Showing papers on "Germination published in 1995"

Seed Development and Germination

Abstract: Part 1 Seed morphology and development: the seed - structure and function morphogenetic processes in embryo development of maize. Part 2 Storage compounds - synthesis and accumulation: transport and accumulation of reserve materials in developing seeds - the seed as a sink seed storage proteins in cereals seed storage proteins in legumes regulation of seed storage protein gene expression synthesis of embryo specific protein during seed development carbohydrate biosynthesis in seeds lipid biosynthesis in developing seeds synthesis and transport of oil body proteins (oleosins) in seeds mechanisms and regulation of mineral storage during seed development. Part 3 From seed development to germination: mechanisms of dessication tolerance in seeds regulatory mechanisms in the transition from seed development to germination genetic control of hormone role in seed development and germination water relations in germination control of seed dormancy and germination in the gaseous environment (O2, CO2, C2H4) recent advances in the control of germination by light and temperature synthesis and secretion of hydrolytic enzymes during germination carbohydrate degradation during germination control of mobilization of storage compounds following germination of dicotyledonous seeds. Part 4 Ecology of germination: pollinators and seed production maternal and environmental effects on seed quality and germination seed bank ecology inhibition and promotion of seed germination in soil - dormancy cycles modelling seed germination of weeds seed germination of root parasitic plants seed germination of halophytes allelopathy and germination seed germination of desert plants. Part 5 Seed quality improvement - technological advances: loss of seed viability in storage - cytological, biochemical, and genetic aspects the implications of seed-associated mycoflora during storage biochemical processes during osmotic priming of seeds improvement of protein quality in seeds overproduction of essential amino acids in seeds artificial seeds.

The promotive effect of smoke derived from burnt native vegetation on seed germination of Western Australian plants

Abstract: Exposure of dormant seed to cold smoke derived from burnt native vegetation had a positive influence on germination in one or more seed provenances in 45 out of 94 species of native Western Australian plants that are normally hard to germinate. When tested under controlled conditions some species showed earlier germination in smoke treatments than controls; in others smoke-treated seeds continued to germinate for several weeks after controls had achieved full germination. In the remainder, treated and control seeds germinated to similar time schedules. A group of 23 species which responded positively had previously been recorded as extremely difficult or impossible to germinate using conventional techniques. These included members of the genera Geleznowia (Rutaceae), Hibbertia (Dilleniaceae), Stirlingia (Proteaceae), Verticordia (Myrtaceae), Actinostrobus (Cupressaceae) and Pimelea (Thymelaeaceae). Both large- and small-seeded species were encountered amongst the positively responding taxa, which encompassed representatives of 15 families and 26 genera of dicotyledons, 5 families and 8 genera of monocotyledons and the gymnosperm Actinostrobus acuminatus. Sowing seeds on smoke-fumigated filter papers or watering with aqueous eluates of smoke elicited similar degrees of stimulation of germination, as did exposure to gaseous smoke in a readily germinating species Anigozanthos manglesii (Haemodoraceae) and the normally intractable species Lysinema ciliatum (Epacridaceae). Exposing recently burnt and unburnt natural bushland sites to smoke, smoked water or smoked dry sand elicited a significant germination response in 15 species. Over one third of the species sampled in the burnt site exhibited germination additional to that caused by the fire. Data are discussed in relation to previous germination studies on Australian and other taxa.

Redefining seed dormancy: an attempt to integrate physiology and ecology

Abstract: Summary 1 The paper reviews the literature on seed dormancy, with special regard to incon­ sistencies in terms and definitions used. It presents a concept of seed dormancy in which physiology and ecology are integrated. Its aim is to increase the understanding of seed dormancy and germination, and to help defining ecological research questions. 2 It is claimed that seed dormancy should not be identified with the absence of germination. Seed dormancy should rather be defined as a characteristic, the degree of which determines the range of conditions in which a seed is able to germinate. Dormancy varies on a continuous scale, which is visualized by continuous changes in the range of conditions suitable for germination. If the conditions required by the seed are met by its environment, the seed will germinate. 3 The concept of dormancy that is described in the paper is partly based on a physiological model for the regulation of dormancy and the stimulation of germi­ nation. In this model dormancy is related to the amount of a hypothetical phy­ tochrome receptor in the seed. 4 It is argued that the process of dormancy release should be clearly distinguished from the germination process itself. It is stated that as yet only temperature has been shown to alter the degree of dormancy in seeds. Factors like light and nitrate are often indispensable for germination, but only by promoting the germination process itself, not by mitigating the requirements for germination. 5 It is suggested that seed dormancy prevents germination when conditions are favour­ able for germination, at a time of the year when it can be expected that the plant originating from the seed will not survive and produce offspring. 6 It is concluded that dormancy should not be regarded as inactivity of seeds. At any degree of dormancy, seeds continuously react to their environment by adjusting their level of dormancy to the changing environment.

Plant Growth Substances - Principles and Applications

Abstract: Historical aspects and fundamental terms and concepts Methodology for the extraction, purification and determination of plant growth substances Chemistry, biological effects and mechanism of action of plant growth substances Seed germination and seedling growth Rooting Dormancy Juvenility, maturity and senescence Flowering Abscission Physiology of fruit set, growth, development, ripening, premature drop, and abscission Tuberization Manipulation of growth and photosynthetic processes by plant growth regulators Weed control

Characterization of streptomyces lydicus WYEC108 as a potential biocontrol agent against fungal root and seed rots.

Abstract: The actinomycete Streptomyces lydicus WYEC108 showed strong in vitro antagonism against various fungal plant pathogens in plate assays by producing extracellular antifungal metabolites. When Pythium ultimum or Rhizoctonia solani was grown in liquid medium with S. lydicus WYEC108, inhibition of growth of the fungi was observed. When WYEC108 spores or mycelia were used to coat pea seeds, the seeds were protected from invasion by P. ultimum in an oospore-enriched soil. While 100% of uncoated control seeds were infected by P. ultimum within 48 h after planting, less than 40% of coated seeds were infected. When the coated seeds were planted in soil 24 h prior to introduction of the pathogen, 96 h later, less than 30% of the germinating seeds were infected. Plant growth chamber studies were also carried out to test for plant growth effects and for suppression by S. lydicus WYEC108 of Pythium seed rot and root rot. When WYEC108 was applied as a spore-peat moss-sand formulation (10(8) CFU/g) to P. ultimum-infested sterile or nonsterile soil planted with pea and cotton seeds, significant increases in average plant stand, plant length, and plant weight were observed in both cases compared with untreated control plants grown in similar soils. WYEC108 hyphae colonized and were able to migrate downward with the root as it elongated. Over a period of 30 days, the population of WYEC108 colonized emerging roots of germinating seeds and remained stable (10(5) CFU/g) in the rhizosphere, whereas the nonrhizosphere population of WYEC108 declined at least 100-fold (from 10(5) to 10(3) or fewer CFU/g). The stability of the WYEC108 population incubated at 25 degrees C in the formulation, in sterile soil, and in nonsterile soil was also evaluated. In all three environments, the population of WYEC108 maintained its size for 90 days or more. When pea, cotton, and sweet corn seeds were placed into sterile and nonsterile soils containing 10(6) or more CFU of WYEC108 per g, it colonized the emerging roots. After a 1-week growing period, WYEC108 populations of 10(5) CFU/g (wet weight) of root were found on pea roots in the amended sterile soil environment versus 10(4) CFU/g in amended nonsterile soil. To further study the in vitro interaction between the streptomycete and P. ultimum, mycelia of WYEC108 were mixed with oospores of P. ultimum in agar, which was then used as a film to coat slide coverslips.(ABSTRACT TRUNCATED AT 400 WORDS)

Soil Temperatures During Experimental Bushfires in Relation to Fire Intensity: Consequences for Legume Germination and Fire Management in South-Eastern Australia

Abstract: 1. Experimental fires were used to determine the influence of fire intensity and subcomponents of intensity (fuel consumption and rate of spread) on soil temperatures (at 0-10 cm depth) in shrub/woodland communities in the Sydney region of south-eastern Australia. 2. Temperatures > 60°C were achieved at depths of 0-3 cm. Such temperatures are sufficient to break seed dormancy in local legume species. 3. Maximum change in soil temperature was not significantly affected by Byram fire intensity. However, at 0-4 cm depth, maximum temperature change was significantly affected by the amount of fine fuel (particles < 6 mm thick) consumed on the ground (mainly litter, twigs and herbs). Fine fuel above the ground (shrub canopies), coarse fuel (6-25 mm thick) on the ground and rate of spread did not significantly affect maximum change in temperature in the top 4 cm of the soil. 4. The results indicate that 0.6-2.0 kg m −2 of fine fuel burnt on the ground is likely to stimulate germination of buried seeds of local legumes (seed dormancy broken at ≥ 60° C). 5. At the upper end of this fuel consumption range, germination is predicted to occur down to 3-cm depth, while consumption at the lower end of the range will stimulate germination to a depth of 1 cm. Post-fire germination in Acacia suaveolens was in accordance with these predictions. 6. These results are discussed in relation to the use of prescribed fire for hazard reduction. Prescribed fires with maximum potential for germination (maximum fuel consumption in the target range) will be close to, or in excess of, the limit for control unless the rate of spread is very low (< 0.10 M S −1 ), thereby imposing constraints on the use of prescribed fire to achieve both protection and conservation objectives

Genetic control and integration of maturation and germination pathways in seed development

Abstract: The viviparous and germination mutants of maize and Arabidopsis thaliana illuminate the mechanism that integrates control of morphogenetic, maturation, dormancy, and germination pathways in seed development. Key elements of this mechanism include (a) developmental control of abscisic acid and gibberellin hormone synthesis and perception, (b) integration of maturation and anthocyanin pathways in the maize seed, (c) functions of the VP1 and ABI3 factors in abscisic acid-regulated gene expression, and (d) intrinsic developmental genes that couple seed maturation to the program of embryo morphogenesis. The scarcity of mutants that affect timing or tissue specificity of hormone synthesis in the seed is an important constraint to progress in understanding the role of hormone signals. The interactions among the abscisic acid-insensitive abil, abi2, abi3, abi4, and abi5 mutants of A. thaliana are consistent with multiple pathways of abscisic acid signal transduction in the seed. The maize Vp1 and A. thaliana Abi3...

A critical update on seed dormancy. I. Primary dormancy

Abstract: The emphasis of modern dormancy research is almost entirely on the form of dormancy that is acquired during seed development, primary dormancy. Abscisic acid (ABA) appears to be intimately involved in its regulation. The action of abscisic acid has also been implied in many other developmental processes. The coincidence of developmental events, such as dehydration and completion of maturation, with the acquisition of primary dormancy suggests that dormancy is influenced by these processes. Germinability, both during development and after maturation, is sometimes directly correlated with ABA content. The lack of such a correlation may be explained by assuming a decisive role for the responsiveness to ABA or other overriding factors. ABA has been detected in all seed components. The different seed tissues may all contribute, to various extents, to the degree of whole seed dormancy. It is concluded that ABA action in dormancy regulation is not restricted to the embryo but is also located in endospermic tissue. In addition, a role of ABA in the morphological development of germination modifying seed tissues is proposed. The mechanism for ABA action appears to be associated with cell wall properties.

Effects of salinity on seed set in rice

Abstract: Salinity reduces fertility in rice (Oryza sativa L.), but little is known of the underlying cause(s), In order to determine the relative importance of pollen viability and stigmatic receptivity for seed setting, plants of the rice cultivar IR36 were treated with 'artificial' sea water (0, 10, 25 or 50 mol m(-3) with respect to NaCl) from 1 month after germination until the main tiller flowered. An increase in the salinity in the medium resulted in a decrease in the number of fertile florets and in the viability of pollen as determined both by pollen germination and by pollen staining with the tetrazolium salt 3-(4,5-dimethylithyazolyl)-2,5-diphenyl monotetrazolium bromide. In order to assess the effects of salt on stigmas, seed production was measured for salt-grown and non-salt-grown female plants pollinated with viable pollen (from plants grown in the absence of salt), The percentage of seed set was reduced by 38% when the female plants were grown in 10 mol m(-3) Na and by 72% at 25 mol m(-3) Na: no seed setting was recorded for plants grown in 50 mol m(-3) Na, Comparisons between crosses involving male and female parents grown at different salinities indicated that effects on the female plants dominated those on pollinator plants. Mineral analysis of leaves of different ages showed that there was a gradient of K concentration from leaf to leaf which was opposite to that of Na and Cl at all levels of applied salinity: K was maximal in the flag leaf, where Na and Cl were minimal, Analysis also revealed that there was an increase in the concentrations of Na and Cl and a decrease in the concentration of K in the pollen grains and stigmas of plants subjected to saline conditions, Correlations between the concentration of Na End Cl in pollen and pollen staining and pollen germination in vitro suggest that Na and Cl per se were responsible for the poor viability, The change in ionic concentrations in pollen and stigmas was much larger than that in the younger leaves, and in particular very much larger than that in the lemmas and paleas.

Glucosinolate-containing plant tissues as bioherbicides

Abstract: Enzymatic hydrolysis of glucosinolates, a class of compounds found in Brassica species, results in a number of products with potential to inhibit seed germination. To investigate the impact of both volatile and water soluble allelochemicals, germination bioassays were conducted with Lactuca sativa seeds in the presence of defatted seed meal of Brassica napus. Seed meal in which glucosinolates were hydrolyzed to remove volatile glucosinolate degradation products was compared with intact seed meal and water controls. Only tissues containing glucosinolates produced volatiles that inhibited germination. Biologically active volatiles were identified by GC-MS as isothiocyanates and nitriles, products of glucosinolate hydrolysis. Water-soluble components also inhibited germination, with analysis confirming the presence of nonvolatile products of glucosinolate hydrolysis. The results suggest that allelochemical control of germination with glucosinolate-containing plants may contribute to reductions in synthetic pesticide usage if weed seeds are targeted.

Salt tolerance of Hordeum and Brassica species during germination and early seedling growth

Abstract: Germination response and early seedling growth of barley (Hordeum vulgare L. 'Franklin', 'Harrington' and 'Abee'), wild barley (H. jubatum L.), canola (Brassica napus L. 'Excel') and wild mustard (B. kaber L. C. Wheeler) were investigated in iso-osmotic solutions of salts (NaCl, Na2SO4 + MgSO4) and polyethylene glycol (PEG) with osmotic potentials close to −0.9 MPa. Germination of Harrington and wild barley was reduced most by the non-penetrating solute PEG, suggesting that ion penetration might have reduced osmotic stress in the salt treatments. Wild barley was more salt tolerant than Harrington based on seedling growth relative to control plants. Of the three barley cultivars, Franklin was similar in salt tolerance to Harrington, while Abee was the most sensitive to all osmotica tested. Barley varieties had the lowest germination rate and poorest seedling growth in the PEG treatment. Compared with canola, wild mustard showed consistently greater tolerance to all osmotica during germination and early see...

Effects of mercury and cadmium on the activities of antioxidative enzymes in the seedlings of Phaseolus aureus

Abstract: Phaseolus aureus Roxb. was exposed to HgCl2 and Cd(NO3)2 either at the germination stage in concentration 0.5, 5 and 25 μM for 48 and 96 h, or at the seedling stage (5th day of germination) in concentration 0.5, 5 and 20 μM for 6, 24 and 48 h. The germination and the growth of roots (germination stage treatment) were less in Hg than in Cd treatment. The seedlings (seedling stage treatment) were, however, more susceptible to Cd than Hg. Both root and leaf tissues of the plant treated at the germination stage showed enhanced lipid peroxidation and activities of the antioxidative enzymes (catalase, guaiacol peroxidase and ascorbate peroxidase), except the catalase in leaf in 25 μM Cd treatment. At seedling stage the content of malondialdehyde increased significantly only in the leaf tissue, during 6 h exposure. The activities of all the enzymes exhibited an increasing trend in both the tissue of the seedlings, particularly the leaf, at least after 24 and 48 h, except the catalase whose activity declined in response to Cd. Active involvement of the guaiacol and ascorbate peroxidases, rather than catalase, in scavenging cellular H2O2 was indicated. It was concluded that the two metals had little primary damaging effect on membranes.

Seed Dispersal, Germination and Seedling Growth of six Helophyte Species in Relation to Water-Level Zonation

Abstract: SUMMARY 1. Seed dispersal, germination, and seedling growth characteristics of six helophyte species. Iris pseudacorus, Phalaris arundinacea, Phragmites australis, Typha angustifolia, T. latifolia and Scirpus lacustris, were investigated in relation to their water-level zonation. 2. The experiments demonstrated a large variation in these characteristics between the species. 3. Propagule floating capacities range from 1000 h (I. pseudacorus). 4. Seed germination in a water-level gradient revealed two groups with respect to germination percentage - exposed soil species (I. pseudacorus, Phalaris arundinacea, Phragmites australis) and submerged soil species (T. angustifolia, T. latifolia). 5. There were two contrasting types of seedling growth response to submergence and exposure: one group of species formed longest leaves under exposed conditions (Phalaris arundinacea, Phragmites australis, I. pseudacorus), and the other under submerged conditions (S. lacustris, T. latifolia, T. angustifolia). 6. The results suggest that early life-history characteristics of the species relate to their locations in the riparian zonation: Phalaris arundinacea and Iris pseudacorus at the higher end, Phragmites australis intermediate, and Typha spp. and Scirpus lacustris at the lower end. Species occurring at lower locations show adaptations to (periodical) flooding of the soil (submersed germination and growth), while those from higher locations require prolonged exposed soil conditions to germinate and to survive the establishment stage.

Genotypic variation in the effect of salinity on fertility in rice

Abstract: The effect of salinity on the reproductive physiology of five rice genotypes (IR54, IR26, IR2153-26-3-5-2, IR15324-117-3-2-2 and BR6), was investigated by treatment from panicle initiation with sodium concentrations of 20, 35 or 50 mol m-3 in an lsquoartificial seawaterrsquo. In an experiment conducted in a glasshouse, plant height and dry weight were little affected by the treatments. There was, however, genotypic variation in the extent of the sodium accumulation, with IR15324-117-3-2-2 containing the highest and IR2153-26-3-5-2 the lowest concentrations: sodium concentrations were higher in older than younger leaves. Salinity delayed flowering, reduced the number of productive tillers, the number of fertile florest per panicle, the weight per grain and the grain yield: effects on grain yield were very much more severe than on vegetative growth. Panicle length was also reduced as was the number of primary branches in a panicle: again there was genotypic variation in the response of these characters to salinity, with the number of branches in IR2153-26-3-5-2 being particularly sensitive. The concentration of sodium increased in the pollen, stigmas, lemmas and paleas with each increment of external salinity. The highest concentrations of sodium in pollen and stigmas was recorded in IR54 and IR15324-117-3-2-2. Pollen viability, whether tested with the tetrazolium salt thiazolyl blue (3-{4,5-dimethylthiazolyl-2}-2,5-diphenyl monotetrazolium bromide or MTT), germination on stigmas, growth through the stylar tissue or F1 seed set, was reduced particularly in those genotypes accumulating most sodium. At all three salt levels, a genotype which accumulated more Na in its pollen produced less-viable pollen than those with less Na in their pollen. Since the amount of Na in the pollen was highly correlated with the Na in the flag leaf, assessment of flag leaf Na should prove a useful indicator of the likely pollen viability. Stigmatic receptivity was also reduced, when estimated either from germination of viable pollen on stigmas of salt-grown plants, its growth through the stylar tissue or F1 seed set. The reduction of seed set in crosses suggested that the overall consequences of salinity are dominated by effects on panicle development, stigmas and grain filling rather than on pollen. Analysis of the data suggests that genotypic variation exists in the extent to which salinity affects aspects of the plants reproductive physiology and development: this variation might be used in attempts to enhance the resistance of rice to salinity.

Seed bank dynamics and coexistence of annual macrophytes in a temporary and variable habitat

Abstract: The seed bank dynamics of annuals in two Mediterranean temporary marshes were studied in order to investigate the impact of the disturbance regime on coexistence. The disturbance regime is made up of drought periods in the marshes and of predation. The density of diaspores buried in the sediment was measured in 4 consecutive years together with the biomass produced during two growing seasons. The total density of diaspores in the sediment varied markedly from year to year but always remained at a high level for all species (between 73000 and 800000 per m 2 ). These perennial seed banks allowed the populations to be maintained despite two successive years without any reproduction. In experimental conditions, the seed bank was not depleted after the sediment samples had been submerged during 5 successive periods. The majority of the seedlings emerged as soon as the first period of flooding and temporary droughts stimulated the germination of Zannichellia spp. and Ranunculus baudotii. The decrease in the number of seeds buried in the soil was essentially due to germination. This was stronger when the seeds were recently produced and situated at the surface of the sediment. The seed density varied only slightly with the depth of the marsh, except in the case of Ruppia maritima. The seed bank is highly variable on a spatial microscale but no aggregation pattern could be demonstrated. In the field, the biomass of a population generally appeared not to be limited by the availability of the diaspores, notably because of the ability to propagate vegetatively which is shown by all species studied. Similarly, a high vegetative biomass does not guarantee a high reproductive output as the droughts occur in a density-independent way. The success of a species is related to the interaction between its life history traits and the environmental conditions met each year. The macrophyte communities we studied function in non-equilibrium, with patterns close to those described in lottery models of coexistence. Establishment, growth and reproduction fluctuate strongly from one year to another for all species, in a partially asynchronous way. This would enable competitive exclusion to be indefinitely delayed. The seed bank introduces a storage effect by magnifying the effect of the favourable years in comparison with the bad years.

Manipulation of intracellular glycerol and erythritol enhances germination of conidia at low water availability

Abstract: The insect pathogens Beauveria bassiana, Metarhizium anisopliae and Paecilomyces farinosus can be effective biocontrol agents when relative humidity (RH) is close to 100%. At reduced water availability, germination of propagules, and therefore host infection, cannot occur. Cultures of B. bassiana, M. anisopliae and P. farinosus were grown under different conditions to obtain conidia with a modified polyol and trehalose content. Conidia with higher intracellular concentrations of glycerol and erythritol germinated both more quickly and at lower water activity (aw) than those from other treatments. In contrast, conidia containing up to 235.7 mg trehalose g-1 germinated significantly (P < 0.05) more slowly than those with an equivalent polyol content but less trehalose, regardless of water availability. Conidia from control treatments did not germinate below 0.951-0.935 aw (identical to 95.1-93.5% RH). In contrast, conidia containing up to 164.6 mg glycerol plus erythritol g-1 germinated down to 0.887 aw (identical to 88.7% RH). These conidia germinated below the water availability at which mycelial growth ceases (0.930-0.920 aw). Germ tube extension rates reflected the percentage germination of conidia, so the most rapid germ tube growth occurred after treatments which produced conidia containing the most glycerol and erythritol. This study shows for the first time that manipulating polyol content can extend the range of water availability over which fungal propagules can germinate. Physiological manipulation of conidia may improve biological control of insect pests in the field.

Effects of temperature, light and gibberellic acid on the germination of seeds of 43 species native to Western Australia

Abstract: Species native to the southwest of Western Aus- tralia, representing a range of plant families, life-history strat- egies, fire-response syndromes, seed-store types and seed weights, were tested for viability using tetrazolium chloride and for germination under combinations of constant tempera- tures of 15 ?C or 23 ?C, constantly dark or 12 h diurnal white- light conditions, and with, or without, addition of gibberellic acid (GA3, 50 mg/1). Species previously known to require a heat-shock treatment to overcome dormancy due to an imper- vious testa were pre-treated prior to imposition of tempera- ture, light and GA3 conditions. The test environmental condi- tions related to differences between winter and autumn tem-

Mechanisms underlying the suppression of forb seedling emergence by grass (Poa pratensis) litter

Abstract: We investigated the mechanism by which grass litter (dead Poa pratensis L. shoots) suppressed the emergence of seedlings of four old-field forbs (Centaurea nigra L., Dipsacus sylvestris Huds., Hypericum perfioratum L., Verbascum thapsus L.) by determining the effect of litter on their seed germination and shoot extension. When seeds were placed beneath litter (715 g m -2 ) that had been collected from an old-field, the germination of all species except Verbascum was reduced significantly by 26% to 41% compared to a no-litter control. When seeds were placed in plastic dishes containing a leachate solution made from litter (7 g dish -1 ), the germination of two species (i.e. Centaurea and Dipsacus) was reduced significantly by 10% to 34% compared to the distilled water control. When germinated seeds were placed beneath litter, the emergence of seedlings of all species was reduced significantly by 95% to 100% compared to a no-litter control. These results indicate that grass litter may suppress forb seedling emergence by reducing seed germination and (or) by preventing shoot extension and that these effects are species dependent.

The effect of a plant-derived smoke extract on the germination of light-sensitive lettuce seed

Abstract: A simple and rapid bioassay using seeds of Lactuca sativa L. Grand Rapids has been developed for the detection of germination-enhancing compound(s) in plant-derived smoke extracts. This light-sensitive species germinates within 24 h in the dark at 20 or 25°C and shows responsiveness to smoke-derived extracts over a wide concentration range. For some seed lots where the Pfr level is high and germination in the dark is unacceptably high, a brief (10 min) exposure to far-red light, one hour after the start of imbibition in the dark, is necessary to clearly demonstrate biological activity in the smoke extracts.

The estimation of pollen viability in rice

Abstract: Methods for testing pollen viability in rice were evaluated by comparing staining with aniline blue in lactophenol, two tetrazolium salts and fluorescein diacetate with germination in an in vitro culture medium. Staining with thiazolyl blue (MTT) was nicely correlated with germination. Under non-saline conditions, rice pollen was only viable for a short period of time, with an approximately 50% loss of viability within 20 min of shedding. When plants were salinized at either panicle initiation or the booting stage, pollen viability was reduced.

Ten-year seed bank and vegetation dynamics of a tidal freshwater marsh

Abstract: A decade-long examination was made of recruitment and establishment in a tidal freshwater high marsh along the Delaware River. Over the 10 yr of the study, seed bank, field seedlings, and vegetation showed variable patterns and significant year-to-year fluctuations. Patterns of each species were unique, perhaps the result of specific germination and/or establishment requirements and seedling morphology. For a given species there was little correlation among seed bank, seedling, and vegetation patterns, and germination success did not guarantee establishment. Species diversity showed significant year-to-year fluctuation, but there was no trend, and perennials did not change in importance during the 10-yr period. Because four annual species (Bidens laevis, Cuscuta gronovii, Impatiens capensis, and Polygonum arifolium) composed over 90% of the seed bank and field seedlings, and 58-89% (x = 70 ? 4) of the cover, community dynamics were dependent on seedling recruitment. For a given species life history stages (seed bank, field seedlings, and vegetation) were not predictable over the temporal scale of a decade. It is predicted, however, that if hydrology remains unchanged, the same suite of species will persist. The importance of the parasite Cuscuta gronovii is noteworthy.

Exploiting weed seed dormancy and germination requirements through agronomic practices

Abstract: Many common agronomic practices affect weed seed dormancy and germination by influencing the microen- vironmental and edaphic conditions surrounding seeds in soil. Factors such as light penetration, soil water content, soil fertility, and temperature are modified by tillage, planting, harvesting, and other production practices, resulting in en- hanced or depressed weed seed germination. Changes in these environmental factors may also indirectly lead to al- terations in phytohormone concentrations during seed devel- opment, which can subsequently affect dormancy status of the mature seed. Integrated approaches that place priority on depleting weed seed banks through interfering with dor- mancy or germination requirements have strong potential to enhance weed management aspects of agricultural sys- tems. Nomenclature: Mouseearcress (Arabidopsis thaliana L. Heynh), barley (Hordeum vulgare L.), common lambsquar- ters (Chenopodium album L.), curly dock (Rumex crispus L.), giant foxtail (Setariafaberi Herrm.), hairy vetch (Vicia villosa Roth), rough stalk bluegrass (Poa trivialis L.), prostrate knot- weed (Polygonum aviculare L.), red brome (Bromus rubens L.), red rice (Oryza sativa L.), red sorrel (Rumex acetosella L.), redroot pigweed (Amaranthus retroflexus L.), rye (Secale cereale L.), silvergrass (Vulpia spp.), sulfur cinquefoil (Poten- tilla recta L.), wild oats (Avenafatua L.), witchweed (Striga asiatica (L.) Kuntze). Additional index words. Cultivation, edaphic factors, seed physiology.

Natural Herbicide Potential of Alfalfa Residue on Selected Weed Species

Abstract: Alfalfa (Medicago sativa L.) contains water-soluble substances that are toxic to itself (autotoxicity) and to other species (allelopathy). Experiments were conducted to determine the potential of using alfalfa residue as a natural herbicide for inhibition of weed seed germination, seedling growth, and development. Various weed species were germinated in aqueous extracts from dried alfalfa using cold (5°C), warm (24°C), and hot (80°C) treatments. Results indicated that inhibition of weed seed germination was dependent on the aqueous extraction method, residue application rate (w/v or w/w), and weed species. The greatest inhibition of germination was 44%, when 60% (w/v) warm aqueous extract was applied to lambsquarters (Chenopodium album L.). Seedling growth was also inhibited by residue application at various rates. Root length was more inhibited than increase in shoot length. In terms of total seedling length, giant foxtail (Setaria faberii Herrm.) was the most resistant species and lambsquarters was the most susceptible among the weed species studied to alfalfa aqueous extracts. Weed seed germination percentage decreased as incubation time increased from 8, 16, 24, and 48 h. An alfalfa aqueous extract incubated for 48 h caused the greatest inhibition of velvetleaf (Abutilon theophrasti Medic.) seed germination (25%). When alfalfa residue was incorporated with silica sand, the growth and development of lambsquarters, pigweed (Amaranthus retroflexus L.), velvetleaf, and crabgrass [Digitaria sanguinalis (L.) Scop.], as measured by plant height, leaf area, and total, shoot, leaf, and root dry weight, were significantly inhibited as the rate increased from 0.0 to 2.0 g kg -1 . Dried alfalfa residue significantly stimulated plant height, leaf area, and total dry weight including shoot, leaf, and root of giant foxtail and cheatgrass (Bromus secalinus L.). Results suggest that alfalfa residue has a contrasting effect on weed growth and development due to water-soluble allelochemicals present in the residue.

Seed germination timing patterns in intermountain penstemon (scrophulariaceae)

Abstract: Regulation of seed germination timing is an important component of population persistence, especially for short-lived plants in seasonal environments with unpredictable year-to-year weather variation. Seed germination patterns were examined in the laboratory for seeds from 135 populations belonging to 38 species and 13 sections of the genus Penstemon (Scrophulariaceae), from habitats ranging from warm desert to alpine tundra. Seeds of most species were dormant at dispersal and required a period of moist chilling to become germinable. Response to chilling was related to probable chilling duration at the collection site. Populations from habitats with severe winters produced seeds with long chilling requirements, while those from habitats with mild winters produced seeds with short chilling requirements. Populations from midelevation habitats produced seeds with intermediate chilling requirements but with a sizeable fraction whose dormancy was not broken by chilling of any length. Another pattern observed mostly in warm desert populations was little primary dormancy at autumn temperatures combined with induction of a fraction into secondary dormancy by short chilling. Species with a wide habitat range included populations with contrasting germination patterns. Parallel habitat-correlated patterns were observed in different sections. Most species showed germination patterns that combined predictive mechanisms with potential for carryover of a persistent seed bank. Results of common garden experiments suggested that germination differences had a strong genetic basis both among populations and among plants in a population. Adaptive radiation in the genus Penstemon has thus included the evolution of habitat-specific germination timing strategies in multiple lineages within the genus.

Seed and Seedling Demography of Four Co‐Occurring Carpinus Species in a Temperate Deciduous Forest

Abstract: In order to clarify regeneration traits and their fitness, we compared seed fall, seedling emergence, and first-year seedling survival of four co-occurring species, Carpinus tschonoskii, C. japonica, C. laxifiora, and C. cordata, in an old-growth temperate deciduous forest in Ogawa Forest Reserve, central Japan. Seedling emergence ratio of C. cordata (5.5%), whose seeds mostly germinated 1.5 yr after seed fall, was lower than the other species (8.5-11.2%). First-year seedlings of Carpinus tschonoskii and C. japonica had much lower survival rates (2.7%, both species) than C. laxifiora and C. cordata (7.5- 8.5%) under closed canopy, suggesting that the former two are more disturbance dependent than the latter two. They are characterized by their seed and seedling performances as seed rain type fundamentally; however, C. cordata and C. laxiflora are able to establish a seedling bank, and C. cordata has a seed bank too. These regenerative strategies partly explain the abundance and population structure of the four species in this old-growth forest. Multiple regression analyses showed that topography was important for survival of all species but C. cordata. This result was consistent with the adult distribution of these species in this forest. Wind dispersal of Carpinus is effective, both to escape from density- or distance- dependent high mortality and to increase the chance of arriving at canopy gaps, where seedling survival rate is high. However, escaping high mortality seems relatively more important for C. laxifiora and C. cordata (seedling bank strategy), and arriving at a canopy gap is relatively more important for C. tschonoskii and C. japonica (seed rain strategy).

Modulation of germination of embryos isolated from dormant and nondormant barley grains by manipulation of endogenous abscisic acid

Abstract: Dormant and non-dormant barley (Hordeum distichum L.) grains with identical genetic backgrounds were obtained by maturing grains under different climate conditions. When isolated embryos from dormant grains were incubated in a well containing a fixed volume of water (300 μl), the germination rate and percentage were dependent on the embryo number per well. A higher embryo number per well was correlated with a lower germination rate and percentage. However, this was not the case for the embryos isolated from nondormant grains. During germination, the endogenous cis-abscisic acid (ABA) in isolated embryos from both dormant and nondormant grains was analyzed. The inhibitory effect on germination of a higher number per well of isolated dormant embryos was due to diffusion of endogenous ABA out of the embryos and accumulation of ABA in the incubation medium. Moreover, there was de-novo synthesis of ABA in embryos isolated from dormant grains during incubation but not in embryos isolated from nondormant grains. The inhibitory effect of ABA on germination of embryos isolated from dormant grains could be mimicked by addition of ABA or the medium in which dormant embryos had been placed. Embryos isolated from nondormant grains were insensitive to addition of ABA and medium from dormant embryos. Our results demonstrate that diffusion of endogenous ABA, de-novo ABA synthesis and ABA sensitivity play a role in the control of germination. It is proposed that dormancy-breaking treatments act via changes to these processes.

Fire-followers in chaparral: nitrogenous compounds trigger seed germination.

Abstract: 1 Application of nitrates (optimal concentration c. 10mM) promoted seed germination in the fire annuals Emmenanthe penduliflora and Phacelia grandiflora and to a lesser extent in the fire-adapted shrub Salvia mellifera. Ammonium ions, although virtually inactive in E. penduliflora, were as effective as nitrate in both P. grandiflora and S. mellifera. 2 Diurnal illuminations and a chilling pretreatment, though of little effect by themselves, significantly enhanced the nitrate-mediated promotion of germination in the two fire annuals. 3 Nitrate was the principal factor inducing germination in E. penduliflora (nitrate or ammonium in P. grandiflora) whereas in S. mellifera light was the principal agent. It was also shown in E. penduliflora that nitrates are not required during chilling, i.e. seed sensitisation by chilling and nitrate-mediated induction of germination are entirely different mechanisms. 4 In the three species tested, the effect on seed germination caused by nitrogenous substances was nearly identical to that produced by an extract of charred wood, although chemical analysis of the extract showed that the combined concentrations of nitrates, ammonium ions and free amino acids could not account for the promotive action of charate. However, the nitrate and ammonium concentrations required to induce germination are very close to the increased values encountered after a fire in the otherwise nitrogen-poor chaparral soil. Therefore, in addition to the possible effect of charred wood, the postfire germination flush observed in chaparral may be induced by the increased levels of available nitrogen as well.

Effect of hypoxia on buried weed seed germination

Abstract: Summary Trials were carried out in order to investigate the effect of hypoxia on seed germination of Datura stramonium L. in Petri dishes and when buried at various depths in soil. Hypoxia was found to cause a decrease in germination capacity and germination rate. This inhibition was partially alleviated by daily exchange of hypoxic gas surrounding the seeds during incubation. Similarly, seed scarification allowed maintenance of a higher germination capacity under conditions of low oxygen availability, showing that the seed coat was only partially gas permeable. Oxygen deficiency led to a decrease in respiratory capacity. However, this was probably compensated for by induction of fermentation metabolism. The possibility of removing the final products of fermentation exerts a decisive influence on seed germination, especially in an environment such as soil, where their diffusion into the surrounding environment is restricted. Thus daily nitrogen flushing partially eliminated this inhibition, even under conditions of low external oxygen availability. It was therefore postulated that the main depth–derived inhibition was not caused directly by oxygen deficiency but by the increasing difficulty in eliminating toxic fermentation products, which was found to be proportional to the degree of hypoxia. Finally, incubation for several days under completely anaerobic conditions induced secondary dormancy. This was probably due to an ecological adaptation mechanism that prevents germination under conditions that are unfavourable for survival.

Enzyme activities of the internal hyphae and germinated spores of an arbuscular mycorrhizal fungus, Gigaspora margarita Becker & Hall

Abstract: SUMMARY A method for isolation of metabolically active internal hyphae from arbuscular mycorrhizas of onion (Allium cepa) is described. Roots of onion plants colonized by Gigaspora margarita were treated with a digestion solution containing cellulase and pectinase for 1 h at 30 °C, then homogenized with a Waring blender at low speed. The internal hyphae were collected from the homogenate by centrifugation on a discontinuous gradient of Percoll, then purified further by filtration. Enzyme histo chemical staining showed that the collected internal hyphae had active succinate dehydrogenase (SDH), alkaline and acid phosphatases (ALP, ACP). Specific activities (protein basis) of several enzymes in a crude extract of the internal hyphae were compared to those of axenically germinated spores of G. margarita. The specific activities of hexokinase, and of the enzymes involved in phosphate metabolism (ALP, ACP) and the TCA cycle (SDH, malate dehydrogenase) were much greater in the internal hyphae than in the germinated spores. The specific activity of phosphofructokinase was similar in both. By contrast, the specific activity of glucose-6-phosphate dehydrogenase was higher in the germinated spores. The metabolic change from non-symbiotic to symbiotic status of the fungus is discussed in relation to these results.