bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation of abnormal sieve elements in roots of wheat (Triticum aestivum L.) affected by colchicine
Authors: ELEFTHERIOU E. P. 
Published: April 2006

SUMMARYProtophloem 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

SUMMARYArbuscular 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

SUMMARYExcised 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

SUMMARYThe 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

SUMMARYRecalcitrant 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

SUMMARYTwo 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

SUMMARYThe 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

summaryIn 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

summaryCarbohydrate 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

summaryPhotoacclimation 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

summaryGrain 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

summaryNuclear 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

summaryDNA 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.