bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cataclysmic response to recent cooling of a natural boreal pine (Pinus sylvestris L.) forest in northern Sweden
Authors: KULLMAN LEIF 
Published: April 2006

summaryInstant stand‐level dieback occurred in boreal coniferous forests of northern Sweden in 1987. A population of pine (Pinus sylvestris L.) and subdominant spruce (Picea abies (L.) Karst.) was analysed with respect to defoliation, age structure, radial increment and soil conditions. Defoliation and mortality were due to frost and drought in response to an early winter with abnormal cold and a thin snow cover. A thick mor humus layer preconditioned ground frost preservation. Annual radial increment had declined steadily over c. 40 years, in variance with climatic cooling and local exposure. Possibly, the growth decline depleted energy reserves and lowered the tolerance to climatic stress during extreme conditions. It is obvious that the structure of northern boreal forests responds perceivably to short‐term thermal decline. The outlined mechanism of dieback may prevent the evolution of climax in the absence of other exogenous disturbances. The present event may be a small‐scale analogue of forest responses to rapid cooling during, for example, the Younger Dryas period and the Little Ice Age.
Localization of sucrose synthase in soybean root nodules
Authors: GORDON A. J. , THOMAS B. J. , REYNOLDS P. H. S. 
Published: April 2006

summaryImmunogold labelling studies using polyclonal antibodies to sucrose synthase suggest that this enzyme is exclusively located in the cytoplasm of soybean nodule cells. A significantly greater intensity of labelling was found in the cytosol of uninfected interstitial cells of the central nodule region compared with the cytosol of the infected cells. Labelling was low in the bulk of the cortical cells but was found to be high in the vascular endodermis and in the cortical cells between the bundle and the infected region. The results are discussed in relation to carbohydrate supply and metabolism and in the context of nodule structure.
The physiological role of old stolon material in white clover (Trifolium repens L.)
Authors: CHAPMAN D. F. , ROBSON M. J. 
Published: April 2006

summaryClonal plants of white clover (Trifolium repens L.), consisting of a single stolon plus roots and either three fully unfolded leaves or one fully unfolded leaf at the stolon apex, were grown in a controlled environment and sampled three times (after 7, 49 and 85 d growth) to examine the effects of increasing respiratory demand imposed by an increasing mass of old stolon material upon carbon allocation patterns and plant morphology.Where the total pool of available carbohydrate remained more‐or‐less constant over time, greater C allocation to stolon tissue was associated with reduced allocation to new leaf growth between d 7 and d 49. Rapid death of old stolon material began about d 70, perhaps as the result of withdrawal of C previously supplied to stolon tissue by leaves at the apex. Current assimilate no longer needed to maintain this old stolon material was, in part, reallocated to the apex region.Stolon death was greater when stolons were covered rather than fully illuminated, reflecting the elimination of direct CO2 assimilation by stolon tissue (estimated to be 12–22% as efficient as leaves in assimilating CO2, on a surface area basis) and accentuation of the carbohydrate deficit. Respiration accounted for an estimated 32% of C fixed by leaves on d 85 when stolons were covered, compared to 25 % when stolons were fully illuminated. The relevance of these results to the seasonal changes in plant morphology in pastures, and the effects of stolon burial, are discussed.
Effects of dry‐deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter II. Chemical content of leaf litters
Authors: NEWSHAM K. K. , INESON P. , BODDY LYNNE , FRANKLAND JULIET C. 
Published: April 2006

summaryAsh (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), sessile oak [Quercus petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from a non‐polluted and a heavily sulphur dioxide (SO2)‐polluted woodland were fumigated with environmentally‐realistic concentrations (0.010–0.030 μl l−1) of SO2 for 16–68 wk in an open‐air field‐fumigation experiment. Fumigation markedly increased sulphate and protons in leachates from the litters and decreased calcium and magnesium contents of the leaves. However, there were few differences in the responses between leaf litters from the two woodlands. This was attributed to rapid sulphate wash‐out from the litters from the heavily polluted woodland, so that the litters from the two sites quickly reached the same sulphate status.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. I. Morphological and cellular changes in mycorrhizas formed by Tylospora fibrillosa (Burt.) Donk and Paxillus involutus (Batsch. ex Fr.) Fr.
Authors: DOWNES G. M. , ALEXANDER I. J. , CAIRNEY J. W. G. 
Published: April 2006

summaryAn age sequence of mycorrhizas formed by Paxillus involutus (Batsch. ex Fr.) Fr. and Tylospora fibrillosa (Burt.) Donk was sampled from 6–9‐month‐old seedlings of Picea sitchensis (Bong.) Carr. grown on peat in root observation chambers. Information about the ageing process was obtained from co‐ordinated studies of mycorrhizal morphology, anatomy, ultrastructure and cell vitality (indicated by FDA‐staining).Newly produced mycorrhizas were pale and turgid over most of their length with obvious extramatrical mycelium. Most mycorrhizas over 50 d old had a light turgid apical portion and a darkened wrinkled proximal portion: extramatrical mycelium was less obvious. Many remained in this state until the sampling stopped at day 142, but some were completely darkened before day 50. The morphological appearance of a mycorrhiza was not a good indicator of its chronological age. Most mycorrhizas displayed periodic busts of growth which added portions of young turgid cortex to an ageing axis.The percentage of cortical cells showing nuclei in 1 μm sections of the apical 1 mm declined from 40–50 % in mycorrhizas < 25 d old to 5–15 % in mycorrhizas 110–140 d old. Cortical cells became more vacuolate as they aged and the number of organelles appeared to decline. Senescence proceeded from the outer to the inner cortex and from proximal to distal regions. Degenerate cortical cells were present in the Hartig net zone of mycorrhizas over 25 days old. Cortical cell degeneration preceded, but was closely followed by, degeneration of adjacent Hartig net.The FDA study supported the general pattern and timing of cell death interpreted from the morphological and ultrastructural study. Cortical/Hartig net fluorescence declined markedly in mycorrhizas over 70–85 d old. The stele was the last tissue in the mycorrhiza to degenerate.It is suggested that a mycorrhiza ceases to function in nutrient and water uptake when no living cortical/Hartig net interface remains. In this study a few mycorrhizas became non‐functional by day 31. For most mycorrhizas the major decline in function took place after 85 days. This estimate is in broad agreement with the estimates of mycorrhizal life span obtained from biomass studies in the field.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. II. Carbohydrate allocation in ageing Picea sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
Authors: CAIRNEY J. W. G. , ALEXANDER I. J. 
Published: April 2006

summaryTranslocation of 14C‐labelled photosynthate was studied in seedlings of Picea sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex observation chambers. Although translocation to young and older mycorrhizas was observed, accumulation of current 14C‐labelled photosynthate was reduced in older compared with young mycorrhizas in the same root system.Non‐structural carbohydrate components of P. sitchensis/T. fibrillosa and undefined beech ectomycorrhizas collected from the field were quantified by gas‐liquid chromatography. Relative differences in accumulated carbohydrates were identified between P. sitchensis/T. fibrillosa and beech mycorrhizas. Levels of total soluble and insoluble carbohydrate were lower in older compared with young P. sitchensis/T. fibrillosa mycorrhizas. The soluble sugars arabitol, glucose and mannitol were detected in significantly lower quantities in older mycorrhizas whilst fructose and trehalose content was similar to that of young mycorrhizas. These results are discussed in relation to the physiology of the ageing mycorrhiza.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. III. Phosphate absorption and transfer in ageing Picea sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
Authors: CAIRNEY J. W. G. , ALEXANDER I. J. 
Published: April 2006

summaryPhosphate absorption and transfer to the host was studied in seedlings of Picea sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex root observation chambers. Phosphate absorption into excised mycorrhizas was reduced in older compared with young mycorrhizas, kinetic analysis indicating physiological differences in phosphate absorption between the two age classes over a range of external concentrations up to 1000μM.Individual young mycorrhizas labelled directly with 32P transferred more 32P to the host than older mycorrhizas in the same intact root system. There was variation in the ratio (young:older) suggesting a progressive reduction in nutrient transfer to the host as the mycorrhiza ages. The results are discussed in relation to nutrient accumulation in the field.
Patterns of microtubule organization in two polyhedral cell types in the gametophyte of the liverwort Marchantia paleacea Bert.
Authors: APOSTOLAKOS P. , GALATIS B. 
Published: April 2006

summaryThe typical scale cells (TSCs) of Marchantia paleacea Bert, contain a well‐developed cortical microtubule (Mt) cytoskeleton, particularly below the anticlinal walls and also display complete but broad preprophase‐prophase Mt bands (PMBs). In contrast, the cortical cytoskeleton of the inner thallus cells (ITCs) is less developed than that of TSCs and the PMBs are incomplete. The latter consist of one to four separate Mt bundles which lie on the cytokinetic plane, but do not form a complete Mt ring. In both cell types PMB formation precedes or keeps pace with the activation of the polar Mt‐organizing centres (MTOCs) and nuclear shaping. The Mts in the PMBs are more numerous and densely packed at the cell edges than on the cell face. The polar MTOCs persist up to late prophase‐prometaphase. Afterwards, the spindle Mts are focused on several minipoles, where endoplasmic reticulum is localized. In postcytokinetic cells the cortical Mts first reappear on the daughter wall surface.Our findings suggest that: (a) The formation of complete or incomplete PMBs in TSCs and ITCs of M. paleacea is related to differences in the development of the interphase cortical Mt arrays, (b) The cell edges are able to form or at least arrange the Mts of the PMB. (c) Tight mature PMBs like those found in flowering plant cells are not formed in the cells examined in the present study. (d) The final orientation of the cell plate is controlled by the PMB cortical zone. (e) The cytoplasm abutting on the postcytokinetic daughter wall has the ability to assemble cortical Mts.
Pollen dispersal and representation on an offshore island
Authors: JACKSON STEPHEN T. , DUNWIDDIE PETER W. 
Published: April 2006

summaryThe effects of spatial isolation on pollen representation were examined in a study of seven small kettle ponds on Block Island, a small, unforested island 19 km off the New England Coast (USA). Modern pollen assemblages from the ponds were compared with modern assemblages from similar ponds on the adjacent, partly forested mainland and in extensively forested northern New York. Representation of pollen from local and extralocal sources was amplified on the island owing to spatial isolation. However, variation among pollen assemblages on the island was not clearly related to spatial variation in vegetation composition. Significant transport of pollen from the mainland to the island was observed. There appeared to be little or no decrease in representation of large, poorly dispersed mainland pollen types between the mainland and island. This latter result may indicate differences between the mainland and island in the predominant modes of pollen transport, or alternatively, effects of local pollen source strength on representation of pollen from distant sources. Based on our results, we propose a theory of pollen representation on islands that can be tested and applied on offshore islands and patchy landscapes.
The Nostoc–Gunnera symbiosis
Authors: BERGMAN B. , JOHANSSON C. , SÖDERBÄCK E. 
Published: April 2006

summary Gunnera L. develops a complex and intimate symbiosis with N2‐fixing cyanobacteria of the genus Nostoc, which renders the plant independent of combined nitrogen. The Nostoc‐Gunnera symbiosis exhibits unique features compared to other cyanobacterial‐plant symbioses: it is for example the only one that involves a flowering plant (angiosperm), the cyanobacterium infects specialized gland organs located on the stems of the host and once it has passed into the interior of the gland the cyanobacterium also enters the Gunnera cells where it starts to differentiate the highest frequency of heterocysts (the N2‐fixing cells) recorded in any cyanobacterial population. Gunnera has attracted scientific attention also for the following reasons: the genus has a peculiar geographic distribution of its subgenera and species in the Southern Hemisphere. It differs morphologically and anatomically from related plants and also shows an anomalous polystelic vascular system (polystely). This review gives an updated account of present knowledge concerning the Nostoc‐Gunnera symbiosis. Emphasis will be on the development of the symbiotic tissue (the gland), the structure and function of the prokaryotic N2‐fixing cyanobacterium, the infection process and on the relationship between the pro‐ and eukaryotic partners prior to and following the establishment of symbiosis.

CONTENTS

Summary
379

I.
Introduction
379

II.
The Gunner a plant
380

III.
The microsymbiont(s)
383

IV.
The symbiosis
384

V.
The gland
385

VI.
The infection process
388

VII.
Specificity
391

VIII.
Impacts on the cyanobiont
392

IX.
N2 fixation and release
393

X.
Photosynthesis
396

XI.
Concluding remarks
397

Acknowledgements
398

References
398
Light‐activated plant defence
Authors: DOWNUM KELSEY R. 
Published: April 2006

summarySunlight provides the energy required for all biochemical, physiological and developmental processes necessary for plant growth, reproduction and survival. The role of light in photosynthesis and photomorphogenesis has been appreciated for some time; however, the role of light in plant defence is a comparatively recent realization. Between 75–100 photosensitizers or phototoxins, molecules that become toxic in the presence of light, have been extracted from higher plant tissues. These biologically‐active compounds have diverse biosynthetic origins and belong to at least 15 different phytochemical classes (i.e. acetophenones, acetylenes, benzophenanthrenes, β‐carbolines, coumarins, extended quinones, furanochromones, furanocoumarins, furanoquinolines, isoquinolines, lignans, pterocarpans, quinolines, sesquiterpenes and thiophenes). Of more than 100 angiosperm families assayed, phototoxins and/or phototoxic activity have been reported inc.40 families representing 32 orders and 8 subclasses of the Magnoliophyta. Most of these allelochemicals are acute toxins with little organism‐specificity. As such, they are effective biocides capable of killing a wide‐range of potentially harmful organisms including: viruses, pathogenic bacteria and fungi, nematodes and herbivorous insects, as well as competing plant species. This review focuses on the phytochemistry, taxonomic occurrence and toxicological consequences of phototoxic metabolites in flowering plants. The available information suggests that phototoxic phytochemicals: (i) are broad‐spectrum allelochemicals capable of protecting plants against a variety of detrimental organisms in nature, (ii) represent a successful defensive strategy in both primitive and advanced plant taxa, and (iii) may be an effective defence under a variety of photoenvironmental conditions.CONTENTSSummary401I.Introduction401II.Chemistry/biochemistry of plant photosensitizers402III.Botanical distribution of photosensitizers403IV.Toxicology405V.Biological activity/defensive role of photosensitizers408VI.Concluding remarks413References415
Content of carbohydrate and activities of fructosyltransferase and invertase in asparagus roots during the fructo‐oligosaccharide‐ and fructo‐polysaccharide accumulating season
Authors: SHIOMI N. 
Published: April 2006

summaryContents of fructo‐oligosaccharides and fructo‐polysaccharides and activities of fructosyltransferases and invertase in asparagus roots harvested between July and November were studied by gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC).Contents of total sugar and fructo‐oligosaccharides and fructo‐polysaccharides were very low in July, and then increased until September. During this period, sucrose accumulated first, second trisaccharides, and then tetra‐, penta‐ and higher‐saccharides increased in that order. 1‐Kestose was the most predominant fructo‐ohgosacchande isomer [degree of polymerization (DP) 3 ∼ 6]. The fructo‐polysaccharide of DP ≥ 9 was 12.8 ∼ 21.7% of total sugar from September to November; polysaccharides estimated to be DP 20∼22 were just detectable.SST activities were very low in July, rose to a maximum in September and then decreased. Change in activity of SST was responsible for change in contents of sucrose and 1‐kestose from July to November. 1F‐fructosyltransferase (1F‐FT) activities increased until September, were almost constant from October to November and then decreased slightly. 6G‐fructosyltransferase (6G‐FT) reached its highest activity early in October. 6r‐SST (6‐kestose producing enzyme) activity was very slight from July to November and was ∼ 1/1000 of SST activity in September. This activity does not contribute to the enzymatic synthesis of the saccharides of asparagus roots. Invertase activity was nearly constant throughout. The change of activities of SST, 1F‐FT and 6G‐FT paralleled closely the accumulation of sucrose, 1‐kestose, neokestose and other saccharides. In vitro synthesis of fructo‐oligosaccharides from sucrose at 0.4, 0.1 and 0.05 M, or from 1‐kestose was investigated in a fraction prepared from asparagus roots harvested in September. 1‐Kestose (isokestose, 3a), neokestose (3b), nystose (4a), 1F (l‐β‐D‐fructofuranosyl)m‐6G(l‐β‐D‐fructofuranosyl)n‐sucrose (4b: m= 0, n= 2; 4c: m= 1, n=1; 5a: m=3, n0; 5b: m=0, n=3; 5c: M=2, n=1; 5d: m=1, n=2) and a mixture of hexasaccharide‐isomers were synthesized from 04 M sucrose in 60 h. In 0.05 and 0.1 M sucrose unidentified heptasaccharides were also produced. Octa‐ and higher‐saccharide, as well as the saccharides synthesized from sucrose, were formed from 0.1 M 1‐kestose. All of the saccharides synthesized from sucrose or 1‐kestose by the asparagus enzyme preparation were identical to saccharides occurring naturally in the roots of asparagus.
Non‐steady state ammonium‐limited growth of the marine phytoflagellate, Isochrysis galbana Parke
Authors: DAVIDSON K. , FLYNN K. J. , CUNNINGHAM A. 
Published: April 2006

summaryThe marine phytoflagellate Isochrysis galbana Parke was followed through two consecutive cycles of ammonium‐limited growth. There was a significant (48 h) lag in cell division following the resupply of ammonium but no discernible lag in biomass growth, which led to a transient increase in the mean biomass per cell. Cell carbon and Coulter volume were linearly correlated. Net chlorophyll synthesis was closely linked to the absorption of extracellular N, while carotenoid synthesis continued until C fixation ceased. Photosynthetic activity (C fixation per unit chlorophyll) varied significantly with the cellular N:C ratio. A rapid rise in the ratio of glutamine to glutamate (0.1–6) during the first 24 h after nitrogen supply indicated a temporary imbalance in the flux of C and N into biomass synthesis. Intracellular ammonium accounted for less than 4% of total cell N, while free intracellular amino acids accounted for 3–5%. Nevertheless, cell numbers were able to double after the medium became depleted of ammonium, presumably by recycling and redistributing high molecular weight intracellular N.
Transfer of symbiotically fixed nitrogen from berseem (Trifolium alexandrinumL.) to maize via vesicular—arbuscular mycorrhizal hyphae
Authors: FREY BEAT , SCHÜEPP HANNES 
Published: April 2006

summaryIn order to examine whether hyphae of VA mycorrhizal fungi may aid the transfer of symbiotically fixed nitrogen from a legume to a non‐legume, the roots of berseem plants inoculated with the VAM fungusGlomus intraradicesandRhizobium leguminosarumbiovar.trifolii(strain RCR 5) were separated by a 2 cm root‐free zone from the roots of maize plants. A 40 um pore size nylon net allowed VAM hyphae to pass through the root‐free zone but prevented root penetration. Replacement of this net by a 0.45 μm pore size membrane prevented penetration of VAM hyphae to the root‐free compartment. When the berseem plants were 63 d old, the plant chambers were sealed in plastic bags to allow the roots of the plants to be exposed to al0N2‐enriched atmosphere for 5 d.Berseem plants that were exposed to a15N2‐enriched atmosphere fixed more15N than did berseem plants maintained under air at natural15N abundance. The total15N excess content of berseem was similar whether or not the mycorrhiza had access to the maize roots. Plant mass (dry weight) of maize was not affected by the mycorrhizal fungus, but total nitrogen content tended to be higher in VAM‐colonized maize than in non‐colonized maize. Furthermore, both atom %15N excess and15N excess content of mycorrhizal maize were significantly increased as compared with non‐mycorrhizal maize or with maize controls without berseem. The amounts of15N transferred were small, accounting for less than 4% of the15N in the N2‐fixing plant.In spite of the 2 cm root‐free separating zone, the presence of the mycorrhizal fungus in the non‐legume increased the transfer of symbiotically fixed nitrogen from berseem to maize plants that were physiologically younger. The implications of these results for nitrogen transfer from a legume to an accompanying non‐legume via VAM hyphae are discussed.
The effect of magnesium ions on the vesicular—arbuscular mycorrhizal infection of maize roots
Authors: GRYNDLER M. , VEJSADOVÁ H. , VANČURA V. 
Published: April 2006

summaryThe effect of magnesium sulphate on the colonization of maize roots by a vesicular‐arbuscular mycorrhizal fungus was studied in hydroponic culture. Increased concentration of MgSO4 in the nutrient solution caused an increase in the percentage of root length infected. The highest infection levels were found when nutrient solutions contained 5 84–11.68 mmol 1−1 of MgSO4. Root colonization was stimulated by the increased concentration of magnesium but not calcium or potassium ions in the nutrient solution. No significant difference occurred in the percentage of root length infected when magnesium chloride was replaced by magnesium sulphate. A broad range of magnesium sulphate concentrations did not cause significant differences in plant biomass. The stimulation of root colonization by magnesium cannot be explained by changes in pH or osmotic pressure of the nutrient solution.