bluuebunny/crossref_metadata_2025 huggingface dataset:
Gaseous ammonia counteracts the response of Scots pine needles to elevated atmospheric carbon dioxide
Authors: PÉREZ‐SOBA MARTA , VAN DER EERDEN LUDGER J.M. , STULEN INEKE , KUIPER PIETER J. C.
Published: April 2006

summary

Four‐year‐old saplings of Scots pine (Pinus sylvestris L.) were exposed for 8 wk in controlled‐environment chambers to charcoal‐filtered air (FA), FA supplemented with 754 mg m−3 (650 μl 1−1)CO2, FA supplemented with l00 μ m13 NH3 and FA+CO2+NH3. Elevated CO2 induced a significant increase in the concentrations of NH4+ and NO3 in the soil solution, while exposure to NH3 enhanced the soil NH4− concentration. Elevated CO2 significantly increased needle biomass and area, and decreased specific leaf are (SLA) and N concentration in the needle. The activity of peroidase (POD) was decreased, while the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were only slightly affected. Gaseous NH3 enhanced the concentration of N. soluble proteins and the GS activity in the needless, while it decreased the POD and GDH activities. The effects of elevated CO2+ NH3 on needle biomass production, N Metabolism and POD activity were smaller than the effects of single exposures to elevated CO2 or NH3. Suggesting that elevated CO2 and NH3 counteract each other and disturb needle physiology. The possible mechanisms underlying the negative interactions of elevated CO2 and NH3 and discussed. The expected stimulation of biomass production by elevated CO2 my be reduced in the presence of atmospheric NH3.
Genotypic and environmental effects on endopolyploidy in the epidermal tissues of Lolium perenne L. and Lolium multiflorum Lam
Authors: GRIFFITHS P. D. , QUGHAM H. J. , JONES R. N.
Published: April 2006

summary

C‐value determinations on nuclei of the adaxial epidermal bulliform cells of leaves of perennial (Lolium perenne) and Italian ryehgrass (Lolium multiflorum) show considerable levels of endopolyploidy. L. multiflorum has more endopolyploidy than L. perenne, and there is an environmental effect which reduces the level of endopolyploidy in L. multiflorum as the temperature is raised.
Changes in gene‐expression in response to sucrose accumulation in leaf tissue of Lolium temulentum L.
Authors: WINTERS A. L , WILLIAMS J. H. H. , THOMAS D. S. , POLLOCK C. J.
Published: April 2006

summary

Sucrose accumulation and subsequent fructan synthesis was initiated in detached, mature leaves of Lolium temulentum by incubating them either in the light or with 200 mM sucrose in the dark. Fructan synthesis was also induced in intact seedlings by lowering root and shoot meristem temperature to 5 °C while maintaining aerial parts of the plant at 20 °C in the light. In this system, subsequent breakdown of fructans was induced by raising root and meristem temperature to 20 °C in the dark. Products of in vitro translations showed that transcripts encoding polypeptides of 17 and 35 kDa increased in sucrose accumulating‐tissue. Transcripts encoding 28 and 32 kDa polypeptide products appeared to be associated with leaf tissue actively exporting carbohydrate. Labelling studies in vivo in mature leaf tissue showed transient increases in the synthesis of polypeptides with MR 59, 60 and 70 kDa during the first 6 h of sucrose accumulation. Polypeptides with an MR of 74 and 27 kDa showed increased amounts later in induction.

Cordycepin and cycloheximide were fed to mature leaf tissue at different stages during induction of sucrose accumulation in the light. Both control and cordycepin‐treated tissue showed higher levels of monosaccharide accumulation compared with cycloheximide‐treated tissue. Cordycepin applied during the first 2 h after excision blocked subsequent synthesis of all fructans. When applied at two‐hour‐stages between 2 and 8 h, subsequent accumulation of 1–kestose occurred without accumulation of higher fructans. Application after 8 h had no effect upon the pattern of fructan accumulation when compared to untreated controls. Application of cycloheximide during the first 8 h following excision blocked all fructan accumulation. Subsequent administration had no effect on the pattern of fructan accumulation. The results are discussed in relation to the changes in gene expression associated with induction of fructan synthesis.
The metabolism of fructans during seed development and germination in onion (Allium cepa L.)
Authors: POLLOCK C. J. , LLOYD E. J.
Published: April 2006

summary

Fructan metabolism was studied during maturation and germination in onion seeds. Fructans formed a significant transient store of carbon during the first 23 d following anthesis with an oligosaccharide distribution which closely resembled that observed in extracts from vegetative tissue. Seed maturation was accompanied by a decline in fructan content and a marked reduction in the number of separable oligosaccharides observed. During imbibition and germination. total fructan contents fell further; however, 4 d after imbibition, there was some elaboration ot higher oligosaccharides. The results are discussed in relation to the activity of the enzymes invoked in fructan metabolism in higher plants.
Response of growth and carbon allocation to elevated CO2 in young cherry (Prunus avium L.) saplings in relation to root environment
Authors: KERSTIENS G. , HAWES C.V.
Published: April 2006

summary

The hypothesis that inadequate rooting volume may reduce the growth stimulation by elevated CO2 in ported tree seedlings and saplings was tested experimentally and by surveying the literature. One‐year‐old cherry saplings were grown for one season in naturally lit growth chambers in eight combinations of CO2 concentration (ambient: ambient+ 250 ppm) and root environment (four types), The latter included (1) moderately restrictive pot volume (41) in combination with two levels of fertilizer addition (la. 1b); (2) 10 l pots with total fertilizer content per pot as in treatment la, and (3) 20 l pots with five plants sharing live times the space and nutrient resources of treatment la. Plants were harvested in April, May, June, August and September. The overall mean effect of high CO2 on plant dry mass by the end of the season was +24%. Interactive effects of root environments and CO2 concentrations on dry mass were not significant at the 5% level, but repealed measurements of basal stem diameter of individual plants indicated a significant impact of root environment on the response to CO2. Overall growth enhancement by elevated CO2 did not differ significantly between harvests, but it tended to increase during the season in those root environments which restricted growth in ambient CO2 most strongly (la and 3). The hypothesis was rejected for this experiment. Leaf area and stem height were not affected by any treatment. The variation of carbon allocation to roots and shoots with plant size was very similar in all treatments. Plants grew faster in elevated CO2 very early in the season, and this resulted in small but significant differences between seasonal patterns of biomass partitioning in ambient and elevated CO2. A survey of 33 studies on growth responses of 47 tree species to elevated CO2 (600–800 ppm) showed that the relative change in biomass was not related to the ratio of plant biomass and pot volume found in either ambient or elevated CO2. We conclude that there is no evidence that inadequate pot volume had a negative impact on the stimulation of growth of true species in elevated CO2.
Effect of magnesium‐deficiency on antioxidative systems in needles of Norway spruce [Picea abies (L.) Karst.] grown with different ratios of nitrate and ammonium as nitrogen sources
Authors: POLLE ANDREA , OTTER TILMAN , MEHNEJAKOBS BEATE
Published: April 2006

summary

The effect of magnesium deficiency and variations of the ammonium to nitrate ratio on chlorophyll, soluble protein and antioxidative systems was investigated in current year's needles of clonal spruce trees [Picea abies (L.) Karst.]. The trees were grown for 1 yr in sand culture with circulating nutrient solutions containing sufficient (0.2 mM) or limiting (0.041 mM) concentrations of Mg. The nitrogen concentration of the nutrient solutions was not varied (5 mM) but the NO3−/NH4+‐ratio was adjusted TO 0.76 in Mg‐sufficient and to 1.86, 0.76 and 0.035 in Mg‐limited plants, Under Mg‐limitation, the chlorophyll, soluble protein and Mg‐contem were lowest in needles of trees supplied with NH4+ and highest in trees supplied with NO4− as major N‐source. Apoplastic peroxidase activities were not affected by changes in nutrition. In total needle extracts, NADH oxidase, ascorbate peroxidase, mimodehydroascorbate reductase, glutatkione reductase and asoorbate content were not, or only little, affected by changes in nutrition, except for trees grown with the highest N4+‐concentrations. Glutathtone content and guaiacol peroxidase were increased in Mg‐deficient needles. Superoxide dismutase activity was decreased in Mg‐limited needles of trees grown with N4+ and increased in needles of trees grown with NO3− as a major N‐source, Except for superoxide dismutase, the activities of antioxidant enzymes and substrates were not correlated with the decree of needle chlorosis. Superoxide dismurase activity was low compared to enzymatic activities involved in H2O2 detoxification. Supposing that the needles suffered from enhanced oxidative stress, these results suggest that scavenging of O2− was a limiting factor in stress compensation rather than the detoxification of H2O2.
Structural aspects of ectomycorrhiza ofPinus pinaster(Ait.) Sol. formed by an IAA‐overproducer mutant ofHebeloma cylindrosporumRomagnési
Authors: GEA L. , NORMAND L. , VIAN B. , GAY G.
Published: April 2006

summary

Mycorrhizas formed onPrinus pinasterby an IAA‐overproducer mutant strain (h1 FIR 4 h1 F1 331) ofHebeloma cylindrosporumare described. The wild strain (hl) was used as reference. The wild type mycorrhiza had a thin mantle and a uniseriate Hartig net, which reached the second layer of cortical cells, as generally described. Conversely, the mutant type mycorrhiza had special features; a large mantle and a highly developed Hartig net (up en seven layers of hyphae in width) which reached the endodermis. Even when the Hartig net was formed of several layers of hyphae, the cortical cells remained alive, indicating that the fungus may aid survival of the host cells. Intracellular hyphae surrounded by invaginated host plasmalemma and by interfacial material, were frequently seen in cortical cells, In this case, both fungal and host cells were alive. Even if the mutant strain is more invasive, the IAA overproduction dries not seem to modify its symbiotic status. It is possible that IAA plays a role in cell wall loosening, allowing the fungus to overcome barriers which normally prevent the invasion of living cortical cells.
Seasonal and geographical variation of terpenes, resin acids and total phenolics in nursery grown seedlings of Scots pine (Pinus sylvestrisL.)
Authors: NERG A. , KAINULAINEN P. , VUORINEN M. , HANSO M. , HOLOPAINEN J. K. , KURKELA T.
Published: April 2006

summary

Variations of terpene, resin acid and total phenolic concentrations in young seedlings of Scots pine (Pinus sylvestrisL.) from nine different seed origins growing in three locations of different latitudes, in Finland and Estonia, were investigated in autumn 1991 and spring 1992. Seasonal variation was remarkable in monoterpene, resin acid and total phenolic concentrations. In spring there was more 3‐carene, α‐pinent. β‐pinene + sabinene and total monoterpenes in pine shoots, and less myrcene and tricyclene compared to autumn. Concentrations of some individual resin acids, levopimaric and dehydroubietic acids, were higher in autumn. The total phenolic concentration was higher in spring. In the most northern location, the concentrations of total monoterpenes and total phenolics were lowest. The total resin acid concentration was highest in the middle location, and individual resin acids, palustric and neoabtetic acids, were more common in the most northern location. Seed origin had no significant effects either to the resin acid or total phenolic concentrations. There were almost equal concentrations of total phenolics and resin acids in northern and southern origins. Instead some individual monoterpenes. limonene, tricyclene, camphene, β‐pinene + sabinene and bornylacetate, were more common in northern seed origins. The results suggest that the origin of the seed material is not so important in affecting the concentrations of secondary compounds as are the environmental factors.
Leaf anatomy, specific mass and water content in congeneric annual and perennial grass species
Authors: GARNIER E. , LAURENT G.
Published: April 2006

summary

Previous experiments have shown that leaf specific mass (LSM: the ratio of leaf dry mass lo area) was lower and leaf water content (LWC) was higher in annuals than in perennials, differences that are more generally found between fast‐and slow‐growing species. Leaf transverse sections of seven annual‐perennial pairs of grass species grown in the laboratory were analyzed to elucidate the anatomical bases of these differences.

Leaf thickness was similar in annuals and perennials, but leaf density was significantly higher in perennials. The proportion of the leaf volume occupied by mesophyll was higher in annuals, at the expense of the three other tissues (i.e. epidermis, sclerenchyma and vascular tissues). The cross‐sectional area of mesophyll cells was higher in annuals than in perennials, but epidermal cell size was similar for both life‐forms.

The ranges of LSM (23.1–49.5 g m −2) and LWC (0.70–0.86 g g−1) displayed by the 14 species were large enough to examine the general relationships between these two parameters and various anatomical characters. LSM was significantly correlated with leaf density, but not with leaf thickness. The anatomical character that best explained interspecific differences in LSM was the volume of cell walls per unit leaf area (approximated by the sum: sclerenchyma + vascular tissues (including its living component) + cell wall components of mesophyll and epidermis). LWC was found to depend on leaf density, and interspecific differences in this parameter were best explained by the proportion of mesophyll protoplast (i.e. proportion of mesophyll minus proportion of mesophyll occupied by cell walls) in the transverse sections.

The physiological and ecological implications of these findings are discussed in terms of a trade‐off between leaf productivity and persistence.
The Late‐Quaternary vegetational history of Loch a'Bhogaidh, Rinns of Islay S.S.S.I., Scotland
Authors: EDWARDS KEVIN J. , BERRIDGE JAMES M. A.
Published: April 2006

summary

Holocene and partial Lateglacial age percentage and concentration pollen diagrams are presented of two profiles from the Inner Hebridean site of Loch a'Bhogaidh, Islay. The Lateglacial deposits may extend back to Lateglacial Interstadial times and a relative lack of Juniperus communis pollen is noted. The early Holocene deposits contain abundant Betula and Corylus avellana‐type pollen, followed by substantial amounts of pollen from other arboreal taxa, namely Pinus Sylvestris, I Ulmus, Quercus, Alnus glutinosa and Salix. There is pollen, charcoal and sedimentary evidence for possible Mesolithic age environmental impacts, and a hunter‐gatherer presence on Islay may date from the 10th millennium BP. Major woodland clearance dates from middle Bronze Age runes onwards (c. 3610 BP) and involved a mixed farming regime. The later Holocene records show that soil deterioration was occurring as heath and acid grassland taxa become prominent. These events may have resulted from land use pressures or climate change.
The Late‐glacial and Holocene vegetation of the Lang Lochs Mire area, Gulberwick, Shetland: a pollen and macrofossil investigation
Authors: HULME P. D. , SHIRRIFFS J.
Published: April 2006

summary

A radiocarbon dated pollen and macrofossil record from Lang Lochs Mire, Shetland, is presented. Late‐glacial minerogenic and early Holocene gyttja sediments underlie mid and late Holocene peal. These indicate that the area was free from ice sometime before 13000 BP and there is evidence for a typical Devensian Late‐glacial climatic sequence as recorded elsewhere in Scotland.

Until c. 10 500 BP an open vegetation with abundant masses amongst dwarf shrubs and herbs characterized the surrounding area. At c. 10500 BP gyttja deposition started, aquatic plants became abundant in the loch and Betula woodland developed around the loch. From r. 9700 BP to C. 7700 BP Corylus was also important. During this rime Alnus, Quercus and Ulmus pollen values rose but remained compatible with a long distance source for the pollen.

At c. 7700 BP gyttja deposition ceased at the sample site and a poor fen developed. Around this, heathland and blanket peat vegetation started to develop from c. 7000 BP. By c. 6000 BP the area was largely treeless and after c. 5000 BP blanket peat spread and eventually dominated all but the steepest slopes.

Pollen profile changes after c. 4500 BP can be attributed to either the spread of blanket peat or the effects of Neolithic peoples. The changes coincide with the arrival of Neolithic people elsewhere in Shetland. The first clear indication of Neolithic activity is dated to c. 3000 BP and coincides with increased activity in agriculturally more favourable areas of Shetland.

Records of phytogeographically significant species are discussed and the value of combined macrofossil and pollen investigations is illustrated. The combined approach has helped to distinguish site and regional components of the pollen rain, the vegetational development of both the site and the surrounding area and has given a more accurate record of the occurrence of a number of taxa than could be achieved by pollen analysis alone.
Diffusion of CO2and other gases inside leaves
Authors: PARKHURST DAVID F.
Published: April 2006

Diffusion of CO2in the intercellular airspaces of the leaf mesophyll is one of the many processes that can limit photosynthetic carbon assimilation there. This limitation has been largely neglected in recent years, but both theoretical and empirical evidence is presented showing that it can be substantial, reducing CO2assimilation rates by 25% or more in some leaves. Intercellular diffusion is fundamentally a three‐dimensional process, because CO2enters the leaf through discrete stomata, and not through a uniformly porous epidermis. Modelling it in one dimension can cause major underestimation of its limiting effects. Resistance and conductance models often fail to account well for the limitation, in part because they are usually one‐dimensional representations, but also because they treat continuously interacting processes as if they were sequential. A three‐dimensional diffusion model is used to estimate the intercellular limitation in leaves of different structural types. Intercellular gaseous diffusion probably limits CO2assimilation by at most a few percent in many of the agricultural plants commonly studied by laboratory physiologists, as they usually have thin, amphistaomatous leaves. However, it may cause substantial limitations in the thicker, often hypostomatous leaves of the wild plants that occupy large areas of the earth. Several physiological implications of intercellular diffusion are discussed. I close by reiterating published suggestions that the gas‐exchange parameter commonly termed pishould be renamed pes(es for evaporating surfaces) to avoid the confusing implication that p1, is‘the’intercellular CO2pressure.

ContentsSummary449I.Introduction450II.Theory of intercellular gaseous diffusion451III.Evidence regarding intercellular gaseous diffusion hmitations461IV.Discussion of assumptions made in §11.1470V.Physiological implications of intercellular gaseous diffusion471VI.Conclusions475Acknowledgements476Appendix, Example showing breakdown of resistance analogy for diffusion with distributed uptake476References477
Annual carbon balance and nitrogen‐use efficiency in tropical C3 and CAM epiphytes
Authors: ZOTZ GERHARD , WINTER KLAUS
Published: April 2006

Over the course of 12 months, diel (24 h) measurements of gas exchange were performed on leaves of three epiphytic species growing in the crown of a kapok tree on Barro Colorado Island, Panama: a drought‐deciduous orchid with the C2, pathway (Catasetum viridiflavum Hook.), an evergreen C2 fern (Polypodium crassifolium L.), and an evergreen epiphyte with an intermediate C3‐C3‐CAM pathway of photosynthesis (Clusia uvitana Pitt.), The gas exchange characteristics of all three species; were strongly affected during the four‐month dry season. Compared with the rainy season, mean daily carbon gain of Clusia uvitana was reduced by almost 40° paralleled bY a strong decrease in daytime CO2 uptake and an increase in CO2 uptake at night. The orchid, growing new leaves in the second half of the dry season, showed markedly decreased stomatal conductances and greatly reduced carbon gain. In the fern, daily carbon balance became negative during the dry season and chronic photoinhibition was indicated by reduced FV/FM ratios and a decreased photon‐use efficiency of photosynthetic O2 evolution. Annual carbon gain was similar far the three species (about 10002 CO2 m‐2 yr‐1) as was long‐term nitrogen‐use efficiency (annual carbon gain/mean leaf nitrogen content, about 1·1 g CO2 mg N‐1 yr‐1). In the C3CAM epiphyte, the long‐term water use efficiency of net CO2 uptake was more than twice as high as in the two C3 epiphytes.
Effects of exposure to ozone and water stress on the following season's growth of beech (Fagus sylvatica L.)
Authors: PEARSON M. , MANSFIELD T. A.
Published: April 2006

Bud break and growth of beech trees were measured during the growing season of 1992. The trees had previously been exposed, through the growing season of 1991, to one of four treatments: (1) episodic ozone for 128 d, total dose = 46‐3 ppm h; (2) air purified by filtration through Purified and charcoal; (3) ozone together with a period of water shortage: (4) filtered air with a period of water shortage.

Despite uniform growth conditions during 1992. the previous water stress treatment caused bud break to begin slightly earlier, but the rates of shoot growth and the length of the first flush branches were reduced (40%). In well‐watered plants ozone caused a reduced Tate of shoot growth during the first week after bud break. The total amount of growth during 1992 was shown to be reduced (36%) by the previous water stress treatment, In the case of the well‐watered trees, exposure to ozone in the previous year reduced the amount of new growth by 17%, which was the result of reduced internal expansion. When ozone was combined with water stress, there was no further reduction in the amount of new growth, but there was a fall in the number of internodes relative to water‐stressed plants grown in filtered air.

Ozone and water stress applied singly reduced growth. A combination of the two stresses, however, caused no additional reduction in growth, but reduced the number of internodes. The possible implications of the aftereffects of these stresses are discussed in relation to reduced productivity and canopy structure.
Simultaneous eutrophication and acidification of a forest ecosystem in North‐East France
Authors: THIMONIER A. , DUPOUEY J. L. , BOST F. , BECKER M.
Published: April 2006

Surveys of ground layer vegetation are a reliable tool for monitoring spatial and temporal variations of the forest environment. In 1991, 47 vegetation plots first sampled in 1972 in a forest of the Lorraine Plain, North‐East France, were resampled. This beech–oak forest had both acidic and calcareous soils depending on the thickness of alluvial deposits above the calcareous bedrock. The mean number of species per sample increased from 32 to 39 during this period and the frequency of nitrophilic species increased throughout the forest. On acidic soils, acidophilic species increased in frequency, while on calcareous soils there were no systematic changes. Multivariate statistical analysis clearly distinguished two gradients in this set of vegetation samples: acidity and nitrogen availability of soils. Along the first gradient, a shift of the plots towards a more acidic state occurred during the past 19 years on acidic soils only. Along the second one. a strong eutrophication happened on both acidic and calcareous soils, indicating an enrichment in nitrogen of forest ecosystems. Possible causes of these changes are discussed, namely sylviculture changes, aging of the stands and pollution. Atmospheric nitrogen inputs seem to be the most probable cause of eutrophication.
The control of cell expansion in roots
Authors: PRITCHARD JEREMY
Published: April 2006

The expansion of roots is considered at the level of the single cell. The water relations of cell expansion are discussed. Water entry, solute import and cell wall properties are considered as possible regulatory points. It is argued that root cell expansion can be understood in terms of cell turgor pressure and the physical properties of the cell wall, provided solute supply is not limiting. Various measurements of cell wall properties in roots are presented and the assumptions underlying their measurements are presented. It is concluded that cell wall properties must be measured over short time periods to prevent alterations in wall properties during the experiment. The radial location of the load‐bearing layers is discussed and it is concluded that, unlike aerial tissue, growth is limited by the properties of the inner layer of the root cortex. Evidence is presented to show that cell wall properties can change both during development and following turgor perturbation. In general, however, turgor itself is tightly regulated, particularly towards the root tip. A number of environmental situations are presented in which root growth is altered. The mechanism of the alteration is discussed at the single cell level. These 'stresses’include osmotic stress, low temperature and soil compaction. In many cases the alteration of root growth is consistent with changes in the ceil wall properties of the growing ceils. Severe stress, resulting in near cessation of root cell extension, can result in a change (usually an increase) in turgor pressure. The change in turgor pressure of the cells in the growing zone is smaller than that which would be expected from a continuation of an unstressed solute import rate. This exemplifies both the change in cell wall properties and the tight turgor homeostasis of root tips.

The biochemical processes which underlie the modulation of cell wall properties are presented as they are currently understood in roots. Measurements of the chemical composition of the wall have not revealed any useful differences which can explain the developmental or stress‐induced changes in cell wall properties. Recent work on cell wall enzymes and proteins may provide information about control of cross‐linkages within the wall.

In the last section the relative importance of apoplastic and symplastic solute transport to the expanding cells is considered. At present the consensus appears to favour the symplastic route, but the apoplastic pathway may also operate, possibly as a scavenging mechanism for leaked ions. The regulation of turgor pressure by linking solute import with wall loosening is discussed.

Contents

Summary
3

I.
Introduction
4

II.
Factors controlling cell expansion
4

III.
Wall extensibility and yield threshold in roots
6

IV.
Environmental effects on root cell expansion
10

V.
Modification of cell wall biochemistry
15

VI.
Linkage of growth with solute import
18

VII.
Future prospects
21

VIII.
Acknowledgements
22

IX.
References
22
Influence of the host on three sub‐Arctic annual facultative root hemiparasites
Authors: SEEL W. E. , PRESS M. C.
Published: April 2006

Light saturated rates of photosynthesis (Asat), water use‐efficiency (WUE) and photosynthetic nitrogen use‐efficiency (PNUE) were measured for three sub‐Arctic annual root hemiparasites (Rhinanthus minorL.,Euphrasia frigidaL. andMelampyrum sylvaticum L.)growing in the Torneträsk region of Swedish Lapland. Photosynthesis and resource use‐efficiency of the hemiparasites were dependent on (i) attachment to a host and (ii) the nature of the host to which attachment was made. The highest rates ofAsatwere recorded in those hemiparasites attached to legumes and the lowest rates were recorded in those which were not attached to a host. Intermediate rates of Asatwere recorded in hemiparasites attached to grasses. Asatand leaf conductance were more closely related in attached than in unattached hemiparasites, WUE was greatest in those hemiparasites attached to legumes, but was not a simple function of nitrogen supply. PNUE was greater in attached than in unattached plants, but was inversely related to the total‐nitrogen concentration of the leaves. In an earlier paper we demonstrated that the growth of these hemiparasites is highly host dependent. Here we demonstrate that the carbon, nitrogen and water relations of these plants are also highly host dependent.
Heavy metal accumulation and tolerance in British populations of the metallophyte Thlaspi caerulescens J. & C. Presl (Brassicaceae)
Authors: BAKER A. J. M. , REEVES R. D. , HAJAR A. S. M.
Published: April 2006

Heavy metai uptake, accumulation and tolerance were investigated in five British populations of the metallophyte Thlaspi caerulescens from metalliferous sites from the north and south Pennines orefields. Analysis of field samples showed mean shoot Zn, Pb and Cd concentrations of up to 21000, 660 and 164/zMug g‐1 respectively. A solution culture experiment designed to investigate both tolerance and metal accumulation is reported. Indices of tolerance of five populations to 12 metals (Ag, Al, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Zn) showed few population differences but unexpectedly high tolerance to metals not present at elevated concentrations in the parent soils. This was paralleled by exceptionally high uptakes of all metals studied. Zn, Cd, Co, Mn and Ni were readily transported to the shoot whereas Al, Cr Cu, Fe and Pb were predominantly immobilized in the roots. The data suggest common mechanisms of absorption and transport of several metals in this species.
Causal mechanisms by which sulphate, nitrate and acidity influence frost hardiness in red spruce: review and hypothesis
Authors: SHEPPARD LUCY J.
Published: April 2006

This paper summarizes results from four experiments in which red spruce seedlings(Picea rubensSarg.) were exposed to simulated acid mist containing SO42‐, NH4‐, NO3‐and H+ions. Seedlings were grown in compost, with or without fertilizer, in charcoal filtered air in open‐top chambers near Edinburgh, Scotland. Plants were sprayed from bud burst between May and November with mist containing different concentrations and combinations of the four major ions to provide a range of doses, which were applied at different frequencies.

Reductions in frost hardiness expressed in terms of the temperature which killed 50% of shoots (LT50) were significantly correlated with the dose of S received by the seedlings. Differences in foliar S concentrations between the controls and treated plants were correlated with S dose. Absolute S concentrations were, however, of limited use for predictive purposes.

Seedlings appear to be more sensitive than older trees to S toxicity because the former have the greatest proportion of newly expanding needles which optimize conditions for foliar uptake. Seedlings are also least well equipped to export SO42‐ions since they have a smaller resource of older foliage to supplement their assimilate pool.

In conditions which promote uncontrolled SO42‐ion uptake byfoliage, i.e. high external SO42‐concentrations and incompletely formed cuticles, the potential exists for the internal build up of SO42‐ions. It is proposed that in the absence of sufficient assimilate and K the presence of these high concentrations of SO42‐ions in the apoplast or cytosol can lead to protein denaturation and loss of membrane integrity. Reductions in frost hardiness appear to result through direct attack by SO42ions on membrane proteins which impairs their function. Indirect effects on hardiness occur through both an increased consumption of sugars reducing the‘pool’available for cryoprotection and a reduction in photosynthetic function, the ability to produce sugars. The presence of NO3‐N mitigates the toxic effects of SO42because SO42ions are consumed in assimilation processes which both utilize and are facilitated by the presence of large amounts of fertilizer N. High concentrations of SO42and H+ are found to be particularly toxic because of the synergistic effects these ions exert on their mutual uptake with devastating consequences for the control of cellular pH.

Trees growing at high altitude sites are likely to be particularly sensitive to SO42‐toxicity because (1) their carbon balance is low, (2) cuticle development is poor and (3) levels of soil available Ca2tend to be low relative to Al3+so that membranes may already be weakened as a result of insufficient Ca2+ions for protein bridging.
The significance of nodal rooting in Trifolium repens L.: 32P distribution and local growth responses
Authors: KEMBALL W. D. , MARSHALL C.
Published: April 2006

The distribution of 32P from single nodal roots, and the consequences of nodal rooting on local growth characteristics were investigated in order to evaluate the importance of nodal rooting in Trifolium repens. The movement of radiophosphate was mostly acropetal, and the principal sinks were the closest components to the supplied root. The branch stolon originating from the same node as the root was the mast significant sink, and its importance as sink increased the older and larger it became. Nodal rooting on the main stolon resulted in a localized increase in secondary branching on the primary branch originating from the same node. The results are discussed in terms of physiological integration in T. repens and other clonal plants.
Effect of indigenous arbuscular mycorrhizal endophytes on the development of six wild plants colonizing a semi‐arid area in south‐east Spain
Authors: ROLDAN‐FAJARDO B. E.
Published: April 2006

The effect of arbuscular mycorrhizal fungi (AMF) an six plant species that frequently grow in areas of Mediterranean climate in south‐east Spain was studied. In semi‐arid soils, the most abundant AMF was Glomus aggregation Schenck and Smith, followed by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe. The vascular plant species studied were Dittrichia viscosa (L.) W. Greuter (Asteraceae); Dactylis glomerata L., Piptatherum miliaceum (L.) Cosson, and Slipa tenacissima L. (Poaceae); Retama sphaerocarpa (L.) Boiss., and Ulex parviflorus Pourret (Fabaceae). Legumes were studied with single and dual symbiosis (Rhizobium and AMF). In a greenhouse experiment, inoculated plants developed better than noninoculared controls, as shown by dry weight and tissue N and P content. Plants inoculated with G. aggregation grew better than plants inoculated with G. mosseae. For this reason G. aggregatum was chosen for a field experiment, in which this AM fungus increased shoot dry mass, shoot length, and percent survival after transplantation. The effects of soil microorganisms on development, survival and fertility of native plants, their influence on the effects of the erosion, and their importance in plant repopulation programmes are discussed.
The role of the extracellular sheath in recognition and attachment of conidia of Discula umbrinella (Berk. & Br.) Morelet to the host surface
Authors: VIRET OLIVIER , TOTI LUIGI , CHAPELA IGNACIO H. , PETRINI ORLANDO
Published: April 2006

The role of the conidial sheath in the recognition process and in the attachment of conidia of the beech endophyte, Discula umbrinella, to the host surface was investigated. After treatment of conidia with different lectins the adhesion of conidia to the host surface was effectively inhibited. A strong fluorescence was observed after treatment of conidia with TRITC‐labelled concanavalin A. Fluorescence with TRITC‐labelled wheat germ agglutinin was observed only on spores subjected to enzymatic digestion with proteases. Observations with the transmission electron microscope (TEM), after labelling sections with colloidal gold conjugated lectins, confirmed the presence of mannose and/or glucose in the extracellular sheath. Chitin was present in the conidial ceil wall but not in the extracellular sheath. Enzymatic treatment of the conidial sheath resulted in strongly reduced attachment and changes in the binding of fluorescence‐labelled lectins. TEM studies of partially digested conidia revealed that snail enzyme modified only slightly the structure of the sheath, while proteases completely dissolved the fibrillar sheath leaving a comparatively smooth cell wall with no fibrillar structures on its surface. We conclude that a proteinaceous sheath is responsible for the adhesion of Discula umbrinella conidia to the host and that glycoproteins are involved in the recognition and attachment process. This attachment mechanism closely parallels the only other recognition system studied biochemically in endophytes, and is similar to the few analogous cases studied in plant‐pathogenic fungi, pointing to the functional relatedness of endophytic and pathogenic interactions.
Atypical, green leaf blotch lesions on barley leaves infected by Rhynchosporium secalis (Oud.) Davis
Authors: DAVIS HELENA , FITT B. D. L. , EVANS R. L.
Published: April 2006

Atypical, green leaf blotch lesions were observed on senescent leaves in winter barley crops and sometimes developed on barley leaves inoculated with conidia of Rhynchosporium secalis in a glasshouse. Similar atypical lesions were induced on barley leaves inoculated with conidia of R. secalis and then grown in controlled environments at 10 °C and 80% rh. Microscopic examination of green lesions from these three sources showed that hyphae of R. secalis had colonized the subsidiary cells of stomata so that guard cells were swollen, resulting in enlarged stomatal pores. Additionally, spore initials had erupted through the leaf cuticle of some leaves. Most spore initials did not develop into mature conidia when leaves were incubated for 24 h at 20 C in a closed chamber at l00% rh, but aerial hyphae grew out from the leaf surface. Thus, atypical green lesions produced a much smaller number of spores than typical leaf blotch lesions.
An epidemiological study of Puccinia punctiformis (Str.) Röhl as a stepping‐stone to the biological control of Cirsium arvense (L.) Scop.
Authors: FRANTZEN J.
Published: April 2006

The infection cycle of the autoecious rust fungus Puccinia punctiformis on the clonal plant Cirsium arvense was described in terms of intensity (amount of pathogen per unit area and used for systemic infection) and extent (area occupied by the pathogen and used for local lesion infection) at four grassland sites in The Netherlands. The incidence of systemic infection was relatively low and systemically infected shoots were typically concentrated at a few locations within a site. Incidence of local lesion infection was relatively high and widespread in ail sites. Spatial and temporal distribution of teliospores, the inoculum for systemic infection, were quantified in order to explain the relatively low and spatially unequal incidence of systemic infection. Because of the large impact of systemic infection on C. arvense shoots, it is concluded that a spatially homogeneous distribution of teliospores may be a prerequisite for the biological control of C. arvense by P. punctiformis.
Chitinase and peroxidase activities are induced in eucalyptus roots according to aggressiveness of Australian ectomycorrhizal strains ofPisolithussp.
Authors: ALBRECHT C. , BURGESS T. , DELL B. , LAPEYRIE F.
Published: April 2006

Peroxidase and chitinase activities were measured in roots ofEucalyptus globulussppbicostataKirkp. during colonization byPisolithussp. isolated from underEucalyptus.Ten fungal isolates, ranging from poor to good root colonizers, were selected to represent a range of ectomycorrhizal aggressivity. The induction of chitinases and peroxidases was strongly related to the aggressiveness of the fungal strain. Only good colonizers, that is strains which rapidly form differentiated ectomycorrhizas, induced a strong response in the plant. Therefore, it can be concluded that these enzymes are not responsible for poor root colonization by the less aggressive strains. The chitinase response ofEucalyptusroots to contact with fungal extracts differed only slightly between weakly and strongly aggressive strains. This suggests that a major component of differential induction observedin vivois the consequence of root colonization, tissue penetration and the ability to deliver elicitors to the plain print to and during rant colonization
Spatial distribution of mycelia of the liana (L‐) biotype of the agaric Crinipellis perniciosa (Stahel) Singer in tropical forest
Authors: GRIFFITH G. W. , HEDGER J. N.
Published: April 2006

A detailed investigation of the Liana biotype (L‐biotype) of Crinipellis perniciosa (Stahel) Sing, was conducted in Ecuador. Basidiocarps of the L‐biotype were consistently found in association with stems or debris of the liana Arrabidaea verrucosa (Standl) A. Gentry, although no symptoms associated with witches’broom disease, were observed. Debris colonized by the L‐biotype were often connected via pseudosclerotial pads to living sterns of A. verrucosa. Pairings between 87 isolates obtained from basidiocarp stipe tissues or liana bark cores from three sites permitted 37 somatic compatibility groupings (SCGs) to be defined. In all cases these were found to be very restricted in geographical distribution, a situation which contrasts markedly with the distribution of SCGs in the pathogenic and non‐outercrossing eocoa biotype. Mating pairings between single basidiospore isolates confirmed chat the outercrossing mechanism of the L‐biotype is muitialletic and that no significant biological barriers to gene flow exist between coastal and Amazonian populations. Several lines of evidence suggested that mycelia belonging to the same SCG (= genet) were isogenic. Correlations between field observations and the distributions of both SCGs and mating type factors art‐ discussed in relation to patterns of dispersal, establishment and spread of this fungus.
Elevated CO2, water relations and biophysics of leaf extension in four chalk grassland herbs
Authors: FERRIS RACHEL , TAYLOR GAIL
Published: April 2006

Diurnal measurements of leaf or leaflet, extension, water relations and cell wall extensibility (ø) were made on young growing leaves of four chalk downland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vulneraria L. and Plantago media L.) growing in controlled environment cabinets and exposed to either ambient or elevated CO2. This study revealed differences in that effect of CO2 and the‐ control of leaf growth between the four species. Leaf extension rate (LER) increased significantly at night (average over 8 h) in elevated C02 for S. minor A. vulneraria and P. Media with a significant increase over the first 4h of darkness for S. minor, L, corniculatus and P. media, whilst for S. minor and P. media average day‐time LER (over 16 h) also increased significantly in elevated CO2, as compared with ambient CO2. Water potential (ψpS), solute potential (ψpS), turgor pressure (P), yield turgor (Y) and the effective turgor for growth (Pe) were measured using psychrometers. Bollrte potentials of s, minor, A. vulneraria and P. media decreased significantly following exposure to elevated co2 with a Significant reduction in ψpS, during the day in A. Vulneraria. Turgor pressure increased significantly in elevated CO2 as compared with ambient CO2 in A. vulneraria but there was no effect of elevated CO2 on P in the uther species. effects of CO2 on ψpS; or ψpS; were observed, Leaf cell wall extensibility (ø) increased significantly in leaves of V. minor, L. corniculatus and P. exposed to elevated Co2. whereas in A. vulneraria, there was no effect of CO2 on extensibility.

These results suggest that the mechanism by which elevated CO2 promotes leaf growth differs between species arisce in S. minor, L. corniculatus, and p media. CO2 through an influence on cell wall properties, whist in A vulneraria higher values of P explain that increased leaf growth in elevated CO2 for this species.
Accumulation of ABA in maize roots in response to root severing
Authors: ZHANG JIANHUA
Published: April 2006

When isolated maize (Zea mays L.) routs were incubated tW 3 h in o fully hydrated state in air, ABA content was found to increase by around 100% in nil the different root tissues examined ‐ i.e. mature primary root sections. young and growing primary root sections, secondary roots and primary root tips ‐ from both well watered plants and previously droughted plants. This ABA increase was not turgor‐related, as usually is the case in draughted plants, and was not quantitatively related to the injury in the cutting surface. A time‐ sequence of ABA accumulation showed a peak accumulation at about 2–3 h after initial incubation. Oxygen was essential for this increase in ABA accumulation because‐ when roots were incubated in pure nitrogen, no such increase was found. Evidence suggests that this increase was derived from xanthophylls. the common precursors for stress‐induced ABA.

Maize leaves did not show such an accumulation when incubated under the same conditions. When halt the root system was severed, ABA content in the remaining half root system increased by Kill 100–200% in 3 h. We suggest that there is a systemic effect on the ABA biosynthesis in the root system following the shock of root severing, and that roots may supply substantial amounts of ABA to the shoots even at time when there is not apparent dehydration.
The epidermal surface of the maize root tip
Authors: ABEYSEKERA R. M. , MCCULLY M.E.
Published: April 2006

The surface of the young epidermal cells of maize roots is composed o) three layers; the inner layer (LI), which is the outer epidermal Wall, overlaid by a pellicle consisting of a thick, coherent inner layer (L2) and a very thin, loosely organized outer layer (L3). The entire surface can be removed intact to produce either narrow, circumferential strips or apical halftones, by gently prying it loose in the circumferential direction by hand with insect pins. Usually only short remnants of anticlinical walls of the epidermal cells remain attached. These isolated surface pieces always curl outward at the free circumferential edges in the longitudinal direction of the original intact root. When the strips are deliberated stretched alone their long axis (i.e., the original circumferential direction) they elongate irreversibly by us much us two thirds of their length, before showing some elastic deformation and breaking. Some plastic deformation may occur in the original longitudinal direction of the root during removal of the strips. The plastic deformation opens the helicoidal array of microfibrils in the L1 layer. Deformation also produces structural changes over the original radial walls and those transverse anticlinal walls that form boundaries of cell packets derived from single cells. In these positions the L1 layers over adjacent cells separate in the direction of the applied stress. This occurs by the separation of the L I layers of adjacent cells and the stretching of the inward projection of the amorphous L2 layer of the pellicle which lies; over these original anticlinal walls. There is much less or no separation of the L1 layers over anticlinal walls Of adjoining daughter cells in the epidermis.

The pellicle always remains firmly attached to the outer epidermal wall during removal of the surface strips. On removal, these strips shorten in their original longitudinal direction in situ, indicating a release of tension imposed by underlying cells. Their outward curling suggests stress between the wall and pellicle of the outer epidermal surface in the intact root.

These findings focus attention on structural differences between sites where anticlinal walls of different origin join the outer surface, and on possible differences in surface extensibility at each sites.