bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of frost damage in plant tissues by rates of electrolyte leakage
Authors: MURRAY M. B. , CAPE J. N. , FOWLER D.
Published: April 2006

A method for assessing frost hardiness of plant tissues [using shoots of Picea rubens Sarg. syn P. rubra (Du Roi) Link] has been developed based upon the rate of electrolyte leakage from shoots immersed in distilled water after exposure to a range of freezing treatments. The relationship between conductivity (the electrolyte concentration in solution) and time has been shown to follow an asymptotic curve, which may be represented by a first‐order equation: Ct–Co= Cauto–Co– C‐kt) where C1 is the conductivity at time t, Co is the initial conductivity, Cautois the conductivity after autoclaving and k is the first‐order rate constant (units time‐1). The rate of electrolyte leakage (k) varies directly with the extent of tissue damage. In P. rebens a rate of 0‐4%, h‐1 distinguished between shoots which eventually died, and shoots which remained alive. A minimum of 3 conductivity measurements (after 1 day, 5 days and after autoclaving) is required for a reliable estimate of k. This objective, quantitative method of assessing frost hardiness may therefore be used directly to estimate LT50 values within a population.
Interpretation of the pollen stratigraphy of Late Devensian lateglacial and early Flandrian sediments at Llyn Gwernan, near Cader Idris, North Wales
Authors: LOWE J. J. , LOWE S.
Published: April 2006

Pollen‐stratigraphic information is presented for two profiles from a high resolution Devensian lateglacial succession at Llyn Gwernan, North Wales. Pollen concentration and preservation data are available for one of these profiles and two series of radiocarbon dates, one based on‘conventional’radiometric counting and one on accelerator mass spectrometry measures, provide age estimates for the succession. The data indicate the following sequence of events at Llyn Gwernan: deglaciation of the area about or shortly before 14200 n. p.; cold, dry climatic conditions from 14200 to 13 200 n. p.; generally stable environmental conditions from 13 200 to 12 100 B.P.; steady deterioration of climate between 12100 and 11 160 B.I.; harsh climatic conditions between 11 160 and 10200–10000 B.P. This interpretation broadly supports that previously proposed for N. Wales on the basis of coleopteran evidence. Implications of some of the differences in pollen stratigraphy between the two Llyn Gwernan profiles and possible evidence for two minor climatic oscillations during the lateglacial interstadial are discussed.
Two pollen diagrams from the same site
Authors: TURNER JUDITH , INNES J. B. , SIMMONS I. G.
Published: April 2006

Two pollen diagrams from within one metre of each other at a blanket peat site on the North York Moors are similar, and fully justify the usual practice of preparing only one diagram. There are however minor differences. These indicate the degree of random variation that can occur and should be borne in mind when interpreting pollen diagrams from blanket peat.
Pollen analysis of a Quaternary peat sequence on Gough Island, South Atlantic
Authors: BENNETT K. D. , GRIBNITZ K.‐H. , KENT L. E.
Published: April 2006

A peat sequence on Gough Island, South Atlantic, is described. The deposit is at least 43 000 years old, and may be early Quaternary in age. Pollen analyses suggest a flora and vegetation on Cough Island similar to those of today, supporting conclusions based on pre‐Holocene pollen samples from islands in the Tristan da Cunha group. The present flora has probably been on Cough Island continuously for at least the last 40000 years, and is not a Holocene immigrant flora.
Instability in the root meristem of Zea mays L. during growth
Authors: CLOWES F. A. L. , WADEKAR R.
Published: April 2006

Primary roots of Zea mays L., when grown to 100 mm long, may display instability in the architecture of their meristems. This occurs over the whole temperature range from 15 to 35 °C, but most frequently at the two extremes of the range and is associated with abnormally low ratios between rates of mitosis in the proximal tier of the cap cells and rates in the cells of the Quiescent centre. Anomalous meristems show either proliferation of the number of cell layers between stelar pole and cap boundary or protrusions of cells derived from the quiescent centre into the cap where they can spread to form new sets of cap initials. The process can be repeated, but there is no evidence to suggest that the originally closed meristem ever operates as an open meristem with only transiently quiescent cells distal to the stelar pole.
Absence of nuclear DNA synthesis in vesicular–arbuscular mycorrhizal fungi during in vitro development
Authors: BURGGRAAF A. J. P. , BERINGER J. E.
Published: April 2006

A study of the in vitro viability of VA mycorrhizal propagules [Glomus caledonium (Nicol. & Gerd.), Gigaspora margarita (Becher & Hall)], indicated that none could be used for continuous in vitro cultivation. Large numbers of nuclei (at least 20000 for G. margarita) were found in the chlamydospores. Nuclear division could not be demonstrated in vitro, during or after spore germination using various cell cycle inhibitors, or by direct isotope labelling of nuclear DNA. Manipulation of secondary messengers (cAMP, calcium) and the microtubule or micro‐filament system did not increase the in vitro growth of the tested VA mycorrhizal strains.
Responses of the non7hyphen;mycotrophic plant Salsola kali to invasion by vesicular–arbuscular mycorrhizal fungi
Authors: ALLEN MICHAEL F. , ALLEN EDITH B. , FRIESE CARL F.
Published: April 2006

Vesicular–arbuscular mycorrhizal fungi reduced the growth and survival of the non‐mycotrophic weed, Salsola kali (Chenopodiaceae) in field and greenhouse experiments. To determine the mechanisms by which mycorrhizal fungi can affect a non‐mycotrophic plant, we mapped the root responses of S. kali and the mycotrophic grass Agropyron dasystachyum to invasion by a mixture of Glomus spp. and by Gigaspora margarita. The fungi invaded the roots of both species within 10 days following seed germination. In A. dasystachyum normal mycorrhizal development occurred and no root browning or autofluorescence was observed, indicating a compatible reaction. In S. kali, the fungi initially invaded the roots and formed arbuscules and peletons. The roots reacted to invasion by autofluorescing bright yellow, suggesting lignification. With 1 or 2 days following root penetration by the fungus, the invaded root segment turned brown and, with the exception of some vesicles, the fungus disappeared from the root. The fungus sometimes then reinvaded new root segments farther down the root.

These observations suggest that there is an incompatible reaction beween this non‐mycotrophic annual and VA mycorrhizal fungi whereby the plant actively rejects infection. This response could form the basis for initiating studies on the genetics of mutualistic versus parasitic symbioses.
Cotton root growth as influenced by phosphorus nutrition and vesicular–arbuscular mycorrhizas
Authors: PRICE N. S. , RONCADORI R. W. , HUSSEY R. S.
Published: April 2006

Cotton, Gossypium hirsutum L., was grown in the greenhouse in sand‐nutrient culture at five phosphorus (P) concentrations, and root systems were examined after 10 and 20 days. Extension rates of primary laterals and numbers of secondary laterals increased with increasing P. Cotton was grown for 6 weeks in environment cabinets in soils of three P concentrations with and without mycorrhizas. Increased P and mycorrhizas both stimulated plant growth (f. wt shoot d. wt), but however specific root length (cm root g' root f. wt) of mycorrhizal plants was reduced.
Use of cryo‐techniques with scanning electron microscopy to study infection of mature red raspberry fruits by Botrytis cinerea
Authors: WILLIAMSON B. , DUNCAN G. H.
Published: April 2006

Scanning electron microscopy (SEM) was used to study the infection of the mesocarp cells of ripe drupelets of the compound fruit of red raspberry (Rubus idaeus L.) by Botrytis cinerea Pers.: Fr. 24 h after the fruit had been wounded and inoculated with dry conidia. Frozen fully hydrated specimens showed that conidia had germinated in juice at the point of inoculation and in partially freeze‐dried specimens hyphae were visible in some cells. However, structural detail was largely obscured by ice segregation zones in the closely packed large columnar, poyhedral cells of the fruit. These artifacts were removed in specimens which had been cryotrimmed and fully freeze‐dried. In such specimens there were four distinct zones around the inoculation wound. Intercellular and intracellular hyphae were visible in the innermost area (zone 1); the walls of some infected cells were swollen, eroded and porous. In zone 2, an area of cells immediately beyond the hyphae, little structure was retained but in zone 3 cell walls were well preserved and showed lamellar or reticulate material in the intercellular spaces. The outer zone (zone 4) consisted of apparently healthy cells.
Interactions between infection by endophytic fungi and nutrient limitation in the grasses Lolium perenne and Festuca arundinacea
Authors: CHEPLICK G. P. , CLAY K. , MARKS S.
Published: April 2006

Although grasses infected by fungal endophytes often exhibit increased growth relative to uninfected plants, the results of infection may be manifested as decreased growth in plants growing under stressful conditions. A preliminary experiment compared perennial ryegrass (Lolium perenne L.) infected by Acremonium lolii Latch, Christensen & Samuels with uninfected plants grown at three soil moistures and three nutrient concentrations. Total biomass, tiller number, and relative tillering rate were significantly affected by nutrient concentration and moisture. Although major differences between infected and uninfected plants were not apparent, relative growth rates of infected plants were significantly greater than uninfected plants in three of nine treatment combinations. Interactions between infection and nutrient limitation were examined in seedlings and adults of perennial ryegrass and tall fescue (Festuca arundinacea Schreb., infected by A. coenophialum Morgan‐Jones and Gams). A significant nutrient × infection interaction for tall fescue seedlings indicated that, compared to uninfected seedlings, infected seedlings had greater biomass at the high nutrient level but a significantly lower biomass at the low nutrient level, suggesting a metabolic cost to the host due to competition with the fungus for nutrients or photosynthate. Infected perennial ryegrass seedlings had significantly more biomass at high and intermediate nutrient levels, but not at low nutrient levels. Although infection did not significantly affect total biomass in perennial ryegrass adults, in tall fescue adults the benefits of endophyte infection to host plants (recorded as greater biomass) became increasingly greater with increasing nutrient availability.
Pollen assemblage–plant community relationships on the Storbreen glacier foreland, Jotunheimen Mountains, southern Norway
Authors: CASELDINE C. J.
Published: April 2006

Present‐day pollen assemblages from 38 sites within differing but closely juxtaposed plant communities from the Storbreen glacier foreland in southern Norway, provide evidence for the degree to which these plant communities can be characterized by distinctive pollen assemblages. Multivariate statistical analyses of the data demonstrate a broad, tripartite division in the pollen record which reflects the three major vegetation types: (i) Pioneer Poa alpina–Trisetum spicatum community; (ii) Snowbed Salix herbacea‐dominated community; (iii) Dwarf‐shrub heath community. Occasional overrepresentation of Salix, Oxyria and Cyperaceae pollen leads to assemblages that are difficult to characterize and remain outside all major groups. Four general pollen indices are derived, each of which provide maximum limiting estimates for the proportion of pollen derived from different potential source areas. Combined with isopollen mapping the indices suggest that in pioneer communities between 20–40% of pollen collected within the community could have derived locally i.e. within the 16 m2 quadrat, whereas in the dwarf‐shrub heath this figure rises to over 60%. The remaining pollen largely originates from long distance transport, i.e. < 1 km, with little movement of foreland‐derived pollen across the foreland itself. Thus the ‘extra‐local’ component appears to play a relatively insignificant role within the area of study. The ability to separate such local and long‐distance elements will prove of particular value in the reconstruction of the history of plant communities beyond the tree‐line.
Superoxide dismutase activation in response to lime‐induced chlorosis
Authors: OSTROVSKAYA L. K. , TRUCH V. V. , MIKHAILIK O. M.
Published: April 2006

Summary

Alterations in superoxide dismutase (SOD) activity were studied on chlorotic grapevines (Vitis vinifera L.) grown under natural conditions on soil containing 30–35% CaCO3, and in lupins (Lupinus luteus L.) grown in a greenhouse with addition of 20% CaCO3 to the soil. In both series of experiments SOD activity in leaves of chlorotic plants was from 20 to 30%, higher. The efficiency and absolute rate of superoxide anion radical formation were found to rise as a result of iron deficiency in the lupin leaves. Increased SOD activity and greater amounts of enzyme isoforms were observed in the leaves of grapevine cultivars resistant to lime‐induced chlorosis as compared to less resistant cultivars. The present investigation suggests that initiation of lime‐induced chlorosis is determined not only by reduced chlorophyll biosynthesis but also by other consequencies of iron deficiency in tissues, particularly by the high rate of formation of superoxide and other activated oxygen species, causing destructive changes in the photosynthetic apparatus. The increased SOD activity may be regarded as a protective mechanism against the formation of superoxide.
On host regulation of the vesicular—arbuscular mycorrhizal symbiosis
Authors: KOIDE ROGER T. , LI MINGGUANG
Published: April 2006

Summary

We investigated mycorrhizal infections caused by Glomus elunicalum Becker & Gerd. in sunflower (Helianthus annuus L.) plants given small concentrations of phosphate. In pure sand given no additional phosphate, infection was only poorly developed. As phosphate availability was increased, the extent of infection also initially increased. We hypothesized that the extent of infection should be regulated by the nutritional status of the shoot. However, by performing a split‐root experiment, we found that the root rather than the shoot was responsible for this regulation.
A technique for dual vesicular–arbuscular endomycorrhizal/ectomycorrhizal infection of Eucalyptus in vitro
Authors: BOUDARGA KHADIJA , LAPEYRIE FRÉDERIÉ , DEXHEIMER JEAN
Published: April 2006

Summary

A few species of plant, including Eucalyptus, bear simultaneously on their root system and even on the same root apex, more than one symbiotic microorganism. The development of techniques allowing mixed inoculations is an essential prerequisite for the study of interactions between different symbionts. A simple in vitro technique for rapid synthesis of dual vesicular‐arbuscular endomycorrhiza/ectomycorrhiza on a single root apex of Eucalyptus seedlings is described. This technique was derived from the paper‐sandwich technique for synthesis of ectomycorrhizas, and was modified to render it compatible with endomycorrhizal infection. Electron microscopy observations of dual endomycorrhiza/ectomycorrhiza showed both symbioses coexisting on the same apex, with no obvious sign of antagonism.
Growth and phosphorus acquisition of karri (Eucalyptus diversicolor F. Muell.) seedlings inoculated with ectomycorrhizal fungi in relation to phosphorus supply
Authors: BOUGHER N. L. , GROVE T. S. , MALAJCZUK N.
Published: April 2006

Summary

Growth and phosphorus acquisition of pot‐grown seedlings of karri (Eucalyptus diversicolor F. Muell.) were examined following inoculation with four ectomycorrhizal fungi –Descolea maculata Bougher (two isolates), Pisolithus tinctorius (Pers.) Coker & Couch, and Laccaria laccata (Scop, ex Fr.) Berk. & Br. Seedlings were raised in steam‐sterilized sand to which 13 rates of phosphorus (0.100 mg P kg−1 soil) were applied.

All fungi except P. tinctorius produced a plant growth response. L. laccata produced the largest growth response. Responses were greatest at low rates of application of P to soil. There was no effect of the fungi on growth at levels of P application above 28 mg P kg−1 soil. A threshold effect (no increase in growth with increasing additions of P) characteristic of non‐mycorrhizal seedlings was eliminated by mycorrhizal infection.

Mycorrhizal inoculation increased P content of plant tissues at sub‐optimal levels of P supply. The effect of mycorrhizas on seedling P status diminished with increasing soil P. One isolate of D. maculata often had greater rates of P accumulation and produced higher concentrations of P in plant tissues than L. laccata, but did not produce greater plant biomass.

Frequency of infection for all fungi was low in soils with no additional P, and greatest with the addition of 2 mg P kg−1 soil (L. laccata and D. maculata isolate A), or 4 mg P kg−1 soil (D. maculata isolate B). Infection was reduced with increasing soil P, and not evident at 36 mg P kg−1 soil or higher levels of soil P. L. laccata had higher infection frequency and mycorrhizal root length at all levels of soil P than the D. maculata isolates.

Two fungi produced basidiomes. This occurred at levels of soil P application ranging from 4 to 28 mg P kg−1 soil for D. maculata (isolate B), and at 4 to 28 mg P kg−1 soil for L. laccata.
Nitrate nutrition of maritime pine (Pinus pinaster Soland in Ait.) ectomycorrhizal with Hebeloma cylindrosporum Romagn.
Authors: SCHEROMM P. , PLASSARD C. , SALSAC L.
Published: April 2006

Summary

In maritime pine seedlings (Pinus pinaster Soland in Ait.), nitrate absorption and reduction capacities were estimated by the incorporation of 15N‐labelled nitrogen. This method allowed us to work on the whole plant Without perturbing plant behaviour. For this purpose, xylem and phloem transports were quantified. After 48 h i nitrate nutrition, mycorrhizal symbiosis with Hebeloma cylindrosporum Romagn. modified neither nitrate accumulation nor absorption and reduction capacities of this anion. Xylem transport of reduced nitrogen was similar in mycorrhizal and non‐mycorrhizal seedlings. Only phloem transport was modified by mycorrhizal symbiosis. The intensity of the phloem transport in mycorrhizal pines was approximately twice that in non‐mycorrhizal plants.
Developmental changes in Sitka spruce as indices of physiological age
Authors: STEELE M. J. , YEOMAN M. M. , COUTTS M. P.
Published: April 2006

Summary

Adventitious rooting ability is considered a good indicator of juvenility in trees and has often been used to assess explants subjected to treatments to alter developmental stage. However, rooting assessments are not always practical and the callusing of needles in vitro was investigated as an alternative bioassay of physiological age. Shoots were sampled from the uppermost whorl of Sitka spruce trees aged 1, 3, 4, 6, 11, 16, 21, 35 and 39 years and from the lowest whorls of 3‐ and 4‐year‐old trees. Needles were sampled for measurement of length, width, length/width ratio, projected and total surface areas, dry weight and specific leaf area. For explants of uppermost whorl origin, there were decreases in the rooting ability of cuttings and the callusing response of needles with increasing age of tree. Associated with the loss in callusing ability was an increase in the production of a black exudate. The changes with age for rooiing, callusing and exudation could each be adequately described by the Gompertz growth function which showed their rates of change to be similar. The observed changes are closely associated with changes in needle area, weight and specific leaf area. Euclidean distances (using the mean values of selected characteristics for each age class) were computed as a measure of physiological age. The shoots and needles of basal shoots are more juvenile in character than those taken from the uppermost whorls of the same trees.
The role of iron in nodulation and nitrogen fixation in Lupinus angustifolius L
Authors: TANG CAIXIAN , ROBSON ALAN D. , DILWORTH MICHAEL J.
Published: April 2006

The effects of iron concentration in solution on nodulation and symbiotic N2 fixation in lupins (Lupinus angustifolius L. ev. Yandee) were studied in solution culture in the glasshouse by comparing plants supplied with NH4NO3 with those reliant on N2 fixation.

At very low iron supply, adding NH4NO2 did not increase shoot growth. Under moderate iron deficiency, where plants were pale green, adding NH4NO3 increased shoot growth, implying that moderate iron deficiency was, operationally, nitrogen deficiency. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic N2 fixation than for those supplied with NH4NO3

Iron deficiency depressed nodule initiation earlier than host plant growth, resulting in decreased nodule number and mass. Alleviating iron deficiency enhanced leghaemoglobin production in nodules and increased nitrogen concentrations in the shoots. Iron concentration in the youngest fully expanded leaves provided a good indication of the severity of iron deficiency‐caused chlorosis.

The results suggest that iron is involved in symbiotic N2 fixation through effects on both nodule initiation and nodule function, and that the symbiosis has a higher iron requirement than that needed for host plant growth.
The effect of zinc contamination from electricity pylons. Contrasting patterns of evolution in five grass species
Authors: AL‐HIYALY S. A. K. , MCNEILLY T. , BRADSHAW A. D.
Published: April 2006

Samples of 8–35 individuals of Agrostis capillaris, A. stolonifera, Anthoxanthum odoratum, Deschampsia cespitosa and Festuca ovina were collected from zinc‐contaminated soils beneath electricity pylons erected in North Wales and Lancashire between 1956 and 1970. Their zinc tolerance was assessed, as was that of two individuals of the same species collected from adjacent uncontaminated soils. Five soil samples from beneath each pylon were collected for evaluating total and extractable soil zinc, soil pH, and soil organic matter.

Some degree of zinc tolerance was detected in all five species, suggesting that evolution of tolerance has taken place relatively rapidly, particularly in A. capillaris, D. cespitosa, and Anthoxanthum odoratum. However, tolerant individuals of all species were not found beneath all pylons even when the species was present in the surrounding vegetation. This confirms and extends to other species previous findings in A. capillaris, that the gene or genes necessary for the evolution of tolerance are not universally present within species.
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

Microfluorimetric 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

At 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

Dispersal, 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

Observations 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

Transcribing 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

Ion 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

An 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

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

The 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

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

The 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

The 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

Roots 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

The 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

Following 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

When 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.
Hybridization between European and Asian dandelions (Taraxacum section Ruderalia and section Mongolica)
Authors: MORITA TATSUYOSHI , MENKEN STEPH B. J. , STERK ADRI A.
Published: April 2006

In order to investigate crossability between the European section Ruderalia Kirschner, H. Øllgaard & Štěpánek and the Asian section Mongolica Dahlst. of the genus Taraxacum Wigg., artificial hybridization experiments were carried out.

After inter‐sectional crosses on the diploid level, Mongolica plants showed high fruit‐set, not strikingly different from either the control (within‐populational crosses) or inter‐specific crosses within the same section. However, a substantial decrease of fruit‐set was detected when Ruderalia plants were the seed parents.

Electrophoretic analysis revealed that Ruderalia seed parents in inter‐sectional crosses showed relatively low out‐crossing rates with low fruit‐set, whereas Mongolica plants as seed parents showed high out‐crossing rates, mostly 100%. These results indicate that the crossing‐barrier is stronger in the direction from Mongolica to Ruderalia than vice versa.

Crosses between diploid Mongolica (♀) and triploid Ruderalia (♂) were also successful, although fruit‐set was far lower than in 2x‐2x crosses, a result which confirms previous reports. Contrary to published accounts, it was found by means of electrophoretic analyses that some 87.5 % of the progeny in 2x‐3x crosses were not true hybrids but sexual diploids originating from self‐fertilization. Only approximately 12.5 % of the progeny were found to be true agamospermous triploid or tetraploid hybrids. A strong doubt is raised concerning reports in the literature which assume that diploid hybrids originate in 2x‐3x crosses. The possible reasons why self‐incompatibility was broken down by triploid pollen are discussed.