Although viable seeds of Mediterranean dry-fruited shrubs are found in herbivore dung, the ecological importance of this observation is still not well understood. We analysed seed retrieval percentages, defecation time and germinability after sheep gut passage for the five most common shrub species of an area in central Spain (Retama sphaerocarpa, Cytisus scoparius, Halimium umbellatum subsp. viscosum, Cistus ladanifer and Lavandula stoechas subsp. pedunculata). Five ewes were fed seeds, and their dung was collected regularly during the following week. Seeds were hand-sorted from dung subsamples and tested for germinability. The defecated seeds were clustered in time, with a majority retrieved in the 24–40 h period, although over 1% of the seeds were retained in the gut for more than 72 h. Data suggested a possible link between seed size and retrieval, with medium-sized seeds less damaged (16–23%) than larger and smaller seeds (10–12%), although only a small number of species were studied. Germination results showed an increased percentage of germination after gut passage for H. umbellatum (x2 test, P<0.05) and a marginally significant difference for C. scoparius (P<0.1). Soft-seeded L. stoechas did not germinate after gut passage. The results indicate a potential role of herbivore endozoochory for the long-distance dispersal of dry-fruited shrubs and their potential colonization of distant sites.

Priming of seeds is generally intended to reduce time to germination, often leading to improved emergence. However, as a negative side effect, priming reduces longevity of seeds. We studied the possibilities to obtain primed seeds with reduced time to germination but with longevity similar to that of untreated seeds. For several species tested we found that the desired longevity could be obtained by keeping the seeds, after a priming treatment, under a mild water and / or temperature stress for a period of several hours to days. Time to germination did not increase again due to such a treatment. Optimal duration and degree of water stress were strongly temperature dependent. The methods applied to obtain primed seeds without loss of longevity are very similar to those used to induce desiccation tolerance in germinated seeds.

Methods of evaluation of seed quality providing accurate prediction of seed performance under field conditions are needed by the seed industry. Various physiological tests, i.e. germination tests in suboptimal conditions of temperature, oxygenation and water potential of the medium, or accelerated ageing and controlled deterioration allow sensitive differentiation between seed lots. A better understanding of the biochemical, cellular and molecular mechanisms involved in the acquisition of seed vigour during seed development, in the germination process and in seed deterioration during ageing could suggest various markers of seed quality. Among these markers, electrolyte leakage and ethylene production during imbibition, cell-cycle markers (DNA replication, β-tubulin), soluble sugar metabolism (in particular, changes in the raffinose family of oligosaccharides), proteins (11S globulin B-subunit, late embryogenesis abundant protein, heat-shock protein) and the efficiency of reactive oxygen species scavenging through antioxidant defence systems (e.g. catalase activity) have potential for the evaluation of the state of seed maturity, seed performance and effectiveness of seed priming treatments. Use of global approaches such as transcriptomic, proteomic or metabolomic analysis could also result in the identification of new markers.

Seed germination and emergence are influenced by the position of seeds in the soil bank profile. Mediterranean grasslands are heavily dependent on seed banks, as these systems are mainly composed of annual species. Seed bank germination experiments in a greenhouse were conducted to analyse the role played by burial depth on seed bank dynamics in annual Mediterranean grasslands. Specifically, they addressed two objectives: (1) to assess the ability of seeds in the shallow layer of the soil bank to emerge when they are buried at different depths, and (2) to ascertain the ability of seeds from deep layers to germinate and emerge to the surface. The study also produced a depth profile of species and seeds. The results show that: (1) all species (100%) and the majority of viable seeds (98.9%) are situated in the first centimetre, with a significant fall in the number of species and seeds in the soil bank as depth increases; (2) for the majority of species (92%) and seeds (85.4%) in the shallow bank, the emergence percentage declines significantly with burial depth; and (3) seeds that are present in deep layers need to rise to the surface in order to produce seedlings. In conclusion, the function of the seed bank in Mediterranean grasslands depends on the number of species and seeds in it, but also on the seed position in the profile and vertical movements that enable them to reach the surface.

Consider the following four quotations concerning the distinction between breaking dormancy and stimulating germination.

Water contents, desiccation tolerance, respiratory rates and subcellular characteristics of three contrasting seed types were studied during development. Avicennia marina (a tropical wetland species) and Aesculus hippocastanum (a temperate species) produce recalcitrant seeds and Phaseolus vulgaris produces orthodox seeds. During development, A. hippocastanum and P. vulgaris seeds showed a decline in water content and respiration rate with a concomitant increase in desiccation tolerance. These parameters did not change during the development of A. marina seeds once they had become germinable. There was a decrease in the degree of vacuolation and an increase in the deposition of insoluble reserves in A. hippocastanum and P. vulgaris seeds, while A. marina seeds remained highly vacuolated and did not accumulate insoluble reserves. Mitochondria and endomembranes degenerated during the development of A. hippocastanum and P. vulgaris seeds, but remained unchanged in A. marina seeds. The data are consistent with the hypothesis that extensive vacuolation and high metabolic rates contribute to desiccation sensitivity. However, the development of recalcitrant A. hippocastanum seeds is similar to that of orthodox P. vulgaris seeds. These data are in accord with the concept of seed recalcitrance being a consequence of truncated development. The results suggest that there may be three categories of seeds: orthodox seeds which develop desiccation tolerance, seeds which show similar development to orthodox seeds, but are shed before desiccation tolerance is well developed, and seeds which show no developmental trends giving rise to increased tolerance.

Mature dry legume seeds may contain up to 30 different soluble carbohydrates. Sucrose is a major component of the total soluble carbohydrates; others include the raffinose family oligosaccharides (RFOs; raffinose, stachyose, verbascose) that are mono-, di- and tri-α-galactosyl derivatives of sucrose. Other galactosides may include α-galactosyl derivatives of the cyclitols myo-inositol (galactinol, digalactosyl myo-inositol and trigalactosyl myo-inositol), d-pinitol (galactopinitol A, digalactosyl pinitol A (ciceritol) and trigalactosyl pinitol A; and galactopinitol B; higher galactosyl oligomers of galactopintiol B have rarely been detected), d-chiro-inositol (fagopyritol B1, fagopyritol B2 and fagopyritol B3) and d-ononitol (galactosyl d-ononitol and digalactosyl d-ononitol). Small amounts of myo-inositol, d-pinitol and d-chiro-inositol may also be present. Raffinose, stachyose and verbascose increase late in seed maturation, with 70% of RFOs accumulating after maximum seed dry weight is attained. RFOs are mostly degraded during germination. Sucrose, myo-inositol, d-pinitol and d-chiro-inositol are synthesized in maternal tissues of some legumes and are transported to and unloaded by seed coats into the apoplastic space surrounding developing seed embryos. Free cyclitols may be 60% of total soluble carbohydrates in leaves and 20% in seed coat cup exudates. Increasing the supply of free cyclitols may increase the accumulation of their respective α-galactosides in mature seeds. Seeds with reduced RFO accumulation, but with normal to elevated concentrations of galactosyl cyclitols (including fagopyritols), have normal field emergence and are also tolerant to imbibitional chilling under laboratory conditions. Molecular structures, biosynthetic pathways, accumulation of soluble carbohydrates in response to seed-expressed mutations and the physiological role of galactosides are reviewed.

Germination and early seedling development are critical for successful stand establishment of plants. Following germination, the cotyledons, which are derived from embryonic tissue, emerge from the seed. Arabidopsis seedlings at post-germinative stages are supported mainly by the supply of nutrition from the cotyledons until vegetative leaves emerge and initiate photosynthesis. The switch to autotrophic growth is a significant transition at the post-germinative stage. Here, we provide evidence that down-regulation of SQUAMOSA PROMOTER-BINDING PROTEIN LIKE13 (SPL13) by microRNA156 (miR156) plays an important role in the regulation of the post-germinative switch from the cotyledon stage to the vegetative-leaf stage. Silent mutations created in the SPL13 sequence in the region that is complementary to the miR156 sequence caused the deregulation of the mutant form of SPL13 (mSPL13) mRNA from miR156. Mutant seedlings over-accumulated miRNA-resistant messages and exhibited a delay in the emergence of vegetative leaves compared to wild-type seedlings. The delay was not observed in control transgenic plants expressing non-mutated SPL13, indicating that the phenotype was caused specifically by the silent mutations and deregulation of SPL13 from miR156. Characterization of the SPL13 promoter indicated that this gene is expressed mainly in the hypocotyl and affects leaf primordium development. These results suggest that the repression of SPL13 by miR156 is essential for normal post-germinative growth in Arabidopsis.

Sunflower (Helianthus annuus L.) seeds show more germination at high temperatures (25–30°C) than at temperatures below 20°C. Osmopriming with polyethylene glycol-6000 for 3–5 days at 15°C strongly increases germination at suboptimal temperatures. This stimulatory effect of priming persists after seed redrying and during subsequent storage at 20°C (55% RH) for at least 14 weeks. However, primed seeds deteriorate faster than untreated seeds during accelerated aging (45°C, 100% RH). The longer the priming treatment, the higher is the amount of germination but at the same time the higher is the sensitivity of seeds to accelerated aging. Priming enhances the respiratory activity of seeds transferred onto water and their ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. These effects remain after drying the seeds and are maintained in part during dry storage, whereas they disappear during accelerated aging. These results suggest that ACC-dependent ethylene production might be a good indicator of seed vigour; it increases with duration of priming and decreases very early during aging, well before significant loss of seed viability. Decrease in ACC conversion to ethylene indicates that aging is probably associated with membrane deterioration since in vivo ACC oxidase activity depends on membrane properties. However, no increase in electrolyte leakage is observed during aging.

Statistical analysis is increasingly used in seed germination/viability studies across different disciplines. The objective of this opinion piece is to assess current trends in statistical analysis of such data, and draw attention of readers to the limitations of the usual inferential statistics in controlling error rates. The assessments are based on a survey of 429 papers published in 139 peer-reviewed journals in the past 11 years. My intention is to identify areas of concern across a wide range of studies. Accordingly, the areas of greatest concern found in the analysis of percentage seed germination and viability data were: (1) pseudoreplication and/or use of a few replicates; (2) ignoring assumptions of ANOVA and non-parametric tests (NPARTs); (3) uncritical data transformation; (4) arbitrary choice of multiple comparison tests; and (5) lack of emphasis on effect sizes. Given the prevalence of these problems, in my opinion we would be building a body of knowledge on a shaky ground. The discussions that follow will: (1) describe situations where germination data violate assumptions of ANOVA and NPARTs; (2) highlight the implications of the various problems to Type I and Type II error rates; and (3) indicate remedial measures based on the recent statistical literature.

Cereal grain germination and early seedling growth involve the co-ordinated action of endosperm and embryo tissues to mobilize the storage reserves of the starchy endosperm. This mobilization is accomplished by hydrolases secreted from the aleurone and scutellar tissues. The breakdown products are then transported to the growing seedling by the scutellum. This resource-harvesting system is regulated at multiple levels. One well-defined aspect of control is brought about by the hormone gibberellin (GA). Gibberellin is released from the embryo upon imbibition and activates the aleurone cells. The secretory apparatus of the aleurone then proliferates, supporting increased hydrolase synthesis and secretion to degrade the starchy endosperm. The molecules that regulate this response to GA are now being increasingly characterized. Elements such as cGMP, calcium, calmodulin and protein kinases are well known as regulators in other eukaryotic cell types and are emerging as key control factors in the aleurone hormone response. However, superimposed upon this molecular regulatory system is another level of control, the structural pattern of tissues and stored macro- molecules that was laid down during grain development. It is the interaction of these structural motifs combined with the molecular regulatory mechanisms that ensure the appropriate timing and positioning of hydrolase production and endosperm reserve mobilization. This integrated control system ensures an extended release of nutrients to fuel early seedling growth.

The unique feature of the seed of tetraploid cotton (Gossypium hirsutum and Gossypium barbadense) is that about 30% of the seed coat epidermal cells develop into cellulose-enriched fibres, while the embryos synthesize oils and proteins. Hence, both the maternal and filial tissues of the cotton seed are of significant economic value. After initiation from the ovule epidermis at or just before anthesis, the single-celled fibres elongate to 2.5–6.0 cm long in the tetraploid species before they switch to intensive secondary cell wall cellulose synthesis. Thus, apart from its agronomic importance, the cotton fibre represents a model single-cell system to study the control of cell differentiation and elongation, carbon partitioning to cellulose synthesis and also the interaction between maternal (fibre) and embryonic tissues in seeds. Over the past decade or so, significant effort has been made to understand the cellular and molecular basis of cotton fibre development and oil biosynthesis in the embryo. Metabolic engineering of the oil biosynthetic pathway in cotton seed has successfully produced healthier and stable oils. A number of candidate genes and cellular processes that potentially regulate various aspects of fibre development have been identified. Further elucidation of the in vivo functions of those candidate genes could significantly deepen our understanding of fibre development and offer potential for improvement of fibre quality through genetic engineering or marker-assisted breeding approaches.

Temperature has a key influence over seed dormancy and germination, allowing wild plants to synchronize their life history with the seasons. In this review we discuss the signalling pathways through which temperature is integrated into seed physiology and the control of primary and secondary dormancy, with an emphasis on understanding maternal effects and responses dictated by the zygotic tissues. A key emerging paradigm is that temperature signalling in seeds must be understood in relation to whole plant genetics and physiology, as overlapping pleiotropic roles for temperature sensing and hormone signalling pathways are commonplace.

This is the first study to determine the class of seed dormancy (or non-dormancy) of a large number of native tree species in a tropical forest, the seasonal moist tropical forest of the Panama Canal Watershed (PCW), or to test the relationships between class of dormancy (or non-dormancy) and various seed and ecological characteristics of the constituent species. Fresh seeds of 49 of 94 tree species were non-dormant (ND), and 45 were dormant (D). Seeds of 23 species had physiological dormancy (PD), 13 physical dormancy (PY), two morphological dormancy (MD), 7 morphophysiological dormancy (MPD) and none combinational dormancy (PY+PD). Seeds with PY were significantly smaller ( < 0.1 g) and drier (moisture content < 16%) at maturity than those that were ND or in the other D classes. Seeds of 62, 42 and 53% of species dispersed in the early rainy, late rainy (LRS) and dry seasons, respectively, were ND. The majority (61%) of species with PD seeds, but only 17% of those with PY seeds, were dispersed in the LRS. The proportion of species with ND seeds was higher in large-size (63%) than in mid-size (35%) and understorey (17%) trees, but differed only slightly between non-pioneers (58%) and pioneers (54%). The proportion of species with D seeds increased only slightly through a precipitation gradient of about 3100 to 1900 mm in the PCW; however, PY increased from 19 to 32% and PD decreased from 63 to 44%.

Temperature is a significant factor influencing seed germination and for many species temperature-mediated germination cues are vital for plant persistence. Rising temperatures forecast as a result of anthropogenic climate change may have a substantial influence on the population and range dynamics of plant species. Here, we report on the thermal constraints on seed germination in natural populations of four congeneric Banksia species collected from a longitudinal climate gradient in Western Australia. We investigated whether germination niche: (1) varied between species; (2) varied among populations of each species; and (3) varied in a consistent manner reflecting the climatic gradients of seed origin. We hypothesized that species would differ and that populations from warmer sites would have a broader temperature window for germination than populations from cooler sites. Species differed in the breadth of their germination niche, but temperatures that stimulated the most rapid and complete germination were similar across all species. A sharp reduction in germination percentage occurred above the optimum temperature, which coincided with significant delays in germination relative to the optimum. The temperatures causing these declines varied among populations. Across the species, there was a significant correlation between optimum germination temperature and mean annual temperature at seed source; however, there was no relationship at the population level for individual species. These data provide insight into the vulnerability of Banksia species to climate change, with those populations that require lower temperatures for germination, or have narrower optimal ranges for germination, likely to be most vulnerable to a warming climate.

Seed dormancy is an important physiological stage in the life cycle of many seed-bearing plants. In an ever-changing environment, dormancy increases survival by distributing germination over time. In general, seed dormancy is a quantitative trait that is influenced by environmental factors. Depending on the species and accession, dormancy is controlled by nuclear factors, maternal factors or both, and dormancy can be genetically the dominant or recessive form of the trait. Wild oat (Avena fatua) is a well developed system for dormancy investigations. Dormancy in wild oat is regulated by three major genes as well as environmental factors, and dormancy is conditionally the recessive form of the trait. This paper summarizes current knowledge on genetic and environmental factors, and the interaction of these factors, on seed dormancy in several cereal grain and dicotyledonous species. Some applications of this knowledge to improve crops and manage weeds are outlined.

A commercial liquid smoke (LS) flavoring product (Reese Hickory brand) in aqueous dilutions of 4–5% (v/v) broke dormancy (40–100% germination) of both intact and dehulled red rice (Oryza sativa). To elicit this response in intact grains, the glumes had to be pricked with a dissecting needle following contact with LS and water rinsing. Germination percentages rose with increasing contact time (up to 7 d), and grains first imbibed with water before transfer to LS showed similar germination percentages as those first incubated with LS before transfer to water. LS dilutions were highly acidic (about pH 3). Dormancy-breaking activity of LS was pH-dependent and was reduced at pH values of 5–7. Buffer controls remained dormant irrespective of pH value. Maximum activity varied primarily among different bottles of LS and only to a minor extent between red rice seed lots. Dry-afterripening at 30°C for up to 14 d increased the sensitivity of unpricked, intact grains to LS compared with water controls. LS concentrations that broke dormancy of intact grains partially inhibited germination of nondormant, fully afterripened grains. Storing grains in containers of flooded soil increased sensitivity to both LS and pricking. Nitrite levels in LS were negligible and insufficient to account for the bioactivity of LS.

Seed germination of the wetland emergent perennial Phragmites australis is stimulated by diurnally fluctuating temperatures. A germination experiment in darkness and light at different temperature regimes showed that P. australis germinated as well in darkness as in light over most of the temperature regimes tested. The germination requirements could partly explain why this species, despite a large annual production of small seeds, does not accumulate a persistent soil seed bank. A second experiment examined the effect of one to four diurnal temperature cycles with amplitude of fluctuations ranging from 0 to 30°C; diurnal mean temperature of 15°C. Germination in the absence of fluctuations was low, and logistic model estimates showed a positive effect of number of temperature cycles which was strongly influenced by amplitude size. For seeds that have fallen on moist ground during the winter, these laboratory results predict that a few large diurnal temperature fluctuations could be sufficient for onset of germination in the subsequently warmer spring period. Seeds that are located under water, however, are predicted to remain ungerminated until the water level falls. Hence, we suggest that the requirement for fluctuating temperature, in addition to being a sensor for ‘exposed’ seed sites, is also effectively acting as a germination timing mechanism.

The endogenous ABA contents of dormant and nondormant barley grains were determined following application of different compounds to break dormancy. The chemicals used for breaking of dormancy in intact dormant grains were weak and strong acids, alcohols, hydrogen peroxide, cyanide, nitrate, salicylic acid, gibberellic acid and fusicoccin. The dormancy-breaking compounds could be classified into two major groups: compounds that caused a decrease in endogenous ABA (class I) and compounds which did not affect endogenous ABA (class II). Class I compounds included gibberellic acid, ethanol, hydrogen peroxide, nitrate, salicylic acid; class II compounds were fusicoccin, acid (H2SO4), sodium azide, n-caproic acid. In addition, these dormancy-breaking compounds were able to stimulate the germination rate when applied to embryos isolated from dormant grains. The concentrations necessary for stimulation of germination of isolated embryos were much lower than the concentrations for breaking the dormancy of intact grains. After embryos were isolated from dormant grains and incubated in water, ABA was determined in both embryos and in the incubation media. The class I compounds stated above also reduced ABA content in the incubation medium of isolated embryos, while class II compounds had no effect on ABA content of the medium. External application of ABA could overcome the effect of dormancy-breaking compounds of class I but not of class II. The results suggest that in the presence of the agents belonging to class II, ABA responsiveness of isolated embryos from dormant grains is decreased, compared to nontreated embryos.

The spatial variation of the soil seed bank in the steppe of Larrea divaricata and Stipa spp. was evaluated in relation to the spatial pattern of the established vegetation, over two years. Plant distribution was expected to affect the spatial pattern of the soil seed bank. It was hypothesized that patches of bare soil are seed-limited, while soil beneath the external crown of vegetation patches contains greater numbers of seeds. The soil seed bank of the steppe of Larrea divaricata and Stipa spp. displayed a patchy distribution associated with the spatial pattern of above-ground vegetation. Seed banks in areas of bare soil showed lower numbers of seeds than those beneath vegetation. The soil seed bank was dominated by annuals, both in open areas of soil and under vegetation canopies. The relative composition of the soil seed bank varied spatially. Annuals (dicots and grasses) were more abundant in grass-shrub patches (GSP) and grass patches (GP) than in incipient grass-shrub patches (IGSP) and bare soil (BS). Seeds of perennial grasses were more abundant under GP, less abundant under grass-shrub mixed canopies (IGSP and GSP) and practically absent in BS. In addition, seeds of perennial dicots were more frequent in grass-shrub mixed canopies, scarcely represented in GP and absent in BS. The concentration of seeds of perennial grasses in GP and GSP indicates that these are essential for the maintenance of the size of grass populations. Sustainable management should be focused to maintain the structure and function of these types of vegetation patches.