Showing papers on "Germination published in 1997"
TL;DR: This review provides both an overview of the essential processes that are associated with germination and a description of the possible impediments thereto that may result in dormancy.
Abstract: Seeds are a vital component of the world’s diet. Cereal grains alone, which comprise -90% of all cultivated seeds, contribute up to half of the global per capita energy intake. Not surprisingly then, seed biology is one of the most extensively researched areas in plant physiology. Even in relation to the topics reviewed here, a casual perusal of the Agricola database reveals that well over 5000 publications on seed germination and 700 on seed dormancy have appeared in the last decade. Yet we still cannot answer two fundamental questions: how does the embryo emerge from the seed to complete germination, and how is embryo emergence blocked so that seeds can be maintained in the dormant state? Obviously, with such a large literature on the subject, this review is far from comprehensive. Nevertheless, it provides both an overview of the essential processes that are associated with germination and a description of the possible impediments thereto that may result in dormancy. With the seed, the independence of the next generation of plants begins. The seed, containing the embryo as the new plant in miniature, is structurally and physiologically equipped for its role as a dispersa1 unit and is well provided with food reserves to sustain the growing seedling until it establishes itself as a self-sufficient, autotrophic organism. Because the function of a seed is to establish a new plant, it may seem peculiar that dormancy, an intrinsic block to germination, exists. But it may not be advantageous for a seed to germinate freely, even in seemingly favorable conditions. For example, germination of annuals in the spring allows time for vegetative growth and the subsequent production of offspring, whereas germination in similar conditions in the fall could lead to the demise of the vegetative plant during the winter. Thus, dormancy is an adaptive trait that optimizes the distribution of germination over time in a population of seeds. Seed dormancy is generally an undesirable characteristic in agricultural crops, where rapid germination and growth are required. However, some degree of dormancy is advantageous, at least during seed development. This is particularly true for cereal crops because it prevents germination of grains while still on the ear of the parent plant (preharvest sprouting), a phenomenon that results in major losses to the
2,545 citations
01 Jun 1997
TL;DR: This work focuses on the recent developments in pollen biology that help to understand how the male gamete survives and accomplishes its successful delivery to the ovule of the sperm to effect sexual reproduction.
Abstract: Many aspects of Angiosperm pollen germination and tube growth are discussed including mechanisms of dehydration and rehydration, in vitro germination, pollen coat compounds, the dynamic involvement of cytoskeletal elements (actin, microtubules), calcium ion fluxes, extracellular matrix elements (stylar arabinogalactan proteins), and control mechanisms of gene expression in dehydrating and germinating pollen. We focus on the recent developments in pollen biology that help us understand how the male gamete survives and accomplishes its successful delivery to the ovule of the sperm to effect sexual reproduction.
778 citations
TL;DR: The phytic acid in the seeds was degraded by the phytase activated during germination, thus increasing the availability of the minerals present in the germinated seeds.
Abstract: The published scientific data concerning the effects of germination on chemical composition, biochemical constituents and anti-nutritional factors of soya bean are reviewed. The amino acid profile did not change to a great extent; only a noticeable increase in aspartic acid was observed whereas there was a gradual decrease in the available lysine level and lipid content as germination progressed. Both the total protein content and the nonprotein nitrogen increased after 5 days of germination. Dietary fibres are partially degraded in germinated seeds. Germinated soya bean is an excellent source of ascorbic acid and riboflavin. Niacin contents increased distinctly after germination. Germination induced a reduction in lipase inhibitor activity. The galactosyl oligosaccharides drastically decreased in germinated seeds. After 4 days of germination, the activity of certain lectins decreased to 4% of that of ungerminated soya beans. The phytic acid in the seeds was degraded by the phytase activated during germination, thus increasing the availability of the minerals present in the germinated seeds. Germination can degrade both Kunitz soya bean trypsin inhibitor and the major Bowman–Birk soya bean trypsin inhibitor; the degradation is enhanced, if germination process lasts more than 4 days. © 1997 SCI.
281 citations
TL;DR: The positive effects of smoke have resulted in it being used as a seed pre-treatment for enhancing conservation of threatened or rare species, the horticultural exploitation of desirable plants and in the reclamation of mine spoils and disturbed land.
Abstract: Slow combustion or burning of dry or green plant material from many sources produces volatile compounds that are water soluble and that stimulate the germination of many seeds with different dormancy strategies. The active principals are apparently produced around 160ndash;200 deg;C and are volatilized at higher temperatures. Once dissolved in water the active compounds also stimulate rooting, seedling growth and flowering. The positive effects of smoke have resulted in it being used as a seed pre-treatment for enhancing conservation of threatened or rare species, the horticultural exploitation of desirable plants and in the reclamation of mine spoils and disturbed land. Presently the identity of the active molecules is unknown but their remarkable effect on seed germination is, already widely utilized.
246 citations
TL;DR: In this article, the seeds of a California chaparral annual were induced to germinate by smoke or vapors emitted from smoke-treated sand or paper, and Nitrogen oxides induced 100 percent germination in a manner similar to smoke.
Abstract: Dormant seeds of a California chaparral annual were induced to germinate by smoke or vapors emitted from smoke-treated sand or paper. Nitrogen oxides induced 100 percent germination in a manner similar to smoke. Smoke-treated water samples inducing germination were comparable in acidity and concentration of nitrate and nitrite to nitrogen dioxide (NO2)–treated samples. Vapors from smoke-treated and NO2-treated filter paper had comparable NO2flux rates. Chaparral wildfires generate sufficient nitrogen oxides from combustion of organic matter or from postfire biogenic nitrification to trigger germination of Emmenanthe penduliflora. Nitrogen oxide–triggered germination is not the result of changes in imbibition, as is the case with heat-stimulated seeds.
236 citations
TL;DR: Although the mechanisms of fungal spore germination still remain unclear, new research directions emerge that will contribute answers to more general questions of cell biology.
224 citations
01 Jan 1997
TL;DR: This work focuses on the regulation of Seed Regulation, Synthesis and Accumulation of Stored Metabolites, and Manipulation of Seeds Through Biotechnology.
Abstract: Section A: Control of Seed Development. 1. Embryogenesis in Dicotyledonous Plants R. Yadegari, R. Goldberg. 2. Development of the Suspensor: Differentiation, Communication, and Programmed Cell Death During Plant Embryogenesis B.W. Schwartz, et al. 3. Endosperm Structure and Development D.A. DeMason. 4. Hormonal Regulation of Seed Development R. Morris. Section B: The Synthesis and Accumulation of Stored Metabolites. 5. The Biochemistry and Cell Biology of Embryo Storage Proteins N.C. Nielsen, et al. 6. The Prolamin Storage Proteins of Wheat and Its Relatives G. Galili. 7. The Prolamin Proteins of Maize, Sorghum and Coix C.E. Coleman, et al. 8. The Storage Proteins of Rice and Oat D.G. Muench, T.W. Okita. 9. The Protease Inhibitors of Seeds K.A. Wilson. 10. Starch Synthesis in the Maize Seed L.C. Hannah. 11. Synthesis and Storage of Fatty Acids J. Browse. 12. Accumulation and Storage of Phosphate and Minerals V. Raboy. 13. Genetic Regulation of Carbohydrate and Protein Accumulation in Seeds M. Motto, et al. Section C: Control of Seed Maturation and Germination. 14. Lea Proteins and the Desiccation Tolerance of Seeds L. Dure. 15. Seed Maturation and Control of Dormancy J. Harada. Section D: Manipulation of Seeds Through Biotechnology. 16. Biotechnological Approaches to Altering Seed Composition E. Krebbers, et al.
211 citations
TL;DR: Considering all indices, the S index was the most sensitive, followed by the AS and CRG indices, which provided the same information, while the GT index was not precise enough in describing allelochemical actions during germination.
Abstract: Allelopathy is often demonstrated by testing allelochemical effects on germination using many germination indices to assess them. The objective of this work was to compare four common germination indices (GT, S, AS, and CRG) previously calculated with the same data in order to discuss their physiological meaning. Each index led to a different interpretation of allelochemical effect on germination. Considering all indices, the S index was the most sensitive, followed by the AS and CRG indices, which provided the same information. The GT index, which gave only a global germination interpretation, was not precise enough in describing allelochemical actions during germination. Nevertheless, none of the indices exactly reflected the germination process. Thus, simple comparisons between the control and the test at each exposure time were more appropriate.
201 citations
TL;DR: The results indicate that the cotyledons have an important nutritional function in the early establishment of seedlings in these species, and propose that large seeds might be an adaptation for enhancing establishment in nutrient-poor soils.
Abstract: summary
We examined the importance of seed size in the early establishment of seedlings of four cotyledonous species restricted to nutrient-impoverished soils in south-western Australia. Experimentally removing cotyledons from seedlings increased mortality and reduced root-penetration, growth rate and final weight of plants after 12 wk, in proportion to seed size. The impact of removal of the cotyledons was least in the smallest-seeded, Eucalyptus loxophleba Benth., grown in the more fertile of two soils, and greatest in the largest-seeded, Hakea psilorrhyncha R. M. Barker, whose growth was otherwise unaffected by soil type. In the smallest-seeded species, cotyledon content of most mineral nutrients increased over time, especially in the more fertile soil, while chlorophyll content showed some decrease by the end of the experiment. In the other species, most nutrients (especially N, P, K and Cu in the less fertile soil) were translocated from the cotyledons to the growing plant, and chlorophyll content declined markedly. The translocated N, P, K, Mg and Cu in these species made up a substantial part of the total plant content by 12 wk after germination, while total Ca and Fe tended to increase in the cotyledons via substantial soil uptake. The results indicate, contrary to reports for some other species, that the cotyledons have an important nutritional function in the early establishment of seedlings in these species. The results also show that, in the larger-seeded species, young seedlings rely to a greater extent on nutrient support from the cotyledons than from the soil. We propose that large seeds might be an adaptation for enhancing establishment in nutrient-poor soils.
199 citations
TL;DR: In this article, the phytotoxicity and phytoavailability of hydrocarbons (HC) were studied in soils artificially contaminated with fuel oil, and the presence of HC in the soil inhibited seed germination and reduced plant growth.
Abstract: The phytotoxicity and phytoavailability of hydrocarbons (HC) were studied in soils artificially contaminated with fuel oil. The presence of HC in the soil inhibited seed germination and reduced plant growth. The germination and development of cultivated plants varied with the chemical structure of HC, the HC concentration in soil, and the plant species. The LC 50 values for germination after 8 d in the presence of a fuel oil varied from 0.3 to 4% (oil/soil, w/w) for lettuce (Lactuca sativa L.), barley (Hordeum vulgare L.), clover (Trifolium repens L.), and maize (Zea mays L.) and from 4 to 9% for bean (Phaseolus vulgaris L.), wheat (Triticum aestivum L.), and sunflower (Helianthus annuus L.). Light aromatics and naphtas were the most phytotoxic HC. The inhibition of plant growth increased with HC concentration but was not linearly proportional to the loading rate. Reduction in aerial biomass was >80% for wheat and bean at a concentration of 0.3% and <30% for maize at 1.2%. No saturated nor aromatic fuel oil HC was detected by gas-chromatography in the stems and leaves of maize grown during 110 d on 1.2% oil-contaminated soil, indicating that no uptake of HC from soils occurred.
193 citations
TL;DR: Variation in success between the two methods confirmed earlier conclusions that substances contained in plant-derived smoke may be inhibitory at high concentrations for particularly sensitive species.
Abstract: Seed germination of many Australian native plant species has consistently proven to be fractious. With the discovery of smoke-mediated germination, it is now possible to better understand the heterogeneity in germination patterns for a wide range of species both in situ and ex situ. In the present study, over 180 species were examined as to viability and smoke responsiveness of freshly collected seed. Soil storage and a number of commonly used seed pre-treatments were employed in combination with smoke to examine both longevity in artificially constructed seed banks, and the role of seed ageing in improved germination. Methods of smoke application for commercial use were also investigated. Viability decline over 1 year varied between 10% and 80%. Reductions of as little as 15% were found to compromise the ability of a number of species to successfully recruit in consecutive seasons. When fresh seed was used,almost 70% of species tested responded positively to smoke whether applied prior to or after sowing. Variation in success between the two methods confirmed earlier conclusions that substances contained in plant-derived smoke may be inhibitory at high concentrations for particularly sensitive species. Only 10% of species under investigation recorded optimum germination with seed ageing alone but when smoke was applied as a treatment after soil storage, 60% of species responded positively. Implications for horticulture, rehabilitation, seed bank research and habitat management are discussed.
TL;DR: The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied.
Abstract: The role of ethylene in the release of primary and secondary dormancy and the germination of non-dormant seeds under normal and stressed conditions is considered In many species, exogenous ethylene, or ethephon – an ethylene-releasing compound - stimulates seed germination that may be inhibited because of embryo or coat dormancy, adverse environmental conditions or inhibitors (eg abscisic acid, jasmonate) Ethylene can either act alone, or synergistically or additively with other factors The immediate precursor of ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid (ACC), may also improve seed germination, but usually less effectively Dormant or non-dormant inhibited seeds have a lower ethylene production ability, and ACC and ACC oxidase activity than non-dormant, uninhibited seeds Aminoethoxyvinyl-glycine (AVG) partially or markedly inhibits ethylene biosynthesis in dormant or non-dormant seeds, but does not affect seed germination Ethylene binding is required in seeds of many species for dormancy release or germination under optimal or adverse conditions There are examples where induction of seed germination by some stimulators requires ethylene action However, the mechanism of ethylene action is almost unknown
The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied
TL;DR: In this paper, cool smoke treatments were applied to unmined Eucalyptus marginata (jarrah) forest soils, rehabilitated bauxite mine soils, and broadcast seed to determine if enhancement in germination could be effected with a view toward maximizng the establishment of species in Bauxite mines in Western Australia.
Abstract: Cool smoke treatments were applied to unmined Eucalyptus marginata (jarrah) forest soils, rehabilitated bauxite mine soils, and broadcast seed to determine if enhancement in germination could be effected with a view toward maximizng the establishment of species in bauxite mines in Western Australia.
Forest sites showed a 48-fold increase in total germinants from the soil seed bank when treated with aerosol smoke. Newly returned bauxite mine soils showed a greater than threefold increase in total germinants after the same treatment. There were also significant increases in the number of species germinating in response to the aerosol smoke treatment in both the forest and the mined soils. Similarly, application of smoked water to the soil seed bank in previously mined sites elicited a significant positive germination response, increasing total germinants and species numbers by 56 and 33%, respectively.
Treatment of mixed seed lots with aerosol smoke before broadcast resulted in highly significant improvement in germination when compared to untreated seed. Both total number of germinants, and number of species emerging from mined sites were positively influenced (85% and 34% increases, respectively).
Ten target species were used to determine the relative effectiveness of different methods of smoke treatment on the germination of broadcast seed. Nine of the species involved displayed a promotive effect with at least two of the treatments. Generally, however, aerosol smoking of seed before broadcast proved to be the more effective approach. As a result of these findings, all broadcast seed for use in Alcoa's bauxite mined areas in the southwest of Western Australia is now routinely smoke treated before application.
TL;DR: Variation in thermoperiod appears to play an important role in recovery of germination of halophytes from salt stress when seeds are transferred to distilled water.
Abstract: Recovery of seed germination from NaCl salinity of desert shrubs (Haloxylon recurvum and Suaeda fruticosa, and the herbs Zygophyllum simplex and Triglochin maritima was studied under various thermoperiods. The percentage of ungerminated seeds that recovered when they were transferred to distilled water varied significantly with variation in species and thermoperiods. Zygophyllum simplex had little recovery from all NaCl concentrations in all thermoperiods. Haloxylon recurvum, S. fruticosa, and T. maritima showed substantial recovery. Percentage recovery was highest in S. fruticosa, followed by T. maritima, and H. recurvum. Thermoperiodic effects varied with the species investigated. There was little thermoperodic effect on the percentage recovery of S. fruticosa, except in the higher salinity treatment at higher thermoperiods. Variation in thermoperiod appears to play an important role in recovery of germination of halophytes from salt stress when seeds are transferred to distilled water.
TL;DR: In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites, which seems consistent with other known effects of ABA.
Abstract: The addition of abscisic acid (ABA) to mature non-dormant seeds inhibits their germination. This effect of ABA might be related to its natural function as an endogenous inhibitor of precocious germination during seed formation. In this work, we studied how ABA affects the germination of mature seeds and the growth of nascent seedlings of Arabidopsis thaliana (L.) Heynh. Our findings were as follows: (i) inhibition by ABA was gradual, dose-dependent, and did not disappear after germination; (ii) inhibition of germination was relieved by the addition of metabolizable sugars or amino acids to the plating media; (iii) the effect of sugars and amino acids was cooperative, indicating that these two groups of metabolites relieve different deficiencies; (iv) ABA caused appreciable alterations in energy and nitrogen metabolism; and (v) ABA prevented the degradation of the seed storage proteins. In summary, ABA appears to inhibit seed germination by restricting the availability of energy and metabolites. This mechanism seems consistent with other known effects of ABA.
TL;DR: California chaparral and South African fynbos are fire-prone communities dominated by species exhibiting remarkable similarities in germination response, and there are marked regional similiarities in the type of germination behaviour associated with certain growth forms.
Abstract: California chaparral and South African fynbos are fire-prone communities dominated by species exhibiting remarkable similarities in germination response. In both regions there are a substantial number of species with germination stimulated chemically by charred wood and smoke. This type of germination behaviour has arisen independently in distantly related families and is interpreted as convergent evolution. Heat-shock is also an important germination trigger that is widespread, although in both regions it is most common in the same families. Phylogeney may play an important role in the presence of this postfire germination cue in both regions, but a much more rigorous analysis is required to show that this trait represents a single unique event in each lineage. In both regions, germination response is not randomly distributed across growth forms and there are marked regional similiarities in the type of germination behaviour associated with certain growth forms. Geophytes largely lack refractory seeds, which require fire-type cues for germination, but the presence of fire-stimulated flowering of bulbs and corms may time recruitment to subsequent postfire years. Annuals that cue germination to postfire conditions are predominantly triggered by chemicals from smoke and/or charred wood.
TL;DR: It is concluded that the immunomodulation of hormones can alter the development programme of target organs, allowing the study of the directly blocked endogenous molecules and manipulation of the system concerned.
Abstract: A single-chain Fv antibody (scFv) gene, which has previously been used to immunomodulate abscisic acid (ABA) activity in transgenic tobacco to create a 'wilty' phenotype, was put under control of the seed-specific USP promoter from Vicia faba and used to transform tobacco. Transformants were phenotypically similar to wild-type plants apart from their seeds. Anti-ABA scFv embryo development differed markedly from wild-type embryo development. Seeds which accumulated similar levels of a scFv that binds to oxazolone, a hapten absent from plants, developed like wild-type embryos. Anti-ABA scFv embryos developed green cotyledons containing chloroplasts and accumulated photosynthetic pigments but produced less seed storage protein and oil bodies. Anti-ABA scFv seeds germinated precociously if removed from seed capsules during development but were incapable of germination after drying. Total ABA levels were higher than in wild-type seeds but calculated free ABA levels were near-zero until 21 days after pollination. We show for the first time seed-specific immunomodulation and the resulting switch from the seed maturation programme to a germination programme. We conclude that the immunomodulation of hormones can alter the development programme of target organs, allowing the study of the directly blocked endogenous molecules and manipulation of the system concerned.
TL;DR: It has been proposed that germination is completed following the production of hydrolases within the surrounding tissues: these are secreted into the cell walls, causing weakening and so allowing the radicle to break out, and evidence for a causal link between the enzyme and germination in seeds of tomato and lettuce is more equivocal.
TL;DR: It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.
Abstract: In order to determine how salinity and exposure time affect seed viability and germination, seeds of five halophytes, Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis were exposed to 3.0, 5.0, and 10.0% NaCl solutions for 30, 60, 90, 365, and 730 d. Recovery experiments in distilled water indicated significantly different species responses to salinity over time. Percentage germination and rate of germination in H. jubatum were dramatically reduced following extended exposure and all seeds exposed to 10% NaCl for > 1 yr failed to germinate. Spergularia marina seeds were stimulated following short-term exposure to 3% NaCl; however, germination was delayed and overall germination was significantly reduced with exposure time in the two higher salinity levels. Percentage germination in A. prostrata decreased over time, but salinity level was not related to this reduction. Germination of S. europaea and S. calceoliformis, the most salt-tolerant species being tested, was stimulated by exposure to high salinity. Both species had a significant increase in percentage germination and in the germination rate when compared to seeds germinated in distilled water. Baseline germination data from seeds placed in 0, 1, 2, and 3% NaCl solutions indicated that S. europaea and S. calceoliformis were the only species to germinate in the 3% NaCl solution. Spergularia marina failed to germinate in the 2% NaCl treatment, and germination of A. prostrata and H. jubatum was significantly reduced at this salinity level. It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.
TL;DR: Monitoring the seed bank and “seed rain” over a 19-mo period in the eastern Mojave Desert of California suggested that virtually all seeds germinate, die, or are harvested by granivores soon after being dispersed, suggesting that understanding of desert granivore foraging and community ecology, and ofgranivore–seed interactions, depends critically on choosing the appropriate measure of seed availability togranivores.
Abstract: Patterns of resource availability mold many ecological processes, but we know little about the availability of resources to consumers in nature, even for well-studied systems such as the granivorous animals of North American deserts. What we do know about seed resources in deserts is based primarily on seeds extracted from soil samples, but this might present a distorted view of resource availability if animals mostly harvest newly produced seeds before they enter the soil seed bank. In order to assess how large the distortion might be, we simultaneously monitored the seed bank and “seed rain” over a 19-mo period in the eastern Mojave Desert of California. The seed bank averaged ≈106000 seeds/m2 and 38 g/m2, much higher than values reported for other North American desert sites. This corresponds roughly to the seed production of a single year, since daily seed rain averaged 262 seeds/m2 and 0.26 g/m2. However, input from the seed rain did not accumulate in the soil. Instead, the seed bank decreased by a daily average of 114 seeds/m2 and 0.007 g/m2 during our study. This suggests that virtually all seeds germinate, die, or are harvested by granivores soon after being dispersed. Large seeds comprised a greater fraction of the seed rain than of the seed bank, suggesting that such seeds are differentially depleted, probably by granivores, before they enter the soil. Because seed drop was seasonal, temporal variation comprised a significant component of among-sample variance in the seed rain. Temporal variance in the seed bank was much smaller, presumably because granivores harvested most of the seed rain. Conversely, spatial variance was a significant component for the seed bank, but not the seed rain, perhaps as a result of spatial patterns of seed harvest or seed caching by granivores. By virtue of these variance patterns, as well as other attributes, seeds in the soil present different challenges to granivores than do newly produced seeds. Our understanding of desert granivore foraging and community ecology, and of granivore–seed interactions, depends critically on choosing the appropriate measure of seed availability to granivores.
TL;DR: The genetic differences for seed germination between two commonly used Arabidopsis thaliana ecotypes Ler and Col, both showing a low level of seed dormancy, were investigated and 14 loci controlling the germination behaviour in the presence of the gibberellin inhibitor paclobutrazol were identified.
Abstract: The genetic differences for seed germination between two commonly used Arabidopsis thaliana ecotypes Ler and Col, both showing a low level of seed dormancy, were investigated. The analysis was performed with 98 recombinant inbred lines (RILs) derived from the cross between the two ecotypes, and these lines had previously been analysed for molecular marker composition by Lister and Dean (Norwich, UK). The analysis of germination was performed on seeds grown in three different maternal environments and each seed batch was tested in three different germination environments: in light, in darkness and in the presence of the gibberellin inhibitor paclobutrazol. Fourteen loci were identified using the multiple-QTL-model (MQM) procedure for mapping quantitative trait loci. At nine loci no significant interaction between the detection of the locus and environmental factors could be detected. However, three other distinct loci controlling the germination behaviour in the presence of the gibberellin inhibitor paclobutrazol had a much lower or no effect when germination was tested in water either in light or darkness. Two other loci affecting germination in darkness and/or light had practically no effect on germination in the presence of paclobutrazol.
TL;DR: Seasonal changes in the densities of dormant seeds in the soil around eight pioneer trees in the 50-ha Forest Dynamics Plot, on Barro Colorado Island, Panami were studied, and how seed dispersal and seed dormancy influenced patterns of seed abundance and distribution were examined.
Abstract: Seasonal changes in the densities of dormant seeds in the soil around eight pioneer trees in the 50-ha Forest Dynamics Plot, on Barro Colorado Island, Panami were studied, and how seed dispersal and seed dormancy influenced patterns of seed abundance and distribution were examined. Twenty-four, 3-cm-deep soil samples were collected on 30 m transects radiating out from each of the trees in each of four time-intervals through the year, and four 21-cm-deep samples were collected beneath the focal tree crowns. In the surface 0-3 cm of soil, germinable seed densities of all species combined declined from a peak of 1090 seeds rrT 2 in the mid-wet season in August, to 330 seeds m" 2 by the end of the wet season in November. In contrast, at soil depths >3 cm, there was little variation in soil seed bank density through the year. Some variation in soil seed bank density for individual species could be accounted for by distance to reproductive conspecifics. Among species, abundance in the soil was negatively correlated with seed size. Seed persistence varied greatly among species at this site; after 1 y of burial in mesh bags, seed germin- ability of four species was near zero, while four other species showed no consistent decline in seed germinability after >2 y of burial. For at least one species, Trema micranlha, prolonged seed dorm- ancy was also possible under natural conditions. Twenty-five percent of Trema seeds extracted from the soil at a site occupied by an isolated Trema tree that died between 1982 and 1985 were still germinable in 1994.
TL;DR: Cattle increase germination at the expense of reduced viability, whereas horses maintain viability but do not contribute to a prompt germination response, and rodents affect seed viability but enhance germination rates.
TL;DR: Three species differences suggest different functions of the mucilage of the seed coat for the three species of annual plant species from local populations that produce mucilaginous seeds.
Abstract: We studied the effect of intact, crushed or sterile cyanobacterial soil crust from the Negev Desert highlands of Israel as substrates for the germination of seeds of three annual plant species from local populations that produce mucilaginous seeds t Plantago coronopus, Reboudia pinnata and t Carrichtera annua Mucilaginous seeds of these species were wetted on local intact cyanobacterial soil crust which inhibited their germination in comparison with their germination on filter paper However, the percentage of germination of each species differed on sterile and crushed soil crust after 72 h of wetting Germination of t Plantago coronopus seeds was inhibited mechanically and biologically on intact soil crust, since it was significantly higher on both crushed and sterile soil crust Germination of t Reboudia pinnata seeds was slightly mechanically and biologically inhibited on intact soil crust, but germination on live crushed crust was higher than on sterile crushed crust By contrast, germination of t Carrichtera annua seeds was not mechanically inhibited by live soil crust but there was significant biological acceleration of germination on intact soil crust relative to crushed soil crust Each of the three species exhibited different requirements for germination Germination of t P coronopus is promoted by disturbances and removing the crust components (including its biological and structural effects) t R pinnata and t C annua germination is less affected by crust disturbance but is generally inhibited after removing the live components of the cyanobacterial crust These species differences suggest different functions of the mucilage of the seed coat for the three species
TL;DR: Results demonstrate the existence of adaptively significant variation in germination response that probably represents the beginning of genetic differentiation as a result of selection among and within founder populations.
Abstract: Bromus tectorum is a winter annual grass that has become extensively naturalized in western North America. Its seeds are usually at least conditionally dormant at dispersal and lose dormancy through dry afterripening. Germination response to temperature for recently harvested seeds and rate of change in germination response during afterripening were examined for collections from 21 western North American populations representing a wide array of habitats. Analysis of variance showed highly significant among-population differences in germination response variables. Principal components analysis of 20 germination variables revealed groups of populations that could be characterized by distinct response syndromes. Degree of dormancy at summer temperatures in recently harvested seeds as well as rate of dormancy loss during dry storage could be related to the risk of premature summer germination in different habitats. Mojave Desert populations showed the most clearly differentiated response. Populations from Intermountain desert and foothill habitats showed intermediate responses and did not form distinct groups. Montane populations showed the widest variation. Fully afterripened seeds from all populations were nondormant and could germinate quickly across a wide temperature range. These results demonstrate the existence of adaptively significant variation in germination response. Such variation probably represents the beginning of genetic differentiation as a result of selection among and within founder populations. Lack of a consistent relationship with habitat reflects the stochastic nature of colonization and the fact that diverse germination strategies may permit persistence, especially in less extreme habitats.
TL;DR: Post-dispersal seed predation and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California, are examined to suggest how seed loss affects seedling recruitment for species with long-lived seed banks.
Abstract: Whether seed consumers affect plant establishment is an important unresolved question in plant population biology. Seed consumption is ubiquitous; at issue is whether seedling recruitment is limited by safe-sites or seeds. If most seeds inhabit sites unsuitable for germination, post-dispersal seed consumption primarily removes seeds that would otherwise never contribute to the population and granivory has minimal impacts on plant abundance. Alternatively, if most seeds ultimately germinate before they lose viability, there is greater potential for seed consumption to affect plant recruitment. Of the many studies on seed consumption, few ask how seed loss affects seedling recruitment for species with long-lived seed banks. We examined post-dispersal seed predation and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California. We followed the fate of seeds in paired experimental seed plots that were either protected or exposed to rodent granivores in grassland and dune habitats. Significantly more seeds were removed by rodents in dunes than grasslands. In dunes, where rodent granivory was greatest (65% and 86% of seeds removed from plots by rodents in two successive years), there is a sparse seed bank (6.6 seeds m−2), and granivory significantly reduced seedling emergence (in the same two years, 18% and 19.4% fewer seedlings emerged from exposed versus protected plots), suggesting seed rather than safe-site limited seedling recruitment. In contrast, rodents removed an average of 6% and 56% of seeds from grassland plots during the same two years, and the grassland seed bank is 43-fold that of the dunes (288 seeds m−2). Even high seed consumption in the second year of the study only marginally influenced recruitment because seeds that escaped predation remained dormant. Burial of seeds in both habitats significantly reduced the percentage of seeds removed by rodents. Results suggest that granivores exert strong but habitat-dependent effects on lupine seed survival and seedling emergence.
TL;DR: It is indicated that Arg could play an important role in the nutrition of loblolly pine during early seedling growth and phenylphosphorodiamidate, a urease inhibitor, supported the hypothesis that arginase participates in Arg metabolism in the seedling.
Abstract: The mobilization and utilization of the major storage proteins in loblolly pine (Pinus taeda L.) seeds following imbibition were investigated. Most of the seed protein reserves were contained within the megagametophyte. Breakdown of these proteins occurred primarily following radicle emergence and correlated with a substantial increase in the free amino acid pool in the seedling; the majority of this increase appeared to be the result of export from the megagametophyte. The megagametophyte was able to break down storage proteins and export free amino acids in the absence of the seedling. Arginine (Arg) was the most abundant amino acid among the principal storage proteins of the megagametophyte and was a major component of the free amino acid pools in both the seedling and the megagametophyte. The increase in free Arg coincided with a marked increase in arginase activity, mainly localized within the cotyledons and epicotyl of the seedling. Arginase activity was negligible in isolated seedlings. Experiments with phenylphosphorodiamidate, a urease inhibitor, supported the hypothesis that arginase participates in Arg metabolism in the seedling. The results of this study indicate that Arg could play an important role in the nutrition of loblolly pine during early seedling growth.
TL;DR: It is hypothesize that the three biotic components investigated could act together to immobilize nutrients and to inhibit tree seedling regeneration and growth in late successional stages of boreal forests.
Abstract: In northern boreal forests ground level species occur which may have the capacity to suppress tree seedling regeneration substantially, particularly in late successional stages. We investigated, through an experiment involving sequential manipulations, the effects of three biotic components operating at the ground layer, i.e. aboveground effects of the ericaceous shrub Empetrum hermaphroditum and of the feathermoss species Pleurozium schreberi and the below-ground effects of extramatrical mycorrhizal hyphae, on the seedling establishment, growth and nutrient acquisition of Pinus sylvestris during two growing seasons. Germination and seedling establishment of P. sylvestris were enhanced by reduction of the above ground components of E. hermaphroditum and P. schreberi but were not influenced by temporary disruption of mycorrhizal hyphae. Seedling growth and nitrogen content were, however, significantly increased when hyphal connections were disrupted and above ground influence of P. schreberi and E. hermaphroditum were reduced. Higher shoot:root ratios were also found in seedlings when hyphal connections were disrupted. Seedlings in treatments where P. schreberi was left intact and above ground interference by E. hermaphroditum was reduced had unusually low shoot:root ratios (1.6) after two growing seasons and significantly lower total amounts of nutrients after one growing season than were initially present in the seeds, indicative of a net nutrient drain during the early establishment phase. The experiment could not explain the mechanisms behind this unexpected nutrient drain. Possible rhizosphere interactions immobilizing nutrients and causing seedling nutrient losses are discussed. From the results of this study and other indirect evidence we hypothesize that the three biotic components we investigated could act together to immobilize nutrients and to inhibit tree seedling regeneration and growth in late successional stages of boreal forests.
TL;DR: A strong genetic potential for salt tolerance during germination within Lycopersicon pimpinellifolium is indicated, and across genotypes, germination under salt-stress was positively correlated with germination in the control treatment.
Abstract: Seed of 42 wild accessions (Plant Introductions) of Lycopersicon pimpinellifolium Jusl., 11 cultigens (cultivated accessions) of L. esculentum Mill., and three control genotypes [LA716 (a salt-tolerant wild accession of L. pennellii Corr.), PI 174263 (a salt-tolerant cultigen), and UCT5 (a salt-sensitive breeding line)] were evaluated for germination in either 0 mM (control) or 100 mM synthetic sea salt (SSS, Na + /Ca 2+ molar ratio equal to 5). Germination time increased in response to salt-stress in all genotypes, however, genotypic variation was observed. One accession of L. pimpinellifolium, LA1578, germinated as rapidly as LA716, and both germinated more rapidly than any other genotype under salt-stress. Ten accessions of L. pimpinellifolium germinated more rapidly than PI 174263 and 35 accessions germinated more rapidly than UCT5 under salt-stress. The results indicate a strong genetic potential for salt tolerance during germination within L. pimpinellifolium. Across genotypes, germination under salt-stress was positively correlated (r = 0.62, P < 0.01) with germination in the control treatment. The stability of germination response at diverse salt-stress levels was determined by evaluating germination ofa subset of wild, cultivated accessions and the three control genotypes at 75, 150, and 200 mM SSS. Seeds that germinated rapidly at 75 mM also germinated rapidly at 150 mM salt. A strong correlation (r = 0.90, P < 0.01) existed between the speed of germination at these two salt-stress levels. At 200 mM salt, most accessions (76%) did not reach 50% germination by 38 days, demonstrating limited genetic potential within Lycopersicon for salt tolerance during germination at this high salinity.
TL;DR: The effects of altitude and seed size on germination and seedling survival were studied in Calluna vulgaris, Erica cinerea and Erica vagans and it was found that large seeds of Ericavagans had higher germination rates and percentages than small seeds.
Abstract: The effects of altitude and seed size on germination and seedling survival were studied in Calluna vulgaris, Erica cinerea and Erica vagans. Experiments were carried out in the laboratory over a one year period. Seeds collected from heathlands of different altitudes were divided in two size classes. They were sowed on moist filter paper inside Petri dishes which were placed in chambers at 20 °C and a photoperiod of 12 h light/12 h darkeness. The seeds of Calluna vulgaris were the first to begin germination and had the highest rate and percentage of germination. The germination of Erica vagans was moderate, while seeds of Erica cinerea germinated later and the germination was very low. Seeds of Calluna vulgaris and E. cinerea collected at the highest altitudes had the highest germination percentages. Seed size in Calluna vulgaris and E. cinerea did not affect germination. However, large seeds of Erica vagans had higher germination rates and percentages than small seeds. The large seed size of Calluna vulgaris contributes to a better survival and growth of its seedlings.