bluuebunny/crossref_metadata_2025 huggingface dataset:
Flandrian vegetational history of southeastern England. Pollen data from Pannel Bridge, East Sussex
Authors: WALLER M. P.
Published: April 2006

Pollen data, plant macrofossil remains and lithostratigraphy are used to reconstruct Flandrian vegetational history from a coastal site in south‐eastern England. The record at this site, Pannel Bridge in East Sussex, extends back to c. 10000 BP and is the most complete so far obtained from this region.

The thirteen pollen assemblages zones defined reflect, in part, the complex development of the site. Prior to c. 8500 BP, wetland in the Pannel valley was localized around the site. Between c. 8500 and c. 6000 BP, in response to changes in coastal configuration, such areas underwent expansion and the valley floor was occupied alternately by sedge fen and Alnus carr. A period of stability followed, with Alnus‐dominated communities prevailing for c. 2000 yr. From c. 4000 to c. 2200 BP local conditions were more open with Cyperaceae and subsequently Myrica the dominant wetland types. Alnus carr became re‐established c. 2200 BP.

The vegetational history of adjacent dryland areas is obscured by the changing local conditions and nature of the deposits investigated. The problems of reconstructing past vegetation from coastal peats are explored. Amongst these are the determination of the pollen source area, establishing an environment of origin for many herb types, and distinguishing the processes controlling wetland vegetational change.

The discussion focuses on the arrival and expansion of arboreal taxa in the early Flandrian and human activity. Unusually, Alnus is present in the pollen and macrofossil record from c. 10000 BP onwards. In dryland areas, after an initial Pinus, Betula phase, Corylus populations expanded c. 9500 BP, Quercus and Ulmus became woodland components from c. 9100 BP and c. 8400 BP onwards respectively. Pollen values for Tilia increased c. 7000 BP and Fraxinus c. 5900 BP though both of these taxa were probably locally present earlier. Openings in the forest canopy appear to have persisted after the arrival of the deciduous trees, possibly as a consequence of human activity during the mesolithic. There is some palynological evidence for human presence accompanying the elm decline, though substantial clearance did not occur until the decline in Tilia, c. 3700 BP. This, and a subsequent phase of disturbance c. 3200 BP, appear not to have been followed by periods of intense human activity. Woodland regeneration may have occurred c. 2000 BP.
Pattern of fructan synthesized in cell‐free extracts from leaf blades of chilled Triticum aestivum
Authors: BANCAL PIERRE , GAUDILLÈRE JEAN PIERRE
Published: April 2006

Fructosyltransferase activities were studied with varying concentrations of sucrose in cell‐free extracts from wheat (Triticum aestivum L.). A C18‐HPLC separation method was used to quantify the synthesized compounds individually. Hexoses and 1‐kestose were the major products at all temperatures and concentrations of sucrose. 1‐Kestose production was maximal at 25 °C, with an apparent Km of about 250 m, but competition for sucrose by invertase affected this value. Neokestose, which is not observed in vitro, and 6‐kestose were also formed in vitro, but at a much lower rate and at lower sucrose affinity than 1‐kestose synthesis. When extracts were incubated with a high initial concentration of sucrose for up to 1 d, five new fructan oligomers appeared. Four of these were also accumulated early in vitro by chilled blades, whereas the fifth belonged to the neokestose series. The rates of synthetic oligomers are compared to those in vivo. Invertase‐linked artefacts are present in wheat, but not overwhelming as they are in Lolium temulentum.
Ultrastructure and chemical composition of some isolated plant cuticles in relation to their permeability to the herbicide, diuron
Authors: GOURET EVELYNE , ROHR RENE , CHAMEL ANDRE
Published: April 2006

The ultrastructure of leaf and fruit cuticles from nine species was investigated before and after their enzymatic isolation. No major alteration was observed in the internal ultrastructure of cuticles after the isolation process. The isolated cuticle preparations showed several levels of complexity from the Pyrus communis L. leaf cuticle represented by a simple layer, to the Vanilla planifolia Andr. leaf cuticle preparation having extensive cell walls on its inner face. Two main ultrastructural types were distinguished; cuticles characterized by an almost entirely reticulate structure and cuticles characterized by an outer lamellate region with an inner reticulate region. The permeability of isolated cuticles to diuron was measured with a double water compartment device using 14C‐diuron. The permeability coefficient (P) ranged from 1.9 to 40.1 nm s−1 for seven species. The mean value of P for cuticles having an entirely reticulate structure was higher than that for cuticles with an outer lamellate zone. Moreover, for each of the two ultrastructural types, the permeability decreased with an increase in soluble wax content expressed per surface unit.
The effects of ozone episodes on autumn leaf fall in apple
Authors: WILTSHIRE J. J. J. , WRIGHT C. J. , UNSWORTH M. H. , CRAIGON J.
Published: April 2006

Mature apple (Malm domestica Borkh.) trees were exposed to episodes of 100 and 150 nl l−1 ozone in 1990 and 1991 respectively, in open‐top chambers at the University of Nottingham, Sutton Bonington Campus, UK. The episodes were for 8 h daily and for not more than 3 d in succession, with a seasonal total of 37 d in each year. Leaf fall was monitored by counting leaves on marked shoots at frequent intervals. A significant interaction between ozone exposure and leaf age was observed: exposure to ozone accelerated autumn leaf fall in old leaves. The relationships between experimental conditions, leaf age and plant material are discussed, and the implications for UK flora are considered.
Resveratrol production as a part of the hypersensitive‐like response of grapevine cells to an elicitor from Trichoderma viride
Authors: CALDERÓN ANTONIO A. , ZAPATA JOSE M. , MUÑOZ ROMUALDO , PEDREÑO MARÍA A. , BARCELÓ A. ROS
Published: April 2006

Suspension cell cultures of grapevine (Vitis vinifera, cv. Monastrell) treated with an elicitor (cellulase, Onozuka R‐10) from Trichoderma viride showed a hypersensitive‐like response. This was characterized by cell plasmolysis and was accompanied by localized cell death, which was concomitant with cell culture browning, itself probably due to an activation of oxidative phenolic metabolism driven by a large increase in endogenous levels of H2O2. In addition to these responses, the treatment of cell cultures with the elicitor produced an increase in amounts of benzoic acid and of resveratrol, the latter a potent phytoalexin of grapevines. This hypersensitive‐like response was specific since none of the above responses was obtained with other cell wall‐degrading enzymes from several sources, or with inocula of either mycelial extracts or culture filtrates of Botrytis cinerea. These results are discussed in the light of a disease‐resistance reaction induced in grapevine cells by a product of T. viride, a fungal agent characterized by its effective biocontrol of Botrytis cinerea, the causal agent of grey mould in grapevines.
Colonization of wheat (Triticum vulgare L.) by N2‐fixing cyanobacteria: III. The role of a hormogonia‐promoting factor
Authors: GANTAR M. , KERBY N. W. , ROWELL P.
Published: April 2006

Initial colonization of the roots of wheat plants by Nostoc 2S9B in liquid culture was by motile hormogonia, irrespective of whether co‐culture was started using a cyanobacterial inoculum consisting of hormogonia or of aseriate packages. In the latter case the aseriate packages differentiated into hormogonia and this was most rapid and extensive when co‐culture was carried out in NO3−‐free BG‐11 medium. Hormogonia‐promoting activity appears to be due to a plant product that can be extracted from roots and is released into the growth medium in the presence or absence of the cyanobacterium. Induction of hormogonia was inhibited by 17 mM NaNO3, the concentration in BG‐11 medium. This effect was apparently not due to the presence of a combined N source (NO3−) per se but appears to be an ionic effect on the functioning of the hormogonia‐promoting factor, since other salts (NaCl and KNO3) had the same effect as NaNO3. The presence in aseriate packages of an autoinhibitor of hormogonia differentiation is inferred from the effects on hormogonia differentiation of washing aseriate packages. The hormogonia‐promoting factor from wheat roots appears to act antagonistically with respect to the autoinhibitor of hormogonia differentiation. Following initial colonization of plants roots by hormogonia, the cyanobacterial filaments progressed through a complete developmental cycle of hormogonia, long filaments and tightly bound aseriate packages, with subsequent differentiation of hormogonia from these aseriate packages giving rise to further colonization of the growing roots. The attachment of Nostoc 2S9B to the root surface may involve an initial attachment of hormogonia via fimbriae, and a subsequent tight binding of the cyanobacterium by means of the mucilaginous sheath.
Growth responses of two contrasting upland grass species to elevated CO2 and nitrogen concentration
Authors: BOWLER J. M. , PRESS M. C.
Published: April 2006

Growth parameters of Agrostis capillaris L. and Nardus stricta L. were measured in relation to ambient and elevated concentrations of CO2 (340 and 550 μl CO2l−1, respectively) and at low and high concentrations of nitrogen (0.8 and 3 mM NH4NO3, respectively). After 60 d of growth A. capillaris had attained approx. four times the total dry weight of N. stricta in all treatments, which was attributed to the greater leaf area ratio of the former. A. capillaris grown at the low nitrogen concentration attained 30% of the total dry weight of plants grown at high nitrogen. Over the 60 d period, destructive harvests (seven in total) showed the growth of N. stricta to be less sensitive than that of A. capillaris to the concentration of nitrogen, but in both species growth analysis showed the lower total dry weight at low nitrogen to be attributable to lower unit leaf rate. There was a differential response of both species to elevated concentrations of CO2, which was nitrogen dependent. A. capillaris grown at elevated CO2 attained a greater total dry weight than at ambient CO2 and this response was proportionately greater at low nitrogen (78% increase) than at high nitrogen (58% increase). In contrast, in N. stricta there was no effect of CO2 concentration on the total dry weight at low nitrogen whilst at high nitrogen plants grown at elevated CO2 had a greater total dry weight after 48 d of growth. Calculation of the allometric coefficient (K) relating root growth to shoot growth indicated that the effect of the lower nitrogen concentration was to increase partitioning to the roots while the higher CO2 concentration did not alter partitioning.
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

Two‐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

Varying 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

This 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

Miniswards 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

Two 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

Tephra‐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

The 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

UsingLeptochloa 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

The 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

Changes 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

Alterations 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

Short‐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

Ecophysiological 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

Double 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
The epidermal surface of the maize root tip
Authors: ABEYSEKERA R. M. , MCCULLY M. E.
Published: April 2006

The mutation Ageotropic (Agt) results in defective development of the surface pellicle which overlies the young epidermal cells of mesocotyl and nodal roots of maize. In roots of plants of the parent, cv. Kys, pellicle development is normal. This structure forms a coherent, smooth covering, up to ∼ 13/μm thick, over the epidermal cells distal to the elongation zone. This pellicle is external to the helicoidal outer wall of the epidermal cells and is composed of a thick inner layer with close‐packed, longitudinally oriented fibrils, and a thin outer layer with less regularly oriented fibrils. Both layers of the normal pellicle and the underlying epidermal wall are strongly stained by the periodic acid‐Schiff's (PAS) reaction. In Agt plants, the pellicle is irregular and diffuse, lacks definition of the two layers and is largely amorphous with occasional wisps of fibrils. Neither this mutant pellicle nor the underlying epidermal wall are PAS‐positive. Mesocotyl and nodal roots of Agt are sensitive to gravity but grow crookedly through soil. It is proposed that a normal pellicle maintains the smooth outer contour of young roots and provides stiffness in the region distal to the zone of elongation. When the pellicle is defective, the root tip is more compliant and bends result when the tip encounters small air spaces and barriers in the soil.
A pre‐Late Devensian pollen site from Camp Fauld, Buchan, north‐east Scotland
Authors: WHITTINGTON GRAEME , HALL ADRIAN M. , JARVIS JACK
Published: April 2006

Recent investigations at Camp Fauld in Buchan, Scotland have yielded two peat deposits of pre‐Late Devensian age. Percentage pollen diagrams are presented. One peat is radiocarbon‐dated to 34–39 ka DP, which prompts correlation with the Hengelo‐Denekamp sequence of NW continental Europe, but the pollen evidence, revealing the presence of a birch‐pine woodland, suggests an earlier stage. The second peat deposit records an open shrub‐tundra in which Bruckenthalia spiculifolia is present. The peat yielded a radiocarbon date of 40–51 ka BP, but is suspected of having been contaminated by younger carbon. That suspicion and the presence of Bruckenthalia suggest that a correlation, based on the radiocarbon date, with the Glinde interstadial, identified in NW Germany, would be incorrect. Correlation with other Scottish pre‐Late Devensian sites has proved to be difficult.
Salt‐induced inhibition of phosphate uptake in plants of cotton (Gossypium hirsutum L.)
Authors: MARTINEZ V. , LÄUCHLI A.
Published: April 2006

Radio‐labelled phosphate (32P) was used to study the effect of 150 mM NaCl on P1 uptake and P distribution in the roots of cotton plants (Gossypium hirsutum L. cv Alcala SJ‐2), Salinity inhibited P, uptake more severely at low P1 concentration (30μM) than at high P, concentration (1 niM). Data of 32P1 uptake at low P1 concentration μM range) in the nutrient solution showed a typical Michaelis‐Menten hyperbolic curve (uptake rate VSmax concentration). NaCl increased the apparent Km (from 2.23 to 4.73 μM and decreased the apparent Vmax (from 1.18 to 0.87 μmol g−1f. wt h−1). High NaCl inhibited P, uptake in the mature root zone. However, salinity enhanced P, uptake in the root tips. We speculate that salinity may induce alkalinization of the cytoplasm in root tips cells, increasing the transmembrane pH gradient and therefore P, uptake. Our results showed an inhibition of 32P transport within the roots and from the roots to the shoots m the salt treatment.
Growth responses of mutants of spring barley to fumigation with SO2 and NO2in combination
Authors: KASANA M. S. , LEA P. J.
Published: April 2006

This study was undertaken to evaluate the range of variation in growth responses of sodium azide‐induced M2mutants (stocks SI and S2) of spring barley, Hordeum vulgare. L. cv. Maris Mink, in relation to air pollution tolerance or sensitivity. The preliminary screening experiment with 150 nl l−1concentrations of SO2 and NO2 in combination for 10 d, yielded well‐defined sensitive and tolerant lines in both the stocks. However, the percentage frequency distribution of plants in different injury classes varied and stock S2 showed a better segregation of different lines. In a subsequent experiment, treatment with a mixture of each gas at 100 nl l−lconcentration for 22 d caused a variable degree of growth reduction. As a result of air pollution treatment, most of the growth parameters were significantly (P < 0.001) reduced in the sensitive lines of both the stocks, whereas the tolerant lines showed a marked resistance to the growth inhibitory effect of the pollutants. The magnitude of the difference between the sensitivities of different lines was usually double or more, and the effects were, more pronounced in stock S2 than in stock SI. Root dry weight was more adversely affected than shoot dry weight in sensitive lines of both the stocks. The results indicated that inter‐line differences in growth responses of these mutants were wide ranging, distinct and consistent. In conclusion, this study clearly demonstrates that artificial mutations may cause a markedly broad base of variation in air pollution sensitivity of crop plants which may be used in future plant breeding programmes of pollution tolerant cultivars.
Biology of the ectomycorrhizal genus, Rhizopogon
Authors: MASSICOTTE HUGUES B. , MOLINA RANDY , LUOMA DANIEL L. , SMITH JANE E.
Published: April 2006

Seedlings of Abies grandis, Alnus rubra, Pinus ponderosa, Picea sitchensis, Pseudotsuga menziesii and Tsuga heterophylla were grown in monoculture and dual culture in the greenhouse and inoculated with spore slurries of 20 isolates representing 15 species of ectomycorrhizal hypogeous fungi (11 Rhizopogon species, Alpova diplophloeus, Truncocolumella citrina, Melanogaster euryspermus and Zelleromyces gilkeyae). The primary objectives were to assess and compare the pattern of host specificity between symbionts and to study the influence of neighbouring plants on ectomycorrhiza development. None of the fungal species had broad host range affinities. A variety of specificity responses were exhibited by the different fungal taxa, ranging from genus‐restricted to intermediate host range. In monoculture, nine species of Rhizopogon (R. arctostaphyli, R, ellenae, R, flavofibrillosus, R. occidentalism R. rubescens, R. smithii, R. subcaerulescens, R. truncatus and R. vulgaris) formed ectomycorrhizas on Pinus ponderosa whereas three Rhizopogon species (R. parksv, R. vimcolor and R. subcaerulescens) formed ectomycorrhizas on Pseudotsuga menziesii. Truncocolumella citrina associated with Pseudotsuga menziesii and Alpova diplophloeus with Alnus rubra. Melanogaster euryspermus and Z. gilkeyae did not form ectomycorrhizas with any hosts. None of the fungi tested developed ectomycorrhizas on Abies grandis, Tsuga heterophylla or Picea sitchensis in monoculture. In dual culture, the same nine Rhisopogun species that formed abundant ectomycorrhizas on Prints pcmderosa formed some ectomycorrhizas on secondary hosts such as Abies grandis, Tsuga heterophylla, Pseudotsuga meitsiesii and Picea sitchensis. Similarly, Truncocolumella citrina formed abundant ectomycorrhizas on Pseudotsuga menziesii and low levels on the secondary hosts Abies grandis, Tsuga heterophytla and Picea sitchensis. Rhizopogon parksii and R. vinicolor only formed ectomycorrhizas on Pseudotsuga menziesii, and Alpova diplophloeus only formed ectomycorrhizas on Alnus rubra. The specificity pattern obtained by using this dual‐culture approach is contrasted with previous pure‐culture synthesis data and is discussed in terms of potential interplant linkages and community dynamics.
Conduit diameter and drought‐induced embolism in Salvia mellifera Greene (Labiatae)
Authors: HARGRAVE K. R. , KOLB K. J. , EWERS F. W. , DAVIS S.D.
Published: April 2006

The relationship between conduit (vessel and tracheid) diameter and water‐stress‐induced air embolism was examined using a double staining technique. Comparisons were made between irrigated control plants at water potentials of −13 MPa and water stressed plants at about −8 MPa. Water stress was induced either by natural drought conditions or by laboratory drying of shoots from previously irrigated shrubs. Stem segments were perfused with 0.1 % basic fuchsin to mark the initially conductive conduits, and, following high pressure perfusion of 10 DIM citric acid to remove embolisms, with 0.1% alcian blue to mark the initially embolized conduits. Hydraulic conductance per pressure gradient (kh) was measured before and after embolisms were removed. Diameters of non‐embolized and embolized conduits were then measured microscopically in transverse stem sections. In irrigated controls there was little embolism and mean diameters were not significantly different for embolized SM. non‐emboltzed conduits. For both artificially dehydrated and naturally droughted plants there was a 91% drop in kh due to embolism, and the mean diameter of embolized conduits was about 30 μm vs. 21 μm vs for non‐embolized conduits. With increasing conduit diameter there was an increased probability of embolism. Wider conduits may have larger pores in their pit membranes, thus increasing their vulnerability to water‐stress‐induced embolism. Alternatively, wider conduits may merely have more pits, thus increasing their statistical chances of having a particularly large pore in an air‐exposed pit membrane. Narrow vessels and tracheids provide an interwoven auxiliary transport system that appears to be of importance to transport when many of the wider, more efficient conduits become embolized.
Effects of low temperature on nitrate uptake, and xylem and phloem flows of nitrogen, inSecale cerealeL. andBrassica napusL.
Authors: LAINE P. , BIGOT J. , OURRY A. , BOUCAUD J.
Published: April 2006

The effect of low temperature on nitrate uptake and subsequent N translocation and cycling was investigated inSecale cerealeL. andBrassica napusL. transferred to 7 °C for 9 d or kept at a warm temperature (20 °C). Some plants were grown with a split root system and15NO3−, labelled to measure NO3−uptake, root‐to‐shoot and shoot‐to‐root translocation of N from NO3−, taken up. Other plants with single‐root system were subjected to15N pulse‐chase labelling to quantify endogenous N remobilization.

Lowering growth temperature from 20 to 7 °C reduced nitrate uptake more strongly in rye (−59%) than in winter rape (−28%). A very large proportion of the nitrate taken up was further translocated to shoots in both species. However, lowering the temperature decreased, xylem N translocation by about 60 and 30% inS. cerealeandB. napus, respectively. Most root N in the latter species came directly from root absorption, while in rye roots the proportions ascribe able to direct root allocation and phloem flow were well balanced. Cold treatment did not significantly modify the imbalance between the two origins. Mobilization of endogenous N from roots to shoot, estimated by pulse‐chase labelling, was limited inB. napusand significant inS. cerealedespite a depressive effect of low temperature. In general, low temperature led to an increase in root N concentration in both species. It is Suggested that low temperature may directly affect the nitrate uptake system, and also that N accumulation in the roots (resulting from greater inhibition of N xylem flow than of NO3−uptake) might increase the inhibition of uptake by higher cellular NO3, and/or amino acid content. The usefulness (for spring growth) of root N accumulation triggered by low temperature is discussed.
Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders associated with subterranean clover produces non‐infective hyphae during sporulation
Authors: PEARSON J. N. , SCHWEIGER P.
Published: April 2006

Subterranean clover (Trifolium subterraneum L.) inoculated with either Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders or Glomus sp. (WUM 10(1)) was grown in 3 kg of Lancelin sand surrounding a fine mesh bag (< 38 μm) filled with 400 g of steamed sand. The mesh size was chosen to allow hyphae to penetrate but to exclude plant roots. Every week, from 3 wk after planting the original plants, subterranean clover seeds were sown into the sand inside the mesh bags. The last sowing date was 8 wk from sowing of the original plants. The seedlings, with their roots growing inside the mesh bags, were allowed to grow for 3 wk. At that stage the seedlings and the original plants were harvested and their roots assessed for mycorrhizal colonization.

The percentage of root length of the original plants colonized by S. calospora decreased from the first harvest onwards, while colonization by Glomus sp. maintained a similar level at all harvests. Seedlings growing in pots whose original plants were colonized by S. calospora had a her percentage of root length colonized at the first two harvests but levels of Colonization decreased substantially thereafter. Seedlings in the Glomus sp. treatment on the other hand, had similar levels of colonization at all but the last harvest. The length of hyphae g−1 soil in the mesh hues increased throughout the experiment for both fungi. However, the length of hyphae in the S. calospora treatment increased at a faster rate. Spore production by S. calospora commenced 7 wk after sowing the original plants.

These results indicate that the hyphae produced by S. colospora after internal colonization had stopped increasing were largely non‐infective, and that these hyphae are primarily involved in the production of spores.