bluuebunny/crossref_metadata_2025 huggingface dataset:
A non-transverse homoclinic orbit to a saddle-node equilibrium
Authors: Champneys Alan R. , Härterich Jörg , Sandstede Björn
Published: September 2008

A homoclinic orbit is considered for which the center-stable and center-unstable manifolds of a saddle-node equilibrium have a quadratic tangency. This bifurcation is of codimension two and leads generically to the creation of a bifurcation curve defining two independent transverse homoclinic orbits to a saddle-node. This latter case was shown by Shilnikov to imply shift dynamics. It is proved here that in a large open parameter region of the codimension-two singularity, the dynamics are completely described by a perturbation of the Hénon-map giving strange attractors, Newhouse sinks and the creation of the shift dynamics. In addition, an example system admitting this bifurcation is constructed and numerical computations are performed on it.
Stochastic stability of Bernoulli toral linked twist maps of finite and infinite entropy
Authors: Nicol Matthew
Published: September 2008

We construct linked twist maps of the two-dimensional torus which are Bernoulli and possess infinite entropy. Inparticular, we construct a Bernoulli toral linked twist map B* of infinite entropy which has smooth, absolutely continuous local (un)stable manifolds and positive Lyapunov exponents defined almost everywhere. This map is continuous at each point save those on two line segments.

B* is shown to be stochastically stable under the following random perturbation: apply the map to a point p and then jump (all points move the same distance and in the same direction) according to a B-process (not necessarily an independent process) such that the expected distance moved is equal to r. Stochastic stability means that given α > 0 if r > 0 is sufficiently small then the perturbed and unperturbed systems are α-congruent. We prove a similar stability result for B* under a perturbation in which the random jump described above is distributed according to a general stochastic process. These stability results are also shown to hold (in a slightly modified form) for a general class of finite-entropy toral linked twist maps under the same perturbations.
On a conjecture about expansive geodesic flows
Authors: Ruggierot Rafael Oswaldo
Published: September 2008

We show that near the geodesic flow of a compact Riemannian manifold with no conjugate points which is expansive, every expansive geodesic flow has no conjugate points. We also prove that in the above hypotheses the geodesic flow istopologically stable.
Accumulation theorems for quadratic polynomials
Authors: Sørensen Dan Erik Krarup
Published: September 2008

We consider the one-parameter family of quadratic polynomials:

i.e. monic centered quadratic polynomials with an indifferent fixed point αtand prefixed point −αt. LetAt, be any one of the sets {0, ±αt}, {±αt}, {0, αt}, or {0, −αt}. Then we prove that for quadratic Julia sets corresponding to aGδ-dense subset ofthere is an explicitly given external ray accumulating onAt. In the caseAt= {±αt} the theorem is known as theDouady accumulation theorem.

Corollaries are the non-local connectivity of these Julia sets and the fact that all such Julia sets contain a Cremer point. Existence of non-locally connected quadratic Julia sets of Hausdorff dimension two is derived by using a recent result of Shishikura. By tuning, the results hold on the boundary of any hyperbolic component of the Mandelbrot set.

Finally, we concentrate on quadratic Cremer point polynomials. Here we prove that any ray accumulating on two symmetrical points of the Julia set must accumulate the origin. As a consequence, the denseGδsets arising from the first two possible choices ofAtare the same. We also prove that, if two distinct rays accumulate both to two distinct points, then the rays must accumulate on a common continuum joining the two points. This supports the conjecture that αtand –αtmay be joined by an arc in the Julia set.
Generalized Fredholm determinants and Selberg zeta functions for Axiom A dynamical systems
Authors: Rugh Hans Henrik
Published: September 2008

We consider a generalized Fredholm determinant d(z) and a generalized Selberg zeta function ζ(ω)−1 for Axiom A diffeomorphisms of a surface and Axiom A flows on three-dimensional manifolds, respectively. We show that d(z) and ζ(ω)−1 extend to entire functions in the complex plane. That the functions are entire and not only meromorphic is proved by a new method, identifying removable singularities by a change of Markov partitions.
Minimizing topological entropy for maps of the circle
Authors: Block Louis , Coven Ethan M. , Nitecki Zbigniew
Published: September 2008

For each n≥2, we find the minimum value of the topological entropies of all continuous self-maps of the circle having a fixed point and a point of least period n, and we exhibit a map with this minimal entropy.
A weakly mixing upside-down tower of isometric extensions
Authors: Glasner S. , Weiss B.
Published: September 2008

On the infinite torus X =, using a category argument, we produce a large family of homeomorphisms such that for every elementSin this family the flow (S, X) is weakly mixing and strictly ergodic. Moreover, writing Xn={n, n+ 1…}and lettingΠn, m, forn<m, be the projection ofXnonXm,Sinduces for everyn, a homeomorphism ofXnand the extensionsare isometric. We also show that, for everySin this family, (S, X) is disjoint from every purely weakly mixing flow.
Theory for high-order bounds in functional principal components analysis
Authors: HALL PETER , HOSSEINI–NASAB MOHAMMAD
Published: September 2008

Functional data analysis, or FDA, is a relatively new and rapidly growing area of statistics. A substantial part of the interest in the field derives from new types of data that are generated through the application of new technologies. Statistical methodologies, such as linear regression, which are effectively finite-dimensional in conventional statistical settings, become infinite-dimensional in the context of functional data. As a result, the convergence rates of estimators based on functional data can be relatively slow, and so there is substantial interest in methods for dimension reduction, such as principal components analysis (PCA). However, although the statistical development of PCA for FDA has been underway for approximately two decades, relatively high-order theoretical arguments have been largely absent. This makes it difficult to assess the impact that, for example, eigenvalue spacings have on properties of eigenvalue estimators, or to develop concise first-order limit theory for linear functional regression. This paper shows how to overcome these hurdles. It develops rigorous arguments that underpin stochastic expansions of estimators of eigenvalues and eigenfunctions, and shows how to use them to answer statistical questions. The theory is based on arguments from operator theory, made more challenging by the requirement of statisticians that closeness of functions be measured in theL∞, rather thanL2, metric. The statistical implications of the properties we develop have been discussed elsewhere, but the theoretical arguments that lie behind them have not been presented before.
The first-order genus of a knot
Authors: HORN PETER D.
Published: September 2008

We introduce a geometric invariant of knots in S3, called the first-order genus, that is derived from certain 2-complexes called gropes, and we show it is computable for many examples. While computing this invariant, we draw some interesting conclusions about the structure of a general Seifert surface for some knots.
On the Berstein–Svarc theorem in dimension 2
Authors: DRANISHNIKOV ALEXANDER N. , RUDYAK YULI B.
Published: September 2008

We prove that for any group π with cohomological dimension at least n the nth power of the Berstein class of π is nontrivial. This allows us to prove the following Berstein–Svarc theorem for all n:

Theorem. For a connected complex X with dim X = cat X = n, we have$\ber_X^n$ ≠ 0 where$\ber_X$is the Berstein class of X.

Previously it was known for n ≥ 3.

We also prove that, for every map f: M → N of degree ±1 of closed orientable manifolds, the fundamental group of N is free provided that the fundamental group of M is.
On the relation between the WRT invariant and the Hennings invariant
Authors: CHEN QI , KUPPUM SRIKANTH , SRINIVASAN PARTHASARATHY
Published: September 2008

The purpose of this paper is to provide a simple relation between the Witten–Reshetikhin-TuraevSO(3) invariant and the Hennings invariant associated to quantum$\fsl2$.
Scientific design rationale
Authors: Haynes Steven R. , Bach Paula M. , Carroll John M.
Published: September 2008

Design rationale should be regarded both as a tool for the practice of design, and as a method to enable thescienceof design. Design rationale answers questions about why a given design takes the form that it does. Answers to thesewhyquestions represent a significant portion of the knowledge generated from design research. This knowledge, along with that from empirical studies of designs in use, contributes to what Simon calledthe sciences of the artificial. Most research on the nature and use of design rationale has been analytic or theoretical. In this article, we describe an empirical study of the roles that design rationale can play in the conduct of design research. We report results from an interview study with 16 design researchers investigating how they construe and carry out design as research. The results include an integrated framework of the affordances design rationale can contribute to design research. The framework and supporting qualitative data provide insight into how design rationale might be more effectively leveraged as a first-class methodology for research into the creation and use of artifacts.
Antecedence and consequence in design rationale systems
Authors: Agouridas Vassilis , Simons Peter
Published: September 2008

Identification of latent or unarticulated customer and other stakeholder needs has been a significant barrier to improving the efficiency and effectiveness of the front-end phase of new product development processes. In-depth determination of stakeholder needs entails analysis of their intentions; the overall aim of the work reported in this article is to establish a framework of intentional analysis, and its associated methods and techniques for improving traceability of design practice during the early phases of the design process. The specific aim of this article is to present a conceptual framework for design rationale systems. The framework built upon the cross-fertilization of approaches and methods drawn from systems engineering and philosophy, focussing on the notions of antecedence and consequence. It was developed in the course of tackling design problems originating in industrial contexts. The methods developed were thus evaluated, updated, and refined in real applications. Two application cases are described that have been drawn from the aerospace and power sectors, respectively. The applications showed that the framework's central antecedent/consequent scheme provides a cell from which to develop either a history of actual successive changes, or a tree of alternative possible projected designs.
Seed development in peas: knowing your three ‘r's’ (or four, or five)
Authors: Wang T. L. , Hedley C. L.
Published: September 2008

The value of the garden pea (Pisum sativum) both as an experimental tool and food crop has led to an accumulated wealth of genetic variation. This paper describes how some of the variation may be harnessed for studying seed development. One can identify genotypic differences for maternal, embryonic and cellular components and the interaction between them. The impact of these components on processes such as cell division, partitioning and the deposition of storage products can then be assessed by utilizing new techniques such as immunocytochemistry andin situhybridization.

Therugosusloci, which induce wrinkling of the seed, are examples of how major genes can be exploited to dissect seed development. Alleles at one of these loci,r, have been defined at both the molecular and biochemical levels. A much clearer picture can now be drawn of the pleiotropic nature of the genes, from their effects on starch composition to those on cellular development, which has implications for seed development in many species. Therugosusloci are the only ones known to affect seed development in peas. By analogy with cereal seeds, however, one would anticipate other mutants in the starch pathway which also affect the shape of the seed. Here, we report the induction of newrugosus-like mutants, compare them to starch mutants in other species and examine the ways in which they may help our understanding of starch biosynthesis and the regulation of seed development.
Stimulation of germination of dormant oat (Avena sativa L.) seeds by ethanol and other alcohols
Authors: Corbineau F. , Gouble B. , Lecat S. , Côme D.
Published: September 2008

Dormant dehusked Avena sativa L. (cv. Moyencourt) caryopses germinated easily at 10°C, but their germination was poor at 25 and 30°C. Ethanol overcame their dormancy and allowed germination at the last two temperatures when given continuously at concentrations ranging from 50 to 200 mm, or at higher concentrations at the beginning of imbibition. Ethanol also promoted germination in hypoxia. Other alcohols which were good substrates for alcohol dehydrogenase (ADH: EC 1.1.1.1), such as butanol-1, propanol-1 and 2-propen-1-ol, had the same stimulatory effect as ethanol, whereas alcohols which could not be oxidized by ADH (propanol-2 and methanol) did not improve germination. Salicylhydroxamic acid (SHAM) did not alter the stimulation of germination induced by ethanol, but 4-methylpyrazole (4-MP, an inhibitor of ADH) completely abolished this stimulation. The improvement of germination by alcohols which were good substrates for ADH was always associated with an increase in oxygen uptake by caryopses, whereas alcohols which were not ADH substrates did not enhance respiration. The stimulation of oxygen uptake induced by ethanol resulted in a decrease in CO2/O2 ratio and was suppressed by 4-MP, but ATP level in embryos was not modified until after the germination of caryopses. All the results obtained seem to demonstrate that the stimulatory action of ethanol on germination of dormant oat caryopses requires its metabolism through ADH and involves an activation of glycolysis and the Krebs cycle.
Protein synthesis during osmopriming of leek (Allium porrum L.) seeds
Authors: Davison P. A. , Bray C. M.
Published: September 2008

An osmotic priming treatment of 14 days in a −1.0 MPa polyethylene glycol solution improves the germination performance of a highvigour seed lot of leek (Allium porrum L., cv. Verina). Using in vivo pulse-labelling, two-dimensional polyacrylamide gel electrophoresis and fluorography, five polypeptides were found to be synthesized in embryonic tissue at 14 days of priming that were not present at 4 days of germination without prior priming. These polypeptides were still synthesized at 6 h of germination following priming. This time point lies in the 6–12 h lag phase in protein synthesis previously observed in leek embryo tissue during germination of primed seeds where there is little increase in the rate of synthesis over that seen at the end of priming. None of the polypeptides was synthesized at 2 days of germination after priming, a period of seedling growth. The five polypeptides appear to be specifically associated with the priming period. Two additional polypeptides were found in leek embryos that were synthesized at higher levels at the end of priming than during germination alone. These continued to be synthesized, at lower levels in leek embryo tissue upon germination after priming. Several polypeptides were identified in leek endosperm tissue which were synthesized at higher levels during priming than during germination and also two polypeptides whose synthesis appeared to be specific to germination.
Endo-β-mannanase activity and reserve mobilization in excised endosperms of fenugreek is affected by volume of incubation and abscisic acid
Authors: Malek L. , Bewley J. D.
Published: September 2008

Galactomannan hydrolysis in isolated endosperms of fenugreek seeds is promoted by the presence of the embryo. Incubation in a large volume in the absence of the axis also results in endosperm mobilization and an increase in endo-β-mannanase activity. This is prevented when endosperms are incubated in a small volume, or when abscisic acid is present in the large volume. Fenugreek endosperms contain abscisic acid which is present in greater concentrations when these tissues have been incubated in a small volume rather than in a large volume. Antibodies prepared against purified tomato endo-β-mannanase detect the fenugreek enzyme on Western blots. Endosperms contain equal amounts of this enzyme whether they are incubated in a large volume, or in a small volume, or in the presence of abscisic acid. Thus, increased enzymic activity may not be related to increased synthesis, but rather to activation or release from the cells into the galactomannan-containing cell walls.
Inhibition of germination inAmaranthus albusseeds by prolonged irradiation: a physiological basis
Authors: Taylorson R. B.
Published: September 2008

Amaranthus albusL. seeds able to germinate in darkness can be prevented from germinating by prolonged irradiation with incandescent light (CIL). The germination in darkness is controlled by pre-existent Pfr. Allowing the seeds to remain in darkness for about 16 h allows an escape from the inhibition by CIL, about comparable with the time required to escape from pre-existent Pfrcontrol. By examining escape from low fluence far-red (FR), it was found that no escape occurred in CIL. It was concluded that the mode of action of CIL in inhibitingA. albusseed germination involved prevention of the action of the pre-existent Pfrand a subsequent dormancy which does not allow a response to the Pfrgenerated by the incandescent light. Other actions of CIL were found but were considered less likely as causative for the inhibition of germination. One was a direct inhibition of radicle elongation and another involved prevention of an increased responsiveness to Pfrinduced by treatment at 40°C.
The effects of the parent environment on seed germinability
Authors: Fenner M.
Published: September 2008

The growing conditions of a parent plant may affect the degree of dormancy of its seeds. This has been demonstrated in numerous species, both wild and cultivated. The evidence comes from field observations and controlled experiments. A survey of the literature shows that some well defined patterns emerge, with certain environmental factors tending to have similar effects over a wide range of species. Lower dormancy (i.e., increased germinability) is generally associated with the following environmental conditions during seed development: high temperatures, short days, red light, drought and high nitrogen levels. The effects are probably the result of changes in the quantity, mobility or activity of growth substances such as abscisic acid. The ecological implications of the phenomenon are briefly discussed.
Morphological stages and storage protein accumulation in developing alfalfa (Medicago sativa L.) seeds
Authors: Xu N. , Coulter K. M. , Krochko J. E. , Bewley J. D.
Published: September 2008

Identification of discrete stages during embryogenesis is important for the consistent and repeatable selection of seeds having similar developmental characteristics. A timetable for staging developing seeds of alfalfa (Medicago sativa L.) has been developed. Morphological characteristics, fresh and dry weights, SDSpolyacrylamide gel electrophoretic protein patterns and total protein content were recorded at various times between fertilization and 36 d after pollination (maturity), stages I–IX. A full complement of storage proteins (2S, 7S, 11S) is synthesized in both developing cotyledons and radicles. Low-salt soluble (S1) and high-salt soluble (S2) storage proteins first appear during embryo elongation. The proportional amounts of some S1 storage proteins change during alfalfa seed development. Markers are thus provided as uniform reference points for staging from the time of anthesis to seed shedding.
The development of seed quality in spring barley in four environments. II. Field emergence and seedling size
Authors: Filho C. Pieta , Ellis R. H.
Published: September 2008

The field emergence ability of a total of 88 seed lots of spring barley (Hordeum vulgare L.) harvested serially during development in 2 years was compared, as was the size of the resultant seedlings. For seedsproduced in each year, field emergence and the mean dry weight of emerged seedlings were significantly greater for seed lots harvested some timeafter physiological maturity (end of the seed-filling period) than for those harvested at or before this developmental stage. This is compatiblewith results for the potential longevity of these lots. It is concluded that barley seed quality continues to increase after physiological maturity, and that the developing seeds attain maximum quality (however this is assessed) close to when the seed crop can be combine harvested. Positive correlations were detected between seedling emergence and seed dry weight (P<0.05) and between the mean dry weight of emerged seedlings and seed dry weight (P<0.005) among seed lots harvested close to when maximum quality was attained in four seed production environments.
Mechanism of seed dormancy in rice
Authors: Seshu D. V. , Dadlani M.
Published: September 2008

Dormancy in rice (Oryza sativaL.) seed is imposed by certain physical and chemical factors associated with its covering structures, i.e.hull and pericarp. The nature of these germination blocks, their mode ofaction, and processes regulating the release of dormancy are not fully understood. Of nine rice cultivars studied, Ching-shi 15, Stejaree 45, PTB10, and Mahsuri are weakly dormant, and Bansphul, Benaful, Kataktara, Dular, and N22 are dormant. Release of seed dormancy in rice by various treatments, oxidative processes and enzymic changes associated with dormancy, and parallelism between natural and artificially imposed dormancy patterns were examined. The influence of the hull in imposing dormancy was stronger and more prolonged than that of the pericarp. Application of GA3was effective in inducing germination only in weakly dormant cultivars. Dormancy was completely released in all cultivars by subjecting the seeds to moist heat treatment, by removing the hull and pericarp, and by applying GA3after dehulling. Dormant cultivars had higher O2uptake rate and peroxidase activity and lower amylase and dehydrogenase activities than the weakly dormant ones. Hull removal substantially decreased peroxidase activity but enhanced amylase and dehydrogenase activities. Nonanoic acid (C90), a short-chain saturated fatty acid (SCSFA), when exogenously applied to non-dormant seeds imposed dormancy. Dry heat treatment or presoaking in 0.01mKNO3or 0.1mH2O2was very effective in releasing SCSFA-imposed dormancy. Amylase activity was greatly reduced by treatments with nonanoic acid (C90) or ABA. Considering earlier reports and results of the present study, it is proposed that seed dormancy in rice is regulated both by the presence of SCSFAs and ABA in the hull and the pericarp. The relative significance of these substances in cultivars of tropical and temperate origins and its implications in terms of ecogeographic adaptability are discussed.
The effect of soaking injury in bean seeds on protein synthesis in embryonic axes
Authors: Pretorius Johan C. , Small J. G. Chris
Published: September 2008

The capacity for protein synthesis in embryonic axes of Phaseolus vulgaris L. cv. Top Crop seeds was reduced markedly by soaking in airsaturated and CO2-saturated water. The former treatment induces soaking injury while the latter treatment prevents injury. After soaking, the capacity for protein synthesis in axes of seeds soaked in air-saturated water declined and the pattern of synthesis remained almost similar to that at the time of termination of soaking. However, the capacity and pattern of protein synthesis in axes of seeds soaked in CO2-saturated water recovered subsequent to soaking and approached that of non-soaked seeds.
Leakage of K, Mg, Cl, Ca and Mn from imbibing seeds, grains and isolated seed parts
Authors: Lott John N. A. , Cavdek Vandy , Carson Joanne
Published: September 2008

Instrumental neutron activation analysis (NAA) was used to quantify the amounts of K, Mg, Cl, Ca and Mn leaked into water from imbibing dry seeds, dry fruits and isolated seed parts. A number of intact monocot and dicot dry seeds or fruits were studied as were some isolated parts such as testa, endosperm and embryo. All samples studied leaked detectable amounts of the five elements measured but the amounts leaked varied greatly. In most cases K was leaked in greater amounts than the other elements while Mn was leaked least. The leakage of Ca was highest from isolated seed coats and from mericarps of three umbelliferous species. Comparisons of the amount of element leaked with the total amount of that element present in the starting material showed that leakage, especially of K, represents a substantial loss of mineral nutrient reserves. The degree of leakage of elements did not appear to be closely related to the types of organic storage reserves present.
The development of seed quality in spring and winter cultivars of barley and wheat
Authors: Ellis R. H. , Filho C. Pieta
Published: September 2008

Seed development and changes in germination ability and longevity were monitored in two spring and two winter cultivars of each of barley (Hordeum vulgare L.) and wheat(Triticum aestivum L.). Physiological maturity (end of the seed-filling period) occurred between 31 and 41 d after 50% anthesis in the eight cultivars, at which time seed moisture contents had declined naturally to 40–49% (wet basis). Most seeds were able to germinate (in 28 d tests at 10°C) following enforced desiccation at this time (normal germination varied from 83% in one cultivar of winter wheat to 97% in one of spring wheat).Potential seed longevity continued to increase after physiological maturity. The intervalbetween physiological maturity and the time when seeds attained maximum potential longevity varied between 3 and 21 d; maturation drying had reduced seed moisture contents to 16–28% (wb) at this time. The results for all eight cultivars contradict the hypothesis that maximum seed quality is attained at physiological maturity and thereafter declines. The term physiological maturity is potentially misleading, therefore; mass maturity is more appropriate to describe this developmental stage. It is shown that the results of accelerated ageing or controlled deterioration tests may provide misleading conclusions in seed quality development studies if the single storage treatment chosen is inappropriate.
Effects of controlled deterioration and osmopriming on protein synthesis of cauliflower seeds during early germination
Authors: Fujikura Yuzo , Karssen Cees M.
Published: September 2008

Profiles of proteins synthesized in vivo in radicle tips were compared among unaged, artificially aged (controlled deterioration: 10% moisture content at 42°C for 3 weeks), osmoprimed (−1.5 MPa polyethylene glycol 6000 at 20°C for 1 week), and artificially aged and subsequently osmoprimed cauliflower (Brassica oleracea L.) seeds. Germination and initiation of incorporation of 35S-methionine into radicle tips were delayed by controlled deterioration. Osmopriming accelerated these processes and also alleviated the delays. The labelled proteins were analysed by two-dimensional gel electrophoresis and fluorography. Proteins were found whose expression correlated with the rate of germination, and was reduced by controlled deterioration but enhanced by osmopriming. Subsequent osmopriming reversed the effect of controlled deterioration and even caused an enhancement up to the level of unaged osmoprimed seeds. These proteins appeared to be related to processes preceding visible germination. In unaged seeds, formation of the proteins in the radicle tip began upon imbibition but decreased towards visible germination. On silver-stained gels, one of the proteins was shown to be mobilized by the time of radicle protrusion, while all were found in dry seeds. Proteins whose pronounced expression was observed only after both treatments were also found.
The effect of soaking injury in bean seeds on aspects of the oxidative pentose phosphate pathway in embryonic axes
Authors: Pretorius Johan C. , Small J. G. Chris
Published: September 2008

Submerging Phaseolus vulgaris cv. Top Crop seeds in air-saturated water for 16 h markedly depresses subsequent germination. This is termed soaking injury. Soaking injury does not occur in seeds soaked in CO2-saturated water. Previous studies have shown that soaking injury can be alleviated by drying seeds or removing seed coats. Submergence therefore leads to a situation in bean seeds which is similar to secondary dormancy.

As with dormant seeds, C6/C1 ratios of embryonic axes of seeds soaked in air-saturated water remained high (0.8–1.0) during and after soaking. This was paralleled by low activities of glucose-6-phosphate dehydrogenase (EC.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). In axes of seeds soaked in CO2-saturated water and in unsoaked seeds C6/C1 ratios declined steadily during soaking/imbibition and reached values of around 0.3 after germination. Slight increases ofglucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities occurred in the pre-germination phase. This was followed by a massive increase after radicle emergence. Synthesis of the plastid isoenzymes was a post-germinative event.

It appears that soaking injury depresses protein synthesis. Lack of oxidative pentose phosphate pathway activity appears to be a causative factor in soaking injury.
Lipid autoxidation and seed ageing: putative relationships between seed longevity and lipid stability
Authors: Ponquett R. T. , Smith M. T. , Ross G.
Published: September 2008

On the premise that seed ageing may be largely a result of free-radical lipid autoxidation, a study was made of the relationship between lipid stability and longevity in seeds of soybean (Glycine max), lentil (Lens culinaris), mungbean (Vigna radiata), chickpea (Cicer arietinum), broadbean (Vicia faba), pea (Pisum sativum), lettuce (Lactuca sativa), and tomato (Lycopersicon esculentum). Seed lipids were examined for α-, γ- and δ-tocopherols, and levels of unsaturated and saturated fatty acids. Using this information, analysis was attempted using linear, multiplicative or exponential models to correlate aspects of lipid stability with seed longevity values from the published literature. No statistically significant correlations could be found between longevity and total lipid unsaturation, tocopherol levels or two protection formulae obtained from the oil chemistry literature. When values for tomato were excluded, a good correlation (r = 0.89, P = 0.007) was obtained using a multiplicative regression model for levels of linolenic acid per unit of total tocopherols in relation to longevity. Possible factors contributing to a lessening of the relationship between lipid stability and seed longevity are discussed.
Transport of nutrients into developing seeds: a review of physiological mechanisms
Authors: Wolswinkel P.
Published: September 2008

After synthesis in the vegetative parts of the plant, assimilates are translocated to fruits through xylem and phloem. Research on factors controlling nutrient transport into developing seeds via the phloem has been stimulated by the development of the empty seed coat technique.

There is a consensus that as assimilates are transported from maternal tissues to filial tissues they are delivered to the extracellular space (the apoplast) separating the two generations, prior to uptake from the apoplast into the tissues of the embryo or endosperm. The empty seed coat technique has been used for the study of several aspects of nutrient transport into seeds, e.g. metabolic control and turgorsensitive transport. The osmotic environment of seed tissues has a strong effect on assimilate transport into empty seeds. Several lines of evidence suggest that one of the main ‘secrets’ of the high sink strength of developing seeds, at least in many taxonomic groups of dicotyledons, is that the sink end of the phloem pathway is ‘bathed’ in an apoplast solution with a high concentration of osmotically active solutes. Data on maize do not fit this pattern. A turgor homeostat mechanism may help to maintain high solute concentrations in the seed apoplast. The apoplast environment of seed tissues may also stimulate synthesis of storage proteins and be involved in the prevention of precocious germination. In addition to the osmotic environment, other factors influencing sink strength are discussed. Some aspects of solute transformation during transport through seed tissues are described.
Regulation of protein synthesis in germinating wheat embryos under polyethylene glycol and salt stress
Authors: Dell'Aquila A. , Spada P.
Published: September 2008

Wheat seeds were imbibed in solutions of polyethylene glycol (PEG) and NaCl, and embryo water content and incorporation of [35S]methionine into proteins were determined. Both osmotica reduced water uptake and protein synthesis, though these were immediately resumed upon removal of stress. Results ofin vivolabelling of newly synthesized proteins showed differences in the synthesis of many polypeptides when embryos that had imbibed in water passed from the radicle pre-emergence phase to early growth. The synthesis of a group of proteins associated with radicle emergence was reduced during imbibition in PEG or NaCl. All the major proteins of the pre-germination phase were produced in PEG-treated embryos, while some new polypeptides (‘salt stress’ proteins?) were actively synthesized in salt-treated embryos. Upon removal of PEG or NaCl, synthesis of proteins common to the phase of early embryo growth increased, while specific saltimbibition proteins disappeared. These findings are consistent with the hypothesis that biochemical processes leading to radicle emergence can be affected by osmotic stress and are likely to be damaged by severe stress.
Histo-differentiation and molecular biology of developing cereal endosperm
Authors: Olsen O.-A. , Potter R. H. , Kalla R.
Published: September 2008

To elucidate the molecular aspects of cereal endosperm development, a good understanding of the histo-differentiation process is necessary. Reviewing the extensive history of lightand electron-microscopic investigations has revealed similarities between cereals with respect to cell ontogeny. Thus, using barley as a model and taking into account many developmental mutants in this and other species, a model for endosperm differentiation is proposed. Based on this model, molecular studies on endosperm gene-regulation are discussed and the available techniques for further investigations are considered.
Influence of plating density, sucrose and light during development on the germination and vigour ofMedicago sativaL. somatic embryos after desiccation
Authors: Anandarajah K. , McKersie B. D.
Published: September 2008

Somatic embryo quality is an important aspect of artificial or synthetic seed production and is dependent on proper morphological development and deposition of sufficient storage reserves to support early growth of the seedling. The abilities of a somatic embryo to survive desiccation and to establish a rapidly growing seedling were used as estimates of quality and were dependent on a number of factors during the elongation and maturation phases of somatic embryo development. Embryo quality was significantly enhanced when the sucrose content of the elongation and maturation media was increased to 50 g I−1from 30 g I−1. This increased dry weight to >2 mg embryo−1suggesting greater deposition of storage reserves. Higher sucrose concentrations were inhibitory and reduced survival after desiccation and seedling vigour. An optimum number of embryos can be supported on one Petri plate; the number was controlled by the plating density of the embryogenic cell clusters spread on the elongation medium. This optimum was dependent to some extent on the sucrose content of the medium, indicating that sucrose had a nutritive effect on embryo development and not solely an osmotic effect. Light intensity was another critical factor. Intensities > 75 μmol m−2s−1photosynthetic photon flux density (PPFD) at the elongation stage of development blocked globular-stage somatic embryo development. Maturing somatic embryos were far less sensitive to high light intensities and development was more rapid at 150 μmol m−2s−1PPFD. Light quality was manipulated by covering plates with filters that selectively transmitted certain regions of the visible spectrum. All filter treatments reduced embryo yield and quality compared with embryos developing under fullspectrum light; varying the light spectrum does not seem to be a viable method of enhancing somatic embryo quality.
DNA synthesis in osmoprimed leek (Allium porrumL.) seeds and evidence for repair and replication
Authors: Ashraf M. , Bray C. M.
Published: September 2008

Osmopriming of leek seeds (Allium porrumL.) in PEG 6000 solution (−10 bars) at 15°C for 14 days leads to reductions in both the spread of germination and mean time to germination, especially in low-vigour seed lots.In vivomethyl [3H]-thymidine pulse-labelling studies have demonstrated constant and low levels of DNA synthesis in leek embryo tissue during the osmopriming treatment. DNA synthesis during osmopriming was not inhibited by aphidicolin, an inhibitor of nuclear DNA replication. Replicative and repair-type DNA synthesis was investigated using BND-cellulose chromatography and these studies revealed that about 30% of the DNA synthesis after 1 day of priming was of a repair-type. DNA repair-type synthesis contributed to approximately 20% of the [3H]thymidine incorporated into DNA during the rest of the priming period in embryo tissue from both high-vigour and low-vigour seed lots. After 1 day of germination following priming, enhanced levels of both replicative and repair-type DNA synthesis were demonstrated. The replicative type of DNA synthesis detected in leek embyros during the priming period was not inhibited by aphidicolin and appears to represent a significant level of mitochondrial DNA synthesis. DNA synthesis could be detected in both nuclei and mitochondria of leek embryo tissue during the osmopriming treatment in the absence of any detectable cell division.
Relief of thermoinhibition in Grand Rapids lettuce seeds by oxygen plus kinetin and their effects on respiration, content of ethanol and ATP and synthesis of ethylene
Authors: Small J. G. Chris , Schultz Colleen , Cronje Elbie
Published: September 2008

Seed germination of Grand Rapids lettuce (Lactuca sativa L.) was inhibited at 38°C (thermoinhibition). Thermoinhibition was totally relieved by a combination of 100% oxygen and 10 mg I−1 kinetin, to a lesser extent by a combination of oxygen and ethylene but not at all by oxygen plus GA3. The combination of oxygen with kinetin or ethylene was more effective in preventing thermoinhibition than a combination of all three hormones and CO2 in air. The beneficial effect of oxygen plus kinetin was not related to either increased production of CO2 or ethylene by the seeds. In air, germination was partially inhibited by 2-aminoethoxyvinyl glycine (AVG) or 2,5-norbornadiene (NBD) and totally inhibited by AVG plus NBD. Oxygen plus kinetin almost completely alleviated their inhibitory effects. It was concluded that oxygen plus kinetin caused seeds to bypass an ethylene requirement for germination or increased the sensitivity of seeds to ethylene. In air at 38°C, seeds exhibited a high level of ethanolic fermentation, while in oxygen plus kinetin they respired aerobically. At 38°C in air, contents of ATP and total adenylates were reduced, while in seeds treated with oxygen plus kinetin these contents were similar or higher than in 25°C controls. A similar response was also observed for adenylate energy charge. It was concluded that part of the mechanism of thermoinhibition could be the failure of ATP content to reach a sufficient level to satisfy the requirement for germination at 38°C. It appeared possible that the prevention of thermoinhibition by oxygen plus kinetin could be related to increased ATP content in seeds caused by this treatment.
Oxygen, free radical processes and seed longevity
Authors: Hendry George A. F.
Published: September 2008

The origin and significance of free radicals is described in the broad setting of animal and plant biology and in the specific context of seeds and seed viability. Evidence is given that free radicals play a central if not causal role in promoting molecular damage under the widest range of environmental stresses and induced ageing in mature plant tissuesIn ungerminated seeds, the evidence is less certain. The reason, we argue, is that many attempts to measure free radical processes in seeds are set not against gradients of damage or ageing (as they are in most other biological tissues) but against one of only two options, either seed germinability or mortality. Because free radical reactions differ quantitatively and qualitatively in living and dead tissues attempts to correlate radicalmediated damage with the viability of a population of seeds may be unreliable particularly when measurements are made at uncertain intervals after death. Despite this, the evidence that seeds, uniquely, are exempt from the ravages of oxygen assault is weak. Instead it ismore probable that oxygen plays a central role in seed mortality and may have significance in the evolution of seed persistence.
Non-destructive X-ray analysis ofArabidopsisembryo mutants
Authors: Bino R. J. , Aartse J. W. , van der Burg W. J.
Published: September 2008

X-radiography is a simple, rapid and non-destructive method for analysing the morphology of embryos in dry, mature seeds ofArabidopsis thaliana.In wild type seeds, the cotyledons, hypocotyl and radicle tip can be readily distinguished. In seeds of the mutant typesknolle, keule, and the double mutantkeulelgnom, aberrations in embryo morphology can be visualized. X-radiography may therefore be useful in the isolation of embryo mutants fromArabidopsisseed samples.
Heat shock and recovery in aged wheat aleurone layers
Authors: Livesley M.A. , Bray C. M.
Published: September 2008

Ageing of wheat seeds (Triticum aestivum cv. Galahad, 1986 harvest) during storage is accompanied by an increase in the proportion of abnormal seedlings produced when aged seed lots germinate. The response of aleurone layers from normally and abnormally germinated seeds to heat shock has been investigated. [14C]-amino acid incorporation into aleurone layers from 3-d normally and abnormally germinated seeds diminished after 4 h at 42°C but the aleurone layers were able to recover significantly during a 5-h period at 20°C following heat shock. [35S]-methionine pulse-labelling of aleurone proteins showed that α-amylase isoenzyme synthesis was abolished upon heat shock in aleurone layers for both normally and abnormally germinated seeds and that only aleurone layers from normally germinated seeds were capable of recommencing substantial α-amylase synthesis during the recovery period. Heat shock caused aleurone layers from abnormally germinated seeds to synthesize polypeptides not synthesized by aleurone layers from normally germinated seeds under the same conditions. The synthesis of certain polypeptides by aleurone layers from abnormally germinated seeds was enhanced at 20°C, 42°C and during recovery compared with normally germinated seeds. These results are discussed in terms of the control of gene expression during heat shock and recovery during seed ageing.
Theoretical basis of protocols for seed storage II. The influence of temperature on optimal moisture levels
Authors: Vertucci Christina W. , Roos Eric E.
Published: September 2008

The premise of this paper is that the chemical potential of water strongly influences aging reactions in seeds, and that there will be an optimal chemical potential of water for seed longevity. If this is true, the optimum moisture content for storage and the optimal drying protocols should vary with the storage temperature, but should be predictable from water sorption isotherms. Isotherms for pea, soybean and peanut are given for temperatures between 65° and −150°C. Relative humidity/moisture content relationships were determined directly for temperatures between 5° and 50°C using saturated salt solutions. At extreme temperatures, isotherms were calculated from heat capacity measurements using differential scanning calorimetry or extrapolations of van't Hoff analyses. The family of isotherms was used to predict optimum moisture contents at storage temperatures between 65°C and −150°C. The optimal moisture contents for these three species are consistently shown to increase as the storage temperature is lowered.
Changes in potential seed longevity and seedling growth during seed development and maturation in marrow
Authors: Demir I. , Ellis R. H.
Published: September 2008

Marrow (Cucurbita pepo L.) seed quality was monitored during seed development and maturation in 2 years. Mass maturity (end of the seed-filling phase) was attained 61–63 d and 54 d after anthesis in 1989 and 1990, respectively, when seed moisture contents had declined to 40–48% (wet basis). Considerable dormancy was encountered during standard germination tests, but was overcome by decoating the seeds. The ability of dried, decoated seeds to germinate normally in standard tests reached near maximal values shortly after mass maturity; these values were more or less maintained in seeds from subsequent harvests. Maximum seed longevity in air-dry storage was detected in seeds harvested 24 d (1989) and 26–31 d (1990) after mass maturity. Seedling dry weights 15 d after sowing were greatest for seeds harvested 2–22 d (basal fruits) or 14 d (apical fruits) after mass maturity in 1989, and were positively correlated (P<0.01) with times from seedling emergence to seedling harvest. Consequently in the subsequent year the hypothesis that these differences in seedling dry weight were solely due to differences in times from sowing to emergence was tested (and confirmed). Seedling relative growth rates did not differ with seed harvest date (P>0.25) in 1990, but absolute seedling size did (P<0.005); seeds harvested 21–31 d after mass maturity had the greatest seedling weight and also growth rate (in absolute terms) at any one time after sowing. Decline in seed quality (when assessed by both potential seed longevity and seedling growth) was not detected until the final harvest interval in 1990 (85–90 d after anthesis, 31–36 d after mass maturity). These results for marrow contradict both aspects of the general hypothesis that seed quality is maximal at the end of the seed-filling phase and that viability and vigour begin to decline thereafter.