bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE AZOLLA‐ANABAENA AZOLLAE RELATIONSHIP
Authors: CALVERT HARRY E. , PETERS GERALD A. 
Published: May 2006

SummaryTwo morphologically distinct classes of epidermal trichomes, termed simple and branched hairs, are shown to occur in Azolla caroliniana Willd. leaf cavities. The two hair types have significantly different frequencies and patterns of distribution during the development and maturation of the leaf cavities. There are only two multicellular branched hairs per cavity. These are consistently found in the same locations along the path of the foliar trace. The number of simple hairs increases rapidly during leaf development. There are about 20 simple hairs in each mature cavity and these are randomly distributed over most of the cavity wall. Clearing techniques confirmed these distributional patterns in Azolla caroliniana Willd., Azolla filiculoides Lam. and Azolla mexicana Presl. The distributional pattern was not altered by the absence of the endophytic Anabaena in Azolla caroliniana Willd. These findings are discussed in regard to the possible function of the two hair types in the Azolla–Anabaena symbiosis.
NITROGEN METABOLISM IN POTERIUM SANGUISORBA DURING WATER STRESS
Authors: TAYLOR A. A. , DE‐FELICE J. , HAVILL D. C. 
Published: May 2006

SummaryWater stress, produced either by the addition of polyethylene glycol 4000 to water culture‐grown Poterium sanguisorba or by withholding water from vermiculite‐grown material, reduced nitrate reductase activity, but increased the level of glutamine synthetase in shoots, in roots the levels of all the nitrogen‐assimilating enzymes studied were reduced. In both tissues these changes were accompanied by a fall in soluble protein and water content and by an increase in the total a‐amino and proline pools. Marked changes in shoot individual amino acids were also induced by water stress, but were reversed when stress was relieved. The significance of these changes are discussed in relation to nitrogen assimilation and the mechanism of proline accumulation during drought.
THE EFFECTS OF LEAF ORIENTATION ON PHOTOSYNTHESIS, TRANSPIRATION AND DIFFUSIVE CONDUCTANCE OF LEAVES OF CONTRASTING FESTUCA SPECIES
Authors: SILCOCK R. G. , WILSON D. 
Published: May 2006

SummaryA comparative study was made of the effect of leaf orientation on photosynthesis, transpiration and diffusive conductance of leaves of Festuca gigantea, F. pratensis, F. arundinacea, F. arundinacea var. atlantigena and F. marei. Conductance was also examined in F. drymeja and F. scariosa. Adaxial leaf surfaces ranged from the relatively flat (F. drymeja and F. gigantea) to the heavily corrugated (F. marei and F. scariosa). Stomatal numbers were greatest on the adaxial surface of all species, whilst the frequency on abaxial surfaces ranged from zero in F. gigantea and F. scariosa to more than 60 mm−2 in F. marei.The photosynthesis/transpiration ratio was slightly greater with the abaxial surface uppermost and greater in those species with relatively flat adaxial surfaces. The small change in the ratio with change in leaf orientation was due to the relatively greater reduction in transpiration than in photosynthesis. Species with heavily corrugated leaves transpired faster than those with flat leaf surfaces. Change in leaf orientation did not affect the ranking of the species in terms of transpiration or of leaf conductance but, because of the contrasting responses of F. gigantea in two separate experiments, ranking was not the same. There was no consistent effect of orientation on total leaf conductance but large differences were found in the relative responses of the two surfaces in some species. In those with very few abaxial stomata the adaxial surface always had greatest conductance, whichever surface was uppermost. Where both leaf surfaces had appreciable numbers of stomata, the upper surface always exhibited the greater conductance, irrespective of whether it was the adaxial or abaxial. F. arundinacea showed the greatest change in the ratio of adaxial leaf conductance in response to change in leaf orientation.
ENZYMATIC STUDIES ON THE METABOLISM OF VESICULAR–ARBUSCULAR MYCORRHIZAS
Authors: MARX C. , DEXHEIMER J. , GIANINAZZI‐PEARSON V. , GIANINAZZI S. 
Published: May 2006

SummaryThe ultrastructural localization of ATPase activities was identical in onion and sycamore mycorrhizas. DES‐sensitive ATPase activity was associated with the fungal plasmalemma and paramural bodies whilst a DES‐insensitive ATPase activity was detected within the fungal vacuole. The development of the mycorrhizal fungus within root cells modified the distribution of DES‐sensitive plasmalemma‐bound ATPase activity of the host. This became concentrated around the finer arbuscule branches and appeared to be a specialization of the invaginated host membrane which occurred when arbuscule structure was favourable for nutrient exchange. These observations strengthen the hypothesis that nutrient exchange in VA mycorrhizas must occur across the living host‐fungus interface and that phosphate is transferred from fungus to host by an active transport mechanism in the finer branches of the arbuscule.
Studies ON THE TOLERANCE TO SULPHUR DIOXIDE OF GRASS POPULATIONS IN POLLUTED AREAS
Authors: AYAZLOO M. , GARSED S. G. , BELL J. N. B. 
Published: May 2006

SummaryGenotypes of Lolium perenne, Festuca rubra, Dactylis glomerata and Holcus lanatus which appeared to be differentially sensitive to acute or chronic SO2 injury were compared in various morphological and physiological studies to examine some possible mechanisms of tolerance. Stomatal number and size showed no relationship with tolerance, but stomatal resistance in clean air showed a relationship with intra‐ and interspecific differences in tolerance to acute injury. Also, acute doses of SO2 increased stomatal resistance in tolerant, but not in sensitive species.Membrane permeability was increased by acute doses of SO2, but there were no differential effects which could be related to tolerance. Uptake of 14CO2 by leaf segments in buffered solution was reduced in the presence of sulphite to a greater extent in genotypes of Lolium perenne sensitive to chronic injury. Prefumigation for 13 months with a low concentration of SO2 increased the sensitivity to sulphite, especially in the sensitive genotypes.The species tolerant of acute SO2 injury, Dactylis glomerata and Holcus lanatus, had lower rates of 14CO2 fixation than sensitive species, and were affected less by sulphite. There were no relationships between prefumigation or sensitivity to chronic injury and the uptake or oxidation of sulphite in three Lolium perenne genotypes. Species sensitive to acute injury absorbed more 35SO2 than tolerant species. Oxidation of the absorbed radioactivity was fastest in the most tolerant and slowest in the least tolerant species.It is concluded that many of the differential responses to acute injury can be explained by avoidance mechanisms. Some potential mechanisms of tolerance to chronic injury are discussed.
THREE FLANDRIAN POLLEN PROFILES FROM THE TEITH VALLEY, PERTHSHIRE, SCOTLAND
Authors: LOWE J. J. 
Published: May 2006

SummaryLithostratigraphies and pollen stratigraphies are described for Flandrian deposits from three infilled kettle‐holes near Callander, the Teith Valley, Perthshire. Differences between the sites, in terms of sediments and inferred hydroseral histories, are described, but broad similarities are recognized in inferred regional forest developments. The sites lie in a transitional zone between the Grampian Highlands, dominated by pine in the mid‐Flandrian, and lowland southeast Scotland, where mixed deciduous woodlands prevailed. The data presented suggest that communities dominated by birch–hazel with oak and elm encroached into the Grampians along major valleys, such as that of the River Teith. The problem of defining the role of pine in Scottish vegetational history, and the implications of an ‘Elm Decline’ recognized at one of the sites, are discussed.
NUTRITIONAL CONDITIONS REQUIRED FOR THE NON‐SYMBIOTIC CULTURE OF AN ACHLOROPHYLLOUS ORCHID GALEOLA SEP TEN TRIO N ALIS
Authors: NAKAMURA SHIN JCHI 
Published: May 2006

Summary Galeola septentrionalis Reichb. f. grew and developed roots and leaves on the agar medium containing commonly used nutrients in the absence of its symbiotic partner when kept in appropriate atmospheric conditions.Glucose, glycerol, fructose, inositol, mannitol, mannose, ribose, sorbitol and xylose were utilized as carbon sources, arabinose, rhamnose and sorbose were not and galactose inhibited growth. Mixture of two monosaccharides in some combinations showed no synergistic effect though they had an additive effect.An amino acid mixture and urea were good nitrogen sources, but allantoin, ammonium salt and nitrate were poor ones. Nitrite and uric acid inhibited growth.Several vitamins did not affect growth when added to or deleted from the culture medium singly or in combinations.Auxins improved growth immediately after germination and cytokinins showed no effect at this phase. The growth and development following this phase, however, were promoted by addition of cytokinins and not by auxins. Cytokinins given during this later phase induced rhizogenic growth at concentrations lower than 10−7 M and induced caulogenic growth at concentrations higher than 10−6 M. Gibberellin at concentrations higher than 3 × 10−7 M retarded growth. G. septentrionalis is considered to be a prototrophic heterotroph and its mycorrhizal fungus may act by supplying commonly known nutrients to this achlorophyllous orchid.
THE DEVELOPMENT OF CHLOROPLASTS IN ROOT MERISTEMATIC TISSUE OF SECALE CEREALE L. SEEDLINGS
Authors: OLIVEIRA LUIS 
Published: May 2006

SUMMARYProplastids of the meristematic region of roots of rye, Secale cereale, seedlings can be induced to develop into chloroplasts after a lengthy period of continuous exposure to light. The transformation involves the formation of prolamellar bodies which eventually become the source of membrane material for the organization of granal and intergranal thylakoids. The process is also accompanied by a two‐step increase in the number of plastidial ribosomes which coincides with the extension of the intraplastidial membrane system and by a progressive accumulation of photosynthetic pigments and development of Hill reaction activity.Overall mature chloroplasts of root meristematic tissue compare well both structurally and functionally with those from the leaves of the same plant.
THE GENETIC BASIS OF TOLERANCE TO SALT SPRAY IN POPULATIONS OF FESTUCA RUBRA L.
Authors: HUMPHREYS M. O. 
Published: May 2006

SUMMARYSalt tolerance, determined as the percentage green leaf remaining after spray treatment, was investigated in plants from three coastal populations of Festuca rubra L. and in their hybrids with the non‐tolerant cultivar Aberystwyth S59. The most tolerant population originated from a cliff site very exposed to natural salt spray. Reciprocal differences found between progeny of tolerant and non‐tolerant maternal parents were explained on the assumption of illegitimate selfs in crosses produced by automatic cross pollination without emasculation. To allow for this, selfing parameters were introduced into a basic additive‐dominance genetic model of generation means. The potential for selfing, estimated from isolated inflorescences, was found to vary between populations. The model gave a good fit with observed generation tolerance values when selfing estimates were included and additive and dominance components of the means were calculated. In general, tolerance was dominant to non‐tolerance at salt levels similar to that of sea water but recessive at much higher salt levels, although populations differed in the degree of dominance expressed in the crosses with S59. These observations are discussed in relation to the nature and evolution of dominance of a quantitative character.
THE INFLUENCE OF NITROGEN SOURCE ON THE TOLERANCE OF HOLCUS LANATUS L.* AND BROMUS ERECTUS HUDS. TO MANGANESE
Authors: McGRATH S. P. , RORISON I. H. 
Published: May 2006

SUMMARYBoth Bromus erectus and Holcus lanatus grew better in NO3‐N than in NH4‐N. NH4‐N inhibited Mn uptake and NO3‐N enhanced it. The concentration of Mn found in both species was greater in NO3‐N than NH4‐N treated plants and increased severity of toxicity symptoms was observed in plants given NO3‐N treatments. In general, uptake and concentration of Mn was greater in Holcus than in Bromus, although Holcus displayed less severe symptoms of toxicity. Root concentrations of Mn were greater than those of shoots in Holcus. As excess Mn generally affects plant tops more severely than roots it is possible that a mechanism reducing upward translocation of Mn conferred a degree of tolerance in Holcus. Growth of the population of Holcus used was affected to a lesser extent than Bromus by large concentrations of Mn in nutrient solution which may partially account for the markedly different frequency of occurrence of these species on soils which contain high concentrations of both NH4‐N and Mn. In Bromus NH4‐N and Mn interact to reduce their combined effects but in both species the adverse effects of NH4‐N on growth for the most part masks that of Mn. Conversely with NO3‐N, itself beneficial, Mn uptake is not depressed as it is with NH4‐N and when Mn‐toxicity occurs, it is more marked. In solution culture Bromus is very sensitive to NH4‐N and also to Mn in the presence of NH4‐N or NO3‐N, whereas in the kind of habitat in which Bromus occurs N is present as NO3 and the adverse effect of any Mn present is neutralized by Ca.
A METHYLAMINE‐RESISTANT MUTANT OF THE BLUE‐GREEN ALGA, NOSTOC MUSCORUM: POSSIBLE INVOLVEMENT OF GLUTAMINE SYNTHETASE IN METHYLAMINE METABOLISM
Authors: VAISHAMPAYAN A. 
Published: May 2006

SummaryPhotoautotrophic growth of the Em‐R het− nif2− strain of the blue‐green alga, Nostoc muscorum, is prevented completely by 1 mM methylamine (MA) but a concentration of 2 mM MA is required to inhibit photoheterotrophic or dark heterotrophic growth. From this strain a mutant has been isolated and characterized. The mutant cannot grow photoautotrophically but its heterotrophic growth is resistant to 5 mM MA; moreover, the mutant can use MA as a carbon and nitrogen source for growth. It is suggested that because the mutant is defective in photosynthetic ability it lacks the step that is inhibited by 1 mM MA and, in the absence of such inhibition, is able to show the ability to metabolize MA by an existing enzyme system. Mutant strain Em‐RMSO‐R het+ nif+, whose growth is resistant to inhibition by l‐methionine‐dl‐sulphoximine, can grow photoautotrophically in 2 mM MA. Because this mutant is known to contain an altered glutamine synthetase, it is suggested that this enzyme may be responsible for methylamine metabolism.
OXYGEN DIFFUSION IN PEA
Authors: ARMSTRONG W. , HEALY M. T. , WEBB T. 
Published: May 2006

SummaryFor roots growing in anoxic media the intercellular pore‐space of the root cortex provides a channel for the diffusive flow of respiratory gases between shoot and root. Three methods were used in an attempt to quantify the diffusive resistance of this pore space (Rp) in pea. Two of the methods were based on polarographic measurements of oxygen flow through the roots: the ‘cooling’ and ‘gas‐mixture’ methods; the third was based upon measurements of porosity and root geometry (‘shape’). The last gave results which agreed closely with those obtained using gas‐mixtures. The relationship between Rp and root length followed a curvilinear form in which there was little change in Rp in the earlier stages of growth (3 to 6.5 cm). The cooling method also produced a curvilinear pattern, but numerically the resistances were considerably higher. Also, resistance rose significantly in the shorter roots. It was found that respiratory activity in the roots at 3 °C could account for these discrepancies; an electrical analogue of the root programmed for resistance (gas‐mixture/root geometry values) and 3 °C respiratory activity, gave results which matched those obtained by the cooling method. It was concluded that the gas‐filled pore space in the pea root forms a relatively non‐tortuous diffusion path and that resistance is very strongly influenced by root shape. As roots extend beyond a length of 7 cm there is an accelerated rise in Rp. An original intention, that of obtaining a measure of diffusive resistance across the root wall, was thwarted by the variability in the data.
GRAFT FORMATION IN CULTURED, EXPLANTED INTERNODES
Authors: PARKINSON M. , YEOMAN M. M. 
Published: May 2006

SummaryA novel method is described in which the two halves of an explanted internode of Lycopersicon esculentum, Datura stramonium or Nicandra physaloides may be grafted together successfully in sterile culture. An absolute requirement for the formation of a successful graft is the application of indole‐3‐acetic acid (IAA at 0.2 to 2.0 mg l−1) to the apical end of the internode. The addition of kinetin (0.2 mg l−1) to the culture medium stimulated graft development but gibberellic acid (GA3 at 0−5 mg l−1) was inhibitory. The development of the graft as measured by an increase in mechanical strength and the formation of vascular connections was similar to that observed in whole plant grafts; however, fewer differentiated wound vessel members (WVMs) were detected. This technique should provide a powerful tool for the further study of graft development in compatible and incompatible combinations.
STRUCTURE AND ULTRASTRUCTURE OF PLASTIDS IN LIGHT‐AND DARK‐GROWN ZAMIA FLORIDANA DC. SEEDLING ROOTS IN VITRO
Authors: WEBB DAVID T. 
Published: May 2006

SummaryIn dark grown aseptic seedling cultures of Zamia floridana DC. amyloplasts with many tightly packed starch grains developed in root cortical cells. In similar cultures exposed to 12 h photoperiods of 5 klx, plastids with characteristics of chromoplasts, chloroplasts and amyloplasts were formed. Light appeared to alter the pathway of plastid development and led to the formation of chloro‐chromo‐amyloplasts in these roots.
SEASONAL CHANGES IN THE TEMPERATURE REQUIREMENTS FOR GERMINATION OF BURIED SEEDS OF APHANES ARVENSIS L.
Authors: ROBERTS H. A. , NEILSON JUNE E. 
Published: May 2006

SUMMARYSeasonal changes in dormancy occurred in seeds of Aphanes arvensis buried in soil under field conditions. During late spring and summer the temperature range for germination extended upwards, reaching that of the surface soil in early August when emergence begins. The seeds were at their least dormant in September but the range then narrowed in autumn and winter, and dormancy was greatest in April. Exposure of seeds buried in pots of soil to high (20 to 30 °C) temperatures alleviated dormancy, while low (4 °C) temperature tended to induce it. The consistent pattern of autumn emergence appears to be determined by these cyclic changes in dormancy status which develop largely as a consequence of the temperatures experienced by the buried seeds.
GENECOLOGICAL STUDIES OF URTICA DIOICA L.
Authors: POLLARD A. J. , BRIGGS D. 
Published: May 2006

Summary Urtica dioica L. shows considerable variation in several characters, including stinging hair density. Members of a particular population found at Wicken Fen are remarkable in that they bear almost no stinging hairs, are tall, unbranched, narrow‐leaved, and late‐flowering. Experimental cultivation of samples from Wicken and a number of other populations showed that:(i) Plants retain many of their distinctive features in cultivation.(ii) Some of the variation is apparently heritable.(iii) There are significant differences between and within populations and between staminate and pistillate plants.(iv) Plants differ in their patterns of phenotypic plasticity.The complexity of variation examined here renders infraspecific taxonomy difficult, but provides a fertile area for research on the ecological and evolutionary significance of variation in U. dioica.
NITRATE REDUCTASE ACTIVITY OF SPHAGNUM SPECIES IN THE SOUTH PENNINES
Authors: PRESS M. C. , LEE J. A. 
Published: May 2006

SUMMARYBulk deposition of nitrate, ammonium and organic nitrogen was greater at a South Pennine blanket peat site than at a similar, relatively unpolluted site in the Berwyn Mountains, North Wales. Sphagnum cuspidatum, transplanted from North Wales to the South Pennines, showed a rapid induction of nitrate reductase activity, which declined after 4 days. A laboratory induction experiment demonstrated a similar phenomenon on solutions containing 1 mM nitrate. In the presence of 1 mM ammonium, much less nitrate reductase activity was induced. Ammonium accumulated in both nitrate grown plants in the laboratory and in field transplants, which suggests that it may be responsible for the observed declines in enzyme activity. The results are discussed in relation to the nitrogen nutrition of blanket bog plants.
CORRELATION OF FUNGAL MORPHOLOGY AND DEVELOPMENT TO HOST GROWTH IN A GREEN ASH MYCORRHIZA
Authors: DOUDS D. D. , CHANEY W. R. 
Published: May 2006

SUMMARYThe relationship between the growth of the host, and development and morphology of a vesicular‐arbuscular mycorrhizal fungus was. studied in green ash (Fraxinus pennsylvanica Marsh.). A yearly cycle with three phases is suggested. Phase I is a period of fast shoot growth, slow root growth, rapid colonization of the root system by the mycorrhizal fungus and greater numbers of fungal arbuscles than vesicles. Phase II is a period of fast root growth and a decline in the percentage of root length infected. Phase III is characterized by senescing leaves, infection percentages increasing to a static level, and greater numbers of vesicles than arbuscles. Mycorrhizal green ash seedlings generally had greater heights, weights and root collar diameters and lower root: shoot ratios than non‐mycorrhizal seedlings.
LIGHT AND SELF‐THINNING
Authors: LONSDALE W. M. , WATKINSON A. R. 
Published: May 2006

SUMMARYMonocultures of Lolium perenne were grown at high densities under various shade regimes to investigate the effects of shade on self‐thinning. Unshaded populations conformed to the minus 3/2 power law when dead matter was taken into account in the calculation of mean weight per plant. In a plot of live weight per plant, populations reached a common minus 3/2 line but then deflected from it.Adherence to the minus 3/2 power law is a characteristic of shoots but not of whole plants of L. perenne. Populations increased in shoot:root ratio as they developed so that the thinning line for shoot plus root weight per plant was shallower than the thinning line for shoot weight per plant. Shoot: root ratios were generally higher in shaded than in unshaded populations. Tiller weights and numbers in experimental populations of L. perenne also conformed to the minus 3/2 power law.Populations grown in deep shade thinned along a line of slope minus 1 when sown at ‘low’ densities but those sown at very high densities underwent an initial period of thinning along a slope of minus 3/2, followed by a switch to a slope of minus 1. Populations at intermediate levels of shade showed a decrease in the intercept of the thinning line with increasing shade but no change in gradient. A schematic diagram is presented to help explain the effects of shade on self‐thinning.
A DEMOGRAPHIC ANALYSIS OF THE LEAVES OF OPEN AND SHADE GROWN PINUS STROBUS L. AND TSUGA CANADENSIS (L.) CARR
Authors: WHITNEY GORDON G. 
Published: May 2006

SUMMARYA demographic analysis of the rates of leaf formation and leaf death was initiated in open and shade grown Pinus strobus and Tsuga canadensis. The greater mean life expectancy of the shade grown leaves was attributed to (1) the evergreen habit and the obvious advantages of utilizing an extended growing season in the understory of a deciduous forest and (2) higher rates of photo‐oxidation in the sun. Tsuga canadensis failed to respond to more open habitats by altering its rate of leaf formation. Pinus strobus was considerably more flexible with regard to the formation of new leaves. Open grown trees were characterized by the production of large numbers of lateral branches and a relatively dense crown.