bluuebunny/crossref_metadata_2025 huggingface dataset:
Formes normales d'équations differéntielles implicites et de champs de Liouville
Authors: Manouchehri M.
Published: September 2008

Consider the partial differential equation f(x, y(x), dy(x)) = 0, where f is a smooth real function on ℝn × ℝ × (ℝn)*. Near each singularity of the characteristic foliation, a Liouville field is associated to the equation; we classify hyperbolic germs of Liouville fields up to symplectic transformations, hence we deduce normal forms for partial differential equations up to transformations which preserve the standard contact form of ℝ2n+1. For n = 1, a theorem of Davydov enables us to deduce normal forms for such equations up to transformations of the x, y plane.
Fractal dimensions of almost periodic attractors
Authors: Naito Koichiro
Published: September 2008

In this paper we estimate fractal dimensions of almost periodic orbits in terms of two kinds of exponents: the exponent in the inclusion lengths for ε-almost period and the exponent in Hölder conditions. Further, we estimate the inclusion lengths for ε-almost period of quasi-periodic functions by using Diophantine approximations. In the n-frequency quasi-periodic case we can show that the fractal dimension of its orbit is majorized by the value n/δ when it is Hölder continuous with exponent δ, 0 < δ ≤ 1.
Transitive maps which are not ergodic with respect to Lebesgue measure
Authors: Van Strien Sebastian
Published: September 2008

In this paper we shall give examples of rational maps on the Riemann sphere and also of polynomial interval maps which are transitive but not ergodic with respect to Lebesgue measure. In fact, these maps have two disjoint compact attractors whose attractive basins are ‘intermingled’, each having a positive Lebesgue measure in every open set. In addition, we show that there exists a real bimodal polynomial with Fibonacci dynamics (of the type considered by Branner and Hubbard), whose Julia set is totally disconnected and has positive Lebesgue measure. Finally, we show that there exists a rational map associated to the Newton iteration scheme corresponding to a polynomial whose Julia set has positive Lebesgue measure.
Hausdorff dimension of Julia sets of complex Hénon mappings
Authors: Verjovsky A. , Wu H.
Published: September 2008

The Hausdorff dimension of closed invariant sets under diffeomorphisms is an interesting concept as it is a measure of their complexity. The theory of holomorphic dynamical systems provides us with many examples of fractal sets and, in particular, a theorem of Ruelle [Ru1] shows that the Hausdorff dimension of the Julia set depends real analytically onfiffis a rational function of ℂ and the Julia setJoffis hyperbolic. In this paper we generalize Ruelle's result for complex dimension two and show the real analytic dependence of the Hausdorff dimension of the corresponding Julia sets of hyperbolic Hénon mappings.
Return times and conjugates of an antiperiodic transformation
Authors: Alpern Steve
Published: September 2008

Denote by G the group of all μ-preserving bijections of a Lebesgue probability space (X, Σ, μ) and by C the conjugacy class of an antiperiodic transformation σ in G. We present several new results concerning the denseness of C in G with respect to various topologies. One of these asserts that given any weakly mixing transformation τ in G and any F with μ(F) < 1, there is a transformation in C which agrees with τ a.e. on F.
Real-expansive flows and topological dimension
Authors: Keynes H. B. , Sears M.
Published: September 2008

We examine generalizations of R. Mañé's results on the topological dimension of spaces supporting an expansive homeomorphism to the case of real-expansive flows. We show that a space supporting a real-expansive flow must be finite dimensional, and a minimal real-expansive flow not exhibiting a type of spiral behaviour must be one-dimensional. This latter class includes all known examples and a slight generalization of Axiom A flows. These results are obtained by introducing a new concept of stable and unstable sets for real flows, and examining real-expansive flows in terms of these sets.
Self-generation of self-replicating maps of an interval
Authors: Parry William
Published: September 2008

We construct C1 symmetric maps of [−1, 1] to itself, satisfying a condition similar to Feigenbaum's: -φ(x) = φ(-x), φ2(bx) = bφ(x), 0<b <1. Under certain conditions, the non-wandering set consists of the one-sided Morse minimal set together with 2n points of period 2n for each n = 1, 2, … The main significance of the construction is its simplicity. Given a certain piece of the map φ, the rest is generated by the required equation.
Divergence type of some subgroups of finitely generated Fuchsian groups
Authors: Rees Mary
Published: September 2008

Let Г be a finitely generated discrete subgroup of the isometries of the hyperbolic plane H2 with at least one parabolic element. We prove that, if Г1 is a subgroup of Г with Г/Г1 abelian, the ‘critical exponent’ of Г1 is the same as that of Г. We give necessary and sufficient conditions-in terms of the rank of Г/Г1, the critical exponent of Г, and the image of parabolic elements of Г in Г/Г1 - for the Poincaré series of Г1 to diverge at the critical exponent.
Amenability, Kazhdan's property T, strong ergodicity and invariant means for ergodic group-actions
Authors: Schmidt Klaus
Published: September 2008

This paper discusses the relations between the following properties o finite measure preserving ergodic actions of a countable group G: strong ergodicity (i.e. the non-existence of almost invariant sets), uniqueness of G-invariant means on the measure space carrying the group action, and certain cohomological properties. Using these properties one can characterize all actions of amenable groups and of groups with Kazhdan's property T. For groups which fall in between these two definations these notions lead to some interesting examples.
Orbit equivalence and rigidity of ergodic actions of Lie groups
Authors: Zimmer Robert J.
Published: September 2008

The rigidity theorem for ergodic actions of semi-simple groups and their lattice subgroups provides results concerning orbit equivalence of the actions of these groups with finite invariant measure. The main point of this paper is to extend the rigidity theorem on one hand to actions of general Lie groups with finite invariant measure, and on the other to actions of lattices on homogeneous spaces of the ambient connected group possibly without invariant measure. For example, this enables us to deduce non-orbit equivalence results for the actions of SL (n, ℤ) on projective space, Euclidean space, and general flag and Grassman varieties.
Design rationale: Researching under uncertainty
Authors: Burge Janet E.
Published: September 2008

Rationale research in software development is a challenging area because although there is no shortage of advocates for its value, there is also no shortage of reasons for why rationale is unlikely to be captured in practice. Despite more than 30 years of research there still remains much uncertainty: how useful are the potential benefits and how insurmountable are the barriers? Will the value of the rationale (design and otherwise) justify the cost of collecting it? Although there have been numerous rationale research projects, many, if not most, received little or no empirical evaluation. There also have not been many studies examining what the needs are of the practitioners who would be supported by the rationale. This article discusses the “doom and gloom” predictions of rationale's failure, provides a survey of evaluations of rationale systems, and discusses what we hope is a brighter outlook for rationale research in the future. There are development standards and synergistic research areas that may help with rationale research and its acceptance in the software community with which we should be working. This article also presents the results of a pilot survey of software developers who were asked how they would envision using rationale and what they believe the most important barriers are. Although some results were as expected, there were also some surprises. Research on technology transfer indicates that, among other things, to transition successfully from research into practice we need to understand the need that is being met and demonstrate the value of our approach. Until we have determined how our work is needed by the people we are trying to help we will remain researching under uncertainty.
Constraint capture and maintenance in engineering design
Authors: Ajit Suraj , Sleeman Derek , Fowler David W. , Knott David
Published: September 2008

The Designers' Workbench is a system developed by the Advanced Knowledge Technologies Consortium to support designers in large organizations, such as Rolls-Royce, to ensure that the design is consistent with the specification for the particular design as well as with the company's design rule book(s). In the principal application discussed here, the evolving design is described using a jet engine ontology. Design rules are expressed as constraints over the domain ontology. Currently, to capture the constraint information, a domain expert (design engineer) has to work with a knowledge engineer to identify the constraints, and it is then the task of the knowledge engineer to encode these into the Workbench's knowledge base. This is an error-prone and time-consuming task. It is highly desirable to relieve the knowledge engineer of this task, so we have developed a system, ConEditor+, that enables domain experts themselves to capture and maintain these constraints. Further, we hypothesize that to appropriately apply, maintain, and reuse constraints, it is necessary to understand the underlying assumptions and context in which each constraint is applicable. We refer to them as “application conditions,” and these form a part of the rationale associated with the constraint. We propose a methodology to capture the application conditions associated with a constraint and demonstrate that an explicit representation (machine interpretable format) of application conditions (rationales) together with the corresponding constraints and the domain ontology can be used by a machine to support maintenance of constraints. Support for the maintenance of constraints includes detecting inconsistencies, subsumption, redundancy, fusion between constraints, and suggesting appropriate refinements. The proposed methodology provides immediate benefits to the designers, and hence, should encourage them to input the application conditions (rationales).
How to evaluate reading and interpretation of differently structured engineering design rationales
Authors: Aurisicchio Marco , Gourtovaia Marina , Bracewell Rob , Wallace Ken
Published: September 2008

Documented engineering design rationale has the potential to become a key source of information about past designs. Ease of comprehension of design rationale might play a crucial role in ensuring that the full potential of documented information is realized and that the effort and time necessary to capture design rationale pay off. This research proposes an empirical methodology for evaluating how structuring design rationale and supplying it with visual nontextual cues influences reading and interpretation. The study compares reading and interpretation of technical documentation presented in different formats to engineering graduate trainees in the aerospace industry.
Chunks, lines, and strategies: A three-component representation to capture and exchange architects' design processes
Authors: Lindekens Jonas , Heylighen Ann
Published: September 2008

This paper presents an approach to capture and exchange the arguments and rationale architects develop while designing. The approach was inspired by experiments conducted in the context of a larger research project on architectural redesign. Protocol analysis revealed that architects tend to use three mechanisms in constructing arguments for design solutions: chunks, lines of thought, and strategies. These three mechanisms were used to record “real-world” design processes in architectural practice, the results of which were evaluated by assessors with different backgrounds. The paper closes by comparing the approach to related work, and outlining challenges for the future.
Kuaba approach: Integrating formal semantics and design rationale representation to support design reuse
Authors: de Medeiros Adriana Pereira , Schwabe Daniel
Published: September 2008

This article presents Kuaba, a new design rationale representation approach that enables employing design rationale to support reuse of model-based designs, particularly, software design. It is shown that this can be achieved through the adoption of an appropriate vocabulary that allows design rationale representations to be computationally processed. The architecture and implementation of an integrated design environment to support recording design rationale using Kuaba is also shown. The Kuaba approach integrates the design rationale representation model with the formal semantics provided by the metamodel of the design method or modeling language used for describing the artifact being designed. This integration makes the design rationale representations more specific according to the design methods and enables a type of software design reuse at the highest abstraction level, where rationales can be integrated and reemployed in designing a new artifact.
Changes in ribosomal RNA integrity in leek (Allium porrumL.) seeds during osmopriming and drying-back treatments
Authors: Davison P. A. , Taylor R. M. , Bray C. M.
Published: September 2008

Loss of vigour in leek (Allium porrumL.) seed lots is accompanied by the appearance of damage to ribosomal RNA in quiescent embryo tissue. Polyethylene glycol osmopriming treatments of such low-vigour seed permit replacement of this damaged ribosomal rRNA over a 7-day priming period. Low-vigour leek seeds germinated for 6 days without a prior osmopriming treatment still exhibit evidence of damaged ribosomal RNA in embryo tissue. Osmoprimed leek seeds dried back whilst still in the desiccation-tolerant state retain most of the benefits conferred by priming treatments. Osmoprimed leek seeds dried back when having reached the desiccation-sensitive state germinate poorly, if at all, and exhibit much reduced rates of protein synthesis in embryo tissue upon rehydration compared to desiccation-tolerant seeds. Embryo tissue from dried back, desiccation-tolerant seeds exhibits the capacity for much higher levels of protein synthesis than embryo tissue from unprimed seeds at equivalent stages of imbibition. RNA levels continue to increase in embryo tissue upon rehydration of dried back, desiccation-tolerant leek seeds but not in desiccation-sensitive seeds. Loss of protein synthetic capacity in desiccation-sensitive seeds during rehydration is accompanied by increasing levels of ribosomal RNA degradation. Such ribosomal RNA degradation may be indicative of the germinative capacity of leek seeds dried back after osmopriming treatments.
Effect of storage temperature and moisture on the germination of papaya seeds
Authors: Ellis R. H. , Hong T. D. , Roberts E. H.
Published: September 2008

Seeds of papaya (Carica papayaL.) stored for 12 months at 15°C with 7.9–9.4% moisture content maintained their original germination. In contrast, many seeds stored cooler or drier lost viability, the losses occurring more rapidly at −20°C than at either 0°C or 15°C. The results are not compatible with the definitions of either orthodox or recalcitrant seed storage behaviour.
Seed storage behaviour in Elaeis guineensis
Authors: Ellis R. H. , Hong T. D. , Roberts E. H. , Soetisna U.
Published: September 2008

Seed viability was maintained in four cultivars of oil palm (Elaeis guineensis Jacq.) during 12 months of hermetic storage at 15°C with 10–12% moisture content (embryo moisture contents of 19–21%). The viability of both these and drier seeds was reduced greatly during this period at cooler storage temperatures of 0°C and −20°C, however. For example, intact seeds at 6.1–7.4% moisture content (embryo moisture contents of 9.1–12.0%, at which freezing damage would not be expected) lost viability more rapidly at 0°C and −20°C than at 15°C. Moreover, desiccation to 4–5% moisture content (4–6% embryo moisture content) reduced seed lot viability in some but not all cultivars. The results confirm earlier reports that oil palm is not recalcitrant, but neither is it orthodox. Thus, seed storage behaviour in oil palm appears to be intermediate between these categories. Additional results are presented which suggest that the seeds of the royal palm (Oreodoxa regia HBK) may also show intermediate seed storage behaviour.
Benzyladenine-stimulation of nuclear DNA synthesis and cell division in germinating maize
Authors: Reyes J. , Jiménez-García L. F. , Gonzalez M. A. , Vázquez-Ramos J. M.
Published: September 2008

We have studied by means of cytology and autoradiography the effect of benzyladenine (BA, a synthetic cytokinin) on DNA metabolism during early maize germination.The data indicate that BA stimulates nuclear DNA replication. The doubling of the amount of nuclear DNA in BA-treated axes occurs earlier than in nontreated axes, and there is a three-fold increase in the mitotic index at 24 h of germination. These results provide further corroboration for the suggestion that the stimulation of DNA synthesis observed relates to a nuclear replicative type of synthesis. Possible mechanisms of action of BA are discussed.
Physiological, biochemical and ultrastructural aspects of imbibitional chilling injury in seeds: a review of work carried out at the Beijing Botanical Garden
Authors: Zheng G. H.
Published: September 2008

This paper is a résumé of research on imbibitional chilling injury of seeds. The following summarizes the experimental results obtained and some views and concepts derived from the studies conducted at Beijing Botanical Garden during the last decade. A lot of evidence has supported and confirmed the hypothesis for imbibitional chilling injury in seeds, i.e. the primary target of harmful effects during the chilling rehydration in seeds is the membrane systems, and the subsequent degree of lasting damage depends highly on the repair of the membrane systems themselves. The two processes of repair, physical and physiological–biochemical processes, can complement each other to a certain extent.
The effects of desiccation on seed survival in Acer platanoides L. and Acer pseudoplatanus L.
Authors: Dickie J. B. , May K. , Morris S. V. A. , Titley S. E.
Published: September 2008

Mature seeds of Norway maple (Acer platanoides L.) are tolerant of desiccation, at least to moisture contents of about 7% (fresh weight basis), but those of sycamore (Acer pseudoplatanus) are killed by drying below about 45% moisture content. Sycamore seeds are thus recalcitrant; while the classification of those of Norway maple as orthodox is confirmed by the fact that between 19% and 7.5% moisture content their longevity is increased in a predictable way by reduction of seed moisturecontent. However, the period of useful storage of the latter in seed banks may be much less than for many crop species. The rates of water loss to a dry environment of both fruits and seeds of sycamore are much less than those of Norway maple, suggesting a degree of desiccationavoidance in the desiccation-intolerant species. Seed physiological maturity (maximum dry weight) occurred 2–3 weeks earlier in Norway maple than insycamore, but in both species this occurred about 150–160 days after peak flowering. Tetrazolium staining is a good indicator of embryo viability in both species, correlating well with germination test results. In Norway maple both methods of viability testing indicated that whole-seed desiccation tolerance coincided with the attainment of maximum dry weight. Tetrazolium staining indicated the development of desiccation tolerance in the radicles/hypocotyls of both species approximately 2–4 weeks before physiological maturity. Possible correlation between changes in the level of embryo dormancy during development and the acquisition of desiccation tolerance are discussed.
An analysis of seed development in Pisum sativum. XV. The influence of seed size on protein content
Authors: Arthur A. E. , Adams H. , Strouts K. , Jones D. A. , Wang T. L. , Hedley C. L.
Published: September 2008

The variation for protein content has been assessed in a series of pea (Pisum sativum L.) lines differing in mean seed size. The range of seed size within each genotype was manipulated by growing the plants in different environments and by altering the structure of the plant. The response of the lines in terms of seed weight to the environments and treatments was inconsistent, but 90% of the total variation was accounted for by differences between genotypes. In contrast, for percentage protein, the genetic component was much weaker with nearly half the variation being accounted for by within (residual) variation. The correlations between seed weight and percentage protein were highly genotype specific. For the largerseeded genotype, percentage protein increased with increasing seed size (r= +0.9, P < 0.01), while for the small-seeded genotype there was mid-range negative value (r = −0.5, P <0.01). It is suggested that any assessment of percentage protein in pea genotypes must take account of seed size.
Onset of water stress tolerance in developingHelianthus annuusembryos
Authors: Le Page-Degivry M. Th. , Garello G.
Published: September 2008

ExcisedHelianthus annuusembryos were capable of precocious germination as early as 7 d after pollination. At this stage they were not capable of withstanding desiccation treatment. The desiccation tolerance was acquired at a stage of development which depended on the rate of water loss to which embryos were subjected. Coincident with the acquisition of tolerance to a rapid desiccation, they gained the capacity to withstand 24 h preincubation in agitated water; this acquisition could be correlated to a sharp decrease of the leaching of electrolytes, amino acids and proteins in the incubation water, suggesting that a change in membrane properties played a key role in this transition. Moreover, the acquisition of tolerance to these stresses was coincident with the increase of endogenous abscisic acid (ABA). ABA appliedin vitroto young embryos induced tolerance both to desiccation and to preincubation in water: thisin vitroacquisition of tolerance was again correlated with a decrease in the leakage.
Seed dormancy inAcer: abscisic acid as a factor in the control of precocious germination and the induction of dormancy
Authors: Pinfield N. J. , Bazaid S. A. M.
Published: September 2008

Immature embryos isolated from fruits ofAcer pseudoplatanusL. at various stages during a 24-week development period, showed a sharply defined transient accumulation of endogenous free ABA, with peak levels at 10 weeks postanthesis (wpa). When this ABA peak occurred isolated embryos showed a high level of germinability when incubated in sterile culture; however, germinability fell rapidly thereafter, reaching minimum values at 14 wpa before recovering as maturity approached. Halfembryos and excised embryonic axes, although showing consistently higher germinability than whole embryos, also showed a similar progressive reduction in germination capacity up to 14 wpa, followed by a recovery in germinability. This peak of free ABA in the embryo also correlated with the start of the most rapid phase of both embryo mass and volume increase. The possibility that endogenous ABA is the causal agent of this short-lived embryo dormancy inA. pseudoplatanusis discussed, as is the possibility that by suppressing precocious germination, ABA frees the embryo to initiate or accelerate its normal developmental processes.
The effects of priming on seed longevity in Ranunculus sceleratus L.
Authors: Probert R. J. , Bogh S. V. , Smith A. J. , Wechsberg G. E.
Published: September 2008

Priming in polyethylene glycol (PEG, −1.5 MPa) for 7 d followed by drying, led to a 4–5 fold increase in mean longevity when achenes (seeds) of Ranunculus sceleratus L. were subsequently stored at 35°C and 9.2% moisture content on a fresh weight basis (67.1% equilibrium relative humidity). The increase in longevity was due to an increase in the standard deviation of the frequency distribution of individual seed lifespans (decrease in the slope of transformed survival curves) and to a lesser extent to an increase in the intercept of survival curves. Priming for 1 d resulted in a smaller but significant increase in longevity independent of whether seeds were primed in PEG, distilled water or a saturated atmosphere (100% RH).

The effects of priming were not due to the prevention of imbibition injury, and there was no evidence that the water relations of whole achenes was affected by priming. The effects of a 7 d priming treatment were dependent on the temperature and nature of the priming medium. However, no differences were recorded between corresponding treatments which were primed in PEG or distilled water. Moreover, the survival and responsivity to priming of R. sceleratus seeds was not related to dormancy status. The effects of priming on the longevity of R. sceleratus seeds are apparently unrelated to seed quality as the response of seeds previously aged for 8 d at 35°C and 7.9% moisture content was similar to that for unaged seeds.

Priming followed by drying did not increase seed longevity in the related species R. acris L. The promotive effects of priming on seed survival appear to be species specific and may be related to ecological factors.
Soybean somatic embryo maturation: composition, respiration and water relations
Authors: Slawinska J. , Obendorf R. L.
Published: September 2008

Embryogenesis was induced on cotyledons of immature zygotic embryos of soybean (Glycine max(L.) Merrill) placed on solid medium containing 62.5 mmglutamine, soybean seed growth medium salts and vitamins, and 40 mg I−12,4-dichlorophenoxyacetic acid (2,4-D) plus 175 mmmaltose, or 8 mg I−1α-naphthaleneacetic acid (NAA) plus 88 mM sucrose. Somatic embryo development was continued in liquid medium containing 0.16 mg I−1indole-3-butyric acid and 2.64 mg I−1abscisic acid, glutamine and salts as above, and 88–438 mM sucrose in progressively increasing steps. Germination was on solid half-strength Murashige-Skoog medium. During maturation, somatic embryos mimicked zygotic embryos in colour, protein concentration, water and solute potentials, and respiration. Protein and lipid accumulated to 329 and 86 g kg−1dry weight in somatic embryos. Fatty acid composition was similar to that of axes of mature seeds. Before desiccation, the water and solute potentials of maturing somatic embryos declined to −1.13 and −1.99 MPa while turgor increased to 0.86 MPa. Concomitantly, a 60% reduction in activity of the cytochrome oxidase pathway of respiration occurred with somatic embryo maturation at 600 g water kg−1fresh weight. Although small (about 8 mg per embryo), 60% of the somatic embryos formed roots and shoots during germination after maturation without drying and 30% germinated after drying to 60 g water kg−1fresh weight. In the greenhouse, somatic plantlets grew to mature plants with seeds.
Nature and utilization of seed reserves during germination and heterotrophic growth of young sugar beet seedlings
Authors: Elamrani A. , Raymond P. , Saglio P.
Published: September 2008

The seed reserves of sugar beet (Beta vulgarisL.) are starch, located exclusively in the perisperm, and lipids, proteins and a small quantity of soluble sugars, located mainly in the cotyledons. It is shown that lipids are the main respiratory substrate used during germination whereas starch and remaining lipids are only hydrolysed after root extrusion, to sustain root and hypocotyl growth. By removing the perisperm during imbibition, it was demonstrated that lipids and proteins alone are sufficient for viable seedling development, though such seedlings grew less than those developing in the presence of perisperm. The utilization of seed reserves was followed during seedling development in the dark in various organs. At 20°C, the reserves were sufficient for 8 d of growth in the dark, the hypocotyl attaining a length of 5 cm. Specific problems relating to field establishment of sugar beet are discussed in relation to these results.
Changes in seed quality during seed development and maturation in tomato
Authors: Demir I. , Ellis R. H.
Published: September 2008

Changes in tomato (Lycopersicon esculentumMill.) seed quality were monitored during seed development and maturation in glasshouse experiments in 2 years. The end of the seedfilling period (mass maturity) occurred 35–41 d after anthesis (differing among trusses) in 1989 and 42 d after anthesis in 1990. Seed moisture contents at this developmental stage were 53–72% (wet basis), while the onset of ability to germinate (during 21-d tests at 20°/30°C) and the onset of tolerance to rapid enforced desiccation occurred just before (1990) or just after (1989) mass maturity. In 1989, seed quality was assessed primarily by seedling size in a glasshouse experiment; maximum mean seedling dry weight 25 d after sowing was not achieved until 24–40 d after mass maturity. In 1990, seed quality was assessed primarily by germination following storage; maximum normal germination after 35 d in storage at 40 °C with 14 ± 0.5% moisture content was attained 23 d after mass maturity, but with little difference among seed lots harvested 10 d earlier or up to 30 d later. The results contradict the hypothesis that maximum seed quality is attained at the end of the seed-filling period and that seed viability and vigour begin to decline immediately thereafter.
Protein disulfide isomerase in germinating wheat (Triticum aestivum) seed and during loss of viability
Authors: Livesley M. A. , Bulleid N. J. , Bray C. M.
Published: September 2008

Protein disulfide isomerase (PDI E.C. 5.3.4.1) catalyses the formation of disulfide bonds in secretory or cell-surface proteins during their biosynthesis. PDI activity is associated with the microsomal fraction of the cell and has been found in several mammalian tissues and in developing wheat endosperm.

The embryo and aleurone layer of germinating seeds of the wheat cultivar Galahad showed PDI activity associated with a microsome-enriched fraction of cell homogenates PDI activity in microsome-enriched fractions from aleurone layers of normally germinating seeds was significantly higher than in their abnormally germinating counterparts and diminished as germination proceeded.

Dry embryos and germinating embryos showed less PDI activity than aleurone layers. There was no significant difference in PDI activity between microsome-enriched fractions from embryos of normally and abnormally germinating seeds at 3 or 6 days of germination.

Wheat aleurone PDI was partially purified using gel filtration and had a molecular mass of 110–130 kDa and a monomeric molecular mass of ca. 57 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis.
Synthesis of extrachromosomal DNA and telomere-related sequences in germinating wheat embryos
Authors: Bucholc M. , Buchowicz J.
Published: September 2008

Nuclear DNA of wheat embryos was probed with a synthetic oligonucleotide (C3TA3C3TA3) to assess changes in the length of telomeres during storage and germination. Chromosomal DNA of dry embryos, especially those derived from long-term-stored caryopses, was considerably depleted of telomeric repeats, but, shortly after the start of imbibition, the chromosomal DNA became rich in sequences hybridizing to the telomeric probe. Simultaneously, newly synthesized telomere-related sequences appeared in an extrachromosomal form that could be separated from bulk nuclear DNA by velocity and isopycnic centrifugations. It is concluded that, in addition to typical repair events, rapid synthesis of telomeric repeats occurs in wheat embryos at the onset of germination.
Watermelon seed germination. 2. Osmomanipulation of photosensitivity
Authors: Thanos C. A. , Mitrakos K.
Published: September 2008

Seed germination of watermelon (Citrullus lanatuscv. Sugar Baby) was fully suppressed by intermittent far-red (FR) irradiation (1 min every 30 min). When the intervening dark period was increased, a linearly increasing final germination percentage was obtained. However, a 4-day intermittent FR treatment induced phytochrome-controlled dormancy and the longer the dark interval the deeper was the dormancy of the non-germinated seeds. When seeds were soaked in a fully inhibitory osmotic solution, no dormancy was imposed. However, a single FR pulse at the time of transfer induced partial, secondary dormancy; the kinetics of the imposition of dormancy followed a negative exponential curve (half-life 1.5 days; 3 days for the cultivar Crimson Sweet). Seeds osmotreated for 10 days in darkness and subsequently dehydrated (with and without a final FR pulse) acquired germination characteristics similar to those in light-requiring and dark-germinating achenes, respectively, of the lettuce cultivar Grand Rapids. In the light-requiring osmomanipulated seed population, the induction of germination was brought about by the low-energy reaction of phytochrome, chilling, dry storage and decoating. The transformation through osmomanipulation of the dark-germinating watermelon seeds (the inhibition of which required prolonged exposure to light) to positively or negatively photosensitive seeds (that responded to brief light pulses), might be attributed to the slow relaxation of existing meta-Fa and meta-Rb phytochrome intermediates to Pfrupon hydration.
Development of desiccation tolerance in Norway maple (Acer platanoides L.) seeds during maturation drying
Authors: Hong T. D. , Ellis R. H.
Published: September 2008

Norway maple (Acer platanoides L.) seeds were harvested at different stages of seed development and maturation in 1989–91. As maturation drying progressed, the seed populations showed increasing desiccation tolerance: at 67–69% moisture content, no seeds survived desiccation below 10% moisture content; maturation drying to 55–57% moisture content (values corresponding with the end of the seed-filling phase) improved desiccation tolerance, but nevertheless most seeds were unable to withstand desiccation to 5–7% moisture content; further maturation drying to 27–28% moisture content enabled the seeds to survive considerable desiccation, no loss in viability occurring in seeds dried to 3% moisture content. This considerable improvement in desiccation tolerance after the end of the seed-filling phase was correlated (P<0.05) with the progress of maturation drying and may be associated with the increase in the potential longevity of seeds of other species that occurs during seed development subsequent to seed filling.
Germination of the seeds of parasitic angiosperms
Authors: Logan D. C. , Stewart G. R.
Published: September 2008

Totalling more than 3000 species, parasitic angiosperms are a most diverse group of organisms. Classified as either shoot or root parasites according to site of attachment, plant parasites are further classified, according to the degree of parasitism, into one of two divisions: holoparasitic or hemiparasitic. Within these divisions, angiosperm parasites are either obligate or facultative.

Obligate parasites cannot survive to maturity without attaching to a host plant, thus the need to germinate in close proximity to a host first characterizes the specialized germination and seed dispersal strategies of these plants. However, seeds of all species of the rootholoparasitic Orobanchaceae and four genera within the Scrophulariaceae have evolved very specialized germination strategies. Once the seeds have undergone an after-ripening period, they require a prolonged imbibition period at temperatures of approx. 30°C before they acquire the potential to germinate. Minute seeds with very little reserves, they must germinate within millimetres of the host root for successful host attachment and continued survival. To this end, germination only occurs in responseto specific chemical germination triggers released from the host root. InStriga hermonthica(Del.) Benth., the perception of the host-derived trigger results in stimulation of endogenous ethylene production and it is this ethylene that initiates germination. It is proposed that the chemical triggers released from the host be consideredas ‘elicitors’ which function primarily as allelochemicals and that the parasite seeds have become adapted in such a way as to have an absolute requirement for external germination triggers.
Changes in protein synthesis in embryonic axes after long-term storage of maize seeds
Authors: Aguilar R. , Reynoso E. , Albores M. , de Jiménez E. Sánchez
Published: September 2008

The aim of this work was to analyse the capacity for protein synthesis in embryonic axes from long-term-stored maize seeds, including the role of proline. Embryonic axes from seeds stored for 13 years (S) and non-stored seeds (NS) were incubated in nutrient media after application of [14C]proline. Transformation of [14C]proline into other amino acids was analysed by thin-layer chromatography. After 6 h of incubation, no other labelled amino acids were found. Incorporation of14C into total soluble and cell-wall (proline-rich) proteins was assessed during this period. Incorporation of [14C]proline into specific cell-wall proteins was lower in S than in NS axes.

Studies using [35S]methionine showed that protein synthesis was slower in axes of S than in NS seeds. Analyses of these proteins by gel electrophoresis and fluorography revealed qualitative differences between the [35S]methionine proteins synthesized by both types of axes. The NS: S ratios for the [35S]proteins were larger than those from the [14C]proline assays. These data may be interpreted as an indication of differential deterioration of transcription or translation in the axes during long-term seed storage.
Effects of (±)-phaseic acid on developing embryos of barley (Hordeum vulgare, L. cv. Bonanza) culturedin vitro
Authors: Hill R. D. , Durnin D. , Nelson L. A. K. , Abrams G. D. , Gusta L. V. , Abrams S. R.
Published: September 2008

The effects of exogenous phaseic acid (PA) on germination and protein accumulation of cultured immature barley embryos were examined. Chemically synthesized PA was racemic, 87% pure and stable over the course of the experiment. Germination was observable in >90% of the untreated embryos after 3 days of incubation, whereas embryos treated with 10μmabscisic acid (ABA) or PA showed no evidence of germination. Buffer extracts from embryos treated with ABA or PA had similar protein profiles when examined by single and two-dimensional electrophoresis. The profiles differed significantly from those of embryos incubated in the absence of the two compounds. Concentrations of α-amylase inhibitor and barley-germ agglutinin (BGA) increased upon treatment of immature embryos with ABA or PA. This was due tode novosynthesis as there was increased incorporation of radioactivity from35S-labelled amino acids into the proteins in treated embryos. Endogenous ABA content in PA-treated embryos was not significantly different from that in untreated embryos. An analogue of ABA, 2′, 3′-dihydroabscisic acid, which cannot be metabolized to phaseic acid, inhibited germination and caused increased synthesis of α-amylase inhibitor and germ agglutinin. ABA and PA may both be active in promoting responses associated with ABA in barley embryos, but the embryos are more sensitive to ABA.
Relation between protein composition and germination capacity of sunflower seeds
Authors: Reuzeau C. , Goffner D. , Cavalié G.
Published: September 2008

Protein composition of sunflower seeds (Helianthus annuusL.) was analysed to identify a possible marker for germination capacity and to evaluate seed viability precociously after harvest and after natural ageing during storage. Electrophoresis on 2-D gels was used to compare total soluble andin vivosynthesized proteins in two seed lots showing different germination capacities. Differences were observed to a greater extent inin vivoprotein synthesis profiles than in total soluble proteins. Inhibition of [35S]methionine uptake and incorporation in seeds with low germinability was also observed. The precise relationship between protein composition and prediction of germinability could not be determined. Other aspects such as membrane damage, capacity for protein synthesis and seed lot homogeneity in relation to germination are discussed.
Coat thickness and hard-seededness in some Medicago and Trifolium species
Authors: Russi L. , Cocks P. S. , Roberts E. H.
Published: September 2008

The seeds of three medics (Medicago orbicularis, M. rigidula and M. rotata) and three clovers (Trifolium stellatum, T. campestre and T. tomentosum) were collected from a pasture in north-west Syria on three occasions: immediately after seed set, at the end of the dry season, i.e. 4 months after seed set, and 16 months after seed set. Complete and sectioned seeds were observed with a scanning electron microscope. Morphological changes and differences in thickness of the seed coat were related to the hard-seededness of the samples collected in the seed bank before the onset of the rainy season. The morphology and structure of the seed coat of all six species were typical of papilionoid legumes. The species with the softest seeds (T. stellatum) showed a very thin and discontinuous cuticular layer at seed maturation (0.16 μm), while a thick and continuous cuticle (4.24 μm) was characteristic of the hardest-seeded species (M. orbicularis). The lens region of seed of all species except T. campestre was weakened after a few months in the field. This weakening was also found in seeds which were certainly hard, but the cracks in the lens region were apparently not deep enough to allow imbibition. Even when large areas of the palisade layer were removed from the lens region of seeds of M. rotata, this was not sufficient to permit water uptake. Differences in the seed coat thickness of the six species accounted for differences in seed dormancy only when seed mass was taken into account.
Seed development in relation to desiccation tolerance: A comparison between desiccation-sensitive (recalcitrant) seeds ofAvicennia marinaand desiccation-tolerant types
Authors: Farrant Jill M. , Pammenter N. W. , Berjak Patricia
Published: September 2008

Development of the highly desiccation-sensitive (recalcitrant) seeds of primarily one species,Avicennia marina, is reviewed and compared with the ontogeny of desiccation-tolerant (orthodox) seeds.A. marinaseeds undergo no maturation drying and remain metabolically active throughout development, which grades almost imperceptibly into germination. While PGR control of histodifferentiation is essentially similar to that characterizing desiccation-tolerant seeds, the phase of growth and reserve deposition is characterized by exceedingly high cytokinin levels which, it is proposed, promote a sink for assimilate import. While some starch accumulation does occur, the predominant reserves are soluble sugars which are readily available for the immediate onset of seedling establishment upon shedding. ABA levels are negligible in the embryo tissues during seed maturation, but increase in the pericarp, which imposes a constraint upon germination until these outer coverings are sloughed or otherwise removed. The pattern of proteins synthesized remains qualitatively similar throughout seed development inA. marina, and no LEA proteins are produced. This suggests both that seedling establishment is independent of maturation proteins and that the absence of LEAs and desiccation sensitivity might be causally related. The study onA. marinareveals that for this recalcitrant seed-type, germinationper secannot be defined: rather, it is considered as the continuation of development temporarily constrained by the pericarp ABA levels. This leads to a reexamination of the role of rehydration as key eventsensu stricto, in the germination processes in desiccation-tolerant (orthodox) seeds.
Comparisons between the roles of the fruit tissues, osmoticum and abscisic acid in maintaining tomato seed development and storage protein synthesis
Authors: Berry Tannis , Bewley J. Derek
Published: September 2008

Five distinct groups of storage proteins are synthesized by embryos during development in the fruit at 35 days after pollination (35 DAP); none of them is synthesized in germinating embryos 48 h after isolation (48 HASI) of the seeds from the fruit. Endo-β-mannanase, a marker of germination and seedling growth, is produced in the isolated seeds, but not in the developing seedin situ35 DAP. When seeds at this stage are removed from the fruit, but remain in intimate contact with the locular and sheath tissue, they continue to synthesize storage proteins for at least 48 HASI. Removal of the sheath from seeds isolated 35 DAP stops storage protein synthesis, and increases endo-β-mannanase activity. Both abscisic acid (ABA) and osmoticum at physiological concentrations maintain the synthesis of storage proteins in seeds isolated 35 DAP for at least 48 HASI, although osmoticum is more effective in preventing their eventual germination. Thus the effects of the sheath and the locular tissue are mimicked by both ABA and osmoticum in relation to the maintenance of storage protein synthesis in seeds 35 DAP and in the suppression of endo-β-mannanase activity for at least 48 HASI.
Nuclear proteins and the onset of cell proliferation in root meristems ofPisum sativum: QP47 a novel acidic protein
Authors: Chiatante Donato , Onelli Elisabetta
Published: September 2008

A protein named QP47 has been purified from quiescent nuclei of root meristems ofPisum sativum, and used to prepare a polyclonal antibody. Immunolocalization of this protein with fluorescent probes revealed a nuclear distribution of thread-like structures. However, the relationship between the distribution of QP47 immunofluorescence and the structural organization of the chromatin required further investigation. The decrease in content of this protein in the nuclei of embryo cells seems to be correlated with the transition from quiescence to proliferation. QP47 degradation seems to depend upon an increase in the state of its phosphorylation. This protein is not present in normally proliferating cells, or in cells whose cell proliferation has been arrested by starvation or differentiation. It is hypothesized that QP47 may be required specifically during the quiescent period for specific structural organization of the chromatin.
Function of DNA synthesis and DNA repair in the survival of embryos during early germination and in dormancy
Authors: Elder Rhoderick H. , Osborne Daphne J.
Published: September 2008

DNA synthesis following the addition of water to excised embryos of non-dormant rye and to embryos of non-dormant and dormant genetic lines of Avena fatua has been examined. All the samples exhibit an early unscheduled DNA synthesis, have similar responses to DNA polymerase inhibitors and a similar increase in DNA ligase function for the first 24 h of imbibition, irrespective of whether they germinate or remain dormant. A β-polymerase-mediated DNA repair activity is indicated immediately upon imbibition with the stable incorporation of 3H-methyl-thymidine into high molecular weight DNA. Following γ-irradiation of dry or imbibed embryos, inhibitor results suggest the appearance of an additional α- or δ-polymerase activity in the ensuing repair. Abscisic acid permits the early unirradiated repair synthesis, but like aphidicolin, it inhibits replicative DNA synthesis and partly inhibits the post-irradiation incorporation of thymidine. DNA synthesis takes place continuously throughout dormancy of imbibed embryos: precursor incorporation into DNA cannot be chased in the short term and occurs in the absence of an S-phase or endoreduplication of nuclear DNA. It is proposed that dormant imbibed embryos maintain the integrity of the genome by a continuous but slow replacement of DNA steered by a non-amplifying and modified form of replicative DNA synthesis and that abscisic acid may play a determining role in this process.