bluuebunny/crossref_metadata_2025 huggingface dataset:
New limiting notions of the IP type in the enveloping semigroup
Authors: Haddad Kamel N.
Published: September 2008

An IP set in ℕ is a subset of ℕ which coincides with the set of finite sums taken from an infinite sequence in ℕ with not necessarily distinct terms. It has been established by H. Furstenberg and others that there is a rich connection between IP sets and idempotents in the enveloping semigroup E(X) of a compact metric dynamical system. Our aim in this paper is to further develop this program by considering special elements of E(X) with various IP properties.
Minimal actions of semisimple groups
Authors: Stuck Garrett
Published: September 2008

We show that a C0 minimal action of a semisimple Lie group without compact factors is either locally free or induced from a minimal action of a proper parabolic subgroup. We describe the orbit structure of the action restricted to a maximal compact subgroup, and then apply this to minimal actions in low dimension. We give some examples, applications, and open problems.
The structure of piecewise monotonic transformations
Authors: Hofbauer Franz
Published: September 2008

Transformations on [0, 1] which are piecewise monotonic and piecewise continuous are considered. Using symbolic dynamics, the structure of their nonwandering set is determined. This is then used to prove results about maximal and absolutely continuous invariant measures.
Mutant knots with symmetry
Authors: MORTON H. R.
Published: September 2008

Mutant knots, in the sense of Conway, are known to share the same Homfly polynomial. Their 2-string satellites also share the same Homfly polynomial, but in general theirm-string satellites can have different Homfly polynomials form> 2. We show that, under conditions of extra symmetry on the constituent 2-tangles, the directedm-string satellites of mutants share the same Homfly polynomial form< 6 in general, and for all choices ofmwhen the satellite is based on a cable knot pattern.

We give examples of mutants with extra symmetry whose Homfly polynomials of some 6-string satellites are different, by comparing their quantumsl(3) invariants.
On the mean square formula of the error term in the Dirichlet divisor problem
Authors: LAU YUK-KAM , TSANG KAI-MAN
Published: September 2008

Let F(x) be the remainder term in the mean square formula of the error term Δ(t) in the Dirichlet divisor problem. We improve on the upper estimate of F(x) obtained by Preissmann around twenty years ago. The method is robust, which applies to the same problem for the error terms in the circle problem and the mean square formula of the Riemann zeta-function.
The Bott cofiber sequence in deformation K-theory and simultaneous similarity in U(n)
Authors: LAWSON TYLER
Published: September 2008

We show that there is a homotopy cofiber sequence of spectra relating Carlsson's deformation K-theory of a group G to its “deformation representation ring,” analogous to the Bott periodicity sequence relating connective K-theory to ordinary homology. We then apply this to study simultaneous similarity of unitary matrices.
Some factors influencing electrolyte leakage from maize (Zea mays L.) kernels
Authors: Bruggink H. , Kraak H. L. , Dijkema M. H. G. E. , Bekendam J.
Published: September 2008

Even though the embryo of a maize (Zea mays L.) kernel contributes relatively little to total kernel weight, it is a main source of electrolytes which leach from the kernel during imbibition. Ageing of maize kernels for 18 days at 40°C and a moisture content of about 15% results in an increase of electrolyte leakage which almost exclusively originates from the embryo. The effect of ageing is most apparent after prolonged periods of imbibition. Mechanical damage increases leakage early during imbibition, the effect of damage being considerably larger for aged than for unaged kernels. The large amount of electrolytes measured after the first hour of imbibition of undamaged kernels comes mainly from the pericarp. The electrolyte content of the pericarp is variety dependent and may interfere with quality testing by conductivity measurements.
Seed quality, cotyledon elongation at suboptimal temperatures, and the yield of onion
Authors: Wheeler T. R. , Ellis R. H.
Published: September 2008

Cotyledon length in onion (Allium cepa, cv. White Lisbon) was linearly related to time from radicle emergence until the formation of the cotyledon hook, but thereafter increased exponentially with time. Within each phase the rate of cotyledon elongation was linearly related to temperature, and these relations were similar among seeds from several percentiles of the germinating populations of three contrasting seed lots. The mean base temperature was 1.4°C. These thermal time relations closely predicted the elongation of cotyledons of seedlings from cohorts of early- and lategerminators from a further lot of this cultivar at two suboptimal temperatures. Eleven cohorts of seedlings from seeds of differing quality were transplanted to the field on both the same date and at the same time from visible germination. The plants were harvested 59 days later. No effect of seed quality on mean plant weight, mean bulb diameter, or interplant variation in bulb diameter was detected. It is concluded that the rate of pre- and post-emergence seedling growth in onion is independent of environmentally induced differences in seed quality (seed vigour). Thus, any effect of this factor on plant size or crop yield, at a given density, is solely a function of time to germinate.
Imbibitional injury in maize seed independent of chilling temperature
Authors: Bochicchio A. , Coradeschi M. A. , Zienna P. , Bertolini M. , Vazzana C.
Published: September 2008

Low and high moisture kernels and embryos were imbibed by soaking in distilled water at 5°C and 25°C. Leaching of seeds and embryos was measured by ion conductivity of imbibition water after fixed time intervals. Imbibed kernels were placed on moist filter paper after 1 h imbibition and embryos on a solid culture medium after 15 min imbibition and germinated at 25°C. Primary root length was measured 3 days after germination.

The leakage from seeds or embryos was correlated with the velocity of water uptake but did not show its highest values when low moisture seeds or embryos were imbibed at chilling temperature. Furthermore germination was apparently not affected by imbibitional chilling of either low moisture content seeds or embryos. In one of the three genotypes tested (B73) seedlings from low moisture content seeds imbibed at 5°C showed a reduction of the primary root growth. However, this reduction was also seen in seedlings from low moisture B73 seeds imbided at 25°C and resulting in higher level of leaching. Thus, injury by imbibition of low moisture seeds appears independent of chilling temperature and not due to loss of semipermeability of membrane lipids. Our results suggest that, in the case of embryos, water inrush into the cells reaches levels injurious for membrane integrity independently of the two moisture contents and temperature considered.
Biochemical events during germination and early growth of somatic embryos and seed of interior spruce (Picea glauca engelmannicomplex)
Authors: Cyr D. R. , Webster F. B. , Roberts D. R.
Published: September 2008

Utilization of lipid and protein storage reserves was examined during germination and early growth of somatic and excised seed embryosin vitro, and seed of interior spruce. High germination frequencies were recorded for somatic and excised seed embryos, and elongation of radicles and hypocotyls observed for both embryo types. Although elongation of the embryo types differed (i.e. somatic ≤ excised seed < seed), fresh weight gain was similar. Utilization of triglycerides in somatic embryos was more rapid than in excised seed and seed embryos, thus it appeared to be under embryo infuence. By contrast, depletion of storage proteins appeared to be influenced by the megagametophyte, with hydrolysis in somatic and excised seed embryos preceding that of the seed embryo by 2 days. Differential utilization of the storage reserves was temporally associated with differences in growth patterns of somatic and seed embryos. The evidence presented indicates that thein vitrogermination medium does not entirely supplant the role of the megagametophyte during germination and early growth. The relevance of these results to artificial seed technology is discussed.
The sensitivity of germinatingTriticum durumL. kernels to saline environment
Authors: Petruzzelli L. , Melillo M. T. , Bleve-Zacheo T. , Marano B. , Taranto G.
Published: September 2008

Osmotic and ionic effects of NaCl were investigated in germinating wheat. Approximately isotonic solutions of NaCl and sorbitol inhibited germination and seedling growth to similar degrees. When dry kernels were pre-imbibed in salt for 24 h and then transferred to water, germination was equivalent to that of kernels imbibed continuously in water and the development of embryos was delayed to about the same extent as kernels pre-imbibed in sorbitol for 24 h. Measurements of water uptake, respiration, biosynthetic activities and rubidium uptake in embryos dissected from grains imbibed in NaCI or sorbitol for the first 24 h demonstrated that salt supplied to dry kernels closely mimicked sorbitol in counteracting the reactivation of embryo metabolism. No toxic effects of salt were observed when dry kernels were pre-imbibed in very high NaCI concentrations for 24 h and then transferred to water, even though embryo sodium contents increased considerably. Ultrastructural observations of embryo tissue further showed that salt influx into dry grains did not produce ion-specific damage in cell organization. On the other hand, salt specific effects became evident when the 24 h salt exposure was applied to kernels pre-hydrated for 24 h and, even more, for 30 h. We conclude that in wheat the inhibition of germination by salt corresponds to that induced by an osmoticum, provided that the caryopsis has not reached the stage of germination associated with active embryo expansion.
Purification and characterization of an aspartyl proteinase from dry jack pine seeds
Authors: Bourgeois Jacqueline , Malek L.
Published: September 2008

A high-molecular-weight aspartyl proteinase complex, sensitive to pepstatin A was purified to near electrophoretic homogeneity from dry seeds ofjack pine (Pinus banksiana, Lamb.). Two partial activities, endo-and exo-proteinolytic, were associated with the complex, judged by the analysis of haemoglobin hydrolysis products. The high activity of this enzyme in dry jack pine seed suggests a possible function in early germination.
The development of seed quality in spring barley in four environments. I. Germination and longevity
Authors: Filho C. Pieta , Ellis R. H.
Published: September 2008

Seed development and changes in germination ability and longevity were monitored in control and shaded spring barley (Hordeum vulgareL.)crops grown in two contrasting years. Shading reduced seed dry matter accumulation rates by 24–28% and delayed maturation drying slightly, but had little effect (0–2 d) on the timing of physiological maturity (end of the seed-filling period); final seed dry weights were 76–85% of controls. Moisture contents (wb) at physiological maturity were 48–55%; final mean seed dry weights in the controls were 40.9 mg(S.E. 0.6) in 1988 and 35.2 mg (S.E. 0.5) in 1989. Shading had little orno effect on germination ability or longevity in either year. Seeds fromthe first harvest were viable when dried below 15% moisture content despite being only 34% (1988) to 63% (1989) filled; desiccation promoted germination. Maximum germination achieved after forced desiccation occurredin seeds harvested 7–10 d (1989) to 11–13 d (1988) after physiological maturity, with little subsequent change during the following 14 (1988) or 27 d (1989). Longevity continued to increase during development until a maximum was reached 18–20 d (1988) to 27 d (1989) after physiological maturity (at moisture contents on the mother plant of 18–19% and 14–15%, respectively). In both years, the longevity of these seeds was greater (P<0.005) than that of seeds harvested either subsequently or earlier at physiological maturity. The results contradict the hypothesis that maximum seed quality coincides with physiological maturity and thereafter declines. Rather, maximum seed quality was attained close to when barley seed crops can be combine harvested The subsequent decline in potential longevity on the maternal plant in the field was quantitatively similar to that expected during post-harvest storage.
Isolation and characterization of an expressed napin gene fromBrassica rapa
Authors: Kridl Jean C. , McCarter David W. , Rose Ronald E. , Scherer Donna E. , Knutzon Deborah S. , Radke Sharon E. , Knauf Vic C.
Published: September 2008

An expressed napin storage protein gene fromBrassica rapa, BcNA1, has been cloned and sequenced. The gene is a member of a family of four to seven napin genes inB. rapaand is highly expressed in developing seeds. An expression cassette containing the DNA flanking the napin coding region of BcNA1 has been engineered and demonstrated to function appropriately, as compared with the gene's endogenous expression, in transgenic rapeseed using the β-glucuronidase reporter gene. TheB. rapaBcNA1 gene and aB. napusnapin gene, gNa, share extremely high nucleotide homology not only throughout their coding regions, but over a DNA locus comprising 4.3 kb. We suggest the gNa gene was contributed by the originalB. rapaprogenitor of the amphidiploidB. napus.
Evidence for inhibitor involvement in thermodormancy of Grand Rapids lettuce seeds
Authors: Small J. G. Chris , Gutterman Yitzchak
Published: September 2008

Prolonged imbibition and incubation of lettuce seeds at a supraoptimal temperature induces secondary dormancy. Such seeds no longer germinate when returned to conditions optimal for germination of non-dormant seeds. The possibility that inhibitors are involved in the induction of thermodormancy was investigated.

Washing of thermodormant seeds restored germination to a small extent. However, continuous leaching of seeds during high-temperature treatment with distilled water, largely prevented the induction of thermodormancy. Such seeds were qualitatively similar to nondormant seeds, i.e. they required only light to germinate at a lower temperature and germinated in the dark if given GA3. The germination water from thermodormant seeds inhibited the germination of non-dormant lettuce seeds. The inhibition was not an osmotic effect. Absorbance in the ultraviolet region was higher in germination water from thermodormant seeds than that of non-dormant seeds. It is concluded that inhibitors are involved in the induction of thermodormancy of lettuce seeds.
DNA ligase activity in deteriorated maize embryo axes during germination: a model relating defects in DNA metabolism in seeds to loss of germinability
Authors: Vázquez Edgar , Montiel Fernando , Vázquez-Ramos Jorge M.
Published: September 2008

Chromosome integrity and DNA polymerase activity are negatively affected by improper storage of maize seeds. We have extended our studies on the effect of improper storage on DNA metabolism by analysing the effect of hot–dry and hot–humid conditions on DNA ligase activity. An assay to measure ligase activity was established by using linearized plasmid DNA as substrate and protein extracts from maize axes. Optimal conditions were established for thein vitroassay. Enzyme activity was importantly reduced under both storage conditions. Activity recovered 6–9 h after imbibition. A model for loss of viability and vigour due to damage of DNA metabolism is proposed.
Seed development in the recalcitrant speciesQuercus roburL.: germinability and desiccation tolerance
Authors: Finch-Savage W. E.
Published: September 2008

Changes in germination and desiccation sensitivity were measured throughout the seed expansion phase of development in fruits ofQuercus roburL. The onset of a reduction in sensitivity to desiccation during development on the tree coincided with acquisition of the capacity for seed germination on moist sand substrate. Tolerance of desiccation then increased throughout development to shedding, but viability was still lost at a relatively high moisture content, and seeds did not therefore pass through a fully desiccation-tolerant phase. These data suggest that desiccation sensitivity inQ. roburmay have resulted from the premature termination of development.

No desiccation was required to initiate germination in prematurely harvested fruits orseeds. Germination rate of seeds on moist sand increased at successive harvests during development, and was also increased by presoaking seeds in water. Variation in germination rate following shedding was not related to seed size or moisture content, but was affected by shedding date. This effect was not observed when the pericarp was removed.
Short-term aerated hydration for the improvement of seed quality in Brassica oleracea L
Authors: Thornton J. M. , Powell A. A.
Published: September 2008

Seeds of the Brussels sprouts cultivar Asmer Aries and the cauliflower cultivar Hipop were subjected to ageing at 20% moisture content and 45°C for 24 or 30 h, respectively; all seeds retained high germination after ageing. Aerated hydration of unaged and aged seeds of both cultivars for 4–8 h at a range of temperatures (10–30°C), followed by drying, resulted in improved performance, except that germination percentage and rate of cauliflower were lower at 10°C. Thus, all treated seeds showed greater germination rate and seedling root length than the control, which may have resulted from the advancement of the process of germination. The deleterious effect of aerated hydration at 10°C on cauliflower could be explained by damage due to rapid imbibition; seeds that had imbibed slowly to close to full imbibition (41% moisture content) before aerated hydration showed no decrease in germination. The improvement of aged seeds after aerated hydration was also revealed by higher germination after the controlled-deterioration test, which indicated less deterioration in treated seeds. Furthermore, the optimum improvements for all seeds were observed at 25°C and were greater when the water was aerated than non-aerated. These observations indicate the activation of metabolic repair processes during aerated hydration, leading to a reversal of the deterioration sustained during ageing.
Leek (Allium porrum L.) seed development and germination
Authors: Gray D. , Steckel J. R. A. , Hands L. J.
Published: September 2008

The effects of development of leek seeds at 20/10°, 25/15° and 30/20°C (day/night) and drying of seed harvested at different developmental stages on subsequent performance were examined in each of 3 years. An increase in temperature from 20/10° to 30/20°C reduced mean seed weight from 2.90 to 2.55 mg as a result of a reduction in the duration of seed growth from 80 to 55 days; seed growth rate was unaffected. Seed moisture content reached a minimum, up to 35 days after the attainment of maximum seed dry weight and 115, 90 and 70 days after anthesis at 20/10°, 25/15° and 30/20°C, respectively. The curves relating seed moisture to time for each temperature regime were mapped onto a single line accounting for >90% of the variation in moisture content, using accumulated day-degrees >6°C instead of chronological time. Seeds were capable of germinating when seed moisture contents were >60% (fresh weight basis), but maximum viability and minimum mean time to germination were not attained until seed moisture contents at harvest had fallen to 20–30%. Germination was little affected by temperature of seed development. Drying immature seeds increased percentage germination. Growing seeds at 30/20°C and drying at 35°C and 30% RH raised the upper temperature limit of germination compared with growing at 20/10°C and drying at 15°C and 30% RH.
Tonoplast and plasma membrane ATPases from maize lines of high or low vigour
Authors: Sánchez-Nieto S. , Rodríguez-Sotres R. , González-Romo P. , Bernal-Lugo I. , Gavilanes-Ruíz M.
Published: September 2008

The effectiveness of ATPase in germinated seed may play an important role in the vigour of germination. The activities of tonoplast and plasma membrane ATPases in two maize (Zea maysL.) lines with different vigour of germination were determined. ATP hydrolysis was measured in microsomal fractions from coleoptiles along with the responses to specific inhibitors for the plasma membrane, tonoplast and mitochondrial ATPases as well as for acid phosphatase. Nitrate-sensitive ATPase activity was 1.5–3.0 times lower in the low-vigour line than in the high-vigour line. Kinetic analysis of ATP hydrolysis at different substrate concentrations revealed the existence of two enzymes in the microsomal fractions of the two lines. TheVmaxof enzyme 1 in the low-vigour line was a third of that in the high-vigour line. This enzyme was identified as the nitrate-sensitive or tonoplast ATPase on the basis of measurements of ATP hydrolysis in the presence of specific inhibitors at high (8.12mm) and low (0.77mm) ATP concentrations.
Trypsin inhibitors inPisum: variation in amount and pattern of accumulation in developing seed
Authors: Domoney C. , Welham T.
Published: September 2008

A survey ofPisumgenotypes for seed trypsin inhibitors revealed a tenfold range in the extent of inhibition. Approximately 90% of trypsin inhibitory activity was associated with two albumin fractions in selected variant lines. The differences among extreme variants were consistent in three environments, between two sources of trypsin tested and whether expressed on a unit protein or dry weight basis.

A study of the appearance of trypsin inhibitors during seed development in selected highand low-inhibitor lines showed differences in the accumulation pattern of active inhibitors. An endogenous protease was identified inPisumseed protein preparations, whosein vitrotrypsin-like activity was predominant in protein from early stages of seed development, when little or no trypsin inhibitor was present. However, there was no correlation between the amount of this protease and the extent of trypsin inhibitory activity in lines that varied for inhibitor content.
Watermelon seed germination. 1. Effects of light, temperature and osmotica
Authors: Thanos C. A. , Mitrakos K.
Published: September 2008

Seeds of watermelon (Citrullus lanatuscv. Sugar Baby) germinated optimally in the dark, throughout the range 20–40°C. Germination was inhibited by continuous (c) irradiation with farred (FR), blue or white incandescent light; short pulses were ineffective. Intermittent FR could fully substitute for cFR; the effect of alternating red and FR pulses during 30-min dark cycles depended upon the timing of the illuminations within each cycle. It is concluded that germination in watermelon is controlled by the low-energy reaction of phytochrome. However, continuous and intermittent red light resulted in partial reductions in germinability. Opening the seed coat at the radicle end enhanced germination in the dark and reduced photosensitivity towards FR. The outer, lignified part of the testa exerted a mechanically restrictive force upon the expanding radicle; this force was estimated to be equivalent to 0.3 MPa. The kinetics, at 25°C in the dark, of the time course of germination and the escape from the inhibitory actions of cFR and osmoticum (0.5mmannitol) were all sigmoid curves, which, upon transformation to normal distributions, had different means, but statistically similar variances. The cFR-irreversible activation of germination by phytochrome and the mannitol-irreversible onset of radicle elongation preceded radicle protrusion (mean at 32 h, 25°C) by 8 and 6 h, respectively. From the results and data on imbition, it is concluded that activation of germination in watermelon takes place during the second, stationary phase of imbibition (20–30 h after sowing at 25°C).
Effects of partial drying on seed germination in the aquatic grasses Zizania palustris L. and Porteresia coarctata (Roxb.) Tateoka
Authors: Aldridge C. D. , Probert R. J.
Published: September 2008

Partial drying of non-dormant seeds had little effect on germination behaviour compared with undried controls. In contrast, partial drying resulted in a marked increase in the germination response of freshly harvested (dormant) seeds of Z. palustris. Partial drying also resulted in a 100-fold reduction in the concentration of gibberellins (GA4+7) required for maximum germination. Although the concentration range of applied abscisic acid (ABA) that permitted germination was unaltered, partial drying increased the final germination percentage at all concentrations tested. The concentration of ABA above which germination was reduced in freshly harvested (dormant) seeds of Z. palustris was 3.16 × 10−7m compared with 10−4m in fresh (non-dormant) seeds of P. coarctata. Changes in the germination response of Z. palustris seeds to applied growth regulators, following partial drying or cold stratification might be explained by similar changes in hormonal status.
Physiological aspects of recalcitrance in embryonic axes of Quercus robur L.
Authors: Poulsen K. M. , Eriksen E. N.
Published: September 2008

The sorption isotherm for excised embryonic axes of recalcitrant (i.e. desiccation-sensitive) Quercus robur L. acorns was determined to find the relation between moisture content and water potential. Subsequently, physiological studies on the effect of desiccating the axes to a range of water potentials were undertaken. The respiratory capacity declined steeply after short exposure to water potentials from −5 to −30 MPa. The leachate conductivity increased significantly after exposure to −5 MPa and rose steeply after exposure to between −12 and −40 MPa. Axes were equilibrated at different relative humidities and the proline content showed a 15-fold increase with a peak value at −10 MPa. It was concluded that the critical water potential for initiation of damage was −5 MPa, and that axes accumulated proline as a response to desiccation stress. The embryonic axes from Q. robur behave more like typical vegetative tissue of angiosperms than like orthodox seeds.
Hard-seededness and seed bank dynamics of six pasture legumes
Authors: Russi L. , Cocks P. S. , Roberts E. H.
Published: September 2008

Six pasture legumes, common in Syrian grasslands, were investigated. Medicago orbicularis and M. rotata had the largest number of hard seeds, with >90% still hard 5 months after shedding; Trifolium stellatum had the least with <30% of hard seeds; T. campestre, M. rigidula and T. tomentosum were intermediate. Hard-seededness in M. orbicularis and M. rotata varied between years. Scarification of hard seeds resulted in almost complete germination in all species. Alternating temperatures (10/20°C) reduced the rate of germination of scarified T. campestre seeds, but had no effect on germination of scarified or unscarified seeds of T. stellatum. The breakdown of hard-seededness in the field in Syria did not begin until 3 months after shedding and greatly increased when seeds overwintered. Breakdown of hard-seededness was slower when seeds were buried at 5 and 10 cm than when seeds remained on the soil surface. Seedling emergence after the rains started in November was highly correlated with the number of soft seeds observed in October. Similarly, a high correlation was found between the percentage of hard seeds in October and carry-over in the seed bank. In small-seeded species (Trifolium spp.), 39% of the initial seed bank was lost in 2 years by causes other than emergence as seedlings. Such losses were only 7% in larger-seeded species (Medicago spp.). The implications of hard-seededness on the utilization and survival of legumes in grasslands are discussed.
Cytoplasmic glass formation in maize embryos
Authors: Bruni F. , Leopold A. C.
Published: September 2008

In order to examine the occurrence of a glassy state in the cytoplasm of maize embryos as a function of water content, isolated embryos were examined using spin-probe electron spin resonance. The glass transition temperature was determined at various degrees of hydration (h) in the range 0.05–0.25 g H2O g−1 dry sample weight. The obtained phase diagram indicates that, at standard storage temperature (−5°C), the cytoplasm of embryos drier than 0.15 g H2O g−1 is in a glassy state.
Metabolism of polyadenylic acid RNA during seed maturation, ageing and germination in carrot (Daucus carota L.)
Authors: Thompson S. , Bryant J. A. , Brocklehurst P. A.
Published: September 2008

Polyadenylic acid (poly(A)) content of carrot seeds reached a peak at 40 days after anthesis and then declined as desiccation occurred. A further decline occurred in the early stages of germination and was more extensive in seeds harvested whilst still immature. Accelerated ageing of seed led to significant losses of poly(A) and the content declined still further when aged seeds were set to germinate. In seeds harvested whilst immature and then subjected to ageing, the resumption of net accumulation of poly(A), a feature of normal germination, was barely detectable or did not occur.
Seed development, the accumulation of abscisic acid and desiccation tolerance in the aquatic grasses Porteresia coarctata (Roxb.) Tateoka and Oryza sativa L.
Authors: Aldridge C. D. , Probert R. J.
Published: September 2008

Seeds of Oryza sativa L. (desiccation tolerant, orthodox) completed each of five distinct stages of development approximately 7 days earlier than seeds of Porteresia coarctata (Roxb.) Tateoka (desiccation intolerant, recalcitrant), despite the fact that O. sativa plants matured under cooler conditions. Isolated embryos of O. sativa were more sensitive to rapid desiccation at 6 days post anthesis (DPA) compared with naked caryopses. More than 90% of the latter were desiccation tolerant at 8 DPA and at all stages tested the germination capacity and/or rate of germination was greater following drying. In contrast, drying resulted in a complete loss of viability in seeds of P. coarctata at all stages tested. In both species, abscisic acid (ABA) began to accumulate in embryos mid-way through development. At the respective peaks, the concentration of ABA in P. coarctata was twice that recorded in O. sativa confirming that ABA levels per se do not determine desiccation tolerance in seeds. The possibility that desiccation tolerance is linked to sensitivity to ABA is discussed.
Effects of developmental status and dehydration rate on characteristics of water and desiccation-sensitivity in recalcitrant seeds of Camellia sinensis
Authors: Berjak Patricia , Vertucci Christina W. , Pammenter N. W.
Published: September 2008

The effect of rate of dehydration was assessed for embryonic axes from mature seeds of Camellia sinensis and the desiccation sensitivity of axes of different developmental stages was estimated using electrolyte leakage. Rapidly (flash) dried excised axes suffered desiccation damage at lower water contents (0.4 g H2O (g DW)−1) than axes dried more slowly in the whole seed (0.9 g H2O (g DW)−1). It is possible that flash drying of isolated axes imposes a stasis on deteriorative reactions that does not occur during slower dehydration. Differential scanning calorimetry (DSC) of the axes indicated that the enthalpy of the melting and the amount of non-freezable water were similar, irrespective of the drying rate.

Very immature axes that had completed morphogenesis and histodifferentiation only were more sensitive to desiccation (damage at 0.7 g H2O (g DW)−1) than mature axes or axes that were in the growth and reserve accumulation phase (damage at 0.4 g H2O (g DW)−1). As axes developed from maturity to germination, their threshold desiccation sensitivity increased to a higher level (1.3−1.4 g H2O (g DW)−1). For the very immature axes, enthalpy of the melting of tissue water was much lower, and the level of non-freezable water considerably higher, than for any other developmental stage studied.

There were no marked correlations between desiccation sensitivity and thermal properties of water. Desiccation sensitivity appears to be related more to the degree of metabolic activity evidenced by ultrastructural characteristics than to the physical properties of water.
Seed protein content and composition of near-isogenic and induced mutant pea lines
Authors: Perez M. D. , Chambers S. J. , Bacon J. R. , Lambert N. , Hedley C. L. , Wang T. L.
Published: September 2008

Total protein content and amounts of albumin, legumin and vicilin have been determined for pea seeds from lines near-isogenic except for genes at therugosusloci,randrb(RR/RbRb; rr/RbRb; RR/rbrb; rr/rbrb). Seeds with the wildtype, round-seeded phenotype (RR/RbRb) had less protein on a total seed dry-weight basis than any of the wrinkled-seeded lines and this protein had a lower proportion of albumin. The lines which had recessive alleles at bothrandrbloci had the highest proportion of protein and the highest proportion of albumin. The roundseeded peas possessed nearly two-fold more legumin than the double recessive line, with proportions for the two single recessive lines falling in between these extremes. Vicilin levels were similarfor all four near-isogenic lines. SDS-PAGE analysis of the isolated albumin, legumin and vicilin fractions revealed no significant differences between the four lines. Differential scanning calorimetry of protein extracts showed that all the wrinkled-seeded near-isolines possessed legumin fractions with diminished thermal stability relative to that from the roundseeded, wild-type line.

Chemically-induced mutants were also analysed for protein content and composition. These mutants have previously been shown to display great variation in starch and lipid levels. Total protein varied from 20.3% to 37.9%; however, relative proportions of albumin, legumin and vicilin were similar in all mutant lines. SDS-PAGE analysis identified two mutant pea lines which possessed a legumin A-chain of 65 000 Mras well as the typical 45 000 Mrform. Differential scanning calorimetry of protein extracts indicated that the legumin in all mutants had lower enthalpies of denaturation than the legumin in the round-seeded parent.

The mutant pea lines possess exceptional variation with respect to starch, lipid and protein which raises opportunities for their use in the food and animal feedstuff industries.
Chilling injury in germinating seeds: basic mechanisms and agricultural implications
Authors: Bedi Seema , Basra Amarjit Singh
Published: September 2008

Germinating seeds of many species, especially those of tropical or subtropical origin, suffer chilling injury when exposed to low but non-freezing temperatures, resulting in poor seedling establishment and reduction in yield. The severity of injury depends upon several factors such as (i) the species or the cultivars involved, (ii) the initial water content of the seed, (iii) the temperature to which seed is exposed, (iv) the duration of chilling exposure and (v) the period during the course of germination when the chilling exposure takes place. The period of imbibition by seeds is the period of sensitivity to the stresses but especially to chilling temperatures. Imbibitional chilling injury is defined as sensitivity to a combination of low seed-water content and imbibition at cold temperature. The mechanism of chilling injury in seeds is different from chilling injury of hydrated tissues and is discussed in relation to the involvement of membranes, respiration, rate of hydration and the concept of discreet moisture levels. Furthermore, the mechanistic and applied aspects of pre-sowing seed treatments for improved germination performance under chilling stress are discussed with an emphasis on hydration-dehydration, osmotic priming and growth regulator treatments.
Conifer seed germination is faster after membrane tube invigoration than after prechilling or osmotic priming
Authors: Downie Bruce , Bergsten Urban , Wang Ben S. P. , Bewley J. Derek
Published: September 2008

Two different pre-emergence treatments preventing radicle protrusion by limiting the extent of imbibition were tested on conifer seeds. Osmotic priming in solutions of polyethylene glycol (PEG) which prevented radicle protrusion during prolonged (3 weeks) treatment resulted in variable percentage germination, mean germination time, and coefficient of uniformity of germination among different seedlots when placed on water. All three germination parameters were either unchanged or inferior in seeds subjected to the various PEG concentrations, treatment temperatures and treatment durations when compared with prechilled controls. In contrast, white spruce and jack pine seeds invigorated at 30% moisture content and 15°C in Gore-Tex membrane tubes consistently germinated faster than prechilled control seeds when subsequently placed on water. Tube invigoration affected neither the ability of seeds to complete germination nor the uniformity of germination. The decrease in mean germination time as treatment duration progressed was always linear and plateaued at approximately 4 days after the tube-invigorated seeds were placed on water regardless of species or seedlot. On average, tube invigoration decreased white spruce mean germination time by 0.13±0.02, and black spruce by 0.23±0.03 day per day of invigoration for up to 20 days of treatment. Jack pine mean germination time decreased 0.2±0.04 day per day of invigoration for up to 14 days of treatment.
Natural and artificial seed ageing in maize: germination and DNA synthesis
Authors: Gutiérrez Germán , Cruz Felipe , Moreno Juan , González-Hernández Victor A. , Vázquez-Ramos Jorge M.
Published: September 2008

The effect of natural and artificial seed ageing has been compared in terms of physiological and biochemical responses of several maize genotypes. The physiological parameters were: viability, germinability, emergence in sand and dry matter accumulation. The biochemical parameters were: DNA synthesis and DNA polymerase activity. A close and direct relationship was found between seed deterioration and DNA metabolism in all maize materials which responded to ageing according to their genetic constitution; i.e., vigorous genotypes suffered less severe damage or recovery was faster than in the low-vigour genotypes. Coordination of events at appropriate times would seem a critical factor for proper seed germination.
The effects of priming on nuclear replication activity and germination of pepper (Capsicum annuum) and tomato (Lycopersicon esculentum) seeds
Authors: Lanteri S. , Saracco F. , Kraak H. L. , Bino R. J.
Published: September 2008

Using flow cytometry, we determined relative DNA amounts expressed as C-values, of large numbers of nuclei isolated from embryo root tips in three seed lots of pepper (Capsicum annuum) and tomato (Lycopersicon esculentum). The nuclei in embryos of fully matured dry pepper and tomato seeds predominantly revealed 2C signals, which indicates that the cells of maturing seeds have arrested at G1 phase of the cell cycle. Priming of pepper and tomato seeds in −1.1, −1.3 or −1.5 MPa polyethylene glycol (PEG) for 14 days reduced the mean time to germination. In all seed lots an induction of 4C signals was found after priming, indicating that during priming the cells of the embryonic root tip had replicated their DNA and arrested at the G2 phase of the cell cycle. For both tomato and pepper, the frequency of 4C signals was highest at the lowest PEG concentration (osmotic potential of −1.1 MPa). A significant inverse correlation was found between the frequency of root tip cells expressing 4C DNA signals and the mean time to germination for each individual pepper and tomato seed lot. However, the effect of a specific osmotic treatment differed between seed lots of the same cultivar, with regard to both the decrease in the mean time to germination and to the percentage of 4C cells, suggesting specific differences among seed lots in the response to priming. The present results indicate that flow cytometry can be used to follow the progress in nuclear replication activities during priming. The advancement in DNA synthesis can thus be used to measure the efficiency of a priming treatment with regard to enhancement of seed lot germination rate.
Differential effects of temperature on ultrastructural responses to dehydration in seeds of Zizania palustris
Authors: Berjak P. , Bradford K. J. , Kovach D. A. , Pammenter N. W.
Published: September 2008

The desiccation tolerance of Zizania palustris seeds has been debatable, but recently it has emerged that survival to low moisture contents is a function of the temperature during dehydration. Survival of dehydration is greatest at 25–30°C and viability declines as the dehydration temperature is reduced. On the other hand, extended hydrated chilling (stratification) is required to break dormancy. The present contribution examines the ultrastructural condition of embryonic axes of Zizania palustris after dehydration at various temperatures, and following reimbibition and stratification. Axis cells sustained least damage when dehydration was carried out at 25°C and ultrastructural deterioration was more severe with lower temperatures during water loss. Damage sustained as a result of unfavourably low dehydration temperatures was visible when seeds were fixed from the dry state and was generally exacerbated during fully imbibed stratification. However, 25°C represented the optimum dehydration temperature; seeds that had been dried at 30°C also showed considerable ultrastructural disturbance when fixed from the dry state. This was largely reversed during fully imbibed stratification, although signs of the damage that had been sustained still persisted. These observations are in keeping with the germination behaviour of Z. palustris seeds dehydrated at temperatures above and below 25°C. The results are discussed in terms of the predominance of one of two mechanisms of membrane deterioration, depending on the dehydration temperature, which are probably not mutually exclusive. It is hypothesized that, at temperatures above 25°C, damage by free-radical-mediated events may predominate, whereas, at temperatures below the optimum, irreversible lipid-phase transitions may be the major factor resulting in membrane damage.
Sucrose and raffinose contents and acquisition of desiccation tolerance in immature maize embryos
Authors: Bochicchio A. , Rizzi E. , Balconi C. , Vernieri P. , Vazzana C.
Published: September 2008

We report preliminary experiments to test the hypothesis that two sugars are involved in the acquisition of desiccation tolerance in immature maize embryos. Sucrose and raffinose were quantified during embryo development, at 16–27 days after pollination (DAP) and during slow dehydration. Embryos were exposed to slow drying either upon excision (18 and 16 DAP) or after an incubation treatment resulting in a decrease in sucrose (18 DAP). The sugars were separated by HPLC with a refractive-index detector; composition was determined by comparing peak areas of interest with those of individual sugar standards. Although further evidence is needed, our results do not appear to support the hypothesis.
Indeterminate development in desiccation-sensitive seeds of Quercus robur L.
Authors: Finch-Savage W. E. , Blake P. S.
Published: September 2008

Fruit and seed development in Quercus robur L. were studied on a single tree over five consecutive seasons. Patterns of growth in the cotyledons and embryonic axes differed between years and resulted in seeds of very different sizes. Moisture content at shedding also differed between years, and late-shed seeds had lower moisture contents than early-shed seeds. Moisture content at shedding was negatively correlated with desiccation tolerance. Seed development in Q. robur therefore appeared indeterminate and did not end in a period of rapid desiccation.

Sensitivity to desiccation in Q. robur was not due to an inability to accumulate dehydrin proteins, ABA or soluble sugars, substances that have been linked with the acquisition of desiccation tolerance in orthodox seeds. There were great similarities between several aspects of Q. robur seed development and that of orthodox seeds before the latter entered the terminal phase of rapid desiccation. This pattern of seed development contrasted with that reported for the highly desiccation-sensitive seeds of Avicennia marina.
Structural aspects and trends in the evolution of recalcitrant seeds in dicotyledons
Authors: von Teichman I. , van Wyk A. E.
Published: September 2008

This review focuses on the possible evolutionary status and functional significance of recalcitrance and certain associated ovule/seed characters, within the framework of modern systems of angiosperm classification. The presence of recalcitrant seed viability in 45 dicotyledonous families is significantly associated with bitegmic and crassinucellate ovules and with nuclear endosperm development, all considered ancestral (plesiomorphic) character states of the ovule; as well as with greater seed size, woody habit and tropical habitat, also regarded as ancestral character states in the dicotyledons. In many species with recalcitrant seeds, the predominant storage reserve is carbohydrate. Recalcitrance is significantly associated with the exalbuminous type of reserve storage. It is proposed that in large recalcitrant seeds, the transfer of the main storage function from endosperm to embryo was probably an early development. In many species with recalcitrance, the ovules/seeds are characterized by extensive vascularization of the integument(s)/seed coat or by a pachychalaza. Pachychalazy is proposed to be a significant functional adaptation for a more efficient transfer of nutrients to the embryo/seed. Recalcitrance and some of the other character states proposed to be plesiomorphic in dicotyledons are also present in some gymnosperms, including presumed sister groups of the dicotyledons. In relatively advanced dicotyledonous families, mostly with orthodox seeds, recalcitrance probably persisted only in isolated relict members. Determination of character polarity is particularly problematic at lower taxonomic levels, because there is always the possibility that, in some taxa, a character state such as recalcitrance may have arisen secondarily as a reversal. Available evidence supports our view that seed recalcitrance can be regarded as a relatively ancestral character state in dicotyledons.
Desiccation and the switch from seed development to germination. Alfalfa embryos can synthesize storage proteins after germination if maturation drying is prevented
Authors: Xu N. , Bewley J. D.
Published: September 2008

Storage proteins (2S, 7S and 11S) are synthesized at the mid- to late stages of development in alfalfa seeds, mainly within the embryos. Mature dry seeds cannot synthesize these proteins upon subsequent germination and growth. When embryos were isolated from the seed during development (stages VII and VIII) and placed on water or nutrient medium, they germinated. They exhibited a pattern of protein synthesis which was identifiable as germinative/post-germinative, and was identical to the pattern synthesized in embryos of germinated dry seeds, and of embryos from seeds that were subjected to drying prematurely at stages VII and VIII. When, after 48 h from the start of imbibition, abscisic acid or osmoticum was introduced to germinated embryos isolated at stage VII and not desiccated, the synthesis of the 11S storage protein was restored to a rate comparable to that of stage-VII embryos before isolation. This was accompanied by an increase in transcription of the 11S storage protein gene. Transfer of germinated stage-VII embryos, which had first been desiccated, to abscisic acid or osmoticum 48 h after imbibition started did not result in any restoration of storage protein synthesis. Thus, desiccation, prematurely or at maturation, off-regulates storage protein synthesis and within the embryos this process is no longer responsive to abscisic acid or osmoticum.