bluuebunny/crossref_metadata_2025 huggingface dataset:
ZINC TOLERANCE IN BETULA SPP.
Authors: DENNY HILARY J. , WILKINS D. A.
Published: April 2006

A survey was made of fungi forming ectomycorrhizas with Betula pendula Roth, and B. pubescens Ehrh. on zinc‐contaminated mine tailings. Strains of Paxillus involutus Fr. from toxic and non‐toxic soils were compared. There was no indication of fungal adaptation to zinc at either the inter‐ or intraspecific level. Most of the typical fungal associates of Betula on normal soils were also found on the zinc‐rich soils. The ability of different strains of P. involutus to (a) grow in pure culture on agar, (b) form ectomycorrhizas with Betula, and (c) produce a beneficial growth and zinc uptake response in the associated plant, all in the presence of raised zinc concentrations, was not related to the zinc status of the provenance. The ameliorating influence of P. involutus on zinc toxicity to Betula seemed to be positively linked to the degree of compatibility between fungal strain and higher plant.
ZINC TOLERANCE IN BETULA SPP.
Authors: DENNY HILARY J. , WILKINS D. A.
Published: April 2006

Aseptic cultures of Paxillus involutus Fr. and clones of Betula pendula Roth, and B. pubescens Ehrh. were used in experiments, involving X‐ray microanalysis and split‐plate culture, to investigate the mechanism of ectomycorrhizal amelioration of zinc toxicity to Betula. Results imply that as the fungal mycelium colonizes fresh soil, zinc is adsorbed to the surface of hyphae, thereby lowering the concentration of zinc in the soil solution surrounding roots. In consequence, less zinc is taken up, and growth is better than in the non‐mycorrhizal condition. The results also show that the metal may be adsorbed to electronegative sites in the hyphal cell walls and extra‐hyphal, polysaccharide slime. The possible dual role of this slime in fungus/Betula compatibility and the amelioration mechanism is discussed.
WATER STRESS MODIFIES INTRASPECIFIC INTERFERENCE BETWEEN RUST (PUCCINIA LAGENOPHORAE COOKE)‐INFECTED AND HEALTHY GROUNDSEL (SENECIO VULGARIS L.)
Authors: PAUL N. D. , AYRES P. G.
Published: April 2006

Populations of groundsel (Senecio vulgaris L.) were grown in the field in bottomless containers which allowed roots to penetrate freely into the natural soil profile. The 36 plants within each population (equivalent to 1250 m−2) were either all inoculated with the rust Puccinia lagenophorae Cooke, all rust free, or were a 1:1 mixture of the two. Rain was excluded from all populations by small shelters. Half the populations were subjected to mild drought, whilst remaining populations were well‐watered. Rust significantly reduced shoot dry weights, especially in droughted populations. The frequency distributions of shoot dry weight showed significant inequality (were strongly skewed) in all treatments and populations. Inequality of the frequency distribution of shoot dry weight was increased in rusted populations because infection increased the proportion of suppressed individuals. Again the effect of rust was most pronounced under conditions of drought and particularly in mixture. Rust significantly lowered mean shoot water potential (ψ) in dry monocultures and in both wet and dry mixtures. Values of ψ at harvest in suppressed, rusted individuals in mixtures were often highly negative. Compared with dry monocultures, water stress in mixtures was ameliorated in the healthy, but exaggerated in the rusted, components. The more negative values of ψ in rusted populations were the result of changes in frequency distributions as well as in mean values. Under dry conditions status in the dry weight hierarchy was closely correlated with ψ These changes are interpreted as reflecting the reduced ability of the root systems of rusted plants to compete for limited water.

The competitive ability of control over rusted groundsel, as measured by relative crowding coefficient (Ker), was 1–09 under well‐watered conditions but increased to 1˙51 under drought. In both well‐watered and droughted populations, the greater impact of rust on the population hierarchy of mixtures was reflected in the inverse relationship between the status of sub‐classes, based on shoot weight and class Ker. It is concluded that water stress probably plays a crucial role in determining the impact of rust on mixed populations in the field.
WHEN IS A CHROMOPLAST?
Authors: WHATLEY J. M. , WHATLEY F. R.
Published: April 2006

Summary

Chromoplasts are heterogeneous organelles and their carotenoids can be associated with several different structural elements including globules, tubules and membranes. In the flower petals of some species, carotenoids are absent or present only in trace amounts. Nevertheless, the plastids in such flowers can closely resemble or even be indistinguishable in structure from chromoplasts.
THE EFFECT OF MANGANESE ON ROOT EXTENSION OF GEUM RIVALE L., G. URBANUM L. AND THEIR HYBRIDS
Authors: WALDREN S. , DAVIES M. S. , ETHERINGTON J. R.
Published: April 2006

Summary

Root elongation of Geum rivale and G. urbanum grown in nutrient solution decreased as manganese concentration was increased above 25 mg dm−3, especially in G. urbanum. Prior exposure of roots to 25 mg Mn dm−3increased their capacity for subsequent elongation in manganese solutions, the effect of such pretreatment being most pronounced in G. rivale. G. rivale was significantly more tolerant of 50 mg Mn dm−3than G. urbanum. Efflux of potassium from root segments, used as a measure of membrane permeability, was significantly higher in G. urbanum than in G. rivale at this concentration. Tolerance of 50 mg Mn dm−3by progeny of hybrid individuals was generally related to morphological intermediacy, although there were some noticeable exceptions. Manganese tolerance of hybrids could not be consistently related to their known tolerance of waterlogging.
COMPARATIVE STUDIES OF PLANT GROWTH AND DISTRIBUTION IN RELATION TO WATERLOGGING
Authors: WALDREN S. , ETHERINGTON J. R. , DAVIES M. S.
Published: April 2006

Summary

Geum rivale L. and G. urbanum L. were grown in drained, continuously flooded or transiently flooded compost for 21 weeks. Leaf and root material harvested after this time was analyzed for Fe, Mn, Ca and P. Mn and Fe concentrations in roots and leaves of both species were increased by flooding. Higher Fe concentrations accumulated in the roots, while Mn was present in roughly equal concentrations in both roots and leaves. Leaf Ca concentration of both species was higher than that of roots. Although Ca concentrations were significantly higher in G. rivale than in G. urbanum, there were no readily interpretable effects of waterlogging. P concentration was decreased in leaves and increased in roots of flooded G. urbanum, although there was much less effect of flooding on P concentration in G. rivale. Fe may be precipitated by phosphate in G. urbanum roots, but this may lead to P deficiency in shoots and roots, resulting in poor growth of this species in waterlogged soil. A different mechanism of Fe immobilization is likely to occur in G. rivale, which does not result in phosphorus deficiency.
AN ANALYSIS OF THE INFLUENCE OF CLONE SIZE AND STOLON CONNECTIONS BETWEEN RAMETS ON THE GROWTH OF GLECHOMA HEDERACEA L.
Authors: SLADE ANDREW J. , HUTCHINGS MICHAEL J.
Published: April 2006

Summary

Two experiments were conducted in which the influence of size of clones and the persistence of stolon connections on subsequent development were examined in Glechoma hederacea. In the first experiment, clones were grown from either one unrooted ramet or from either one, two or three connected, rooted ramets, for 8 weeks, in either nutrient‐rich or nutrient‐poor sand. The survival, number of ramets and dry weight of the clones produced were dependent on the number of established ramets at the start of the experiment. Clones in nutrient‐rich sand developed a greater number of ramets, stolon branches, total length of stolon, mean leaf area per ramet and total leaf area per clone than clones of corresponding initial size in nutrient‐poor sand. In the second experiment, the stolon connections between ramets of G. hederacea clones growing in boxes were either left intact or severed soon after each ramet had rooted. After 10 weeks of growth, the total dry weight of the intact clones and the mean dry weight of their ramets were significantly greater than the corresponding values for severed clones. The spatial distribution of ramets showed marked differences between the treatments. Severed clones produced a greater number of rooted ramets within the boxes and a smaller number of unrooted ramets beyond the box edges than intact clones. Density of ramets more than doubled when stolons were severed.

Maintenance of stolon connections in G. hederacea is advantageous because it improves the probability of daughter ramet survival, promotes rapid lateral expansion of the clone and reduces inter‐ramet competition through the production of fewer, larger ramets.
THE DYNAMICS OF AN EXPERIMENTAL POPULATION OF SALVIA LYRATA: THE POPULATION CAGE APPROACH APPLIED TO PLANTS
Authors: SHAW RUTH G. , ANTONOVICS JANIS
Published: April 2006

Summary

We report a four‐year study of the dynamics of a population of Salvia lyrata L., growing in a greenhouse. The study exemplifies the population cage approach, which has been the basis of many long‐term studies of dynamics of animal populations for over 50 years, but which has been overlooked by plant population biologists. The cohort of plants that founded the population had a very high probability of survival and, as adults, produced the greatest numbers of seeds and seedlings. Thereafter, the numbers of individuals in each stage class declined. This decline appeared to be a consequence of density‐dependent processes. At the conclusion of the study, the population density was far lower than at the onset. The behaviour of the population differed from that of the population of S. lyrata studied in a nearby mown field in several respects, including timing of seedling emergence, average size of individuals and final density. Likely causes of these differences are discussed. We recommend the use of population cages in further studies of plant populations. Because it facilitates long‐term observation, this approach can be of great use in elucidating the dynamic consequences of demography.
TRANSPORT OF SUGAR IN PHYTOPHTHORA PALMIVORA (BUTL.) BUTL.
Authors: SHEARD J. , FARRAR J. F.
Published: April 2006

Summary

The kinetics of uptake of sucrose, glucose and fructose by Phytophthora palmivora are all biphasic. At low concentrations, glucose and fructose share a common, high‐affinity, hexose carrier, and sucrose is probably hydrolyzed extracellularly at these concentrations before the transport of the resultant hexoses by this carrier. At higher concentrations, a low‐affinity carrier may transport sucrose directly, but this carrier appears to have a higher affinity for glucose than sucrose. Activity of neutral invertase (β‐D‐fructofuranoside fructohydrolase) in both soluble and particulate (cell‐wall) preparations is considerably in excess of the highest rates of sucrose uptake.
CHLOROPLAST DEVELOPMENT IN LIGHT‐ AND DARK‐GROWN SPOROPHYTES OF PHAEOCEROS LAEVIS (L.) PROSK. (ANTHOCEROTOPHYTA)
Authors: LIGRONE R. , FIORETTO A.
Published: April 2006

Summary

Chloroplast development in light and in darkness was investigated in the sporophyte of the anthocerote, Phaeoceros laevis (L.) Prosk. In both light‐and dark‐grown sporophytes, chloroplasts with an elaborate inner membrane system were found in chlorenchyma cells about 3 mm from the sporophyte base. Development in the dark resulted in a net increase of the average number of grana per unit of chloroplast area and of thylakoids per granum, and a parallel diminution in the chlorophyll a/b ratio. Substantial amounts of chlorophyll were synthesized in the dark. Small, paracrystalline arrays of membranes associated with extensive thylakoid stacks were found in immature plastids of dark‐grown sporophytes. These structures disappeared during early stages of subsequent chloroplast differentiation. These results are the first indication that the anthocerotes do not require light for the differentiation of their photosynthetic apparatus.
EFFECTS OF DROUGHT STRESS ON GROWTH RESPONSE IN CORN, SUDAN GRASS, AND BIG BLUESTEM TO GLOMUS ETUNICATUM*
Authors: HETRICK B. A. DANTELS , KITT D. GERSCHEFSKE , WIILSON G. THOMPSON
Published: April 2006

Summary

The responses of mycorrhizal corn (Zea mays L.), sudan grass [Sorghum vulgare (Piper) Hitch.], and big bluestem (Andropogon gerardii Vitman) under drought stress were compared. Although growth of each of the plant species benefited from the mycorrhizal fungus under adequately watered conditions, inoculation had no effect on the growth of corn or sudan grass when cyclic drought stress was imposed on these plants. In contrast, growth of mycorrhizal big bluestem was significantly greater than non‐mycorrhizal big bluestem, even under severe drought stress. Drought‐stressed mycorrhizal plants without phosphorus amendment were not larger than drought‐stressed, non‐inoculated, fertilized (15 mg kg 1p) plants, suggesting no increased drought tolerance.

The ability of Glomus etunicatum Becker & Hall to benefit plant growth under drought stress was apparently plant‐mediated and possibly related to the dependency of the plant on this mycorrhizal fungus. Under adequately watered conditions, inoculated corn and sudan grass were respectively 1.23 and 1.13 times larger than non‐inoculated plants, while inoculated big bluestem was 6.56‐fold larger than non‐inoculated control plants.
WATER RELATIONS OF MYCORRHIZAL AND PHOSPHORUS‐FERTILIZED NON‐MYCORRHIZAL CITRUS UNDER DROUGHT STRESS*
Authors: GRAHAM J. H. , SYVERTSEN J. P. , SMITH M. L.
Published: April 2006

Summary

Rootstock seedlings of Carrizo citrange (Poncirus trifoliata (L.) Raf. x C. Sinensis (L.) Osbeck) and sour orange (Citrus aurontium L.) were grown in a sandy soil low in phosphorus (P) and either inoculated with Glomus intraradices Schenck & Smith (vesicular‐arbuscular mycorrhizal; VAM) or fertilized with soluble P (non‐mycorrhizal; NM). Five‐month‐old VAM and NM seedlings of each rootstock were comparable in size, P sufficiency, and relative growth rate whether they were kept well‐watered or subjected to two drought‐stress cycles of short duration. Under well‐watered conditions, whole plant transpiration, leaf water status, and root hydraulic conductivity were similar for VAM and NM plants of each rootstock. During drought‐stress and recovery periods, VAM plants also had very comparable whole‐plant transpiration rates and leaf water potentials to NM plants, but mycorrhiza reduced root hydraulic conductivity of Carrizo citrange and sour orange 66 and 49%, respectively. These data do not support the hypothesis that mycorrhiza significantly enhance water relations of citrus under the drought‐stress conditions studied.
THE PROCESSES OF ANTHER DEHISCENCE AND POLLEN DISPERSAL
Authors: KEIJZER C. J.
Published: April 2006

Summary

The development of the locule of Gasteria verrucosa (Mill.) H. Duval and Lilium hybrida cv. Enchantment, especially the border between the sporophyte and the gametophyte, is investigated by means of light and electron microscopy, histochemistry and micromanipulation and related to pollen dispersal. The pecto‐cellulosic cell walls of both the middle layer and the tapetum and a part of the endothecium disappear, and the tapetum cells are covered with sporopollenin‐containing tapetal membranes and orbicules. The cell contents of the tapetum turn into the hydrophobic pollenkitt. In the locule, similar changes are observed as the pecto‐cellulosic and callose walls of the meiocytes disappear and the future pollen grains are covered with the sporopollenin‐containing exine. Due to their non‐wettability, these hydrophobic substances on both sides of the sporophyte–gametophyte surface are important in pollen dispersal.

The transfer of pollenkitt from the tapetum to the locule appears to be due to capillary forces in the locule after the continuous expansion of the pollen, rather than to active flow or to direct attraction by the pollen grains.
THE EFFECT OF ABSCISIC ACID ON CALCIUM‐MEDIATED REGULATION OF HETEROCYST FREQUENCY AND NITROGENASE ACTIVITY IN NOSTOC 6720
Authors: SMITH R. J. , HOBSON S. , ELLIS I. R.
Published: April 2006

Summary

Abscisic acid (ABA) promoted a significant increase of the heterocyst frequency in cultures of Nostoc 6720. A significant interaction between ABA and the concentration of Ca2+ in the growth medium was detected. Studies using 45Ca2+ confirmed that the intracellular Ca2+ content was raised by 20% in the presence of 10−6 M ABA. Verapamil, a Ca2+ channel antagonist, inhibited the ABA‐induced increase in heterocyst frequency. Trifluoroperazine, a known inhibitor of Ca2+/protein binding, also inhibited the response to ABA.

The characteristics of the response to ABA were similar to those of the Ca2+ ionophore, A23187. Both promote an increase in the total nitrogenase activity of the culture, which, it is suggested, may result from a Ca2+‐dependent protective mechanism similar to that proposed for Gleocapsa. A Ca2+‐dependent repression of dinitrogen fixation is suggested to account for the increased nitrogenase activity in cultures induced to form heterocysts in the presence of lanthanum or when the concentration of Ca2+ in the growth medium is less than 10−4 M.
COMPARATIVE STUDIES OF PLANT GROWTH AND DISTRIBUTION IN RELATION TO WATERLOGGING
Authors: TALBOT RICHARD J. , ETHERINGTON JOHN R.
Published: April 2006

Summary

Rooted cuttings of Salix caprea and of S. cinerea ssp. oleifolia were supplied with 0 to 320 mg Fe2+ dm3 as sulphate dissolved in nutrient solution either at a constant concentration or supplied incrementally. Photosynthesis and respiration of the treated plants was monitored by infrared gas analysis for periods of 4 to 7 d.

Control shoots, in air‐bubbled or nitrogen‐bubbled solutions, maintained constant rates of photosynthesis and dark respiration during the experimental period. S. cinerea was unaffected by a constant concentration of 160 mg Fe2+dm3 or incremental additions reaching 320 mg Fe2+ dm−3. S. caprea was unaffected by 10 mg Fe2+ dm3, but a constant concentration of 40 mg Fe2+ dm3 or incremental additions reaching 40 mg Fe2+ dm3 caused almost total inhibition of photosynthesis and considerable reduction of respiration.

Repeating these experiments using cuttings with excised roots increased the sensitivity of both species so that, even in S. cinerea, 10 mg Fe2+ dm3 was inhibitory to photosynthesis.
GROWTH AND MAINTENANCE RESPIRATION OF PERENNIAL ROOT SYSTEMS IN A DRY GRASSLAND DOMINATED BY AGROPYRON DASYSTACHYUM (HOOK.) SCRIBN.
Authors: REEKIE E. G. , REDMANN R. E.
Published: April 2006

Summary

Respiration coefficients were determined for laboratory‐grown root systems of Agropyron dasystachyum (Hook.) Scribn. (northern wheatgrass). The growth respiration coefficient (0˙85 g g−1) was similar to published rates for species from mesic sites. The maintenance coefficient (0˙037 g g−1 d−1) was relatively low, suggesting that plants growing in semi‐arid habitats have inherently low maintenance costs per unit of biomass. The proportion of total root biomass requiring maintenance (degradable fraction) was determined by measuring the non‐structural root biomass. The degradable fraction (0˙13) was substantially lower than published measurements of functional (or ‘live’) biomass, because the latter include structural biomass, which has no maintenance requirement. Respiration parameters, root growth, degradable root fraction, soil temperature and soil moisture were used to construct a model of root respiration in field‐grown roots. The maintenance coefficient was adjusted downward during periods of water stress and low temperature when roots probably were dormant. Parameters in the model, particularly the degradable biomass fraction, explained much of the discrepancy between respiration rates of laboratory‐grown and field‐grown root systems. Maintenance respiration represents a substantial outlay in the carbon budgets of dry grasslands but is lower than expected considering the large root biomass in these systems.
RESPIRATORY METABOLISM IN ISOLATED ORCHID PETAL CELLS
Authors: HEW C. S. , YIP K. C.
Published: April 2006

Summary

A respiratory drift has been demonstrated in cells isolated from petals of Aranda flowers at different stages of development. Tight buds had a respiratory quotient of 0˙5; this increased to 0˙7 in the first flower and reached 1˙0 in the mature flower. There appeared to be a non‐glycolytic pathway contribution in addition to the EMP pathway in tight bud and newly opened flower stages. Carbohydrate metabolism in the mature flower proceeds predominantly via the EMP pathway. Cyanide‐insensitive respiration was demonstrated in the tight bud. There was a shift towards cyanide‐sensitive respiration as the flower developed.
THE DIURNAL PATTERN OF DINITROGEN FIXATION BY CYANOBACTERIA IN SITU
Authors: GRIFFITHS MARK S. H. , GALLON JOHN R. , CHAPLIN ALAN E.
Published: April 2006

Summary

The diurnal patterns of cyanobacterial acetylene reduction (nitrogen fixation) and seasonal variations in these patterns were investigated in situ on a salt marsh and in a limestone cave. In the field, the non‐heterocystous species fixed N2 mainly at night, while heterocystous species fixed N2 mainly during the day. These basic patterns could be influenced by environmental conditions such as O2 availability and temperature. No acetylene reduction was observed in December, January or February.
NITROGEN ASSIMILATION AND ZINC TOXICITY TO ZINC‐TOLERANT AND NON‐TOLERANT CLONES OF DESCHAMPSIA CESPITOSA (L.) BEAUV.
Authors: SMIRNOFF N. , STEWART G. R.
Published: April 2006

Summary

The effect of nitrate and ammonium nutrition on the toxicity of zinc to zinc‐tolerant and non‐tolerant clones of Deschampsia cespitosa (L.) Beauv, was investigated. Zinc and nitrogen source interacted in their effect on root growth and zinc tended to be less toxic if ammonium was the nitrogen source. Root growth of the non‐tolerant clone was inhibited by ammonium. Zinc caused chlorosis in nitrate‐grown tolerant plants but not in ammonium‐grown plants. Zinc caused a decrease in the concentrations of reduced nitrogen compounds in leaves and decreased nitrate translocation to them. The zinc concentration in roots was slightly decreased in ammonium‐grown plants. In vivo nitrate reductase activity was stimulated by high zinc concentrations in the tolerant clone. Asparagine and proline accumulated in response to zinc treatment in the non‐tolerant clone. Ammonium nutrition also induced asparagine accumulation and such accumulation was much greater in the non‐tolerant clone.

The small decrease in zinc toxicity when ammonium is the nitrogen source could be only partly accounted for by lower zinc uptake. It is suggested that asparagine which accumulates in ammonium‐grown plants, forms an intracellular complex with zinc and thereby decreases its toxicity.
ROOT HAIRS AND PLANT GROWTH ATLOW NITROGEN AVAILABILITIES
Authors: ROBINSON DAVID , RORISON I. H.
Published: April 2006

Summary

Four grass species, Holcus lanatus L., Deschampsia ftexuosa (L.) Trin., Poa annua L. and Lolium perenne L. cv. S.23 and cv. ‘Norlea’ were grown for 28 d in continuous flow nutrient solution containing nitrogen (N) at one of three concentrations (0.02, 0.21 or 4.0 mol m−3) as nitrate or ammonium. Growth, N uptake and root hair production were measured.

Root hair growth in D. flexuosa and P. annua was the most responsive to low N availability. These responses were generally greater to ammonium than nitrate.

The possible effects of the absence of root hairs on growth were tested via empirical relationships between relative growth rates and N inflow rates to estimate the contributions made to growth by root hairs. Only in D. flexuosa at the lowest N concentration were significant contributions found. Nitrate and ammonium had no differential effect in this respect.
NH4+ UPTAKE BY THE UNICELLULAR ALGA CYANIDIUM CALDARIUM
Authors: RIGANO VITTORIA DI MARTINO , VONA VINCENZA , MANZO LUIGI , RIGANO CARMELO
Published: April 2006

Summary

Measurements of NH4+ uptake by Cyanidium caldarium (Tilden) Geitler, an acidophilic thermophilic non‐vacuolate unicellular red alga, were made with cells grown either in batch culture with excess ammonium or in continuous culture with nitrogen limitation.

Batch‐grown cells absorbed NH4+ at a lower rate than chemostat‐grown cells, and uptake was greatly inhibited in darkness (83 %) and by CO2 deprivation (74%). In chemostat‐grown cells, in contrast, darkness inhibited uptake by only 20 to 30%. In chemostat‐grown cells subjected, after the addition of ammonium, to alternate light/dark cycles over 7 h of incubation, the rate of NH4+ uptake in the successive dark periods progressively decreased and fell to only 15% of the initial rate after 5 h incubation. In the successive light periods, in contrast, there was a 15% decrease in rate from one light period to the next, and after 7 h the rate of uptake was still 50% of the initial value. At this time, transfer of the cells from light to darkness resulted in 85% inhibition of uptake. It is suggested that in C. caldarium the overall process of ammonium assimilation is controlled, at the level of ammonium entry into the cell, either through the involvement of two independently controlled uptake systems or through multiple interconvertible forms of a single system, sharing different regulatory properties.
HYDROXYLAMINE METABOLISM IN MONORAPHIDIUM BRAUNII
Authors: BALANDIN TERESA , APARICIO PEDRO J.
Published: April 2006

Summary

Cells of Monoraphidium braunii L‐egnerova metabolized hydroxylamine, reducing it stoichio‐metrically to ammonium in darkness. In light, the rate of hydroxylamine disappearance was slightly higher than that of the ammonium release to the medium. This may indicate photo‐oxidation of hydroxylamine. Hydroxylamine much impaired ammonium assimilation. Therefore its reduction always resulted in the release of the generated ammonium.

Light‐dependent nitrite utilization by the cells was also severely impaired by hydroxylamine, whereas the hydrogen‐dependent nitrite reduction carried out by anaerobic dark‐adapted cells was unaffected. Hence, hydroxylamine does not appear to inhibit nitrite reductase. There was a close correlation between the kinetics of nitrite utilization and those of oxygen evolution.

Hydroxylamine prevented photosynthetic cell growth, but when the cells had removed hydroxylamine from the medium growth resumed.
DYNAMIC EXPERIMENTAL EVIDENCE FOR THE PLASMA MEMBRANE ATPase DOMAIN HYPOTHESIS OF HAUSTORIAL TRANSPORT AND FOR IONIC COUPLING OF THE HAUSTORIUM OF ERYSIPHE GRAMINIS TO THE HOST CELL (HORDEUM VULGARE)
Authors: GAY JOHN L. , SALZBERG A. , WOODS A. M.
Published: April 2006

Summary

Barley coleoptile epidermes, prepared in special mounts for microscopic examination, were infected with Erysiphe graminis D.C. ex Merat (powdery mildew) and, after 2 d, used for experiments in which reagents were introduced to the exposed underside. Fluorescein, introduced by means of fluorescein diacetate, fluoresced for periods of over 45 min in the epidermal cytoplasm and for longer in the Haustoria which had developed. Cytoplasmic streaming in the epidermal cells continued for over 24 h. The duration of fluorescence was reduced by FCCP, but fusicoccin increased both the duration and intensity.

In similar experiments in which the upper surfaces of infected leaves were detached so that the epidermal cells were disrupted and the extrahaustorial membranes were in direct contact with the experimental solutions, the duration of haustorial fluorescence was shorter than as described above in controls and with FCCP. Fusicoccin had no effect.

The fluorescence, interpreted as an indicator of intracellular pH, confirms the ATPase domain hypothesis of haustorial transport and indicates that each haustorium is ionically coupled to the cytoplasm of its host cell.
GENOME HETEROGENEITY AND CLASSIFICATION OF THE POACEAE
Authors: KING G. J. , INGROUILLE M. J.
Published: April 2006

Summary

Intragenomic base composition heterogeneity was investigated in 35 species of the grass family Poaceae, using high‐resolution thermal denaturation of DNA to produce base composition distributions. These show a pattern of peaks and shoulders which represent overlapping components of discrete base composition and provide a ‘fingerprint’ of the genome of a species. Quantitative comparison of distribution by distance matrix and cluster analysis supported traditional groupings within the Poaceae and allowed clarification of previous artificial relationships between taxa. The technique was most successful in distinguishing between taxa within subfamily, from tribal to generic level. Use of an absolute measure of all sequences present in a genome avoids problems inherent in commonly used DNA/DNA hybridization methods for determining homology. The non‐random distribution of DNA base composition components conserved among related genomes is discussed in relation to chromosome architecture and to exploitation of the gene pool of the Poaceae.
SECONDARY EMBRYOGENESIS IN LONG‐TERM CULTURES OF WINTER OILSEED RAPE, BRASSICA NAPUS SSP. OLEIFERA
Authors: SHU W. , LOH C. S.
Published: April 2006

Summary

Secondary embryogenic potential of winter oilseed rape, Brassica napus ssp. oleifera (Metzg.) Sinsk. cv. Primor, was maintained for over six years without diminution. Cytological analysis of 22 randomly selected secondary embryoids showed that they were all haploid. Many factors affect secondary embryogenesis in culture. The frequency of secondary embryogenesis was enhanced by the incorporation of 15 g l−1 sucrose into the medium; sucrose at 60 to 120 g l−1 inhibited secondary embryogenesis. Incubation in continuous darkness or continuous light led to a marked suppression of secondary embryogenesis. The best light regime for secondary embryogenesis was 16 h light/8 h dark. Incorporation of activated charcoal into the culture medium and the application of gamma radiation suppressed secondary embryogenesis. Further secondary embryogenesis was significantly reduced when only part of the secondary embryoid was cultured. The results discussed are based on the possibility that endogenous growth regulators may be involved in the initiation of secondary embryoids.
PLASTID DIMORPHISM IN LEAVES OF THE TERRESTRIAL ORCHID, OPHRYS SPHEGODES MILLER
Authors: LUX A. , HUDÁK J.
Published: April 2006

Summary

The leaves of the terrestrial orchid Ophrys sphegodes Miller possess two entirely different types of plastid. Mesophyll cells contain chloroplasts with well‐developed grana and scattered plastoglobuli. By contrast, vascular parenchyma cells have plastids which lack thylakoids. Their shape varies from spherical to irregularly cup‐shaped.
THE EFFECTS OF LIGHT AND TEMPERATURE ON THE GROWTH OF AND BALANCES OF CARBON, NITROGEN AND POTASSIUM BETWEEN VICIA FABA L. AND APHIS FABAE SCOP.
Authors: GARSED S. G. , DAVEY H. , GALLEY D. J.
Published: April 2006

Summary

The effects of light, temperature and infestation by Aphis fabae Scop, on Vicia faba L. were examined in a factorial experiment. Light was 1116 or 40 μmiol m‐2 s‐1 PPFD and temperature 15/10 °C or 25/20 °C (16 h day/8 h night). Plants and aphids were harvested after 9 d at 25/ 20 °C and 13 d at 15/10 °C. High light and high temperature increased the relative growth rate (RGR) of aphid colonies, but without interaction. Under high light, alatae produced more nymphs which grew larger. High temperature did not affect nymph production, but mature apterae weighed less. More honeydew was produced at high light. High temperature increased honeydew at high light, but decreased it at low. Reduction in dry weight (d.w.) of infested plants was similar to the calculated dry matter (d.m.) ingested by the aphids except at high light/low temperature, where it was much less. Calculated NAR was increased by high light, but reduced by high temperature. In infested plants, ‘true’ NAR (calculated from plant d.w. + ingested d.m.) was compared with ‘apparent’ NAR (calculated from plant d.w. alone). Infestation decreased ‘apparent’ NAR, but the effect was small at high light/low temperature because ‘true’ NAR increased. Infested plants at low light/high temperature had negative ‘apparent’ NARs. High light and high temperature generally decreased leaf diffusive resistance, except that uninfested plants at high light/low temperature had large values. Stem, leaf and root d.w. were all increased by high light and decreased by infestation. Leaf carbohydrate showed similar responses. Chlorophylls were reduced at high light, particularly at low temperature in uninfested plants. These plants showed positive relationships between chlorophyll and (1) the starch: sucrose ratio and (2) leaf total nitrogen, but a negative relationship with leaf diffusive resistance. Leaf potassium (K) and amino nitrogen showed only small responses to light and temperature. Aphids retained > 80 % of N ingested and < 20 % of K. Ingested material contained more K than N, but the ratio of both to carbohydrate was much greater under low light, particularly at high temperature. Aphids under these conditions appeared starved of carbohydrate. Low light increased the proportions of proline, amides and ammonia in both leaf extracts and aphid honeydew.
DEVELOPMENT OF TOTAL AND VIABLE EXTRARADICAL MYCELIUM IN THE VESICULAR–ARBUSCULAR MYCORRHIZAL FUNGUS GLOMUS CLARUM NICOL. & SCHENCK
Authors: SCHUBERT A. , MARZACHÍ C. , MAZZITELLI M. , CRAVERO M. C. , BONFANTE‐FASOLO P.
Published: April 2006

Summary

Clover (Trifolium repens L.) plants were inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus clarum Nicol. & Schenck in three experiments performed in similar environmental conditions. Extra radical mycelium was separated from soil by the membrane filter technique and its total length was measured; viable amounts were assessed after staining with the fluorescent dye fluorescein diacetate (FDA). Total mycelium increased steadily, and reached its maximum length 8 weeks after inoculation, unlike viability rate which decreased, from an initial value of about 100% to less than 15% after a period of 5 to 8 weeks. Consequently, the length of viable mycelium decreased after the first weeks following inoculation. The viability of extra radical mycelium may be an important factor influencing nutrient uptake and translocation by the VAM fungus.
A POST‐GLACIAL POLLEN SEQUENCE FROM LOCH A'MHUILINN, NORTH ARRAN: A RECORD OF VEGETATION HISTORY WITH SPECIAL REFERENCE TO THE HISTORY OF ENDEMIC SORBUS SPECIES
Authors: BOYD W. E. , DICKSON J. H.
Published: April 2006

Summary

A sequence of lake muds and fen peat deposits from Loch a'Mhuilinn, north Arran, contains evidence for the local vegetation history for parts of the Flandrian Interglacial. The main components of this history are as follows: Sedimentation occurred under open‐water conditions during early Flandrian times. By around 5000 B.P., fen peat was accumulating, and during the 2nd millenium B.P., an unexplained reversion to open‐water conditions occurred.

The earliest recorded vegetation immediately predates the Corylus rise and is characterized by Betula‐rich woodland with Juniperus and Salix being present in places. The Corylus rise, occurring at around 8600 B.P., marks the beginning of a period of Corylus‐rich Betula woodland. Subsequent increases of Ulmus, Quercus, Pinus and Alnus pollen represent further forest development. Fluctuations in the composition of this mixed forest are recognized, as can a distinction between areas of Betula‐Quercus, Corylus‐rich and Alnus‐rich woodland.

At around 5000 B.P., the vegetational development, previously representing broad regional changes, appears to respond to local processes. Fluctuations in the proportions of trees and Gramineae pollen may reflect vegetational disturbance, although sedimentation processes may be influencing the pollen deposition at this time. This period is followed by apparently greater woodland stability, with minor indications of human activity. By around 4000 B.P., early stages of Calluna‐rich heath are apparent. The development of the heath vegetation is not recorded, but by the 2nd millenium B.P., Calluna heath and grassland appear to be well established in north Arran.

The history of Sorbus spp. is examined in as much detail as the fossil evidence allows. By around 6500 B.P., Sorbus aucuparia L. is present in the area, and by around 5400 B.P., evidence for non‐aucuparia Sorbus species is present. This evidence may represent the former presence of 5. rupicola (Syme) Hedl. and/or one or both of the two endemic species 5. arranensis Hedl. and S. pseudofennica E. F. Warb.
Effects of open‐air fumigation with sulphur dioxide on the growth and yield of winter barley
Authors: McLEOD A. R. , ROBERTS T. M. , ALEXANDER K. , CRIBB D. M.
Published: April 2006

summary

An open‐air fumigation system was used to expose a winter barley crop (Hordeum vulgare L.) to controlled concentrations of SO2 from November 1982 to July 1983. Monitoring data from a rural site were used as a basis for simulating mean concentrations of 0.023, 0.038 and 0.058 μl 1−1 SO2 at a location where background concentrations were 0.01μl 1−1 SO2. There was no evidence of a reduction or stimulation of crop growth over the winter period. During the spring, the crop in SO2 fumigated plots had a higher green leaf area and dry weight than in control plots which may have resulted from a reduction in the occurrence of the fungal pathogen brown rust (Puccinia Hordei Otth.). After car emergence a delay in senescence of leaves was observed in fumigated plots which gave the plants an extended period for assimilation during grain filling. There was no evidence that the yield of barley was reduced within the range of ambient SO2 concentration in the UK (annual mean 0.03μ1 l−1SO2). However, at 0.058μl 1−1 SO2, reductions in yield were observed. Treatment with 0.023μl 1−1 SO2 produced increased grain yield.
Alleviation and induction of dormancy by temperature in Impatiens glandulifera Royle
Authors: MUMFORD PAULINE M.
Published: April 2006

summary

Embryo dormancy in seeds of Impatiens glandulifera Royle can be overcome by maintaining them imbibed at 4 °C. The period of chilling required depends on the age and storage conditions of the dry seed; it decreases with seed age and is reduced by a high storage temperature. Fully imbibed seeds can remain dormant for several years at 20 °C if the stratification requirement is not met. Interrupting stratification at 4 °C with a period at 20 °C increases the chilling requirement in proportion to the length of the warm period. However interrupting stratification by desiccation has no effect on the chilling period required. The ecological implications of these findings are discussed.
Responses ofHedysarum borealeNutt. to mycorrhizas andRhizobium: plant and soil nutrient changes in a disturbed shrub‐steppe
Authors: CARPENTER ALAN T. , ALLEN MICHAEL F.
Published: April 2006

summary

Effects of inoculation ofHedysarum borealessp.borealeNutt. (Fabaceae) with mycorrhizal fungi (topsoil inoculum) andRhizobium(pure inoculum) were studied in the field in southwestern Wyoming, USA. After 3 years, plants receiving both inocula had greater total aboveground biomass and leaflet biomass, more leaves, higher aboveground nitrogen and phosphorus contents and greater survival than plants which received single or no inoculum. Soil 20–40 cm deep (where roots were concentrated) beneathHedysarumindividuals from all treatments had a lower concentration of total nitrogen than did soil between plants.Hedysarumplants, inoculated or not, apparently extracted sufficient nitrogen from the soil, as they had similar leaflet nitrogen concentrations.Hedysarumdecreased the size of the pool of soil nitrogen even withRhizobiuminoculation on disturbed land in a semi‐arid environment during the first 3 years of growth.
Evidence against a key role for metallothionein‐like protein in the copper tolerance mechanism of Deschampsia cespitosa (L.) Beauv.
Authors: SCHULTZ CAROLINE L. , HUTCHINSON THOMAS C.
Published: April 2006

The role of sulphur and copper‐inducible thiol‐rich protein in the copper tolerance‐ of the grass Deschampsia cespitosa (L.) Beauv. was investigated. Sulphur deficiency, induced by growing tillers in nutrient solution without sulphur had no effect on the copper tolerance of two clones from a site contaminated with copper and nickel. In contrast sulphur deficiency increased the susceptibility of two non‐tolerant clones from an uncontaminated site‐to copper toxicity. Tolerance of a copper‐tolerant clone screened from seed of a non‐tolerant population was unaffected by sulphur deficiency. Sulphur deficiency reduced the amount of copper‐inducible thiol‐rich protein in roots of both the tolerant and non‐tolerant clones exposed to excess copper. Roots of the tolerant clones grown in micronutrient copper solutions without sulphur for 26 d and then exposed to 1.61 μM copper for a further 4 d both produced 75% less copper‐inducible thiol‐rich protein than those grown with sulphur. In an experiment with one of the tolerant clones, the amount of thiol‐rich protein did not increase between 4 and 30 d of exposure to excess copper despite a 43% increase in copper in the cell‐free extract. Sulphur deficiency reduced the amount of thiol‐rich protein to a lesser extent in the non‐tolerant clones, with a 57% decrease in one clone and a 31% decrease in the other. In the presence of sulphur both non‐tolerant clones produced considerably more thiol‐rich protein when exposed to excess copper than did the tolerant clones.
The effects of polyamine biosynthesis inhibitors on infection of Hordeum vulgare L. by Erysiphe graminis f. sp. hordei Marchal
Authors: WEST H. M. , WALTERS D. R.
Published: April 2006

The effects of the inhibitors of polyamine biosynthesis, 2‐difluoromethylornithine (DFMO), (E)‐2‐(fluoromethyl) dehydroornithine (Δ‐MFMO), (K)‐2‐(fluoromethyl) dehydroornithine methyl ester (A‐MFMO. CM3), 2‐hydrazinoornithine, (2R,5R)‐6‐heptyne‐2,5‐diamine (RR‐MAF), 2‐difiuorornethylarginine (DFMA), cyclohexylamine (CHA) and methylglyoxal‐bis (guanylhydrazone) (MGBG) on infection of barley Leaves (Hordeum vulgare L.) by Erysiphe graminis f.sp. hordei Marchal, were examined. Various concentrations of the inhibitors were sprayed onto barley leaves ev. Golden Promise as post‐inoculation treatments. DFMO, MGBG and a combination of the two were also applied as pre‐inoculation treatments. Each inhibitor substantially reduced mildew infection. DFMO was as efficient as the more recently developed ornithine analogues. With the exception of the DFMA treatments, post‐inoculation sprays were more effective than pre‐inoculation ones. When DFMO, MGBG and DFMA were sprayed onto leaves at different times, DFMO and MGBG most effectively controlled mildew when sprayed on the third day after inoculation. DFMA was more efficient as a pre‐inoculation treatment. Addition of polyamines to DFMO sprays increased mildew infection, compared to that resulting from the DFMO treatment alone, but infection was less than in the controls.
The effect of the gp gene on fruit development in Pisum sativum L.
Authors: PRICE D. N. , HEDLEY C. L.
Published: April 2006

Photosynthetic activity in the yellow pods of gp.gp lines has been compared with that in normal Gp.Gp pods. As expected from a previous structural study, the occurrence of aberrant plastids in the mesocarp resulted in reduced activity in the gp.gp lines.

Illuminated green fruits, 5–16 d post‐anthesis showed net uptake of CO2, from the atmosphere. Positive carbon gain was extended until d 28 in deseeded pods. Conversely, in yellow (gp.gp) fruits no net uptake of CO2, from the atmosphere was observed at any stage, even in deseeded pods, but carbon losses in the light were restricted compared with those in the dark, indicating some photosynthetic activity.

Analysis of the photosynthetic machinery within the yellow pods showed considerable differences in the effect of the gp gene on the mesocarp and endocarp layers. Compared with those of green pods, concentrations of RuBP carboxylase in the mesocarp were depressed, and the Hill reaction activity of isolated chloroplasts was virtually undetectable. However, in the parenchyma layer of the endocarp, RuBP carboxylase reached higher concentrations than in Gp.Gp pods, and Hill reaction rates were comparable. There was little difference between the lines in their PEP carboxylase concentrations in either tissue.
Action of ozone on foliar gas exchange in Glycine max L. Merr: a potential role for endogenous stress ethylene
Authors: TAYLOR GEORGE E. , ROSS‐TODD B. MONTY , GUNDERSON CARLA A.
Published: April 2006

A rapid surge in the foliar production of ethylene (C2H4), a growth regulator, is a well documented phenomenon in plants experiencing a variety of environmental stresses. The physiological significance of this stress‐induced C2H4 is not resolved. Because exogenous C2H4 can induce changes in foliar gas exchange in a variety of plant species, we tested the hypothesis that the endogenous production of stress C2H4 due to the representative environmental stress of ozone (O3) is linked to observed changes in stomatal conductance to water vapour (gsH2o) and carbon dioxide assimilation (A) in Glycine max (L.) Merr. This objective was accomplished using seedlings in hydroponic culture which were administered aminoethoxyvinylglycine (AVG), a metabolic inhibitor of stress C2 H4 synthesis, and subsequently challenged with O3. The responsiveness to O3 stress of gsH2O and A was either substantially diminished (A) or eliminated GS, H2O) when stress C2H4, production in the leaf interior was metabolically inhibited by AVG. These data support the hypothesis that the rapid surge in production of stress CJJH, in response to chronic‐level stresses in general and O3 specifically is not simply an indicator of the plant's physiological activity but rather is a chemical messenger or trigger that subsequently mediates some of the notable changes in carbon gain, stomatal physiology, and water use.
Growth and maintenance respiration in leaves of bean (Phaseolus vulgarisL.) exposed to ozone in open‐top chambers in the field
Authors: AMTHOR JEFFREY S.
Published: April 2006

Bean (Phaseolus vulgarisL. CV. pinto) plants were grown in pots in open‐top chambers in the field and exposed to three ozone (O3) regimes at a rural site in northwestern New York state: (1) charcoal‐filtered air with O3concentrations during the day of about 40–50% ambient (CF), (2) charcoal‐filtered air with O3added to attain approximately ambient concentrations in real time (1 ×), and (3) charcoal‐filtered air with O3added to attain approximately twice ambient concentrations in real time (2×). Unifoliate leaf blade relative growth rate (RGR) and specific dark respiration rate were measured on 214 plants 12‐ to 17‐d‐old. For a given plant age, RGR was significantly reduced by increasing O3dose, and for a given RGR, specific respiration rate was significantly increased. When the specific respiration rate was mathematically partitioned into growth and maintenance components, it was found that thegrowth coefficientwas unaffected by O3but themaintenance coefficientwas significantly increased by increasing O3dose: 7.3% between the CF and 1×treatments, and 25% between the 1×and 2×treatments. These results corroborate earlier findings with plants grown in high light conditions in chambers and exposed to 10 or 90 nl O31−1, and suggest that ambient levels of O3inhibit plant growth in part by diverting respiratory substrate from growth to maintenance and repair processes.