bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of an antibiotic from Oscillatoria sp. on phytoplankters, higher plants and mice
Authors: Chauhan V. S. , Marwah J. B. , Bagchi S. N.
Published: April 2006

When cultured with an axenic planktonic Oscillatoria sp., growth of some cyanobacteria and a green alga was suppressed owing to release of an algicidal metabolite (antibiotic). Growth inhibition was also detected on exposure to a cell‐free extract of Oscillatoria or to an ether extract. The ether extract abolished the photosystem (PS) II activity of Anacystis nidulans. Experimentation with a combination of photosynthetic electron acceptor‐donor systems indicated that the antibiotic also inhibited PS II in isolated chloroplasts, primarily interacting at a site before P680 on the electron transport chain. The cyanobacterial product also suppressed growth of some natural isolates of cyanobacteria and green algae in controlled conditions and decreased the population density of a green alga (phytoplankton) in nature. Growth of higher plants was also affected, though only when the Oscillatoria extract was applied to leaves. Experimental mice were unaffected by the antibiotic. Upon thin layer chromatography of the ether extract, two fractions with algicidal activity fluoresced under ultraviolet light. Long‐chain saturated fatty acids were the major components of the fractions. The suitability of the antibiotic in control of toxic algae is discussed.
Effects of osmotic stress (NaCl and polyethylene glycol) on nitrate uptake, translocation, storage and reduction in ryegrass (Lolium perenne L.)
Authors: OURRY ALAIN , MESLÉ SYLVIE , BOUCAUD JEAN
Published: April 2006

In order in investigate the effects of osmotic stress on metabolism of NO3− in Lolium perenne L. cv. Réveille, plants were exposed to NaCl or polyethylene glycol 6000 in the culture medium. Four‐week‐old plants were kept in the dark for 36 h in order to decrease nitrate reductase activity (NRA). Afterwards, they were placed in a greenhouse for 27 h under continuous illumination with a nutrient solution containing 1 mM 14NH415NO3. To induce osmotic stress, the solution was supplemented with either NaCl or PEG 6000 to give an osmotic potential of —0·335 MPa in the medium. Osmotic adjustment in PEG treated plants was strongly limited, because PEG could not be absorbed. Over 70% of the osmoregulation in NaCl treated plants resulted from chloride uptake. Compared to control plants, PEG 6000 treatment decreased absorption (by 40%) and reduction (by 60 %) of NO3− in the leaves, leading to NO3− storage in the vacuolar pool. In contrast, addition of NaCl in the medium did not significantly affect either uptake or reduction of NO3−. The proportion of NO3− translocated to the leaves was unaffected by osmotic stress and represented about 76% of consumed NO3−. Nitrate reductase activity, measured in vivo with exogenously supplied NO3−, was not significantly different between treatments. Compared to reduction of p15NO3− in control plants, it appeared that reduction of NO3− in leaves of PEG‐treated plants was not limited by enzyme activity or by the amount of reducing power. Availability of NO3− at the site of reduction therefore seems to be limiting when PEG 6000 is added to the medium.
Salt tolerance of the coastal salt marsh grass, Sporobolus virginicus (L.) kunth
Authors: MARCUM K. B. , MURDOCH C. L.
Published: April 2006

summary

Growth responses, leaf water and osmotic relations, and tissue ionic and organic solute contents of Sporobolus virginicus (L.) Kunth, grown under solution culture in salinities of up to 450 mM NaCl, were studied. Shoot growth was stimulated by intermediate salt levels, concurrent with both an accumulation of Na+ and Cl− in shoots and a slight increase in shoot succulence. Root growth was stimulated at salinities of up to 450 mM NaCl, Osmotic adjustment of shoots was predominantly due to Na+, Cl−, and soluble carbohydrate accumulation, though a slight reduction in shoot succulence may have played a minor role at high salinity. Shoot Na+ and Cl− accumulation was tightly controlled, not exceeding levels required for osmotic adjustment, due in part to ion secretion by leaf salt glands. Shoots were selective for K+ over Na+, maintaining fairly constant K+ concentrations with increasing salinity, resulting in relatively high K+/Na+ ratios at high salinity. Increasing NaCl stimulated the accumulation of K+ in roots, which may have acted as a reservoir of K+ for shoots at high salinity. Glycinebetaine, and to a lesser extent proline and trigonelline, accumulated in shoot tissues with increasing salinity, though trigonelline concentrations were insufficient to be osmotically significant. Accumulation was closely associated with increases in shoot sap osmolality. It is proposed that glycinebetaine may act as a compatible solute in S. virginicus, as levels were sufficiently high to effect total osmotic adjustment of the cytoplasm at high salinity.
Seasonal variation in the ecophysiology of Littorella uniflora (L.) Ascherson in acidic and eutrophic habitats
Authors: ROBE W. E. , Griffiths H.
Published: April 2006

summary

The ecophysiology of the submersed aquatic macrophyte, Littorella uniflora (L.) Ascherson, has been compared at acidic and eutrophic habitats in the Lake District. The physico‐chemical environment (bulk‐water and sediment‐interstitial‐water pH, CO2, O2, nutrient concentrations and PAR) have been related to seasonal photosynthesis (CAM activity, [CO2]1 and CO2 and PAR response characteristics) and leaf growth rate of adult plants and ramets. In general, the environment was more favourable for plant growth at Esthwaite Water (the eutrophic site) than at Red Tarn (acidic). Although bulk‐water pH was higher at Esthwaite, sediments were deeper and interstitial water CO2 concentrations greater. Concentrations of nitrate and ammonium, phosphorus and potassium were also higher. However, shading by phytoplankton blooms and epiphytes reduced PAR incident on Esthwaite plants. Photosynthetic characteristics and growth of L. uniflora followed the seasonal changes in PAR and temperature. However, Esthwaite L. uniflora showed greater CAM activity, and slightly higher [CO2]1 and photosynthetic capacity. Esthwaite plants also possessed more numerous, shorter leaves with greater chlorophyll and nitrogen content, and leaf growth rate and ramet production were greater than for Red Tarn plants, Esthwaite L. uniflora transplanted to Red Tarn showed higher rates of growth than native Esthwaite plants, while Red Tarn L. unifiora transplanted to Esthwaite performed poorly and retained the lower rate of ramet growth found in native Red Tarn plants. End of season productivity was greatest in Esthwaite to Red Tarn transplants and lowest in Red Tarn to Esthwaite transplants. The relationships between environmental conditions and plant performance at the two sites are discussed in the context of the disappearance of L. uniflora from acidic and eutrophic sites in N. Europe in recent years.
Structure of fructopolysaccharide (asparagosin) from roots of asparagus (Asparagus officinalis L.)
Authors: SHIOMI NORIO
Published: April 2006

Fructopolysaccharide (asparagosin, fructan) was prepared from an extract of asparagus roots by chromatography on carbon‐Celite, paper and Toyopearl HW‐40S (gel permeation). The asparagus fructopolysaccharide was a mixture of saccharides ranging from DP (degree of polymerization) 12 to 22 approximately. It yielded fructose and glucose by hydrolyzing with acid or yeast β‐fructofuranosidase. The ratio of fructose to glucose in the enzyme hydrolysate was 13:1 by HPLC analysis. Structural determinations were made by 13C‐NMR spectroscopy. Strong signals corresponding to carbon‐1 (C‐l), C‐2, C‐3, C‐4, C‐6 and C‐5 of fructose residues in the fructopolysaccharide were observed at δ61.08–61.77, 103.64–104.26, 77.42–78.08, 74.43–75.09, 62.71–63.00 and 81.74 respectively. These chemical shifts were similar to those of inulin. Moreover, weaker signals were also detected at δ92.85, 71.80, 73.13, 69.79 and 72.23 due to C‐l, C‐2, C‐3, C‐4 and C‐5 of the glucose residue. The chemical shifts are almost identical to those of glucose carbons in raffinose, neokestose, 6G(l‐β‐D‐fructofuranosyl)2sucrose and lF,6G‐di‐β‐D‐fructofuranosyl sucrose. These findings were confirmed by analysis of methanolysate from permethylated fructopolysaccharide by using gas‐liquid chromatography. The fructopolysaccharide from asparagus roots was composed of saccharides possessing approximately 11–21 fructose residues linked by β‐2,l bonds and a non‐terminal glucose residue bound with fructose residues at positions C‐l and C‐6.
The uptake of glucose, fructose and sucrose into pea powdery mildew (Erysiphe pisi DC) from the apoplast of pea leaves
Authors: AKED J. , HALL J. L.
Published: April 2006

Patterns of sugar uptake into the mycelium of Erysiphe pisi DC have been investigated. Discs of mildewed pea (Pisum sativum L. cv. Onward) leaves were floated on radiolabelled sugar solutions. The mycelium was then removed and its total radioactive content was measured. The uptake from 1 mol m−3 fructose and 3‐O‐methylglucose (3‐OMG) was linear for at least 3 h, whereas the rate of uptake of glucose and sucrose increased with time. The uptake of glucose was markedly more rapid than that of the other three sugars, while 3‐OMG was the least well transported to the mycelium. Over a range of sugar concentrations, uptake of glucose and fructose was biphasic; however, whereas uptake of fructose showed a rapid linear increase over a higher concentration range (> 20 mol m −3), uptake of glucose and sucrose tended to plateau with sucrose hardly changing in rate of uptake at concentrations above 10 mol m−3. Increasing the pH of the uptake solution from 5 to 8 caused a slight but steady decrease in the uptake of glucose, fructose and sucrose. Decreasing the temperature from 25 to 4 °C decreased the uptake of all 3 sugars by 75–85 %. The effects of erythrosin B, parachloromercuribenzene sulphonic acid and carbonyl cyanide m‐chlorophenylhydrazone on sugar uptake were investigated. It appears that much of glucose uptake into the mycelium may be by facilitated diffusion driven by a concentration gradient. This gradient could be maintained by rapid metabolism of glucose in the fungal cytoplasm. It is concluded that there are probably carriers for all three sugars operating at lower concentrations (< 10 mol m −3).
Comparison of sulphite oxidation mechanisms in three lichen species
Authors: MISZALSKI ZBIGNIEW , NIEWIADOMSKA EWA
Published: April 2006

Three species of lichen: Hypogymnia physodes (L.) Nyl., Pseudevernia furfuracea (L.) Zopf and Usnea filipendula Stirt. with differing sensitivities to SO2 were examined for differences in their ability to carry out sulphite oxidation. The factor responsible for sulphite oxidation is not connected with the metabolic activity of thalli and probably the oxidation does not take place in reaction with O2− The rate of sulphite oxidation may well depend on the content of heavy metals in the thalli.
Effects of phosphate and nitrogen application on death of the root cortex in spring wheat
Authors: ELLIOTT G. A. , ROBSON A. D. , ABBOTT L. K.
Published: April 2006

Programmed senescence and relative sink‐strength have both been proposed as mechanisms controlling cell death in the root cortex. To distinguish between the two, seedlings of spring wheat (Triticum aestivum L.) were grown for 23 d in a glasshouse, with five rates of phosphorus and three rates of nitrogen, and cortical cell death over the length of the first seminal root axis assessed after staining with acridine orange.

The percentage of cortical cell death was greatest in plants moderately deficient in phosphorus and was less in plants receiving severely deficient or adequate‐to‐luxury supplies. Nitrogen supply did not affect the percentage of anucleate cells in the cortex. Both phosphorus and nitrogen supply influenced the distribution of cortical death with distance along the root except in regions close to the root tip. Nitrogen supply, however, had no effect on the extent of cortical cell death in regions of comparable age, except in plants receiving twice the level of phosphorus required for maximum plant growth.

Phosphorus supply influenced the extent of cortical death through effects on both the ratio of root to shoot weight, and the length of the total root system. These findings cannot be completely explained by the process of natural programmed senescence, but are compatible with the theory that cortical cell death is related to the distribution or activity of assimilate sinks within the root.
Variation in the chromosome number of Parnassia palustris L. in the British Isles
Authors: GORNALL R. J. , WENTWORTH J. E.
Published: April 2006

The varieties of Parnassia palustris L. in the British Isles (var. palustris and var. condensata Travis & Wheldon) each have two cytodemes: a diploid (2n= 18) and a tetraploid (2n= 36). The distribution of the cytodemes is loosely correlated with the limits of the Devensian glaciation.
Recovery after freezing in Avena sativa L., Lolium perenne L. and L. multiflorum Lam.
Authors: EAGLES C. F. , WILLIAMS J. , LOUIS D. V.
Published: April 2006

The pattern of recovery in seedlings of cultivars of Lolium perenne, L. multiflorum and Avena sativa was studied after an artificial freezing test at various stages of hardening. Unhardened plants of the three species were killed at about –6°C. The temperature at which plant mortality of hardened plants occurred was lower and was characteristic of the genotype, the hardening environment and the duration of the hardening treatment. A detailed analysis of the mode of recovery showed that the actively growing apex of the main tiller did not appear to develop increased resistance to freezing since it was killed at about –6°C in all hardening treatments. Improved survival of hardened plants at lower freezing temperatures could not be attributed to improved hardiness of the main apex but depended on the ability to establish viable regrowth from lateral tiller buds during the recovery period. This method of recovery is discussed in relation to possible physiological mechanisms of freezing tolerance including the release of apical dominance after death of the main apex and the sufficiency of post‐freezing carbon assimilation.
Cultivar responses to water stress in potato: effects of shoot and roots
Authors: JEFFERIES R. A.
Published: April 2006

Two experiments using self‐ and reciprocal grafts, examined interaction between shoot and root in determining the response of potato (Solanum tuberosum L.) to water stress. Single‐stemmed plants of the cultivars Cara and Desiree were grown in 15m pipes containing compost. Ten days after emergence, plants were either self‐ or reciprocally grafted. After the grafts had established, plants were either fully irrigated or subjected to drought treatments. Canopy expansion and leaf conductance were measured at regular intervals from the time that drought treatments were imposed. The production of shoot, root and tubers, and the distribution of root down the soil column were examined at the end of the experiments.

Scions had a dominant effect in determining the partitioning of dry matter between shoot, root and tubers, with those of the cultivar Cara having larger shoots and roots and less partitioned into tubers. The influence of root stock and, by inference, tuber type was less significant. In both irrigated and draughted treatments leaf conductance was determined predominantly by the scion, with scions of Desiree having significantly greater leaf conductance than those of Cara. On only six occasions did the root stock have a significant effect. On these occasions leaf conductance was greater in plants with Desiree root stocks than in those with Cara root stocks. Drought reduced both dry matter production and the proportion of dry matter partitioned into tubers, and increased the proportion of dry matter in shoots and roots. Drought also increased the root: shoot ratio indicating that root growth was maintained to a greater extent than shoot growth. Specific root length (root length: weight ratio) was increased by drought in one experiment but not in the other. Differences among grafts in response to drought were determined largely by the scion, and only to a lesser extent by root stock, with scions or root stocks of Cara showing a greater shift in partitioning in favour of tubers to shoots and roots than those of Desiree.
Uptake of two chlorinated chemicals in conifer needles: reversibility and compartmental analysis
Authors: SCHREIBER LUKAS , SCHÖNHERR JÖRG
Published: April 2006

The distribution of pentachlorophenol and 2,4‐dichlorophenoxyacetic acid in conifer needles was studied following uptake from aqueous solutions for up to 21 h. Desorption kinetics revealed two compartments (C1j and C2) in which organics were sorbed reversibly and one compartment (Cs) from which organics could not be desorbed. Reversible sorption proceeded very rapidly (less than 1 h for equilibration) and was made up of sorption to the surfaces of cuticular waxes and sorption in waxes and cutin. C3 appears to be identical with the apoplast and the symplast of needles. Penetration into C3 proceeded slowly and remained steady up to 21 h (longer periods not tried). The distribution of organics between the three compartments varied with time of loading and depended on plant species and properties of solutes. Data are discussed in relation to methods of exposure monitoring.
Abscission in leaf and fruit explants of Prunus persica (L.) Batsch
Authors: ZANCHIN  , BONGHI C. , CASADORO G. , RAMINA A. , RASCIO N.
Published: April 2006

Structural and enzymatic aspects of leaf and fruit abscission in explants treated with exogenous ethylene were studied and compared with those previously observed under field conditions. Light and electron microscopy observations reconfirm that differences in abscission occur in leaf and fruit, and in explants cell separation is accelerated, with a more dramatic degradation of the cell walls. In fruit, digestion starts from the middle lamella, and subsequently extends to the entire parietal mass. In the leaf the process involves the primary cell wall, leaving, at the end, undigested materials. In fruit the lytic activity is sustained by endocellulase, and by exo‐ as well as endopolygalacturonase. In the leaf only endocellulase activity has been found. Cell enlargement phenomena occur subsequent to abscission zone activation in both leaf and fruit explants, involving the cells of either the separation layer or the adjacent region.
The development and patterning of stomata and glands in the epidermis of Peperomia
Authors: SACHS T. , NOVOPLANSKY N.
Published: April 2006

The leaf epidermis of Peperomia obtusifolia includes both stomata and glands, distributed in a joint spacing pattern. The questions asked concerned the relations between the development of glands and stomata and the determination of their distributions within the epidermis. For these purposes it was essential to follow development in vivo, by repeated replicas of the same epidermal surface. The development of both stomata and glands started by characteristic divisions. These were generally unequal and it was the smaller product that became the mother cell of the future specialized structure. The initial divisions differed, so that the nature of the mature structure, as a stoma or a gland, could normally be predicted at an early stage. But glands and stomata still shared developmental processes: their formation involved additional characteristic divisions in the mother cell and oriented divisions in neighbouring cells. Furthermore, some lineages started as glands and matured as stomata and vice versa. Statistical measurements showed that each individual structure was surrounded by a region that was free of both similar and other specialized structures. Where these regions involved stomata they could be accounted for by the cell lineages forming not only a stoma or a gland but also their surrounding cells. Yet the relations between neighbouring glands had an additional component, indicating a specific inhibition that declined gradually as the distance from the gland increased.
Isolation and purification of intralamellar vesicles from Lemna minor L. chloroplasts
Authors: PICHER M. , GRENIER G. , PURCELL M. , PROTEAU L. , BEAUMONT G.
Published: April 2006

Intralamellar vesicles (IV) from chloroplasts of Lemna minor L. have been isolated and purified on a sucrose gradient, following sonication. Electron microscopy studies and lipid composition analyses suggest that IV are different in structure and in lipid composition from plastoglobuli. The presence of a high galactolipid composition (70%) suggests that IV are surrounded by a membrane (unit or half‐unit). The ratio of diacylgalactosylglycerol/diacyldigalactosylglycerol (3.9) of IV is similar to that of thylakoid membranes facing the stroma.
Effect of photoacclimation on the energy partitioning between cyclic and non‐cyclic photophosphorylation
Authors: HERZIG RONNY , DUBINSKY ZVY
Published: April 2006

The effect of photoacclimation on cyclic (CPP), non‐cyclic (NCPP), and oxidative phosphorylation was investigated in three algal species: Isochrisis galbana, Scenedesmus quadricauda and Synechococcus leopoliensis. The relative contribution of the three phosphorylative pathways to the incorporation of 32P into soluble and particulate cellular pools was assessed. To block NCPP we used 1 μm dichlorophenyl‐dimethylurea (DCMU) which does not interrupt CPP. Oxidative phosphorylation was blocked by purging oxygen with N2. In all three species the ratio of CPP to the total photophosphorylation (PP) increased in the process of photoacclimation to high light. We suggest that the observed increase in CPP in high‐light‐adapted cells allows bypassing the relatively slow enzymatic reactions in NCPP while channelling excess electrons to the faster CPP. This redistribution of energy increases ATP supply for the augmented metabolic requirements of fast growing, high‐light‐adapted cells.
Calcification rate in Emiliania huxleyi Lohmann in response to light, nitrate and availability of inorganic carbon
Authors: NIMER N. A. , MERRETT M. J.
Published: April 2006

The relationship between photosynthesis and calcification was investigated in a high‐calcifying strain of Emiliania huxleyi. At pH 8.3 and a photon flux density of 50 μmol m−2 s−1 calcification and photosynthetic 14CO2 fixation were carbon saturated at 1 mM DIC (dissolved inorganic carbon) but at a photon flux density of 300 μmol m−2 s−1 calcification and photosynthetic 14CO2 fixation were not saturated at the DIC concentration of sea‐water, 2 mM. When HCO3− provides the bulk of inorganic carbon the stoichiometry between photosynthetic 14CO2 fixation and calcification was 1:1. In the high‐calcifying strain of E. huxleyi the stoichiometry between photosynthetic 14CO2 fixation and O2 evolution was 2:1 but in a low calcifying strain the stoichiometry was 1:1. High nitrate concentrations, i.e. 1000 μM were required to inhibit calcification. The optimum pH for calcification and photosynthetic 14CO2 fixation was 7.8. From the results a model is proposed in which a molecule of HCO3− is the precursor of calcite in the coccolith vesicle with the extrusion of H+ into the cytosol, while another HCO3− provides CO2 in the chloroplast with the extrusion of OH−. The interaction of these processes maintains cytoplasmic pH near neutrality.
Dissolved inorganic carbon utilization in relation to calcite production in Emiliania huxleyi (Lohmann) Kamptner
Authors: DONG L. F. , NIMER N. A. , OKUS E. , MERRETT M. J.
Published: April 2006

The relationship between calcite production and dissolved inorganic carbon (DIC) utilization was investigated using high‐ and low‐calcifying strains of Emiliania huxleyi aerated with either air (0.03 % v/v CO2) or CO2‐free air. With cultures grown on air, calcite production was eight‐fold greater in the high‐calcifying culture, but growth rates for high‐ and low‐calcifying cultures were similar. Growth and calcite production were accompanied by a concomitant decrease in DIC and free CO2 in the high‐calcifying culture, showing that HCO3− provides inorganic carbon for calcite synthesis. In low‐calcifying cultures DIC and free CO2 were relatively constant, confirming that cells acquire inorganic carbon mainly by the diffusive entry of free CO2.

When cultures were aerated with CO2‐free air the free CO2 concentration was below the K0.5[CO2] for high‐ and low‐calcifying cells and the low‐calcifying cells were unable to grow. Growth of high‐calcifying cells was observed, and the calcite yield was little changed from cultures gassed with air (0.03 % v/v CO2). At these minimal CO2concentrations HCO3− may provide inorganic carbon for calcite synthesis and CO2 for photosynthesis, allowing growth to occur. Calcite synthesis by E. huxleyi decreases DIC and carbonate alkalinity in cultures not in equilibrium with the gas phase.
Effect of nutrients on CO2 assimilation by mosses on a sub‐Antarctic island
Authors: SMITH V. R.
Published: April 2006

N and P, especially when added together, significantly enhanced CO2 assimilation rate in four moss species from a range of habitats on sub‐Antarctic Marion Island. NO3− always caused a greater increase in assimilation rate than did NH4+, but this might have been due to Cl− added with the NH4+. Possibly for the same reason, K+ addition (as KCl) in some cases depressed CO2 assimilation rate compared with the controls (tapwater addition), as did K + N or K + P compared with N or P alone. The degree to which the mosses were apparently sensitive to Cl− was related to their tissue water content and to the soil water content in the habitats in which they occur. The results are discussed in the context of extremely low levels of available soil nutrients in, and small precipitation inputs of nutrients to, plant communities predominated by bryophytes on the island.
Variability in the distribution of photoassimilates along leaves of temperate Gramineae
Authors: WILLIAMS J. H. H. , COLLIS B. E. , POLLOCK C. J. , WILLIAMS M. L. , FARRAR J. F.
Published: April 2006

Gradients of photoassimilates were determined at various positions along the length of mature leaves of wheat (Triticum aestivum L.) and Lolium temulentum L. Attached leaves showed greater accumulation in the tip region. This distribution was reversed in excised leaves illuminated uniformly on the adaxial surface. Internal transport of assimilate was detected both by sub‐dividing excised leaves prior to illumination and by the administration of 14CO2 to the tips. The results are discussed in terms of the heterogeneity likely to occur in bulk extracts of leaf tissue and the ability of environmental perturbations to alter the balance of assimilates within leaves as well as their overall concentrations.
Structure and quantity of fructan oligomers in oat (Avena spp.)
Authors: LIVINGSTON DAVID P. , CHATTERTON N. JERRY , HARRISON PHILIP A.
Published: April 2006

Fructan in oat had previously been separated and quantified according to size class. To determine structure, fructan oligomers with a degree of polymerization (DP) of 3–5 were separated and purified by HPLC using a combination of ion exchange and reversed‐phase chromatography. Linkage analysis was performed on purified oligomers using gas chromatography, mass spectroscopy of partially methylated alditol acetates. DP 3 isomers consisted predominantly of 1‐kestose and neokestose. Three DP 4 isomers were based on neokestose and one of the 3 isomers contained 2,6‐linkages. In addition, the seven DP 5 isomers purified were also based on neokestose with two isomers containing 2,6‐linkages exclusively, three with 1,2‐linkages exclusively and two with both 2,6‐and 2,1‐linkages. A fructan fraction obtained by ethanol precipitation had an average DP of 12–3 and consisted exclusively of neokestose‐based isomers with 2,6‐linkages and no branching. Standard curves were obtained with the 13 purified oligomers and the curves were used to quantify oligomers in 49 oat accessions from five species. On a fresh weight basis the fructo‐oligomer in highest concentration in all but 3 of the accessions was 6G,6‐kestotetraose (F2‐6F2‐6G1‐2F).
Variation in fructan content in the underground organs of Vernonia herbacea (Veil.) Rusby at different phenological phases
Authors: DE CARVALHO M. A. MACHADO , DIETRICH S. M. C.
Published: April 2006

The contents and composition of fructans in underground organs (rhizophores) of Vernonia herbacea (Veil.) Rusby, a perennial herb native to the Brazilian cerrado, were analyzed at different phenological stages. Fructopolysaccharides were always present in higher concentrations than oligosaccharides but variations in amounts of both fractions occurred together. A marked decline in total fructan and an increase in free fructose were observed between sprouting and flowering, suggesting the occurrence of hydrolysis in association with the growth of new aerial shoots and flower development. There were higher amounts of total fructan at the end of summer and at dormancy, alternating with lower amounts at early dormancy. In spite of these variations the mean molecular mass of the fructo‐polysaccharides remained nearly constant throughout the cycle, except for the higher value found in vegetative plants at the end of summer. The maintenance of the mean molecular mass of fructo‐polysaccharides in the flowering phase concurrent with a marked reduction in total fructans suggests a peculiar mechanism of depolymerization in this plant, while the variation pattern found for fructan contents over the phenological cycle points to their role as reserve compounds in Vernonia herbacea.
Distribution of fructose polymers in herbaceous species of Asteraceae from the cerrado
Authors: TERTULIANO M. F. , FIGUEIREDO‐RIBEIRO R. C. L.
Published: April 2006

Underground organs of 35 herbaceous species of Asteraceae, representing 6 tribes, were collected from a restricted area of the Brazilian cerrado. Occurrence, histological location, concentration and composition of fructans were determined in thickened underground organs of 19 species in the tribes Eupatorieae, Heliantheae and Vernonieae. Spherocrystals of inulin were histologically detected in approximately 80 % of all species examined; these are distributed in the reserve parenchyma cells, particularly in the Vernonieae. In the Heliantheae and Eupatorieae they are found in the parenchyma, sometimes associated with vascular tissue. Total fructans as a proportion of dry mass range from 2.4 % in Vernonia brevifolia to 55% in Calea platylepis, regardless of the water contents of the storage organs. The highest degree of polymerization is observed in the Heliantheae. Thin‐layer chromatography demonstrates that isokestose predominates throughout and that different proportions of fructo‐oligosaccharides are present, depending on species.

The patterns of fructo‐oligosaccharides are similar at generic and tribal levels, suggesting phylogenetic relationships within the Asteraceae.
Effects of ozone and carbon dioxide mixtures on two clones of white clover
Authors: HEAGLE ALLEN S. , MILLER JOSEPH E. , SHERRILL DOROTHY E. , RAWLINGS JOHN. O.
Published: April 2006

The effects of mixtures of ozone and carbon dioxide on growth and physiology of an O3‐sensitive (NC‐S) and an O3‐resistant (NC‐R) clone of white clover (Trifolium repens L.) were determined. The experiment was performed in a greenhouse with O3 treatments of 5 and 82 nl l−1 (ppb) for 6 h d−1 and CO2 treatments of 380 (ambient), 490,600, and 710 μl l−1 (ppm) for 24 h d−1. Enrichment with CO2 decreased foliar gas exchange (measured as stomatal resistance) of NC‐R more than that of NC‐S whereas O3 decreased gas exchange of NC‐S more than that of NC‐R. Ozone caused extensive foliar injury of NC‐S but caused only slight injury of NC‐R. CO2 enrichment suppressed O3‐induced foliar injury of NC‐S as measured after 4 wk of exposure, but this effect diminished after 8 wk of exposure. CO2 enrichment decreased the relative chlorophyll content (μg of chlorophyll mg−1 of leaf tissue sampled) but not the total chlorophyll (total chlorophyll in the leaves sampled). There were no O3× CO2 interactions for foliar chlorophyll. High concentrations of CO2 caused reddening of new leaves near the end of the 8 wk exposure period. CO2 enrichment decreased foliar concentrations of N, P, K, S, Cu, B, and Fe, increased foliar concentrations of Mn, but did not affect Zn, Ca, or Mg. Ozone exposure did not modify the CO2 effects on foliar nutrient concentration. Ozone decreased growth of NC‐S but not NC‐R while CO2 enrichment stimulated growth of both clones. The highest CO2 concentration appeared to decrease the effects of O3 on growth of NC‐S. However, except for a transitory effect on foliar injury, there was no evidence that CO2, at concentrations less than the highest used in this study, will protect white clover from the effects of tropospheric O3.
Influence of temperature on seed germination and the nutritional requirements for embryo growth in Arum maculatum L.
Authors: PRITCHARD H. W. , WOOD J. A. , MANGER K. R.
Published: April 2006

The temperature requirements for seed germination and nutritional requirements for embryo growth were investigated in seed populations of Arum maculatum L. plants growing in South‐east England. Seeds freshly harvested from orange‐red berries were shown to require a protracted period of chilling at about 6 °C for germination to occur in either the light (12 h photoperiod) or the dark. There was no obligate requirement for chilled seeds to be transferred to higher temperatures for germination to occur, although such treatment did facilitate germination. Germination rate at cold temperature varied over three consecutive harvest years with faster germination rates apparently related to warmer temperature during seed development on the parent plant. This positive effect of warm temperature pretreatment on cold temperature germination rate was also evident in harvested seeds. Depending on the initial level of seed dormancy, the effect could be saturated after only a few weeks at 25 °C. The observation that similar germination rates occurred in seed which had been incubated in the light or dark for up to 1 yr at 11–28 °C indicated that such treatments neither altered seed viability nor induced secondary dormancy. Whereas extensive periods of time at low temperatures are a prerequisite for seed germination, isolated embryos were capable of development in vitro without chilling, even on a minimal medium of KNO3 and sucrose only, but not on water or KNO3 alone. In vitro seedling development progressed optimally through tuber formation to first leaf production within 9 months. It is concluded that the seed dormancy mechanism in this spring geophyte serves to facilitate germination after the winter. Furthermore, the ability to retain viability in the hydrated state suggests that seeds which remain dormant after the first winter are physiologically capable of surviving the first summer and germinating after the second winter.
External hyphae of vesicular–arbuscular mycorrhizal fungi associated with Trifolium subterraneum L.
Authors: JOHANSEN A. , JAKOBSEN I. , JENSEN E. S.
Published: April 2006

Subterranean clover (Trifolium subterraneum L. cv. Nuba) was grown alone or in symbiosis with Glomus intraradices Schenck and Smith in containers divided by a fine nylon mesh into a root compartment (RC) and a root‐free hyphal compartment (HC). Extraradical hyphae spread into the HC where 32P and 15NH4+ were applied at 2 or 5 cm distance from the RC, when the plants were 42 d old. The time‐course of hyphal transport of the tracers was followed by measuring the content of 32P and 18N in leaflets sampled at various times during a 30 d labelling period.

Plants colonized by G. intraradices had accumulated more of the applied tracers than the non‐mycorrhizal controls at the end of the experiment and hyphal transport of both P and N could be demonstrated. The levels of 32P in the leaflets of mycorrhizal plants already exceeded those of non‐mycorrhizal plants after 3 and 4‐5 d with the tracers applied at 2 and 5 cm distance from the RC, respectively. Leaflets of non‐mycorrhizal controls contained only traces of 32P, but considerable amounts of 15N, and mycorrhizas increased the concentration of 15N‐labelled N in leaflets only with tracers applied at 5 cm distance from the RC. The total recovery of applied 15N was 70 % higher in mycorrhizal than in non‐mycorrhizal plants when tracers were applied at 2 cm distance from the RC. When the distance from the RC and the tracers was increased to 5 cm, the total recovery of applied loN was 175% higher in mycorrhizal than in non‐mycorrhizal plants. The content of 32P and 15N in the external hyphae at the various distances from the RC confirmed that hyphal transport of P and N was directed towards the host plant.
Root colonization ofLupinus latifoliusAgardh. andPinus contortaDougl. byPhialocephala fortiniiWang & Wilcox
Authors: O'DELL T. E. , MASSICOTTE H. B. , TRAPPE J. M.
Published: April 2006

Root colonization patterns were studied afterPhialocephala fortiniiwas inoculated onLupinus latifolius(broad‐leafed lupin), a nitrogen‐fixing legume, andPinus contorta(lodgepole pine). The fungus colonized epidermal and cortical cells in the root hair zone on ultimate pine roots, as well as cortical and epidermal cells of primary roots of both hosts. Fungal colonization was inter‐ and intracellular with sclerotia forming in cells of both hosts. Labyrinthine tissue, a type of fungal differentiation that occurs in the Hartig net of ectomycorrhizas, formed sporadically on pine roots. Similar colonization has been observed on conifers and many other plants, but this report is the first showing that a single fungus can form such structures on both pine and lupin.
Retention and spread of a genetically engineered pseudomonad in seeds and plants of Zea mays L. – a preliminary study
Authors: FISHER P. J. , BROAD S. A. , CLEGG C. D. , LAPPIN SCOTT H. M.
Published: April 2006

The survival of a genetically engineered strain of Pseudomonas fluorescens introduced to the seeds, stems and leaves of maize plants was monitored using viable cell counts on selective agars. The bacterium was introduced to the seeds under vacuum and stored at either room temperature or 5°C. The bacterium was detected after 1 d, but not after 8 d, in seeds stored at room temperature, whereas at the lower temperature it was still detected after 43 d. Other inoculated seeds were grown either in a nutrient solution or in potting compost. Studies of survival within both seed remnants and roots, and on the aerial parts of the plants, demonstrated that the majority of bacteria remained in the seeds with some movement into the roots. Seeds retained a greater colonization frequency than roots in plants grown in both soil and nutrient solution. Those plants grown in nutrient solution maintained higher bacterial populations in seed remnants and roots than those grown in soil. Viable counts of P. fluorescens within seed remnants and roots decreased in soil‐grown plants over a 43 d monitoring period. No introduced organisms were detected in either stem core sections or other aerial parts of any of the inoculated plants, yet the cores were shown to contain an indigenous population of up to 4.8 × 104 cells g−1 tissue. When mature plants were injected with the bacterium viable counts of the pseudomonad below and above the injection points demonstrated the ability of the bacterium to translocate in the stem after the wounding process. P. fluorescens applied to the leaf surfaces remained viable for at least 20 d but showed great variations in numbers with values ranging from 0 to 1.4 × 106 g−1 tissue. The practical applications of introducing genetically engineered microorganisms into plants as control measures against pathogens and insect pests are briefly discussed.
Annual changes in dormancy and germination in seeds of Sisymbrium officinale (L.) Scop.
Authors: BOUWMEESTER HARRO J. , KARSSEN CEES M.
Published: April 2006

The effect of environmental conditions on changes in dormancy and germination of seeds of Sisymbrium officinale (L.) Scop, was studied. Seeds were buried in soil in the field or in incubators and at regular intervals, germination of exhumed seeds was tested over a range of conditions. Seeds that were buried in the field showed clear seasonal changes in dormancy. Fluctuations in soil moisture and nitrate content were not required for the changes in dormancy. Temperature seemed to be the only factor regulating these changes. Dormancy was relieved in periods of low temperatures and induced in periods of high temperatures. Fresh seeds and seeds buried for only a few months germinated best at elevated temperatures whereas seeds buried for a longer time germinated best at low‐temperatures. Light, nitrate and desiccation stimulated germination of exhumed seeds. As a consequence, these treatments extended germination over a much longer period of the year. Germination of exhumed seeds in Petri dishes at field temperature was reasonably described by a model based on the dual role of temperature, in the regulation of both dormancy and subsequent germination.
The effect of temperature on the sensitivity of nitrogenase to oxygen in the cyanobacteria Anabaena cylindrica (Lemmermann) and Gloeothece (Nägeli)
Authors: GALLON JOHN R. , PEDERSON DENNIS M. , SMITH GEOFFREY D.
Published: April 2006

Transient exposure to elevated temperature (37‐40 °C) inhibited N2 fixation (acetylene reduction) in cultures of the heterocystous cyanobacterium Anabaena cylindrica (Lemmermann) ATCC 27899 and the unicellular, non‐heterocystous cyanobacterium Gloeothece sp. (Nägeli) ATCC 27152. In neither organism was inhibition of N2 fixation due to thermal inactivation of nitrogenase. Rather, inactivation of N2 fixation at elevated temperature was a consequence of increased sensitivity to inhibition by O2 In A. cylindrica, thermally induced inactivation of N2 fixation by O2 could be correlated with inhibition of uptake hydrogenase. However, in Gloeothece, inhibition of carbon‐supported respiratory O2 consumption by elevated temperature was the probable cause of the increased sensitivity of N2 fixation to O2.
Delayed NH3 and N2O uptake by maize leaves
Authors: GRUNDMANN G. L. , LENSI R. , CHALAMET A.
Published: April 2006

15N was used to give evidence of NH3 and N2O absorption by maize leaves. A short‐term labelling method (90 min) was chosen with high NH3 concentration (40 μ1 1−1) to assess uptake mechanisms. Two initial entry pathways were suggested for NH3: fast uptake with immediate metabolism and fast storage with progressive metabolism. A storage compartment delayed NH3 absorption after exposure. Similar mechanisms might be involved in N2O uptake.
Do inorganic solutes limit growth of the facultative hemiparasite Rhinanthus minor L in the absence of a host?
Authors: SEEL W. E. , PARSONS A. N. , PRESS M. C.
Published: April 2006

The response of the facultative hemiparasitic angiosperm Rhinanthus minor to inorganic solutes was investigated by supplying plants not attached to a host with nitrogen, phosphorus and potassium. Solutes were supplied both individually (in pots) and in combination (under field conditions). Only phosphorus resulted in any significant stimulation of growth. The phosphorus treated plants also had higher rates of light saturated photosynthesis and higher water use efficiencies than control plants. In contrast to many autotrophic plants, nitrogen neither stimulated growth nor photosynthesis.
Morphological plasticity of the clonal herb Lamiastrum galeobdolon (L.) Ehrend. & Polatschek in response to partial shading
Authors: DONG MING
Published: April 2006

The present experiment investigates the morphological plasticity of Lamiastrum galeobdolon (L.) Ehrend. & Polatschek in response to light patchiness. In a garden experiment, stolons of the plant were grown under the following six light regimes: high light, low light, from low light to high light, from high light to low light, under high light but with the apical region of the stolon under low light, and under low light but with the apical region under high light. The low‐light conditions provided 50% of high light PAR and 28% of high light R/FR ratio (ratio of red to far red light), and simulated the canopy‐like shade that may be relevant to this species in its natural habitat.

Plants growing under different light treatments did not show significant differences in total plant dry weight, total number of ramets, number of primary ramets, number of secondary ramets, and number of branches per clone. L. galeobdolon plants growing under high‐light conditions formed shorter internodes, shorter petioles and smaller laminas with lower SLA, and showed higher branching intensity than those growing under low‐light conditions. Accordingly, when growing between patches of different light conditions, the primary ramets had shorter internodes, shorter petioles and smaller laminas with lower SLA in high‐light than in low‐light patches. Exposing the apical region, of an otherwise shaded stolon, to high light shortened its internodes, compared with those of plants growing entirely under low‐light conditions. Shading the apical region, of otherwise unshaded stolon, had no effect on the lengths of these internodes. In contrast, the morphology of the leaf responded to local light conditions only.

Elongation of stolon internodes was completed much faster (within 2 or 3 wk) than lamina expansion and petiole extension, which took at least 6 wk.

These results are interpreted in terms of the efficiency of exploitation of high‐light patches within the habitat of L. galeobdolon.
Carryover effects on the clonal growth of the grass Holcus lanatus L.
Authors: BULLOCK J. M. , MORTIMER A. M. , BEGON M.
Published: April 2006

The effects of clipping and daylength treatments and their carryover effects on the clonal growth of the perennial grass Holcus lanatus L. were investigated. Plants from ten clones were grown in six combinations of two daylength and three clipping treatments. Both clipping and low daylength reduced the tillering rate of all the clones but the clones differed in their degree of response to these treatments. After eight weeks, the treatments were discontinued and plants were grown in a common environment for seven weeks. Four‐week‐old tillers from the plants were repotted and grown in a common environment to examine the possibility of ‘carryover’ effects of the parental environments. After 8 wk of growth, there were main and interaction carryover effects of daylength and clipping on the tillering rates, biomass and tiller extension rates of the plants, which, however, differed greatly among clones. These differences among clones in both direct and carryover treatment effects, on clonal growth, indicate how the effects of many different environmental variables may interact to produce an environment that is highly heterogeneous in space and time, influencing the coexistence of genotypes and species.
Competition between diploid and derivative autotetraploid Dactylis glomerata L. from Galicia. Implications for the establishment of novel polyploid populations
Authors: MACEIRA N. O. , JACQUARD P. , LUMARET R.
Published: April 2006

The competitive ability of a tetraploid, and its morphologically indistinguishable progenitor diploid Dactylis glomerata L., from Galicia (Spain), was tested in a two‐year study, using isolated plants and the same individuals grown at two densities (16 and 36 plants per pot, respectively). Inverse linear regression equations were used to quantify the response of the different ploidy levels (hereafter cytotypes) to density. For the diploids, inter‐cytotype competition coefficients were significantly higher than intra‐cytotype coefficients. The substitution rate increased from 1. in the first year to 3.9 in the second year, when most of the diploids failed to flower and some died. The competitive superiority of the tetraploids was associated with higher mean tiller weight, particularly in the mixed cultures. The tetraploids also had heavier seeds and faster leaf production in early spring, and they flowered earlier than the diploids. Several of these differences between cytotypes appear to be due to differences in ploidy level and may play a major role in the establishment of the tetraploids in Galician pastures, where competition is high.