bluuebunny/crossref_metadata_2025 huggingface dataset:
A 12 500 year record of vegetational history at Sluggan Bog, Co. Antrim, N. Ireland (incorporating a pollen zone scheme for the non‐specialist)
Authors: SMITH A. G. , GODDARD I. C.
Published: April 2006

summary

A radiocarbon‐dated pollen diagram from a typical lowland raised bog in County Antrim is presented, together with a limited stratigraphic study. The record of vegetational development described is unusually complete for the last 12 FDD years. The pollen diagram is divided into ten pollen zones which it is hoped will be useful to the non‐specialist. A visual summary is given in Figure 5.

Deposits of the Midlandian late‐glacial are contained in a small basin beneath the reedswamp and later Sphagnum peats of the mire. Birch woodland developed early in the sequence (approx, 12 350 BP) in the Belling interstadial period. Declines of this woodland occurred at approx. 12 200 BP and 11 700 BP. The probability that the 12200 BP decline represents the end of the thermal maximum of the late‐glacial interstadial is discussed. In the period equivalent to the classical Allerod interstadial, the vegetation appears to have been essentially treeless. A summary comparison of Irish Late‐glacial pollen assemblage zones is given. All radiocarbon dates are conventional, without calibration.

The birch woods of the early post‐glacial (early Littletonian) were subject to a set‐back at approx. 9400 BP that lasted some 200 years during which time there appears to have been a reversion to the unstable soils characteristic of earlier times. The possibility of an early post‐glacial climatic oscillation is discussed.

In the zonation scheme, attention is drawn to the decline of hazel pollen at approx. 8600 bp which appears to represent a turning point in woodland development. The mire surface was invaded by pines in the Late Boreal period. The decline of the pine pollen curve at the Boreal‐Atlantic transition (our S: V1‐S: VII pollen zone boundary, dated to approx. 7000 DP) is discussed in relation to evidence of burning and possible human activity.

Neolithic forest clearance activity on a minor scale is attested at the elm decline which at Sluggan falls rather late in the usual range for this horizon, at approx. 4900 bp. Major episodes of forest clearance took place in the Bronze Age. Thereafter woodland largely regenerated before further clearance starting in the seventh century AD which must have become substantial by Viking times. The local woodlands appear to have recovered again, however, and despite some further clearance in the Late Anglo‐Norman period persisted substantially until relatively recent times.

The possibility of climatic influences on the later vegetational history is discussed, particularly in relation to declines of the pollen curves of elm at approx. 4200 BP and AC 300, and of pine at approx. 3800 BP.
Tuberculate mycorrhizas of Castanopsis horneensis King and Engelhardtia roxburghiana Wall
Authors: HAUG I. , WEBER R. , OBERWINKLER F. , TSCHEN J.
Published: April 2006

summary

Tuberculate mycorrhizas of Castanopsis borneensis King (Fagaceae) and Engelhardtia roxburghiana Wall. (Juglandaceae) were studied by light and electron microscopy. The tubercles of both trees showed similar structure and morphology. The fungal partner is an unidentified basidiomycete. Beside normally developed mycorrhizas in each tubercle some heavily‐infected roots were found. These roots are characterized by a very thick hyphal mantle around a dead root tip and a circle‐like ingrowth of the fungus up to the vascular tissue – the strangulation zone. All cells distal to the strangulation zone were dead, but basipetal to it, normal cortical tissue with an epidermal Hartig net was present. The outer cortex in this region showed wall ingrowths along the inner tangential walls and an accumulation of ER and mitochondria. The formation and function of the heavily‐infected roots is discussed.
Mineral nutrition and mycorrhizal infection of seedling oak and birch
Authors: NEWTON A. C.
Published: April 2006

summary

In order to assess the factors influencing the extent and composition of ectomycorrhizal infection, and the consequences for seedling growth, seedlings of oak (Quercus robur L.) and birch (Betula pendula Roth.) were established in both field plots and pots of soil from two forested sites (Thetford Chase and Leith Hill). Seedlings were harvested after one growing season, and analysed for ectomycorrhizal infection.

When a single root system of pot‐grown oak was analysed in detail seven mycorrhizal types were differentiated. The relative abundance of these types varied depending on whether infection was assessed by counting branched mycorrhizas, or individual mycorrhizal tips. This reflected variation in the pattern of branching of the different mycorrhizal types. Of the 41 mycorrhizal types differentiated in the entire survey of 1800 seedlings, five were consistently recorded as unbranched, and six were found to produce second‐order branches. Different mycorrhizal types displayed contrasting patterns of abundance, both with respect to site and host species. For example, 21 types were recorded infecting oak, whereas only 15 were found on birch; only three types were found infecting both oak and birch on both sites.

In this survey, seedlings tended to be dominated by between one and three mycorrhizal types. Two types were particularly dominant: those formed by Scleroderma citrinum (Pers.) and Paxillus involutus (Batsch) Fr., which accounted for up to 61 and 92 % of the mycorrhizas of oak and birch respectively. These fungi were exceptional amongst those encountered in the present analysis, in producing both highly branched mycorrhizas and mycelial strands.

The relationship between ectomycorrhizal infection and seedling growth was assessed by correlation. Total seedling dry mass was in general found to be positively correlated with the total number of ectomycorrhizal tips, but poorly correlated with the extent of ectomycorrhizal infection, except where seedling growth had previously been shown to be limited by phosphate availability (i.e. in the case of pot‐grown birch on soil from Leith Hill). Seedling dry mass was also in general poorly correlated with number of mycorrhizal types, with two exceptions (i.e. field‐grown oak and pot‐grown birch on soil from Thetford Chase).

These results are discussed in the context of the role of ectomycorrhizal infection during seedling establishment, and implications for the methodologies utilized in assessing mycorrhizal infection are highlighted.
Enzymatic studies on the metabolism of vesicular—arbuscular mycorrhizas
Authors: GIANINAZZI‐PEARSON V. , SMITH S. E. , GIANINAZZI S. , SMITH F. A.
Published: April 2006

summary

Cytochemical methods were used to localize ATPase activity in different phases of development of the vesicular‐arbuscular mycorrhizal association between Allium cepa L. and Glomus intraradices Schenck & Smith. In the absence of inhibitors the pattern of lead deposition (indicative of ATPase activity) at the arbuscular interface was similar to that previously published, whether material was prefixed in glutaraldehyde or formaldehyde. Considerable activity was detected along both plant and fungal plasma membranes and in the interfacial matrix associated with young arbuscules; this decreased with senescence of arbuscules. The fungal plasma membranes of external and intercellular hyphae also showed ATPase activity, but the peripheral plant membranes interfacing with these stages of fungal development showed little or none. The only precipitates observed in the absence of ATP were in the fungal vacuoles.

Inhibitors of plasma membrane H+‐ATPase (DES, SW26 and vanadate) greatly reduced the lead precipitate due to ATPase activity on the fungal and plant membranes and completely inhibited its formation in the interfacial matrix. Vanadate has been reported to inhibit ATPases other than the H+‐ATPase, and the other inhibitors may also be less specific than previously believed. Molybdate, which inhibits non‐specific phosphatase activity but not the H+‐ATPase, completely inhibited the interfacial activity but consistently left a fine precipitate along the plant membrane surrounding arbuscular hyphae and on the plasma membrane of intercellular and arbuscular trunk hyphae. Fine arbuscular branches often completely lacked activity after treatment with molybdate. EDTA, which chelates Mg2+necessary for Mg2+‐ATPase activity, and low temperature prevented the formation of membrane‐associated lead deposition in the presence of ATP, although scattered precipitates were formed over the plant and fungal cytoplasm.

Incubation with β‐glycerophosphate of material prefixed with either glutaraldehyde or formaldehyde gave a picture different from that with ATP. Precipitates were heavy along the peripheral host plasma membrane and tonoplast but no or only light enzyme reactions were detected in the interfacial matrix and along the adjacent plant membrane surrounding young arbuscules, increasing in cells where arbuscular senescence was occurring. These enzyme activities were completely inhibited by molybdate but not by DES.

The present observations strongly suggest that plasma membrane H+‐ATPase is a component of the ATP‐hydrolysing activities in host‐fungus interfaces of VA mycorrhiza. Interpretation of the localization of ATPase activities using cytochemical methods is discussed, together with possible changes in the distribution of the enzymes following mycorrhizal infection and their role in nutrient transfer between the symbionts.
Influence of nitrogen on accumulation of isosojagol (a newly detected coumestan in soybean) and associated isoflavonoids in roots and nodules of mycorrhizal and non‐mycorrhizal soybean
Authors: MORANDI D. , LE QUERE J. L.
Published: April 2006

summary

A newly detected coumestan was found to accumulate in roots of soybean (Glycine max. L., var. Amsoy 71), after infection by a vesicular arbuscular (VA) mycorrhizal fungus (Glomus intraradices, Schenck & Smith) and very strongly in nodules after nitrogen application. This coumestan was identified as a 3,9 dihydroxy 10 (γ,γ‐dimethylallyl) coumestan called isosojagol. Three other associated isoflavonoids were analysed: glyceollin I, coumestrol and daidzein. Nitrogen application decreased the concentration of these three compounds in roots, particularly in non‐mycorrhizal soybeans, whilst their concentration in nodules was not significantly affected. VA mycorrhizal infection decreased the accumulation of all the compounds analysed in nodules, although the fungus was never observed inside the nodule, but increased their accumulation in roots.
Mobilization of nitrogen in swards of Trifolium subterraneum L. during regrowth after defoliation
Authors: CULVENOR R. A. , SIMPSON R. J.
Published: April 2006

summary

The net mobilization of nitrogen compounds (total N, soluble protein, amino N, membrane‐bound protein) from different plant parts after defoliation, and the extent to which mobilized nitrogen contributed to new leaf growth, were studied in small swards of Trifolium subterraneum L. cv. Seaton Park (subterranean clover) either completely dependent on nitrogen fixation (‐N treatment) or receiving abundant nitrate at defoliation (+ N treatment).

Net mobilization of nitrogen from nodulated roots (75 % of mobilized nitrogen) and branches (25 % of mobilized nitrogen) accounted for most of the nitrogen in new leaf growth for up to 5 d in – N swards and for at least 2 d in +N swards. In – N swards, nodules degenerating as a result of defoliation were a major source of mobilized nitrogen for 2 d (50 % of mobilized nitrogen), after which the fine roots became the largest net contributor of mobilized nitrogen. Overall, a net 17% of the nitrogen present in residual organs was mobilized.

Soluble protein was the major form of mobilized nitrogen for which assays were performed, accounting for 50 % of the decline in total N in the – N treatment. The relative loss of soluble protein from sward components declined in the order, nodules (47 % over 5 d), fine roots (44 % over 9 d), branches (38 % over 9 d) and taproots (37 % over 5 d). The amino N pool increased sharply in size for two days after defoliation, possibly indicating breakdown of soluble protein in excess of the nitrogen demand for regrowth or to provide a respiratory substrate.

It was concluded that, in plants of adequate nitrogen status, leaf growth was unlikely to be nitrogen‐limited during the first few days after defoliation.
Some aspects of the kinetics of cadmium and thallium uptake by fronds of Lemna minor L.
Authors: KWAN K. H. M. , SMITH S.
Published: April 2006

summary

A study of influx and accumulation of Tl and Cd by Lemna minor has revealed a number of contrasting features which arise from the basic physicochemical properties of the two elements. Short‐term influx of Cd over a range of concentration (0·1–10 üM) followed a linear trend while that of Tl over the same range produced a profile with a plateau at the higher concentrations, indicating saturation of the absorption mechanisms. Application of Ca and K antagonists aiming to indicate the nature of the absorption mechanisms did not reveal any consistent trends. Long‐term exposure of the plant to Cd and Tl produced steady‐state concentrations after 250 and 140 h respectively, by which stage Lemna had accumulated nearly twice as much Cd than Tl. It appears that a significant amount of Cd is probably in the Donnan free‐space and strongly bound to cell constituents from which the element is depurated slowly and continuously in Cd‐free medium. It is concluded that Tl is tenaciously held in the plant tissues, perhaps in the cell vacuole, as 80 % of the steady‐state concentration is retained by the plant even after 140 h in Tl‐free medium. The influence of several external physical and chemical factors further emphasizes the contrasting nature of the two elements; Tl uptake is almost entirely an active process and ion activity of Tl is relatively unaffected by changes in pH and ligand concentration. Cd uptake involves both active and passive components, ion activity is markedly reduced at low H+ion concentrations and in the presence of ligands, such as EDTA. Inhibition of uptake was found for both elements in the presence of competing ions.
Stomatal responses to abscisic acid in three lupin species
Authors: HENSON I. E. , TURNER N. C.
Published: April 2006

summary

Stomatal responses to exogenous abscisic acid (ABA), supplied to detached leaves via the transpiration stream, were examined in Lupinus augustifolius L., L. cosentinii Guss, and L. luteus L. Stomatal closure, indicated by reduced leaf conductance, was induced by ABA in all three species. This confirmed previous work with L. cosentinii, but contrasts with a report of stomatal insensitivity to ABA in L. luteus. Possible reasons for this are discussed.

In all the lupin species, the abaxial leaf surface was more responsive to exogenous ABA than the adaxial surface. Comparable differences were also evident in stomatal closure in response to water deficits. ABA concentrations in abaxial and adaxial epidermal strips were found to be similar and to increase when plants were subjected to water deficits or fed ABA through the petiole. Differences in stomatal density on the two surfaces were consistent with differences in conductance observed between the surfaces of turgid leaves with low ABA levels, whilst the differential sensitivity of the two surfaces to ABA and water deficits may be related to differing amounts of ABA available per stomatal complex. The greater availability of ABA per stomatal complex on the abaxial compared to the adaxial epidermis when the lupins were subjected to water deficits or to exogenous ABA is consistent with the greater sensitivity to water deficits and ABA in abaxial compared to adaxial stomata.
Histological determination of ozone injury symptoms of primary needles of giant sequoia (Sequoiadendron giganteum Bucch.)
Authors: EVANS LANCE S. , LEONARD MICHAEL R.
Published: April 2006

summary

Giant sequoia (Sequoiadendron giganteum Bucch.) is a unique resource that exists only in groves on the western slopes of the Sierra Nevada in California. Since Sequoia and King's Canyon (SEKI) National Parks are experiencing ozone concentrations phytotoxic to some species of Pinus, we performed several experiments on S. giganteum seedlings to determine the ozone sensitivity of their primary needles and their suitability as sensitive bioindicators during the seedlings stage of growth. Current‐year seedlings were fumigated in open‐top chambers during 1986 and 1987. Treatments included (1) carbon‐filtered air (no ozone); (2) ambient ozone; (3) 1.5 times the ambient amount of ozone; and (4) a no‐chamber treatment. In 1986, ozone doses ranged from 100 to 221 ppm h−1while those in 1987 ranged from 125 to 216 ppm h−1. In neither year did the percentages of plasmolysed cells correlate with ozone dose. In 1986, however, the percentages of amorphously stained and dead cells taken together showed a significant (P= 0.028; r2= 0.721) linear response to dose (y = 29.9 + 0.260x). In the 1987 fumigation, there was no significant relationship between ozone dose and the percentage of either amorphously stained or dead cells. The narrow range of ozone doses (from 125 to 216 ppm h−1) and the short duration of exposure (48 d) may have resulted in high percentages of amorphously stained cells (between 61 and 81 %). In both experimental fumigations, higher ozone doses killed more cells in the needles. When data of the percentages of dead cells from both experiments were pooled, there was a statistically significant (P= 0.0036) correlation coefficient of 0.744 with a line slope of y = 2.472 + 0.051x. There was no evidence of a curvilinear response. The overall anatomy of primary needles from SEKI was similar to that of those sampled from the fumigation experiment; SEKI samples exhibited a high degree of amorphous cell staining (between 67 and 81 %). Cell death averaged 5.1% from all the park samples, a percentage within to the range of cell death (0.9–6.2 %) in the ambient air chambers.
Leaf demography and the seasonal internal cycling of nitrogen in sycamore (Acer pseudoplatanus L.) seedlings in relation to nitrogen supply
Authors: MILLARD P. , PROE M. F.
Published: April 2006

summary

The dynamics of the seasonal internal cycling of nitrogen (N) in Acer pseudoplatanus were studied in relation to N supply and leaf demography. Trees were grown in sand culture, and throughout 1988, supplied with either 1.0 mol N m −3(Low N) or 6.0 mol N m −3(High N), labelled with 15N to 5.0 atom %, in order to precondition their growth and capacity for N storage over the winter period. In 1989, the initial spring growth of leaves was independent of the current N supply at either 1.0 or 6.0 mol N m−3, and depended only upon the N supplied in 1988. A net loss of 15N from perennial tissues and recovery of 15N in the growing leaves confirmed that the current N supply had no effect on the remobilization of N from winter stores in the roots and stem. After 22 May 1989, remobilization of stored N for leaf growth had ceased and leaf demography was influenced by the current N supply. Plants preconditioned to 6.0 mol N m −3in 1988, but receiving only 1.0 mol N m−3in 1989, were unable to sustain previous leaf growth after 22 May and there was a decrease in leaf mass and area due to leaf abscission. In contrast, trees preconditioned with 1.0 mol N m−3in 1988, but receiving 60 mol N m−3in 1989 greatly increased their leaf growth after 22 May. This was a consequence of the stimulation by N uptake of growth of many small leaves on axillary shoots at the base of the canopy. Although leaf number increased, mean area per leaf decreased.

The trees were inefficient at withdrawing N from senescing leaves in both years, allowing most of the N to fall from the tree with the leaves. The spring remobilization of N, therefore, was dependent largely upon the direct uptake of N into the stem and roots, in late summer and autumn, for storage over the winter period. The results are discussed in relation to leaf demography and the nitrogen use efficiency of deciduous trees.
Induction of cadmium tolerance by acclimation transferred between ramets of the clonal fern Salvinia minima Baker
Authors: OUTRIDGE P. M. , HUTCHINSON T. C.
Published: April 2006

summary

Changes in the cadmium tolerance of ‘daughter’ ramets resulting from prior acclimation to Cd by ‘parent’ plants were examined in the clonal fern Salvinia minima Baker. In two experiments, parents were acclimated to 0, 10, 25 or 50μg Cd l−1, and subsequently produced daughter ramets in a Cd‐free medium. Parent acclimation to 25μg Cd l1increased the daughter ramets' tolerance index by 13–17% (based on chlorophyll‐a content), while 10μg Cd l−1had no effect. Acclimation to 50μg Cd l−1produced ‘carry‐over’ toxicity (i.e. reduced growth and chlorosis) in daughter ramets in Cd‐free solution. Their tolerance index was 28 % higher than the control when tested with 15 μg Cd l−1in one experiment. In contrast, there was no such increase when they were tested with 25μg Cd l−1in a second experiment. This may be due to the higher Cd concentration in the latter test, combined with carry‐over toxicity, overwhelming induced tolerance. ‘Tolerant’ daughter ramets, which maintained higher chlorophyll concentrations during Cd exposure than control ramets, also grew slower, a seeming contradiction. A possible explanation is that induced tolerance, involving protection of chlorophyll synthesis by phytochelatin binding with Cd, has an accompanying metabolic cost due to glutathione depletion.

These data may be the first evidence of (a) induced metal tolerance in a vascular plant other than grasses, and (b) increased metal tolerance of daughter ramets due to acclimation of their parent clones. In patchily metal‐contaminated habitats, the latter phenomenon may benefit rhizomatous clonal plants over non‐integrated clones or annual plants. Daughter ramets connected to acclimated parents may be more likely to survive in other contaminated patches, increasing the possibility that the clone will grow into uncontaminated areas.
A reassessment of the influence of NAA on aerenchyma formation in maize roots
Authors: JUSTIN S. H. F. W. , ARMSTRONG W.
Published: April 2006

summary

The effect of 1‐naphthylacetic acid (NAA: 10−9to 10−5M) on extension growth and aerenchyma formation in second‐whorl adventitious roots of Zea mays L. (cv. LG11) was examined. Treatments were applied continuously for 12, 8 or 3 d following initial periods in NAA‐free solution. NAA at 10−9M stimulated root elongation, but with increasing concentrations there was a progressive inhibition of growth. Gas space was increased by low levels of NAA and appeared to be reduced by the higher levels. When root length was taken into consideration, however, no NAA treatment produced less aerenchyma than would be expected from control roots of similar length in stagnant NAA‐free media, and there was some evidence that the NAA had promoted aerenchyma formation. Since NAA promotes ethene formation in roots the results would accord with an NAA induced ethene effect.
Aberrant sieve element differentiation in primary leaves of Vigna sinensis Endl. affected by colchicine
Authors: GALATIS B.
Published: April 2006

summary

In primary leaves of Vigna sinensis Endl. seedlings growing in the presence of colchicine, some giant polyploid cells at the phloem pole of the vascular bundles differentiate into an extraordinary cell type acquiring most of the prominent features of the sieve elements. These aberrant sieve elements (a‐SEs) show some exceptional features not found in normal sieve‐tube elements. A heavy secondary thickening is deposited on their walls, which in surface view exhibits a reticulate or ‘pitted’ appearance. The thickenings reach the same depth into the cytoplasm and show a diffuse orientation of cellulose microfibrils. Amorphous callose is deposited around some fine cytoplasmic strands penetrating the secondary wall up to the primary one along the longitudinal and particularly the transverse walls. In the latter walls sieve pores are not formed. At first, the a‐SEs undergo a partial protoplasmic degradation like normal sieve‐tube elements but finally autolyse completely. During this process, the major portion of the unmasked primary and secondary wall is dissolved.

The observations show that (a) a vascular bundle initiation and development proceeds in the affected primary leaves, in the absence of cell divisions.‘Vascular bundles' are formed consisting of a single row of cells, in which a‐SE differentiation dominates. (b) The ‘sieve element differentiation’ is initiated without differential divisions. (c) Although the microtubules arc absent, the cells determined to become a‐SEs activate another morphogenetic mechanism to control a more or less patterned deposition of a secondary wall layer.
Fungal decomposition of attached angiosperm twigs
Authors: GRIFFITH G. S. , BODDY LYNNE
Published: April 2006

summary

Interspecific interactions between fungi frequently isolated (isolation frequency < 5 %) from dead, attached ash twigs were studied on agar and in twigs at different water potentials in the laboratory, and in twig lengths resuspended in the field. Under laboratory and field conditions the following observations were made. The main primary colonizers of dead attached ash twigs, Phomopsis platanoidis Died., Fusarium lateritium Nees. and Sp. 12, did not replace each other. Two of the common secondary colonizers, Libertella fraxinea Oganova and Acremonium sp. A, did not actively replace primary colonizers, except that L. fraxinea partially replaced P. platanoidis when associated with bacteria. The secondary colonizer Peniophora lycii (Pers.) v. Holm & Litsch was, however, more combative and replaced all other species, provided that water potential was not lower than –4 MPa. There was some evidence that under field conditions P. lycii, arriving via the air spora could not replace P. platanoidis or Sp. 12; it apparently required a well established base in the resource. However, it could replace F. lateritium and consequently gain a suitable foothold in twigs naturally colonized in the field. Also, P. lycii demonstrated polar growth in twigs, progressively replacing other species.

Active mechanisms by which fungi could resist replacement included the production of pseudosclerotial plates by P. platanoidis and the production of a volatile antifungal agent by Sp. 12. There was also some evidence that other fungi, in particular F. lateritium, produced diffusible antifungal substances, or altered growth conditions, which inhibited other fungi.
Detection of extracellular cellulolytic and proteolytic activity in ectomycorrhizal fungi and Heterobasidion annosum (Fr.) Bref.
Authors: MAIJALA P. , FAGERSTEDT K. V. , RAUDASKOSKI M.
Published: April 2006

summary

Proteolytic and cellulolytic activities were studied in the ectomycorrhizal fungi Amanita regalis (Fr.) Maire, Paxillus involutus (Batsch ex Fr.) Fr. and Suillus bovinus (L. ex Fr.) O. Kuntze and the necrotrophic root pathogenic fungus Heterobasidion annosum (Fr.) Bref. using plate assays, native gel electrophoresis and substrate gel replicas. All the fungi produced carboxymethyl cellulose (CMC)‐hydrolysing activity. Two CMCase bands were detected in H. annosum and P. involutus and one in A. regalis and S. bovinus. In the plate assays, extracellular proteolytic activity was found in all the fungi and the activities were visualized in H. annosum and A. regalis after native polyacrylamide gel electrophoresis.
Vesicular–arbuscular mycorrhizas respond to corn and soybean cropping history
Authors: JOHNSON NANCY COLLINS , PFLEGER F. L. , CROOKSTON R. KENT , SIMMONS STEVE R. , COPELAND PHILIP J.
Published: April 2006

summary

Communities of vesicular‐arbuscular (VA) mycorrhizal fungi were studied in a long‐term crop rotation experiment at two locations (Waseca and Lamberton, Minnesota, USA). Spores of mycorrhizal fungi were counted and identified in experimental plots with a cropping history of either corn (Zea mays L.) or soybean [Glycine max (L.) Merrill]. Mycorrhizal fungal communities were affected by both location and cropping history. At Waseca, Glomus aggregation Schenck & Smith, G. leptotichum Schenck & Smith and G. occultum Walker spores were more abundant in soil with a corn history than a soybean history, while spores of G. microcarpum Tul. & Tul. exhibited the reciprocal pattern. Approximately 90% of the spores recovered at Lamberton were G. aggregation and did not vary with crop history. However, the spores of three other species: G. albidum Walker & Rhodes, G. mosseae Gerdemann & Trappe, and G. occultum, were more abundant in plots with a corn history than a soybean history. Densities of G. aggretatum spores were negatively correlated with soil pH at Waseca, but were unrelated to pH at Lamberton were the mean soil pH was lower. Our results indicate that mycorrhizal fungal species are individualistic in their responses to cropping history and edaphic factors.
Seed dormancy in Mediterranean Senecio vulgaris L.
Authors: REN Z. , ABBOTT RICHARD J.
Published: April 2006

summary

Fresh seed derived from a Mediterranean population of non‐radiate Senecio vulgaris L. showed strong innate dormancy over a wide temperature range. In contrast, fresh seed of British S. vulgaris exhibited < 80% germination at 20 °C. Dormancy in Mediterranean seed was overcome by: prolonged storage at 15 °C and above; a short stratification treatment (2 wk at 4 °C); prolonged leaching with water; treatment with gibberellic acid (GA3) alone (and with kinetin); and to a lesser extent, by wounding (i.e. removal of a small portion of the fruit and seed coat). A petroleum ether extract from fresh Mediterranean seed strongly inhibited the germination of previously non‐dormant seed (of British origin). This implies that dormancy may be caused by an inhibitor present in the embryo or seed coat which might act by preventing the synthesis or liberation of gibberellins required for germination. The innate dormancy exhibited by seed of non‐radiate Mediterranean S. vulgaris, enables the species to adopt a winter annual life cycle which is typical of Mediterranean ephemerals.
The use of the fluorescent dye, 3,3′‐dihexyloxacarbocyanine iodide, for selective staining of ascomycete fungi associated with liverwort rhizoids and ericoid mycorrhizal roots
Authors: DUCKETT JEFFREY G. , READ DAVID J.
Published: April 2006

summary

The lipophilic fluorochrome 3,3′dihexyloxacarbocyanine iodine [DiOC6(3)], previously used to visualize mitochondria and ER in animal and plant tells, when applied at concentrations of 0.01–5 μg ml−1selectively stains ascomycetous hyphae in ericaeous roots and in the rhizoids of liverworts in the families Lepidoziaceae (both tropical and temperate species), Calypogeiaceae, Adelanthaceae, Cephaloziaceae and Cephaloziellaceae. Basidio‐mycetes forming endophytic associations with liverworts and ectomycorrhizas in seed plants, are stained with DiOC6(3) only at concentrations at and above 50 μg ml−1. VA mycorrhizal fungi in liverworts, pteridophytes and angiosperms fail to stain. Hyphae of the ericoid mycorrhizal fungus, Hymenoscyphus ericae, grown in axenic culture, are stained with much lower concentrations of DiOC6(3) than are those of a range of ectomycorrhizal fungi, an orchid fungus and Oidiodendron griseum which has been reported occasionally to form ericoid mycorrhizal associations. In contrast to other fluorescent probes that recognize fungal wall components, DiOC6(3) is a vital stain of fungal cytoplasm. Greater membrane permeability, compared to that in other fungi, is the likely basis for the selective staining of Hymenoscyphus ericae and the root and rhizoid‐inhabiting ascomycetes with this dye. DiOC6(3) offers a rapid means for identifying intracellular ascomycetous mycorrhizas and for determining the distribution of living hyphae within these associations.
Localization of aluminium in the roots of Norway spruce [Picea abies (L.) Karst.] inoculated with Paxillus involutus Fr.
Authors: HODSON M. J. , WILKINS D. A.
Published: April 2006

summary

Norway spruce [Picea abies (L.) Karst.] seed lots from populations growing on acid soil in the Black Forest (BF), and from a calcareous soil in the Schwäbische Alb (SA), West Germany, were grown in perlite and treated with 0 and 6 mM Al. Some of the plants were inoculated with the fungus Paxillus involutes Fr., while some were not. Fungus was associated with the roots of the inoculated plants, but mycorrhizas did not form.

Mineral element distribution in the roots was investigated using X‐ray microanalysis of freeze substituted sections in TEM. Seven elements were detected: aluminium, silicon, phosphorus, sulphur, chlorine, potassium, and calcium. Aluminium was almost entirely confined to the cortical cell walls, and was not detectable inside the endodermis. The presence of P. involutus significantly increased aluminium concentrations in the cortical cell walls of both seed lots, while silicon concentrations in the aluminium‐tolerant (BF) plants increased in response to aluminium treatment.
Effects of summer ozone on membrane lipid composition during subsequent frost hardening in Norway spruce [Picea abies (L.) Karst]
Authors: WOLFENDEN J. , WELLBURN A. R.
Published: April 2006

summary

Norway spruce trees [Picea abies (L.) Karst] were exposed to ozone during the summers of three consecutive years and the fatty acid composition of the chloroplast membrane lipid, monogalactosyl diglyceride (MCDG) was analysed over the last 14 months. Significant variations in the degree of unsaturation and the percentage of linolenic acid (18:3) were not found, either on a seasonal basis or in relation to ozone treatment. The proportion of octadecatetraenoic acid (18:4) and other Δ5fatty acids increased during autumn in trees grown in filtered air, but this seasonal effect was less pronounced in ozone‐treated trees. The ratio of two forms of linoleate, Δ5,918:2 and Δ9,1218:2 also increased significantly during the frost hardening period but not in trees previously exposed to ozone. This implies that two separate biosynthetic pathways exist, one for the Δ12and one for the Δ12desaturated series, which operate at different relative rates, depending on environmental conditions. It is suggested that ozone may interfere with the biosynthesis of 18:4 during frost hardening by inhibiting the Δ5desaturation of oleate.
Seasonal uptake and allocation of phosphorus in Eriophorum vaginatum L measured by labelling with 32P
Authors: JONASSON SVEN , STUART CHAPIN F.
Published: April 2006

summary

Seasonal measurements of phosphorus (P) pools in the tussock‐forming sedge Eriophorum vaginatum L. indicated low annual P uptake, but pronounced fluxes of P to growing biomass from below‐ground stores in spring, and a return in autumn. Additions of 32P to tussocks in early spring and mid summer confirmed this deduction. Addition of 32P caused a rapid incorporation of about 10% of the labelled P in the tillers within a few days. Subsequent uptake was negligible, presumably because the 32P not immediately absorbed was fixed in the soil and unavailable to plants. This demonstrates that nutrient pulses were more important than steady‐state mineralization in supporting P uptake by Eriophorum vaginatum. After the 32P additions, roots initially retained 60% of the total 32P taken up. During the following weeks, part of the 32P was transported slowly to stem bases and leaf sheaths, the principal storage organs. A lower proportion was transported to the leaf blades. We suggest that storage and recirculation of nutrients are the main sources of the annual nutrient supply to growth of E. vaginatum under normal field conditions, where P fixation in the soil and low rate of P diffusion towards the roots limit P uptake from soil except during periods of pulsed release.
Environmental factors influencing photosynthetic efficiency of the micro red alga Porphyridium cruentum (Agardh) Nägeli in light‐limited cultures
Authors: LEE EDMUND T. Y. , BAZIN MICHAEL J.
Published: April 2006

summary

Steady state growth of the red alga Porphyridium cruentum was obtained in light‐limited chemostat cultures at different temperatures, pH and salinities over a range of specific growth rates. Geometric design of the reactors was found to have no effect on the yield and photosynthetic efficiency (PE) of the biomass. Under optimal growth conditions, that is at 23 °C, pH 8 and NaCl concentration of 0.42 M, the maximum specific growth rate was 0.065h−l which corresponded to a generation time of 10.7 h. With a given light input the biomass output rate was found to be constant over the range of specific growth rates studied. The values of the maximum growth yield (YG) and maximum PE of P. Cruentum were in the range of 0.0064–0.0074 g kj−1 and 13.4–15.5% respectively, when growth was optimal. This PE value corresponds to a quantum demand of 15 per O2 molecule evolved. Different temperatures, pH and salinities were demonstrated to cause a 1.5 to 2‐fold variation in the maximum PE. The maintenance energy was found to be virtually zero under all conditions.
Identification and quantification of trehalose in vesicular‐arbuscular mycorrhizal fungi by in vivo13C NMR and HPLC analyses*
Authors: BÉCARD G. , DONER L. W. , ROLIN D. B. , DOUDS D. D. , PFEFFER P. E.
Published: April 2006

summary

Natural abundance in vivo13C NMR spectra were obtained from spores of three species of VA mycorrhizal fungi: Glomus intraradix Schenck & Smith, Glomus etunicatum Becker & Gerdemann and Gigaspora margarita Becker & Hall. The presence of trehalose was established in the spectra of Gl. etunicatum and Gi. margarita. HPLC analyses supported these observations and indicated that Gl. intraradix spores also contained small amounts of trehalose, not readily detectable by 13C NMR. Trehalose constituted between 0.06% and 1.6 %(w/w) of the spore dry weight, depending on the species. Only trace amounts of other sugars, including glycerol, were detected. An in vivo NMR time course experiment indicated that trehalose was readily utilized during spore germination.
The effect of soil water potential on seedling growth of some British plants
Authors: EVANS CERI E. , ETHERINGTON JOHN R.
Published: April 2006

summary

Seedlings of 15 species from a range of habitats contrasting in soil water status were grown at known soil water matric potentials ranging from near field capacity to the permanent wilting potential (−0.05. −0.5, −1.0 and − 1.5 MPa). Root and shoot growth were differentially very sensitive to soil water matric: potential: root growth continued at lower soil water matric potentials than shoot growth. All Species from drier habitats established better in drier soils than wetland species, with increased root growth in drier soils in contrast to decreased root growth of wetland species in drier soils. Seed size was thought to be an important factor in determining establishment in dry soils; the only wetland species to maintain substantial root growth in dry soils had comparatively large seeds. The seedling growth responses were compared with the same species' germination responses in relation to the above range of soil water matric potentials (established in a previous study). Sensitivity to soil moisture may occur at the germination or seedling stage of growth.
The distribution of planktonic dinoflagellates and their cysts in the eastern and northeastern Atlantic Ocean
Authors: DODGE J. D. , HARLAND R.
Published: April 2006

summary

Data are presented on the distribution of both planktonic dinoflagellates and their cysts from 20° N to 70° N and from the western coasts of Europe and Africa to 25° W in the eastern and northeastern Atlantic Ocean. Although most of the thecate dinoflagellates are widely distributed, sometimes with a discontinuous pattern, the cysts are generally more restricted. There is an increase in the ratio of cyst types to thecate plankton and in cyst diversity from ocean to inshore and from low to high latitudes; in both cases paralleling an increase in diversity of the plankton. Cyst distributions may also be discontinuous, occurring around the British Isles and also in the upwelling area off N.W. Africa. Particular species show similar distribution patterns for cyst and thecae e.g. Polykrikos schwarzii; distribution patterns where the cyst is less widely distributed than the thecae e.g. Spiniferites bentori/Gonyaulax digitalis; and where the cysts are more widespread than the thecae as in the problematical Gonyaulax spinifera‘complex’. Difficulties identified in comparing data sets include the lack of detailed knowledge of dinoflagellate life cycles, the need to know more about environmental parameters affecting encystment, and knowledge of cyst transportation and preservation in sediments. Overall cyst distribution patterns may be compared to the broad coccolithophorid zones recognised in the Atlantic Ocean.
Mechanisms of action of abscisic acid at the cellular level
Authors: HETHERINGTON ALISTAIR M. , QUATRANO RALPH S.
Published: April 2006

summary

Abscisic acid (ABA) has been implicated in the control of a diverse range of physiological processes in higher plants. In this review, we focus on the events which constitute the cellular responses to ABA. Current evidence suggests that it is possible to classify the responses to ABA on the basis of whether they are rapid, involving ion fluxes (typified by the stomatal response), or slower and requiring alterations to gene expression (for example the response of cereal embryos to ABA). In our consideration of ABA stimulus response coupling pathways, we have chosen to highlight the role of the calcium ion in the rapid responses, while we have concentrated on the contribution of as‐acting elements and trans‐acting factors in the regulation of ABA‐responsive genes. We also draw attention to the possibility that interaction may exist between these pathways.

Additionally, we discuss the controls of ABA concentrations during development and in response to environmental stimuli. Factors which contribute to the controls of ABA sensitivity are also reviewed. In our conclusions, we suggest that a general role for ABA may be to prepare tissue for entry into a new and different physiological state, perhaps by resetting the direction of cellular metabolism.

CONTENTS

Summary
9

I.
Introduction
10

II.
Stimulus response coupling
17

Synopsis
27

Acknowledgements
28

References
28
Adaptation of a white clover population to ozone stress
Authors: HEAGLE ALLEN S. , McLUGHLIN MICHAEL R. , MILLER JOSEPH E. , JOYNER RONALD L. , SPRUILL SUSAN E.
Published: April 2006

summary

White clover (Trifolium repens L.) ‘Regal’ and tall fescue (Festuca arundinacea Schreb.) ‘Kentucky 31’ were grown together in a field and exposed for two seasons in open‐top chambers to six ozone (O3) regimes ranging from 0.59 to 1.95 times the ambient O3 concentration. Plants that survived were propagated clonally and used in the present study to determine whether selection for resistance or sensitivity to O3 had occurred. Relative foliar sensitivity of surviving clones to various short‐term O3, exposure regimes was determined with and without infection by several viruses. In tests of all surviving clones with viruses present, higher percentages of clones that survived two seasons at the high O3 levels were resistant to short‐term exposure to O3, than were those that survived exposure to the low O3 treatments. Only one of the 33 clones that survived exposure to charcoal‐filtered air (059 treatment) was O3‐resistant while 19 of the 30 clones surviving the 1.95 treatment were O3‐resistant. Conversely, eight clones that survived the 0.59 treatment were sensitive to O3 while none of those that survived the l.95 treatment were sensitive. The results indicate that selection pressure in the presence of O3 stress was for resistance to O3. Various combinations of five common viruses of clover were present among the surviving clones. Shoot‐rip meristem culture was used to free one O3‐resistant and one O3‐sensitive clone from at) viruses. The relative O3 sensitivity of these two clones was not affected by viruses. Further testing is required to determine the relationships between relative foliar sensitivity to short‐term O3 exposure and relative sensitivity to growth effects caused by long‐term exposure.
Soil nitrogen and chronic ozone stress influence physiology, growth and nutrient status ofPinus taedaL. andLiriodendron tulipiferaL. seedlings
Authors: TJOELKER M. G. , LUXMOORE R. J.
Published: April 2006

summary

The effects of soil nitrogen availability and chronic ozone stress on carbon and nutrient economy were investigated in loblolly pine (Pinus. taedaL.) and yellow‐poplar (Liriodendron tulipiferaL.). One‐year‐old seedlings were planted individually in pots in forest soil of low (58 μg g−1), medium (96 μg g−1) or high (172 μg g−1) initial concentrations of soluble nitrogen. The seedlings were exposed to ozone in open‐top field chambers at sub‐ambient (charcoal‐filtered air), ambient, and elevated (ambient + 60 nl 1−1O3) (32, 56, 108 nl 1−1O3,1h seasonal mean, respectively) levels for 18 weeks. At final harvest loblolly pine dry matter increased by 50% at the highest soil K level relative to the low with the largest gains in new needle biomass. Elevated ozone reduced the biomass of current‐year needles by 20% in plants grown at the highest N level. Higher soil N supply increased the concentration of nitrogen in needles, stimulated current‐year needle photosynthesis and increased needle and whole‐plant water‐use efficiencies. Ozone treatment had no significant effect on photosynthesis or water‐use efficiency in either species, although ozone exposure tended to reduce‐ stomatal conductance in loblolly pine. The low N treatment increased the proportion of dry matter allocated to fine roots in yellow‐poplar, but whole‐plant dry weight had not responded to N fertilization at the final harvest, suggesting other limitations on growth. Ozone exposure increased leaf abscission and doubled leaf turnover m yellow‐poplar. Although yellow‐poplar was highly sensitive to ozone‐induced leaf abscission, final whole‐plant dry weights were not affected. The indeterminate growth habit of yellow‐poplar permitted compensatory leaf growth which may have ameliorated effects of chronic ozone stress on biomass gain. Ozone exposure also decreased shoot weight more than root weight, resulting in higher root:leaf ratios in loblolly pine and a similar trend m higher fine roor:leaf ratios in yellow‐poplar. Greater proportional allocation of carbon to roots in response to nutrient deficiency may preclude an increased allocation to shoots often observed in response to air pollution stress. Interspecific differences in growth response to chronic ozone and nutrient stress may be influenced by differences in leaf growth habit.
Utilization of microbial siderophores by mycorrhizal and non‐mycorrhizal pine roots
Authors: LEYVAL C. , REID C. P. P.
Published: April 2006

summary

In iron‐deficient conditions, most bacteria and fungi are known to release siderophores, iron‐chelating compounds. Most plants do not produce siderophores, but seem to use microbial siderophores as iron sources. Although ectomycorrhizal fungi have been found to release siderophores in pure culture, little research has addressed production by mycorrhizas and the consequences for plant iron nutrition.

The objectives of this study were to determine the effect of an ectomycorrhizal fungus [Pisolithus tinctorius (Pers.) Coker and Couch] on the utilization of siderophore (ferrioxamine B) by slash pine (Pinus elliottii Engelm.) roots grown under iron‐deficient or iron‐sufficient conditions. Experiments were conducted with excised roots and whole seedlings. Uptake of 55Fe from ferrioxamine B was lower by mycorrhizal roots than non‐mycorrhizal roots. Growth under iron‐deficient conditions had little effect on iron uptake by non‐mycorrhizal roots but increased the uptake by mycorrhizal roots. Uptake of iron from a non‐purified siderophore isolated from a pure culture of P. tinctorius was also lower by mycorrhizal roots. The uptake of iron was not dependent on the pH of the uptake solution. Differential responses could be attributed to different mechanisms of iron uptake between fungal cells and root cells. However, the higher iron content of mycorrhizal roots may indicate a negative feedback effect on uptake.