bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of acidic mist on frost hardiness and nutrient concentrations in red spruce seedlings
Authors: SHEPPARD LUCY J. , CAPE J. N. , LEITH I. D. 
Published: April 2006

SUMMARYTwo‐year‐old red spruce (Picea rubensSarg.) of Pittston provenance and 3‐yr‐old plants of Chatham provenance were exposed to acid mist in replicated open‐top chambers supplied with charcoal‐filtered air near Edinburgh, Scotland. Plants of Chatham provenance had already been exposed to acid mist throughout the previous growing season. The plants were exposed to mist, equivalent to 4 mm rainfall per week, containing an equimolar mixture of sulphuric acid and ammonium nitrate at pH 2.5 or pH 5.0 (1.6 or 0.01 mol m3) from May to November. This weekly dose was delivered at a low frequency (2 mm twice a week), or high frequency (1 mm on 4 consecutive days each week) to chambers fitted with ceilings to exclude rain. The low frequency dose was also applied to chambers without ceilings, to examine the effect of natural washing by rain. Frost hardiness, estimated by exposing detached shoots to controlled freezing and then measuring rates of electrolyte leakage, was determined during the misting period at the end of October and in December. Foliar nutrient concentrations were measured during the dormant period after treatment had ceased.At the end of October, plants which had received acid mist were less frost hardy than plants receiving mist at pH 5. The temperature causing 50% shoot death (LT50) increased by 6 °C for low frequency application, and by 10 °C at high frequency, relative to the plants receiving mist at pH 5. Exclusion of ambient rainfall had no detectable effect on the frost hardiness response to acid mist. In December, 3 wk after the cessation of misting, all plants were more frost hardy than in October. Significant effects of the acid mist treatment could no longer be detected. Differences in nutrient concentrations were small among treatments, although K+concentrations in the low frequency treatment with acid mist with rain exclusion were 50 % below those in other treatments. Ca concentrations were 50% larger in the acid mist treatment with rain exclusion than without. The data suggested enhanced sulphate uptake resulting from increasing the frequency of exposure, but the increase was not significant.There was no clear relationship between the pattern of frost hardiness and nutrient concentrations except for S, which was 30% smaller in the control plants (pH 5) than in the high frequency pH 2.5 treatments.It is concluded that excluding rainfall, an experimental artifact introduced in evaluating effects of acid mist, does not influence the frost hardiness response of red spruce seedlings. The much greater effect of exposure to the same dose at double the frequency suggests that such experiments may underestimate effects in the field, if those trees are exposed to more frequent episodes of polluted cloud water than experimental plants.
Responses to ozone of varieties of common bean (Phaseolus vulgar is L.)
Authors: GUZY MICHAEL R. , HEATH ROBERT L. 
Published: April 2006

SUMMARYVarying modes of ozone sensitivity were detected in 12 varieties of Phaseolus vulgaris. Seedlings were exposed to 0.4–0.5 μl 1−1 ozone for 75–135 min in growth chambers, until the most sensitive variety manifested visible damage at the leaf margins. Sensitive varieties showed ozone‐induced chlorophyll loss and/or inhibition of photosynthesis. A set of physiological characters thought to mediate ozone response was also assayed in control and fumigated plants: stomatal conductance, the regulator of ozone entry into the leaf; glutathione (as non‐protein sulphydryl) and ascorbate, the antioxidants; and polyphenol oxidase activity, a measure of the wound response.Some ozone‐tolerant varieties appeared to lower chlorophyll loss solely by blocking ozone entry through decreased stomatal conductances, whereas other ozone‐tolerant varieties appeared to mitigate ozone damage through the action of the antioxidants, ascorbate, and non‐protein sulphydryl. Similarly, ozone‐sensitive varieties showed possible alternative mechanisms of sensitivity. Damage appeared to derive from either comparatively high stomatal conductances, or comparatively low levels of antioxidants in spite of low stomatal conductances. Only one variety showed elevated photosynthesis rates in response to ozone, indicating a potential to repair ozone damage. Elevated ascorbate concentrations appeared to protect some varieties from post‐fumigation depressions in photosynthesis. The results were inconclusive regarding the role of polyphenol oxidase as the wound response.
Factors determining lobe growth in foliose lichen thalli
Authors: ARMSTRONG R. A. 
Published: April 2006

SUMMARYThis study investigates the relative importance of climate, lobe morphology and lobe interactions in determining the radial growth of individual lobes in foliose lichen thalli. The radial growth of 75 lobes from thalli of Parmelia conspersa (Ehrh. ex Ach.) Ach. and Parmelia glabrulata ssp. fuliginosa (Fr. ex Duby) Laund. was measured over 22 successive months in relation to climatic factors. Individual lobes showed a fluctuating pattern of radial growth with alternating periods of fast and slow growth. In 17/75 (23 %) of lobes studied, monthly radial growth was correlated with a climatic factor, usually total rainfall or the frequency of sunshine hours. In addition, the radial growth of 54 lobes of P. conspersa was measured over four months in relation to lobe morphology and the radial growth and morphology of adjacent lobes. Radial growth was correlated with lobe length and with the radial growth of adjacent lobes. In addition, the pattern of lobe branching appeared to be related to lobe width and to a lesser extent to lobe length and the width of adjacent lobes. The radial growth in one year of exceptionally long lobes which had grown beyond the thallus margin was similar to more normal lobes, but experimentally bisected lobes had significantly reduced radial growth compared with control lobes. These results suggested that the fluctuating pattern of radial growth in individual lobes may be determined by climate and the pattern of lobe branching. In addition, the pattern of lobe branching was related to lobe width and may be influenced by adjacent lobes.
The relative contribution of remobilization and root uptake in supplying nitrogen after defoliation for regrowth of laminae in four grass species
Authors: THORNTON B. , MILLARD P. , DUFF E. I. , BUCKLAND S. T. 
Published: April 2006

SUMMARYMiniswards of Lolium perenne, Festuca rubra, Agrostis casteUana and Poa trivialis were grown in a sand‐limestone mixture and fed with a complete nutrient solution containing 3 mol m−3 NH4NO3. The miniswards were cut weekly to a height of 4 cm until a steady state of growth, based on weight of clippings removed, was achieved. After clipping (day 0) the nutrient solution was replaced by one in which all the nitrogen (N) was enriched with 15N to 5 atom per cent, but was otherwise identical. This allowed discrimination of remobilization from current root uptake when considering the supply of N for regrowth of laminae. Destructive harvests were made over the following 28‐d period, while unharvested plants continued to receive a weekly clip.The proportion of the total uptake of labelled N which appeared in the clipped material was of the order L. perenne > P. trivialis > A. castellana > F. rubra. The change in unlabelled N in the roots plus leaf bases over time was modelled as a proportion of the amount present on day 0. A simple exponential model with a non‐zero asymptote was found to model the data; the asymptote was assumed to represent the proportion of unlabelled N not readily available for remobilization. Species differences in the asymptotes were found, with F. rubra having a significantly larger asymptote than A. castellana and P. trivialis, which in turn both had significantly larger asymptotes than L. perenne.All species used both root uptake and remobilization to supply N for post‐defoliation regrowth of laminae. However, the relative contribution of each source was species‐dependent. The proportion of N in the clipped material derived from remobilization was significantly greater for F. rubra than A. castellana, which in turn had a significantly greater proportion derived from remobilization than P. trivialis and L. perenne.
The role of crassulacean acid metabolism (CAM) in the adaptation of plants to salinity*
Authors: LÜTTGE ULRICH 
Published: April 2006

SUMMARYTwo case studies are presented illustrating how the behaviour of plants using crassulacean acid metabolism (CAM) provides adaptation to salinity.Perennial cacti having constitutive CAM show adaptation at the whole‐plant level, engaging regulation of stomata, internal CO2‐recycling and root physiology with salt exclusion. They are stress avoiders.Annual plants such as Mesembryanthemum crystallinum, with inducible CAM, are salt includers. They are stress‐tolerant and show reactions at an array of levels: (i) regulation of turgor and gas exchange at the whole‐plant level; (ii) metabolic adjustments at the cellular level; (iii) adapptive transport proteins at the membrane level and also (iv) at the macromolecular level; and (v) inductive changes at the gene expression level of the enzyme complement for metabolism (in particular involving glycolysis and malic‐acid synthesis with phosphoenolpyruvate carboxylase (PEPC) as the key enzyme, and gluconeogenesis (with pyruvate–phosphate dikinase (PPDK) as a key enzyme) and membrane transport (in particular involving the tonoplast ATPase).
Tephra‐dated lowland landscape history of the north of Ireland, A.D. 750–1150
Authors: HALL V. A. , PILCHER J. R. , McCORMAC F. G. 
Published: April 2006

SUMMARYTephra‐linked pollen diagrams from lowland raised peats at three sites in the north of Ireland show extensive landscape changes between A.D. 750 and A.D. 1150. By A.D. 860 woodland had been cleared and agricultural activity was widespread but, by the start of the twelfth century, woods had regenerated and agriculture had declined. The gap in the Irish dendrochronological record between A.D. 730 and A.D. 850 is bridged by timbers from corn grinding mills, strengthening the case for spreading arable agriculture at this time.
The epidermal surface of the maize root tip
Authors: ABEYSEKERA R. M. , McCULLY M. E. 
Published: April 2006

SUMMARYThe surface of the meristematic epidermis of maize roots is tri‐partite. A helicoidal primary wall follows the contours of the tops of the columnar epidermal cells and is continuous with their buttressed anticlinal walls. Two overlying layers form a smooth covering over the root which obscures the cell outlines. This compound surface is similar architecturally to outer epidermal surfaces of shoots. The two outer layers are distinct structurally and in their staining properties from the wall and are together here referred to as the pellicle. Both pellicle layers are fibrillar but not helicoidal. Their development begins in the boundary between the cap and the root proper and they reach maximum thickness over the meristematic region. The outer layer then disintegrates and is absent from the elongation zone. The inner layer thins irregularly as the columnar cells elongate to their final tabular form and usually persists only over the groove above anticlinal walls and at the base of root hairs. The cell wall thins to about half its maximum thickness during this elongation. Emerging root hairs broach the pellicle and the original primary wall. Remnants of both these layers form a short, tight collar at the base of each hair; this collar adheres to the primary wall of the hair which is continuous with a new, thin wall which is formed interior to the original outer wall of the parent cell.Failure to recognize the complex structure and transitory nature of the epidermal pellicle has led to confusion in the literature regarding the nature of root‐surface and rhizosphere mucilaginous components and their origin. These interpretations are compared with those arising from this study.
Ion distribution in relation to leaf age inLeptochloa fusca(L.) Kunth* (Kallar grass) II. Anions*†
Authors: KLAGGES SABINE , BHATTI A. SAEED , SARWAR G. , HILPERT ANDREA , JESCHKE W. DIETER 
Published: April 2006

SUMMARYUsingLeptochloa fusca(L.) Kunth (Kallar grass) plants, the distribution of Cl−, NO3−, H3PO4−, SO42−and malate between leaves of various ages has been studied. Plants grown in a reclaimed, salt‐affected field, in solution culture and in soil at 10, 100 and 125 mM NaCl have been analyzed. Apparently due to excretion by salt secreting glands onL. fuscaleaves and to phloem export, Cl−concentrations did not increase strongly with leaf age. On a leaf f. wt basis, chloride secretion was constant over the series of increasingly aged mature leaves. If it was related to the chloride increments in the leaves, chloride secretion increased strongly from younger to mature leaves and reached between ISO and 200% of the concurrent Cl−deposition in the lamina. Changes in the tissue concentrations of nitrate and phosphate with leafage showed a maximum in recently matured leaves. Decreases in older leaves were attributed to nitrate reduction and export of reduced nitrogen and to retranslocation of phosphate. In leaves of field‐grownL. fuscanitrate was non‐detectable. Sulphate and malate concentrations in laminae continued to increase from the youngest to the oldest leaves. The increasing negative charge resulting from these increases in divalent anions can be accounted for by the loss of charge occurring in connection with reduction of nitrate and export of phosphate. Higher external salinity led, apart from increases in tissue Cl−, to noticeable decreases in tissue nitrate and phosphate but not in sulphate and malate concentrations, the latter being even increased at higher external NaCl. The observed changes in anion concentrations are compared with and discussed in relation to changes found inRicinus communisand inAtriplex hortensis.
Nutrient concentrations of foliage and soil in South‐western Australia
Authors: FOULDS W. 
Published: April 2006

SUMMARYThe element found in highest concentration in the shoots of the South‐western Australian plants surveyed is N followed by K ≤ Ca ≤ Cl ≤ Mg ≤ P ≤ Mn ≤ Zn ≤ Cu. The oligotrophic families (mainly primitive Australian pioneer families Proteaceae, Casuarinaceae, Restionaceae and Epacridaceae) have the lowest nutrient concentrations. The nitrogen‐fixing Mimosaceae and Papilionaceae have the highest N concentrations though the nitrogen‐fixing Casaurinaceae have relatively low N concentrations. The native shrubs have lower tissue concentrations than the introduced species.Certain families possess a great variation in the concentration of tissue Mn (e.g. Proteaceae, Casuarinaceae) with certain individuals containing high concentrations compared to the average South‐west Australian species.Increased amounts of soil nutrients can cause an increase in shoot concentration of the species found growing there, e.g. rich habitats (limestone heath) tend to have higher concentrations than those found on depleted habitats (sandplain heaths).There was no correlation found between shoot concentrations and mean annual rainfall.
Carbohydrates and water status in wheat plants under water stress
Authors: KAMELI A. , LÖSELδ D. M. 
Published: April 2006

SUMMARYChanges in sugar content during water stress and recovery were examined in leaves of two varieties of durum wheat (Triticutn durum). The drought‐resistant Mohamed Ben Bachir (MBB) from Algeria and the drought‐sensitive European variety Capdur differed in the time and type of sugar increase during water stress. Glucose accumulated at a rate closely corresponding with decreasing water potential but more rapidly and to a higher concentration in MBB than in Capdur. Sucrose content correlated less well than that of monosaccharides with changes in water potential. Glucose and, to a lesser extent, fructose appeared to play an important role during water stress and to be more sensitive indicators of the degree of stress and of potential tolerance than proline which increased later and to the same extent in both varieties. After rewatering, the amounts of accumulated solutes in leaves of both types fell quickly to normal, coincident with relatively rapid growth.
Functional aspects of secondary carotenoids in Haematococcus lacustris (Girod) Rostafinski (Volvocales)
Authors: HAGEN C. , BRAUNE W. , BIRCKNER E. , NUSKE J. 
Published: April 2006

SUMMARYAlterations of photosynthetic activity were investigated during accumulation of secondary carotenoids in Haematococcus lacustris (Girod) Rostafinski. Using several methods regarding (i) pigment pattern and pigment content (cytophotometry, computer‐aided microscopic image analysis, in vivo absorption spectroscopy, high‐performance liquid chromatrography) and (ii) photosynthesis (microfluorometry, modulated chlorophyll fluorescence and luminescence detection, O2 evolution and consumption measurement, 77 K fluorescence spectroscopy) we examined single cells and cell suspensions of the green alga.The results indicate decrease of both the photosystem II activity and the linear electron transport accompanying synthesis of secondary carotenoids. On the other hand, activation of those processes leading to an increased transthylakoid proton gradient could be established during early accumulation period. This is assumed to be an active adaptation of the photosynthetic apparatus to energetic requirements given by secondary carotenoid biosynthesis in H. lacustris.
Seed rain quantity and quality, 1984–1992, in a high altitude old‐growth spruce forest, northern Sweden
Authors: HOFGAARD ANNIKA 
Published: April 2006

SUMMARYShort‐term regeneration ability of a cold‐marginal Picea abies forest was studied by analyzing spruce seed rain during nine years and by assessing resulting recruitment at the end of the studied period. Quantitatively large differences occurred between studied years, and seed viability was low during the whole study period. Only exceptionally did seed viability exceed 1 %. Sparse regeneration occurred in 1984, which is the year when most viable seeds/ha were recorded. In addition, the results are compared with recruitment data from the 1930s (from the same forest), a time period when regeneration peaked. It is suggested that the period 1984–1992, due to the sparse regeneration, retrospectively probably will appear as a regeneration trough or a decreasing regeneration trend. Furthermore, it is concluded that, in a long‐term perspective, periodic regeneration is sufficient for maintenance of the forest because of the longevity of spruce. Additionally, climatically induced variations of regeneration success give rise to natural fluctuations in stand density.
Ecophysiological responses of plants to global environmental change since the Last Glacial Maximum
Authors: BEERLING D. J. , WOODWARD F. I. 
Published: April 2006

SUMMARYEcophysiological information on the responses of plants to past global environmental changes may be obtained from Quaternary fossil leaves by measurements of (i) stomatal density, (ii) stomatal dimensions and (iii) 13C discrimination (Δ13C). The stomatal density and stomatal dimensions of leaves can be used to calculate stomatal conductance, while leaf Δ13C values provide independent information on stomatal conductance and plant water use efficiency. In this paper, stomatal conductance is calculated for a sequence of radiocarbon dated fossil leaves of Salix herbacea L. which, together with herbarium and fresh material, represents a time‐series spanning from the Last Glacial Maximum (LGM) (16500 yr BP) to the present day. The calculated values were then tested against leaf Δ13C values previously reported for the same material.Our calculations show that stomatal conductance is negatively correlated with increases in atmospheric CO2 concentration over the last 16500 yr. This represents the first evidence of long‐term response of stomatal conductance to increases in atmospheric CO2 concentration and confirms the response observed in experimental systems exposing plants to lower‐than‐present CO2 concentrations in controlled environments. The calculated decrease in conductance was positively correlated with leaf Δ13C values, supporting this interpretation. The mean leaf Δ13C value for the 18th and 19th centuries was significantly (P≥ 0.05) lower than the mean for the interval LGM‐Holocene (10000 yr BP) implying an increase in plant water‐use‐efficiency over this time. These two lines of evidence, together with the stomatal density record from a glacial cycle, and experimental studies growing C3 plants in glacial‐to‐present CO2 concentrations, strongly imply that the water use efficiency of vegetation during the LGM was lower than at present and that it has increased since that time. Further evidence in support of this conclusion comes from the pattern of world vegetation types present during the LGM previously reconstructed using palaeoecological data. This evidence demonstrates that the distribution of vegetation types during the LGM was significantly different from that of the present day and showed a contraction in the area of rain forest and a major expansion of desert areas.
Male gametes and fertilization in angiosperms
Authors: KNOX R. B. , ZEE S. Y. , BLOMSTEDT C. , SINGH M. B. 
Published: April 2006

SUMMARYDouble fertilization appears to have evolved as a product of change directly related to an accelerated rate and timing of reproduction. In this review, the focus is on the angiosperm male gametophyte, where changes include a reduction in the number of mitoses, establishment of the male germ unit and involvement of both members of the pair of sperm cells in reproduction.The organization of the generative cell during mitosis indicates that there may be basic similarities between this process in plant and animal cells. The microtubular organization of generative cells alters after isoiation. However, mitosis inAllamanda, proceeds as usual duringin vitroculture. The presence of actin microfilaments within generative cells has previously been shown inRhododendronand here we provide further evidence that actin microfilaments are indeed present in generative cells. Two different kinds of intermediate‐filament‐like systems (IFS) are present in the generative cells ofAllamanda: one in the cytoplasm and the other closely associated with the surface domain of chromosomes, both identified by the use of monoclonal antibodies. This is the first report of an IFS existing in the vegetative nucleus of pollen.Two alternate views have been proposed for the involvement of sperm cells in double fertilization of angiosperms. First, the chance hypothesis assumes that sperm fusions with the egg and central cell are random interactions. Second, the specific receptor hypothesis proposes that one of the pair of sperm (the true male gamete) is destined to fuse specifically with the egg. Support for this latter view has come from demonstrations of sperm cell dimorphism, both in size and content of mitochondria and plastids. The production of monoclonal antibodies which bind to surface domains on the reproductive cells of higher and lower plants, and specifically to the cytoplasm of generative and sperm cells also suggest that directed fertilization occurs. Recently, the existence of translatable mRNA pools within the generative and sperm cells indicates that, with the use of recent technological advances such as the polymerase chain reaction, the potential exists to identify male gamete‐specific genes.ContentsSummary679I.Introduction680III.A cell biological perspective681IV.Two hypotheses for double fertilization687V.Isolation of living sperm from flowering plants687VI.Sperm surface antigens of plants688VII.Molecular characterization690VIII.Conclusions691Acknowledgements691References692