bluuebunny/crossref_metadata_2025 huggingface dataset:
Root porosities and radial oxygen losses of Rumex and Plantago species as influenced by soil pore diameter and soil aeration
Authors: ENGELAAR W. M. H. G. , VAN BRUGGEN M. W. , VAN DEN HOEK W. P. M. , HUYSER M. A. H. , BLOM C. W. P. M.
Published: April 2006

The effects of hypoxia in ballotini and quartz sand with respectively large and small soil pore diameters on root porosity was studied for Rumex palustris Sra., Rumex acetosa L. and Plantago major L. ssp. major. Under hypoxic conditions R. palustris produced large root pores when large soil pores were present. Absence of such large soil pores resulted in the collapse of the root structure and a reduced root growth. Increases in intercellular spaces in P. major roots seemed to result in a higher root porosity upon hypoxia, a small soil pore diameter or a combination of both but this was not significant. Only a limited number of roots with large root pores was produced. The morphological structure of P. major roots without large root pores remained intact also in soils with a small soil pore diameter. R. acetosa only slightly increased its root porosity upon hypoxia and its morphological structure also remained intact when soil pore diameter was small. Radial oxygen loss (ROL) was found in R. palustris roots when grown in waterlogged, uncompacted soils. P. major had some roots with ROL in all treatments except in waterlogged, compacted soil. R. acetosa did not produce any roots showing ROL. Under field conditions aerenchyma is of no use in water saturated, compacted soils. This explains why a species like R. palustris only grows on hypoxic soil when it is not compacted, in contrast to P. major which will grow on moist, compacted soils. R. acetosa cannot be found on either very moist or heavily compacted soil, since it does not produce a healthy root system under these conditions.
Sugar uptake by protoplasts of the ectomycorrhizal fungus, Amanita muse aria (L. ex fr.) Hooker
Authors: CHEN XIAO‐YA , HAMPP RÜDIGER
Published: April 2006

Protoplasts have been isolated from the ectomycorrhizal fungus, Amanita muscaria, for the first time. Yields were about 108 protoplasts per g fr. wt of mycelial suspension cultures treated with a combination of Novozym 234, chitinase and cellulase Onozuka R‐10, and osmotically supplemented by 0–55 M sorbitol or 035 M KC1. Silicon oil filtration was used to investigate the uptake of metabolites by protoplasts using labelled compounds. About 66% of the initial protoplast population passed the oil layer after 50 s of centrifugation. Both glucose (as well as 3‐O‐methylglucose) and fructose were taken up by the protoplasts but not sucrose and mannitol. The Km for glucose (fructose) uptake was 1.25 mM (11.3), Vmax was 18 (30) pmoles (106 protoplasts min)−1. Uptake of fructose was strongly inhibited by glucose but not vice versa; uptake of both was not inhibited by sucrose. The much higher affinity for glucose than for fructose suggests that glucose should be the main carbohydrate source for this fungus. Treatment of protoplasts with 10 μM antimycin A lowered cellular ATP/ADP ratios to well below 1 and significantly inhibited uptake of sugars.
Differentiation of abnormal sieve elements in roots of wheat (Triticum aestivum L.) affected by colchicine
Authors: ELEFTHERIOU E. P.
Published: April 2006

Protophloem sieve elements (PSEs) of seminal roots of wheat (Triticum aestivum L.) treated with 2 MM colchicine solution differentiate into an extraordinary cell type not found in normal roots. Colchicine‐treated PSEs stop elongating and increase in diameter considerably. Abnormal ultrastructural features appear gradually with increasing time of exposure to the drug. Microtubules disorganize and disappear first. Cell divisions are blocked and nuclei become polyploid, with multiple lobes and deep imaginations. Profuse paracrystalline material, presumably consisting of tubulin or, more likely, of tubulin‐colchicine polymers, accumulates in the cytoplasm of the polyploid cells. Endoplasmic reticulum (ER) cisternae do not aggregate in stacks and mitochondria are not enveloped by ER cisternae, as normal. Golgi bodies appear active and distinct, while unusual vesicles with dense contents occur in the cytoplasm. However, development of plastids and degeneration of nuclei do not seem to be significantly affected by colchicine. The rate of development of affected PSEs is retarded considerably, as judged from ultrastructural features (plastid inclusions, wall thickenings), which appear much later in the vertical files of cells. Due to the retardation and to the overall stoppage of Toot elongation, differentiation of PSEs is caught up by other vascular elements such as protoxylem elements and metaphloem sieve elements. The aberrant PSEs undergo autolysis and reach maturity, but plastids, mitochondria, nuclear remnants and ER configurations characterizing normal PSEs are retained. Transverse walls differentiate into abnormal sieve plates, in which sieve pores are not formed. Lateral walls develop unusual thickenings projecting in the cytoplasm.

The observations show that: (a) Differentiation of the affected PSEs proceeds in the absence of divisions; (b) the number and degree of aberrations depend largely on the timing of exposure to the drug, and (c) strands of paracrystalline material and vacuoles are formed in microtubule‐free PSEs after long and continuous colchicine treatment.
The distribution of arbuscular mycorrhizas in the British flora
Authors: PEAT H. J. , FITTER A. H.
Published: April 2006

Arbuscular mycorrhizal (AM) associations with higher plants are common in many ecosystems but some plant species are consistently never or rarely infected. These species may differ morphologically or occur in different habitats from species which are usually mycorrhizal. A large data‐set on the ecology of British angiasperms was used to test for relationships between the mycorrhizal status of British angiosperms and several morphological and environmental variables (life form, root diameter, seed weight, soil fertility, soil water availability, soil pH and habitat type). No relationship was found between soil fertility or soil water availability and frequency of infection with AM fungi. AM species, however, can grow in habitats with a higher pH than non‐mycorrhizal species and perennial AM species occur in a significantly greater number of habitat types than perennial species which are never, or rarely, arbuscular mycorrhizal. Non‐mycorrhizal species tend to have thinner roots, smaller seeds and occur mainly in aquatic, wetland and saline habitats.
The current status of the acid‐growth hypothesis
Authors: KUTSCHERA U.
Published: April 2006

Excised coleoptile segments that were depleted of endogenous auxin after pre‐incubation in water respond to the phytotoxin fusicoccin (FC) and the plant hormone auxin (indole‐3‐acetic acid, IAA) with an enhancement of growth. This promotion of organ elongation is caused by an increase in the extensibility of the thick, growth‐limiting outer epidermal wall. The acid‐growth hypothesis postulates that both FC and IAA cause wall‐loosening and the concomitant induction of growth by rapid acidification of the extension‐limiting cell wall. At saturating concentrations FC and IAA cause very similar growth responses. However, the equilibrium‐pH in the incubation medium (∼ pH of the peripheral cell wall) of abraded FC‐treated segments is 3.5–4.0, whereas in the presence of IAA a pH of 4.8–5.0 is established. The FC‐ and IAA‐mediated induction of growth can be stimulated by an external buffer of pH 3.5–4.0. Acid buffers of pH 5, however, cause almost no enhancement of growth compared WJth the water‐control. FC‐mediated growth can be inhibited by neutral buffers infiltrated into the outer epidermal wall, but a substantial growth response occurs after addition of IAA under identical conditions. A sub‐optimal concentration of FC was used to mimic the effect of IAA on acid secretion. When a pH of 4.8–5.0 was established by FC in the peripheral wall no promotion of growth occurred. Hence, IAA‐induced proton excretion is insufficient to cause cell‐wall loosening in the coleoptile. Abraded segments that rapidly elongate in acid buffers (pH 3.5–4.0) respond to IAA with an additional enhancement of growth, but under identical conditions FC is without effect. The growth‐promoting effects of acid and IAA are additive, i.e. IAA and acid act via separate mechanisms. These results are consistent with the acid‐growth hypothesis of FC action. However, they indicate that IAA induces growth by a mechanism independent of cell‐wall acidification. Alternative hypotheses of IAA‐mediated cell‐wall loosening are discussed.

Contents

Summary
549

I.
Introduction
550

II.
Segment elongation and the organismal concept of multicellularity
550

III.
FC‐ and IAA‐mediated acid secretion
552

IV.
The acid‐growth hypothesis of FC action
555

V.
The acid‐growth hypothesis of IAA action
560

VI.
Conclusions
567

Acknowledgements
568

References
568
The role of low molecular weight organic acids in the mechanism of increased zinc tolerance in Silene vulgaris (Moench) Garcke
Authors: HARMENS HARRY , KOEVOETS PAUL L. M. , VERKLEIJ JOS A. C. , ERNST WILFRIED H. O.
Published: April 2006

The possible role of low molecular weight organic acids in the mechanism of increased zinc tolerance is investigated in Silene vulgaris (Moench) Garcke. In the leaves, the malate concentration is higher in zinc‐tolerant plants than in zinc‐sensitive ones, but no consistent differences are observed in the roots. Therefore, since the mechanism of increased zinc tolerance operates also in the roots themselves, a primary role for malate in the mechanism of increased zinc tolerance is doubtful. Exposure to 2inc does not affect the malate concentration in the plants. The citrate concentration in both the roots and leaves is higher in tolerant plants than in sensitive ones. A clear‐cut effect of zinc on the concentration of citrate in the plants is not found. Citrate does not seem to play an important role in the sequestration of zinc in root cells, in view of its low concentration in the roots of tolerant plants. The possible role of citrate as a carrier for zinc in the cytosol is discussed. Oxalate, the most abundant organic acid, might play an important role in the sequestration of zinc, because of its high concentration in the plants. However, this cannot explain increased zinc tolerance, because the oxalate concentration is higher in the sensitive plants than in the tolerant ones. Neither succinate nor maleate play a prominent role in the mechanism of increased zinc tolerance. Malate and citrate are the only organic acids detected in the xylem fluid. The malate concentration in the xylem fluid is the same in sensitive and tolerant plants and it is not affected by the concentration of external zinc. The citrate concentration in the xylem fluid is about three times higher in the tolerant control plants than in the sensitive ones, but it decreases to the same level as in the sensitive plants after exposure to zinc. Differences in the citrate concentrations in the xylem fluid of sensitive and tolerant plants are not related to differences in the allocation of zinc.
Role of superoxide, lipid peroxidation and superoxide dismutase in membrane perturbation during loss of viability in seeds of Shorea robusta Gaertn.f.
Authors: CHAITANYA K. S. KRISHNA , NAITHANI SUBHASH CHANDRA
Published: April 2006

Recalcitrant seeds of Shorea robusta (sal) exhibit 100% viability up to 4 d after maturity. The rapid loss of viability after 4 d is associated with the reduction in moisture content below the lowest safe moisture content (37°o). Seed becomes non‐viable on 8 d. Increased leakage of electrolytes in seeds and lipid peroxidation in embryonic axes was discernible immediately from 0 d. In embryonic axes, very low levels of superoxide (O2−) were maintained up to 4 d and a sharp increase was registered up to 7 d. It is suggested that loss of moisture content in sal seeds below 37% (after 4 d) induces substantial leakage loss probably due to increased lipid peroxidation and O2−) radical formation which are responsible for severe membrane perturbations leading to rapid loss of viability. In embryonic axes SOD activity was recorded only in 100% viable seeds.
Effect of mechanical impedance on root growth and morphology of two varieties of pea (Pisum sativum L.)
Authors: TSEGAYE TEZERA , MULLINS C. E.
Published: April 2006

Two pea (Pisum sativum L.) varieties (Progreta and Solara) were grown under controlled conditions for 7 or 15 days in perspex cylinders filled with moist vermiculite and for 10 days in moist sandy clay loam topsoil packed to bulk densities of 1.0, 12, 1.4 or 17 Mg m−3(with initial penetration resistances (PR) of; 0.037, 0.101, 0.246, 0.506 and 2–366 MPa respectively). The increase in PR from 0.101 to 0.506 MPa significantly decreased axis growth rate of Progreta but not of Solara. However, at a PR of 2366 MPa, axis growth rate of Solara was reduced to significantly less than that of Progreta. Thus experiments to describe intervarietal differences in root response to mechanical impedance need to be performed at a range of different mechanical impedances.

Few, if any, laterals emerged from axes growing across large gaps between aggregates suggesting that regular stimulation of the root tip is required to trigger lateral emergence. Significant correlations (P= 0.001) between first order lateral diameter and elongation rate were observed for roots of both varieties grown in moist vermiculite but not in soil. This relationship may indicate a general feature that thinner roots of any order are slower growing in a gap‐free and uniformly aggregated medium.
In situ and in vitro specificity between Rhizoctonia spp. and Spiranthes sinensis (Persoon) Ames, var. amoena (M. Bieberstein) Hara (Orchidaceae)
Authors: MASUHARA GAKU , KATSUYA KEIZO
Published: April 2006

The relationships between the orchid Spiranthes sinensis (Persoon) Ames. var. amoena (M. Bieberstein) Hara and Rhizoctonia spp. were investigated in situ at germination and in adult plants, Seeds of the orchid placed in cotton gauze were buried at 210 sampling points in turf grassland, the orchid habitat (in situ germination). Eight weeks later, protocorm development of the orchid was confirmed at 67 of the 210 sampling points. Isolation of fungi from protocorms showed that in situ germination was induced mainly by Rhizoctonia rapens Bernard. Similarly, R. repens was the dominant mycorrhizal fungus isolated from roots of adult plants. The number of adult plants within a radius of either 30 or 50 cm of burial points did not influence seed germination.

The distribution of Rhizoctonia spp. other than R. repens in the sample site was examined with a baiting method using buckwheat stems. Thirty‐two isolates consisting of binucleate Rhizoctonia anastomosis group (AG)‐A, AG‐B, AG‐G, and AG‐1, R. solani Kuhn AG‐4, Waitea circinata Warcup & Talbot, which anastomozed with WAG‐O and WAG‐Z, and a multinucteate Rhizoctonia sp. were isolated. Three AG‐G isolates were obtained from the points at which protocorm development was induced by R. repens. Seeds of S. sinensis var. amoena were inoculated in vitro with these isolates to test for symbiotic germination. Most Rhizoctonia spp, not associated with the germination in situ induced seed germination in vitro. Seedlings which developed with these isolates in vitro were transferred to ex vitro conditions. New leaves developed and elongated as seedlings continued to grow for 3 months, The seed burial method enabled the clarification of the differences in orchid‐fungal specificity in situ and in vitro. We concluded that the specificity between S. sinensis var. amoena and fungi in situ conditions was different to that in vitro.
Cell differentiation and the cytoskeleton in Acetabularia
Authors: MENZEL DIEDRIK
Published: April 2006

summary

In multicellular organisms, differentiation of individual cells is typically linked to the development of the whole organism. As cells acquire tissue‐specific morphologies and become functionally specialized they lose in turn a number of other functions. A free living, single celled organism, however, maintains all such functions. Compartmentalization and intracellular communication are two basic principles by which expression of specialized features is achieved within a unicell. Both in turn depend on the structure and dynamics of the cytoskeleton. Giant algal unicells lend themselves as experimental models for the study of the cytoskeleton, because the cytoskeletal arrays inside these cells become equally enormous in size. Some of these organisms are large enough to be mistaken for multicellular plants, equipped with holdfast, stem and assimilatory organ. The marine green alga Acetabularia is one of these giant cells, which has already been well known to phycologists and cell biologists for several decades. The current review discusses recent progress in the study of the cytoskeleton in Acetabularia and examines classic concepts of cell morphogenesis from the perspective of cytoskeletal function.

Contents

Summary
369

I.
Introduction
369

II.
Morphogenetic stages
371

III.
Post‐transcriptional control of morphogenesis
687

IV.
Apparent plasticity of morphogenesis
389

V.
Prospects of using molecular approaches
391
Fructan biosynthesis in excised leaves of wheat (Triticum aestivum L.): a comparison of de novo synthesis in vivo and in vitro
Authors: PENSON SIMON P. , CAIRNS ANDREW J.
Published: April 2006

summary

Carbohydrate accumulation by excised, continuously illuminated leaves of wheat (Triticum aestivum L.) was followed over a 24 h period. At 0 h, the tissue contained no detectable fructan. In the initial 6 h, only sucrose was accumulated. After 6 h the de novo synthesis of fructans was induced. Fructans accumulated in the sequence 1‐kestose, bifurcose, nystose, oligofructans of apparent degree of polymerization (DP) up to 9 and finally, 6‐kestose, which was first detected after 22 h.

A cell‐free protein extract from leaves illuminated for 24 h catalyzed the de novo synthesis of fructan from sucrose. The properties of this fructan synthetic activity (FSA) were characterized. The FSA was stable, exhibiting < 20% loss of activity when stored at 5 °C or 25 °C for 6 h. The FSA exhibited an apparent Km,suc of 114 mM, and an apparent pH optimum at 5.5. The in vitro synthesis of fructan of DP > 3 was not inhibited by sucrose even at 1000 mM. Pyridoxal‐hydrochloride at 20 mM did not enhance rates of enzymatic fructan synthesis or significantly inhibit the release of free fructose in the optimized enzymatic reaction.

The rate of oligofructan synthesis in the optimized reaction approximated to rates of accumulation in the leaf (1.35 mg g h−1 and 1.18 mg g h−1 respectively). The sequence of oligofructan synthesis in vitro was the same as that observed in the leaf, with the exception that 6‐kestose was synthesized early in the time course, in parallel with 1‐kestose and bifurcose. Fructans of apparent DP ≤ 8 were detected after 10 h of incubation.

When incubated with bifurcose as sole substrate, the cell‐free preparation liberated free monosaccharides, without the accumulation of trisaccharide or sucrose as intermediates. The results are discussed with reference to current, conflicting models for the biosynthesis of fructan in cereals.
Acclimation of photosystem II in a cyanobacterium and a eukaryotic green alga to high and fluctuating photosynthetic photon flux densities, simulating light regimes induced by mixing in lakes
Authors: IBELINGS BAS W. , KROON BERND M. A. , MUR LUUC R.
Published: April 2006

summary

Photoacclimation of Scenedesmus protuberans Fritsch and Microcystis aeruginosa Kützing emend. Elenkin to high and fluctuating PPFD was studied in continuous cultures with computer‐controlled variable light regimes. The aim of the work was to provide a better understanding of species‐specific acclimation to high PPFD (as encountered by cyanobacteria in surface waterblooms), and of suppression of the growth of colony‐forming cyanobacteria during periods of prolonged mixing in lakes. The dynamics of a set of variables was followed during the light period, including pigment composition, maximum rate, efficiency and minimum quantum requirement of photosynthesis, PS II cross‐sections, and fluorescence variables. Both the green alga and the cyanobacterium displayed strong photo‐inhibition of photosynthesis in the sinusoidal light regime, which simulated a natural light regime in the absence of mixing. Pmax, α, QR and the ratio of variable to maximum fluorescence declined, and the number of inactive PS II centres and PS IIβ centres increased towards midday. Introduction of oscillations in the diurnal light regime, simulating different intensities of wind‐induced mixing in lakes, mitigated photo‐inhibition. Microcystis showed a prompt non‐photochemical quenching of fluorescence in all light regimes, even at low to moderate PPFD. The sustained presence of zeaxanthin in Microcystis possibly induced instant, thermal dissipation of excitation energy from the antenna. Microcystis also exhibited a more reluctant acclimation to fluctuating PPFD. Growth rate of Scenedesmus was higher in all light regimes. This implied that if (known) differences in loss processes were ignored, Scenedesmus would outcompete Microcystis in lakes. The results underlined the importance of buoyancy regulation in increasing the daily light dose of cyanobacteria (but at the same time preventing over‐excitation), and ultimately in the success in Microcystis in stable lakes.
Energy content, construction cost and phytomass accumulation of Glycine max (L.) Merr. and Sorghum bicolor (L.) Moench grown in elevated CO2 in the field
Authors: AMTHOR JEFFREY S. , MITCHELL ROBERT J. , RUNION G. BRETT , ROGERS HUGO H. , PRIOR STEPHEN A. , WOOD C. WESLEY
Published: April 2006

summary

Grain sorghum [Sorghum bicolor (L.) Moench, a C4 crop] and soybean [Glycine max (L.) Merr. cv. Stonewall, a C3 crop] plants were grown in ambient (c. 360μl 1−1) and twice‐ambient (c. 720 μl 1−1) CO2 levels in open‐top chambers in soil without root constriction. Plant dry mass, energy content, composition and construction cost (i.e. amount of carbohydrate required to synthesize a unit of plant dry mass) were assessed at the end of the growing season. Elevated CO2 (a) increased phytomass accumulation (kg per plant) in both species, (b) had little affect on energy concentration (MJ kg−1 plant) but caused large increases in the amount of plant energy per ground area (MJ m−2 ground), and (c) did not alter specific growth cost (kg carbohydrate kg−1 plant growth) but greatly increased growth cost per ground area (kg carbohydrate m−2 ground) because growth was enhanced. For soybean, twice‐ambient CO2 resulted in a 50 % increase in the amount of nitrogen and energy in grain (seed plus pod) per ground area. This response to elevated CO2 has important implications for agricultural productivity during the next century because the rate of human population growth is exceeding the rate of increase of land used for agriculture so that future food demands can only be met by greater production per ground area.
NH4+ assimilation in the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton, a 15N‐NMR study
Authors: MARTIN FRANCIS , CÕTÉ RICHARD , CANET DANIEL
Published: April 2006

summary

Nuclear magnetic resonance spectroscopy was used to monitor 15NH4+ assimilation and amino acid biosynthesis in the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton. (strain S238). In mycelium growing rapidly on 15NH4+, [amido‐15N]glutamine was the major 15N‐labelled species. When 15N‐labelled mycelium was transferred into medium containing 14NH4+, the resonance for [amino‐15N]glutamine decreased with a half‐life of about 3.0 h, whereas the resonance for [amino‐15N]glutamine remained unchanged. Such behaviour is consistent with glutamine synthetase (GS) being the major route of 15NH4+ assimilation. However, the higher accumulation of [15N]alanine observed in the presence of the GS inhibitor, methionine sulfoximine, indicated that a part of the glutamate pool was formed by the glutamate dehydrogenase (GDH) pathway. When the mycelium was in stationary phase (i.e. low extracellular NH4+), the intramolecular 15N labelling of glutamine suggested that the GDH and GS pathways were simultaneously assimilating NH4+. The N supply and the growth stage, therefore, influence the expression of the activities of GDH and GS. The current isotopic data identify other fates of absorbed 15N: glutamate decarboxylation gives rise to γ‐aminobutyrate; transamination between glutamate and pyruvate yields alanine; and arginine accumulates. It is concluded that GS is the main pathway of primary assimilation of NH4+ in L. bicolor, but GDH may also contribute significantly to this process.
Variation in DNA C value in natural populations of Dactylis glomerata L.
Authors: CREBER H. M. C. , DAVIES M. S. , FRANCIS D. , WALKER H. D.
Published: April 2006

summary

DNA C values were determined for eighteen natural populations of Dactylis glomerata L. collected from various sites in Europe to examine the extent of intraspecific variation in C value and how this variation may be related to latitude and altitude of origin. A sub‐set (8) of these populations represent an altitudinal transect (350–1120 m) in northern Spain whilst the remainder represent a latitudinal range (38.53–57.47 °N). Preliminary experiments established optimum acid hydrolysis times for the Feulgen reaction of 62 min and 20 min for D. glomerata cv. S26 and the standard Hordeum vulgare L. cv. Sultan (C = 5.6 pg), respectively. The data emphasize the necessity of using the optimum hydrolysis time for both the standard and unknowns for C value determination, whether using 5 M HCl at 25 °C or 1 M HCl at 60 °C. This procedure has not been followed in the majority of published estimates of C value.

Seventeen of the natural populations were tetraploid (2n= 4x= 28) whilst the southernmost population was diploid (2n= 2x= 14). The 17 tetraploid populations exhibited a 28.7 % variation in DNA C value, ranging from 4.35 to 5.60 pg, whilst the C value of the diploid population was 3.3 pg. There was neither a significant relationship between the C value and latitude of origin of the 10 populations which comprised the latitudinal transect (1 diploid and 9 tetraploid) nor with the tetraploids alone. However, the C values of the eight populations which formed the altitudinal transect in the Galicia mountains in N. Spain were negatively correlated with their altitude of origin. Possible reasons for this relationship are discussed.
Relationship between hyphal and arbuscular colonization and sporulation in a mycorrhiza of Paspalum notatum Flugge
Authors: DOUDS DAVID D.
Published: April 2006

summary

Experiments were conducted to determine correlation between sporulation by an arbuscular mycorrhizal (AM) fungus to proliferation of arbuscules or intercellular hyphae. Paspalum notatum Flugge seedlings were inoculated with the AM fungus Gigaspora margarita Becker & Hall and treated with either tap water, nutrient solution without P, or nutrient solution with P to manipulate colonization levels. Plants receiving the nutrient solution without P tended to have greater colonization than plants receiving water only (e.g. 62 vs 54%, respectively at week 7) but lesser percentage root length with arbuscules (e.g. 27 vs 38% respectively at week 7). Mycorrhizas receiving the nutrient solution without P sporulated sooner (week 7) than the water only treatment and had larger spore populations (e.g. 20.9 vs 14.2 spores cm−3 at week 13). Nutrient solution with P did not completely inhibit colonization, and though these plants had total colonized root lengths similar to those of the water treatment, spore populations were much less (2.9 cm−3 at week 13), Spore populations correlated equally well with total root length as with root length colonized and root length with arbuscules in the water and nutrient solution without P treatments. Populations were not correlated to these measures for the nutrient solution with P, indicating that the host may have limited the ability of a unit length of colonization to produce spores in this treatment.
Uptake and translocation of prey‐derived 15N and 32P in Utricularia vulgaris L.
Authors: FRIDAY LAURIE , QUARMBY CHRIS
Published: April 2006

summary

The rootless submerged carnivorous hydrophyte Utricularia vulgaris L. is a potentially useful subject for the quantitative study of foliar nutrient uptake and use, because known quantities of nutrients can be supplied precisely to individual leaves. We report here results obtained by hand‐feeding prey labelled with 15N and 32P to leaves of known age in plants growing in near‐natural conditions.

Prey‐derived 15N was rapidly taken up and translocated: in plants fed via 3‐d‐old leaves, about 30% of the prey 1SN appeared in the immature parts of the plant within 2 d. Almost all parts of the plant that were immature at the time of feeding received and retained prey 15N throughout the 20 d experiment. Some backward translocation of 1SN was observed, but only up to the second day after feeding.

32P was also taken up and translocated rapidly, but was not retained by young tissues after they had become mature. Backward translocation of 32P was observed into side‐shoot meristems and flowers arising on parts of the plant older than the fed leaves. This is in contrast to 15N uptake, where side‐shoot buds and flowers received labelled nitrogen only if they arose on parts of the plant younger than the fed leaves.
Reproductive biology of eight sympatric Myrtaceae from Central Brazil
Authors: PROENÇA CAROLYN E. B. , GIBBS PETER E.
Published: April 2006

summary

Eight species of Brazilian Myrtaceae were studied for their flowering phenology, pollination biology, breeding system and fruiting success: Eugenia dysenteries, Siphoneugena densiflora, Blepharocalyx salicifolius, Campomanesia pubeacens, C. velutina, Myrcia linearifolia, M. rhodosepala and Psidium firmum. Flowering strategies were mass‐flowering and steady‐state types, with two species showing a pulsed flowering. All species were bee‐pollinated with pollen as the floral reward; flowers opened early in the morning and lasted one day; buzz‐pollination was registered in three species. Pollinator‐sharing of Bombus spp. bees occurred in the four savanna shrubs, pre‐dawn pollination by Ptiluglossa sp. (Colletidae) was found in arboreal 5. densiflora and the remaining two trees had open pollination systems. The three forest species were markedly self‐incompatible, and two of the savanna species were effectively so, whilst three savanna species showed self‐compatibility.
Characteristics of secretion of nectar in Pyrostegia venusta (Ker‐Gawl.) Miers (Bignoniaceae)
Authors: GALETTO L. , BERNARDELLO L. M. , JULIANI H. R.
Published: April 2006

summary

Secretion patterns and characteristics of nectar of an Argentinian population of Pyrostegia venusta at different times of the day are described with respect to flower age. Flowers are protandrous and hummingbird‐pollinated, producing exudate before and after anthesis. There is a concomitant increase in both concentration and volume in 1‐d‐old flowers, followed by a sharp increase in concentration and decrease in nectar volume in 2‐d‐old flowers.

Removal of nectar throughout the flower lifetime increases the volume produced but reduces the concentration. Flowers with nectar removed three times produced 73% more nectar volume than the controls, and those with nectar removed twice produced 20% more. However, the total mass of sugar produced was comparable in all three sets.

Two experiments were designed to determine the effect of changes in volume and concentration on nectar production: (a) the concentration was initially maintained while the volume was changed (halved, doubled and untouched as a control), and (b) the concentration was reduced to a minimum replacing nectar by different volumes of distilled water as in the previous experiment. These concentration‐volume changes do not essentially affect total nectar production irrespective of treatment. A powerful homeostatic mechanism would operate by which the plant maintains both these variables in the nectar. The differences observed in the nectar production rate among treatments would indicate its existence.
Use of 15N labelling and 15N natural abundance to quantify the role of mycorrhizas in N uptake by plants: importance of seed N and of changes in the 15N labelling of available N
Authors: HÖGBERG PETER , NÄSHOLM TORGNY , HÖGBOM LARS , STÅHL LENA
Published: April 2006

summary

15N labelling and variations in natural 15N abundance offer possibilities to quantify the importance of mycorrhizas in plant N uptake. When atom %15N or 15N natural abundance of mycorrhizal and non‐mycorrhizal plants are compared in experiments, one, however, has to account for dilution effects of seed N and the interaction between changes in sslabelling of the available pool and N uptake. This has been considered in studies of N2 by diazotrophs, but has not been explicitly corrected for in studies of N uptake by mycorrhizal plants. An example is given, where ectomycorrhizal plants obtained an atom %15N different (P < 0.01) from that of non‐mycorrhizal plants, but where this could be ascribed to dilution effects of seed N and differences in N uptake rates interacting with changes in 15N labelling, rather than to variations in use of N sources or to isotope fractionation during uptake. Careful N and l5N budgets based on seed N and sequential harvests, as well as frequent measurements of atom % or abundance of 15N in available pools of N, are thus necessary in studies of this kind. Regressions of 15N on total N are a useful alternative to comparisons of means of atom % only.
The influence of IAA, carbohydrate and mineral concentration in host tissue on ectomycorrhizal development on Pinus sylvestris L. in relation to nutrient supply
Authors: WALLANDER B HÅKAN , NYLUND JAN‐ERIK , SUNDBERG BJÖRN
Published: April 2006

summary

Concentrations of indole‐3‐acetie acid (IAA) in lateral roots, fungal biomasa (ergosterol) in lateral roots and extrametrical mycelium, and carbohydrates and minerals in shoots were measured in mycorrhizal and non‐mycorrhizal Pinus sylvestris L. seedlings supplied with different amounts of N and P. IAA concentrations in lateral roots of mycorrhizal seedlings were the same or lower than those in control seedlings. The concentrations of IAA in mycorrhizal root tips of Laccaria bicolor inoculated seedlings were 40% lower than those in lateral roots. IAA concentrations in lateral roots of L. color‐inoculated seedlings were positively related to X supply. A rise in N supply reduced the development of extramatrical mycelium of L. bicolor and the fungal biomass in lateral roots of Hebeloma crustuliniforme‐inoculated seedlings. High N supply reduced concentrations of starch, Ca and Mg in shoots but increased those of glucose and fructose. P had no effect on fungal growth or on concentrations of IAA. Fungal growth was negatively correlated with levels of soluble carbohydrates in shoots, shoot concentrations of N, P and K, relative growth rate and the shoot: root ratio of the seedlings. Starch, Mg and Ca concentrations in the shoot were positively correlated with fungal growth. No support was found for the hypothesis that IAA is important in regulating mycorrhizal colonization.
Ectomycorrhizas and rhizosphere microorganisms of seedlings of Pseudotsuga menziesii (Mirb.) Franco planted on a degraded site and inoculated with forest soils pretreated with selective biocides
Authors: COLINAS C. , MOLINA R. , TRAPPE J. , PERRY D.
Published: April 2006

summary

Inoculation of planting holes with small amounts of soil from a mature forest or a plantation can improve formation of ectomycorrhizas on Pseudotsuga mensiesii (Mirb.) Franco seedlings in degraded eleareuts in southwestern Oregon. To determine the component (s) of transferred soil responsible for increased ectomycorrhiza formation, we treated soil from a clearcut, a mature forest, and a plantation with one of the following: fertilizer to test for the effect of nutrients, dimethoate and carbufuran to test for the effect on microarthropods or nematodes, fumagillin to test for the effect on protozoa, captan to test for the effect on fungi, penicillin and oxytetracycline to test for the effect on bacteria, pasteurization to test for the effect of active forms of organisms. Tyndallization to test for the effect of resting forms of organisms, or water as a control. We studied the effect of inoculation with soil subjected to these treatments on number and types of ectomycorrhizas, and length of active mycelium, and number of active bacteria in the rhizosphere. Inoculation with untreated forest or plantation soils increased the number of ectomyeorrhizas but did not change the mycorrhizal types present. Most agents had different effects in different soils, inoculation with pasteurized and Tvndallized clearcut and plantation soils increased the number of Rhizopagon‐ and Thelephora‐type ectomyeorrhizas and decreased the number of active bacteria, as did untreated forest soil. We hypothesize that the role of the soil transfer is to provide a rhizosphere environment free from a deleterious organism present in the clearcut. In this environment, beneficial organisms present in the clearcut or brought in with the seedling from the nursery can proliferate.
Wound‐induced hydraulic signals and stimulus transmission in Mimosa pudica L
Authors: MALONE M.
Published: April 2006

summary

The mechanism of wound signalling in Mimosa is discussed with a brief historical survey. It is demonstrated that strong wound‐induced hydraulic signals occur in Mimosa pudica L., as in many other plants, and that the basipetal mass flows associated with these events could disperse solutes from the wound site at rates of at least 15 mm s−1 and possibly up to 300 mms−1. When such wound‐induced ‘hydraulic dispersal’ is taken into account, Ricca's theory of chemical signalling can explain long‐distance transmission in Mimosa. The pattern of long‐distance wound signalling in Mimosa is shown to be consistent with such a model.

Implications for theories of electrical signalling in Mimosa are discussed and it is concluded, in agreement with some previous workers, that systemic wound‐induced electrical phenomena in Mimosa are not travelling signals, but are local responses to the travelling chemical messengers.
Storage and secretion processes in the spore of Gigaspora margarita Becker &Hall as revealed by high‐pressure freezing and freeze substitution
Authors: BONFANTE PAOLA , BALESTRINI RAFFAELLA , MEND GEN KURT
Published: April 2006

summary

Spores of Gigaspora margarita Becker &Hall, an arbuscular mycorrhizal fungus, were cryofixed using high‐pressure freezing and prepared for Transmission electron microscopy by freeze substitution. The cryotechniques improved the ultrastructural preservation of the Spore cytoplasm and revealed storage and secretion processes in the germinating sports of G. margarita. The storage structures in the hydrated and /or germinating spores have been identified as belonging to three different classes: (i) lipid droplets limited by 3 membrane, (ii) protein‐like bodies inside specialized vacuoles., and (ii) glycogen particles. During germ‐tube differentiation, an abundant membranous system was observed. It consists of rough KR. tubules and balloon‐like Golgi equivalents, which produce vesicles associated with electron‐dense granules. The granules seem to be incorporated into the wall. The results suggest that secretion and Storage occur in the fungal spore during events comparable to those in yeasts or plant cells.
Effects of soil phosphorus on spore germination and hyphal growth of arbuscular mycorrhizal fungi
Authors: DE MIRANDA J. C. C. , HARRIS P. J.
Published: April 2006

summary

The direct effects Of soil phosphorus on sport germination and hyphal growth of the arbuscular mycorrhizal fungi (AM), Glomus etunicatum Beck &Beck &Gerd., E3 and Scutellospora heterogama (Nicol &Gerd) Walker &Sanders, were investigated by means of two soil‐agar plate experiments. In the first experiment, the percentage spore germination and hyphal length of G. etunicatum, measured at ten different P levels and three periods of incubation, were affected by the P status of the soil. The best correslation with P level in the soil occurred at 7 d of incubation for spore germination and at 14 d far hyphal growth and hyphal growth increment. Spore germination was stimulated when 12.5 μ PO g−1 was applied to the soil and decreased with further soil P increments. Hyphal growth decreased significantly with soil P amendments above 37.5 μg P g−1 In the second experiment including three different P levels and the three AM endophytes, soil P affected spore germination and hyphal growth, and both decreased at the high phosphate treatment for G. etunicatum and S. heterogama. The K3 spare germination was similar to the other two species, but the hyphal growth was poorer. S. heterogama was more sensitive to P fertilization than the Glomus spp. and for the three species the hyphal production was not proportional to spore size.
Allocation of 14C‐carbon in ectomycorrhizal willow
Authors: DURALL D. M. , JONES MELANIE D. , TINKER P. B.
Published: April 2006

summary

The flow of carbon from plant to fungus in ectomycorrhizal associations has not been well quantified. The objective of this study was to use 14C to quantify the increase in fixed carbon translocated below ground in ectomycorrhizal relative to non‐mycorrhizal willow (Salix viminalis L, Bowles hybrid). Rooted cuttings were inoculated with Thelephora terrestris (Ehrh). Fr. or left non‐mycorrhizal. Non‐mycorrhizal plants were grown at the same (4 mg kg−l bicarbonate‐extractable P) (NM‐P) or at a higher (21 mg kg−1) soil P concentration (NM +P), one at which the non‐mycorrhizal plants were similar in size to the mycorrhizal (M‐P) plants. At 41, 51, 76 and 89 days after planting, the shoots were exposed to a pulse of 14CO2. Plants were harvested after a 202 h chase period. The 14Cactivity was quantified in live fractions: shoot tissue, shoot respiration, ‘root’ tissue (= roots plus fungi), ‘root’ respiration (= CO2 released below ground) and soil. Of the total 14C detected in these five fractions, M‐P plants allocated from 3.9% (harvest 1) to 11.5% (harvest 4) more to the below‐ground fractions (‘root’ tissue, soil and ‘root’ respiration), than did the NM‐P plants. Differences between NM+P and M‐P plants were only half of those above (3.1 % and 4.4% at harvests 2 and 3, respectively, compared to 6.4 % and 7.4%, respectively for the difference between NM‐P and M‐P). Correction for differences in root/shoot ratio between M‐P and NM‐P plants eliminated the observed differences in carbon distribution only at the first three harvests. There was no evidence for increased ‘root’ respiration fates or rhizodeposition being responsible for the increased carbon diverted below ground by M‐P plants.
Carbon use efficiency in mycorrhizas theory and sample calculations
Authors: TINKER P. B. , DURALL D. M. , JONES M. D.
Published: April 2006

summary

The benefit to a fungus by a mycorrhizal association is that it gains carbon from its host. A benefit to a host is usually a nutritional one, but any resulting increase in dry weight may be counteracted by the carbon consumed by the fungus. The carbon costs of mycorrhizal fungi have been calculated using 14C pulse‐chase experiments in the laboratory or by estimating turnover rates in the field. Both of these techniques have their limitations, but estimates have been remarkably consistent amongst most laboratory studies. Carbon demands of the fungus may not reduce theoretical growth enhancement in plants which are sink‐limited but would be expected to do so iii source‐limited plants. A model of carbon use efficiency is developed based on the economic concepts of cost and benefit. Efficiency is defined in terms of carbon gained via the growth response to infection, and the carbon expended supporting the fungus. Practical considerations of measuring carbon allocation, and calculating carbon use efficiency are discussed. In an experiment on Salix viminalis L., colonized by Thelephora terrestris (Ehrh.) Fr., the carbon use efficiency calculated by this method was on overage 85% based on shoot tissue production, and 95% based on whole plant production.
Reproductive responses to mycorrhizal colonization of Abutilon theophrasti Medic, plants grown for two generations in the field
Authors: SHUMWAY DURLAND L. , KOIDE ROGER T.
Published: April 2006

summary

Plants of Abutilo theophrasti Medic, were grown for two consecutive years in the field. First generation (maternal) plants were grown either with or without mycorrhizal inoculation with Glomus intraradices Schenck & Smith. We collected early and late cohorts of seeds which were used to product second generation (offspring) plants. Offspring plants were grown either with or without mycorrhizal inoculation with G. intraradices. Irrespective of maternal mycorrhizal status, we found that offspring of early cohort seeds had greater percent mycorrhizal colonization early in the growing season, a greater proportion of plants flowering early in the season, and a greater number of capsules per plant at the end of the season compared with offspring of late cohort seeds. These differences were observed despite the fact that shoot N and P concentrations were greater in offspring of late cohort seeds. We found that mycorrhizal colonization of maternal plants decreased the average time to reproductive maturity in offspring plants, but did not significantly influence any other vegetative or reproductive trait in the offspring plants. Mycorrhizal colonization of offspring plants resulted in a greater number of branches per plant and a greater number of mature capsules per branch. Mycorrhizal colonization of offspring plants also resulted in a significant increase in seed P content, bur only for seeds that were produced late in the growing season, We conclude that mycorrhizal colonization of the offspring generation was more important than mycorrhizal colonization of the maternal generation m determining offspring reproductive output, but maternal seed cohort is an important interacting factor that influences offspring fecundity.
Effects of nitrogen supply on the source of nitrogen used for regrowth of laminae after defoliation of four grass species
Authors: THORNTON B. , MILLARD P. , DUFF E. I.
Published: April 2006

summary

Plants of Agrostis castellana, Festuca rubra, Lolium perenne and Poa trivials were grown in sand culture and supplied with a complete nutrient solution containing either 0.5 or 1.5 mol m−3 NH4NO3. Plants were clipped weekly to a height of 4 cm. At the time of the ninth clipping (day Q) the nutrient solution was replaced by one in which all nitrogen (N) was enriched with 15N to 5 atom %, but otherwise identical. Weekly destructive harvests were taken from day 0 to day 35. whilst unharvested plants continued to receive the weekly clipping. The 15N‐labelling allowed discrimination between remobilization within the plant from current root uptake in supplying N for laminae regrowth. For all four species a poor N supply reduced both N uptake by roots and the potential N available for remobilization, as welt as allocation of both these sources to laminae regrowth. Overall the N supply derived from root uptake was reduced by a greater extent, and the proportion of N in laminae regrowth derived from remobilization increased with low N supply. The rate of remobilization of the N which was accessible was slower with a reduced supply of N. The species order for increasing proportion of N for laminae regrowth being derived from remobilization was L. perenne < P. trivialis < A. castellana < F. rubra irrespective of N supply.