Authors: TISSERA PREENI , AYRES P. G. 
Published: May 2006

SUMMARYRust infection of proximal halves of leaves of Vicia faba L. potentiates the sustained production of ethylene by abiotically wounded but uninfected distal regions. When epidermal strips were isolated from distal regions, either before or after incubation in aqueous media, stomatal opening was inhibited compared to that in strips from leaves of healthy, control plants. This inhibition, and the even greater inhibition seen in strips from rusted tissues, was reversed to differing extents by inclusion in the medium of inhibitors of the action of ethylene, namely silver ions (6 × 10−2 mol m−3), or of its biosynthesis, namely cobalt ions and AVG (both at 1 × 10−1 mol m−3). When ACC, a precursor of ethylene, was supplied to healthy leaves it promoted ethylene evolution after wounding and inhibited stomatal opening in strips isolated from those leaves. The cytokinins zeatin and kinetin (1 × 101 mol m−3) also promoted opening in strips from both healthy and rusted regions of infected leaves, but only fusicoccin (1 × 10−2 mol m−3) promoted wide opening in rusted regions. It is proposed that endogenous ethylene is an effective regulator of stomatal behaviour in epidermal strips prepared from either healthy or rusted regions of infected leaves of V. faba.
THE RESPONSES OF CYNOGLOSSUM OFFICINALE L. AND VERBASCUM THAPSUS L. TO DEFOLIATION IN RELATION TO NITROGEN SUPPLY *
Authors: VERKAAR H. J. , VAN DER MEDIJDEN E. , BREEBAART L. 
Published: May 2006

SUMMARYThe effects of defoliation of Cynoglossum officinale L. and Verbascum thapsus L. on growth, net assimilation rate and dry matter distribution were studied under various nitrogen regimes. At high levels of nitrogen supply, there was a higher net assimilation rate (NAR) and a higher leaf weight ratio in defoliated plants than in undefoliated plants resulting in a faster growth of defoliated plants. In V. thapsus growth of defoliated plants did not differ significantly from undipped plants. In a low nitrogen regime all defoliated V. thapsus plants died. In the same regime C. officinale had a low NAR and thus showed little regrowth. Leaf nitrogen content was not significantly different from control plants.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN FIELD‐GROWN CROPS
Authors: JAKOBSEN I. 
Published: May 2006

SUMMARYThe importance of vesicular‐arbuscular mycorrhiza (VAM) and P fertilizer for P nutrition and dry matter production in field peas (Pisum sativum L.) was studied in moderately P‐deficient soil. Half of the experimental plots were fumigated to reduce the level of VAM infection. Shoots and 0 to 30 cm soil cores were sampled on three occasions.An extensive VAM infection was rapidly established in untreated soil, whereas infection levels were low in fumigated soil. Root growth responded to fumigation by increased root length and decreased root diameter. Fumigation reduced the P content in shoots considerably, and correspondingly the mean rates of P inflow per unit root length were 60% lower in fumigated than in untreated soil during flowering. These effects of fumigation were ascribed to the low levels of VAM infection in fumigated soil. The production of dry matter was not decreased accordingly in fumigated plots, although both it and P uptake were increased by adding P fertilizer. The possible reasons for this discrepancy are discussed.A supplementary survey on infection development at five other field sites showed that peas are extensively colonized by VAM fungi, even in soils where a standard procedure is being used. These results indicate that VAM is of major importance to P uptake by the field‐grown pea.
INCREASED RATES OF PHOTOSYNTHESIS IN LOCALIZED REGIONS OF A BARLEY LEAF INFECTED WITH BROWN RUST
Authors: SCHOLES J. D. , FARRAR J. F. 
Published: May 2006

SUMMARYThe rate of photosynthesis was examined in whole leaves of barley infected with brown rust (Puccinia hordei Otth.) and within localized regions of the infected leaf, within brown rust pustules and in regions between them, from flecking to green island formation. In addition, oxygen evolution was measured from localized regions of a rusted leaf after feeding with inorganic phosphate (Pi) to investigate the hypothesis that fungal sequestration of Pi from the host cytoplasm may, totally or partially, be responsible for the decline in photosynthesis. The rate of net photosynthesis and the quantum yield of oxygen evolution declined in whole infected leaves as the disease progressed. However, the rate of gross photosynthesis (per unit chlorophyll) was increased in rusted leaves. Autoradiographic and oxygen evolution studies showed that the decline in net photosynthesis could be attributed largely to a reduction in the rate of photosynthesis in the regions between pustules. Within areas of the leaf invaded by the fungus, gross photosynthesis was increased in comparison to control tissue. Feeding leaf tissue with Pi did not significantly increase the rate of photosynthesis in pustules or regions between pustules, implying that Pi was not previously limiting the rate of photosynthesis. Possible mechanisms underlying the increase and decrease in photosynthesis in different regions of an infected leaf are discussed.
TOWARDS THE SELECTION IN VITRO FOR RESISTANCE TO ALTERNARIA BRASSICICOLA (SCHW.) WILTS., IN BRASSICA NAPUS SSP. OLEIFERA (METZG.) SINSK., WINTER OILSEED RAPE
Authors: MACDONALD MARY V. , INGRAM D. S. 
Published: May 2006

SUMMARYCulture filtrates of Alternaria brassicicola (Schw.) Wilts, were found to be toxic to secondary embryoids of Brassica napus ssp. oleifera (Metzg.) Sinsk. The culture filtrates were partially purified and added to tissue culture media to produce a selection medium. Different secondary embryoid lines of B. napus were found to differ in their sensitivity to the selection medium, and it was possible to select lines which showed increased resistance to the selection medium. Some plants that were regenerated from secondary embryoids were found to be more resistant to the pathogen than were seed‐grown plants of the same cultivar, although there was no correlation between sensitivity to the selection medium and susceptibility to the pathogen.
COMPETITION BETWEEN THREE LICHEN SPECIES USING A FACTORIAL EXPERIMENTAL DESIGN
Authors: ARMSTRONG R. A. 
Published: May 2006

SUMMARYCompetition between three foliose lichens common on slate rock in south Gwynedd, Wales was studied in the field using a factorial experimental design. The lichens were grown as fragments glued to pieces of slate in two‐ and three‐species mixtures. In the two‐species mixtures, Parmelia conspersa (Ehrh. ex Ach.) Ach. outcompeted Parmelia glabratula ssp. fuliginosa (Fr. ex Duby) Laund. strongly and Physcia orbicularis (Neck.) Poetsch less strongly, while P. orbicularis outcompeted P. glabratula weakly. Significant two‐factor interactions indicated that the results from the three‐species mixture could not be predicted from the two‐species mixtures. Parmelia glabratula and P. orbicularis grew better in the presence of two competitors than one. This result suggests that the three species may co‐occur on well‐lit rock surfaces at the site.
THE ASSESSMENT OF NITROGEN FIXATION AND THROUGHPUT BY LICHENS IV. NITROGEN LOSSES FROM PELTIGERA MEMBRANACEA (Ach.) Nyl. IN AUTUMN, WINTER AND SPRING
Authors: MILLBANK J. W. , OLSEN J. D. 
Published: May 2006

SUMMARYUndisturbed associations of Peltigera membranacea and associated mosses were held under simulated autumn, winter and spring conditions in a specially constructed, controlled‐environment chamber providing an atmosphere enriched with labelled nitrogen. Simulated rainfall via a programmable sprinkler system was incorporated, and the liquid run‐off was collected during 4 week experimental periods. Dry weight, total nitrogen and 15N labelling of the moss, lichen and run‐off liquid were determined, and nitrogenase activity of the lichen thalli was estimated by acetylene reduction at the end of the tests. It was estimated that the mosses derived direct nutritional benefit from nitrogen compounds leached from the lichen thalli, but due to simultaneous nitrogen‐fixing activity by epiphytes strictly quantitative estimates of the beneficial effects of the lichen were unobtainable.
EFFECTS OF ZINC ON CELL, NUCLEAR AND NUCLEOLAR SIZE, AND ON RNA AND PROTEIN CONTENT IN THE ROOT MERISTEM OF A ZINC‐TOLERANT AND A NON‐TOLERANT CULTIVAR OF FESTUCA RUBRA L.
Authors: POWELL M. J. , DAVIES M. S. , FRANCIS D. 
Published: May 2006

SUMMARYThe effects of a 4 d exposure to Zn on some cellular characteristics in the root meristem were investigated in seedlings of a Zn‐tolerant cultivar of Festuca rubra L. (Merlin) and in a non‐tolerant cultivar (S59). In S59, 0.1 and 0.2 μg Zn cm−3 resulted in a 7% and 17% reduction, respectively, in the mean area of mitotic cells compared with controls grown in the absence of Zn. Moreover, mean nuclear volume (13% and 28%) and total nucleolar volume (43% and 65 %) of G2 cells and RNA content (9 % and 44 %) and protein content (6 % and 17 %) of mitotic cells were also reduced by Zn. In Merlin, however, the mitotic cell area was 4 % and 19 % larger at 0.1 and 0.2 μg Zn cm−3 compared with the controls. Treatment with Zn also increased nuclear volume (13% and 47%) and total nucleolar volume (42 % and 86%), of G2 cells and RNA content (40 % and 32 %) and protein content (8 % and 33 %) of mitotic cells. The concentration of protein in mitotic cells was also increased by Zn treatment in Merlin. The data are discussed in relation to the previously established effects of Zn on the duration of the cell cycle in these cultivars.