In contrast to reports in the literature that seeds of Dodonaea viscosa from China and Pakistan are non-dormant, or nearly so, we found that a high percentage of seeds of this species collected in north-western India have a water-impermeable seed coat at maturity, i.e. physical dormancy. Thus, seeds that were mechanically scarified and boiled (to open a ‘water gap’ in the seed coat) germinated to much higher percentages (84% and 77%, respectively) than did those that were non-scarified (24%). Our results agree with studies of seed dormancy in this species in various other parts of its large geographical range.

The heat production of seeds during germination comes from metabolism as well as hydration. Previous studies either lack continuous measurements, or are based on samples composed of more than one seed, thus failing to characterize differences among the critical phases of germination. This study examines the potential of isothermal calorimetry to characterize water uptake and metabolism in single seeds. Seeds of malting barley (Hordeum vulgare L.) and winterfat [Krascheninnikovia lanata (Pursh) A.D.J. Meeuse & Smit], two species with contrasting seed size, structure, composition and selection history, were used to determine patterns of heat production rate by isothermal calorimetry during water uptake and germination. Embryos of malting barley contributed less than 4% of total seed weight, and metabolic heat production during Phase I of germination was negligible compared to that due to hydration. Embryos accounted for 74% of seed mass for winterfat, and the majority of heat produced in Phase I was due to metabolic heat release. The total heat production rate in Phase I decreased rapidly in malting barley due to slowing of hydration reactions, but increased gradually in winterfat due to an increasing metabolic rate. The heat production rate at the end of Phase II was about twice as high in malting barley as in winterfat. This indicates a higher metabolic activity for malting barley than for winterfat seeds during germination, which may have also contributed to the rapid increase in the heat production rate of malting barley seedlings during Phase III, compared to the gradual increase in heat production rate of winterfat. The comparison between excised embryos and intact seeds indicates that the covering tissues delay radicle emergence in malting barley, but not in winterfat, due to differences in seed structure between the two species.

Crop seeds accumulate soluble carbohydrates as part of their maturation process. In legume seeds, the major soluble carbohydrates are sucrose and its galactosides raffinose, stachyose and verbascose. In buckwheat (Fagopyrum esculentum Moench) seeds, the major soluble carbohydrates are sucrose and galactosides of d-chiro-inositol, named fagopyritols. This study was conducted to determine changes in soluble carbohydrate accumulation in embryos of buckwheat seeds after feeding solutions containing the free cyclitols D-chiro-inositol, myo-inositol and d-pinitol to stem–leaf–seed explants. Feeding D-chiro-inositol to explants resulted in a fourfold to fivefold increase in the accumulation of free d-chiro-inositol, fagopyritol A1 and fagopyritol B1 in embryos of mature seeds, but resulted in 30% less embryo dry weight compared to the control treatment without cyclitols. Feeding myo-inositol to buckwheat explants increased d-chiro-inositol in leaves and increased accumulation of fagopyritol A1 and fagopyritol B1 fivefold in embryos, fagopyritol A2 and fagopyritol B2 fourfold; fagopyritol A3 and fagopyritol B3 were also detected, with no reduction in accumulated embryo dry weight. Feeding d-pinitol to buckwheat explants resulted in accumulation of free d-pinitol in mature embryos, but not galactopinitols. D-Pinitol, galactopinitol A and galactopinitol B were not detected in embryos from explants fed solutions without d-pinitol. Feeding d-pinitol also resulted in reduced D-chiro-inositol accumulation by buckwheat seeds. The results indicate that myo-inositol may be the precursor to d-chiro-inositol synthesis, and fagopyritols accumulated in response to d-chiro-inositol availability in the embryo. We suggest that increasing myo-inositol in buckwheat maternal tissues may be an effective means to enhance the accumulation of D-chiro-inositol and fagopyritols in seeds, compounds that may be beneficial for the treatment of non-insulin-dependent diabetes mellitus.

Anatomical differentiation and storage product accumulation were studied during avocado (Persea americana Mill.) zygotic embryo development using histological techniques. The results were correlated with the germination capacity under in vitro conditions. The histodifferentiation phase, characterized by active cell division and differentiation, was accomplished by 100 d after pollination (DAP), when embryos reached 16–18 mm in length. After a phase in which there were no morphological changes, the maturation phase commenced at 125 DAP in embryos 24–26 mm in length. Accumulation of starch granules and the appearance of protein bodies occurred at this time. Germination was significantly influenced by the embryo developmental stage. Different parameters used as indicators of germination quality (germination percentage, germination speed and recovery of complete plantlets) showed a positive correlation with the age of the embryos. However, germination in vitro was not achieved fully until the end of zygotic embryo development, when the embryo reached physiological maturity.

As part of a larger survey of biodiversity in private gardens in Sheffield, UK, we examined the composition and diversity of the soil seed banks in each of 56 gardens. Six soil cores from each garden revealed 2759 seedlings of 119 taxa, although the real species richness is likely to be much higher than this. By far the most abundant species were weedy natives, while the most common alien was Buddleja davidii. Seeds of perennial herbs were more abundant than hundreds of all other life forms combined. More frequent species were also more abundant, but the relationship was weak. Numbers of species in the seed bank and in the garden flora were positively but very weakly related. Seeds were quite evenly distributed between 0–5 cm and 5–10 cm soil layers, and most seeds were of species known to have persistent seed banks. Seeds of some species were largely confined to gardens in which the plant was growing, but others were not.

The seed bank of Heracleum mantegazzianum, native to the western Caucasus and invasive in Europe, was studied in the Slavkovský les Protected Landscape Area, the Czech Republic, during the course of two growing seasons. In each of seven study sites with dominating stands of the species, soil samples were taken in October (after the fruit release), April (before germination) and June–July (before the fruit release). Ten samples were taken from each site using a soil hand bore, 4.6 cm in diameter. Seeds elutriated from the samples were immediately germinated in laboratory conditions (10°C, 12 h light/12 h dark); those that germinated during 1 month were considered as non-dormant. Non-germinated but viable seeds, tested for viability by tetrazolium, were considered as dormant. The number of dead seeds was also recorded. The total number of seeds significantly increased with mean density of flowering plants at a site. Of the total variation in seed-bank size, about four-fifths were attributed to that among sites, and one-fifth to that within sites. The number and proportion of living seeds differed significantly between years in summer, but not in autumn and spring. Total number and the numbers of dormant, non-dormant, living and dead seeds significantly differed among the autumn, spring and summer samples. The percentage of living seeds in the total seed bank decreased from 56% in autumn to 42% in spring to 15% in summer. The percentage of non-dormant seeds among those living was 0.3% in autumn, it increased to 87.5% in the spring sample, and decreased to 3% in summer. Pooled across all sites, the average seed numbers (expressed per m2) were 6719±4119 (mean±SD) in autumn, 4907±2278 in spring and 1301±1036 in summer for the total number of seeds, and 3759±2906, 2044±1198 and 192±165, respectively, for living seeds. The majority of seeds (95%) were concentrated in the upper 5 cm soil layer. However, some seeds were present in lower soil layers, which indicates a short-term persistent seed bank. The present data are the first quantitative estimate of the seed bank in H. mantegazzianum, and show that the reproductive potential of the species is enormous, which seems to be a crucial feature of its invasion success.

Fire ephemerals are short-lived plants that primarily germinate after fire. Fresh and laboratory-stored seeds are difficult to germinate ex situ, even in response to fire-related cues such as heat and smoke. Seeds of eight Australian fire ephemeral species were buried in unburnt and recently burnt sites of natural bushland during autumn. Seeds were exhumed after 6 and 12 months and incubated in water and smoke water, either with or without a heat treatment at 70°C for 1 h. Generally, germination did not increase after 6 months of burial, but after 12 months of burial germination was enhanced in seven of the eight species. Actinotus leucocephalus produced higher germination following 12 months of burial without any further treatment, and smoke water and heat further improved germination. The four Gyrostemonaceae species, Codonocarpus cotinifolius, Gyrostemon racemiger, Gyrostemon ramulosus and Tersonia cyathiflora, only germinated in the presence of smoke water, and their germination was enhanced by burial. Burial improved germination in response to a heat treatment in Grevillea scapigera and Alyogyne huegelii seeds, but did not enhance Alyogyne hakeifolia germination. During concurrent dry laboratory storage of seeds at 15°C, only Actinotus leucocephalus produced increased germination in response to smoke water and heat over time. In summary, soil burial can alter the dormancy status of a number of Australian fire ephemeral seeds, rendering them more responsive to germination cues such as smoke water and heat. The requirement for a period of burial before seeds become responsive to smoke and/or heat would ensure that seeds persist in the soil until a subsequent fire, when there is an increase in nutrients available for growth and reduced competition from other plants.

This study investigated the effects of various temperature regimes on dormancy and germination in Eupatorium cannabinum, a common wetland species in Central Europe. Germination of dry-stored achenes was tested at increasing amplitudes of temperature fluctuations, and stratified achenes were germinated at constant temperatures. Dormancy release was examined in the laboratory at constant temperatures of 3, 8, 12, 15 and 18°C. The effect of an increase in temperature during stratification from 5°C to 15, 18 or 20/10°C on dormancy was tested. Moreover, achenes were exposed to yearly seasonal temperature cycles in the soil in an experimental garden. Germination of dry-stored achenes was not promoted by fluctuating temperatures, while stratified achenes germinated (>5%) over a range of constant temperatures between 9 and 36°C. Dormancy was relieved at all stratification temperatures, but temperatures ≤12°C were more effective than higher temperatures, since germination occurred over a wider range of test conditions after these pretreatments. An induction of secondary dormancy occurred only if the temperature was increased during stratification. Annual dormancy cycles were apparent when achenes were germinated at 15°C, while at 25 and 15/5°C germination was always >60%. The germination behaviour of Eupatorium is that of a typical wetland species. Thus, non-dormant achenes germinated at relatively high temperatures, and germination was promoted by fluctuating temperatures. The annual course of dormancy revealed that achenes can germinate throughout the growing season under favourable conditions. Achenes sown in an experimental garden germinated in spring, when daily mean temperatures were around 14°C. A decline in viability of achenes after 19 months' burial indicated that Eupatorium does not form a long-term persistent seed bank.

Dry plants of Mesembryanthemum nodiflorum L. (Aizoaceae), with mature seeds enclosed in their dry capsules, were collected in the Judean Desert near Jericho, Israel, in the summer of 1972, and have been stored dry under room conditions [15–30°C, 15–25% relative humidity (RH)] since then. More than 31 years after maturation, these unimbibed seeds retained an annual rhythm of germination. A significantly higher percentage of seeds originating from the terminal, central and basal parts of the capsules germinated in February or March compared to other months of the year. This phenomenon was repeated in all three groups of seeds in 2001, 2002 and 2003 for germination in darkness at 15°C, and in terminal seeds germinated at 25°C in darkness for 4 years from 2001 to 2004. The annual rhythm of M. nodiflorum germination may regulate the season and percentage of seeds that germinate at the proper time of the year, even after many years. But the open question still remains: how do dry seeds measure time, and what are the mechanisms involved?

This study addressed the difficulty of germinating drupelets (hereafter seeds) in the multi-seeded stony dispersal units (drupes) of Leptecophylla tameiameiae (Ericaceae). Embryos in fresh seeds were 77% the length of the endosperm, and seeds inside the intact drupes imbibed water. We monitored germination at 15/6, 20/10 and 25/15°C for 162 weeks, after which each drupe was cut open and ungerminated seeds counted. Drupes contained 1–6 seeds, and the total number of seeds in all treatments and controls was 1977, with 20, 29, 25, 18, 7 and <1% of them occurring in one-, two-, three-, four-, five- and six-seeded drupes, respectively. The percentage of seeds germinating in one-, two-, three-, four-, five- and six-seeded drupes was 74, 66, 65, 72, 56 and 0, respectively. Neither warm nor cold stratification for 6 or 12 weeks significantly increased germination percentages, compared to controls incubated continuously at 25/15°C for 162 weeks, where 72% of the seeds in the drupes germinated. At 25/15°C, 24–49 weeks were required for 20% of the seeds to germinate. Warm followed by cold stratification did not promote germination, and there was no widening of the temperature range for germination. Like seeds of other species known to have deep physiological dormancy (PD), those of L. tameiameiae required extended periods of time (16 to ≥162 weeks) to come out of dormancy and germinate, gibberellic acid (GA3) did not promote germination and excised embryos failed to grow. Thus, we conclude that seeds of L. tameiameiae have deep PD. However, unlike seeds of other species with deep PD, those of L. tameiameiae required an extensive period of warm rather than of cold stratification to come out of dormancy. It is suggested that a subtype a (seeds require a long period of cold stratification to come out of dormancy) and a subtype b (seeds require a long period of exposure to warm stratification to come out of dormancy) of deep PD be recognized in the Nikolaeva formula system for classifying seed dormancy.

Studies were conducted to determine if small embryos (i.e. low embryo length:seed length ratio) in mature dwarf seeds (0.2–2 mm) are underdeveloped. In this case, they would grow (inside the seed) prior to germination, and seeds would have morphological or morphophysiological dormancy. Prior to radicle emergence, embryo length in seeds of Drosera anglica (Droseraceae), Campanula americana, Lobelia appendiculata, L. spicata (Campanulaceae) and Sabatia angularis (Gentianaceae) increased 0, 103, 182, 83 and 57%, respectively. Since embryo growth did not occur in seeds of D. anglica prior to germination, embryos, although small, are fully developed; seeds have only physiological dormancy. The underdeveloped embryo in seeds of C. americana has little or no physiological dormancy; thus, seeds have morphological dormancy. On the other hand, underdeveloped embryos in seeds of L. appendiculata, L. spicata and S. angularis are physiologically dormant, and seeds have morphophysiological dormancy. Therefore, since small embryos in dwarf seeds may or may not be underdeveloped, assignment of seeds to a dormancy class requires that studies be done to determine if embryos grow inside the seed before germination can occur. Such information is important in understanding the evolutionary relationship of the different kinds of seed dormancy.

Seed banks play a crucial role in arid plant communities because they confer stability and long-term persistence. However, seed banks have high temporal and spatial variability, with dramatic changes in density and composition. The aim of this study was to test whether seasonal change affected seed bank community structure and spatial pattern. Moreover, we wanted to know if the effect driven by environmental factors on the seed bank was constant year round. We sampled the seed bank at 188 points along seven parallel transects through a gypsum system in central Spain. Soil samples were taken twice (September and April) in contiguous plots. In each plot we measured environmental parameters, including micro- and macroslope, vegetation band, shrub cover, lichen crust cover and landform. A nearly threefold decrease in seed bank density occurred between September (16,230 seeds m–2) and April (5960 seeds m–2). Seasonal changes in density varied widely among species; however, a seed bank was present for most species at both sampling dates. For several well-studied species (Lepidium subulatum and Helianthemum squamatum), seed losses were within the range of losses by emergence reported in the literature. In both seasons, seed bank composition was controlled mainly by community band and microslope. Sampling season had a significant, but minor effect on seed bank composition. Moreover, a high spatial correlation existed in terms of seed density and richness through the two studied seasons. These results show that the seed bank keeps a constant structure even under substantial variation in density.

There are two ideas regarding changes in the physiological and ecological tolerances and requirements within plant lineages through geological time. One is that these attributes have changed very little, or not at all (trait stasis), and the other is that they have undergone considerable change (adaptation), as plants shifted to new climatic and vegetation zones. We tested these ideas for seed dormancy-breaking and germination requirements of four species in a subclade of Aristolochia subgenus Siphisia: the three temperate species, A. macrophylla and A. tomentosa (the basal species in the subclade) of eastern USA and A. manshuriensis of East Asia, and the Mediterranean-climate species A. californica endemic to California, USA. A long period at cold-stratifying temperatures was required for growth of the underdeveloped embryo and seed germination in A. californica, whereas embryos grew and seeds germinated in the other three species at warm temperatures, either before or after they were cold stratified. Thus, seeds of A. californica have either intermediate or deep complex morphophysiological dormancy (MPD), whereas those of the three temperate species have either morphological dormancy or non-deep simple MPD. Further, there were quantitative differences in temperature requirements for dormancy-break and germination between the Appalachian A. macrophylla, which did not differ from its sister species A. manshuriensis, and the lowland A. tomentosa. Thus, within this lineage there has been both trait stasis and divergence (adaptation) in the physiology and ecology of seed dormancy and germination.

Seeds that store proteins in protein storage vacuoles are attractive bioreactors for producing and storing large amounts of pharmaceutical proteins. However, foreign proteins expressed in transgenic plants are subjected to the delivery and modification processes present within plant cells. Here, it is demonstrated that unique membrane sequences deliver a yellow fluorescent protein (YFP) to the seed protein storage vacuoles in transgenic tobacco (Nicotiana tabacum L.) plants, where the YFP is then separated from its membrane anchors. This precise targeting and separation is required for the successful delivery of useful proteins to seed protein storage vacuoles for their stable accumulation in transgenic crops.

In the paper ‘NO News’, Preston et al. (2004) make a number of erroneous assumptions regarding nitrogen oxide chemistry. These authors also present some very significant misinterpretations of previous research into the effects of various nitrogen oxides on germination of post-fire followers. Methodological differences between the study by Preston et al. (2004) and previous work are also problematic, such as using NO-donors in solution versus the use of direct application of various nitrogen oxides in the gaseous phase. A closer review of these studies, with the proper understanding of nitrogen oxide chemistry, and interpretations of the available literature, would lead to the conclusion that, contrary to the authors' assertions, the Preston et al. (2004) study supports, rather than refutes, earlier findings by Keeley and Fotheringham (1997, 1998a, b, 2000).

In their rebuttal, Fotheringham and Keeley (2005) (F&K, hereafter) assert that misinterpretations of previous research, errors in the presentation of the chemistry of nitrogen oxides and devious presentation of experimental results led to the conclusion of Preston et al. (2004). [These conclusions refute those of Keeley and Fotheringham's publication in Science (Keeley and Fotheringham, 1997).] We disagree and argue that the experimental evidence is consistent with the hypothesis that the ecologically relevant germination signals for the two post-fire annuals, Emmenanthe penduliflora and Nicotiana attenuata, are the specific pyrolysis products of cellulose rather than chemical scarification by nitrogen oxides (Keeley and Fotheringham, 1997).