bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variations in chromatin structure in host nuclei of a vesicular arbuscular mycorrhiza
Authors: BERTA G. , SGORBATI S. , SOLER V. , FUSCONI A. , TROTTA A. , CITTERIO A. , BOTTONE M. G. , SPARVOLI E. , SCANNERINI S. 
Published: April 2006

SUMMARYMicrofluorimetric and flow cytometric analyses were used in nuclei of cortical cells of roots in the endomycorrhizal systemAllium porrumL. + aGlomussp., strain E3(from Rothamsted Station), in an attempt to explain nuclear hypertrophy. No variation of DNA content in comparison with the controls was observed in mycorrhizal roots. An increase of fluorescence (about 25 %) was observed in mycorrhizal root nuclei stained with an undersaturating concentration of DAPI. This can be explained by a greater accessibility of DNA to fluorochromes owing to a lower degree of chromatin condensation, as confirmed by ultrastructural data.Our results suggest a possible explanation of nuclear hypertrophy and, further, show that variations of chromatin condensation can occur in mature plant cell nuclei, even though this, in differentiated plant cells, is generally considered to be independent of the cellular functions.
Mycorrhizas formed byGigaspora calosporaandGlomus fasciculatumon subterranean clover in relation to soluble carbohydrate concentrations in roots
Authors: THOMSON B. D. , ROBSON A. D. , ABBOTT L. K. 
Published: April 2006

SUMMARYAt several times during plant growth, we compared the effects of two irradiances (plants were either not shaded or were shaded to reduce 60–70% of the photon flux in the glasshouse) and two concentrations of soil phosphorus (P) (35 and 105 μg−1P g−1soil) on the formation of vesicular‐arbuscular (VA) mycorrhizas onTrifolium subterraneumL. byGigaspora calospora(Nicol. & Gerd.) Gerd. and byGlomus fasciculatum(ThaxtersensuGerd.) Gerd. & Trappe.By the fifth week from sowing, the proportion of root length infected by bothG. calosporaandG. fasciculatumwas reduced in plants grown at the greater concentration of P and in plants grown without shade. These effects were associated with decreased concentrations of soluble carbohydrates in roots at earlier harvests. Decreased concentrations of soluble carbohydrates in the roots of unshaded plants were not associated with increased concentrations of P in the plant.The percentage of root length infected byG, calosporawas decreased to a greater extent than that ofG. fasciculatumwith similar reductions in the concentrations of soluble carbohydrates in roots. This effect may partly explain why the percentage of root length infected byG. calosporais more sensitive than that ofG. fasciculatumto increasing P supply.G. calosporaandG. fasciculatummay also differ in the extent to which P may directly affect their ability to form mycorrhizas.The effects of P supply and shading on the percentage of root length infected byG. calosporaand byG. fasciculatumwere not apparent before the fourth week from sowing. These factors may have affected the ability of the mycorrhizal fungi to spread by secondary infections.
Dispersal, establishment and survival of soredia and fragments of the lichen, Hypogymnia physodes (L.) Nyl
Authors: ARMSTRONG R. A. 
Published: April 2006

SUMMARYDispersal, establishment and survival were studied in a population of Hypogymnia physodes (L.) Nyl. growing on an isolated tree (Primus blireiana L.) at a site in North Seattle, U.S.A. Lichen propagules were trapped daily on adhesive strips pinned to various sites on the tree over a period of 36 days. Both soredia and fragments were deposited on the strips, particularly on the upper branches of the tree, with soredia being considerably more numerous than fragments. Daily variation in total soredia deposited did not correlate with 10 climatic variables including wind speed, relative humidity and average temperature. Establishment and survival of propagules were studied by introducing soredia and fragments into various sites on the bark and by observing the distribution of small thalli in different microsites. Microtopography of bark significantly influenced establishment and survival, survival was poor on smooth bark compared with survival on algal or lichen crusts and on rough bark. Survival of soredia did not vary significantly at different locations on the tree. It is likely that colonization of the tree by H. physodes occurs largely by soredia. Colonization appears to be limited more by the range of dispersal over the tree than by differential survival over different parts of the tree.
The ecological significance of grazing on planktonic populations of cyanobacteria by the ciliate Nassula
Authors: CANTER HILDA M. , HEANEY S. I. , LUND J. W. G. 
Published: April 2006

SUMMARYObservations on the grazing of planktonic cyanobacteria (blue‐green algae) by the ciliate Nassula aurea Ehr. are described from three lakes in the English Lake District, Cumbria. Substantial declines in blooms of Aphanizomenon flos‐aquae f. gracile Ralphs ex Born, et Flah. due to feeding by N. aurea are documented from Esthwaite Water and Blelham Tarn. The differential grazing by Nassula only on certain cyanobacteria present in the lakes is discussed in relation to the production of cyanobacterial mucilage. Density‐dependent predator/prey relationships are considered together with the significance of grazing episodes on interannual variability of cyanobacterial Populations and their periodicity. A suctorian (Podophrya sp.) which parasitizes Nassula and a biflagellate fungus (Eurychasma sp.) which parasitizes the Podophrya are illustrated and briefly described.
Pollen counting on a pocket computer
Authors: BENNETT K. D. 
Published: April 2006

SUMMARYTranscribing pollen counts from count sheets or mechanical counters into a micro‐ or mainframe computer is tedious, time‐consuming and liable to error. The use of a pocket computer to handle these tasks is described. Similar systems have been available on microcomputers for several years but the unit cost of microcomputers is too great to allow one on the desk of each pollen analyst in a laboratory. Pocket computers can now be purchased and run for less than the cost of mechanical counters and with considerable advantages for the ease and efficiency of collecting and handling of phynological data. A program called polltax, running on a Psion Organiser II, designed to collect and handle pollen counts and point count estimates of charcoal, is described.
Reviews
Authors: Evans M. C. W. , Scott I. M. , Berry D. R. , Henderson D. M. , Cox E. J. , Whittington G. , Holden M. A. 
Published: April 2006

Books reviewed in this article: Molecular Biology of Photosynthesis. Ed. By Govindjee, H. J. Bohnert, W. Bottomley, D. A. Bryant, J. E. Mullet, W. L. Ogren, H. Pakrasi and C. R. Somerville. Biochemical and Physiological Aspects of Ethylene Production in Lower and Higher Plants. Ed. by H. Clijsters, M. de Proft, R. Marcelle and M. Van Poucke. Nitrogen, Phosphorus and Sulphur Utilisation by Fungi. By L. Boddy, R. Marchant and D. J. Read. Fungi and Ecological Disturbance. Ed. by L. Boddy, R. Watling and A. J. E. Lyon. Phytoplankton, 2nd Edn. By A. D. Boney. The Holocene: An Environmental History. By Neil Roberts. Chambers Biology Dictionary. Ed. by P. M. B. Walker, C.B.E., F.R.S.E.
Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies
Authors: TESTER MARK 
Published: April 2006

SUMMARYIon channels are proteins which catalyse rapid, passive, electrogenic uniport of ions through pores spanning an otherwise poorly permeable lipid bilayer. Among other processes, fluxes through ion channels are responsible for action potentials – large, transient changes in membrane potential which have been known of in plants for over 100 years. Much disparate information on ion channels in plant cells has accumulated over the past few years. In an attempt to synthesize these data, the properties of at least 18 different ion channels are collated in this review. Channels are initially classified according to ion selectivity (Ca2+, Cl−, K+ and H+); then gating characteristics (i.e. control of opening and closing), unitary conductance and pharmacology are used to distinguish further different sub‐types of channels. To provide a background for this overview, the fundamental properties which define ion channels in animal cells, namely conduction, selectivity and gating, are described. Appropriate techniques for the study of ion channels are also assessed. The review concludes with a discussion on the role of ion channels in plant cells, although any comment on functions beyond turgor regulation and general statements about signalling remains largely speculative. The study of ion channels in plant cells is still at an early stage and it is hoped that this review will provide a framework upon which further work in both algae and vascular plants can be based.

CONTENTS

Summary
305

I.
Introduction: plant electrophysiology
306

II.
A general description of ion channels
306

III.
Ion channels in plants
310

IV.
Ca2+ channels
313

V.
Cl‐ channels
315

VI.
K+ channels in the plasma membrane
318

VII.
K+ channels in the tonoplast
322

VIII.
Channels in thylakoids
324

IX.
H+ channels
324

X.
Functions of channels
325

XI.
Conclusions
328

Acknowledgements
328

References
329
H+extrusion and organic‐acid synthesis in N2‐fixing symbioses involving vascular plants
Authors: RAVEN JOHN A. , FRANCO AVILIO ANTONIO , de JESUS ELI LINO , JACOB‐NETO JORGE 
Published: April 2006

SUMMARYAn analysis of published data suggests that the N2‐fixing symbiotic vascular plants extrude more H+per unit N fixed than would be expected from data on the same genotypes growing on NH4+if the plants had the same chemical composition when grown on the two N sources. The H+/N ratio with urea as the N source is similar to that with N2. The higher H+/N ratio and higher organic acid/N ratio with N2or urea as N source implies higher whole‐plant energy and water costs per unit of biomass and, ultimately, inclusive fitness, produced. The rhizosphere acidification resulting from H+extrusion may serve to change rhizosphere pH to some ‘optimal’ value, and to increase the availability of such limiting resources as P, Mo and Fe which are especially needed in diazotrophy. Data in the literature are consistent with these possibilities in the few cases examined.Within the plant, data on xylem and phloem sap composition in conjunction with shoot composition, of diazotrophically‐growing legumes suggest that shoot acid‐base homoiostasis can be maintained via the import of appropriate solutes in the xylem and the export of appropriate solutes in the phloem. Acid‐base regulation of the nodules in the absence of any H+exchange with their environment can also probably be explained in terms of the solutes supplied in the phloem and exported in the xylem. This conclusion is based on data in the literature on the composition of stem phloem sap and of xylem sap exuding from detached nodules of diazotrophic vascular plants. These considerations do not exclude the possibility of net H+efflux from nodules fixing N2in contact with an aqueous medium. The limited data available are consistent with extrusion of some of the H+generated in nodules as an alternative to their neutralization by metabolism of organic anions entering in the phloem. Such H+extrusion by nodules could aid in their acquisition of Fe from the medium, albeit not always at a phase in the life or the nodule when there is a net requirement for Fe.
Intraclonal translocation of ammonium and nitrate nitrogen in Carex bigelowii Torr. ex Schwein. using 15N and nitrate reductase assays
Authors: JÓNSDÓTTIR INGIBJÖRG S. , CALLAGHAN TERRY V. 
Published: April 2006

SUMMARY Carex bigelowii Torr. ex Schwein. forms extensive rhizome systems consisting of numerous long‐lived tiller generations with only the roots and the rhizome remaining alive, and only few tillers with above‐ground shoots. The hypothesis that benefits to the young photosynthetic tillers are provided by the non‐photosynthetic tiller generations through the uptake and translocation of nutrients was tested by tracing the movement of nitrogen within clones growing in the field in the Swedish Lapland.Application of nitrate to individual roots of 3‐ to 7‐year‐old tillers induced nitrate reductase activity (NRA) in the youngest tiller generations after 2‐3 days. The subsequent application of 15N‐nitrate and 15N‐ammonium to individual roots of old tiller generations showed that both ions were taken up by these old roots, but ammonium‐N was taken up in greater quantities. The l5N was mainly translocated distally to the younger tillers, but some Proximal translocation was also detected which was greater for ammonium‐N. Nitrate‐N was translocated at a higher rate than ammonium‐N, resulting in a greater accumulation of nitrate‐N in the youngest tiller generation during the 2 days of the experiment.The independent NRA and 15N methods confirm (a) the continuing resource acquisition by old non‐photosynthetic tillers; (b) a long period of ramet interdependence extending over at least 7 years; (c) a division of labour between ramet generations and (d) the abilities of C. bigelowii clones to assimilate both ammonium and nitrate nitrogen. These aspects of clonal integration have important consequences for the fitness of C. bigelowii in its cold and nutrient‐poor environments.
Regulation of nitrate reductase in the ectomycorrhizal basidiomycete, Hebeloma cylindrosporum Romagn., cultured on nitrate or ammonium
Authors: SCHEROMM P. , PLASSARD C. , SALSAC L. 
Published: April 2006

SUMMARYThe growth of Hebeloma cylindrosporum Romagn. on nitrate medium is associated with nitrate reductase activity equivalent to that measured in herbaceous angiosperms. Nitrate is not indispensable for the induction of NR, as thalli cultivated in ammonium have the same NR activity as thalli cultured on nitrate. However, the simultaneous presence in the culture medium of ammonium with an organic acid such as malate, citrate or succinate causes a diminution of NR activity. Glutamine or asparagine, by‐products in the assimilation of ammonium and malate, could intervene in the regulation of this enzyme. The data suggest that the absence of nitrogen or the presence of a nitrogen source, such as ammonium, inappropriate for growth derepresses nitrate reductase in this fungus.
Ectomycorrhiza formation in Eucalyptus.
Authors: DELL B. , MALAJCZUK N. , GROVE T. S. , THOMSON G. 
Published: April 2006

SUMMARY Mesophellia and Castorium are common hypogeous macrofungi in the karri (Eucalyptus diversicolor F. Muell.) and jarrah (Eucalyptus marginata Donn ex Sm.) forests of south‐western Australia.Sporocarps of Mesophellia and Castorium develop 5‐20 cm below the soil surface in close association with eucalypt roots. During differentiation of the sporocarps, eucalypt roots become trapped within the peridium where they branch profusely and form a dense ectomycorrhizal layer. Mature sporocarps of M. trabalis nom. ined. contain approximately S m of roots of 45 cm2 surface area. Anatomical studies have shown that these roots have Hartig nets penetrating to the hypodermis and are similar to the superficial eucalypt ectomycorrhizas formed in soil and litter. The association of Mesophellia and Castorium sporocarps with tree roots suggests that these are important mycorrhizal fungi in forests of southern Australia.
The roots and mycorrhizas of herbaceous woodland plants
Authors: BRUNDRETT MARK , KENDRICK BRYCE 
Published: April 2006

SUMMARYThe time‐course of development of the roots and endomycorrhizas of five common herbaceous plants in a southern Ontario hardwood forest (Arisaema atrorubens, Erythronium americanum, Asarum canadense, Smilacina racemosa, and Trillium grandiflorum) was examined. Root growth of these species was very slow. Formation of vesicular‐arbuscular (VA) mycorrhizas was quantified by measuring the average distance from growing root tips at which (i) hyphal contact, (ii) root penetration, and (iii) arbuscule formation by hyphae of VA mycorrhizal fungi first occurred. The rate at which mycorrhizal colonies within roots expanded was also quantified. These measurements allowed the rate of mycorrhizal colonization of roots of species to be compared. All events were slower in woodland plant roots than in other previously investigated species. The rate of VA mycorrhizal colony‐expansion was found to be significantly faster in roots containing longitudinal air channels, which apparently facilitated the spread of hyphae. Environmental factors may also have been important since events were even slower in those roots produced by Erythronium in the autumn. Reasons why slow, steady, root and mycorrhiza formation could be advantageous to woodland plants are considered.
The roots and mycorrhizas of herbaceous woodland plants
Authors: BRUNDRETT MARK , KENDRICK BRYCE 
Published: April 2006

SUMMARYThe morphology of vesicular‐arbuscular (VA) mycorrhizas in the roots of five species of herbaceous woodland plants, in which root growth and mycorrhiza formation were quantified in the first part of this study was examined. The root anatomy of these species was also examined in detail, using various staining procedures to observe cell wall structure, especially in the region where mycorrhizal colonization was initiated. The morphology of mycorrhizal colonies within the roots of these species was observed at different stages of development using light microscopy. It was found that modifications of endodermal and exodermal cell‐walls could determine the way in which fungi entered the roots. It was also found that properties of the cortex considerably influenced the localization of hyphae and arbuscules within roots. Features of VA mycorrhizas that were probably associated with particular endophytes were also noted. It is considered likely that some aspects of root structure have evolved means of regulating the efficiency of mycorrhizal associations.
High resolution cytochemical study of the vesicular–arbuscular mycorrhizal association, Glomus clarum×Allium porrum
Authors: JABAJI‐HARE S. H. , THÉIREN J. , CHAREST P. M. 
Published: April 2006

SUMMARYRoots of leek, colonized or not by Glomus clarum Nicolson & Schenck, were ultrastructurally examined for the presence of different sugars using lectin‐gold complexes. N‐acetyl‐d‐glucosamine (GlcNAc), N‐acetyl‐d‐galactosamine (GalNAc), l‐fucose (l‐FUC), d‐mannose (d‐Man) and sialic acid sugar residues were localized in various cellular components of the mycorrhizal fungus. GlcNAc, GalNAc, d‐Man and sialic acid residues were localized in the colonized host, particularly in the plasmalemma and cytoplasm surrounding the arbuscular hyphae. The same sugars were not present in the non‐colonized host. These results indicated that the production of these sugars had been triggered during the plant‐fungus association. In the interfacial matrix, GalNAc and d‐Galactose (d‐Gal) residues were present in moderate amounts. In cell walls and protoplasm of non‐colonized and colonized hosts, mainly d‐Gal was detected. Ribonucleic acid (RNA) was cytochemically localized in the fungus and host by means of a RNAse‐gold complex. Of interest, was the specific localization of RNA in the granular wall layer of vesicles. The ultracytochemical results are discussed in relation to host‐symbiont interaction, along with speculations on the function and significance of these macromolecules.
The sporophyte–gametophyte junction in the hornwort, Dendroceros tubercularis Hatt (Anthocerotophyta)
Authors: LIGRONE R. , RENZAGLIA K. S. 
Published: April 2006

SUMMARYThe placenta of the anthocerote, Dendroceros tubercularis Hatt., consists of long and branched haustorial cells, that arise from the foot and gametophyte transfer cells. Both cell types contain electron‐dense vacuolar deposits that were digested by pronase and therefore are assumed to be protein. These deposits were negative to the PATAg test for carbohydrates. Protein bodies were also found in the parenchyma cells of the foot and younger meristematic cells at the base of the capsule. Vacuolar deposits of osmiophilic material in the gametophyte cells external to the placenta were stained non‐specifically with PATAg method and were not affected by pronase. The haustorial cells have pleomorphic plastids lacking starch and a thylakoid system, whereas the transfer cells have well developed chloroplasts. No pronase‐sensitive material was detected in the apo plastic space separating gametophyte and sporophyte cells. These results suggest that protein is synthesized in the haustorial cells, perhaps from precursors provided by transfer cells, and is then transferred, via plasmodesmata, to the parenchyma cells of the foot and eventually to the cells of the growing capsule.
The size of quiescent centre in roots of Allium cepa L. grown with ascorbic acid
Authors: INNOCENTI A. M. , BITONTI M. B. , ARRIGONI O. , LISO R. 
Published: April 2006

SUMMARYFollowing ascorbic‐acid treatment a large number of quiescent centre cells undergo DNA synthesis and, at the same time, the cell proliferation in the entire root meristem of Allium cepa is stimulated. The effects of ascorbic acid on dividing cells in the meristem proper and on the quiescent centre are long‐lasting since they are obtained in both short‐ and long‐term experiments. Whatever the time of treatment with ascorbic acid and whatever the starting size of the quiescent centre (450 or 1000 cells), there is always a minimum number of quiescent centre cells (90‐100) which remain in the G1 phase.
The role of the exine coating in pollen–stigma interactions in Brassica oleracea L
Authors: ELLEMAN CAROLE J. , DICKINSON H. G. 
Published: April 2006

SUMMARYWhen the dehydrated pollen grain of Brassica oleracea L. alights on a receptive stigma the pollen coat flows out from the exine to form an appresoria‐like ‘foot’ and, within a matter of some 30 min, gross ultrastructural changes become visible both within the protoplast and in the foot itself. These changes are interpreted as reflecting the limited movement of water, and presumably other materials, from the stigma to the grain. The compatible pollen grain then continues to take up water, whilst undergoing other cytoplasmic changes and eventually producing the pollen tube. The tube grows from the colpus towards the point of contact with the stigma, beneath which the outer layer of the papillar wall has become more loosely packed. The pollen tube enters the wall at this point and, as a consequence of its rapid extension, the grain is frequently lifted away from the papilla. The tube then grows between two layers of the pectocellulosic papillar wall into the stigmatic parenchyma, where it follows an intercellular route. These events are discussed in terms of current views of the relationship between male and female cells at these early stages of the pollen stigma interaction.