bluuebunny/crossref_metadata_2025_split huggingface dataset:
METAL UPTAKE IN TERRICOLOUS LICHENS
Authors: GOYAL R. , SEAWARD M. R. D. 
Published: May 2006

SummaryLaboratory experiments critically assess the role of rhizinae and thallial surfaces of Peltigera canina in the accumulation and translocation of metals (Cu, Fe, Mn, Ni, Pb and Zn) from the external medium to and within the thallus. The patterns of metal localization, within the different thallial components (rhizinae, medulla and phycobiont) observed from the analyses of field materials, are supported by laboratory experiments. The rhizinae were found to be capable of absorbing, accumulating, translocating and regulating metals. Both upper and lower surfaces were capable of metal translocation. The mode of translocation through one or both of the two surfaces was very similar. Metal cations were able to move freely from the rhizinae to the upper thallial surface and vice versa. The rhizinae and medulla play a significant role in metal accumulation and translocation, especially at higher metal concentrations when the metal uptake capacity of the upper thallial surface is reduced. The observed competitive metal uptake sequences by the rhizinae and thalli with rhizinae removed were consistent with an ion‐exchange process modified by a metal complex formation. The loss of K induced by metals was maximal from the rhizinae and medulla. Most of the metal binding sites are interpreted as occurring near, on, or within the fungal hyphae. Finally, modes of tolerance to high metal accumulations and detoxification are discussed in the light of the following observations: metal localization within the thallus, the role of rhizinae and thallial surfaces in metal uptake, and the lichen's morphological and histological performances in metal‐polluted environments. The factors limiting metal uptake and the effect of metal accumulations on the lichen's biological performance are given.
STUDIES ON THE CONTRIBUTION OF LIGNIN AND SUBERIN TO THE IMPEDANCE OF WOUNDED CARROT ROOT TISSUE TO FUNGAL INVASION
Authors: GARROD B. , LEWIS B. G. , BRITTAIN M. J. , DAVIES W. P. 
Published: May 2006

SummaryDuring repair, phloem parenchyma cells near wound surfaces accumulated suberin and lignin. At 15 °C, all cells in the surface layer had become suberized within 48 h of wounding but lignification was slower, reaching a maximum at 168 h and the distribution was patchy. When fresh wounds were inoculated with Fusarium culmorum, Botrytis cinerea or Mycocentrospora acerina, patterns of lignification were not related in a simple way to pathogenicity; only Mycocentrospora acerina was stimulatory and remained localized in the wound surface bounded by heavily‐lignified cells.If a 250 μm layer of tissue was removed from the surface of fresh or healed wounds its high impedance to Mycocentrospora acerina was substantially reduced by removal of antifungal substances. We therefore conclude that the development of structural barriers is less important than the accumulation of antifungal substances in the resistance of healing wounds.A method for the quantitative estimation of lignin is described.
INTERACTION OF LIGHT AND MINERAL NUTRIENT SUPPLY IN THE GROWTH OF IMPATIENS PARVIFLORA
Authors: PEACE W. J. H. , GRUBB P. J. 
Published: May 2006

Summary(1) Plants of Impatiens parviflora were grown on a boulder‐clay woodland soil at four levels of irradiance with and without addition of ammonium nitrate and calcium phosphate.(2) Addition of nitrogen and phosphorus fertilizer increased dry wt yield and relative growth rate at all four levels of irradiance, and there was a true interaction between the level of irradiance and nutrient supply.(3) At the three higher levels of irradiance the increased growth resulted from an increase in unit leaf rate and leaf weight ratio, but at the lowest level an increase in leaf weight ratio alone was found.(4) Evidence was obtained for lower rates of respiration in the leaves of plants grown with fertilizer at high irradiance. Mycorrhizas were absent from all fertilized plants, but were well developed in the unfertilized plants at high irradiance and absent from unfertilized plants at the lowest irradiance.(5) Plants grown at high irradiance with additional phosphate alone responded initially exactly like plants with additional nitrogen and phosphorus but grew poorly later; plants with additional ammonium nitrate alone showed no response initially, but grew about as fast as plants with additional nitrogen and phosphorus later on.(6) Plants grown one per small pot responded only to additional phosphate in the short term, but plants grown 10 per small pot responded only to additional nitrogen.(7) Emphasis is placed on the important effects of the differential mobilities of nitrate and phosphate ions in experiments on the limiting mineral nutrients in soils.(8) The results are discussed in relation to earlier work, and the penetration of deeper shade by herbs on soils of higher pH is tentatively related to a superior supply of nitrate.
DEGENERATION OF THE SALT GLANDS ACCOMPANYING FOLIAR MATURATION IN AVICENNIA MARINA (FORSSKÅL) VIERH
Authors: DRENNAN PHILIPPA M. , BERJAK PATRICIA 
Published: May 2006

SummaryThe salt excreting glands on both the adaxial and the abaxial surfaces of a sequential developmental series of leaves of Avicennia marina were studied at the light microscopic and ultrastructural level. Scanning electron and light microscopy have shown that there is a decrease in the total number of glands on the adaxial and abaxial surfaces as the leaf matures. From transmission electron microscopy it was established that the glands of emerging, unexpanded leaves exhibited most of the cytological features common to gland cells of all plant species. However, as the leaf expanded, the gland cells were observed to autolyse and the entire glandular structure to collapse. This loss of structural integrity of the glands coincided with abaxial stomatal development and the shift of salt excretion to this surface.
THE LATE‐GLACIAL AND EARLY FLANDRIAN DEPOSITS AT TRAETH MAWR, BRECON BEACONS, SOUTH WALES
Authors: WALKER M. J. C. 
Published: May 2006

SummaryPollen‐stratigraphic investigations are described from a site on the northern slopes of the Brecon Beacons, South Wales, in which over 5.0 m of Devensian Late‐glacial and early Flandrian sediments have accumulated. Relative (percentage) pollen concentration, and deteriorated pollen diagrams were constructed and these data were augmented by radiocarbon dates from the major stratigraphic boundaries. The evidence shows that relatively mild conditions characterized the Late‐glacial Interstadial, but these were succeeded at c. 10600 B.P. by the markedly colder phase of the Loch Lomond Stadial during which a severe periglacial climatic regime prevailed in the area. Climatic amelioration at c. 10000 B.P. led to a rapid sequence of vegetational changes and the establishment of a birch–hazel woodland on the lower slopes of the Brecon Beacons, possibly in the space of 1000 years. Of particular interest in the profile are fluctuations in both pollen percentages and pollen concentration values during the Late‐glacial Interstadial which are interpreted as reflecting major landscape changes around the site. Possible explanations for the fluctuations, which may well have been climatically‐induced, are discussed in the context of other Late‐glacial records from Wales, Highland Britain and northwest Europe.
EFFECT OF AMBIENT HUMIDITY AND LEAF DISPOSITION ON LEAF DIFFUSIVE CONDUCTANCE OF FESTUCA ARUNDINACEA CV. S170
Authors: SILCOCK R. G. , WILSON D. 
Published: May 2006

SummaryThe effects of changes in humidity on leaf diffusive conductance of Festuca arundinacea cv. SI 70 during a sequence of changes in leaf orientation were studied in a controlled environment cabinet. Reducing the vapour pressure deficit from 0.95 to 0.32 kPa at 25 °C (increasing relative humidity from 70 to 90 %) increased total leaf conductance by 73 %. Leaf orientation markedly influenced the conductance of individual leaf surfaces, the uppermost nearly always having the greater conductance.Total leaf conductance was greater when the ridged adaxial surface was uppermost and, overall, the adaxial surface was more sensitive than the abaxial to humidity and orientation changes. Mean leaf conductance was significantly greater 8 h after the lights were switched on than after 1 and 4 h. Leaves which naturally displayed the adaxial surface upwards had a higher leaf conductance than those in which the abaxial surface was normally uppermost for most of their length.
DIFFERENTIAL ABAXIAL AND ADAXIAL STOMATAL RESPONSES TO INDOLE‐3‐ACETIC ACID INCOMMELINA COMMUNISL.
Authors: PEMADASA M. A. 
Published: May 2006

SummaryThe responses of abaxial and adaxial stomata to indole‐3‐acetic acid (IAA) were examined on isolated epidermis ofCommelina communis.IAA was remarkably effective in producing wide adaxial apertures accompanied by a massive increase in the stomatal K+content, and, therefore, eliminating the normal disparity in both the opening and K+accumulation between abaxial and adaxial stomatal cells; it also reversed the suppressive effect of abscisic acid. IAA may affect the transport of K+either directly or indirectly through its control of the proton pump. If the IAA‐induced adaxial opening and K+accumulation is a result of a stimulation of proton extrusion, then, under normal conditions, the proton pump should operate at a lower capacity in adaxial than in abaxial guard cells. Alternatively, the lack of stomatal sensitivity to IAA in the presence of Na+ions suggests a possibility that it might have a direct effect on the K+transport. In either case, as reported here, an external supply of IAA would enhance K+accumulation in adaxial guard cells. The inherent disparity in opening and accompanied K+accumulation between abaxial and adaxial stomatal cells is postulated to be a result of differences in endogenous auxin level between the two epidermes and/or of differential adaxial and abaxial sensitivity to auxin. Thus, the results indicate a hormonal basis for the differential adaxial and abaxial opening.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS
Authors: WHITTINGHAM J. , READ D. J. 
Published: May 2006

SummaryThe functional role of mycorrhizal interconnections between plants was investigated in pot experiments which were designed to simulate some of the circumstances of the regeneration niche in grassland.Young plants of Festuca ovina L. and Plantago lanceolata L. were grown in pots in close association with adults of the same species in the mycorrhizal (M) and non‐mycorrhizal (NM) condition. 32P or nutrient solution was applied to isolated parts of mature ‘source’ plants and transport of the nutrients to younger ‘sink’ plants was examined in the mycorrhizal and non‐mycorrhizal condition. Transport was determined either by measuring 32P in, or total yield of, sink plants at sequential harvests.Greater movement of 32P occurred into roots of mycorrhizal plants of both species. The differences were stastistically significant after only 24 h in F. ovina and after 48 h in P. lanceolata. Application of nutrient solution to source plants led to significantly greater yield in M sinks after 18 and 30 weeks.It is concluded that direct transfer of nutrients between living source and sink plants occurs by way of connecting mycorrhizal hyphae. The significance of these observations for nutrition and survival of young plants is assessed and the broader implications for nutrient cycling in ecosystems considered.
THREE FLANDRIAN POLLEN PROFILES FROM THE TEITH VALLEY, PERTHSHIRE, SCOTLAND
Authors: LOWE J. J. 
Published: May 2006

SummaryDeteriorated pollen grains have been recorded from Flandrian sediments in three sites near Callander in Perthshire, and diagrams are presented of deteriorated pollen as opposed to the overall pollen totals discussed in the previous paper. The problems of interpreting records of deteriorated pollen are discussed, a format for pollen diagrams conveying detailed information on deteriorated grains is introduced, and the palaeoenvironmental implications of the records are considered. It is shown that major changes in deteriorated pollen totals are common to all three diagrams, with low percentages in the early Flandrian, and pronounced increases in deteriorated totals coincident with the Corylus decline at each site. It is suggested that similar studies at other sites in northern Britain may prove these trends to be consistent features of Flandrian pollen diagrams.
THE ESTABLISHMENT OF THE PLASTID THYLAKOID SYSTEM
Authors: WHATLEY JEAN M. , HAWES C. R. , HORNE J. C. , KERR J. D. A. 
Published: May 2006

SummaryMaking use of serial thin sections of conventionally fixed tissue we have constructed a model of the thylakoid system in a pre‐granal, dividing chloroplast. The three‐dimensional configuration of this plastid is compared with the thylakoid configurations seen in 1μm thick sections of the zinc iodide‐osmium impregnated tissue which were examined with a high voltage electron microscope. A comparison has also been made between the differential staining characteristics of the various membranous invaginations, vesicles and tubules which are frequently associated with the plastid envelope and which may play a part in development of the thylakoid system.
PATTERNS OF TURNOVER OF FRUCTANS IN LEAVES OF DACTYLIS GLOMERATA L.
Authors: POLLOCK C. J. 
Published: May 2006

SummaryThe patterns of labelling of fructans with different molecular weights and of fructose residues within chains were determined after cold‐grown plants of Dactylis glomerata L. were fed 14CO2. The coincidence of fructan mobilization and chain elongation, together with the occurrence of asymmetry in the labelling of individual chains, was taken as evidence for reversible transfer of terminal fructose residues between fructan chains during accumulation. These patterns are discussed in relation to the role of fructans in winter growth and survival in temperate grasses.
THE DEVELOPMENT OF MYCORRHIZAL POPULATIONS ON POT‐GROWN SEEDLINGS OF EUCALYPTUS ST‐JOHNII R.T. BAK
Authors: CHILVERS G. A. , GUST L. W. 
Published: May 2006

SummaryThe development of a population of mycorrhizas on the root system of a pot‐grown Eucalyptus seedling has many of the characteristics of a disease epidemic. For example, the number of mycorrhizal apices tends to increase exponentially in the early stages. The disposition of these mycorrhizal apices is non‐random, a fact which should engender care when sampling during field surveys. The final pattern of distribution of mycorrhizal apices within the root system reflects the degree of pre‐infective ectotrophic spread, the frequency and location of primary infection events, the perpetuation of mycorrhizal apices by forward growth, the extent to which they proliferate by branching, and the contribution of later secondary infections from mycorrhiza‐derived inoculum. The relative importance of these different processes is determined, as in a plant disease, by interaction between prevailing fungal, plant and environmental factors. The importance of inoculum availability and the capabilities of the fungus with respect to different regions of the root surface are stressed. The different modes of origin of mycorrhizal apices must be taken into account in any studies which seek to understand the mechanisms involved in conversion of normal root apices into mycorrhizas.
COBALT AND THE CONTRIBUTION OF CROWN AND LATERAL NODULES TO NITROGEN FIXATION OF LUPINUS ANGUSTIFOLIUS L.
Authors: RILEY IAN T. , DILWORTH M. J. 
Published: May 2006

SummaryThe contribution of crown and lateral nodules to the nitrogen supply of inoculated cobalt deficient and sufficient narrowleaf lupin (Lupinus angustifolius L.) was studied in a glasshouse experiment using cobalt‐deficient Lancelin sand. As found earlier, cobalt deficient plants bore more lateral nodules but fewer crown nodules, than normal plants and the nitrogen fixing ability of the deficient plants improved throughout the growth period. This improved nitrogen fixing ability resulted solely from the increased lateral nodulation of cobalt deficient plants. Nitrogenase specific activity of the lateral nodules did not improve with time and crown nodule activity fell to effectively zero.
FLORAL BIOLOGY AND BREEDING SYSTEM OF STERCULIA CHICHA ST. HIL. (STERCULIACEAE)
Authors: TARODA NEUSA , GIBBS P. E. 
Published: May 2006

SummaryThe neotropical, monoecious, forest species Sterculia chicha has been shown to have flowers which are adapted for pollination by Diptera, such as medium‐sized species of the sapromyo‐philous genera Acroglossa, Cachliomya, Gaemnochaetopsis, Ornidia and Parasarcnphaga. Controlled pollination experiments show that the species is self‐incompatible. The fact that pollen tube growth proceeds to the ovule following both compatible and incompatible pollinations suggests that the incompatibility mechanism is based on the non‐fusion of gametes in the embryo sac, as in the Theohroma‐type, originally known only in the related Theobroma cacao.
PLANT‐INDUCED CHANGES IN THE RHIZOSPHERE OF RAPE (BRASSICA NAPUS VAR. EMERALD) SEEDLINGS
Authors: HEDLEY M. J. , WHITE R. E. , NYE P. H. 
Published: May 2006

SUMMARYRape plants that were grown in thin layers of 32P‐labelled Begbroke sandy loam (initial pH 6.1) attained such high root densities (> 90 cm cm−3) that after c. 14 days, all the soil volume became rhizosphere soil. At this time, the rhizosphere pH began to decrease and the quantity of plant available P in the rhizosphere soil, as measured by the L value, exceeded the isotopically exchangeable soil P (E value), determined on samples of incubated but unplanted soil. The P concentration of the rhizosphere soil solution dropped to a minimum of 0.6 μM at 14 days, and remained low, but the phosphatase activity of the rhizosphere soil increased to 10 times that of the control soil after 35 days.In an identical experiment, after 20 and 41 days of growth, organic P (Po) and inorganic P (Pi) in the control and rhizosphere soils were fractionated into the following forms: that extractable by an anion‐exchange resin, 0.5 M NaHCO3 (pH 85), 0.1 M NaOH, 1 m NaOH, 1 m HCl and residual P. Fractionation of the soil P indicated that during the first 21 days, when the rhizosphere pH did not decrease, only resin Pi 0.5 m NaHCO3 Pi and 0.1 m NaOH Pi were significantly depleted by plant uptake. After 41 days, however, when the rhizosphere pH had fallen to 5.3, in addition to depletion of resin Pi 0.5 m NaHCO3 Pi and 0.1 m NaOH Pi there was substantial depletion of acid‐soluble forms of soil Pi and residual P. It is suggested that acidification of the rape rhizosphere (Parts I and II) led to the dissolution of acid‐soluble forms of Pi that were not exchangeable with 32P.In these experiments, there was no evidence for significant hydrolysis of soil Po. Indeed, there was a slight increase in Po in the rhizosphere soil due to the accumulation of fine root debris and microbially immobilized Pi. A possible combination of processes leading to the solubilization of soil P in the rape rhizosphere is proposed.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: MACFARLANE J. D. , KERSHAW K. A. 
Published: May 2006

SUMMARYThe potential control by temperature and moisture of the movement of glucose from the phycobiont in Collema furfuraceum, Peltigera polydactyla and Peltigera rufescens is examined. The ratio of labelled mannitol to labelled glucose after exposure to 14CO2 is used as a measure of the amount of glucose transported and converted to mannitol in the lichen thallus over a range of experimental temperatures and levels of thallus hydration. The results show that temperature has little effect on the proportion of the total label appearing in mannitol except at 5°C. This is interpreted as a minimum temperature requirement for the conversion of glucose to mannitol within the mycobiont. The effect of thallus hydration, however, shows that in Peltigera polydactyla the major movement of fixed carbon from the phycobiont to the fungal partner occurs at, or close to, full thallus saturation. Below 300% thallus moisture by weight the amount of label appearing in mannitol declines sharply. Conversely, in Collema furfuraceum and Peltigera rufescens, transport of glucose continues at a constant rate down to very low levels of thallus hydration.These results are discussed in relation to our previous findings using Peltigera praetextata, and in relation to the balance of total photosynthate between the lichen symbionts during a drying cycle. It is evident that the rate of transport of glucose is closely controlled by the level of thallus hydration which in turn correlates with the xeric or mesic preference of each species. Alternate wetting and drying cycles effectively ensure that each biont obtains an adequate supply of the fixed carbon resources, thus maintaining the integrity of the lichen.
OXYGEN EXCHANGE WITH THE LACUNAE AND ACROSS LEAVES AND ROOTS OF THE SUBMERGED VASCULAR MACROPHYTE, LOBELIA DORTMANNA L.*
Authors: SAND‐JENSEN KAJ , PRAHL CLAUS 
Published: May 2006

SUMMARYThe oxygen dynamics of Lobelia dortmanna were examined by continuous oxygen measurements in the lacunae and in the water around leaves and roots during light/dark cycles. Lobelia exchanges about six times more oxygen over the root than the leaf surface. The exchange rates per unit of surface area are two or three times higher across roots than leaves in accordance with a similar difference in permeability constants. The delay in reaching constant rates of exchange across roots is about 45 min after switching to dark and about 25 min after switching to light. This delay corresponds to the time necessary to change the oxygen concentration in the lacunae to a new steady state gradient with the water around roots. The oxygen pools in lacunae and root‐water change at the same rate at equilibrium. During incubation in a closed system it is necessary to correct for changes in the lacunal oxygen pool when it is significant relative to the oxygen pool in the external water. The lacunae of Lobelia are an effective pathway for gas movements between leaves and sediment. The extensive lacunae, and the diffusional barrier for gases in Lobelia, should facilitate recycling of oxygen, and probably carbon dioxide, within the plant‐sediment system.
THE ADVANCEMENT INDEX VINDICATED
Authors: SPORNE KENNETH R. 
Published: May 2006

SUMMARYIn a recent publication, Muller has listed those families whose pollen can be recognized in the fossil record. Those recorded as being in existence before the Palaeocene have an average advancement index which is significantly lower than that of the present‐day world flora, while those which appeared only after the Oligocene have a significantly higher one. Statistical analysis shows that many primitive characters are more abundant in the early arrivals than in the present‐day world flora. Muller's data, therefore, provide strong support for the concept of an advancement index calculated on the basis of statistically correlated characters.