bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

SUMMARYThe 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

SUMMARYTwo 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

SUMMARYThe 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

SUMMARYStructural 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

SUMMARYThe 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

SUMMARYIntralamellar 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYN 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

SUMMARYGradients 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

SUMMARYFructan 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

SUMMARYThe 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

SUMMARYUnderground 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

SUMMARYThe 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

SUMMARYThe 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

SUMMARYSubterranean 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.