bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of abscission zones in the flowers and fruits of peach [Prunus persica (L.) Batsch]
Authors: ZANCHIN A. , MARCATO C. , TRAINOTTI L. , CASADORO G. , RASCIO N.
Published: April 2006

Cell wall hydrolases, their mRNAs, and ultrastructural details of cell wall digestion have been studied in peach abscission zones (AZ) located at the base of flower bud (AZ1) and the base of flower receptacle (AZ2), respectively.

Induction of abscission was obtained by treatment of explants with exogenous ethylene. Cell separation patterns of the two examined abscission zones have been compared with those of other already known AZs of peach, i.e. the AZs located between fruit and peduncle and the leaf AZ. Analyses have shown similarities in response to ethylene treatment between AZ1 and leaf AZ and between AZ2 and AZs, respectively. Results have been discussed considering the precise position of AZ1 and AZ2 on the flower bud. The timing of functional differentiation, evaluated as the cells’ability to respond to induction by ethylene treatments, showed that AZ1 and AZ2 became functional after bud breaking and bud scale shedding. Later on, they lost their functionality at about 6–7 wk from anthesis. AZ3 became functional very precociously and could be activated 1 wk after anthesis in the fertilized flowers. In the latter zone the cells could also undergo a morphological predifferentiation, even though it occurred a long time after the acquisition of the ethylene responsiveness. This finding shows that morphological differentiation is not necessarily a prerequisite for those cells to become competent to respond to the abscission inducing stimuli.
Ectomycorrhizal fungal succession in jack pine stands following wildfire
Authors: VISSER SUZANNE
Published: April 2006

A study was conducted to determine if ectomycorrhizal fungi in an age sequence of jack pine (Pinus banksiana Lamb.) stands which had regenerated following wildfire disturbance followed a successional pattern. Ectomycorrhizal development and number of symbionts were assessed in the forest floor and 0‐20 cm deep mineral soil in 6, 41, 65 and 122‐yr‐old stands by conducting a macrofungal fruit body survey and examining pine root tips microscopically for mycorrhizal status and types of fungi forming the symbiosis. The majority of roots were located in the mineral soil with no substantial invasion of the forest floor except in the 122‐yr‐old stand. Over 90 % of the jack pine root tips were mycorrhizal and the majority of fruit bodies were produced by ectomycorrhizal species, regardless of stand age. There was no decrease in ectomycorrhizal colonization of roots with stand age. Both fruit body and root assessments revealed a distinct sequence of mycorrhizal fungi with stand age consisting of early‐stage fungi [Coltricia perennis (L:Fr.) Murr., Thelephora spp., E‐strain]; multi‐stage fungi [Suillus brevipes (Pk.) Kuntze, Inocybe spp., Cenococcum geophilum Fr., Mycelium radicis atrovirens Melin] and late‐stage fungi [Cortinarius spp., Lactarius spp., Russula spp., Tricholoma spp., Hygrophorus spp., Hydnellum peckii Banker, Suillus tomentosus (Kauff.) Sing., Snell & Dick, Piloderma byssinum (Karst.) Jül. and Sarcodon scabrosus (Fr.) Karst.]. Many of the basidiomycete species fruiting above ground were detected also on the roots below ground. Fruit bodies of SO species of ectomycorrhizal fungi were recorded while 39 distinct mycorrhizal types were identified on the roots. There was a significant increase in mycorrhizal species richness between the 6 and 41‐yr‐old stands and this was primarily the result of partial replacement of Suillus brevipes on the 6‐yr‐old trees by late‐stage fungi in the older stands. Very few species present in the 6‐yr‐old stand were completely replaced in the older stands; rather, the multi‐stage species present in the young stand were joined by late‐stage species in the mature stands. The species abundance distribution of fungi on the roots in the 6‐yr‐old stand was best described by a geometric series which is typical of an early successional community while the distributions in the three oldest stands conformed to a lognormal series which is indicative of a stable, species rich community. Both the composition and structure of the ectomycorrhizal community had stabilized 41 yr after wildfire.
Differential toxicity of heavy metals is partly related to a loss of preferential extraplasmic compartmentation: a comparison of Cd‐, Mo‐, Ni‐ and Zn‐stress
Authors: BRUNE ANDREAS , URBACH WOLFGANG , DIETZ KARL‐JOSEF
Published: April 2006

Barley was grown at inhibitory concentrations of cadmium, molybdenum, nickel and zinc. Primary leaves were analyzed for cellular and sub cellular compartmentation of the heavy metals. Epidermis and mesophyll protoplasts, mesophyll vacuoles and chloroplasts were isolated and apoplasmic washing fluid prepared, and the heavy metal contents of the various fractions determined. Efflux experiments showed that heavy metals were not lost from the preparations within the time span of the experiment. The different heavy metals were subjected to distinct distribution mechanisms within the leaves: (1) On a relative basis, the order of preferred epidermal accumulation was Cd = Zn > Mo > Ni (P < 0.01). (2) Within the mesophyll, Mo showed the highest degree of vacuolar compartmentation, whereas Ni was compartmentalized into the cytoplasm including chloroplasts to almost 80%. (3) The low degree of vacuolar compartmentation was correlated with the development of damage in the leaves, as visualized by chlorosis and decreased quantum yield efficiency. (4) Damage was inversely correlated with apoplasmic compartmentation. (5) Interestingly, sulfhydryl contents of stressed leaves were neither positively nor negatively correlated with toxicity of the heavy metals: maximum induction was seen in the presence of Cd, followed by Zn, and no changes under Ni and Mo‐stress. Increases in leaf SH‐contents were small as compared with induction in the roots.
Acid invertase in mycorrhizal and non‐mycorrhizal roots of Norway spruce (Picea abies [L.] Karst.) seedlings
Authors: SCHAEFFER CHRISTOPH , WALLENDA THOMAS , GUTTENBERGER MARTIN , HAMPP RÜDIGER
Published: April 2006

Sucrolytic enyzme activities and concentrations of hexoses typically increase in plant/microbe symbioses. However, there is little information on ectomycorrhizal associations. We measured invertase activity and soluble sugar contents in roots of mycorrhizal and non‐mycorrhizal Norway spruce [Picea abies (L.) Karst.] seedlings. We used two ectomycorrhizal fungi, a basidiomycete [Amanita muscaria (L. ex Fr.) Hooker] and an ascomycete (Cenococcum geophilum Fr.). Mycorrhizas and non‐mycorrhizal short roots, as well as other parts of the root system, were investigated at different developmental stages by micro‐analytical methods.

Neither sucrose nor invertase could be detected in fungal mycelia. In vitro measurable invertase activity and the sucrose, glucose and fructose content were reduced in both types of mycorrhizas compared with the non‐mycorrhizal short roots. Correction of data for the fungal component in the mycorrhizas, indicated that there were no differences in plant‐specific amounts of sucrose and acid invertase activity in mycorrhizal and non‐mycorrhizal roots. However, amounts of glucose and fructose, which are present in both partners, were clearly reduced in the mycorrhizas. As high fructose levels inhibit acid invertase, a reduction in the amount of fructose in the symbiotic tissue could favour in vivo acid invertase activity. Our results indicate that the situation in ectomycorrhizas may be different from those in other biotrophic interactions.
Kinetic analysis of Cd uptake in Cd‐tolerant and intolerant populations of the moss Rhytidiadelphus squarrosus (Hedw.) Warnst and the lichen Peltigera membranacea (Ach.) Nyl.
Authors: WELLS J. M. , BROWN D. H. , BECKETT R. P.
Published: April 2006

Cadmium uptake by photosynthetically Cd‐tolerant and intolerant populations of the moss Rhytidiadelphus squarrosus (Hedw.) Warnst and the lichen Peltigera membranacea (Ach.) Nyl. was investigated. Intolerant plants showed increased intra cellular Cd uptake compared to Cd‐tolerant material. Kinetic analysis indicated that reduced intracellular Cd uptake by Cd‐tolerant plant material was reflected in an increased Km or decreased Vmax for Cd. Pretreatment with KNO3 modified the extra cellular ion content of plant material, significantly reduced the apparent Km and could increase or decrease the Vmax for intracellular Cd uptake. Changes in kinetic constants caused by K pretreatment could be related to altered chemical equilibria when plant material was incubated in Cd solutions. Selective exclusion of Cd from intracellular locations was excluded as a tolerance mechanism in R. squarrosus and P. membranacea. Contrasting kinetic constants for intracellular Cd uptake in intolerant and Cd‐tolerant plant material were due to the prevailing extra cellular ion content when collected from the field. In R. squarrosus, K pretreatment resulted in increased uptake capacities and cell‐wall binding affinities for Cd in field‐grown moss apices. Laboratory‐grown apices, following K pretreatment, displayed increased uptake capacities but reduced affinities for Cd. Increased extra cellular Cd uptake in K‐pretreated moss apices was interpreted as additional weak electrostatic binding. Kinetic analysis indicated that electrostatic binding by extra cellular sites was less influential than the available supply of wall‐bounds ions on intracellular Cd uptake by moss apices.
Current trends in studies of long‐term plant community dynamics
Authors: RITCHIE J. C.
Published: April 2006

Long‐term plant community dynamics has been investigated by analyses of macro‐ and microfossil remains found in unconsolidated limnic and terrestrial sediments, chiefly of Late‐Quaternary and Recent age. Plant macrofossils preserved in packrat (Neotoma) midden sites in semi‐arid regions have yielded the most informative data for the period between the lastest glacial to the present day. The remains can, with few exceptions, be identified to species level, they represent a large (>75%) proportion of the species composition of vegetation within a radius of 30‐50 m of a site, and they can be dated by the accelerator mass‐spectrometric radiocarbon method. Most sites have been found in the arid southwest of the United States and significant contributions have been made recently to understanding of long‐term changes in species composition and shifts in range and elevational limits of species. Similarly, analysis of macrofossils in lake, mire and river sites can draw on the taxonomic precision, small source area and potential for precise radiocarbon dating of samples, to provide detailed reconstructions of the local vegetation of lacustrine, mire and fluvial habitats. The vast literature reporting these investigations deals with sites chiefly in northern temperate regions, but recent studies from tropical and warm‐temperate regions show the promise of the approach. The use of analyses of microscopic charcoal preserved in sediments has increased significantly in the past few decades as part of attempts to reconstruct forest tire history and, when combined with other analyses (pollen, physical chemistry), to investigate past community dynamics. The major limitations of the method are poor chronological control in many sediments, uncertainties about source area and limited taxonomic precision. On the other hand, macroscopic remains of charcoal can usually be identified to species level, can be dated accurately and have readily defined source areas. However, sites with high frequencies of sample occurrence spanning long, continuous time intervals are very rare, as a remarkable example from the humid tropics of Africa illustrates. Pollen analysis of lake and mire sediments has a long history and has yielded a vast literature. Its weaknesses as a tool in the three main fields of interest where it is used ‐ palaeoclimatology, cultural history and plant community dynamics are well known and increase in regions farther north and south of the boreal and

Contents

Summary
469

I.
Introduction
470

II.
Types of evidence
471

III.
Problems and prospects
487

Acknowledgements
490

References
490
Stem and root nodules on the tropical wetland legume Aeschynomene fluminensis
Authors: LOUREIRO M. F. , JAMES E. K. , SPRENT J. I. , FRANCO A. A.
Published: April 2006

Aeschynomene fluminensis Veil., originally obtained from flooded areas of the Pantanal Matogrossense region of Brazil, was grown under stem‐flooded or non‐flooded conditions for 70 d after inoculation with isolates of photosynthetic stem nodule rhizobia obtained from native A. fluminensis. Stem nodules formed only on submerged stems of flooded plants (mean of 25 per plant), and did not form on aerial parts, although they were capable of growing and fixing N2 after drainage of the stems. Root nodules formed on both non‐flooded and flooded plants but were usually decreased in number by flooding (from means of 124 to 51 per plant, respectively). Flooding (and stem‐nodulation) resulted in an increase in shoot (and a decrease in root) dry weight, regardless of rhizobial isolate.

Stem nodules were attached by a wide collar of aerenchymatous tissue at the base of the nodule. There were large air spaces in the stem where nodules were subtended and these were continuous with nodule aerenchyma/outer cortex. In addition, aerenchyma and spongy tissue at the base of the nodule connected both flooded and non‐flooded root nodules to large intercellular spaces in the root cortex. The stem and root nodules were ovoid in shape, and essentially aeschynomenoid in type, i.e. the central infected tissue was without uninfected, interstitial cells. Root nodules had a similar structure to stem nodules (although stem nodules were generally larger), and flooded root nodules were approximately twice the size of non‐flooded nodules. The infected tissue of root and stem nodules consisted of spherical, bacteroid‐containing cells containing one or two rod‐shaped bacteroids per peribacteroid unit and prominent organelles. Infection threads were observed in root but not in stem nodules.

The cortex of stem and root nodules had an apparent oxygen diffusion barrier, consisting of concentric layers of small cells with interlocking cell walls and few intercellular spaces. Cell layers external to these consisted of larger cells and intercellular spaces, with some spaces being occluded with an electron‐dense material that contained a glycoprotein recognized by the monoclonal antibodies MAC236 and MAC265. The amount of glycoprotein occlusions did not appear to differ between nodule types or treatments, although stem nodules contained intracellular glycoprotein vesicles adjacent to cell walls. The exterior of the nodules consisted of an epidermis of thin flattened cells with occasional lenticels. Amyloplasts were common in lower stem and hypocotyl nodules, but fewer in flooded or non‐flooded root nodules. Upper stem nodules (i.e. those within 6 cm of the water surface) differed from more profoundly submerged stem nodules by having chloroplasts throughout the cortex. Root nodules did not contain chloroplasts, and undifferentiated plastids were found mainly in lower stem nodules.
Ultrastructure of cortical root cells of Alnus incana infected by Penicillium nodositatum
Authors: SEQUERRA JEANINE , CAPELLANO ANDRE , GIANINAZZI‐PEARSON VIVIENNE , MOIROUD ANDRE
Published: April 2006

Penicillium nodositatum Valla penetrates Alnus incana (L.) Moench roots through deformed root hairs. It then colonizes the cortical cells and induces the formation of myconodules which have structures similar to those of young actinorhizas. The ultrastructure of infected cortical cells has been compared with that of cells infected by pathogenic or symbiotic fungi as well as with that of cells infected by Frankia. Our observations show that an infected host cell shows few visible signs of resistance to the fungal invasion. As soon as P. nodositatum enters the cell, it is surrounded by a wall‐like pecto‐cellulosic matrix produced by the host cell. The host plasmalemma, invaginated around the endophyte, keeps its integrity as it does in symbiotic associations. At the beginning of the infection, the host cytoplasm and the fungus are intact but when the cell is completely invaded, the host cytoplasm becomes disorganized and subsequently the fungus also senesces, as in roots of Ericaceae infected by an endomycorrhizal fungus or as in older tissues of actinorhizas. P. nodositatum could survive the dead host cell by using its own reserves. Uninfected neighbouring host cells remain intact. P. nodositatum can be considered to behave as a neutral microsymbiont of A. incana, in a way similar to that of a compatible but ineffective Frankia strain.
Gas exchange rates and chlorophyll content of epi‐ and endolithic lichens from the Trieste Karst (NE Italy)
Authors: TRETIACH M. , PECCHIARI M.
Published: April 2006

The photosynthetic activity of calcicolous endo‐ and epilithic lichens from the Trieste Karst area (NE Italy) was investigated. The data consist of: (a) gas exchange rates of Acrocordia conoidea, Petractis clausa, Rinodina immersa (endolithic), and Aspicilia calcarea (epilithic), recorded at different combinations of temperature, water content and radiation flux values, (b) chlorophyll content values of nine species, and (c)δ13C values measured in 24 lichen species with different growth‐forms. The results show that: (1) the maximum photosynthetic rates of endolithic lichens are rather small, ranging between 0·2 and 1·5μmol CO2 m‐2 h‐1 at optimal conditions; (2) the relation between thallus water content and photosynthesis differs from that of foliose and fruticose lichens; the optimum water content of endolithic lichens is particularly small, when expressed in g H2O cm‐2; (3) the algae of endolithic lichens, which belong to different systematic groups, are light‐saturated at a small radiation flux; (4) chlorophyll contents of endolithic lichens are rather large, being similar to those of some parmelioid lichens. The ecological implications of the endolithic growth‐form are briefly discussed. Endolithic lichens should be regarded as slow‐growing, stress‐tolerant organisms, which are rather similar in their physiology to epilithic crustose lichens; they have a high resistance to CO2 diffusion, saturation being reached only at a very large CO2 concentration.
Differential response of leaf conductance, carbon isotope discrimination and water‐use efficiency to nitrogen deficiency in maritime pine and pedunculate oak plants
Authors: GUEHL JEAN‐MARC , FORT CHRISTINE , FERHI ANDRÉ
Published: April 2006

Growth, CO2 assimilation rate (A), leaf conductance (g), transpiration efficiency (W= ratio biomass production/plant water use) and carbon isotope discrimination (Δ) were assessed in maritime pine (Pinus pinaster Ait.) and pedunculate oak (Quercus robur L.) grown on a sand–peat mixture with three levels of fertilization: F100, optimal complete fertilization; F25, 25% of the optimal fertilizer supply; F0, no fertilization. Leaf phosphorus (P) and potassium (K) concentrations were affected little by the diminishing nutrient availability. Reduced fertilization decreased plant nitrogen (N) concentration in both species but leaf N concentration was less affected in oak than in pine. In pine W was markedly reduced in response to reduced leaf or whole plant N concentration, which was consistent with the sharp decrease also observed for plant intrinsic water‐use efficiency (ratio A/g) both at the instantaneous (gas exchange data) and time‐integrated (A/g derived from Δ measurements) levels. In this species, lowered W in the N deficient conditions was primarily associated with enhanced values of g. The existence of such a stomatal response pattern, confirmed by the increase in plant transpiration between F100 and F25, has not been reported before. In oak, both A and g were decreased in F25 and F0 as compared with F100. W was not affected – and instantaneous as well as time‐integrated A/g values were only slightly decreased – in relation to decreasing plant N concentration. For F100, no difference in W was noticed between pine and oak though the Δ values were 2·6‰ lower in oak. We speculate that this discrepancy was linked with higher plant‐carbon losses through processes like respiration, fine‐root mortality or root exudation in oak. The isotopic approach proved useful for assessing the effects of nutritional status on W, but has to be used with caution when comparing different species.
Interactions between drought and elevated CO2on osmotic adjustment and solute concentrations of tree seedlings
Authors: TSCHAPLINSKI T. J. , STEWART D. B. , NORBY R. J.
Published: April 2006

Although drought tolerance of tree species is a critical determinant of forest composition, how elevated CO2affects drought tolerance is uncertain. Interactions between elevated CO2and drought on osmotic potential and osmotic adjustment of American sycamore (Platanus occidentalisL.), sweetgum (Liquidambar styracifluaL.), and sugar maple (Acer saccharumMarsh.) were investigated using 1‐yr‐old seedlings, planted in 81 pots and grown in four open‐top chambers, containing either ambient air or ambient air enriched with 300 μmol mol−1CO2. A well‐watered treatment with plants watered daily and a droughted treatment in which plants were subjected to a series of drought cycles were included within each chamber. Sugar maple and sweetgum seedlings completed a total of seven drying cycles, whereas sycamore seedlings, because of their greater leaf area and plant size, completed 11 cycles. The mean soil water potential at re‐watering for droughted seedlings in ambient CO2was –0·5, –0·7, and –1·8 MPa for sugar maple, sweetgum and sycamore, respectively, compared with –0·2, –0·7, and –1·2 MPa, respectively, under elevated CO2. By contrast, all well‐watered plants were maintained at soil water potential – 0·1 MPa.

Drought under ambient CO2reduced osmotic potential at saturation for leaves of sycamore and sweetgum by 0·30 MPa and 0·61 MPa, respectively, but leaves of sugar maple did not display osmotic adjustment to drought. Elevated CO2increased osmotic potential at turgor loss for leaves of sugar maple by 0·33 MPa under well‐watered conditions, and 0·48 MPa under drought. This response was not evident in the other species and might be related to the rapid growth of sugar maple causing a depletion of solutes. Whereas drought reduced the total solute concentration in roots of sugar maple, primarily the result of a reduction in K, elevated CO2did not alter the concentration of total solutes in roots of any of the three species. Elevated CO2has differing effects on drought tolerance among tree species, and thus might alter the competitive relations between species.
Flood‐induced leaf elongation in Rumex species: effects of water depth and water movements
Authors: BANGA M. , BLOM C.W. P. M. , VOESENEK L. A. C. J.
Published: April 2006

Several species from the genus Rumex are found in Dutch river forelands. Species such as R. palustris Sm. From the low, frequently flooded areas are well adapted to wet conditions, Rumex species from higher and less frequently flooded sites are poorly adapted and therefore sensitive to flooding. One of the adaptations to flooding is enhanced shoot elongation upon complete submergence, enabling plants to restore leaf‐air contact, provided that the water is not too deep. This paper demonstrates the strong variation in the absolute extent of flood‐induced leaf elongation among species of the genus Rumex. The effects of flooding on shoot dry and fresh weight and internal gas volumes of an elongating and a non‐elongating species, R. palustris and R. acetosella L., were compared. Net water uptake in response to complete submergence was observed in the shoots of both species. Based on results presented here, we conclude that in plants of R. palustris water enters the cells and is used for cell expansion leading to petiole elongation, whereas in plants of R. acetosella at least part of the water taken up fills the intercellular gas spaces. Elongation of completely submerged Rumex plants does not vary with different depths of submergence, This was concluded from the observation that there is little effect of either hydrostatic pressure or irradiance on leaf elongation during complete submergence. However, when R. palustris plants were subjected to a changing water depth, i.e. alternate periods of complete submergence and waterlogging, they elongated less strongly than under permanent complete submergence. Water movements did not affect leaf elongation induced by submergence.
Fructan exohydrolase activities from Lolium rigidum that hydrolyze β‐2, 1‐ and β‐2, 6‐glycosidic linkages at different rates
Authors: BONNETT G. D. , SIMPSON R. J.
Published: April 2006

Five fructan exohydrolase activities from Lolium rigidum Gaudin were separated and partly purified by a combination of salt precipitation, affinity chromatography, gel‐filtration chromatography, anion‐exchange chromatography and isoelectric focusing. The activities were identified by incubating enzyme fractions with fructan from both Lolium rigidum and Cichorium intybus. On the basis of activities when (6,6,6)‐kestopentaose and (1,1,1)‐kestopentaose were used as substrates, it was concluded that three of the activities hydrolyzed β‐2, 6‐glycosidic linkages faster than β‐2,l‐glycosidic linkages and two activities hydrolyzed β‐2,l‐glycosidic linkages faster than β‐2, 6‐glycosidic linkages. Fructan exohydrolases that hydrolyze β‐2,l‐glycosidJc linkages faster than β‐2, 6‐glycosidic linkages, and fructan exohydrolases that hydrolyze β‐2, 6‐glycosidic linkages faster than β‐2,1‐ glycosidic linkages have not previously been identified together in a temperate grass. All fructan exohydrolases were inhibited markedly by sucrose. It is proposed that the classification of β‐fructofuranosidases be reconsidered because EC 3.2.1. 80 is presently used to designate all fructan exohydrolases irrespective of the rates at which they hydrolyze β‐2, 6 or β‐2, 6‐glycosidic linkages in fructans.
Reorganization of the endoplasmic reticulum in pea leaf epidermal cells infected by the powdery mildew fungus Erysiphe pisi
Authors: LECKIE CALUM P. , And JAMES A. CALLOW , GREEN JONATHAN R.
Published: April 2006

During the formation of haustoria by biotrophic pathogens the synthesis of extra host plasma membrane (PM) is required to accommodate the invagination of the PM and its transition to the extrahaustorial membrane. This implicates alterations in host exocytosis, membrane trafficking and targeting. Probes for endoplasmic reticulum (ER) and whole‐cell imaging by confocal laser scanning microscopy (CLSM) have been used to examine the organization of the endoplasmic reticulum (ER) in compatible interactions between pea leaf cells and Erysiphe pisi DC ex Saint‐Amans. In uninfected epidermal cells, the dicarbocyanine dye DiOC6(3) and the ER‐specific anti‐HDEL antibody showed cortical ER was an open network of tubules interspersed with lamellar cisternae, immediately beneath the cuticle. Endoplasmic reticulum in infected cells could not be stained with DiOC6(3) but anti‐HDEL labelling revealed that the ER was no longer evenly distributed throughout the cortical cytoplasm but was concentrated in a tight network in the viciniti, of the haustorium particularly at early stages of infection. In some infected cells there was intense ER staining very close to the extrahaustorial membrane. Endoplasmic reticulum was also observed as large cisternae adjacent to the haustorial complex (HC), contrasting with tubular ER structures distal to the HC. In Western blots, anti‐HDEL labelled one major band at 70 icDa (probably the BiP homologue) in extracts from uninfected and infected epidermis, mycelia and haustoria. Additional proteins at 55 and 80 kDa were recognized in the fungal extracts. A minor protein at 50 kDa in uninfected pea is possibly upregulated in infected leaves. Overall, the results show that in a compatible pea powdery mildew interaction, the host cortical ER reorganizes around the developing HC from early to late stages of the infection process. This reorganization is likely to be involved in the exocytosis of new membrane and matrix materials which contribute to the expanding HC.
Root hair length determines beneficial effect of a Glomus species on shoot growth of some pasture species
Authors: SCHWEIGER P. F. , ROBSON A. D. , BARROW N. J.
Published: April 2006

Differences between plant species in the benefit derived from arbuscular mycorrhizal colonization have often been attributed to differences in physical properties of their roots, especially in root hair development. To test this hypothesis, the growth response to phosphate of five pasture species which differed markedly in the length of their root hairs was measured. Plants in the mycorrhizal treatments were inoculated with a Glomus sp. (isolate WUM 10(1)) while non‐mycorrhizal plants received control inoculum. Benefit was described as the relative effectiveness of phosphorus (P) for the mycorrhizal plants compared with non‐mycorrhizal plants. The beneficial effect of Glomus sp. was inversely related to root hair length of the host plant but it was not well related to root diameter, root length per plant or root/shoot ratio. It is suggested that root hairs and external hyphae of Glomus sp. act as alternative, similar ways of shortening the distance for the diffusion of phosphate in soils.
Chitinolytic activities of Eucalyptus pilularis and Pinus sylvestris root systems challenged with mycorrhizal and pathogenic fungi
Authors: HODGE A. , ALEXANDER I. J. , GOODAY G. W.
Published: April 2006

The chitinolytic activities of Pinus sylvestris L. and Eucalyptus pilularis Sm. roots were measured after an exposure for 24 h to either ectomycorrhizal (Pisolithus tinctorius (Pers.) Coker and Couch) or root‐infecting pathogenic fungi (Heterobasidion annosum (Fr.) Karst. and Phytophthora cinnamomi Rands.). P. sylvestris roots not exposed to fungal hyphae had low levels of β‐N‐acetylglucosaminidase. This activity greatly increased after exposure to H. annosum but not P. cinnamomi or P. tinctorius.β‐N‐Acetylglucosaminidase activity in E. pilularis roots was unchanged after exposure to P. cinnamomi or P. tinctorius. Exo‐ and endochitinase activity increased after P. sylvestris roots were challenged with H. annosum, but not by the other fungi. These results suggest that β‐N‐acetylglucosaminidase might be an important early response to chitinous pathogens.
Nitrogen metabolism in the ectomycorrhizal fungus Hebeloma crustuliniforme
Authors: QUORESHI ALI M. , AHMAD IFTIKHAR , MALLOCH DAVID , HELLEBUST JOHAN A.
Published: April 2006

With glucose as the carbon source, the ectomycorrhizal basidiomycete Hebeloma crustuliniforme (Bull. ex. Amans) Quel. utilizes nitrate, ammonium and amino acids as sources of nitrogen. Inoculated as a suspension of fine hyphae in such liquid media, the fungus expands rapidly, exhibiting a distinct exponential phase with a doubling time of 1–2 d and a maximum content of mycelial protein during the first 7 d of growth. Its growth when amino acids serve as sole carbon and nitrogen source is, however, less rapid, and requires several days of induction under these conditions. In H. crustuliniforme, assimilation of ammonium appears to be carried out primarily via the NADPH‐glutamate dehydrogenase (GDH) pathway. Its NADPH‐GDH levels in exponentially growing mycelia are several times greater than the apparent nitrogen assimilation rates of the mycelia. Its levels of glutamine synthetase activity in comparison are very small during the exponential period of growth. The greatest levels of NADH‐GDH are found in glucose‐grown cultures during the post‐exponential period, and in glucose‐free amino acid‐grown cultures during the active period of growth. This suggests a catabolic role for the NADH‐GDH. Aspartate aminotransferase and alanine aminotransferase in H. crustuliniforme are highly active during the exponential period of growth, and their concentrations are increased further in the presence of amino acids as sole nitrogen sources, suggesting a key role for these enzymes in interactions between pathways of amino acid metabolism and carbon metabolism in the fungus.
The effects of rind damage and regeneration on permeability of the apoplast in sclerotia of Sclerotinia minor
Authors: YOUNG NICOLA , ASHFORD ANNE E.
Published: April 2006

summary

Sclerotia of Sclerotinia minor Jaggar have the ability to regenerate a new rind when the old rind is damaged before or after maturity. Regeneration involves growth of a completely new rind to cut off the exposed damaged surface. New, more or less spherical rind and cortical cells form by outgrowth of existing medullary hyphae. The new rind cells become pigmented over several days and new cortical cells contain reserves when the new rind has become fully pigmented. This process is most rapid in immature sclerotia but even in mature sclerotia, a new rind is fully regenerated within 8 d. Intact mature sclerotia exclude the apoplastic tracer sulforhodamine C but when the rind is damaged they become leaky to the fluorochrome. Regeneration of a new rind reduces permeability to sulforhodamine but the initial impermeable state is not fully regained, even when regeneration is complete. Sclerotia that have been damaged in the field, despite regeneration, might be more susceptible to external influences than those in which the rind has remained intact.
Evolutionary comparative analyses of the relationship between leaf structure and function
Authors: BEERLING D. J. , KELLY C. K.
Published: April 2006

summary

We have applied evolutionary comparative methods to control for phylogenetic relationships between species in order to determine if three recently proposed relationships between leaf structure and function are upheld, using a large database comprising a wide range of species from tropical and temperate ecosystems. The three hypotheses tested were: (i) leaf thickness is positively correlated with total stomatal density (adaxial and abaxial values summed); (ii) amphistomatous leaves (stomata present on the upper and lower surfaces) have a higher maximum stomatal conductance than hypostomatous (stomata on the lower surface only) leaves, and (iii) changes in the stomatal density on upper and lower leaf surfaces are regulated in a compensatory manner. The results showed that, contrary to several mathematical modelling studies, thicker leaves were not associated with more stomata either in species from lowland tropical rain forests or from central Europe. Amphistomatous leaves had a higher maximum stomatal conductance, indicating that one aspect of previous modelling work is correctly underpinned after accounting for relatedness. Finally, we found no evidence that the stomatal densities on upper and tower leaf surfaces are closely regulated. These three physiological traits are discussed with reference both to the modelling of leaf gas exchange and to plant function in relation to microclimate.
Allometric relations and growth in Pinus taeda: the effect of elevated CO2, and changing N availability
Authors: GEBAUER RENATE L. E. , REYNOLDS JAMES F. , STRAIN BOYD R.
Published: April 2006

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Loblolly pine (Pinus taeda L.) seedlings were grown for 138 d at two CO2 partial pressures (35 and 70 Pa CO2) and four N solution concentrations (0.5, 1.5, 3.5 and 6.5 mM NH4NO3). Allometric regression analysis was used to determine whether patterns of biomass allocation among functionally distinct plant‐parts were directly controlled by CO2 and N availability or whether differences between treatments were the result of size‐dependent changes in allocation. Both CO2 and N availability affected growth of loblolly pine. Growth stimulation by CO2 at nonlimiting N solution concentrations (3.5 and 6.5 mM NH4NO3) was c. 90%. At the lowest N solution concentration (0.5 mM NH4NO3), total plant biomass was still enhanced by 35% under elevated CO2. Relative growth rates were highly correlated with net assimilation rates, whereas leaf mass ratio remained unchanged under the wide range of CO2 and N solution concentrations. When differences in plant size were adjusted apparent CO2 effects on biomass allocation among different plant parts disappeared, indicating that CO2 only indirectly affected allocation through accelerated growth. N availability, by contrast, had a direct effect on biomass allocation, but primarily at the lowest N solution concentration (0.5 mM NH4NO3). Loblolly pine compensated for N limitation by increasing specific lateral root length and proportional biomass allocation to the lateral root system. The results emphasize the significance of distinguishing size‐dependent effects on biomass allocation from functional adjustments made in direct response to changing resource availability.
Contents of free amino acids in Scots pine needles from field sites with different levels of nitrogen deposition
Authors: HUHN G. , SCHULZ H.
Published: April 2006

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The response of pine stands in areas with three different levels of nitrogen deposition was analysed on samples of the current year's needles. Each test area was subdivided into five test sites. Clear changes in the amounts of amino acids in relation to the nitrogen content of pine needles were found. Analyses were mainly focused on the amino acids glutamate (Glu), glutarnine (Gin) and those forming the urea cycle. The concentration of Gin increased significantly with response to increasing needle nitrogen content. Arginine (Arg) accumulated dramatically (up to 100‐fold) at high levels of needle nitrogen, but had the highest variation within the test sites. Ornithine (Orn) showed an increase only if the needle nitrogen content was very high. No clear relationship found in the case of Glu. Glutarnine and Arg are useful bioindicators of nitrogen pollution in pine stands.
Root colonization of mycorrhizal and non‐mycorrhizal pepper (Capsicum annuum) by Pseudomonas fluorescens 2–79RL
Authors: MARSCHNER PETRA , CROWLEY DAVID E.
Published: April 2006

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The survival and physiological status of a plant‐beneficial pseudomonad on the roots of mycorrhizal and non‐mycorrhizal pepper were examined. Pepper plants were grown for 20 d in split‐root microcosms with one side of the root system mycorrhizal with Glomus deserticola (GD) or Glomus intraradices (GI), while the other side was non‐mycorrhizal. Plants with both sides non‐mycorrhizal served as controls. The soil was inoculated with a bioluminescence‐marked strain, Pseudomonas fluorescens 2–79RL. Due to a ribosomal promoter that has been coupled to a lux gene cassette, P. fluorescens 2–79RL emits light in its exponential growth phase. Previous studies showed that the length of the lag phase of bioluminescence after transfer of soil‐cultured cells into rich medium can be used to assess the physiological status of this strain. After 20 d, shoot and root weight of the mycorrhizal plants in comparison with the control plants was decreased by 35% and 45% by GD and GI, respectively, indicating a high carbon cost of the mycorrhizal infection. Mycorrhizal infection was only 6% for GD, whereas it was 40 % for GI. Compared with the non‐mycorrhizal plants, GD affected P. fluorescens 2–79RL on the roots only on the side where the fungus was present, but had no effect on the non‐mycorrhizal side. On the mycorrhizal side, GD decreased the population density of P. fluorescens 2–79RL by 50 % and its physiological status by one order of magnitude. By contrast, GI decreased both the population density and the physiological status on the mycorrhizal and the non‐mycorrhizal side by one order of magnitude. On individual root segments, there was no correlation between the percentage mycorrhizal infection and the population density of P. fluorescens 2–79RL. It is concluded that some mycorrhizal fungi can reduce both the population density and the physiological status of certain bacterial groups in the rhizosphere.
Isozyme variation and somatic incompatibility in populations of the ectomycorrhizal fungus Suillus collinitus
Authors: EL KARKOURI K. , CLEYET‐MAREL J.‐C. , MOUSAIN D.
Published: April 2006

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Isozyme variation and somatic incompatibility were investigated in order to study intraspecific genetic variation and to identify genets in natural populations of the ectomycorrhizal fungus Suillus collinitus (Fr.) O. Kuntze, Forty‐three isolates, obtained from basidiocarps collected in 11 forest sites under Pinus trees, were examined. Isozyme analysis indicated high intraspecific variation between isolates from the same location and from different locations. Phenetic analysis based on calculated dissimilarity values derived from isozyme banding patterns separated the isolates into two main groups (I and II) with 35% dissimilarity. A specific and highly active acid phosphatase isoform (ACP‐2) was detected in most group II isolates. Dikaryotic isolates displaying isozyme similarity coefficient of 100 % were found to be somatically compatible and were considered to originate from the same genet. The same genet was never found at more than two forest sites. This study showed a high correlation between the results of electrophoretic isozyme analysis and those of somatic incompatibility reactions. The results were discussed in terms of population biology.
Sulphur dioxide effects on fungi growing on leaf litter and agar media
Authors: DURSUN S. , INESON P. , FRANKLAND JULIET C. , BODDY LYNNE
Published: April 2006

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Respiration of four decomposer fungi (Mycena galopus (Pers.) Kutnmer, Aureobasidium pullulans (de Bary) Arnaud, Phoma exigua Desm. and Cladosporium cladosporioides (Fres.) de Vries) growing on four species of leaf litter (Pinus sylvestris L., Picea sitchensis (Bongard) Carriére, Fraxinus excelsior L. and Corylus avellana L.) was inhibited by dry‐deposited SO2 in a laboratory experiment. Mycelial extension of the four fungi growing on four different agar media was inhibited by SO3 fumigation (40 nl l−1) in the laboratory, and media containing carbohydrates decreased the inhibitory effect of SO2 fumigation. Fumigation caused a statistically significant reduction in the mycelial extension of all species tested on tap‐water agar. These experiments demonstrate that decomposition of leaf litter is inhibited by environmentally realistic concentrations of SO2 and that the effect is exerted via inhibition of saprotrophic fungi.
Late Quaternary vegetational history at Navarrés, Eastern Spain. A two core approach
Authors: CARRION J. S. , DUPRE M.
Published: April 2006

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Percentage and concentration pollen diagrams are presented for two cores (taken 5 m apart) at an upper Pleistocene and Holocene site at Navarrés (Valencia, eastern Spain). Chronological information is provided by an internally consistent radiocarbon dating series that extends from c. 20700 to 3075 yr BP. The results highlight the dangers of relying on a single core in interpreting the patterns of variation of particular taxa. Significant palynological differences, seemingly locational, are described between the two cores. The upper Pleistocene records accords well with the widely recognized European sequence of (a) upper Pleniglacial, (b) Bölling‐Allerod warm period, and (c) Younger Dryas crisis. However, the sequence does not show disruption of vegetation patterns following the commencement of the Holocene, and Pinus continues to be dominant up to c. 5500–6000 yr BP. Later, there is evidence for Quercus forest, mesophilous trees, and xerosclerophyllous Mediterranean vegetation, which is coincident with eutrophication of the study site. These vegetation changes are discussed in the context of anthropogenic disturbance by Neolithic people, competitive exclusion, and climatic change.
Antimicrobial defences in the wood of living trees
Authors: PEARCE R. B.
Published: April 2006

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The wood (xylem) in a living tree is protected from microbial attack by the secondary plant surface (periderm and rhytidome), which provides an effective barrier preventing the entry of most potential pathogens, and by constitutive and induced defence mechanisms in the bark (cortex and phloem). Although a few pathogens are able To penetrate these outer tissues directly, most xylem pathogens gain entry through wounds that expose this tissue and render it more vulnerable to attack. In functional sapwood, microbial colonization might be restricted by active defence mechanisms, or by passive microenvironmental restriction consequent upon the high water content and low availability of O2in healthy conductive xylem. These factors are not mutually exclusive: indeed, they may operate in concert in many host‐pathogen interactions. Sapwood lesions made by wood‐decaying fungi are characteristically bounded by multiccllular walls OT barrier zones (compartmentalization wall 4 barriers and reaction zones (column boundary layers)), which may function both as inhibitory or degradation‐resistant barriers to further pathogen spread, and as seals to maintain xylem function and prevent the drying and aeration that could predispose to further infection. A range of putative antimicrobial defence mechanisms contributing to the effectiveness of such barriers has been identified in sapwood tissues. This includes cell wall alterations, constitutive and induced antimicrobial compounds, necrotic responses of living cells and the deposition of gummy materials, often resinous or polyphenolic, at the host‐pathogen interface. Nutritional, environmental and anatomical features of living wood might also contribute to pathogen restriction. Although there might be differences in detail, the defences operating in gymnospenns and angiosperms are generally similar. Defence responses against a variety of pathogen categories also have much in common. Dynamic studies are crucial in elucidating the roles of the various components of the host‐pathogen interaction in the wood of living trees. A model for the protection and defence of xylem tissues in woody angiosperms is suggested, based largely upon results from dynamic studies of host‐pathogen interactions in the wood of sycamore (Acer pseudoplatanusL.).

CONTENTSSummary203I.Introduction204II.Xylem pathogens205III.Bark the first line of defence206IV.Defence in functional sapwood207V.Defence in heartwood222VI.Dynamic aspects of the host‐pathogen interaction in wood223VII.Genetic control of resistance in xylem tissues224VIII.Antimicrobial defence in the living xylem of trees: towards a consensus model225Acknowledgements227References227
Analysis of stomatal CO2uptake by a three‐dimensional cylindrically symmetric model
Authors: VESALA T. , AHONEN T. , HARI P. , KRISSINEL E. , SHOKHIREV N.
Published: April 2006

summary

A numerical model is introduced that solves the steady‐state diffusion equation for a single stoma and the mesophyll surrounding. This system has cylindrical symmetry, and diffusive transport of carbon dioxide in the gas phase is coupled with transfer in mesophyll alone with y photosynthetic sink rate and respiratory production rates. The mesophyll is treated as a continuously distributed liquid phase, and the photosynthetic rate is determined by the carbon dioxide concentration, the photosynthetic photon flux density and the chlorophyll concentration. Photorespiration is proportional to the photon flux density, and dark respiration is assumed to be constant. The model offers a rigorous way to investigate the roles of physics and geometrical structure in stomatal gas exchange. Lateral (radial) diffusion and differences between hypostomatous and needle‐like leaves are analysed with special attention. To vield realistic stomatal behaviour, the model requires that the diffusion coefficient describing mesophyllic transport must be somewhat larger than carbon dioxide diffusivity in pure liquid water. The mesophyllic carbon dioxide concentration slopes sharply towards a constant value as a function of distance from the surface of a sub‐stomatal cavity. The optimal placement of chlorophyll is close to the surface containing stomata.