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  • 1
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A generalized model of the higher plant body is proposed in order to assemble the discrete knowledge of the actions, and sites of biosynthesis, of phytohormones. In this model, we attempt to explain the differential sensitivities of different tissues. With this model most effects of plant hormones appear to be reasonable, and even expected. The model is based on a new anatomical and physiological classification of plant tissue. In higher plants the integration of an outer-inner polarity and an upper-lower polarity plays a major role in phytohormone behaviour.Plant tissues and organs which are derived from the cortex of paleophytes (the bud, the mesophyll of the leaf, the cortex of the stem, and the root cap) are classified as the outer pole of the plant. On the other hand, tissues and organs which are derived from the stele of paleophytes (the root, the stele of the shoot, and the vein of the leaf), are classified as the inner pole. It is suggested that tissue sensitivities to phytohormones are mainly determined by the outer-inner polarity. Phytohormones which are synthesized from one pole act on the other, whereas they exert either much less or no effect, or an inverse effect on their own pole. This is shown for both promoters and inhibitors of the phytohormones for both cortical and stelar vegetative tissues of plants.
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abastract Measurements of growth increments on the shaded and the irradiated sides of phototropically stimulated maize (Zea mays L.) coleoptiles, obtained over the entire fluence range of the first positive curvature, indicate that the curvature is induced by growth stimulation on the shaded side and compensating inhibition on the irradiated side (length increments on the coleoptile flanks were determined 100 min after 30 s phototropic induction with blue light). At high fluences of blue light, overall stimulation of growth takes place, but this tendency is largely eliminated when only the tip of the coleoptile is irradiated. Time courses for growth increments obtained for the maximum first positive response show that the growth stimulation on the shaded side and the growth inhibition on the irradiated side commence almost simultaneously 20-30 min after the phototropic induction. The growth on the irradiated side almost ceases, but the growth rate on the shaded side is doubled, relative to the control rate. The onset of differential growth migrates basipetally from the tip at a velocity similar to that for polar auxin transport. The first positive phototropic response of the coleoptile is concluded to be the consequence of lateral redistribution of growth, which is not necessarily accompanied by changes in the net growth. The results are consonant with the Cholodny-Went theory of tropisms, in which lateral redistribution of auxin is considered to be the cause of tropic responses.
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  • 3
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Stem chlorenchymatous cells from well-watered and water-stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52-58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress.
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Plants of Pinus radiata of two physiological ages, juvenile (seedlings and micropropagated plantlets) and adult (rooted cuttings from mature trees), were grown under lighting fromthree combinations of metal halide (MH) and tungsten halogen (TH) lamps for up to 10 months in controlled environment rooms. The three lamp combinations, MH alone, 50: 50 MH: TH and 25:75 MH: TH by wattage, produced red: farred ratios of 4.59, 1.51, and 1.15, respectively. Photosynthetic photon flux density was 700 μmol m−2 s−1. An increase in proportion of TH lamps markedly increased shoot elongation and internode length, decreased numbers of fascicles per unit stem length and increased the proportion of stem weight in both juvenile and adult material. In addition, in adult material, it increased the number of fascicle initials and expanded fascicles per growth flush, reduced the duration of the ‘rest’ phase between growth flushes, accelerated the rate of elongation growth during each flush, and increased apical dominance. Tracheid length, but not diameter or wall thickness, was significantly affected by light quality and found to be associated with longer internodes. Any treatment effects on needle weight or length, stem diameter or root weight were non-significant or very small. Different clones from either the juvenile micro-propagated material or the mature rooted cuttings each showed similar patterns of response, although they often differed in the degree of response to light quality. The main response could be related solely to the red: far-red ratio and the calculated phytochrome photoequilibrium. This is the first report of phytochrome-controlled photomorphogenesis in older specimens of a woody perennial. Recommendations for artificial light sources for growing P. radiata and some ecological implications of the results are presented.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. In a highly saline environment high rates of ion uptake are required to generate sufficient osmotic pressure to maintain the turgor that is needed for the continued growth of plants. We estimate the rates of net uptake of Cl− and Na+ required by growing cells to sustain cell expansion at an external NaCl concentration of 500 mol m−3. We also estimate the ion fluxes required to regulate turgor of expanding and fully expanded cells during diurnal changes in transpiration. Passive fluxes could contribute significantly to osmotic regulation, but active fluxes are still essential and would consume a substantial amount of energy. We discuss whether a limitation to growth at high salinity would arise from lack of energy, or from insufficient capacity for ion uptake. There is insufficient evidence to choose between these possibilities.
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  • 6
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The ultrastructural features of the abscisic-acid-induced turion of Spirodela polyrrhiza are briefly described and a comparison between turion and vegetative frond tissue was made by stereological analysis. The turion is characterized by its small size, reniform shape, and dark-brown coloration; the mesophyll is undifferentiated and totally lacking the substantial acrenchyma development found in the vegetative frond. The turion cells have a smaller vacuole and a denser cytoplasm than the cells of the vegetative frond. Stereological analysis showed that the tissues differed quantitatively only in three main respects: air space formation, vacuolation, and starch and cell wall material accumulation. During development, it is suggested that the cells of the turion, while reaching the same final size as the vegetative frond cells, accumulate numerous starch grains, thick cell walls, and large deposits of tannins and anthocyanin pigment at the expense of the vacuolar expansion characteristic of the normal maturity programme. Certain features of the turion ultrastructure indicate a differential cell sensitivity to ABA.
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  • 7
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Book reviewed in this article: MICROMOLECULAR EVOLUTION, SYSTEMATICS AND ECOLOGY. By O. R. Gottlieb OPPORTUNITIES FOR MANIPULATION OF CEREAL PRODUCTIVITY. Edited by A. F. Hawkins & B. Jeffcoat
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  • 8
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 9
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 10
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Peristomatal transpiration is defined as the relative high local rate of cuticular water loss from external and internal surfaces around the stomatal pore and its decisive role in the control of stomatal movement is re-emphasized. As the resistance towards changes in air humidity is low in the pore surroundings, the state of turgor is particularly unsteady there. Due to the inherent instability the guard cell ‘senses’ fluctuations in the supply-demand relationship of water and is thus the control unit proper. The environmental variables (supply and demand) are cross-correlated within the subsidiary cell and the information is transmitted to the guard cell through the water potential gradient between the two cells. A conceptual segregation of a ‘humidity response’ by ‘passive’ stomatal movements is rejected.As ions always accumulate at the most distant point of the liquid path and as this point varies with pore width according to the prevailing water potential gradients, it is felt that the water stream is causing the characteristic pattern of ion distribution within the epidermis. Passive import of ions is attributed to local concentration gradients which are steepened by continuous supply and by water uptake into the guard cell in response to starch hydrolysis. A mechanistic model supplements the discussion.
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  • 11
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Two strains of Dunaliella, both grown at 25°C were analysed for their α-amino acid and neutral soluble carbohydrate content. Glycerol was found as a major cell constituent in both varieties; the amount was roughly proportional to the outside NaCI concentration between 0.5 and 3 kmol m−3, and varied from 3.4% to 45% of the total dry weight of packed cells. The sum of sugars and α-amino acids did not amount to more than 2% of the total dry weight at any NaCI concentration.
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  • 12
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The effect on seed germination of the red/far-red ratio of light (ζ) as modified by a leaf canopy was studied. The artificial light sources used and daylight filtered through leaves appeared to have identical effects in tests with lettuce seed.The sensitivity of the seeds to ζ varied with the environmental conditions during pretreatment and during the actual germination test. Freshly harvested and dry-stored seeds of Cirsium palustre were strongly inhibited at low ζ; after stratification, the inhibition was much less. The fact that C. palustre emerges mainly after the coppice is felled could not be explained from these results combined with field data on ζ and the response of germination to temperature.The ecological significance of inhibition at low ζ is to be found directly after dispersal. Seed germination will then be delayed until the following spring or later. Geum urbanum showed primary dormancy, which was released by a stratification treatment. No inhibition of germination at low ζ was found in the spring and seeds germinated in light and darkness at low temperatures. These results explain why the species emerges early in spring regardless of the presence of the ash canopy.
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  • 13
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Summary. Soluble potassium concentrations were determined for the slightly vacuolated, unicellular, walled alga Chlorella emersonii. Sap of cells grown in 1 mol m−3 NaCI contained 140 mol m−3 K+ and sap of cells grown in 125, 200, and 335 mol m−3 NaCI contained 160-180 mol m−3 K +.The possible regulation of K + concentrations by a system of lurgor and volume maintenance was investigated by supplying 3-0-methylglucose. This solute accumulates to 85-230 mol m−3 in C. emersonii, but is not metabolized. Accumulation of 3-0-methylglucose increased the volume of cells grown at both low and high NaCI by about 10%. Furthermore, accumulation of 3-0-methylglucose also increased turgor pressures of cells grown in 1 and 125 mol m−3 NaCI by 0.3 and 0.2 MPa, respectively. (Similar measurements were not attempted for cells grown in 200 and 335 mol m−3 NaCI, because of the insensitivity of available methods to measure turgor pressure of cells exposed to high external osmotic pressures.)At all NaCI concentrations, the K + concentrations of cells which had accumulated 3-0-methylglucose were only 10-20 mol m−3 lower than K+ in cells which had not been supplied with 3-0-methylglucose. In contrast, accumulation of 3-0-methylglucose greatly decreased concentrations of the endogenous osmotic solutes, proline and sucrose, which accumulated in cells grown in 125 mol m−3 and higher NaCI concentrations.It is concluded that K+ concentrations in Chlorella emersonii are not controlled by a system of turgor and volume maintenance.
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  • 14
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 6 (1983), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 15
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: CLONING AGRICULTURAL PLANTS VIA IN VITRO TECHNIQUES. Edited by B. V. Conger EFFECTS OF HEAVY METAL POLLUTION ON PLANTS. VOLUME 1. EFFECTS OF TRACE METALS ON PLANT FUNCTION (352 pp.). VOLUME 2. METALS IN THE ENVIRONMENT (257 pp.). Edited by N. W. Lepp STOMATAL PHYSIOLOGY. Edited by P. G. Jarvis AND T. A. Mansfield DEVELOPMENTS IN PLANT AND SOIL SCIENCES. VOLUME 3. CARBON AND NITROGEN METABOLISM. Edited by J. D. Bewley ECOLOGICAL STUDIES. VOLUME 36. PHYSIOLOGICAL PROCESSES IN PLANT ECOLOGY. TOWARD A SYNTHESIS WITH ATRIPLEX, By C. B. Osmond, O. Björkmanand D. J. Anderson PHYSIOLOGICAL PROCESSES LIMITING PLANT PRODUCTIVITY. Edited By C. B. Johnson MATHEMATICS AND PLANT PHYSIOLOGY. Edited by D. A. Roseand D. A. Charles-Edwards BIOSYNTHESIS OF ISOPRENOID COMPOUNDS, VOLUME 1. Edited by J. W. Portkr and S. L. Spurgeon STRUCTURE AND FUNCTION OF PLANT ROOTS. Edited by R. Brouwhr, O. Gas̈paiuková, J. Kolek & B. C. Loughman THE CELL CYCLE (Society for Experimental Biology, Seminar Series No. 10). Edited by P. C. L. John
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  • 16
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Reeve & Crozier (1980) have recently proposed a method of evaluating the accuracy of a plant growth substance analysis by using information theory to estimate whether the analysis would distinguish the growth substance from all other components of the sample. In the present article, it is argued that their method requires knowledge of the relevant analytical characteristics of all potential components of the sample, and hence is not applicable to plant extracts. Instead, the identity of a growth substance in a plant extract can only be conclusively established using techniques which yield information on its chemical structure.
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  • 17
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Re-analysis of published data on the gecocurvature and nutation of the primary root of maize is presented. This analysis demonstrates clear evidence of nutalional oscillations occurring during georesponse. The importance of this evidence in relation to theories of nutation mechanism is discussed.
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  • 18
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. A system is described whereby seedling development can be analysed in terms of growth rates of specific 1 mm regions of the hypocotyl. The technique involves time-lapse photography of marked hypocotyls in a specially designed chamber which accommodates seedlings in various orientations with respect to gravity, and under irradiation regimes differing in light quality, quantity and direction. The results of a preliminary study of the upward growth of etiolated or green cress seedlings in darkness or overhead while light are reported. Highest growth rates in etiolated seedlings were observed in zones in the upper one-third of ihe hypocotyl. In green seedlings, growth was more prominent within the subapical zones. Light further restricted growth of the median and basal zones in both types of seedling. However, in their immediate responses to the onset of irradiation, green and etiolated seedlings differed markedly. In etiolated seedlings, recovery of growth at the apex was accompanied by the development of inhibition in the median-basal regions; green seedlings showed a transient inhibition of growth in the apical zone together with a strong immediate inhibition in the median-basal regions.
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  • 19
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle.
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  • 20
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Growth rates throughout an organ curving phototropically under continuous, unilateral while light were monitored by lime-lapse photography of cress hypocotyls marked into 1 mm sections by two rows of ion-exchange beads. Curvature resulted from an integrated sequence of changes in growth rate on each side of the organ, but the actual patterns of change and, therefore rales of curvature, differed within even this one species, depending upon the immediate pretreatment of the seedlings. Transference of seedlings from darkness to unilateral irradiation gave immediate growth inhibition on both sides of the organ. Curvature resulted from differential recovery of growth rate, being seen first on the shaded side, most prominently in the apical regions; only 2h after initial exposure to light did growth recover on the lit (lower) side. On the other hand, transfer of seedlings from omnilateral to unilateral irradiation of the same intensity resulted in simultaneous growth inhibition on the irradiated side and stimulated growth on the shaded side: this growth stimulation of the shaded side was greater than occurred in totally darkened control plants.
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  • 21
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The leakage of electrolytes and the localization of chloride within the cells of NaCl-imbibed seeds indicates the plasmalemma is quite permeable during the early stages of imbibition. However, lanthanum is not able to penetrate the plasmalemma, suggesting that the plasmalemma is not entirely porous. Freeze-fracture microscopy indicates that the plasmalemma is highly convoluted but reveals a fairly normal fracture plane. These observations suggest the membrane is a bilayer and leakiness may be more related to the degree of order within the bilayered membrane than to a primary restructuring and/or reorganization of the membrane components in the dry state.
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  • 22
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm−3(140 p.p.m.) O3 for 30 min. Sixty-eight per cent of the cells were plasmolysed after 15 min O3 exposure with disruption of organelles similar to that previously described in higher plants. Freeze-fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O3for short periods. After 20 min O3 90% of the cells cross-fracture, which indicates a change in molecular interactions in the membrane exposed to O3 The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O3 Changes in 86Rb influx occur during a similar time. After more extended exposure to O3 the plasma membrane P face shows regions of lipid phase transition to the crystalline state.
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  • 23
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Rates of proton extrusion and potassium (86Rb) influx by intact roots of barley (Hordeum vulgare cvs. Fergus, Conquest and Betzes) plants were simultaneously measured in short-term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K+ concentrations (0.01 to 1 mol m−3), H+ efflux and K+ influx were strongly correlated in both low- and high-K+ roots, although K+: H+ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m−3), H+ efflux was either reduced or remained unchanged while K+ influxes increased. In the presence of Na2SO4, rates of H+ extrusion demonstrated similar cation dependence, although below 10 mol m−3 Na2SO4, H+ fluxes were generally 50% lower than in equivalent concentrations of K2SO4. These observations are considered in the context of current hypotheses regarding the mechanisms of k+/H+ exchange.
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  • 24
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Seedlings of Pharhitis nil show a circadian rhythm in the capacity to flower in response to the timing of a second red light pulse given at various times after a first saturating exposure to red when this is given together with a benzyladeninc spray. There are also changes in the photon irradiance required for half maximum response to the second red pulse.The photochemical properties of phytochrome in the photoperiodically sensitive cotyledons were also shown to change rhythmically. Oscillations in both pr→ Pfr and Pfr→ Pr photoconversion characteristics persisted over at least two circadian cycles with a periodicity of about 12 h. There were, however, no significant oscillations in either Pfr peak absorbance or in Δ(ΔA). The changes in sensitivity for the photoconversion of Pr→ Pfr did not parallel the much larger changes in sensitivity of the flowering response to red light. The amplitude of the Pr→ Pfr rhythm was at least as great as that for Pr→ Pfr, but the flowering response to far-red light was not rhythmic, nor was there any large change in sensitivity. The changes in photoconversion properties may reflect a basic biochemical oscillation which affects both photoreceptor properties and sensitivity to photoreceptor input.There was also a marked rhythm in the Pfr/P ratio that would be established by a saturating pulse of red light and this too may have affected the flowering response to such a pulse.Far-red light inhibited flowering when given at any time during the inductive night. After 14 h in darkness, Pfr could still be measured in the cotyledons and it was concluded that far-red light inhibited flowering by removing Pfr As red light also inhibited flowering at this time, there may be two pools of phytochrome with different kinetic properties.
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  • 25
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Regulation of the concentration of osmotic solutes was studied in Chlorella emersonii grown at external osmotic pressures (II) ranging between 0.08 and 1.64MPa. NaCl was used as osmoticum. The total solute content of the cells was manipulated by applying 2 mol m−3 3-O-methylglucose (MG), which was not metabolized, and accumulated at concentrations ranging between 60 and 230 mol m−3 within 4 h after its addition to the medium. Methylglucose uptake resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high external II. The responses were consistent with the hypothesis that proline and sucrose concentrations are controlled by a system of osmotic regulation, with turgor and/or volume as a primary signal. Short-term experiments showed that even very small increases in turgor and/or volume, due to accumulation of methylglucose, resulted in large decreases in proline and sucrose. Over the first 30-60 min the total solute concentration in the cells increased by at most 15 osmol m−3 which would represent an increase in turgor pressure of at most 0.04 M Pa. Yet, the decreases in proline and sucrose were as fast as those in cells exposed to a sudden decrease of 0.25 MPa in external II, when the turgor pressure would have increased by at least 0.15 MPa. High concentrations of methylglucose in cells grown at high II did not affect the rapid synthesis of proline and sucrose which started when the cells were transferred to yet higher II. Thus, methylglucose had no direct effects on proline and sucrose metabolism, and it has been assumed that it acted solely as an inert osmotic solute within the cell.
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  • 26
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 5 (1982), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The non-osmotic volume (NOV) of Connnelina communis L. guard cells was estimated by observing the volumes of guard cell protoplasts incubated in mannitol solutions of different solute potential, and applying the Boyle-van't Hoff relation to the results. NOV values of between 517 and 1782 μm3 were obtained for different batches of protoplasts. There was a negative correlation between NOV and apparent protoplast solute contents, and the NOV and solute content were observed to alter when pretreatments affecting stomatal aperture were given. H is hypothesized that changes in guard cell chloroplast starch levels could account for variation in NOV and solute content.For closed stomata, it is calculated that the NOV could reduce the proportion of the total guard cell volume which is osmotically active by over 40%. Serious inaccuracy may thus result if the NOV is not taken into account in the estimation of guard cell solute potential or solute concentration from measurements of solute levels per cell. The error is maximal at low stomatal apertures.
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  • 27
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The effect of accumulation of 3-O-methylglucose (MG) on growth and steady-stale concentrations of the endogenous osmotic solutes proline and sucrose was studied in Chlorella emersonii grown at external osmotic pressure (II) of 0.08-1.64 MPa. NaCL was used as osmoticum. The total solute content of the cells was manipulated by supplying 2 mol m−3 MG for 4 and 48 h. MG accumulated to 50–230 mol m−3 within 4h and was not metabolized. Uptake of MG resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high II. After 4 or 48 h growth in the presence of MG, the decreases in concentration of proline and sucrose were as predicted from the contribution of MG to the total solute content of the cell.
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  • 28
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Fluence-response and reciprocity data were collected for response to end-of-day FR in several light-grown plants. Coleoptile elongation in oat and hypocotyl elongation in sunflower and mung bean are stimulated by end-of-day FR, and anthocyanin accumulation in mung bean hypocotyls is decreased by the same treatment. All responses have threshold fluences at about 200μmol m−2 and saturation fluences between 4000 and 10,000 μmol m−2 Responses to end-of-day FR were reversible by subsequent R with threshold fluences between 2.0 and 3.0 μmol m−2 and saturation fluences between 300 and 1000 μmol m2 Rapid, reverse reciprocity failure which could not be explained by escape from photoreversibility was observed only for stimulation of oat coleoptile elongation by end-of-day FR. Oats also showed apparent reverse reciprocity failure for R, but it was entirely explainable by escape. Rapid, reverse reciprocity failure is not a ubiquitous phenomenon for responses to end-of-day irradiations.
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  • 29
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. A comparative study of two chromosomal races of the winter-active ephemeral Machaeranthera gracilis showed that the seasonal magnitudes of photosynthesis were only slightly greater for a progeny desert race than for an ancestral foothills race. Maximum observed photosynthetic capacity and the seasonal reduction in foliar photosynthesis occurred earlier in the year for the desert race. The relative growth rate was higher in this race up until the time of its peak seasonal biomass. A ratio of harvested net production to estimated gross primary production decreased until anthesis. Photosynthesis contributing to net growth continued into periods with moderate environmental stress. The continuation of growth by the desert race was enhanced by maintenance of a higher root-shoot ratio, as well as greater relative stem growth. During reproduction, foliar CO2 assimilation could not solely provide the measured dry matter accumulation, suggesting the importance of assimilate contribution by photosynthetic stems. Seasonal increases in the enthalpy content of whole plants and plant organs occurred for both races, indicating the absence of significant translocation during reproduction and the potential for stem photosynthesis.
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  • 30
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The CAM plants Kalanchoe tubiflora and K. blossfeldiana were grown under photoperiodically controlled conditions (short days). In these plants, phos-phoenolpyruvate carboxylase capacity and the sensitivity of the enzyme to the effectors L-malate (inhibitor) and glucose-6-phosphate (activator) were measured throughout the diurnal CAM cycle. In K. tubiflora, enzyme capacity was higher if measured at pH 7.0 than at pH 8.0 and displayed a rhythmical behavior with highest values at the end of the light period. As reported earlier, in K. blossfeldiana PEP-C capacity was higher during the night. It was more pronounced when plants were kept in CO2-free air during the dark period. In both plants, the sensitivity of the enzyme to the effectors showed very clear diurnal changes: inhibition by malate and activation by glucose-6-phosphate were strikingly higher during the day than during the night; the effect depended on PEP concentration. The changing activation of the enzyme by glucose-6-phos-phate reflects diurnal changes of the Km for PEP which was found to be higher during the day than during the night. Manipulations of malate accumulation by nocturnal application of CO2-free air did not influence these effects. The results are discussed in context with the metabolic control of CAM.
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  • 31
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Accumulation of the lipophilic cation tri-phenylmethylphosphonium (TPMP+) has been used to estimate the plasmalemma potential (Φm) of Porphyra purpurea (Rhodophyta, Bangiales) and Ulva lactuca (Chlorophyta, Ulvales). Values of Φm obtained using the Nernst equation were −61 mV and −54 mV respectively; these values compare well with those obtained using glass microelectrodes. A trend of hyperpolarization of Φm in P. purpurea was observed with decreasing external salinity. This hyperpolarization was shown to be primarily due to changes in external K+ concentration. Varying external Na+ concentration was found to have little effect on Φm. The present data suggest that the membrane potential of P. purpurea is not wholly due to a K+ diffusion potential, but may have an electrogenic component.
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  • 32
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 4 (1981), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Chilling the leaves of the extremely chill-sensitive plant Episcia reptans for only a few hours at 5°C causes ultrastructural changes such as swelling and disorganization of chloroplasts and mitochondria, and vesiculation of cytoplasmic membranes. Rewarming plants after 5–6 h chilling causes further deterioration in chloroplast and mitochondrial structure and the appearance of fibrous material in the cytoplasm of epidermal, mesophyll and vascular cells. The nature of the deposit is not known but it may be the cause of the rapid development of chilling-injury on return of plants to the warmth.
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  • 33
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. It is widely believed that the root cap participates in geotropism by acting both as a sensor of the direction of gravity and as a source of at least one regulator of root growth, which may be abscisic acid (ABA). It has been suggested that this regulator accumulates within the prospective concave (or lower) half of the root and there causes a retardation of growth that brings about bending. A re-examination of the evidence upon which this inhibitor hypothesis of geotropic control is based reveals that (1) it is derived almost entirely from microsurgical studies and the deductions from such experiments still require corro-orations from analyses of inhibitor content and action; (2) the evidence that ABA is the inhibitor seems poor at present; (3) in maize and lentil, two well-studied species, geocurvature is probably a consequence of accelerated growth within the prospective convex (or upper) half rather than inhibited growth within the concave (or lower) half; (4) the geotropic signal from the cap may be one that redirects a pre-existing basipetal flow of inhibitor away from the upper
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  • 34
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 4 (1981), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The belief that the shoot apex plays a special role in geotropism is shown to be erroneous and the implications of this widely held misconception are discussed.
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  • 35
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Characteristics of the geotropic response of de-etiolated mung bean hypocotyls are presented. Geotropic sensitivity is not confined to the apical tissue but exists throughout the responding zone. The presentation time is estimated to lie between 0 and 30 s for this tissue. Anatomical features of the presumed geoperceptive tissues are described. Rapid sedimentation and cyclosis of statolith amyloplasts in living tissue are reported, which are fast enough not to preclude the possibility of receptor sites situated at or near the lateral wall of statocytes.
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  • 36
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The changes in the levels of two different isozymes of cellulase (EC 3.2.1.4) have been followed during the abscission of the primary leaves of bean (Phaseolus vulgaris c.v. Red Kidney), using antibodies raised against the 9.5 form of the enzyme. Data from both radioimmune and direct assay show that the 9.5 form of cellulase is undetectable prior to the induction of abscission. After a 12 h lag this isozyme increases in activity, the increase preceding a decrease in integrity of the abscission zone cell walls. The results are consistent not only with the view that this specific isozyme is involved in wall hydrolysis but also with previous data which showed that cellulase is synthesized ‘de novo’.The 4.5 isozyme of cellulase is more widely spread throughout the plant, being most active in young tissues. During abscission the activity of this isozyme in the abscission layer falls and consequently it is not thought to be involved directly in the abscission process.
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  • 37
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract After the onset of imbibition, the dormant seeds of Rumex obtusifolius and R. crispus are stimulated to germinate by a change from an initial low temperature to a warmer temperature for a relatively brief period: the warmer that temperature the shorter is the optimum period spent at it, and this optimum value is unaffected by the initial temperature. The optimum period is more critical in R. crispus than in R. obtusifolius (about 1 h and 2.5 to 4 h, respectively, for a warmer temperature of 35°C in the dark); in the light the length of the period at the warmer temperature is less critical in both species. The sensitivity of the seeds to the change to the warmer temperature increases with time from the start of imbibition at a rate which is positively related to the initial temperature. In R. obtusifolius maximum sensitivity was typically reached after 3 to 5 d when the initial temperature was 20°C and then remained constant, or declined only slightly, over the period investigated (10 d). At the same initial temperature, however, R. crispus showed a cyclical pattern of sensitivity with peaks occurring at 3–4 d intervals from the start of imbibition.
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  • 38
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 4 (1981), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A theoretical analysis of yield components of Hevea brasiliensis is attempted in this paper. The effect of the major yield components, i.e. initial flow rate per unit length of tapping cut, length of the cut, percentage rubber content and plugging index on rubber yield is represented by the formula<displayedItem type="mathematics" xml:id="mu1" numbered="no"><mediaResource alt="image" href="urn:x-wiley:01407791:PCE81:PCE_81_mu1"/>Variation in yield within and between clones can be ascribed to variation to any one of the above components. The importance of high growth rate for maintaining high yield throughout the life cycle of the tree is theoretically elucidated. While the present contention of a theoretical maximum yield of 9.5 t ha−1 with a stand of 350 trees is questioned, the theoretical possibility of attaining that yield by increasing the stand per ha to 600 is analysed.
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  • 39
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Maize, barley and sunflower plants were grown in the field, well supplied with water and nutrients. During growth, net CO2 exchange and transpiration of the crops at varying ambient CO2 concentrations and irradiance were determined by infra-red gas analysis. In maize the net photosynthetic rate (Pn) was linearly related to the irradiance (I) and independent of the ambient CO2 concentration (Ca). The transpiration rate (ET) was also linearly related to I but decreased strongly with increasing Ca. In sunflower and barley Pn increased and ET decreased with increasing Ca. A mean stomatal conductance and intercellular CO2 concentration (Ci) were calculated. In all three species the internal CO2 concentration was independent of the irradiance. In maize it was also independent of Ca, but in sunflower and barley Ci was proportional to Ca with a ratio of 0.6.It is concluded that differences in stomatal behaviour are only partly species-specific and depend mainly on growing conditions. The importance of stomatal regulation for crop growth under conditions of water shortage and CO2 depletion is discussed.
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  • 40
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Radioisotope equilibration techniques have been used to determine the intracellular concentration of K+, Na+ and Cl−, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of 42K+, 24Na+ and 36C1− are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K+ and Cl− and against Na+. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K+ and Cl− influx and Na+ efflux. ‘Active’ uptake and ‘passive’ loss of K+ and Cl− are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K+ and Cl− may be due to ‘exchange diffusion’ (K+/K+ and Cl−/Cl−antiport).
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  • 41
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Sites of acid-phosphatase activity were found in the differentiating root protophloem of Nymphoides peltata by lead-salt and by azo-dye methods. Different substrates revealed different subcellular locations of the enzyme. The substrates β-glycerophosphate (β-GP) and naphthol ASBI phosphate revealed enzyme activity at similar sites within the sieve element. These sites included plasmodesmata, dictyosomes and small vacuoles in the cytoplasm. The substrate p-nitrophenylphosphate (p-NPP), however, revealed additional sites of acid-phosphatase activity which were not detectable by either naphthol ASBI phosphate or β-GP. For example, the inner region of the wall in mature sieve elements showed conspicuous acid-phosphatase activity only when p-NPP was used as substrate. The significance of the different locations of acid phosphatase within the sieve element is discussed.The convoluted ER, characteristic of immature sieve elements of N. peltata, failed to show acid-phosphatase activity whichever substate was used. By contrast, the stacked ER found in the parietal layer of mature sieve elements showed prominent acid-phosphatase activity regardless of the substrate used. The demonstration of acid-phosphatase activity in the stacked ER, and by both lead-salt and azo-dye methods, suggests that this organelle is a true site of acid-phosphatase activity.The onset of acid-phosphatase activity in the ER in later stages of sieve-element differentiation is compatible with the view that stacked ER plays a role in the final autolysis of the sieve-element protoplast.
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  • 42
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Starch levels in Commelina communis epidermis, were shown to be higher in the dark than in the light, from plants kept under an imposed photoperiodic regime. These changes were also inversely correlated with diffusive conductance (1/diffusive resistance, 1 /R) of the leaves used. Even after advancing the photoperiod by 7 h the changes in starch levels continued for at least 1 d and were still inversely correlated with 1/R.Corresponding changes in glucose levels were measured in the same tissue and were found to correlate with 1/R at the end of the dark period and mid photoperiod, but not at the beginning of the dark period. These changes are discussed in relation to possible mechanisms of stomatal opening and closing.
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  • 43
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A range of aliphatic, aromatic and amino acids at a concentration of 5 mol m-3 inhibited the extension of roots of barley seedlings. Acetic acid is one of the least toxic but its action has the greatest ecological significance because it can be formed in phytotoxic concentrations by micro-organisms in soil. Its uptake and toxicity were greatest at low pH. Of the plant species which were examined, those most affected were barley, wheat and maize, followed by rape and clover. In aerobic conditions, microbial breakdown of the acid decreased its activity, but in atmospheres containing small concentrations of oxygen the acid prevented the germination of seeds. The toxicity could be partially alleviated by calcium carbonate applied as ground chalk to seeds.
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  • 44
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Biomass increase, C and N content, C2H2 reduction, percentage dry weight and chlorophyll a/b ratios were determined for clones of Azolla caroliniana Willd., A. filiculoides Lam., A. mexicana Presl., and A. pinnata R. Br. as a function of nutrient solution, pH, temperature, photoperiod, and light intensity in controlled environment studies. These studies were supplemented by a glasshouse study. Under a 16 h, 26°C day at a light intensity of 200 μmol m−2 s−1 and an 8 h, 19° C dark period, there was no significant difference in the growth rates of the individual species on the five nutrient solutions employed. Growth was comparable from pH 5 to pH 8, but decreased at pH 9. Using the same photoperiod and light intensity but constant growth temperatures of 15–40°C, at 5°C intervals, the individual species exhibited maximum growth, nitro-genase (N2ase) activity and N content at either 25° or 30°C. There was no difference in the temperature optima at pH 6 and pH 8. The tolerance of the individual species to elevated temperature was indicated to be A. mexicana> A. pinnata> A. caroliniana> A.filiculoides. At the optimum temperature, growth rates increased with increasing photoperiod at both pH 6 and pH 8 but N2ase activity was usually highest at a 16 h light period. At photon flux densities of 100, 200, 400 and 600 μmol m−2 s−1, during a 16 h light period and optimum growth temperature of the individual species, N2ase activity was saturated at less than 200 μmol m−2 s−1 and growth at 400 μmol m−2 s−1.No interacting effects of light and pH were noted for any species, nor were light intensities up to 1700 μmol m−2 s−1 detrimental to the growth rate or N content of any species in a 5 week glasshouse study with a natural 14.5 h light period and a constant temperature of 27.5°C. Using the optimum growth temperature, a 16 h light period, and a photon flux density of at least 400 μmol m−2 s−1, the Azolla species all doubled their biomass in 2 days or less and contained 5–6% N on a dry weight basis.
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  • 45
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Two-week old, glasshouse-grown seedlings of spring and winter oats (Avena sativa cv. Margam and Pennal respectively) were transferred to growth rooms where the daylength was 8 h and the temperature was either 20° or 5°C. Leaves from the 20°C treatment were harvested 1 week after transfer and those from the 5°C treatment after 3 weeks. Measurements were made, at temperatures in the range 5–20°C, of the rate of senescence of excised leaf sections; the rate of in vivo tetrazolium (TTC) reduction; the NADH-MTT tetrazolium diaphorase (NMD) activity of a membrane preparation isolated by sucrose gradient centri-fugation; and Hill activity of isolated chloroplasts. Data from these experiments, either untransformed or plotted in accordance with the Arrhenius equation, were analysed by the method of maximum likelihood for the occurrence of rate-temperature discontinuities. Distinct breakpoints at 14.2–16.3°C were detected for senescence, TTC reduction and NMD in winter oat leaves from the 20°C treatment, but spring oats grown at the same temperature gave a significant discontinuity only in the rate of senescent yellowing. After the hardening treatment, 3 weeks at 5°C, senescence and TTC reduction in winter oats exhibited breakpoints at 10.1–12.4°C and spring oats gave breaks at 11.8–17.3°C. No breakpoint was observed for Hill activity from either variety under either temperature treatment. The use of this approach in studies of growth at chilling temperatures and its potential as a screening method are discussed.
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  • 46
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Responses of stomata to light and CO2 were smaller when detached epidermis of Commelina communis L. was incubated on a medium containing 50 mol m−3 NaCl than when an equimolar KCl solution was used. Although opening in the light in the absence of CO2 seemed to be the same whichever salt was present, apertures on KCl solutions were smaller in the dark or with CO2-containing air. The response to 10−7 mol dm−3 ABA was similarly reduced in the presence of NaCl. If there is an optimal NaCl concentration for stomatal CO2 and light responses it is at or below 25 mol m−3. These findings point towards control of stomatal movements by light, CO2 and ABA at the level of cation uptake or extrusion.
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  • 47
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Lipophilic cations inhibit nocturnal malic acid accumulation in leaf cells of the Crassulacean Acid Metabolism plant Kalanchoë tubiflora. perhaps by interacting directly or indirectly with active malic acid transport into the vacuoles. Lipophilic cations do not affect passive efflux of malic acid from the vacuoles. Membrane potentials are depolarized, oxygen uptake is stimulated by lipophilic cations and there may also be stomatal responses. Thus it is striking that lipophilic cations do not alter the stoichiometry of 2 titratable H : 1 enzymatically-determined malate2− during diurnal malic acid oscillations of Crassulacean Acid Metabolism in Kalanchoë. This suggests that coupling between protons and malate during transport into the vacuole must be tight. Transport as undissociated acid is unlikely because the dissociation equilibrium in the cytoplasm is largely on the side of malate2−. These results appear to suggest an intimate molecular interaction between a proton pump and a presumed malate2− translocator at the tonoplast of leaf cells with Crassulacean Acid Metabolism.
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  • 48
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Shading of all side leaflets of a determinate soybean cultivar during pod filling significantly increased rates of photosynthesis in the unshaded centre leaflets, compared to centre leaflets of controls. Higher rates were associated with both higher stomatal and mesophyll conductances, and were reversible within 2 days when shades were removed. These higher rates of photosynthesis were not associated with decreased percentage enhancement by low oxygen, indicating that treatment effects were probably not associated with changes in photorespiration relative to photosynthesis. Percentage enhancement did, however increase as the plants approached physiological maturity, chiefly because of a decrease in photosynthesis.In spite of these increases in rates of photosynthesis seed weight per plant was decreased by 37% in plants with side leaflets shaded for the entire pod-filling period and by 28% in plants shaded for only the second half of the period. In plants where shades were removed during the second half of pod filling seed yield was reduced by only 19% because shade removal delayed leaf senescence. The four treatments reduced yield by different mechanisms. Plants shaded continuously during pod filling produced fewer seeds than controls, but the weight per seed was similar. When shading was applied during the second half of pod fillings seed number was unchanged but weight per seed was significantly reduced. In contrast when shades were removed for the second half of pod filling, seed number remained similar to that of continuously shaded plants, but seed weight increased.Although all shading treatments reduced yield, the reduction was not proportional to the 63% reduction in leaf area available for photosynthesis. This was because (1) photosynthetic rates in the centre leaflet of shaded plants were higher than rates in controls, (2) stem and lower surface photosynthesis in shaded leaf-lets contributed to whole leaflet photosynthesis.
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  • 49
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. An acid phosphatase is isolated and purified to homogeneity from sycamore cell walls. The enzyme, which has a molecular weight close to 100,000, is a glycoprotein and is most probably made up of one polypeptide chain only. Its amino acid composition has been determined. Although homogeneous to polyacrylamide gel electrophoresis under non-denaturing conditions, the enzyme preparation still contains protease traces that tend to split polypeptide chain in two fragments.
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  • 50
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The response of stomatal conductance in Pinus sylvestris L. to a sequence of progressively changed photon flux densities showed hysteresis when the direction of the sequence was reversed. Hysteresis was most evident when 1 h was allowed for stabilization at a temperature of 10°C and a leaf-air vapour pressure difference of 0.5 kPa. The hysteresis was largely eliminated by a stabilization time of 2.5 h or a temperature of 20°C. Elimination of self shading also largely eliminated the hysteresis and resulted in light saturation of stomatal conductance at about 600 μE m−2 s−1 whereas with the normal grouping of fasicles light saturation was not achieved at 1750 μE m−2 s−1 even with bilateral illumination. Hysteresis was also eliminated by reduction in the maximum attainable conductance as a result of large leaf-air vapour pressure differences (> 1.8 kPa) but reducing the ambient CO2 concentration to the compensation concentration or below had no effect on hysteresis. In addition to the hysteresis, there was a carry-over effect of the previous treatment. When the direction of the sequence of photon flux densities was changed, stomatal conductance continued to change in the direction appropriate to the previous sequence for at least 1 h. The presence of a transportable chemical intermediate is postulated, the amount or activity of which would take some time to change after a change in photon flux density. The presence of such an intermediate could account for both the sluggishness of the stomata and the carry over effect. As a result of the sluggish behaviour and carryover, in the field stomatal conductance will tend to follow the general trend in photon flux density and will be very insensitive to short term fluctuations.
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  • 51
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Purified acid phosphatase from sycamore cell walls is not activated by increasing the ionic strength of the reaction mixture. However activation occurs when the enzyme is bound to small cell wall fragments. The apparent activation of the bound enzyme by ions is paralleled by a decline of the substrate concentration C1/2, that results in half of the maximum rate. Above ionic strengths of about 0.05 the bound and solubilized enzyme forms behave in the same manner. Titration of cell wall fragments at different ionic strengths show that the local pH, inside the cell wall fragments, is lower than the pH in bulk solution. These results are explained in the light of poly-electrolyte theory. The negative charges of the cell walls generate an electrostatic potential that results in the attraction or repulsion of ions. The local concentration of organic phosphate (the substrate of the enzyme) is then lower than its concentration in bulk solution. This concentration difference explains that the value of C1/2, or of the apparent Km of the bound enzyme, is greater than the true Km of the solubilized enzyme. Increasing the ionic strength tends to equalize bulk and local ion concentrations, and therefore apparently activates the bound enzyme.
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  • 52
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. We measured phytochrome content by radioimmunoassay in green, light-grown oats (Avena sativa L., cv. Garry) grown under several light regimes. Phytochrome content increased linearly to six times the light-grown level during a 24-h dark incubation and to fifty times the light-grown level after 48 h darkness. Phytochrome content, in response to a cycle of 12-h light, 12-h dark photoperiods, increased to three times the light-grown level in darkness and returned to the light-grown level during the subsequent light period. Plants given far-red light immediately prior to a 12-h dark period contained about four-fold more phytochrome than light-grown oats, compared with a three-fold increase in plants treated identically except given no far-red light. We also attempted, unsuccessfully, to eliminate a general nonspecific interference by crude plant extracts with the radioimmunoassay.
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  • 53
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    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Potential sources of reductant for the pathway of nitrate assimilation in non-photosynthetic tissue are considered in terms of the intracellular distribution of the enzymes involved (relative to those of nitrate assimilation), their maximum catalytic capacity, the availability of their respective substrates, and the form in which the reductant is produced. According to these criteria, the principal sources appear to be the reactions catalysed by NAD-glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NAD-malate dehydrogenase and NADP-malic enzyme. Mitochondrial metabolism may also make a limited contribution, although the evidence is inconclusive. The capacity to generate reductant by carbohydrate oxidation within the proplastids appears insufficient to meet the demand, and an influx of reducing power from the cytoplasm in the form of dihydroxy acetone phosphate may be necessary to support nitrite reduction and the glutamate synthase reaction which occur there.
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  • 54
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. It is proposed that the growing plant can be divided into three compartments with reference to carbon: soluble, storage and structural. Experiments carried out at 10, 15, 20 and 30°C in the light followed changes in size of these compartments in barley plants 10–24 days old. The redistribution of I4C photo-assimilated by 10 day old plants was monitored simultaneously. The soluble and storage compartments are a higher percentage of plant weight at lower temperatures, and are turned over rapidly at all temperatures; they form the source of respired 14C. About 30% of the 14C fixed enters structural material; in the first 24 h after labelling, for each unit of 14C entering the structural compartment, between 0–9 (at 15°C) and 3.2 (at 30°C) units of 14C are lost by respiration. At 15°C in the dark, respiratory loss of 14C is initially from soluble and storage compartments; thereafter respiration of I4C occurs at the expense of structural material.
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  • 55
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Paraquat treatment of susceptible Lolium perenne seedlings (cultivar Kent Indigenous) rapidly inhibited CO2 uptake and after 1 h chloroplasts exhibited abnormal fusions of the thylakoid membranes. Further ultrastructural changes occurred within the chloroplasts until 8 h after treatment, when cytoplasmic damage also became evident. The localization of primary damage within the chloroplast differs from previous reports of paraquat toxicity in other species. Paraquat treatment of tolerant L. perenne seedlings (line PRP IX) resulted in little change in CO2 uptake and ultrastructural effects were generally confined to the gradual development of deposits in the chloroplast stroma. These observations are discussed in relation to the mechanism of action of the herbicide and the proposed mechanism of paraquat tolerance in L. perenne.
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  • 56
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Measurement of the electrical field along soybean hypocotyls shows the development of a positive electrical potential in the lower side approximately 1 min after horizontal placement. The time is as fast or faster than the geotropic presentation time of soybean seedlings. The maximum positive electrical field potential is produced in a zone 1–2 cm below the hook, which is the region showing the geotropic curvature.
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  • 57
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The effect of sub-lethal concentrations of copper upon tolerant and non-tolerant strains of Chlorella vulgaris was investigated. Copper concentrations of 0.2 and 0.4 mg dm−3 increased the lag phase of both strains, the effect being greater in the non-tolerant strain. No difference was observed in the toxicity of copper to the photosynthetic rates of the isolated chloroplasts of either strain. However, significant differences were shown at the whole cell level.Lower copper uptake was shown by the tolerant cells. In both strains initial uptake of copper was followed by a phase of desorption before cell division occurred. In cultures of both strains the concentration of ionic copper was decreased by complexation with extracellular organic material. Over a 14 day growth period more organic material was produced by the tolerant cells. The organic material produced by the tolerant cell formed organo-copper complexes which had a higher conditional stability constant.It is proposed that the cell wall acts as a barrier to copper in the tolerant cells and prevents copper from affecting cell metabolism. Organo-copper complexation occurs at this barrier and this complex is then released into the medium.
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  • 58
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Diurnal measurements of total water potential and stomatal opening were made at six sites. Pressure-volume curves were established on parallel leaf samples. In eastern Austria, the species investigated were Cornus mas L., Cornus sanguinea L., Crateagus monogyna Jacq., Sorbus aria (L.) Crantz and Viburnum lantana L. in southern France Crateagus monogyna, and in southern Turkey Crateagus monogyna and Olea europaea L. Osmotic adjustment, defined as a change in osmotic potential larger than the passive change resulting from the loss of cell water, was relatively small from day to day or week to week in mature, non-senescing leaves. Cornus sanguinea was an exception. A recently suggested method for the demonstration of diurnal active osmotic adjustment seems not to be reliable without further independent corroboration. Changes in the leaf water potential threshold for stomatal closure were either insignificant when the pressure-volume characteristics of the plant material were stable, or significant when shifts in such parameters as the turgor loss point occurred (Cornus sanguinea).
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  • 59
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Leaf sections (1 × 1 cm) from Chenopodium rubrum L. were floated on Murashige–Skoog medium at constant 20°C and 8800 Lux white fluorescent light. During a period of 4–6 days after inoculation the leaf tissue showed rapid growth and cell division in the mesophyll. Subsequently, after 4 days on a rotary shaker the leaf tissue completely disintegrated and released a great number of single cells into suspension. This procedure, which by-passes the callus culture stage, is well-suited to the rapid production of standardized cell suspension cultures.
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  • 60
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 3 (1980), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Books reviewed in this article: NICOTIANA: PROCEDURES FOR EXPERIMENTAL USE. Edited by R. D. Durbin VIROIDS AND VIROID DISEASES. By T. O. Diener
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  • 61
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Stomatal conductances (gs) were measured on the leaves of 3–4 year old Golden Delicious trees and of seedlings of two other cultivars. Measurements were made on container grown trees in the field with a diffusion porometer in 1975 and 1976, and in controlled conditions in a leaf chamber in the laboratory in 1976. Stomatal densities in the Golden Delicious leaves were assessed from scanning electron micrographs. Stomatal density on extension shoot leaves was higher than on other leaf types after June.The response to irradiance shown by both the porometer and the leaf chamber results could be described by a rectangular hyperbola: <displayedItem type="mathematics" xml:id="mu1" numbered="no"><mediaResource alt="image" href="urn:x-wiley:01407791:PCE13:PCE_13_mu1"/>where gmax is maximum conductance and β indicates the sensitivity of gs to photon influx density (Qp). The values of β were in the range 60–90 μmol m−2 s−1.There was no evidence that apple stomata are sensitive to temperature per se, but gs was reduced by increasing leaf to air vapour pressure deficits (D). There was a linear relationship between gs and D which was not attributable to feed-back to leaf water potential (ψL) as the latter did not affect gs until a threshold of about −2.0 to −2.5 MPa was reached. Conductance generally declined with increasing ambient CO2 concentration.
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  • 62
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Pervasive L and L ≪ S tectonites of the Mariánské Lázně eclogites include pencil fabrics, constrictional folds and mullions, that result from the first deformation increment observed. Petrological and microstructural data suggest that these structures formed by constrictional flow at deep subduction levels after, or even during, the eclogite facies stage and before the subsequent high-pressure granulite facies overprint. Constriction at mantle depths is explained by taking into account the geometry and seismic properties of recent subduction zones. Here, constrictional strain and associated L ≫ S tectonites should be expected below the rheologycontrolled slab bend (at about 40 km depth), where dip-parallel extension and a reduced viscosity of the downgoing slab are compatible with a coaxial flow regime.
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  • 63
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The origins and volumes of waters which mass-transport silica in sedimentary basins remain obscure. Many previous analytical studies have illustrated cases where quartz cements in sandstones originate from complex and variable fluids. By contrast we show, by using a combination of separation and analytical techniques, that in Lower Permian sandstones of the southern North Sea the cementing fluid was isotopically uniform during growth of quartz cement with a δ1BO of 19.6 + 1.0%‰ V-SMOW. In this relatively uniform fluid quartz cements grew and developed complex cathodoluminescence (CL) zonations. Petrographic data show that 8–10% quartz cement (locally 30%) was imported into this 380 km2× 180 m thick aeolian sandstone, and cement distribution controlled by depositional permeabilities. We infer a large-scale, high volume, flux of evolved meteoric fluid during 2 km deep burial, and show that complex CL zonation may arise from relatively subtle changes in water composition.
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  • 64
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Magmatism in the central part of the Variscan orogenic belt in Europe has occurred in several distinct episodes. Each episode spanned a few million years and was characterized by a distinct geochemical signature and geodynamic setting: (i) between 340 and 330 Ma (Visean), high-K diorites and granitoids within a zone extending parallel the orogen axis, possibly tracing a palaeosuture; (ii) at 310–307 Ma (Westphalian), calc-alkaline granitoids in the Intra-Alpine domain; (iii) at 304–295 Ma (Stephanian), subalkaline granitoids in Intra-Alpine and Pennine domains; and finally (iv) at 280–270 Ma (Permian) granitoids in Pennine, Austroalpine and South-Alpine domains. The generation and emplacement of granitoid melts in the Variscan crust are suggested to be short-term pulses that are controlled by extensional processes in the lithosphere such as thermal erosion and relaxation of the lithospheric mantle, and decompressional melting.
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  • 65
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Cliff-front dunes are a common coastal feature, but this is the first time that the structures indicative of their formation are documented. A late Pleistocene cliff-front dune in southern Mallorca has been studied. Owing to early lithification of the calcarenite, its morphology is well preserved. The dune occurs in front of a curved, near-vertical coastal cliff, but the bedform cannot be classified as a fixed echo dune. The dune grew with time and its brinkline gradually moved closer to the cliff front. In the final stage of evolution the top of the dune reached a height of at least 23 m. The dune is composed of wind-ripple strata. These strata are arranged in critical to supercritical climbing-dune cross-stratification recording its growth stages. The angle of climb of the dune increases toward the cliff and reaches 50°. The morphological features of cliff-front dunes result from both cliff slope and whether the cliff front is curved or straight.
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  • 66
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Compositions and distributions of mafic dykes in the Antarctic Peninsula continental arc show that tapping of several mantle sources was tectonically controlled. In the Cretaceous to Tertiary, between 135 Ma and 55 Ma, calc-alkaline dykes intruded the arc. In the late Cretaceous, however, between 95 Ma and 65 Ma, there was a pulse of compositionally diverse magmatism. This change resulted from collision of an ocean spreading centre with the trench. As a consequence, non-partitioned dextral transtensional shear in the overriding plate became partitioned into strike-slip and extensional domains. Calc-alkaline magmatism was, therefore, replaced by strike-slip-related shoshonitic magmatism towards the rear-arc and extensionrelated tholeiitic magmatism towards the fore-arc. OIB-like dykes were emplaced because of the break in otherwise continuous subduction. During the early Tertiary subduction continued but ceased after a late Tertiary ridge-trench collision.
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  • 67
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Until recently the Younger Dryas cooling event was thought to be restricted to the North Atlantic region. However, preliminary evidence based on magnetic susceptibility and stable isotope data from Lake Hetongchahannor, a hypersaline alkaline lake in Inner Mongolia indicates that this event is observed in NE Asia. In addition we find indications of wetter climatic conditions between 9000 and 6000 yr BP, possibly due to increased monsoon activity, followed by a progressive aridification towards the present time.
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  • 68
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Ion-microprobe U-Pb zircon ages of detrital zircons from a metasediment of the Loch Maree Group, Lewisian Complex, NW Scotland show striking similarities to those in coeval Palaeoproterozoic belts of Laurentia and Fennoscandia, and confirm previous suggestions of a connection between them. Late-Archaean zircons (3.06–2.48 Gyr old) represent derivation from Lewisian quartzofeldspathic gneisses, andlor a contemporaneous terrane. Palaeoproterozoic zircons (2.2–2.0 Gyrold) place a maximum age constraint upon deposition. An appropriate quartzofeldspathic source for these latter zircons is not presently known, either in the Lewisian or the wider Laurentia-Fennoscandia region, although its requirement would be consistent with a development of the Loch Maree Group, together with juvenile magmatic arc rocks, at an active margin which was probably removed by lateral tectonics. Comparisons are made with contemporaneous supracrustal sequences throughout the Laurentia–Fennoscandia region, which exhibit marked similarities in source region age characteristics, lithologies, and inferred depositional environment.
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  • 69
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Argand (1924) and later Holmes (1965) proposed that the Himalayan orogeny and Tibet uplift were the result of large underthrusting of the Indian continental crust beneath Tibet. Since then, plate motion studies have yielded new constraints on the relative displacements of India and Asia and a large number of geological and geophysical investigations have helped to determine the structure of the Himalayas and Tibet, the best natural laboratory for understanding mountain belts. The aim of this paper is to review briefly the various models of Himalayan mountain building in light of recent geological and geophysical data and to estimate the role of continental subductions.
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  • 70
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Changes in North Atlantic sea surface temperature (SST) are regarded as a key element of the climate during the Quaternary. However, there are relatively few long-term records providing quantitative SST estimates from this region. Using planktic foraminiferal-derived SSTs together with changes on species level and iceberg-rafted debris, the last 500 ka were studied. Pronounced SST changes, as determined from the last glacial–interglacial cycle, characterize most colder periods. Peak interglacial temperatures were found for marine isotope stages (MIS) 1, 5e and 11, the latter two being the warmest. The warm substages within MIS 7 and 9 are marked by enhanced dissimilarity coefficients, indicating that SSTs obtained for these times appear to be overestimated. This is corroborated by differences within the species assemblage, which show enhanced cold water components. It is therefore concluded that detailed analysis down to species level is a crucial prerequisite to better reconstructions of SST.
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  • 71
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Variation of seawater chemical composition during the Phanerozoic is still a contentious subject. Br concentration in primary marine basal halites was used to indicate variations in seawater composition during the past 550 Ma. Evaporation experiments and thermodynamic modelling suggests that the partition coefficient of Br in halite depends on the composition of the seawater. A combination of this correlation with the time-dependent models for ocean chemistry of Hardie leads to a prediction of Br in basal halite during the Phanerozoic. This prediction is in good agreement with data from different ancient evaporite basins. The Br data give evidence for rapid and massive changes in seawater chemistry during the Phanerozoic and are thus a first independent test for the Hardie model.
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  • 72
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Using the example of the Isle of Skye in Scotland, we investigate the influence of pressure variations in upper-crustal magma reservoirs on the development of rift-type normal faulting around central volcanoes. The regional synmagmatic stress regime is of strike-slip type in Scotland during the Lower Tertiary. During a prolonged period of overall high pressure in the Skye magma reservoir (gabbro intrusion stage), crustal extension results from the injection of basaltic dykes parallel to the trend of the far-field maximum stress. During a subsequent period of pressure decrease in the reservoir (granites intrusion stage) normal faults trending parallel to the dykes are initiated. These faults tilt the upper-crustal blocks along with the former dyke swarm and associated lava pile. Finite-element modelling shows that a decrease of magma pressure in a circular cavity may lead, as in Skye, to a change from a regional strike-slip to a local rift-type normal stress regime.
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  • 73
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 15 (2003), S. 0 
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: In the Basle region of Switzerland we demonstrate that rockfall blocks can be dated accurately using the radiocarbon method. Soil beneath rockfall blocks containing organic macro-remains was sampled at four cliff sites in the Tabular Jura south-east of Basle. A lightweight drilling rig drills a 101-mm-diameter hole through rockfall blocks up to 6 m in height. A downhole sampler is used to recover soil samples from below the blocks. Eighteen radiocarbon dates on charcoal, wood, needles of conifers and organic macro-remains from 11 blocks gave dates between 970 and 440 bp. Calibrated ages range between ad 1210 and ad 1450. These results, along with field observations and historical research, suggest that a large number of blocks toppled as rockfalls within a short time interval in the epicentral area of the ad 1356 Basle earthquake.
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  • 74
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 9 (1997), S. 0 
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The frequently observed parallelism between rifts and the preexisting orogenic fabric of continents suggests that the inherited tectonic fabric of the lithosphere influences the rupture of continents. We propose that the existence of a pervasive fabric in the lithospheric mantle induces an anisotropic strength in the lithosphere, that guides the propagation of continental rifts. Subcrustal mantle mechanical anisotropy is supported by (i) the anisotropic strength of olivine, (ii) an ubiquitous tectonic fabric in exposed mantle rocks, and (iii) measurements of seismic and electrical anisotropy. During major episodes of continent assembly, a pervasive deformation of the lithosphere induces a lattice-preferred orientation of olivine in mantle rocks. Later on, this crystallographic fabric is ‘frozen-in’ and represents the main source of shear wave splitting. This olivine fabric may entail a mechanical anisotropy in the lithospheric mantle. During subsequent tectonic events, especially during rifting, mechanical anisotropy may control the tectonic behaviour of the lithosphere
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  • 75
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Modern terrestrial speleothem-like calcareous deposits in streams draining a disused lime quarry on Black Mountain, South Wales have anomalously negative δ18O and δ13C compositions compared with other similar European deposits. Black Mountain water chemistry is unusual only in its locally very high pH (> 11.5) and carbonate ion concentrations. The high pH is caused by dissolution of lime spoil, resulting in high OH– concentrations. This high alkalinity causes uptake of atmospheric CO2 and strong fractionation of both carbon and oxygen stable isotopes, resulting in calcite precipitates with unusually negative isotopic compositions. Since shifts in δ18O of < 1° are highly significant for Holocene palaeoclimate reconstructions, depletions caused by hyperalkaline waters must be avoided. While extreme lime spoil contamination should be obvious, less heavily affected sites will record smaller fractionation effects and might escape detection. Even small depletions from low-level contamination will have large effects on palaeotemperatures based on carbonate crust δ18O values.
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  • 76
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An integrated interpretation of seismicity, fault plane solutions and deep seismic reflection data suggests that the NE–SW to NW–SE trending Rhone–Simplon fault zone and the gently S-dipping basal Penninic thrust separate fundamentally different stress regimes in the western Swiss Alps. North of the Rhone-Simplon fault zone, strike-slip earthquakes on steep-dipping faults within the Helvetic nappes are a consequence of regional NW–SE compression and NE–SW extension. To the south, vertical maximum stress and N–S extension are responsible for normal mechanism earthquakes that occur entirely within the Penninic nappes above the basal Penninic thrust. Such normal faulting likely results from extension associated with southward movements (collapse) of the Penninic nappes and/or continued uplift and relative northward displacements of the underlying Alpine massifs. Geological mapping and fission-track dating suggest that the two distinct stress regimes have controlled tectonism in the western Swiss Alps since at least the Neogene.
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  • 77
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The distribution of barium and other elements related to biological productivity has been studied in two Palaeocene sections from the Middle East. In the bathyal Ben Gurion section, Israel, Ba* (= Ba/Al2O3× 15%) concentrations are low, in the range 0.04% to 0.3% in the lower Palaeocene, and very high, 1% to 2%, throughout most of the upper Palaeocene. In the neritic Gebel Aweina section in Egypt Ba* values are low, < 0.1%, throughout the entire Palaeocene. The Ba* enrichments at Ben Gurion and their correlations with increases in P2O5 and opaline silica, and local and global δ13C maxima, indicate that upwelling and high productivity were important in this region during the late Palaeocene. The absence of Ba* enrichments in the shallower Gebel Aweina section probably reflects the strong depth dependence of biobarium deposition.In the uppermost Palaeocene, at the level where the global benthic extinction event is registered, Ba* concentrations in the Ben Gurion section increase to anomalous 6%. which suggests that upwelling and possibly wind strengths intensified during this event. The results speak against deep-water formation in this region since downwelling and not upwelling is required.
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  • 78