bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE CONTROL OF LEAF GROWTH OF BETULA AND ACER BY PHOTOENVIRONMENT
Authors: TAYLOR GAIL , DAVIES W. J. 
Published: May 2006

SummaryLeaf extension of one‐year‐old seedlings of silver birch (Betula pendula Roth.) and sycamore (Acer pseudoplatanus L.), was measured using linear variable transducers (LVDTs) interfaced to a microcomputer. Birch and sycamore seedlings exhibited contrasting patterns of leaf extension during a diurnal cycle with a 16 h photoperiod. Birch leaves grew more rapidly when illuminated; growth during the photoperiod was approximately doubled when compared with growth in the dark. Mean relative growth rates ±SE at ‘lights‐on + 3 h’ and ‘lights‐off + 5 h’ were 0.0136 ± 0.0016 and 0.0066 ± 0.0005 h−1 respectively. In direct contrast, growth of sycamore leaves was increased when leaves were darkened; mean relative growth rates + SE at ‘lights‐on+3 h’ and ‘lights‐off + 5 h’ were 0.0056 ± 0.0005 and 0.0094 ± 0.0008 h‐1 respectively.When leaves of birch and sycamore were darkened, increased leaf turgor was measured in both species, but only in sycamore was this higher night‐time turgor associated with a higher rate of leaf growth.Cell wall extensibility (WEX), an indication of the ability of cell walls to loosen and extend irreversibly, and cell surface pH were assessed in darkened and illuminated leaves of both species. An increase in WEX was measured when birch leaves were illuminated (P≤ 0.001) and this was accompanied by a decline in cell surface pH (P≤ 0.001). However, when leaves of sycamore were illuminated, WEX declined (P≤ 005) and cell surface pH increased (P≤ 0.001).The ability of these species to survive beneath a woodland canopy is discussed in relation to the cellular factors controlling their leaf growth.
PHYTOALEXINS, WATER‐STRESS AND STOMATA
Authors: PLUMBE ALISON M. , WILLMER C. M. 
Published: May 2006

SummaryThere are certain features shared by phytoalexins (which can be loosely defined as microbial stress compounds) and water‐stress compounds such as ABA. Therefore, a study was made to determine if phytoalexins behaved in a similar fashion to water‐stress compounds and in this report phytoalexin accumulation in water‐stressed leaves was investigated.Phytoalexins were not detected in mildly water‐stressed leaf tissue of Pisum sativum L. or Vicia faba L. However, if plants were severely water‐stressed resulting in damaged and dead areas in their leaves, a fungitoxic substance corresponding to pisatin was detected in the damaged areas of pea leaves and, to a lesser extent, in areas which recovered full turgor, while a number of fungitoxic substances, two of which corresponded to wyerone and wyerone acid, occurred in the damaged and recovered areas of V. faba leaves.Thus, although phytoalexins may accumulate in severely water‐stressed leaves they do not apparently behave in a similar manner to water‐stress compounds such as ABA which would be expected to accumulate in leaves even under mild water‐stress.
DISPERSAL, GERMINATION AND EARLY ESTABLISHMENT OF HALOPHYTES AND GLYCOPHYTES ON A GRAZED AND ABANDONED SALT‐MARSH GRADIENT
Authors: BAKKER J. P. , DIJKSTRA M. , RUSSCHEN P. T. 
Published: May 2006

SummaryIn a study of an abandoned salt‐marsh on Schiermonnikoog in the Netherlands, including an area where cattle grazing had been resumed, it was discovered that upper salt‐marsh and dune species did not spread to the lower salt‐marsh. Glass‐house experiments, carried out on germination and dry matter production under increasing salinities, suggested that the high salinity of the lower salt‐marsh was an important factor. On a grazed area of formerly abandoned salt‐marsh, lower salt‐marsh species spread to the upper salt‐marsh and dune. This could be partly due to the better germination of lower salt‐marsh species than upper salt‐marsh and dune species, since the salinity of the uppermost cm was higher temporarily and locally in the grazed than in the abandoned salt‐marsh. The canopy structure determining the amount of light reaching the soil also seemed to be an important factor enabling lower salt‐marsh species to spread. In experiments, in which seeds of different taxa were sown into vegetation, lower salt‐marsh species became established, particularly in the grazed area. The results of glass‐house experiments, on germination and dry matter production under a range of light intensities, were consistent with studies of early establishment in upper salt‐marsh and dune species in both the grazed and abandoned areas. Tidal seed dispersal resulted in the occurrence of lower salt‐marsh species in the seed bank and seedling populations in the low and open canopy of the grazed upper salt‐marsh and dune. Seed transport by cattle and geese could be important in the dispersal of some halophytes of the lower salt‐marsh.
DIFFERENTIAL TOLERANCE OF THREE CULTIVARS OF AGROSTIS CAPILLARIS L. TO CADMIUM, COPPER, LEAD, NICKEL AND ZINC
Authors: SYMEONIDIS L. , MCNEILLY T. , BRADSHAW A. D. 
Published: May 2006

SummaryRoot growth of seedlings of the Agrostis capillaris L. cultvars Parys (copper tolerant), Goginan (lead/zinc tolerant), and Highland (non tolerant) was measured after 14 d growth in solution cultures with increasing concentrations of Cd, Cu, Pb, Ni and Zn.Increasing inhibition of root growth of all three cultivars occurred with increasing concentrations of all five metals, Highland being most affected. In Cu, Parys was least affected; in Pb and Zn Goginan was least affected. Parys and Goginan thus display specific resistence to these metals. They are also similar in having greater root lengths at higher metal concentrations of all five metals than Highland. They thus exhibit non‐specific low level tolerance to metals other than those present at toxic levels in the soils from which they were derived.
INTERPOPULATION VARIATION IN TOLERANCE TO CADMIUM, COPPER, LEAD, NICKEL AND ZINC IN NINE POPULATIONS OF AGROSTIS CAPILLARIS L.
Authors: SYMEONIDIS L. , MCNEILLY T. , BRADSHAW A. D. 
Published: May 2006

SummarySamples of 15000 seeds from each of nine populations of Agrostis capillaris L. were screened for ability to root in solution cultures containing cadmium, copper, lead, nickel, and zinc at levels which severely inhibited root growth in non‐metal‐tolerant seed population samples.Differences were found in the extent to which tolerant individuals could be selected from the populations. Only the copper‐tolerant cv. Parys and lead‐/zinc‐tolerant cv. Goginan had relatively high frequencies of individuals tolerant to each metal. Screening one population did not reveal any tolerant individuals.The ability to root in such solutions may reflect the potential populations have to evolve metal‐tolerant populations. Populations exhibit considerable variation in this respect and the potential to evolve tolerance is clearly a characteristic of populations, not the species.
PALAEOECOLOGY OF ALNUS (ALDER): EARLY POST‐GLACIAL RISE IN A VALLEY MIRE, NORTH‐WEST WALES
Authors: CHAMBERS F. M. , PRICE S.‐M. 
Published: May 2006

SummaryData are presented in summary form in both percentage and influx radiocarbon‐dated pollen diagrams from a site (MYG) in a valley mire near Moel y Gerddi, Ardudwy, 4 km north‐east of Harlech, north‐west Wales.Evidence indicates that this valley mire was dominated by alder (Alnus) carr soon after the inception of peat growth, which dates from 8700 B.P. These data confirm the notion of an early empirical limit of Alnus in north‐west Wales (advanced in a previous paper) and, compared with other sites in Wales and the rest of Britain, indicate a very early rational limit here for Alnus (c. 8465 B.P.).Ideas on the migration route and on the spread of Alnus into Britain in the Post‐glacial may need substantial revision in the light of this evidence for an earlier presence of Alnus in upland Ardudwy, north‐west Wales, than yet known from lowland south‐east England.Conceivably, Mesolithic activity might have facilitated the local establishment of Alnus; the evidence for this in upland Ardudwy is evaluated.
AMINO ACID AND AMIDE METABOLISM IN THE HULLS AND SEEDS OF DEVELOPING FRUITS OF GARDEN PEA, PISUM SATIVUM L.
Authors: Murray D. R. 
Published: May 2006

SummaryPea plants (Pisum sativum L. cv. Melbourne Market), each with a single developing pod, were pulse‐fed with [14C]homoserine supplied through the cut stem at stages of pod development ranging from 12 to 21 d after full blossom. The pods were removed after 24 h and the hulls and seed components were frozen for later analysis. Except at the youngest stage, or unless the pod had been enclosed in foil to prevent the development of chloroplasts, the seeds received a higher proportion of total label in the fruit (about 60%). The distribution of label in soluble metabolites of the hull, seedcoats, embryo sac liquid and embryo was determined by paper chromatography and radioautography. The results indicate turnover of homoserine within the hull, and confirm that the seedcoats are responsible for a shift in metabolism leading to secretion of threonine into the embryo sac instead of homoserine.
NITROGEN OXIDES PRODUCED DURING CO2 ENRICHMENT
Authors: MORTENSEN LEIV M. 
Published: May 2006

SummaryEight cultivars of Lycopersicon esculentum (tomato) and six cultivars of Lactuca sativa (lettuce) were subjected to CO2‐enriched air (1000 μ11−1) containing 0.7 or 0.9 μll−1 nitrogen oxides (NOx).CO2 enrichment without NO2 significantly increased the dry weight of all tomato (35–81%) and lettuce cultivars (25–101%). In six of the eight tomato cultivars the dry weight was reduced by the addition of NOx. The mean relative growth rate (RGR) decreased by 4–19% depending on the cultivar. This meant that the benefit of CO2 enrichment was almost completely eliminated in most of the cultivars. Marginal leaf necrosis appeared in some of the cultivars, while in others no visible injury developed. None of the lettuce cultivars was significantly affected by the addition of NO x.
CARBON ECONOMY OF SOYBEAN–RHIZOBIUM–GLOMUSASSOCIATIONS
Authors: HARRIS D. , PACOVSKY R. S. , PAUL E. A. 
Published: May 2006

SummaryCarbon uptake and allocation in plants that were largely dependent on microbial symbionts for N and P was compared to that in plants given inorganic fertilizer. Soybeans (Glycine maxL. Merr.) were grown in sterilized soil and were either left uninoculated, or were inoculated withRhizobium japonicum(Kirschner), or bothR. japonicumandGlomus fasciculatum(ThaxtersensuGerd.). Uninoculated plants were given N and/or P fertilizer at rates required to produce plants similar in size to inoculated plants. Carbon flows to plant parts, root nodules and vesicular‐arbuscular mycorrhizas were measured in six‐ and nine‐week‐old plants by determining the distributions of14C after pulse labelling with14CO2.Root nodules in non‐mycorrhizal plants utilized 9% of total photosynthate; this was increased to 12% in nodulated, mycorrhizal plants. Mycorrhizas used 17% of the total photosynthate of six‐week‐old plants; this fell to 8% after nine weeks. Rates of14CO2fixation in leaves of nodulated or nodulated plus mycorrhizal plants were up to 52% higher than in plants without microbial symbionts. Part of the increase was due to higher specific leaf area in plants colonized by symbionts, but other factors such as source‐sink relationships, starch mobilization and leaf P concentrations were also involved in the host‐plant adaptations to the C demand of the microbial endophytes.
LACK OF SPREAD OF ENDOMYCORRHIZAS OF CENTAURIUM (GENTIANACEAE)
Authors: McGEE P. A. 
Published: May 2006

SummarySeedlings of Centaurium died in the absence of inoculum of vesicular‐arbuscular (VA) mycorrhizal fungi in a soil low in nutrients. The morphology of endomycorhizas of Centaurium and Eustoma grandiflora (Raf.) Shim, differed from that of commonly studied VA mycorrhizal hosts in that coils, arbuscules and vesicles were formed but rapidly collapsed.Endomycorrhizal infection spread down the roots of Centaurium erythraeq Rafn. when it was grown with a companion plant, Trifolium dubium Sibth. but when grown alone infection was restricted to the vicinity of the inoculum. Several different VA mycorrhizal plants did not become mycorrhizal when inoculated with mycorrhizal roots of Centaurium.
THE LOCALIZATION AND FREQUENCY OF HAUSTORIA IN COLONIES OF BROWN RUST ON BARLEY LEAVES
Authors: KNEALE J. , FARRAR J. F. 
Published: May 2006

SummarySerial sections were taken through colonies of brown rust (Puccinia hordei Otth.) on barley leaf blades. Fungal haustoria occurred in cells of the mesophyll, parenchymatous bundle sheath and epidermis (excluding guard cells) but not within the mestome sheath or vascular bundles. Within a colony, each cell contained 1.2 to 2 haustoria; each colony had about 104 haustoria on a total hyphal length of about 1 m. Surface areas of haustoria and intracellular hyphae were calculated and used to show that all of the hexose needed to sustain fungal growth and respiration could be taken up through either cell type.
GROWTH ANALYSIS OF ACHILLEA MILLEFOLIUM L. (YARROW) IN THE PRESENCE AND ABSENCE OF A COMPETITOR –HORDEUM VULGAREL. (BARLEY)
Authors: BOURDǑT G. W. , FIELD R. J. , WHITE J. G. H. 
Published: May 2006

SummaryThe performance of Achillea millefolium L., from early summer until early spring, in the presence and absence of Hordeum vulgare L. was assessed by growth analysis. Growth analytical quantities were derived for a 307 d experimental period from splined cubic polynomial exponential functions fitted to dry matter and leaf area data.Ontogenetic drifts in the net assimilation rate and leaf area ratio of A. millefolium were highly modified by interference from H. vulgare resulting in a diminished total plant relative growth rate and maintenance of the vegetative state. The relative growth rate of A. millefolium increased during the autumn and early winter in response to rises in net assimilation rate and leaf area ratio induced by the harvesting of the H. vulgare. During the post‐harvest period, the relative growth rate of the rhizome increased and exceeded those of leaf and total weight resulting in a substantial increase in rhizome dry matter during autumn and winter and a pronounced rise in the rhizome weight ratio.
EFFECTS OF IRRADIANCE AND SPECTRAL QUALITY ON THE GERMINATION OF VERBASCUM THAPSUS L. AND OENOTHERA BIENNIS L. SEEDS
Authors: GROSS KATHERINE L. 
Published: May 2006

SummaryGermination of Verbascum thapsus L. and Oenothera biennis L. seeds was investigated over a range of irradiance levels and under different canopy types in the laboratory. Both species colonize early successional and disturbed habitats, and their seedlings establish only in bare soil. In the laboratory, Verbascum seeds germinated to equivalent levels (70 to 80%) over a broad range of irradiance levels and required only brief exposure to light (5 s) to germinate subsequently in darkness. In contrast, germination of Oenothera seeds increased with irradiance to a maximum of approximately 80% at 13 W m−2. Oenothera seeds also required a longer duration of exposure (1 h) to induce germination, and percentage germination increased directly with exposure time to a maximum of 80 % after 22 h of exposure. Germination of both species was significantly reduced in light filtered through leaves, but the responses differed under different canopy types. Exposure to red and blue light had no effect on germination of Verbascum seeds but had an inhibitory effect on that of Oenothera seeds. The results are discussed in relation to the observed patterns of seedling emergence and survival of these species in the field; a possible evolutionary basis is suggested for their differences in response to light.
SUGGESTED INVOLVEMENT OF CALCIUM AND CALMODULIN IN THE RESPONSES OF STOMATA TO ABSCISIC ACID
Authors: DE SILVA D. L. R. , COX R. C. , HETHERINGTON A. M. , MANSFIELD T. A. 
Published: May 2006

SummaryA requirement for calcium during the inhibition of stomatal opening by abscisic acid (ABA) was reported in a previous study, and evidence is now presented which gives further indications of the part played by calcium. Calcium‐channel blockers (lanthanum, verapamil and nifedipine) reduced the ability of stomata to respond to ABA. A calcium ionophore (A 23187) reduced stomatal opening, presumably because it mimicked the effect of ABA in increasing permeability of the plasma membrane to calcium. In the presence of three calmodulin antagonists, the inhibitory effect of ABA was much reduced. The synthetic auxin naphth‐l‐ylacetic acid (NAA) prevented stomatal opening, but this action did not appear to be dependent on calcium ions.It is suggested that the action of ABA on guard cells requires a free passage of calcium ions into the cytosol. They may act as second messengers, interacting with calmodulin to produce the overt cellular responses to ABA.Although the data presented apply only to stomata, these experiments may have provided insight into the basic mechanism by which ABA acts on cellular processes. It is suggested that some reported effects of Ca2+on the action of other plant growth substances could have resulted from complex interactions involving endogenous ABA.
HOST DETERMINANTS OF MYCORRHIZAL DEPENDENCY OF CITRUS ROOTSTOCK SEEDLINGS
Authors: GRAHAM J. H. , SYVERTSEN J. P. 
Published: May 2006

SummarySeedlings of five citrus rootstocks were grown in a low phosphorus (P) sandy soil and were either (1) inoculated with Glomus intraradices Schenck & Smith, (2) non‐inoculated and fertilized with P, or (3) non‐inoculated without added P. The order of mycorrhizal dependency (MD) of the five rootstocks was sour orange = Cleopatra mandarin > Swingle citrumelo > Carrizo citrange > trifoliate orange. The less dependent rootstocks, trifoliate orange and its hybrid Carrizo citrange, had greater leaf P, finer roots (greater length per unit of dry root) and slower growth rates than sour orange and Cleopatra mandarin. Rootstocks with lower MD also generally had greater hydraulic conductivity of roots, and greater transpiration and CO2 assimilation rates. Under well‐watered conditions, VAM plants of all five rootstocks did not differ in morphology, anatomy or physiology from non‐mycorrhizal plants fertilized with P of similar size, growth rate and P status.
THE CYANOBACTERIUM‐ZAMIA SYMBIOSIS: AN ULTRASTRUCTURAL STUDY
Authors: LINDBLAD P. , BERGMAN B. , HOFSTEN A. V. , HÄLLBOM L. , NYLUND J. E. 
Published: May 2006

SummaryFilamentous cyanobacteria are found intercellularly in a zone between inner and outer cortex of coralloid roots, growing below the soil surface, from the cycad Zamia skinneri Warsc. The zone is transversed by elongated Zamia cells interconnecting the two cortex layers. These host cells show characteristics of transfer cells, i.e. considerably expanded cell walls, numerous mitochondria and amyloplasts. An involvement of these cells in the transfer of solutes between cyanobacterium and host is therefore suggested. The cyanobacterium belongs to the genus Nostoc and consists of vegetative cells, heterocysts and a few akinetes. Healthy vegetative cells contain thylakoids with phycobilisomes, carboxysomes, cyanophycin and glycogen granules. Thus, no distinct subcellular modifications due to a symbiotic mode of life in the absence of light were observed.
THE TIMING OF DIVISION IN CHLAMYDOMONAS
Authors: McATEER MARY , DONNAN LORRAINE , JOHN PETER C. L. 
Published: May 2006

SummaryThe duration of the cell cycle of Chlamydomonas is determined by two timed periods which each follow an initiating stimulus. A commitment timer, initiated by the beginning of growth in autonomous daughter cells, is dependent upon concurrent growth and controls the time of first commitment to divide. Division processes, which are then initiated, occupy a second timer period of 6 h duration at 25°C.Absence of division control by an endogenous oscillator was indicated by an unfluctuating ability to resume cycles of consistent duration when daughter cells were held in darkness or when growing cells in light were subjected to darkness. A consistent time from the beginning of daughter growth to commitment was also observed when daughter formation was delayed by an earlier temperature reduction. Ethanol, which commonly affects circadian oscillators, did not disturb synchrony.The division cycle is controlled by growth and not by direct response to light, since commitments ceased when growth was prevented by lack of CO2 in the light. Growth in daughter cells initiated the timer leading to commitment since commitment was reached at similar times after resupply of CO2 or reillumination. Division synchrony in diurnal cycles of periodic illumination is not caused by entrainment of an oscillator but by the growth requirement of the hourglass timer leading to commitment. A model of division control is presented.
THE ABSENCE OF AN EFFECT OF THE Na/Ca RATIO ON SODIUM CHLORIDE UPTAKE BY RICE (ORYZA SATIVA L.).
Authors: YEO A. R. , FLOWERS T. J. 
Published: May 2006

SummaryThe effect of the Na/Ca ratio in the growth medium on the response of the salt‐sensitive crop species Oryza sativa L. to NaCl salinity was investigated. No effects on growth or salt concentration in the shoot were found over a range of Na/Ca ratios (5 to 25) considered likely to be commonly encountered in saline situations in the field, and even at extreme Na/Ca ratios (100 to 500) there were only marginal increases in NaCl entry to the shoot. Increasing the Ca concentration in the growth medium over a wide range did not, therefore, ameliorate the effects of salinity on rice seedlings. Polyethylene giycol at low, osmotically negligible, concentrations reduced the movement of CI to the shoot by 60 to 70% even in the presence of adequate (3.5 mol m−3) Ca. It is concluded that membranes of rice roots respond weakly to Ca and that they are capable of better permeability control than is evoked by Ca ions. The relevance of this to the salt sensitivity of rice is discussed.
MEMBRANE INTEGRITY IN LEAVES OF BARLEY INFECTED BY BROWN RUST: AN EXAMINATION USING TRACER EFFLUX AND IN VIVO CHLOROPHYLL FLUORESCENCE
Authors: AHMAD I. , FARRAR J. F. , WHITBREAD R. 
Published: May 2006

SummaryThe kinetics of ion efflux from leaf discs were used to show that there is no general increase in the permeability of plasmalemma or tonoplast resulting from infection of barley leaves by brown rust (Puccinia hordei Otth.). An assay of in vivo chlorophyll fluorescence showed that there were clear differences between chloroplasts in healthy and diseased tissue, but overall the thylakoid lamellae function well in rusted barley leaves. We conclude that in this biotrophic system there is no gross impairment of host membrane integrity, and show that delivery of host nutrients to the apoplast is at rates greatly in excess of those needed to accommodate fungal nutrient uptake. This does not preclude localized effects of the pathogen on host membranes.
SOME PHYSIOLOGICAL EFFECTS OF TWO SEED‐TRANSMITTED VIRUSES ON FLOWERING, SEED PRODUCTION AND SEED VIGOUR IN NICOTIANA AND CHENOPODIUM PLANTS
Authors: WALKEY D. G. A. , BROCKLEHURST P. A. , PARKER J. E. 
Published: May 2006

SummaryThe effects of infection by spinach latent (SLV) and arabis mosaic virus (AMV) upon flowering, seed production and seed vigour, were studied in Nicotiana and Chenopodium species. Infection frequently caused mother‐plants to produce flowers earlier than healthy plants, and AMV induced C. amaranticolor Coste & Reyn., which normally flowers only under ‘short‐day’ conditions, to flower in ‘long‐days’.Infection with SLV or AMV generally caused a significant reduction in normal seed numbers and a corresponding increase in aborted seed. Mean seed weights were often lower from infected than from healthy plants, but in some infections lower seed production was correlated with a compensatory increase in the weight of individual seeds. The viability of seeds from infected plants was slightly reduced in some instances but, even when seed viability was not affected, tests of accelerated ageing indicated that seed vigour was impaired.