bluuebunny/crossref_metadata_2025 huggingface dataset:
Mycorrhizal formation by Paxillus involutus strains in relation to their IAA‐synthesizing activity
Authors: RUDAWSKA M. L. , KIELISZEWSKA‐ROKICKA B.
Published: March 2003

summary

IAA production by the ectomycorrhizal fungus Paxillus invotutus grown in pure culture was investigated by testing IAA accumulation or IAA‐synthesizing activity. All the Paxillus involutus strains studied released indole compounds either when incubated with 0.5 mM tryptophan or in its absence. HPLC analyses of indole compounds all yielded two main peaks identified by reference to controls as being IAA and indole‐3‐carboxylic acid and a small peak of indole‐3‐aldehyde. Mass spectrometry unequivocally confirmed IAA production in the culture filtrates and in the incubation solution used to study in vitro IAA‐synthesizing activity. The IAA‐synthesizing activity was found to vary widely, from 7.6 to 137.4 nmol IAA h−1 g−1 f. wt, between strains. The mycorrhizal activity of these strains with seedlings of Pinus sylvestris cultured under aseptic conditions was tested. Fungal strains that were characterized in pure culture conditions by high LAA‐synthesizing activity induced more fine roots and significantly higher numbers of mycorrhizas than strains which showed a low activity of IAA synthesizing enzymes. The increased ectomycarrhiza formation was generally accompanied by an increased growth of seedlings.
Ozone‐induced accumulation of carbohydrates changes enzyme activities of carbohydrate metabolism in birch leaves
Authors: EINIG W. , LAUXMANN U. , HAUCH B. , HAMPP R. , LANDOLT W. , MAURER S. , MATYSSEK R.
Published: March 2003

summary

Birch cuttings (Betula pendula Roth) were grown in a sand‐culture system with two concentrations (0.05, HF and 0.005%, LF) of fertilizer containing macronutrients and micronutrients, and were exposed to 90/40 nl 1−1 O3(day/night) and < 3 nl 1−1 O3 (control) for one growing season in the field fumigation chambers at Birmensdorf (Switzerland). Leaves of different ages were analysed for gas exchange, contents of chlorophyll, protein, and for metabolites as well as enzyme activities of carbohydrate metabolism.

Ozone reduced net photosynthesis and chlorophyll contents in mature leaves of both fertilization treatments, whereas that of protein was only reduced in high‐fertilized plants (HF). However, net photosynthesis, chlorophyll, and protein increased in young leaves of low‐fertilized plants (LF). The effects of ozone on enzyme activities of carbohydrate metabolism were most pronounced in leaves of LF plants. Specific activities of the sucrose‐cleaving enzymes, sucrose synthase and alkaline invertase, were induced, whereas acid invertase was unchanged. Extractable activity of sucrose phosphate synthase, which is a key enzyme of sucrose synthesis, was reduced. Levels of fructose 2,6‐bisphosphate, an inhibitor of sucrose synthesis, were increased in leaves of O3/LF plants, but reduced in O3/HF plants. In addition, activities of enzymes involved in starch metabolism, ADP‐glucose pyrophosphorylase and starch phosphorylase, were lowered in ozone‐treated samples and the ratio of ATP: ADP was increased.

It is concluded that chronic ozone exposure leads to an inhibition of sucrose synthesis and favours sucrose degradation. This effect is modulated by the nutrient status of the plants, indicating higher O3 tolerance in HF plants. Furthermore, as the metabolic responses in the ozone‐treated samples resemble very closely those observed under end‐product inhibition of photosynthesis, we assume that the O3 effect is mainly due to reduced photosynthate export.
Heterogeneity of fungal and plant enzyme expression in intact Scots pine–Suillus bovinus and –Paxillus involutus mycorrhizospheres developed in natural forest humus
Authors: TIMONEN SARI , SEN ROBIN
Published: March 2003

Isozyme expression of nutrient‐mobilizing and defence‐related enzymes were examined in different functional components of intact Scots pine (Pinus sylvestris L.) ectomycorrhizal root systems developed in natural unsterilized forest humus. Scots pine seedlings colonized by Suillus bovinus (L. ex Fr.) O. Kuntze or Paxillus involutus (Batsch ex Fr.) strains were grown on humus in two‐dimensional Perspex⌖ microcosms to allow development of complete ectomycorrhizal root systems. Soluble proteins from uncolonized short roots, whole mycorrhizal root tips or dissected mantle and core fractions, fungal strands and the outermost soil colonizing fine hyphae were subjected to native polyacrylamide gel electrophoresis and stained to detect esterase, acid phosphatase, peroxidase and different polyphenoloxidase isozyme activities. Tissue‐specific esterase isozymes were detected in all components and most, including unique Hartig net isozymes, were of fungal origin. High fungal acid phosphatase activities were detected in mycorrhiza and fine hyphae of S. bovinus, supporting earlier findings of active phosphatase activity at the fungal interface in the Hartig net region and in the fine hyphal margins of extramatrical mycelium actively colonizing the humus. All compartments in the P. involutus mycorrhizosphere had weaker acid‐phosphatase activities. Peroxidases formed a large part of the soluble‐protein content in non‐mycorrhizal short roots. The amount of peroxidases, on a tissue f. wt basis, was similar in mycorrhizal and non‐mycorrhizal roots, but differential isozyme expression was detected, indicating a change in root peroxidase activities following mycorrhiza formation. The expression of DL‐3,4‐dihydroxyphenylalanine metabolizing polyphenol oxidase enzymes was reduced in mycorrhizas compared with non‐mycorrhizal short roots. In the extramatrical mycelial components, fine hyphae expressed the highest polyphenoloxidase activity. P. involutus displayed some polyphenol‐oxidizing isoenzymes not detected in S. bovinus systems. Laccase activity was not detected in the plant and fungal components examined. It is concluded that enzyme activities and isozyme expression are differentially regulated in the different functional components of Scots pine mycorrhizospheres.
A seasonal cycle of cell wall structure is accompanied by a cyclical rearrangement of cortical microtubules in fusiform cambial cells within taproots of Aesculus hippocastanum (Hippocastanaceae)
Authors: CHAFFEY N. J. , BARLOW P. W. , BARNETT J. R.
Published: March 2003

Aspects of the structure and ultrastructure of the fusiform cambial cells of the taproot of Aesculus hippocastanum L. (horse chestnut) are described in relation to the seasonal cycle of cambial activity and dormancy. Particular attention is directed at cell walls and the microtubule and microfilament components of the cytoskeleton, using a range of cytochemical and immunolocalization techniques at the optical and electron‐microscopical levels. During the dormant phase, cambial cell walls are thick and multi‐layered, the cells possess a helical array of cortical microtubules, and microfilament bundles are oriented axially. In the early stages of reactivation, vesicle‐like profiles are associated with the cell walls, whereas arrangement of the cytoskeletal elements remains unchanged. In the succeeding active phase, the cell walls are thin, and cortical microtubules form a random array, although microfilament bundles maintain a near‐axial orientation. The observations are discussed in relation to the seasonal cycle of wall structure and cortical microtubule rearrangement within the vascular cambium of hardwood trees. It is suggested that the cell‐wall thickening at the onset of cambial dormancy, which is associated with the presence of a helical cortical microtubule array, should be considered to be secondary wall thickening, and that selective lysis of this secondary wall layer during cambial reactivation restores the thinner, primary wall found around active cambial cells.
Association between microtubules and symbiotic fungal hyphae in protocorm cells of the orchid species, Spiranthes sinensis
Authors: UETAKE YUKARI , PETERSON R. LARRY
Published: March 2003

Seeds of the orchid species, Spiranthes sinensis (Pers.) Ames, were sterilized and germinated in vitro with the symbiotic fungus Ceratobasidium cornigerum (Bourdot) Rogers. Colonized embryos developed into protocorms and these were examined for changes in microtubule arrays, after initial invasion of fungal hyphae into embryos and during peloton formation and degradation. Methods utilized to detect microtubules included immunofluorescence combined with laser scanning confocal microscopy, conventional transmission electron microscopy combined with morphometric analysis, and immunogold labelling. Microtubules were regularly found in close association with intracellular hyphae and degraded hyphal masses. Cortical microtubules disappear during peloton formation but reappear in cells that show fungal lysis. With conventional transmission electron microscopy and immunogold labelling the microtubules associated with fungal hyphae and degenerated hyphal masses were located close to the perifungal membrane that separates fungal hyphae from protocorm cytoplasm.
Abscisic acid in lichens: variation, water relations and metabolism
Authors: DIETZ S. , HARTUNG W.
Published: March 2003

For the first time the well known drought stress hormone abscisic acid, which is involved in regulating processes increasing desiccation tolerance in many plant systems, was analysed in lichens. ABA was detected in all 26 species investigated. In contrast to higher plants and liverworts, the ABA content increased after hydration of air dry lichen thalli and decreased in desiccating lichen material. Experiments with Baeomyces rufus (Huds.) Rebent indicated that the mycobiont might be the major site of ABA biosynthesis. After incubation of hydrated lichen thalli with radioactive ABA for up to 72 h no metabolism to phaseic acid and dihydrophaseic acid could be detected. Fluctuations of internal ABA might be a result of ABA release to the external medium.
Endophytic fungi associated with the temperate palm, Trachycarpus fortunei, within and outside its natural geographic range
Authors: TAYLOR J. E. , HYDE K. D. , JONES E. B. G.
Published: March 2003

Fungal endophytes associated with the palm, Trachycarpus fortunei, within and outside its natural geographic range were investigated. Endophytes were relatively common with colonization rates of 23–57% at the four sites sampled. The endophyte assemblages at the different sites were diverse with 75 fertile species of ascomycetes and mitosporic fungi. The assemblage composition at each site was similar and between seven and 13 species comprised 81–89% of the taxa present in relative frequencies of >1%. Glomerella cingulata and Phomopsis spp., were consistently dominant, and a large number of rare species were recorded. The diversity at each site was similar in number, but the abundance of isolates varied. The results obtained were comparable to those of previous studies of palm endophyte assemblages, but the assemblages showed more affinity with unrelated temperate hosts than with tropical palm hosts. Quantitative and qualitative differences in endophyte assemblages from old and young tissues were observed, and more isolates were recovered from old tissues independent of the age of the palm. The composition of the assemblage varied with several taxa being exclusively or more commonly isolated from old tissues (e.g. xylariaceous taxa, Oxydothis sp. nov.) or young tissues (e.g. Stagonospora spp., Phoma multirostrata). Some differences in the composition of the assemblage and in relative frequencies of various species were observed in trees and saplings. Significantly more isolates were recovered from the vein than intervein tissues, independent of leaf age or tree age. Tissue specificity was not exhibited by any taxa isolated from either leaf or petiole tissues, except for xylariaceous taxa in leaf tissues. Some other taxa showed a preference for leaf tissues or petioles, whereas others were equally distributed amongst all tissues. Endophyte assemblages of palms from continuous distributions were similar, but those from disjunct distributions (i.e. outside the natural geographic range of the palm, such as Australia and Switzerland), differed significantly from each other and from assemblages within continuous distributions. The relative importance values of endophyte species at the two sites in China indicates the site‐specific nature of the endophyte assemblages. Most previous studies on the endophytes of palm hosts have concentrated on tropical palms. However, this study examines the endophytes of the warm temperate palm Trachycarpus fortunei, and investigates the relative importance of host and climate related processes.
The response of sensitive and tolerant clones of Populus tremuloides to dynamic ozone exposure under controlled environmental conditions
Authors: YUN SUNG‐CHUL , LAURENCE JOHN A.
Published: March 2003

Both sensitive and tolerant clones of aspen (Populus tremuloides) were exposed to ozone using four different exposure regimes under controlled environmental conditions. Based on data on ambient ozone from 10 cities in the USA, three treatments of 4‐wk exposure to the same SUM06 (an accumulation of hourly O3 concentrations greater than 0.06 ml l−1) were constructed. The regimes allowed us to investigate: (a) the importance of long (3 wk, treatment 1) versus short (1 wk, treatment 2) duration of regimes with high peaks; (b) the effect of treatments with variable peak occurrence (treatments 1 and 2) versus uniform peak occurrence (treatment 3) during the exposure period. Nonfumigated control plants were maintained at ozone concentrations <10 nl l−1. Bifacial black necrosis, a typical symptom of ozone injury on aspen leaves, occurred on both clones after 2 wk exposure. Up to 60% of the leaves on the sensitive clone were injured, with an average of 6% of total leaf area injured. In the tolerant clone only 10% of the leaves were injured, with less than 1% of the total leaf area symptomatic. The severity of injury was consistently greatest in treatment 2, followed by treatments 1 and 3, respectively. The interval between peak exposures was less important than the occurrence of peaks versus a stable maximum concentration. Premature leaf abscission occurred in the sensitive clone. Measures of gas exchange demonstrated reduced photosynthesis under ozone fumigation, but exposure regime was not a significant factor. Concentrations of two antioxidants, ascorbic acid and glutathione, were almost always greater in the resistant than in the sensitive clone, but the differences were not statistically significant. The levels of these antioxidants in aspen leaves did not change with ozone fumigation or leaf age.
The influence of atmospheric NH3 on the apoplastic pH of green leaves: a non‐invasive approach with pH‐sensitive microelectrodes
Authors: HANSTEIN S. , FELLE H. H.
Published: March 2003

The apoplastic pH of intact green leaves of Bromus erectus was measured non‐invasively by inserting blunt microelectrodes through stomatal openings. After making electrical contact, the recorded signal was stable for hours, yielding a pH of 4.67±0.10. The leaves responded to ‘light‐off’ with an initial transient acidification and subsequent sustained alkalinization of 0.2–0.3 pH; ‘light‐on’ caused the opposite response. Flushing the leaves with 280 nmol NH3 mol−1 air within 18±6 s alkalinized the apoplast by 0.22±0.07 pH, followed by a slower pH increase to reach a steady‐state alkalinization of 0.53±0.14 after 19±7 min. This pH shift was persistent as long as the NH3 was flushed, and readily returned to its initial value after replacing the NH3 with clean air. The resultant [NH4+] increase within the apoplast was measured with a NH4+‐selective microelectrode. In the presence of 280 nmol NH3 mol−1 air, apoplastic NH4+ initially increased within 15±10 s to 1.53±0.41 mM, to reach a steady state of 1.62±0.16 mM after 27±7 min. An apoplastic buffer capacity of 6 mM pH−1 unit was calculated from the initial changes of pH and [NH4+], whereas the steady‐state values yielded 2.7 mM pH−1. Infiltrated leaves responded to NH4+ with concentration‐dependent depolarizations, the maxima of which yielded saturation kinetics indicating carrier‐mediated NH4+ uptake into adjacent cells, as well as a linear component indicating non‐specific transport. We infer that the initial alkalinization is due to rapid conversion of NH3 to NH4+, whereas the slower pH increase would be caused by regulatory processes involving both membrane transport, and (mainly) NH4+ assimilation. Possible consequences of the NH3‐induced pH shift for the development of plants growing in polluted areas are discussed.
Spatial organization of the gravitropic response in plants: applicability of the revised local curvature distribution model to Triticum aestivum coleoptiles
Authors: MEŠKAUSKAS AUDRIUS , JURKONIENE SIGITA , MOORE DAVID
Published: March 2003

The revised local curvature distribution model, which provides accurate computer simulations of the gravitropic response of mushroom stems, was found to produce accurate simulations of the gravitropic reaction of wheat (Triticum aestivum) coleoptiles. The key feature of the mathematical model that enables it to approach universality of application is the assumption that the stem has an autonomic straightening reaction (curvature compensation or ‘autotropism’). In the model, the local bending rate for any segment of the organ is determined by the difference between the ‘bending signal’ (generated by the gravitropic signal perception system) and a ‘straightening signal’ (which is proportional to the local curvature of the segment). The model reveals three major differences between the gravitropic reactions of wheat coleoptiles and Coprinus mushroom stems. First, in Coprinus, the capacity for autonomic straightening is much more concentrated in the apical region of the stem. Second, local perception of the gravitropic signal, which is necessary for exact simulation in Coprinus, is not needed in wheat coleoptiles (the corresponding constant in the model can be set to zero). Third, the transmission rate of the gravitropic signal is about seven times faster in wheat coleoptiles than in the mushroom stem. Thus, we demonstrate that a single model, depending on the values given to its parameters, is able to simulate the spatial organization of the gravitropic reaction of wheat coleoptiles and Coprinus mushroom stems. The model promises to be a valuable predictive tool in guiding future research into the gravitropic reaction of axial organs of all types.
Methods of assessing leaf‐fracture properties
Authors: ARANWELA N. , SANSON G. , READ J.
Published: March 2003

Numerous authors have attempted to quantify the physical properties of leaves in relation to aspects of leaf ecology, including decomposition, sclerophylly, herbivory, and leaf function and longevity. This paper examines the relative merits of the punch‐and‐die, tearing and shearing tests for assessing leaf physical properties. We conducted a series of these three mechanical tests on leaves of Solanum laciniatum, and determined the effect of various test parameters on the measurement of fracture properties. For the punch‐and‐die test, the parameters considered were machine speed, clearance between the punch and the die, edge definition of the punch, and area of the punch. Aspects of the tearing test examined were notch length, end effects, and length‐to‐width requirements of test strips, and for shearing tests the effects of blade proximity, angle and sharpness were investigated. All the test parameters investigated were found significantly to affect the assessment of leaf‐fracture properties. In addition, fracture properties were found to vary significantly within leaves. Some general principles for designing and implementing tests are outlined. This study suggests that while punching and shearing tests are useful means of quantifying leaf fracture properties, the value of the tearing test may be reduced as it is most constrained by the biological nature of the test material.
Nitrogen‐fixing legumes and silvigenesis in a rain forest in French Guiana: a taxonomic and ecological approach
Authors: ROGGY J. C. , PRÉVOST M. F.
Published: March 2003

The nodulation status and nodule morphology of 62 taxa of Leguminosae in a rain forest in French Guiana are reported according to the taxonomy of the family. The N2‐fixing species are then fitted into ‘functional groups’ according to their behaviour towards illumination, in order to evaluate their importance in the global dynamics of the stand. The results showed that 67% of the observed species were nodulated (50, 71 and 77% of the Caesalpiniaceae, Mimosaceae and Papilionaceae, respectively). In the Caesalpiniaceae, nodule‐like structures were reported in the genus Crudia and in the species Senna quinquangulata, although this needs to be confirmed. All the nodules studied in this subfamily were astragaloid and mucunoid. In the Mimosaceae, the ability of a new genus (Balizia) to form nodules was reported, as well as nodulation on aerial roots in Inga stipularis. The nodules studied were mainly mucunoid. In the Papilionaceae, nodulation on aerial roots in Poecilanthe hostmannii and on conventional roots of the genus Paramachaerium were reported for the first time. All types of nodular structures were found in this subfamily but the structures were quite uniform at the tribal level. These are consistent with suggestions that nodule morphology has a taxonomic value. Eight functional groups of N2‐fixing species are proposed, ranging from light dependance to shade tolerance. These results indicate the important role played by N2‐fixing species in the global dynamics of the stand and that N inputs by N2 fixation were continuous along the gradient of energetic resources that characterizes the silvigenetic process. The interactions between the photosynthetic capacities of the species and the ability to fix N2 in low light conditions are discussed.
The effects of elevated CO2 and light environment on growth and reproductive performance of four annual species
Authors: LEISHMAN MICHELLE R. , SANBROOKE KAREN J. , WOODFIN RICHARD M.
Published: March 2003

To predict changes in the range and density of plant species as a consequence of elevated atmospheric CO2, it is essential to characterize the effect of elevated CO2 on key components of plant life history stages such as rate of establishment and maturation of individuals, reproductive output and offspring fitness. We measured vegetative response, phenology, reproductive output and seed quality of four annual C3 plant species, grown from seed to senescence under ambient and elevated (ambient+200 ppm) CO2 and ambient and reduced (33% shade) light. Few previous studies have included all stages of a plant's life as well as characteristics of the next generation. Elevated CO2 had no effect on the vegetative attributes of Cardamine hirsuta, Spergula arvensis or Poa annua whereas Senecio vulgaris produced longer leaves and greater biomass. Both Senecio and Poa had faster maturation times. The vegetative response of Senecio was not translated into increased seed output, although seed mass and carbon∶nitrogen ratios were significantly increased. By contrast, Poa showed no vegetative response to elevated CO2, but had significantly increased seed production. Thus we found no evidence for a simple translation from vegetative response to elevated CO2 into reproductive response. There was also no consistent light‐mediated response to elevated CO2 among the four species. However, the effect of reduced light (33% shade) on vegetative and reproductive output was consistent across the four species and significantly stronger than the effect of elevated CO2. On the basis of this glasshouse study, we predict that Poa would be most likely of the four species to show significant increases in population size and migration potential, as a result of increased reproductive output, under elevated atmospheric CO2. However, this response may be relatively small compared with variation in growth and reproduction as a result of environmental heterogeneity in resources such as light.
How Agrobacterium rhizogenes triggers de novo root formation in a recalcitrant woody plant: an integrated histological, ultrastructural and molecular analysis
Authors: FALASCA GIUSEPPINA , REVERBERI MASSIMO , LAURI PAOLA , CABONI EMILIA , DE STRADIS ANGELO , ALTAMURA MARIA MADDALENA
Published: March 2003

Adventitious rooting might be induced in recalcitrant woody genotypes by infection with Agrobacterium rhizogenes, and, in some cases, might also require exogenous auxin. The objective of the present study was to determine how agrobacteria trigger root formation in the stem of a recalcitrant woody microcutting, which cytological events result from the combined presence of infection and exogenous auxin, and which types of roots are induced by infection. Microcuttings of a recalcitrant walnut (Juglans regia), infected or not with A. rhizogenes strain 1855, were cultured with either indolebutyric acid (IBA), IAA, or without exogenous hormones, to induce rhizogenesis. They were cytohistologically and ultrastructurally investigated at various times in culture. Southern blot and PCR analyses were performed to verify the frequency of transgenic, chimeric and bacterium‐containing roots. The infection was sufficient per se to stimulate rhizogenesis. Rooting on the infected cuttings was enhanced by exogenous IBA, which accelerated and increased root meristemoid formation, in comparison with without‐hormone treatment. Meristemoids were organized both directly by the cambial cells and indirectly by the callus, and showed a pluricellular origin. Inter and intracellular bacteria were observed in the stem throughout the culture period (30 d). They were preferentially present in the vessels, and mainly in those showing polyphenol deposition. In the infected IAA‐treated cultures, a high level of secondary xylem formation occurred instead of rhizogenesis. Nontransformed roots were preferentially produced by the infected cuttings treated with the auxins. Bacterium‐containing and chimeric roots were produced by infected cuttings independently of the treatment. Thus, in a recalcitrant walnut, nontransformed root meristemoids are stimulated by combining infection and exogenous indolebutyric acid. Furthermore, the persistence of bacteria in the stem during the culture and the pluricellular origin of the meristemoids explain the presence of the bacterium‐containing and chimeric roots.
Comparative kinetic analysis of ammonium and nitrate acquisition by tropical lowland rice: implications for rice cultivation and yield potential
Authors: KRONZUCKER H. J. , GLASS A. D. M. , SIDDIQI M. Y. , KIRK G. J. D.
Published: March 2003

Nitrogen limitation compromises the realization of yield potential in cereals more than any other single factor. In rice, the world's most important crop species, the assumption has long been that only ammonium‐N is efficiently utilized. Consequently, nitrate utilization has been largely ignored, although fragmentary data have suggested that growth could be substantial on nitrate. Using the short‐lived radiotracer 13N, we here provide direct comparisons
of root transmembrane fluxes and cytoplasmic pool sizes for nitrate‐ and ammonium‐N in a major variety of Indica
rice (Oryza sativa), and show that nitrate acquisition is not only of high capacity and efficiency but is superior to that of ammonium. We believe our results have implications for rice breeding and molecular genetics as well as the design of water‐management and fertilization regimes. Potential strategies to harness this hitherto unexplored N‐utilization potential are proposed.
Reproductive biomass in Holcus lanatus clones that differ in their phosphate uptake kinetics and mycorrhizal colonization
Authors: WRIGHT WENDY , FITTER ALASTAIR , MEHARG ANDREW
Published: March 2003

In normal populations of the common grass Holcus lanatus there is a polymorphism for arsenate resistance, manifested as suppressed phosphate uptake (SPU), and controlled by a major gene with dominant expression. A natural population of SPU plants had greater arbuscular‐mycorrhizal colonization than wild type, nonSPU plants. It was hypothesized that, in order to survive alongside plants with a normal rate of phosphate (P) uptake, SPU plants would be more dependent on mycorrhizal associations. We performed an experiment using plants with SPU phenotypes from both arsenate mine spoils and uncontaminated soils, as well as plants with a nonSPU phenotype. They were grown with and without a mycorrhizal inoculum and added N, which altered plant P requirements. We showed that grasses with SPU phenotypes accumulated more shoot P than nonSPU plants, the opposite of the expected result. SPU plants also produced considerably more flower panicles, and had greater shoot and root biomass. The persistence of SPU phenotypes in normal populations is not necessarily related to mycorrhizal colonization as there were no differences in percentage AM colonization between the phenotypes. Being mycorrhizal reduced flower biomass production, as mycorrhizal SPU plants had lower shoot P concentrations and produced fewer flower panicles than non‐mycorrhizal, nonSPU plants. We now hypothesize that the SPU phenotype is brought about by a genotype that results in increased accumulation of P in shoots, and that suppression of the rate of uptake is a consequence of this high shoot P concentration, operating by means of a homeostatic feedback mechanism. We also postulate that increased flower production is linked to a high shoot P concentration. SPU plants thus allocate more resources into seed production, leading to a higher frequency of SPU genes. Increased reproductive allocation reduces vegetative allocation and may affect competitive ability and hence survival, explaining the maintenance of the polymorphism. As mycorrhizal SPU plants behave more like nonSPU plants, AM colonization itself could play a major part in the maintenance of the SPU polymorphism.
Genetic variation and heavy metal tolerance in the ectomycorrhizal basidiomycete Suillus luteus
Authors: COLPAERT JAN V. , VANDENKOORNHUYSE PHILIPPE , ADRIAENSEN KRISTIN , VANGRONSVELD JACO
Published: March 2003

Twenty‐one isolates of the ectomycorrhizal fungus Suillus luteus were screened for their tolerance to the heavy
metals Zn, Cd, Cu and Ni, measured as inhibition of radial growth and biomass production. Two populations from
even‐aged pine stands were investigated: 10 isolates were obtained from an area polluted with high levels of Zn,
Cd and Cu, and 11 isolates were obtained from a control population located in a nearby unpolluted area. RFLP
patterns of the internal transcribed spacer region of the isolates confirmed the morphological identification of the
carpophores. All isolates were maintained on basic medium without elevated metals to avoid phenotypically
acquired metal tolerance. The in vitro Zn and Cd tolerance of the S. luteus isolates from the polluted habitat were
significantly higher than the tolerances measured in the isolates from the nonpolluted site. This observation
suggests that the elevated soil metal concentrations might be responsible for the evolution of adaptive Zn and Cd
tolerance. Tolerance was maintained in an isolate not exposed to elevated metals for 3 yr. The two S. luteus populations did not differ in tolerance to Cu and Ni. The mechanisms for the adaptive Zn and Cd tolerance are not identical as there was no correlation between response to the two metals; the most Zn‐tolerant isolate was the most sensitive for Cd in the metal‐tolerant population. Zinc did not accumulate in basidiocarp tissue, whereas Cd levels in basidiocarps were significantly higher in the population on the polluted site. Inter‐simple sequence‐repeat fingerprints showed that 90% of the isolates were from different individuals. The genetic variation in the population from the unpolluted site was considerably larger than that observed at the polluted site.
NH3 and NO2 fluxes between beech trees and the atmosphere – correlation with climatic and physiological parameters
Authors: GESSLER ARTHUR , RIENKS MICHAEL , RENNENBERG HEINZ
Published: March 2003

The dynamic‐chamber technique was used to investigate the correlation between NH3 and NO2 fluxes and
different climatic and physiological parameters: air temperature; relative air humidity; photosynthetic photon
fluence rate; NH3 and NO2 concentrations; transpiration rate; leaf conductance for water vapour; and
photosynthetic activity. The experiments were performed with twigs from the sun crown of mature beech trees
(Fagus sylvatica) at a field site (Höglwald, Germany), and with 12‐wk‐old beech seedlings under controlled
conditions. Both sets of experiments showed that NO2 and NH3 fluxes depended linearly on NO2 and NH3
concentration, respectively, in the concentration ranges representative for the field site studied, and on water‐vapour conductance as a measure for stomatal aperture. The NO2 compensation point determined in the field
studies (the atmospheric NO2 concentration with no net NO2 flux) was 1.8–1.9 nmol mol−1. The NH3 compensation point varied between 3.3 and 3.5 nmol mol−1 in the field experiments, and was 3.0 nmol mol−1 in
the experiments under controlled conditions. The climatic factors T and PPFR were found to influence both NO2
and NH3 fluxes indirectly, by changing stomatal conductance. Whilst NO2 flux showed a response to changing
relative humidity that could be explained by altered stomatal conductance, increased NH3 flux with increasing
relative humidity (>50%) depended on other factors. The exchange of NO2 between above‐ground parts of beech
trees and the atmosphere could be explained exclusively by uptake or emission of NO2 through the stomata, as
indicated by the quotient between measured and predicted NO2 conductance of approx. 1 under all environmental
conditions examined. Neither internal mesophyll resistances nor additional sinks could be observed for adult trees
or for beech seedlings. By contrast, the patterns of NH3 flux could not be explained by an exclusive exchange of
NH3 through the stomata. Deposition into additional sinks on the leaf surface, as indicated by an increase in the
quotient between measured and predicted NH3 conductance, gained importance in high air humidity, when the
stomata were closed or nearly closed and/or when atmospheric NH3 concentrations were high. Although patterns
of NH3 gas exchange did not differ between different months or years at high NH3 concentrations (c. 140 nmol
mol−1), it must be assumed that emission or deposition fluxes at low ambient NH3 concentration (0.8 and 4.5 nmol
mol−1) might vary significantly with time because of variation in the NH3 compensation point.
Tansley Review No. 117
Authors: PALMQVIST KRISTIN
Published: March 2003

Lichens are nutritionally specialized fungi (the mycobiont component) that derive carbon and in some cases nitrogen from algal or cyanobacterial photobionts. The mycobiont and photobiont live together in an integrated thallus, but they lack specific tissue for the transport of metabolites and resources between them. Carbon is acquired through photosynthesis in the photobiont, which is active when the lichen is wet and exposed to light. Lichen photosynthesis is limited primarily by water, light and nitrogen, but can also be constrained by slow diffusion of CO2 within the wet thallus. The assimilated carbon is exported from photobiont to mycobiont, which also predominates in terms of biomass, and apparently regulates the size of the photobiont population. It has therefore generally been assumed that most of the carbon is used for growth and maintenance of the fungal hyphae. However, the extent of photobiont respiration in relation to mycobiont respiration has seldom been quantified; neither do we know the pool sizes of various carbon sinks within lichens. Owing to this lack of fundamental data we do not know whether, or how, carbohydrate resources are regulated to maintain an optimal balance between energy input and expenditures in these symbiotic organisms. This review summarizes data on growth, carbon gain and carbon expenditures in lichens, with particular emphasis on factors determining the photosynthetic capacity of their photobionts. An attempt is made to introduce an economic analysis of lichen growth processes, a view that has often been adopted in studies of higher plants. Areas in which more data are needed for the construction of a model on ‘lichen resource allocation patterns’ are discussed.

Contents

Summary
11

I.
INTRODUCTION
12

II.
LICHEN BIONT CHARACTERISTICS
12

III.
LICHEN GROWTH
13

IV.
CARBON ACQUISITION
16

V.
CARBON SINKS AND EXPENDITURES
28

VI.
CONCLUDING REMARKS
30

Acknowledgements
31

References
31
Allometric determination of tree growth in a CO2‐enriched sweetgum stand
Authors: Norby Richard J. , Todd Donald E. , Fults Jason , Johnson Dale W.
Published: March 2003

In a free‐air CO2 enrichment (FACE) study, above‐ground growth of Liquidambar styraciflua (sweetgum) trees was measured in a closed‐canopy stand to test hypotheses about long‐term effects of rising [CO2] in a deciduous forest.

 Allometric relationships were established between above‐ground dry mass and basal area, height, taper and wood density for all trees in the 314‐m2 plots. Leaf area index was calculated from leaf litter mass.

 In the first year of exposure, elevated [CO2] stimulated stand‐level aboveground dry matter increment by 33%, but in the second year the growth stimulation was reduced to 15% and was no longer statistically significant. Leaf area index was not affected by CO2 enrichment in either year.

 These results indicate that large trees that are no longer in an exponential growth phase retain the capacity to respond to elevated [CO2]. The combined 2‐yr response of a 24% increase in growth per unit leaf area is consistent with predictions from earlier studies. A longer‐term data set is needed to resolve the reason for different responses in the 2 years.
Flooding‐tolerant legume symbioses from the Brazilian Pantanal
Authors: James EuaN. K. , Loureiro M. de Fatima , Pott Arnildo , Pott ValI. J. , Martins Claudia M. , Franco Avilio A. , Sprent Janet I.
Published: March 2003

Nodulated legumes in some of the flooded and seasonally flooded areas of the Pantanal Mato‐Grossense wetlands in Brazil are described here.

 In the permanently flooded lakes (baias) of the Caracara national park Discolobium pulchellum, Mimosa pellita, Sesbania exasperata and Vigna lasiocarpa (syn. Phaseolus pilosus) were the most abundant, whereas close to Corumbá, at the edges of the river Paraguai, Neptunia spp. were also common. Adaptations that allow these legumes to fix N2 in a flooded environment included a floating growth habit, aerenchyma and nodulated adventitious roots.

 By contrast, Aeschynomene spp. (A. ciliata, A. denticulata, A. fluminensis, and A. sensitiva) were the dominant nodulated legumes in the seasonally flooded pastures of Nhumirim.

 Stem‐nodulation was commonly observed, particularly on seasonally flooded Aeschynomene and seasonal/permanently flooded Discolobium spp., but also, in a modified form, on floating stems of V. lasiocarpa. The structures of stem and/or root nodules on Aeschynomene spp., Discolobium leptophyllum and V. lasiocarpa are described in detail, and nodulation by D. leptophyllum and Neptunia pubescens is reported for the first time.
Protein tyrosine phosphatases in higher plants
Authors: Luan Sheng , Ting Julie , Gupta Rajeev
Published: March 2003

Reversible protein phosphorylation is the most common mechanism for cellular regulation in eukaryotic systems. Indeed, approximately 5% of the Arabidopsis genome encodes protein kinases and phosphatases. Among the thousands of such enzymes, only a small fraction has been examined experimentally. Studies have demonstrated that Ser/Thr phosphorylation and dephosphorylation play a key role in the regulation of plant physiology and development. However, function of tyrosine phosphorylation, despite the overwhelming importance in animals, has not been systematically studied in higher plants. As a result, it is still controversial whether tyrosine phosphorylation is important in plant signal transduction. Recently, the first two protein tyrosine phosphatases (PTPs) from a higher plant were characterized. A diverse group of genes encoding putative PTPs have been identified from the Arabidopsis genome sequence databases. Genetic analyses of various PTPs are underway and preliminary results have provided evidence that these PTPs serve critical functions in plant responses to stress signals and in plant development.
Mycorrhizas and nutrient cycling in ecosystems – a journey towards relevance?
Authors: Read D. J. , Perez‐Moreno J.
Published: March 2003

Progress towards understanding the extent to which mycorrhizal fungi are involved in the mobilization of nitrogen (N) and phosphorus (P) from natural substrates is reviewed here. While mycorrhiza research has emphasized the role of the symbiosis in facilitation of capture of these nutrients in ionic form, attention has shifted since the mid‐1980s to analysing the mycorrhizal fungal abilities to release N and P from the detrital materials of microbial faunal and plant origins, which are the primary sources of these elements in terrestrial ecosystems. Ericoid, and some ectomycorrhizal fungi have the potential to be directly involved in attack both on structural polymers, which may render nutrients inaccessible, and in mobilization of N and P from the organic polymers in which they are sequestered. The advantages to the plant of achieving intervention in the microbial mobilization–immobilization cycles are stressed. While the new approaches may initially lack the precision achieved in studies of readily characterized ionic forms of N and P, they do provide insights of greater ecological relevance. The results support the hypothesis that selection has favoured ericoid and ectomycorrhizal systems with well developed saprotrophic capabilities in those ecosystems characterized by retention of N and P as organic complexes in the soil. The need for further investigation of the abilities of arbuscular mycorrhizal fungi to intervene in nutrient mobilization processes is stressed.
Relationship between the curriculum system and the understanding of nutritional terms in elementary school children
Authors: Suzuki Yoko , Rowedder Martha
Published: March 2003

To clarify the relation between the curriculum system and the understanding of nutrition terms, 944 students aged 8–12 years living in Japan, the USA and the UK, were asked about the recognition, medium for recognition, and understanding of nutrition terms. The effect of nutrition education from an early stage in elementary schools in the UK and the USA was confirmed. These results suggest the possibility of beginning nutrition education earlier in the elementary school in Japan. American students had paid attention to food labels. These results showed that a learning and teaching strategy founded on comprehensively based subjects in the USA had influenced good behaviour for dietary life. On the other hand, there was not a relationship between an understanding of nutrition terms and a developmental stage. Many students in three countries were influenced by television commercials to buy candy or soda. We think that it is important to develop a curriculum that includes practical learning and ensures hours of teaching for the purpose of acquirement of nutritional knowledge. It is also necessary to encourage critical thinking skills to evaluate television commercial messages through school lessons.
Furosine content, loss of o‐phthaldiadehyde reactivity, fluorescence and colour in stored enteral formulas
Authors: Rufián‐Henares J A , García‐Villanova B , Guerra‐Hernández E
Published: March 2003

Heat effects induced during the storage of enteral formula under laboratory and industrial conditions were evaluated using the following indicators: furosine; loss of available amino groups, measured by decrease in o‐phthaldialdehyde (OPA) reactivity; fluorescence associated with the Maillard reaction (345 nm excitation, 415 nm emission); and colour (absorbance at 420 nm). The storage of formulas A and B (with different protein content) at 4, 20 and 30°C during 12, 24 and 36 weeks produced an increase in furosine values. Under industrial storage conditions at 55°C for between 1 and 12 weeks the behaviour of furosine differed between the two types of formulas. In Formula A (lesser protein content), there was a decrease in furosine level after the third week, whereas in formula B (greater protein content) a decrease was observed after the eighth week.

The loss of OPA reactivity reached 18% and 22%, respectively, for formula B and formula A stored at 30°C for 36 weeks. In adverse storage conditions (55°C), the loss of OPA reactivity reached 50%.

Fluorescence intensity (FI) and absorbance at 420 nm increased at all time/temperatures assayed. It reached values of 22.5 and 27.5 for FI and 0.161 and 0.173 for A420, respectively, for formula A and B, stored for 36 weeks at 30°C.

Furosine, loss of OPA reactivity, fluorescence intensity and colour are useful indicators of nonenzymatic browning during storage of enteral formulas.
Rheological quality and stability of yog‐ice cream with added inulin
Authors: El‐Nagar G , Clowes G , Tudoricǎ C M , Kuri V , Brennan C S
Published: March 2003

Research was conducted to examine the effect of inulin on the rheological and textural characteristics of yog‐ice cream desserts in relation to their sensory attributes. Addition of inulin to yog‐ice cream was shown to increase viscosity of the yogurt‐ice cream mix and increase hardness of the resulting yog‐ice cream. Meltdown characteristics of the yog‐ice creams demonstrated a clear relationship between increased oligosaccharide levels and improved melting properties.
Influence of milk‐clotting enzymes on acidification rate of natural whey starter culture
Authors: Meinardi C A , Alonso A A , Hynes E R , Zalazar C A
Published: March 2003

The aim of this work was to study the influence of milk‐clotting enzymes on whey starter culture and hard cheesemaking. Four cheeses were prepared simultaneously per cheesemaking day, and the experiment repeated on eight consecutive days. Adult bovine rennet was used in the control cheeses, and three formulations of fermentation‐produced chymosin (FPC) in the experimental cheeses. Whey cultures were obtained from the whey of the preceding cheeses, incubated individually for 24 h at 42°C. pH values of the control and experimental whey did not differ significantly before incubation, but after 24 h incubation the pH of the FPC whey was significantly higher than that of the control. Soluble nitrogen content in trichloroacetic acid 2% and 12% and in phosphotungstic acid 2.5% was significantly lower for all experimental whey samples than for control whey. This probably explains the decrease in the acidification rate of the whey cultures when bovine coagulant is replaced by FPC in hard cheesemaking.
Optimization of ingredients for the manufacture of soft‐serve ice‐cream (Softy) by response surface methodology (RSM)
Authors: Sharma H K , Prasad K , Jindal S , Sood P , Pandey H
Published: March 2003

Soft ice‐cream samples were prepared with different proportions of cream and skimmed milk powder (SMP) and were examined for quality by physico‐chemical parameters and sensory attributes. The specific proportions of cream and SMP were designed using the central composite rotatable design (CCRD). Response surface analysis indicated that sensory flavour, texture and overall acceptability (OAA) scores of soft ice‐cream varied from 7.12 to 8.86, 6.66 to 8.03 and 6.90 to 8.45, respectively. The differences in the sensory scores for respective attributes were highly significant (P ≤ 0.01). The soft ice‐cream containing a minimum level of 3.24% cream and 4.94% SMP resulted in a product having a minimum of 4.3% fat, 5.7% lactose and 33% total solids, with a minimum OAA score of 8. The derived mathematical second‐order polynomial models against cream (X) and SMP (Y) were found to be adequate as coefficients of multiple determinants (R2) were more than 80% except for melting resistance.