bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of repeated nitrogen fertilization on mycorrhizal infection in heather [Calluna vulgaris (L.) Hull]
Authors: CAPORN S. J. M. , SONG W. , READ D. J. , LEE J. A.
Published: April 2006

summary

The effects of repeated nitrogen fertilization over three years (1989–92) on mycorrhizal infection of Calluna vulgaris (L.) Hull growing in peat soils in north Wales are described. Solutions of NH4NO3 were added at regular intervals (10 to 20 times annually) to provide 0, 40, 80 or 120kg N ha−1 a−1 above background deposition. An estimate of mycorrhizal biomass in washed roots from soil cores sampled in May and July 1992 was gained by determining the concentration of ergosterol, a fungal metabolite, in ethanol extracts. The concentrations of ergosterol (per mg fresh weight) were significantly greater in fine hair roots than in thicker roots and also higher in surface horizons than deeper in the soil core. In May, the only significant effect of nitrogen application was found in the fine roots in the surface (0–15 mm) soil. In this fraction, ergosterol was significantly higher in the plots which received 80 kg N ha−1 a−1 plots than in all the other treatments. However, in July the ergosterol concentration in the fine, surface root fraction were not changed by the nitrogen additions. No changes were observed in the soil nutrients (total N and P, extractable base cations) or surface pH, but nitrogen fertilization did stimulate shoot growth, flowering and litter production. Nitrogen concentrations in living shoots and litter were raised as a result of the N inputs while the levels of other main nutrients P and K were not altered. Given the relatively small changes measured in the amount of mycorrhizal infection in the recent experiment, this measurement may be a poor indicator of excess atmospheric nitrogen deposition to heathlands soils.
Functional compatibility in arbuscular mycorrhizas measured as hyphal P transport to the plant
Authors: RAVNSKOV S. , JAKOBSEN I.
Published: April 2006

summary

The functional compatibility of symbioses between host plants and arbuscular mycorrhizal fungi was measured as hyphal P transport to plants. Cucumber (Cucumis sativus L.), wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) were inoculated with Glomus caledonium (Nicol. & Gerd.) Trappe & Gerdemann (isolate RIS42, BEG 15) and Glomus invermaium Hall (isolate WUM10) or left uninoculated and grown for 28 days in soil divided into three compartments. One side compartment was separated from the main compartment by a 20 um nylon mesh, and radioactive labelling with 32P was used to determine hyphal P uptake. The other side compartment was separated from the main compartment by a 700 um nylon mesh and 33P was used to determine the combined P‘uptake by roots and hyphae.

All plant‐fungus combinations were compatible with respect to mycorrhiza formation, measured both as root colonization and growth of external hyphae. In contrast, the symbioses differed markedly with respect to functional compatibility as phosphorus uptake by each fungus depended on the species of host plant. The hyphal transport of 32P was high in G. caledonium in symbioses with all three plant species, whereas G. invermaium transported significant amounts of 32P only when associated with flax. Consequently, to determine the P‐transport effectiveness of a mycorrhizal fungus is meaningful only in the context of its associated host plant species.
Arbuscular mycorrhiza and phosphorus as controlling factors in the life history of Hyacinthoides non‐scripta (L.) Chouard ex Rothm.
Authors: MERRYWEATHER JAMES , FITTER ALASTAIR
Published: April 2006

summary

This investigation aimed to assess the degree of dependence of young plants of Hyacinthoides non‐scripta (L.) Chouard ex Rothm. on the formation of arbuscular mycorrhiza (AM) at different stages of its life cycle. H. non‐scripta is a bulbous perennial with a restricted root system of coarse, unbranched elements which are plainly inadequate for the acquisition of phosphate (P) from soil. In a glasshouse experiment non‐mycorrhizal H. non‐scripta were unable to take up sufficient P to maintain a positive P budget, confirming that the species is obligately mycorrhizal when adult.

We needed to be able to assess the ages of field‐collected plants. The bulb of H. non‐scripta, which is totally rebuilt annually, provides no indicator of age other than size. The development of individual bulbs was monitored in reconstructed soil profiles for several years and the relationship of size and age calculated in order to determine the age structure of a population in the field and to quantify the mycorrhizal colonization of their roots according to age and depth in the soil.

Seedlings of H. non‐scripta are supplied with a P‐rich endosperm and initially inhabit upper soil horizons where P is plentiful. However, they are at risk from winter frosts, summer drought and, possibly, predators. During their first four to five seasons they descend in the soil to a depth of approximately 20 cm, down a gradient of decreasing soil phosphorus concentration; simultaneously, their roots become increasingly colonized by arbuscular mycorrhizal fungi. Because of the change in environment, they appear to become increasingly dependent on the symbiosis, suggesting that the association changes from facultative to obligate during the plant's life history.
Leaf development in Lolium temulentum L.: photosynthesis in relation to growth and senescence
Authors: GAY ALAN P. , THOMAS HOWARD
Published: April 2006

summary

Length, area, weight and concentrations of pigment were measured from just after emergence until senescence of the fourth leaf of Lolium temulentum L. seedlings grown in nutrient solution in a controlled environment. At the same time the progress of photosynthesis, respiration and carbon contents of the leaf were recorded. A new approach to calculating photosynthesis indices for grasses was developed, based on logistic curves fitted to leaf lengths. Dry weight and photosynthetic rates per unit area were greatest in young leaves. Subsequently photosynthetic capacity at light saturation declined, as did photosynthetic rates at the light incident on the leaf, although the decrease was less pronounced in the latter case. Dry weight per leaf remained fairly constant once full expansion was reached, with perhaps a slight rise in the oldest leaves. The photosynthesis and carbon content data were combined to calculate the carbon balance of leaf 4, with respect both to the atmosphere and to the rest of the plant. Net gas exchange became positive about 7 d before full leaf expansion. Leaf weight continued to increase so that the carbon balance with the rest of the plant did not become positive until just after final leaf size had been attained. These results are discussed in relation to the likely contribution of the various components of the balance to plant productivity.
Relationships and hybridization between British species of Polygala– evidence from isozymes
Authors: LACK ANDREW J.
Published: April 2006

summary

In Britain there are four species of Polygala, three diploids, P. serpyllifolia, P. calcarea and P. amarella, and a tetraploid, P. vulgaris, all of which are morphologically similar. Isozymes of six enzyme systems in these species were compared. Using evidence from both morphology and isozymes, the closest relationship within the group is between P. serpyllifolia and P. vulgaris. Despite this, P. serpyllifolia and P. vulgaris do not hybridize, whereas P. calcarea and P. amarella both hybridize with P. vulgaris in natural populations. In four sites, where P. calcarea and P. vulgaris occur together, there is good evidence for introgression via hybrids of P. calcarea genes into the tetraploid P. vulgaris, despite the high level of sterility in hybrids. Introgression of P. vulgaris genes into P. calcarea might have occurred at one site.
Effects of SO2 on the concentrations of carbohydrates and secondary compounds in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings
Authors: KAINULAINEN P. , HOLOPAINEN J. K. , OKSANEN J.
Published: April 2006

summary

Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings of open‐pollinated progenies and clonal cuttings were exposed to various concentrations of SO2 (50–155 nl l−1) in several growth chamber experiments. No visible foliar injury was observed in any SO2 exposure. The total sulphur concentrations of the exposed needles were significantly greater than in the control needles. Exposure to SO2 (100 and 155 nl l−1) reduced concentrations of glucose and fructose and increased concentrations of sucrose in pine needles. By contrast, one spruce clone had more glucose and fructose and less sucrose in needles exposed to SO2 (100 nl l−1), but in other spruces of clonal or open‐pollinated progenies no changes in sugar concentrations were detected in different SO2 exposures (50–155 nl l−1). Exposure to SO2 had no effects on concentrations of individual or total monoterpenes in pine or spruce needles. Concentration of total resin acids was significantly smaller in needles exposed to the greatest concentration of SO2 (155 nl l−1), but no changes were detected in other exposures (50–150 nl l−1) in either tree species. Concentrations of minor individual resin acids, palustric and neoabietic acids, were also affected by SO2 in needles of pine (155 nl l−1 SO2) and clonal spruces (100 nl l−1 SO2). Exposure to SO2 did not affect foliar concentration of total phenolics in pine and spruce seedlings. In exposure to 0, 50, 100 and 150 nl l−1 SO2, total phenolic concentration of spruce roots was increased linearly with elevated SO2 exposure level. By contrast one spruce clone had decreased concentrations of phenolics in roots after exposure to 155 nl l−1 SO2. The present results suggest that in conifers the response of carbohydrate and secondary metabolism to SO2 varies with the origin of tested seedlings and the SO2 concentration. Therefore, generalizations about the SO2 effects on suitability of food quality for folivorous herbivores are difficult to draw, except that a better supply of sulphur will be available from SO2 exposed seedlings.
The effect of natural and simulated insect herbivory, and leaf age, on the process of infection of Rumex crispus L. and R. obtusifolius L. by Uromyces rumicis (Schum.) Wint.
Authors: HATCHER PAUL E. , AYRES PETER G. , PAUL NIGEL D.
Published: April 2006

summary

The development of uredinia of Uromyces rumicis (Schum.) Wint. was studied on Rumex crispus L. and R. obtusifolius L. plants inoculated in the laboratory. Fewer uredinia developed on leaves injured by simulated insect herbivory, those fed upon by Gastrophysa viridula Degeer (Coleoptera: Chrysomelidae), and young, incompletely expanded leaves, than on uninjured, fully expanded control leaves. The effect of simulated herbivory and leaf age on the process of U. rumicis infection was investigated using Calcofluor staining and epifluorescence microscopy. Simulated insect herbivory reduced significantly the proportion of sporelings producing appressoria and the proportion of sporelings with appressoria that entered the substomatal cavity. In R. obtusifolius, leaf injury also reduced the proportion of penetration hyphae that formed substomatal vesicles. The proportion of sporelings that produced intercellular hyphae in injured leaves was reduced by 58 % in R. crispus and 89 % in R. obtusifolius. G. viridula feeding induced similar resistance in R. obtusifolius leaves.

Simulated insect herbivory reduced both uredinial density and the area occupied by intercellular hyphae by between 65% and 89%. Injury had a greater effect than leaf age on sporelings in the pre‐haustorial stages of development. However, the total area occupied by intercellular hyphae in young leaves was reduced by between 42% and 78% compared to mature leaves, owing to a lower uredinial density and, in R. obtusifolius, also to a significant reduction in the size of individual uredinia.
Diversity of fungal symbionts in arbuscular mycorrhizas from a natural community
Authors: CLAPP J. P. , YOUNG J. P. W. , MERRYWEATHER J. W. , FITTER A. H.
Published: April 2006

summary

The arbuscular mycorrhizal (AM) association between fungi in the order Glomales and the roots of a very wide range of vascular plants is of global ecological significance but has proved particularly intractable to study in the field. We have developed a reliable technique to identify the fungal symbionts in roots taken directly from natural communities. Selective Enrichment of Amplified DNA combines the use of recently‐developed specific DNA primers with a novel method based on the principle of subtractive hybridization to remove interfering plant‐derived DNA after amplification with the polymerase chain reaction. Using this technique we have shown that endomycorrhizas of bluebells (Hyacinthoides non‐scripta) sampled directly from a woodland habitat are multispceies communities of varying composition which contain at least three genera of mycorrhizal fungi. The technique works well on a range of plant species and should have wide application to the identification of other symbionts, including pathogens. A spore survey has indicated that two particular AM types are associated with bluebells and this observation corroborates the molecular data. The presence of a Glomus species in bluebell roots was not expected from the spore data.
Endophyte infection effects on stomatal conductance, osmotic adjustment and drought recovery of tall fescue
Authors: ELMI A. A. , WEST C. P.
Published: April 2006

summary

Presence of the endophytic; fungus Acremonium coenophialum Morgan‐Jones and Gams in tall fescue (Festuca artuidinacea‐ Sehreb.) enhances host persistence in drought‐prone environments. However, the physiological mechanism is not well understood. We investigated the influence of endophyte infection and water deficit on osmotic adjustment, stomatal conductance, tiller survival and leaf elongation rate of genotype GA87‐122 and cv. Kentucky‐31 (KY31) of tall fescue. Plants were grown in a greenhouse in pots containing fine‐silty topsoil (experiment 1) or sand (experiment 2). In expt 1, endophyte‐infected (EI) and endophyte‐free (EF) isolines of GA87‐122 were exposed to two drought preconditioning cycles, after which all pots were re‐watered and osmotic adjustment determined. Osmotic adjustment was −0.46 and −0.51 MPa in El leaf blades and tiller bases and −0.29 and −0.13 MPa in EF leaf blades and tiller bases, respectively. In expt 2, EI and EF GA87‐122 and KY31 Mere exposed to severe drought after two preconditioning cycles, then re‐watered. During the second preconditioning drying cycle of KY31, stomatal conductance tended to be lower in EI than in EF plants, but the difference was significant (P⩽ 0–05) only at two sampling times. Shoot tissues osmotically adjusted 0.17–0.31 MPa more in EI than in EF plants. Tiller survival and leaf elongation rates were higher (P⩽ 0.05) in preconditioned EI than in EF plants. Basal‐zone osmotic adjustment was correlated with tiller survival rate in GA87‐122 and KY31 (r = 0.87, P⩽ 0.01 for both). Enhanced osmotic adjustment in the meristematic and growing zone might account far improved survival of tillers by facilitating protection of the apical meristem.
Leaf growth of hybrid poplar following exposure to elevated CO2
Authors: GARDNER SIMON D. L. , TAYLOR GAIL , BOSAC CREANA
Published: April 2006

summary

Leaf extension was stimulated following exposure of three interamerican hybrid poplar clones (Populus trichocarpa P. deltoides); ‘Unal’, ‘Boelare’, and ‘Beaupre’ and a euramerican clone ‘Primo’ (Populus nigra×P. deltoides) to elevated CO2, in controlled environment chambers. For all three interamerican clones the evidence suggests that this was the result of increased leaf cell expansion associated with enhanced cell wall extensibility (WEx), measured as tensiomerric increases in cell wall plasticity. For the interameriean clone ‘Boelare’, there was also a significant increase in cell wall elasticity following exposure to elevated CO2 (P⩽ 0.001). The effect of elevated CO2 in stimulating cell wall extensibility was confirmed in a detailed spatial analysis of extensibility made across the lamina of expanding leaves of the clone ‘Boelare’. For two of the interamerican hybrids, ‘Unal’ and ‘Beaupre’, both leaf cell water potential Ψ and turgor pressure (P) were lower in elevated than in ambient CO2. By contrast, no significant effects on the cell wall properties or leaf water relations for the euramerican hybrid ‘Primo’ were observed following exposure to elevated CO2. suggesting that the mechanism for increased leaf extension in elevated CO2, differed, depending on clone. The cumulative total length of leaves of ‘Boelare’ grown in elevated CO2, was significantly increased (P≤ 0.05) and since leaf number was not significantly increased in any inter‐american clone it is hypothesized that final leaf size was stimulated in elevated CO2 for these clones. By contrast, there was no significant effect of CO2 on cumulative total leaf length for the euramerican clone ‘Primo’, but leaf number was significantly increased by elevated CO2. The measurements suggest that total tree leaf area was stimulated for a range of poplar hybrids exposed to elevated CO2. Given the short rotation of a coppiced crop, it is likely that increased leaf areas will result in enhanced stemwood production when hybrid poplars are grown in the CO, concentrations predicted for the next century.
Secondary thickening in roots of Arabidopsis thaliana: anatomy and cell surface changes
Authors: DOLAN LIAM , ROBERTS KEITH
Published: April 2006

summary

The root of Arabidopsis thaliana (L.) Heynh. undergoes dramatic morphological changes during secondary thickening. We have used monoclonal antibodies that recognize two cell surface arabinogalactan protein epitopes (AGPs) and a pectic polysaccharide to document cell surface changes during the process of secondary thickening. These antibodies recognize cells in various stages of differentiation. An AGP epitope recognized by JIM 14 is expressed at the plasma membrane of most tells in the root, but is most highly expressed in mature sieve tube elements, JIM 13 identifies an epitope that is expressed in a discrete ring of cells in the periderm and during xylem vessel element differentiation, disappearing as lignificntion of the vessel elements proceeds, These antibodies reveal a biochemical differentiation at the surface of cells which mirrors obvious morphological differentiation events. Since AGPs have been shown previously to have a dramatic effect on the developmental capabilities of cells it is possible that the epitopes recognized by these antibodies might have an important developmental role during differentiation.
The influence of CO2concentration on stomatal density
Authors: WOODWARD F. I. , KELLY C. K.
Published: April 2006

summary

A survey of 100 species and 122 observations has shown an average reduction in stomatal density of 14.3% (SE ±2.2 %) with CO2enrichment, with 74% of the cases exhibiting a reduction in stomatal density. A sign test demonstrated that stomatal density decreases, in response to CO2, significantly more often than expected by chance. Repeated observations on the same species indicated a significant repeatability in the direction of the stomatal response. Analyses which removed the potential effect of taxonomy on this data set showed no significant patterns in the dependency of the degree of stomatal change on growth form (woodiness vs. non‐woodiness; trees vs. shrubs), habitat (cool vs. warm) or stomatal distribution on the leaf (amphi‐ vs. hypostomatous).

Forty‐three of the observations had been made in controlled environments and under a typical range in CO., enrichment of 350–700 μmol mol−1. For these cases the average stomatal density declined by 9% (SE ± 3.3%) and 60% of the cases showed reductions in stomatal density. When analyses were restricted to these 43 observations, amphistomatous samples more frequently had greater changes in stomatal density than did hypostomatous samples.

The degree of reduction in stomatal density with increasing CO2increases with initial stomatal density, after the influence of taxonomy is removed using analyses of independent contrasts. When the data were examined for patterns that might be due explicitly to the effects of relatedness, the subclasses of the Hamamelidae and the Rosidae showed highly significant reductions in stomatal density with CO2(87% of the species studied in the Hamamelidae and 80% of the species in the Rosidae showed reduction with CO2enrichment) and correlations between initial stomatal density and degree of reduction in stomatal density. The species sampled in the Hamamelidae were dominantly trees, whereas herbs dominated the species in the Rosidae. There were insufficient species studied at lower taxonomic levels to warrant further statistical analyses. This problem results from experimental and observational data being most often restricted to one species per taxonomic level, typically up to the level of order, a feature which can severely limit the extraction of taxonomically‐related and ecologically‐related plant responses.
A rapid change in ozone resistance of Plantago major after summers with high ozone concentrations
Authors: DAVISON A. W. , REILING K.
Published: April 2006

summary

Ozone concentrations in Britain vary greatly from year to year. In the mid‐1980s they were relatively low but in 1989 and 1990 the number of hours when concentrations exceeded 60 nl 1−1 was 3–4 times greater than in the preceding 2 yr. Previous experiments suggested that this might have resulted in an increase in ozone resistance of Plant ago major L. populations, so a comparison was made of seed‐grown plants collected from the same three sites in Derbyshire/South Yorkshire in the 1980s and 1991. Ozone resistance was measured by exposure to charcoal‐filtered air or air containing 70 nl 1−O3 (7 h d−1) and expressed as R%, the mean relative growth rate in ozone expressed as a% of that in charcoal‐filtered air. Ozone resistance changed significantly in two of the populations (ISP and Totley) between the years 1985 and 1991. There was no significant change in the resistance of the Scaftworth population between 1988 and 1991 when expressed as R% but there were significant physiological differences between the collections. The changes in R% were accompanied by differences in the response of the stomata to ozone and in effects on dark respiration, but not in assimilatory capacity. This is the first report of a change in ozone resistance in populations over a short period of time. It is not known if the 1 991 plants were the descendants of the 1985/88 plants or whether there had been an invasion by new genotypes from outside the area. The role of other environmental factors in determining ozone resistance, and the implications of the data for the definition and mapping of critical levels are both discussed. It is predicted that if the reported changes were caused by ozone, the region where future changes in ozone resistance are most likely to occur is that between the Midlands and the north of England.
Short‐term exposure to atmospheric ammonia does not affect low‐temperature hardening of winter wheat
Authors: CLEMENT JOHANNES M. A. M. , VENEMA JAN HENK , VAN HASSELT PHILIP R.
Published: April 2006

summary

The effect of atmospheric NH3 an low‐temperature hardening of winter wheat (Triticum acstivum L. cv. Urban) was investigated. Growth and photosynthesis were stimulated by ammonia exposure. After a 14 d exposure at moderate temperatures (day/night 18.5/16°C) total nitrogen content was enhanced by 45 % compared with the controls. During that period, water‐soluble sugar content was not affected by NH3. After lowering the temperature to 4/3 0C, sugar content of the control plants doubled within 2 d, whereas in the plants exposed to NH3 it increased to a much lesser extent. Total nitrogen content further increased, leading to an 85%, higher level in the NH3‐exposed plants. Frost hardiness was not affected by atmospheric ammonia. It is concluded that winter wheat is tolerant Ed high ammonia concentrations, even under unfavourable growth conditions.
Axenic in vitro nitrogen and phosphorus responses of some Dutch marsh orchids
Authors: DIJK EEUWE , ECK NELLY
Published: April 2006

summary

Seedlings of Dactylorhiza majalis (Reichb.) Hunt & Summerh., D. praetermissa (Druce) Soó var.junialis (Vermen.) Sengh., D. incarnata (L.) Soo and D. maculata (L.) Soó ssp. maculata were grown axenically in vitro at various concentrations of ammonium nitrate and phosphate to assess the extent of growth depression owing to high nutrient availability. Only large nitrogen concentrations had a general negative effect on orchid axenic growth. Responses to both nutrients were highly species‐specific. D. praetermissa responded positively to addition of mineral nitrogen in the media, whereas D. incarnata showed the most negative response. D. majalis differed in showing preference for the greatest phosphate concentrations, in contrast to D. practermissa. Axenic nutrient responses might explain differences in distribution patterns between the tested species in the field.
Piceirhiza nigra, an ectomycorrhiza on Picea abies formed by a species of Thelephoraceae
Authors: AGERER REINHARD , KLOSTERMEYER DÖRTE , STEGLICH WOLFGANG
Published: April 2006

summary

Ectomycorrhizas of Picea abies (L.) Karst., previously described as Piceirhiza nigra, are shown to be formed by a member of the Thelephoraceae by virtue of the presence of thelephoric acid.
Diurnal water relations and gas exchange of two slash pine (Pinus elliottii) families exposed to chronic ozone levels and acidic rain *
Authors: JOHNSON J. D. , BYRES D. P. , DEAN T. J.
Published: April 2006

summary

Seedlings from two half‐sib families ofPinus elliottiivar.elliottiiEngelm. differing in sensitivity to ozone were grown in open‐top chambers for 22 months under simulated acidic rain (pH 3‐3) and four concentrations of ozone. The ozone concentrations were: charcoal‐filtered air (CF); non‐filtered ambient air (NF); twice the NF level (2X), thrice the NF level (3X). Ozone exposures were computer controlled to follow diurnal and seasonal fluctuations in ambient ozone concentrations.

On two days, 24 April and 29 May, in the spring of 1990, trees were sampled repeatedly for xylem water potential, needle conductance and photosynthesis from sunrise to sunset on the oldest needle age class attached to the main stem (first needle cohort produced in 1989, and therefore, exposed the longest to ozone). On 30 May, three needle age classes (first age class of 1989, the last age class of 1989 and first ape class of 1990) were sampled over the day for needle conductance in trees exposed to CF and 3X ozone.

Soil moisture measurements indicated that the 3X trees used significantly more water from the 75–l00 cm soil depth even though leaf area on these trees was about 30% less. Tree response showed very consistent xylem water potential among sample days, families and ozone treatments. By contrast, needle conductance and photosynthetic rate showed significant ozone and family differences. In addition, the response of needle conductance to vapour pressure deficit lessened as ozone exposure increased. The putative ozone‐sensitive family (106‐56) exhibited less needle conductance in the 2X and 3X treatments as well as reduced photosynthesis on both sample days, suggesting prior ozone injury. The youngest needle age class of this same family when exposed to 3X ozone showed higher needle conductance in the afternoon which could lead to both excessive water loss and uptake of ozone.

The interactive effects of chronic ozone exposure, limited soil moisture and genetics altered the water relations and gas exchange of slash pine growing in north Florida. Changes in sromatal conductance along with possible adjustments in the hydraulic properties of the roots and stems appeared to be responsible for the control of water potentials in trees of differing sizes and leaf area. The importance of the contribution of different needle age classes to the water and carbon economy of slash pine, and their modification by cumulative ozone exposure, cannot he overlooked in interpreting air pollution effects on evergreen trees.
B chromosomes in plants
Authors: JONES R. NEIL
Published: April 2006

summary

This review of supernumerary B chromosome systems in flowering plants deals mainly with work published in the last 15 yr, hut also includes older material which has not hitherto been presented systematically. The term B chromosome (B) is defined, and there is an introductory overview dealing with general characteristics and the significance of Bs as a widespread chromosome polymorphism. Detailed sections are then presented covering the occurrence of Bs in different taxa, their structure and molecular organization, their irregular modes of inheritance, their phenotypic effects, population dynamics and origin. Particular attention is paid to the research growth points in molecular analysis of the structure and genome organization of Bs, and to transmission genotypes in the context of their adaptive versus their selfish properties. Where appropriate, reference is also made to likely future lines of research, and also to the usefulness of B chromosomes in genetic analysis and as model systems to study general phenomena of genome organization and evolution, nuclear physiology and architecture, chromosome polymorphism and selfish DNA.

CONTENTS

Summary
411

I.
Introduction
411

II.
Occurrence
411

III.
Structure and organization
415

IV.
Inheritance
422

V.
Phenotypic effects
426

VI.
Populations
429

VII.
Applications
430

VIII.
Origin
430

Acknowiedgements
430

References
431
On the cause of offspring superiority conferred by mycorrhizal infection of Abutilon theophrasti
Authors: KOIDE ROGER T. , LU XIAOHONG
Published: April 2006

summary

In previous studies we demonstrated that for Abutilon theophrasti Medic, offspring of mycorrhizal plants grew more rapidly than did offspring of non‐mycorrhizal plants. This observation was verified in the current study. We hypothesized that the faster growth of offspring of mycorrhizal plants was caused by a superior ability to absorb nutrients, since offspring of mycorrhizal plants produced faster‐growing root systems with higher phosphatase activities. We tested the hypothesis by growing offspring plants in distilled water. Despite the absence of any nutrients short‐term growth rates of offspring of mycorrhizal plants were still significantly greater than those of offspring of non‐mycorrhizal plants. We conclude that the faster growth of offspring of mycorrhizal plants is nor caused by a superior ability to acquire external resources.
Nitrogen fixation by Alnus incana and nitrogen transfer from A. incana to Pinus sylvestris influenced by macronutrients and ectomycorrhiza
Authors: EKBLAD ALF , HUSS‐DANELL KERSTIN
Published: April 2006

summary

The aims of this study were to evaluate the effect of macronutrients on nitrogen fixation in mycorrhizal and non‐mycorrhizal grey alder (Alnus incana (L.) Moench), and to evaluate the effect of ectomycorrhizal mycelium on the transfer of symbolically fixed nitrogen from grey alder to Scots pine (Pinus sylvestris L). One alder and one pine were grown together in pots with root systems separated by a 20μm mesh nylon filter which allowed hyphae but not roots to penetrate. Half the plants of both species were inoculated with Paxillus involutus (Ft.) Ft. and all alders were inoculated with Frankia. Nutrient solutions were added with macronutrient (N, K, P, Ca, Mg and S) concentrations varied according to a two‐level fractional factorial design. The plants were harvested after two growing periods in a growth chamber. Nitrogen fixation by alder and transfer of symbiotically fixed N from alder to pine was measured by 15N‐dilution. Fixed N (mg) correlated with nodule biomass in both mycorrhizal and non‐mycorrhizal alders. On average, specific nodule activity over the two periods was 510 mg N fixed R' nodule d. wt. This was not affected by mycorrhizal infection or by the different nutrient treatments. By contrast there was a strong nutrient effect on the proportion of N derived from fixation. These results indicate that the regulation of nitrogen fixation was via nodule growth rather than via nodule specific activity. Nitrogen had a strong negative effect and P a positive effect on the percentage of N derived from fixation (%Ndfa). However, the effect of N depended on the level of P. This N × P interaction resulted in a %Ndfa when N was high, of 5‐10%, at low P and 45–48%, at high P. The highest value of 90% Ndfa was found at the combination of low N and high P. Potassium had a small but statistically significant effect on the %Ndfa but Ca, Mg and S had no significant effects. No mycorrhizal effect was found on the %Ndfa in alder. By contrast, the %Ndfa and biomass were lower in mycorrhizal than in non‐mycorrhizal alders. The proportion of fixed N in pine, transferred from alder, was greatest (9%) when the pine was nitrogen starved and mycorrhizal and the alder was fixing maximally (low N and high P). However, the amount of fixed N transferred to pine was not statistically different from zero.
Allocation of carbon in mycorrhizalPinus ponderosaseedlings exposed to ozone
Authors: ANDERSEN CHRISTIAN P. , RYGIEWICZ PAUL T.
Published: April 2006

summary

The effect of ozone on tree growth and metabolism has been studied widely. Despite the research emphasis, relatively little is known about how the below‐ground component responds when shoots are exposed to ozone, even though evidence suggests that ozone can affect roots more than shoots. Undemanding how ozone affects carbohydrate allocation throughout the plant is essential to understanding the mechanisms of response to ozone. The purpose of this study was to follow the allocation and metabolism of carbon in aPinus PonderosaLaws.‐Hebeloma crustuliniforme(Bull.: St. Amans) Quel seedling system under ozone stress. The hypothesis that ozone affects carbon transport below ground and overall sink strength of roots. similarly in mycorrhizal and non‐mycorrhizal seedlings was tested. To test the hypothesis, a unique culturing system was used to quantify carbon movement to all components of the symbiosis and to construct an overall budget for carbon for both mycorrhizal and non‐mycorrhizal seedlings. Fluxes of CO2and carbon allocation were followed by measuring instantaneous CO2flux and by14C labelling. Two experiments were conducted that differed in their total ozone exposure (39.3 ppm h in expt 1, and 58.1 ppm h in expt 2). Mycorrhizal inoculation significantly increased CO., assimilation rates(A)and A/R (R = shoot respiration) ratios in both experiments compared with non‐mycorrhizal seedlings. Ozone exposure in expt 2 significantly decreased theA/Rratio (P < 0.003) in both mycorrhizal treatments. Below‐ground respiration was significantly greater in mycorrhizal than in non‐mycorrhizal seedlings in both experiments, and was not affected by ozone exposure, Intact, extramatrical hyphal respiration was lower by 33% in seedlings exposed to ozone, but differences were not statistically significant (P ≤ (0.167). Mycorrhizal seedling roots reached maximum respiratory14CO2release rates c. 5 h and < 20 h earlier than non‐mycorrhizal seedlings in expts 1 and 2, respectively, suggesting accelerated transport of14C below ground in mycorrhizal seedlings. Mycorrhizal seedlings also exhibited greater rates of14C release below ground than non‐mycorrhizal controls. The maximum rate of respiratory release of14CO2below ground was significantly reduced by exposure to ozone in both mycorrhizal and non‐mycorrhizal treatments. Ozone significantly reduced14C activity in the fungus of mycorrhizal plants. This constitutes the first report of an ozone‐induced reduction in carbon allocation to the fungal symbiont in a mycorrhizal association. The results suggest a substantial impact of ozone on the carbon balance of the mycorrhiza: however, there was no evidence to suggest that mycorrhizal and non‐mycorrhizal ponderosa pine seedlings responded differently to ozone stress.
An improved Solardome system for exposing plants to elevated CO2 and temperature
Authors: RAFAREL C. R. , ASHENDEN T. W. , ROBERTS T. M.
Published: April 2006

summary

Ventilated Solardomes (hemispherical glasshouses) have been used for 20 yr for studying the effects of gaseous pollutants on plants. This paper describes a computer‐operated facility for studying the effects of CO2× temperature regimes on plants. The eight chambers were set up for factorial design experiments ‐ with two levels of CO2 (ambient and ambient + 340 ppmv), two levels of temperature (ambient and 3 °C tracked continuously above ambient) and two replicates of each CO2× temperature treatment. Monitoring of environmental conditions within the chambers over a 2 yr period has shown highly effective control of CO2 and temperature regimes. Even with high‐quality and u.v.‐B transmitting glass, the irradiance in the PAR region Was reduced by 18% within the domes. Variation in temperature across the radii of the domes increased with higher photosynthetic photon flux density (PPFD). Vapour pressure deficits CVPDs) in the ambient temperature domes compared well with outside conditions hut were higher in the elevated temperature domes. The watering regime within the domes affected intermittently the relationship between ‘dome’ and ‘outside’ VPDs. The Solardome facility has been used extensively for studies of the impacts of climate change within the UK Programme on Terrestrial Initiative on Global Environmental Research (TIGER).
Growth responses of Polytrichum commune and Hylocomium splendens to simulated environmental change in the sub‐arctic
Authors: POTTER J. A. , PRESS M. C. , CALLAGHAN T. V. , LEE J. A.
Published: April 2006

summary

Total moss cover and the growth responses of the two dominant bryophytes within a sub‐arctic heath ecosystem,Polytrichum communeHedw, andHylocomium splendens(Hedw.) Br. Eur., were investigated in response to simulated environmental change. Temperature, water supply and nutrients (NPK fertilizer) were increased in a factorial field study in Swedish Lapland. After 3 yr of treatment, total moss caver on fertilized plots was found to be less than 50% of that on unfertilized plots.H. splendensmade a smaller contribution to total cover, and also had fewer shoots on the fertilizer treated plots. The relative contribution ofP. communeto the bryophyte community was greater on the fertilized plots, although total shoot numbers ofP. communewere not greater. There was, however, a larger number of dead shoots ofP. communeon the fertilized plots. Total moss cover, relative contribution to moss cover by P.communeandH. splendens, and the numbers of shoots of these two species, were unresponsive to both the temperature and water treatments. The growth of the current year's segment ofH. splendenswas retarded by both the fertilizer and temperature treatments. Furthermore, the dry weight of the physiologically active shoot was found to be significantly altered by all three treatments. The current year's growth ofP. communeshowed increases in d. wt and morphological parameters in response to the fertilizer treatment. There were also interactive effects of both the fertilizer and temperature treatments with the water treatment on the current year's stem length increment.
Nuclear differentiation in the filamentous caulonema of the moss Funaria hygrometrica
Authors: KINGHAM KEITH I. , DUCKETT JEFFREY G. , GLYN MATTHEW C. P. , LEITCH ANDREW R.
Published: April 2006

summary

Nuclei from different cell types in plants and animals show many features of differentiation; they differ in shape, volume, structure, ultrastructure and in the distribution of nuclear components. Using the filamentous caulonema of the moss Funaria hygrometrica Hedw. this study records the changes in cytoplasmic organization alongside the reorganization of the interphase nucleus, Events taking place in the meristematic cells at or near the lip of the advancing caulonemal filaments (e.g. acquisition of polarity, tip growth, nuclear and cell division, side branch initiation] are associated with haploid nuclei (1C DXA amount 0.5 pg) that are spherical or slightly oval, with no blocks of condensed chromatin, and a large central nucleolus with a large granular component. Maturation of the caulonemal cells involves wall thickening and pigmentation concomitant with suspension of elongate plastids in linear arrays along endoplasmic strands. Many cells become highly polarized with the majority of the organelles at their apical ends. These eytoplasmic changes are associated with endoreduplication of the genome to about 8C, endoreduplication occurs by amplification of the 1C genome to give nuclei with IC‐SC DNA amounts. There is no evidence of differential amplification of the genome. The amplification in the copy number of ribosomal RNA genes is associated with the heterochromatinisation of the genes within the nucleolus. At the same time the nucleolus reduces in volume owing to a diminution of the granular component and all components of the nucleolus become spatial separate. There is an increased nuclear volume associated with endoreduplication and the nucleus elongates causing an increase in the surface area of the nuclear envelope. These major nuclear reorganizations are associated with a stable distribution of the ‘D’ polypeptide involved in pre‐mRNA splicing. Scrutiny of published data suggests that similar differentiation events might be encountered commonly in other organisms. The changing nuclear morphology probably reflects the changing activity of the nucleus and the cell. It might be that nuclear reorganization changes the balance of genes or gene products and the spatial distribution of the component pans to enable the new nuclear functions. These results suggest that nuclear differentiation is a fundamental feature of cell differentiation.
Biochemistry and molecular biology of lignification
Authors: BOUDET A. M. , LAPIERRE C. , GRIMA‐PETTENATI J.
Published: April 2006

Lignins, which result from the dehydrogenative polymerization of cinnamyl alcohols, are complex heteropolymers deposited in the walls of specific cells of higher plants. Lignins have probably been associated to land colonization by plants but several aspects concerning their biosynthesis, structure and function are still only partially understood. This review focuses on the modern physicochemical methods of structural analysis of lignins, and on the new approaches of molecular biology and genetic engineering applied to lignification.

The principles, advantages and limitations of three important analytical tools for studying lignin structure are presented. They include carbon 13 nuclear magnetic resonance, analytical pyrolysis and thioacidolysis. The use of these methods is illustrated by several examples concerning the characterization of grass lignins,‘lignin‐like’materials in protection barriers of plants and lignins produced by cell suspension cultures.

Our present limited knowledge of the spatio temporal deposition of lignins during cell wall differentiation including the nature of the wall components associated to lignin deposition and of the cross‐links between the different wall polymers is briefly reviewed.

Emphasis is placed on the phenylpropanoid pathway enzymes and their corresponding genes which are described in relation to their potential roles in the quantitative and qualitative control of lignification. Recent findings concerning the promoter sequence elements responsible for the vascular expression of some of these genes are presented.

A section is devoted to the enzymes specifically involved in the synthesis of monolignols: cinnamoyl CoA reductase and cinnamyl alcohol dehydrogenase. The recent characterization of the corresponding cDNAs/genes offers new possibilities for a better understanding of the regulation of lignification.

Finally, at the level of the synthesis, the potential involvement of peroxidases and laccases in the polymerization of monolignols is critically discussed.

In addition to previously characterized naturally occurring lignin mutants, induced lignin mutants have been obtained during the last years through genetic engineering. Some examples include plants transformed by O‐methyltransferase and cinnamyl alcohol dehydrogenase antisense constructs which exhibit modified lignins.

Such strategies offer promising perspectives in gaining a better understanding of lignin metabolism and functions and represent a realistic way to improve plant biomass.

Contents

Summary
203

I.
Introduction
204

II.
Main structural features of lignins
205

III.
Lignification and cell wall differentiation: spatio‐temporal deposition of lignins and inter‐relations with other wall components
213

IV.
Enzymes and genes involved in the biosynthesis and polymerization of monolignols
216

V.
Lignin mutants as a way to improve plant biomass and to explore lignin biochemistry and metabolism
226

VI.
Concluding remarks
229

Acknowledgements
230

References
230
The growth and gas exchange response of soil‐planted Norway spruce [Picea abies(L.) Karst.] and red oak (Quercus rubraL.) exposed to elevated CO2and to naturally occurring drought
Authors: DIXON MARTIN , THIEC DIDIER LE , GARREC JEAN PIERRE
Published: April 2006

Norway spruce and red oak trees were planted directly into the soil and exposed to 700 μmol mol‐1CO2in open‐top chambers. There were large inter‐specific differences in response to naturally occurring drought during the second year of exposure to elevated CO2. Both species had decreased assimilation rates. CO2‐treated red oak had no loss of photosynthetic enhancement when undroughted, whereas CO2‐treated Norway spruce showed a relative increase in assimilation rates only when draughted. The effect of CO2on radial growth of both species was less marked in the second growing season, but this may have been a result of different biomass partitioning as Norway spruce shoot extension had a different pattern of growth in elevated CO2. Stomatal density and chlorophyll content were largely unaffected by the CO2treatment. A precise method for measuring Norway spruce needle surface area was also developed.
Carbon allocation and water use in juvenile Douglas fir under elevated CO2
Authors: GORISSEN A. , KUIKMAN P. J. , VAN DE BEEK H.
Published: April 2006

In this study the impact of an elevated CO2 level on allocation of assimilates and water use efficiency of Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] was investigated. Juvenile Douglas firs were exposed to a long‐term treatment at 350 and 700 μ 1‐1 CO2 for 14 months and subsequently crosswise transferred to phytotrons for a short‐term treatment with 350 and 700 μ l ‐1 CO2 for 4 wk in an atmosphere continuously labelled with 14CO2. No interactive effects on total net uptake of 14CO2 between long‐term treatment and short‐term treatment were observed. The short‐term treatment with 700 μ 1‐1 CO2 increased the total net uptake of 14CO2 by 22%, compared with the 350 μ l ‐1 CO2 treatment. The long‐term pretreatment did not affect the total net uptake, suggesting that photosynthetic acclimation had not occurred. However, expressed per unit of needle mass a 14% reduction was observed in the trees pretreated at 700 μ l‐1 CO2. This was not because of a reduced sink strength of the root system. This reduced uptake per unit of needle mass after long‐term treatment may have implications for carbon storage in forest ecosystems. The results showed that an initial growth stimulation can eventually be annulled by developing physiological or morphological adaptions. 14CO2 in the root/soil respiration increased in the short‐term treatment with 700 μ l‐1 CO2, indicating a stimulated use of current carbon compounds either by roots or microorganisms. The water use efficiency during the short‐term treatment with 700 μ l‐1 CO2 increased by 32 %, but was not affected by the long‐term pretreatment. Water use per unit needle mass during the short‐term treatment was decreased both by the short‐term treatment and by the long‐term pretreatment by about 15%. Some of the observed effects appeared to be persistent, such as decreased water use per unit needle mass, whereas others, stimulation of total net 14CO2 uptake and water use efficiency, were transient.