bluuebunny/crossref_metadata_2025 huggingface dataset:
Soluble and membrane‐associated nitrate reductases in the dinoflagellate Peridinium gatunense
Authors: WITT FEDERICO G. , STÖHR CHRISTINE , ULLRICH WOLFRAM R.
Published: March 2003

An improved method of cell fractionation allowed the extraction of soluble (sNR) and membrane‐associated (mNR) forms of nitrate reductase (NR) from a dinoflagellate, even though in previous studies only mNR had been found in these algae. Both activities were assayed in cell‐free extracts of Peridinium gatunense from Lake Kinneret, Israel, after disruption of the cells and differential centrifugation. In the cultures used, sNR showed much higher NO3−‐reducing activity. Only a low proportion, 2.5–3% of NR activity, was found to be associated with mNR. Moreover, mNR comprised two forms as indicated by protein solubilization: a tightly membrane‐bound and a more weakly attached NR. Ascorbate inhibited all NR activities, but that of mNR recovered after its removal. Polyvinyl pyrrolidone (PVP) and DTT also diminished sNR and mNR activities. For both enzymes, pH optima (7.65) and temperature optima (13–25°C) were similar, and agreed with those for optimum growth of P. gatunense both in culture and in the lake. The most efficient electron donor was NADH, though NADPH sustained low NR activities. Carboxylic anions such as succinate and malate did not support any reduction of NO3−, nor did they cause any stimulation of sNR or mNR activities. Both forms of NR showed a high affinity for their substrates: Km was c. 10 μM for NO3− and c. 5 μM for NADH. The high efficiency of NO3− assimilation by Peridinium seems to be limited mainly by energy under otherwise optimal nutritional conditions and, at low nitrate concentrations, the low Km may be one of the main reasons for the high competitivity of this alga in Lake Kinneret.
Nitrogen uptake by rhizomes of the clonal sedge Carex bigelowii: a previously overlooked nutritional benefit of rhizomatous growth
Authors: BROOKER R. W. , CALLAGHAN T. V. , JONASSON S.
Published: March 2003

Studies on the rhizomatous clonal sedge Carex bigelowii, at a fellfield site in subarctic Swedish Lapland examined the ecological potential of rhizomes as nitrogen uptake systems. Direct application of a solution of 15NH415NO3 to the rhizomes of C. bigelowii significantly enriched the 15N content of the plant tissue. The pattern of enrichment indicated movement of labelled nitrogen into rhizomes and adjoining tissue (including roots and shoots), showing both uptake and translocation via the rhizome system. There was a gradient of decreasing 15N enrichment with increasing distance from the point of labelling, and estimation of the total mass of nitrogen taken up via labelled rhizomes showed low levels and rates of uptake. Quantification of the size of rhizome and root systems of C. bigelowii at the study site indicates that 80% of the living biomass may be below ground, and that the surface area of the rhizome system of C. bigelowii is approx. two‐thirds that of the roots. The rhizome system of C. bigelowii can therefore act as a route for nitrogen uptake, with the potential to exploit almost as great a volume of soil as the root system. This mechanism of nitrogen uptake may play an important role in the Arctic, where many species have a clonal, rhizomatous growth form. In addition, plant growth in many arctic ecosystems is limited by low soil nutrient availability, a result of low temperatures (leading to slow soil decomposition rates) and patchy resource distribution. Nitrogen uptake via rhizomes may provide plants with the capacity to take advantage of transient nutrient supplies, and may partly compensate for the cost of developing and maintaining persistent rhizome networks in ecosystems where nutrient resources are in short supply.
Phosphate solubilization by organic anion excretion from rice growing in aerobic soil: rates of excretion and decomposition, effects on rhizosphere pH and effects on phosphate solubility and uptake
Authors: KIRK G. J. D. , SANTOS E. E. , SANTOS M. B.
Published: March 2003

Rice (Oryza sativa) plants were grown with their roots sandwiched between thin layers of phosphorus‐deficient soil from which they were separated by fine mesh, and root‐induced changes in the soil affecting phosphate solubility were measured. The concentrations of low molecular weight organic anions in the thin layers, particularly citrate, increased in the presence of the plants. Apparent rates of citrate excretion from the roots, calculated from the quantities in the soil and rates of decomposition calculated with a first order rate constant measured independently, varied from 337–155 nmol g−1 root f. wt h−1 over the course of plant growth, equivalent to 2–3% of plant d. wt. Rates of excretion were similar for NH4+ and NO3−‐fed plants. The soil pH decreased from its initial value by up to 0.6 units for the NH4+‐fed plants and increased by up to 0.4 units for the NO3−‐fed ones. The contribution of organic anion excretion to the pH changes was small compared with that of the inorganic cation‐anion balance in the plants. The extent to which the observed excretion of citrate and root‐induced pH changes could account for the observed phosphate solubilization and uptake was assessed using a mathematical model. Previous work had shown that phosphate solubilization by rice in this soil could not be explained by enhanced phosphatase activity in the rhizosphere, and the roots were not infected with mycorrhizas. The model allows for the diffusion of the solubilizing agent (citrate or H+) away from the roots, its decomposition by soil microbes (citrate only); its reaction with the soil in solubilizing phosphate and diffusion of the solubilized phosphate to the roots. The model contains no arbitrary assumptions and uses only independently measured parameter values. The agreement between the measured time course of phosphorus uptake and that predicted for solubilization by citrate was good. Root‐induced acidification by NH4+‐fed plants resulted in additional solubilization, the acidification enhancing the solubilizing effect of citrate. However, the final phosphorus uptake by NH4+‐fed plants was no greater than that of NO3−‐fed plants, presumably because the acidification inhibited plant growth. The mechanism of solubilization by citrate involved formation of soluble metal‐citrate chelates rather than displacement of phosphate from adsorption sites.
Patterns of arbuscular mycorrhiza down the profile of a heavy textured soil do not reflect associated colonization potential
Authors: NEHL D. B. , McGEE P. A. , TORRISI V. , PATTINSON G. S. , ALLEN S. J.
Published: March 2003

Colonization of roots by arbuscular mycorrhizal (AM) fungi in several annual crops in two consecutive seasons was compared with, in the second season, the density of fungal propagules in the soil with the use of a bioassay. Root density decreased down the soil profile in both years in all crops, and a high proportion of roots were mycorrhizal throughout the profile. AM colonization decreased down the profile in cotton and lablab in the second season only. The bioassay indicated that most propagules of AM fungi in soils under cotton were located near the surface, with virtually no propagules at 1 m. The absence of propagules at depth indicates a lack of mycelium deep in the soil, and suggests that mycorrhizas are primarily initiated in the surface soil and that the fungi colonize the root system mostly through secondary spread down the profile. The use of AM colonization in the field as an indicator of propagule density and symbiotic function should be qualified by an understanding of the depth in the soil from which roots were extracted.
Silicon promotes nodule formation and nodule function in symbiotic cowpea (Vigna unguiculata)
Authors: NELWAMONDO A. , DAKORA F. D.
Published: March 2003

Applying silicon in the form of metasilicic acid (H4SiO3) or silicic acid (H4SiO3) to Bradyrhizobium‐infected, hydroponically grown cowpea seedlings resulted in a significant (P⩽0.05) increase in the number of nodules, nodule dry matter, and nitrogen fixed on a per plant basis. Total dry matter of plants increased with silicon supply, and the differences were significant (P⩽0.05) at the higher silicon concentrations. Cowpea plants cultured in sand were also assessed for their response to silicic acid. Nodule number and nodule mass increased with silicon supply to sand cultured plants, though nitrogen fixation was unaltered. Although silicon is not essential for growth of cowpea, it is important for nodule formation and nodule functioning in hydroponically grown plants. Consequently, data collected and conclusions drawn from earlier glasshouse experiments, which have excluded silicon from nutrient solutions, may be flawed. Future studies on nodulation and nitrogen fixation using legumes in liquid culture must therefore include silicon as a nutrient element.
The importance of xylem constraints in the distribution of conifer species
Authors: BRODRIBB T. , HILL R. S.
Published: March 2003

Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (ϕ50) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi‐arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides. Mean ϕ50 was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of ϕ50 was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO2 concentration (ci) in the leaves of these species during artificial drought was strongly correlated with ϕ50 suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade‐off between xylem conductivity and xylem vulnerability was tested in a sub‐sample of four species, but no evidence of an inverse relationship between ϕ50 and either stem‐area specific (Ka) or leaf‐area specific conductivity (K1) was found.
Simultaneous collection of xylem sap from Rhinanthus minor and the hosts Hordeum and Trifolium: hydraulic properties, xylem sap composition and effects of attachment
Authors: SEEL W. E. , JESCHKE W. D.
Published: March 2003

The facultative hemiparasite Rhinanthus minor was grown alone, or with either Hordeum vulgare or Trifolium alpestre as a host. All plants were fed 5 mM nitrate. In the parasites, successful attachment led to dramatic increases in growth (particularly with barley as host) and in tissue concentrations of total N, NO3−, H2PO4− and K+, as well as moderate increases in Cl− and SO42−. Mg2+ and Ca2+ concentrations either remained unchanged, increased or decreased, depending on the host. Xylem sap was collected from leaf veins (barley) or the stem (Rhinanthus and clover), by applying pneumatic pressure to the rooted soil to raise the soil water potential so that in vivo xylem sap exuded from small incisions once the applied pressure balanced the tension exerted by transpiration. High balancing pressures were needed for unattached Rhinanthus, whereas simultaneous collection of xylem sap from attached Rhinanthus and its host, at a much lower balancing pressure, was possible only when the parasite was enclosed in polyethylene film and high transpiration abolished. From plots of xylem sap volume flow versus applied pressure, the hydraulic conductivity Lp and the overall hydraulic resistance r were obtained. The value of r was high in unattached Rhinanthus and dramatically decreased by attachment to a host, highlighting the improved access to water gained by Rhinanthus when parasitizing a host. For the parasites, attachment resulted in greatly increased concentrations and solute flow rates in xylem of K+, NO3−, H2PO4− and amino acids, and decreased concentrations of Ca2+ and Mg2+. Estimates of NO3− reduction in the parasite showed that 99% was reduced in unattached plants, 85% in those attached to clover and 52% in those attached to barley. In the parasitized hosts, ion concentrations in xylem sap were somewhat increased relative to unparasitized controls. Conversely, xylem sap amino‐acid concentrations in infected hosts were decreased. Glutamine (Gln) was the principal amino acid in xylem sap of unattached Rhinanthus, but after attachment to both hosts asparagine (Asn) predominated. In clover, Asn was the major transport amino acid, suggesting massive transfer of Asn from host to parasite. In unparasitized barley, however, Gln was the major xylem sap amino acid, but unexpectedly, in this species Asn was induced as the principal amino acid when parasitized. The results are discussed in terms of mutual host–parasite interactions.
Short‐term phosphorus uptake rates in mycorrhizal and non‐mycorrhizal roots of intact Pinus sylvestris seedlings
Authors: COLPAERT JAN V. , VAN TICHELEN KATIA K. , VAN ASSCHE JOZEF A. , VAN LAERE ANDRÉ
Published: March 2003

Short‐term phosphate uptake rates were measured on intact ectomycorrhizal and non‐mycorrhizal Pinus sylvestris seedlings using a new, non‐destructive method. Uptake was quantified in semihydroponics from the depletion of Pi in a nutrient solution percolating through plant containers. Plants were grown for 1 or 2 months after inoculation at a low relative nutrient addition rate of 3% d−1 and under P limitation. Four ectomycorrhizal fungi were studied: Paxillus involutus, Suillus luteus, Suillus bovinus and Thelephora terrestris. The Pi‐uptake capacity of mycorrhizal plants increased sharply in the month after inoculation. The increase was dependent on the development of the mycobionts. A positive correlation was found between the Pi‐uptake rates of the seedlings and the active fungal biomass in the substrate as measured by the ergosterol assay. The highest Pi‐uptake rates were found in seedlings associated with fungi producing abundant external mycelia. At an external Pi concentration of 10 μM, mycorrhizal seedlings reached uptake rates that were 2.5 (T. terrestris) to 8.7 (P. involutus) times higher
than those of non‐mycorrhizal plants. The increased uptake rates did not result in an increased transfer of nutrients to the plant tissues. Nutrient depletion was ultimately similar between mycorrhizal and non‐mycorrhizal plants in the semihydroponic system. Net Pi absorption followed Michaelis–Menten kinetics: uptake rates declined with decreasing Pi concentrations in the nutrient solution. This reduction was most pronounced in non‐
mycorrhizal seedlings and plants colonized by T. terrestris. The results confirm that there is considerable heterogeneity in affinity for Pi uptake among the different mycobionts. It is concluded that the external mycelia of ectomycorrhizal fungi strongly influence the Pi‐uptake capacity of the pine seedlings, and that some mycobionts are well equipped to compete with other soil microorganisms for Pi present at low concentrations in soil solution.
Endogenous polyamine content and metabolism in the ectomycorrhizal fungus Paxillus involutus
Authors: FORNALÉ SILVIA , SARJALA TYTTI , BAGNI NELLO
Published: March 2003

Endogenous polyamine content of the ectomycorrhizal fungus Paxillus involutus, as well as the activity of its biosynthetic enzymes in relation to mycelia ageing were investigated in this work. Polyamines in free, PCA‐soluble and insoluble conjugated forms, are present in Paxillus involutus mycelia in relatively high amounts and the ratio of putrescine to spermidine is age‐dependent. Both arginine‐ and ornithine‐decarboxylases are present, but putrescine biosynthesis proceeds mostly via ornithine decarboxylase and decreases with the age of mycelia. There was a large release of free polyamines from mycelia which showed age‐dependent features. Clear polyamine uptake was observed in 2‐wk‐old mycelia and no competition between putrescine and cadaverine was detected. Putrescine uptake seems to reduce ornithine decarboxylase activity, but does not affect arginine decarboxylase.
Molecular diversity within and between ericoid endophytes from the Ericaceae and Epacridaceae
Authors: McLEAN C. B. , CUNNINGTON J. H. , LAWRIE A. C.
Published: March 2003

This study investigated the relationships between ericoid mycorrhizal endophytes of the Ericaceae (Northern Hemisphere) and the Epacridaceae (Australia). Over 200 fungi were isolated from the roots of two species of Epacridaceae from Victoria, Australia. The isolates were divided into 12 groups by morphology on quarter‐strength potato dextrose agar. All were slow‐growing and most were dematiaceous, but groups varied from white through pink to dark olive. The ITS1–5.8S–ITS2 ribosomal DNA was amplified and sequenced from eight isolates, forming typical ericoid mycorrhizal morphology in Epacris impressa and one nonmycorrhizal isolate. Sequences were compared, by using similarities and maximum‐parsimony analysis, with those of Hymenoscyphus ericae (Leotiales) and Oidiodendron species (Hyphomycetes), the most common endophytes of the Ericaceae. Maximum‐parsimony analysis produced four clusters: (1) all Oidiodendron species (at least 90% similarity); (2) all five Victorian dark grey‐olive isolates (at least 96% similarity); (3) one Victorian isolate and Cistella grevillei (88% similarity); (4) two light‐coloured Victorian isolates and H. ericae (81% similarity). This suggests that these isolates from the Epacridaceae do not belong to the same species as those forming ericoid mycorrhiza in the Ericaceae.
Ozone threshold doses and exposure–response relationships for the development of ozone injury symptoms in wild plant species
Authors: BERGMANN E. , BENDER J. , WEIGEL H.‐J.
Published: March 2003

The relative ozone sensitivities of 25 German native herbaceous plant species, representative of arable field margins or disturbed habitats, were examined over three consecutive growing seasons. Plants were grown from seed, potted into natural soils and exposed in open‐top chambers for the entire season to different ozone‐exposure regimes covering a range of concentrations from <5 to 48 ppb (seasonal 8 h daily mean). The assessment of ozone effects was carried out by recording the first day of visible symptom appearance and the percentage of injured leaves at the end of vegetative growth. Species exhibited contrasting patterns of symptom expression under ozone stress, with either ozone‐specific symptoms or ozone‐enhanced foliar pigmentation and senescence. Classifications of species according to their ozone susceptibility varied depending on whether measurement was of the total extent of visible injury, ozone threshold doses for the incidence of symptoms, or modelled exposure–response relationships. The most sensitive species exhibiting ozone‐specific symptoms were Cirsium arvense and Sonchus asper, which responded to accumulated ozone exposures <1500 ppb.h (AOT40). For these and three other species, an AOT40 peak of a single day was found to be responsible for the incidence of ozone‐specific symptoms, i.e. injury occurred rapidly within a few days of the day with the highest AOT40, while other species responded only to longer‐term ozone exposures. The relative ozone sensitivity of the species was calculated by combining the different sensitivity criteria, and possible systematic trends (taxonomic or evolutionary features) are pointed out. The results suggest it may be possible to use a particular group of native herbaceous plant species with contrasting patterns of ozone sensitivity as a biomonitoring system in the field. This allows plant responses to be related either to peak values or to prolonged ozone exposure, making it possible to distinguish between short‐ and long‐term effects of ozone.
The role of carbonic anhydrase in photosynthesis and the activity of the carbon‐concentrating‐mechanism in bryophytes of the class Anthocerotae
Authors: SMITH ELIZABETH C. , GRIFFITHS HOWARD
Published: March 2003

The role of carbonic anhydrase in the carbon‐concentrating‐mechanism of bryophytes of the class Anthocerotae was investigated by comparing the gas‐exchange characteristics of material which had been incubated in the membrane‐permeable Carbonic Anhydrase inhibitor ethoxyzolamide, with those of untreated material and material which had been incubated in buffer solution. In Phaeoceros laevis (Anthocerotae), incubation in ethoxyzolamide caused a depression in the rate of gross assimilation and a decrease in CO2 affinity beyond that which could be attributed to increased diffusion limitation. A range of liverworts and mosses, in which a carbon‐concentrating‐mechanism is absent, were also investigated. These showed no depression of rates of gross assimilation after incubation in ethoxyzolamide relative to those of untreated material. The CO2 compensation point and CO2 uptake characteristics of Phaeoceros laevis were significantly affected by incubation in ethoxyzolamide. Values of CO2 compensation point for Phaeoceros laevis rose from 2.5 Pa, after incubation in buffer, to 20 Pa after incubation in ethoxyzolamide. The CO2 compensation point for the liverworts Pellia epiphylla and Marchantia polymorpha was not significantly affected by incubation in ethoxyzolamide. Measurements of the release of CO2 at the end of a short (15 min) period of illumination revealed that, after suppression of carbonic anhydrase activity, the rapid release of a CO2 pool occurred in Phaeoceros laevis but not in the liverworts. There were also significant differences between values for fractionation measured in units per mil (‰), measured instantaneously, for Phaeoceros laevis incubated in ethoxyzolamide, compared with fractionation values for this species after incubation in buffer. Incubation in ethoxyzolamide caused fractionation values to rise from 12.4–22.7‰, indicating that the carbon‐concentrating‐mechanism of this species had been inactivated. Incubation in ethoxyzolamide had no effect on fractionation values for the liverworts. The convexity of the light saturation curves of liverworts and Phaeoceros laevis was also investigated, but there were no differences between groups before or after the two treatments. The data indicate an important role for carbonic anhydrase in the functioning of the carbon‐concentrating‐mechanism in the Anthocerotae.
Cadmium for all meals – plants with an unusual appetite
Authors: Krämer Ute
Published: March 2003

Since the beginning of the Bronze Age the acquisition of metals and the mastering of metal processing has been a driving force in human civilisation. It is difficult to imagine, however, how a plant could possibly profit from accumulating excessive amounts of a metal for which there is no metabolic need. Leaving behind an environmentally degraded wasteland, human mining and smeltering activities contributed to providing the niches for such plants, sometimes even accomplishing seed dispersal – through seeds attached to the boots of migrating miners. A stunning example of this is found in the healthy populations of Thlaspi caerulescens in the Cevennes (southern France), the leaves of which have been found to contain the toxic and non‐essential metal cadmium (Cd) at concentrations between 1000 and 3000 mg kg−1 dry biomass (R. D. Reeves, unpublished). In this issue, experiments under controlled experimental and glasshouse conditions are reported, confirming an extraordinary level of Cd accumulation and tolerance in these populations (Lombi et al., pp. 11–20).
Aluminium effects on microtubule organization in dividing root‐tip cells of Triticum turgidum. I. Mitotic cells
Authors: FRANTZIOS G. , GALATIS B. , APOSTOLAKOS P.
Published: March 2003

The effects of aluminium (Al) on dividing root‐tip cells of Triticum turgidum were investigated with tubulin immunolabelling and electron microscopy. Aluminium affects the mechanisms controlling the organization of microtubule (MT) cytoskeleton, as well as tubulin polymerization, and induces the following aberrations in mitotic cells. (1) It delays the MT disassembly during mitosis, resulting in the persistence of preprophase MT bands in the late prophase cells, the presence of prophase spindles in prometaphase cells, and a disturbance in the shortening of kinetochore MT bundles in anaphase cells. (2) It interferes with the self‐organization process of MTs into bipolar systems, inhibiting the formation of prophase and metaphase spindles. (3) Aluminium induces the formation of atypical MT arrays, which in the immunofluorescent specimens appear as ring‐like tubulin aggregations in the cortical cytoplasm of the preprophase/prophase cells and as endoplasmic tubulin bundles in prophase and metaphase/anaphase cells; abnormal preprophase MT bands are assembled, consisting of atypical cortical and endoplasmic MT bundles, the latter clearly lining the nuclear envelope on the preprophase MT band plane. (4) It disorders the chromosome movements carried out by the mitotic spindle. In addition, after prolonged Al treatments chromatin condensation is inhibited. The outcome is greatly disturbed organization and function of the mitotic apparatus, as well as inhibition of cells from entering mitosis. This study shows that the MT cytoskeleton is a target site of Al toxicity in mitotic root‐tip cells of T. turgidum. The possible mechanisms by which Al exerts its toxicity on MT organization and function are discussed.
An arbuscular mycorrhizal inoculum enhances root proliferation in, but not nitrogen capture from, nutrient‐rich patches in soil
Authors: HODGE A. , ROBINSON D. , FITTER A. H.
Published: March 2003

Most work on root proliferation to a localized nutrient supply has ignored the possible role of mycorrhizal fungi, despite their key role in nutrient acquisition. Interactions between roots of Plantago lanceolata, an added
arbuscular mycorrhiza (AM) inoculum and nitrogen capture from an organic patch (Lolium perenne shoot material)
dual‐labelled with 15N and 13C were investigated, to determine whether root proliferation and nitrogen (N) capture
was affected by the presence of AM fungi. Decomposition of the organic patch in the presence and absence of roots
peaked in all treatments at day 3, as shown by the amounts of 13CO2 detected in the soil atmosphere. Plant N
concentrations were higher in the treatments with added inoculum 10 d after patch addition, but thereafter did
not differ among treatments. Plant phosphorus concentrations at the end of the experiment were depressed by the
addition of the organic residue in the absence of mycorrhizal inoculum. Although uninoculated plants were also
colonized by mycorrhizal fungi, colonization was enhanced at all times by the added inoculum. Addition of the
AM inoculum increased root production, observed in situ by the use of minirhizotron tubes, most pronouncedly
within the organic patch zone. Patch N capture by the end of the experiment was c. 7.5% and was not significantly
different as a result of adding an AM inoculum. Furthermore, no 13C enrichments were detected in the plant
material in any of the treatments showing that intact organic compounds were not taken up. Thus, although the
added AM fungal inoculum benefited P. lanceolata seedlings in terms of P concentrations of tissues it did not
increase total N capture or affect the form in which N was captured by P. lanceolata roots.
Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue
Authors: MARTRE PIERRE , DURAND JEAN‐LOUIS , COCHARD HERVE
Published: March 2003

Xylem maturation in elongating leaf blades of tall fescue (Festuca arundinacea) was studied using staining and
microcasting. Three distinctive regions were identified in the blade: (1) a basal region, in which elongation was
occurring and protoxylem (PX) vessels were functioning throughout; (2) a maturation region, in which elongation
had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function; (3) a distal,
mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic
conductivity (Kh) was measured in leaf sections from all these regions and compared with the theoretical axial
hydraulic conductivity (Kt) computed from the diameter of individual inner vessels. Kt was proportional to Kh
throughout the leaf, but Kt was about three times Kh. The changes in Kh and Kt along the leaf reflected the
different stages of xylem maturation. In the basal 60 mm region, Kh was about 0.30±0.07 mmol s−1 mm MPa−1.
Beyond that region, Kh rapidly increased with metaxylem element maturation to a maximum value of 5.0±0.3
mmol s−1 mm MPa−1, 105 mm from the leaf base. It then decreased to 3.5±0.2 mmol s−1 mm MPa−1 near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.
Beetle grazing reduces natural infection of Rumex obtusifolius by fungal pathogens
Authors: HATCHER P. E. , PAUL N. D.
Published: March 2003

In previously reported laboratory experiments, infection of Rumex obtusifolius by the rust fungus Uromyces rumicis
was decreased on leaves which had prior herbivory by the beetle Gastrophysa viridula. In this paper we investigate
whether this interaction is robust for natural infection by a variety of fungi in field experiments carried out in
spring and autumn with plants given different levels of nitrogen fertilization. Grazing by G. viridula led to a
decrease in lesion density of Ramularia rubella and Venturia rumicis in the spring and V. rumicis and U. rumicis
in the autumn experiment. For V. rumicis and U. rumicis significant reductions in lesion density occurred on the
undamaged leaves of damaged plants, compared with similar leaves on undamaged plants, suggesting systemic
induced resistance. This induced resistance was usually independent of the amount of nitrogen fertilization,
although the inhibitory effect of grazing on R. rubella in the spring and V. rumicis in the autumn experiment was
enhanced by increasing nitrogen fertilization and was inhibited by increasing nitrogen fertilization for V. rumicis
in the spring. In both experiments, the lesion density of V. rumicis was greater on leaves on which R. rubella was
also present, and the presence of U. rumicis in the autumn experiment was linked to a similar but greater effect
on V. rumicis lesion density. We found no evidence of induced resistance by fungi against fungi in these experiments. We highlight the complex interactions between inhibitory and facilitatory processes acting on leaf fungal infection. These results are compared with the proposed molecular mechanisms of induced resistance(s) and we consider the benefits of closer integration between molecular and ecological investigations of induced resistances that occur in the field.
Histochemical and biochemical approaches to the study of phenolic compounds and peroxidases in needles of Norway spruce (Picea abies)
Authors: SOUKUPOVÁ J. , CVIKROVÁ M. , ALBRECHTOVÁ J. , ROCK B. N. , EDER J.
Published: March 2003

The three youngest age‐classes of needles of Norway spruce (Picea abies) were collected from four sites in the
Krusne Hory Mountains (Czech Republic) characterized by different levels of damage caused by environmental
pollution. Histochemical methods did not reveal any differences in localization of phenolics among the needles.
Mesophyll cells close to the epidermis of needles and cells around resin ducts and substomatal cavities often
accumulated higher amounts of phenolics than the rest of the mesophyll cells, but this was independent of age and
damage. Needles of different age‐ and damage‐class did not show any marked changes in general lignification
pattern. However, a lower intensity of histochemical detection of lignin was observed in needles from the most
damaged site. This finding was confirmed by chemical analysis using thioglycolic acid. Generally, the amount of
lignin in mesophyll cells was lower in damaged trees than in healthy ones. Using the Folin–Ciocalteau method,
no significant differences in the total content of phenolics were observed in the needles, although HPLC revealed
marked alterations in the forms of seven phenolic acids. Concentrations of conjugated forms of phenolic acids
(esters and glycosides) were higher in damaged needles (255.9 μg g−1 f. wt) than in healthy needles (189.8 μg g−1
f. wt). By contrast, content of esterified phenolic acids incorporated into cell walls was higher in needles from
healthy trees (101.1 μg g−1 f. wt) than in damaged needles (78.3 μg g−1 f. wt). Marked differences were also observed in the activity of soluble peroxidases, although the activity of ionically bound forms was approximately the same in healthy and damaged needles. The total amounts of chlorophylls and carotenoids decreased as environmental damage increased.
Root dynamics and global change: seeking an ecosystem perspective
Authors: NORBY RICHARD J. , JACKSON ROBERT B.
Published: March 2003

Changes in the production and turnover of roots in forests and grasslands in response to rising atmospheric CO2
concentrations, elevated temperatures, altered precipitation, or nitrogen deposition could be a key link between
plant responses and longer‐term changes in soil organic matter and ecosystem carbon balance. Here we summarize
the experimental observations, ideas, and new hypotheses developed in this area in the rest of this volume. Three
central questions are posed. Do elevated atmospheric CO2, nitrogen deposition, and climatic change alter the dynamics of root production and mortality? What are the consequences of root responses to plant physiological processes? What are the implications of root dynamics to soil microbial communities and the fate of carbon in soil? Ecosystem‐level observations of root production and mortality in response to global change parameters are just starting to emerge. The challenge to root biologists is to overcome the profound methodological and analytical problems and assemble a more comprehensive data set with sufficient ancillary data that differences between ecosystems can be explained. The assemblage of information reported herein on global patterns of root turnover, basic root biology that controls responses to environmental variables, and new observations of root and associated microbial responses to atmospheric and climatic change helps to sharpen our questions and stimulate new research approaches. New hypotheses have been developed to explain why responses of root turnover might differ in contrasting systems, how carbon allocation to roots is controlled, and how species differences in root chemistry might explain the ultimate fate of carbon in soil. These hypotheses and the enthusiasm for pursuing them are based on the firm belief that a deeper understanding of root dynamics is critical to describing the integrated response of ecosystems to global change.
The DL gene system in common bean: a possible mechanism for control of root–shoot partitioning
Authors: HANNAH M. A. , IQBAL M. J. , SANDERS F. E.
Published: March 2003

Crosses between certain genotypes of common bean result in dwarfing of F1 plants and lethal dwarfing in a proportion of the F2 population. This is under the control of the semi‐dominant alleles, DL1 and DL2 at two
complementary loci which are expressed in the root and shoot respectively. The various DL genotypes can be
simulated by grafting. The graft combination DL1DL1dl2dl2/dl1dl1DL2DL2 was found to have a significantly
higher root dry matter fraction than either parent. Lethally dwarfed plants (DL1DL1DL2DL2) and the analogous
lethal graft combination (dl1dl1DL2DL2/DL1DL1dl2dl2) exhibit failure of root growth and have very low root fractions. Hybrids or graft combinations with failed roots ceased growth and accumulated large amounts of starch throughout their hypocotyls. In sterile culture, both lethal dwarfs and lethal graft combinations were able to grow roots if sucrose was added to the growth medium. This indicates that a failure of sucrose translocation to the roots is probably responsible for failed root growth. Data from screening the DL genotypes of 49 cultivars could be fully explained using the DL system hypothesis, and grafting proved to be efficient for identifying DL genotype. The DL system might be of fundamental importance in root–shoot partitioning. Current evidence favours the hypothesis that failure of root growth is the outcome of excessively high sink strength of shoots compared to roots, which might arise from signalling incompatibilities between the genotypes.
A fossil fern indicator of epiphytism in a Tertiary flora
Authors: POOLE IMOGEN , PAGE CHRISTOPHER N.
Published: March 2003

The first known indicator of probable fern epiphytism in the Tertiary fossil record is documented from the Eocene London Clay of southeast England. This pyritised fern rachis exhibits major deviation from the basic form of petiolar vascular trace morphology shown by the other London Clay fossil ferns and is here attributed to the Polypodiaceae. This represents the first known occurrence of this family in the London Clay macroflora, and brings the total of distinct fern rachis types from the Lower Tertiary of southeast England to six. The significance of this find is interpreted in relation to its probable origins from a tropical rainforest palaeoflora in which it is proposed that this specimen represents the first occurrence of an epiphytic component.
Tansley Review No. 120
Authors: ROCK CHRISTOPHER D.
Published: March 2003

Recent progress in ABA signalling is summarized from the perspectives gained by genetic (mutant) analysis, ‘reverse genetics’ (starting from unknown ABA‐inducible sequences and working backwards) and biochemical studies. What emerges is a cell‐biological model of overlapping tissue‐specific stress (e.g. drought, salt and cold) and developmental (e.g. sugars and other hormones) response pathways that integrate into responses mediated by ABA, including but not limited to seed maturation, dormancy, inhibition of cell division and germination, stomatal closure and changes in gene expression leading to stress adaptation. ABA signalling involves putative ABA receptors (extracellular or intracellular), cell‐surface membrane proteins including ion channels, glycoproteins and membrane trafficking components, secondary messengers such as phosphatidic acid, inositol 1,4,5‐trisphosphate, cyclic ADP‐ribose and calcium, and protein phosphorylation/dephosphorylation cascades leading to chromatin remodelling and binding of transcriptional complexes to ABA‐responsive promoter elements. The large gaps in our understanding of complex regulatory networks such as ABA signalling can be best addressed by multidisciplinary, integrated approaches such as those discussed.

Contents

Summary

I.
INTRODUCTION
358

II.
GENETIC ANALYSIS OF ABA RESPONSES
359

III.
‘REVERSE GENETIC’ ANALYSIS OF ABA‐REGULATED GENE EXPRESSION
371

IV.
BIOCHEMICAL AND CELLULAR ANALYSES OF ABA SIGNALLING
378

V.
CONCLUSIONS AND PERSPECTIVES
387

Acknowledgements
387

References
387
Extraradical hyphae of the mycorrhizal fungus Glomus intraradices can hydrolyse organic phosphate
Authors: KOIDE R. T. , KABIR Z.
Published: March 2003

Organic phosphorus sources make up a large fraction of the total P in some soils. Vesicular–arbuscular mycorrhizal fungi provide a large surface area for the absorption of inorganic P. The question of whether or not they have direct access to organic P by producing extracellular phosphatases has hitherto been controversial because experiments had not been performed in the absence of other soil microorganisms. We used a split‐dish in vitro carrot mycorrhiza system free from contaminating microorganisms. The extraradical hyphae of Glomus intraradices hydrolysed both 5‐bromo‐4‐chloro‐3‐indolyl phosphate and phenolphthalein diphosphate. Moreover, they transferred significantly more P to roots when they had access to inositol hexaphosphoric acid (phytate) than when they did not. Thus we show unequivocally that extraradical hyphae of G. intraradices can hydrolyse organic P, and, further, that the resultant inorganic P can be taken up and transported to host roots.
Interactions between pea root‐inhabiting fungi examined using signature fatty acids
Authors: Larsen John , Bødker Lars
Published: March 2003

• Interactions are investigated between the arbuscular mycorrhizal fungus, Glomus mosseae, and the root pathogen, Aphanomyces euteiches, on pea (Pisum sativum) roots, as arbuscular mycorrhiza are known to suppress a broad range of root pathogens.

•  Phospholipid (PLFA) and neutral lipid (NLFA) fatty acids were used as indicators of biomass and energy reserves, respectively, of A. euteiches and G. mosseae in inoculated roots of pot‐grown pea seedlings.

• Symbiosis between pea and G. mosseae had no effect on the severity of disease caused by A. euteiches, which decreased pea shoot and root dry weight. However, the presence of G. mosseae in pea roots reduced both biomass and energy reserves of A. euteiches, indicated by a reduction in PLFA 14 : 0 and both NLFAs 14 : 0 and 14 : 1ω9. Similarly, a reduction in PLFA and NLFA 16 : 1ω5 indicated reduced biomass and energy reserves of G. mosseae in A. euteiches‐infected roots.

•  Signature fatty acids can be used to quantify biomass and energy reserves of G. mosseae and A. euteiches simultaneously, in pea root; this appears to be a promising method for studying interactions between arbuscular mycorrhizal fungi and root pathogens in planta.
Rice carbon balance under elevated CO2
Authors: Sakai Hidemitsu , Yagi Kazuyuki , Kobayashi Kazuhiko , Kawashima Shigeto
Published: March 2003

Season‐long effects of elevated CO2 concentration ([CO2]) on the carbon balance of the rice (Oryza sativa) canopy are reported here.

 The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol−1[CO2] (ambient) in three chambers, or at 650 µmol mol−1 (elevated) in the other three chambers. Canopy net photosynthesis and night‐time respiration were determined in the chambers by mass balance.

 Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the CO2 enrichment. But CO2‐induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated [CO2] was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew.

 These results show that the increase in rice biomass by elevated [CO2] results more from the increase in carbon gain at early rather than later stages of growth.
Arbuscular mycorrhiza in mini‐mycorrhizotrons: first contact of Medicago truncatula roots with Glomus intraradices induces chalcone synthase
Authors: Bonanomi Athos , Oetiker Jürg H. , Guggenheim Richard , Boller Thomas , Wiemken Andres , Vögeli‐Lange Regina
Published: March 2003

The association of plants with arbuscular mycorrhizal (AM) fungi is widespread in nature, but little is known about molecular aspects of this symbiosis. Particularly during the early stages of the AM symbiosis, it is difficult to monitor growth of the two partners, to dissect gene expression patterns and to correlate them with plant, fungal or symbiosis development.

 A new system, the ‘mini‐mycorrhizotron’, was established to cultivate seedlings of Medicago truncatula in mycorrhizal symbiosis with Glomus intraradices under gnotobiotic conditions. This system allows natural growth of the symbiotic partners and permits the continuous noninvasive observation of the development of plant and fungus under a microscope.

 The mini‐mycorrhizotron was used to determine the stage of induction of a mycorrhiza‐related gene detected by differential display‐reverse transcription‐PCR, namely a novel chalcone synthase (Mt‐chs1). The gene is induced in roots at the stage of the first fungal contact.

The mini‐mycorrhizotron allowed identification and cloning of a symbiosis‐related gene, and the correlation between its expression and the developmental stage of the symbiosis was established. This provides a useful tool for molecular and developmental studies of the early stages of AM symbioses.

Mt‐chs1 nucleotide sequence can be found at the Genbank data base (accession no. AJ277211). The following sequences were also used: Glycine maxchs (X52097), chs1 (X54644); chs2 (X65635), chs3 (X53958), chs5 (L07647), chs6 (L03352), chs7 (M98871); Pisum sativumchs (X80007), chs1 (D10661), chs2 (X63334), chs3 (D88261), chs4 (D88260), chs5 (D88262), chs7 (D88263); Medicago sativachs1 (L02901), chsI (X68106), chs2 (L02902), chs4–1 (U01018), chs8 (L02904), chs9 (L02905), 12–1 (U01021); Medicago truncatulachs1, this work (AJ277211); Trifolium subterraneumchs1 (M91193), chs2 (M91194), chs3 (L24515), chs4 (L24516), chs5 (L24517), chs6 (M91195); Phaseolus vulgarischs (X06411) and Vigna unguiculatachs (X74821).
Canopy position affects the temperature response of leaf respiration in Populus deltoides
Authors: Griffin Kevin L. , Turnbull Matthew , Murthy Ramesh
Published: March 2003

• Leaf respiration and its temperature response were measured in 4‐m‐tall, 1‐yr‐old Populus deltoides trees to assess the effect of within‐canopy distribution of respiratory physiology on total foliar C exchange of a model ecosystem at Biosphere 2.

• Over the course of five nights, air temperature was varied over a 10°C range and the steady‐state rate of leaf respiration was measured. These data were then modeled to calculate the temperature response of leaf and canopy respiration.

• Results indicate that there is considerable within‐canopy variation in both the rate of respiration and its temperature response and that these variables are most strongly related to leaf carbohydrate and leaf N. Scaling these results to the ecosystem level demonstrates the importance of quantifying the vertical distribution of respiratory physiology, particularly at lower temperatures.

• Simplifying assumptions regarding the variation in respiration and its temperature response with canopy height tend to result in an underestimation of the actual C loss if the assumptions are based on lower‐ or mid‐canopy leaf physiology, but overestimate C loss if the model assumptions are based on upper‐canopy physiology.
What has QTL mapping taught us about plant domestication?
Authors: Paterson Andrew H.
Published: March 2003

The aim of this paper is to survey the general area of quantitative trait locus (QTL) mapping, and its specific impact on current understanding of plant domestication. Plant domestication is not only of historical interest, but is also of ongoing importance as changing human needs and availability of nonrenewable resources impel continuing (and perhaps even accelerated) investigation of prospective new crops. New genomic tools applied in conjunction with now‐established approaches such as QTL mapping are opening new doors into searches for the ‘footprints’ of domestication, and promise to accelerate and streamline the identification of specific genes integral to domestication(s), building on early successes. Better understanding of plant domestication promises to enhance knowledge about the developmental basis of some of the more striking evolutionary events known, to guide efforts to catalog plant biodiversity, and to accelerate progress in improving existing and new crops to sustain humanity.ContentsSummary591I.Introduction592II.A backdrop: QTL mapping basics593III.The tempo of domestication596IV.Domestication and polyploidy601V.New approaches to identifying the footprints of domestication603VI.Perspectives605Acknowledgements606References606