This issue of Seed Science Research is my last at the helm. Some of you will cheer and some will sigh. As editor for the past 10 years, I have done much of what I set out to do.

The five versions of the M.G. Nikolaeva seed dormancy terminology and formulae system are correlated to each other and to the dormancy terminology proposed by Baskin and Baskin [Seed Science Research14, 1–16 (2004)]. The proposal is made that the dormancy formula scheme of Nikolaeva [Botanicheskii Zhurnal86, 1–14 (2001)] be adopted as part of an international seed dormancy classification system, and her logic for derivation of the new formulae for physiological and morphophysiological dormancy is discussed via examples. We conclude that there are several advantages of adopting formulae into a seed dormancy classification system. However, Nikolaeva's scheme, especially the part for morphophysiological dormancy, probably needs a small amount of further refinement.

The ability to initiate radicle elongation, or germination potential, occurs in developing embryos before the completion of seed maturation. Green embryos after the walking-stick stage in developing Arabidopsis thaliana seeds germinate when excised from seeds and incubated in Murashige–Skoog (MS) medium containing 1% sucrose. Germination potential is not observed during early embryogenesis at the globular, heart and torpedo stages. Here, we describe an Arabidopsis mutant with embryos arrested at early stages of development, but still exhibiting germination potential. The mutant, termed embryo ball (eb), produced shrunken seeds containing round or irregularly shaped embryos that did not germinate. The round embryos excised from developing eb seeds were capable of growing a primary root with root hairs when incubated in media. In contrast, cotyledons were absent at the apical region of the eb embryos, although the apical region produced leaf-like structures with trichomes, indicating vegetative leaf identity. These observations suggested that morphological maturation was not essential for the induction of germination potential. The eb embryos exhibited partial desiccation tolerance that is characteristic of mature embryos at later stages of development, suggesting that cell maturation was also independent of morphological maturation. The eb mutant provides novel information on cell and tissue identity in developmental biology, as well as a useful tool to dissect the mechanisms underlying the induction of germination potential in developing seeds.

The present study assessed the desiccation sensitivity of the excised embryonic axes of the following Amaryllidaceae species: Scadoxus puniceus, Amaryllis belladonna, Nerine huttoniae, N. humulus, N. bowdenii, N. filifolia, Haemanthus humulus humulus, H. coccineus, H. deformis, H. bakerae, Brunsvigia gregaria, Brunsvigia orientalis, Boophane disticha, Strumaria discifera, Crinum macowanii and C. bulbispermum. Excised embryonic axes were rapidly dehydrated (flash-dried). Curves of water content (g g− 1) and viability (%) versus drying time (min) were used to interpolate the water content (WC) and drying time (DT) values corresponding to 80% viability (WC/DT, V = 80) for individual species, and used to compare desiccation sensitivity between developmental stages and among years, provenances, species and genera. The seeds of all 16 species were shed with high axis water contents (2.25 ± 1.34 to 6.95 ± 0.89 g g− 1) and were sensitive to desiccation, with WC V = 80 values ranging from 0.13 to 3.15 g g− 1. Germination in amaryllids is unusual in that part of the cotyledon, to which the embryonic axis is attached, grows right out of the seed. It is at this stage that the axes were found to be more desiccation-sensitive in six out of nine species investigated. Seed fresh mass (SFM), axis shedding water content (SWC) and the degree of desiccation sensitivity were species characteristic. SWC, SFM and drying time were not significantly related to desiccation sensitivity. Parent plants were not confined to any particular biome type, occurring in areas characterized by seasonal dry spells. Parent plant habitat and seed characteristics were not useful in predicting the degree of desiccation sensitivity across species belonging to the same family.

The effects of maternal air temperature and soil moisture upon seed physiological dormancy (PD) alleviation of an Australian native Asteraceae were investigated. From the onset of flowering, Actinobole uliginosum plants growing ex situ were subjected to either a warm (mean 26°C) or cool (mean 17°C) temperature regime, with adequate or limited water availability. In the warm environment, the reproductive phase was accelerated, and plants yielded fewer seeds over a shorter, earlier harvest period, when compared to those in the cool environment. Initial germination of all seeds was low ( < 20% at 15°C) due to PD, which was gradually alleviated by a dry after-ripening (DAR) treatment (34/20°C, 40% relative humidity, in darkness). Seeds from plants grown in the warm environment were more responsive to DAR than seeds from the cool environment, but maternal plant water availability had little effect on dormancy status. Germination was higher at 15°C than at 25/15°C, reaching a plateau of c. 80% germination after 20 weeks DAR. Before DAR, application of GA3 had little impact on seeds, which would consequently be classified as having deep PD if tested at the time of dispersal. However, DAR caused seeds to become increasingly responsive to GA3, reaching 97% germination at 15°C following just 4 weeks of DAR, which would indicate non-deep PD if seeds were tested following a period of warm, dry storage. Maternal air temperature regulates PD status of A. uliginosum, such that seeds collected from a warmer environment are likely to be more responsive to DAR. Post-harvest storage in an environment suitable for DAR affects seed response to GA3, which has implications for germination stimulation and dormancy classification.

Plant KRP proteins are cyclin/cyclin-dependent kinase subunit (Cdk) inhibitors that share a limited homology with mammalian p27Kip1 proteins. Several KRPs have been reported in maize (Zea mays L.), of which Zeama;KRP1 was studied during maize germination. Expression of the Zeama;KRP1 gene did not vary during the 24 h germination period. A homologous antibody raised against the 13 kDa carboxy end of the Zeama;KRP1 polypeptide, a sequence containing the cyclin/Cdk inhibitory domain, indicated the existence of a 22 kDa protein in maize embryonic axes, the amount of which also remained unchanged during germination. Neither abscisic acid nor cytokinins modified the amount of protein. The purified Zeama;KRP1 polypeptide inhibited the kinase activity associated with Zeama;PCNA and Zeama;CycD2;1, and also the kinase activity in p13Suc1-pulled-down complexes. However, there were differences in the inhibition pattern during germination. Whereas kinase activity in proliferating cell nuclear antigen (PCNA) or CycD2;1 immunoprecipitates was strongly inhibited mainly during early germination, that in p13Suc1-pulled-down complexes was mainly inhibited at late times, suggesting that each protein complex is composed of different cyclins and/or Cdks.

The rice (Oryza sativa L.) cv. Taichung 65, a japonica subspecies, was used to characterize the isoform, protein and gene expression patterns of endo-β-mannanase during and after seed germination. Activity assays and isoform analyses of whole grains or seed parts (scutellum, aleurone layer and starchy endosperm) revealed that seeds began to express endo-β-mannanase activity at 48 h from the start of imbibition at 25°C, after the completion of germination of most seeds. Three isoforms of endo-β-mannanase (pI 8.86, pI 8.92 and pI 8.98) were detected in the aleurone layer and starchy endosperm, but only two (pI 8.86 and pI 8.92) were present in the scutellum. The endo-β-mannanase in the starchy endosperm was mainly from the aleurone layer. Western blot analysis, using a tomato anti-endo-β-mannanase antibody, indicated that an endo-β-mannanase protein was present in an inactive form in dry grains. The amount of this protein decreased in the scutellum, but increased in the aleurone layer during and after germination. Thus, the increase in endo-β-mannanase activity in rice grains may be due to the activation of extant proteins and/or the de novo synthesis of the enzyme. Northern blot analysis showed that four putative rice endo-β-mannanase genes (OsMAN1, OsMAN2, OsMAN6 and OsMANP) were expressed in germinating and germinated rice grains. However, OsMANP was not expressed in the scutellum. The amount of OsMAN6 mRNA decreased after the completion of germination and paralleled the decline in endo-β-mannanase protein. In the aleurone layer, the increase of OsMAN2, OsMAN6 and OsMANP mRNA was prior to the increase of endo-β-mannanase protein.

Lannea microcarpa, a multipurpose tree species from the dry African savanna, sheds seeds that often display inhibition of germination. The underlying mechanism was investigated using seeds processed from fully matured fruits collected from natural stands in Burkina Faso. Germination of fresh seeds was variable (16–28%), while they did not germinate after drying and rehydration. Mechanical scarification of the endocarp at the proximal end of the seeds increased germination to 83–94%. Scarification on the distal end led to delayed radicle emergence through the produced hole in c. 40% of the seeds. The endocarp was permeable to water and respiratory gases. Increased water content in scarified seeds was associated with radicle extension during germination. Intact and scarified non-germinated seeds displayed a moderate rate of respiration with respiratory quotient (RQ) values of c. 1. Respiration increased and RQ decreased to c. 0.7 with radicle emergence. Ethylene evolution peaked in both intact and scarified seeds at the beginning of incubation and then decreased to low values. Inhibition of ethylene production by 1–5 mM 2-amino-ethoxyvinylglycine (AVG) caused only a partial decrease of germination of the scarified seeds. Intact non-germinated seeds gradually lost viability during incubation at 30°C, but could be rescued by delayed scarification before day 15 of incubation. It is concluded that radicle emergence in dry L. microcarpa seeds is inhibited only mechanically. The mechanical properties of the endocarp are attributed to irreversible structural changes of the lignin–hemicellulose complex, which occur during drying.

When detecting the adventitious presence of transgenic plants (AP), it is important to use an appropriate testing method in the laboratory. Dorfman's group testing method is effective for reducing the number of laboratory analyses, but does not consider the case where AP is diluted below the sensitivity of the analyses, which causes the rate of false negatives to increase. The objective of this study is to propose binomial and negative binomial probabilistic models for determining the required sample size (n), number of pools (g), and size of the pool (k) for detecting individuals possessing AP with a probability ≥ (1 − α) (for a small α) given: (1) pool size (k); (2) estimated proportion of individuals with AP in the population (p); (3) concentration of the trait of interest (AP) in individual seeds (w); and (4) detection limit of the test (c) (AP concentration in a pool below which it cannot be detected). The proposed models consider the different rates of false positives (δ) and false negatives (λ), and the assessment of consumer and producer risks. Results have shown that when using the negative binomial, a required sample size n can be determined that guarantees a high probability that m individuals or g pools containing AP will be found. The pools formed have an optimum size, such that one element with AP will be detected at a low cost. The negative binomial distribution should be used when it is known that the proportion of individuals with AP in the population is p < 0.1; thus, it is guaranteed that m individuals or g pools of individuals with AP will be detected with high probability.

In temperate plant communities, seed size is often inversely related to seed longevity at the species level. We tested if the inverse relationship between seed size and seed longevity holds among individuals within populations of Ambrosia trifida L. (Asteraceae), a summer annual agricultural weed in the eastern United States Corn Belt that typically emerges in two successive flushes: one before 1 May and one after 1 May. The effects of maternal phenotype on seed morphology, seed weight, late emergence (emergence after 1 May) and seed-bank persistence were determined in two 1-year experiments. All seeds were collected from individuals at weekly intervals for 3 weeks. Sixty seeds per collection were used in the analysis. Despite fluctuating environmental conditions during seed development, seed weight within maternal families remained constant for different maturation times. Differences among families constituted 69% of total variation in seed weight, whereas differences within maternal families composed 31% of the variation in seed weight. Percentage late emergence and percentage seed-bank persistence varied among maternal families. In four maternal families, either 0% or 100% of seedlings emerged after 1 May, but a majority of other maternal families produced seedlings both before and after 1 May. Seed-bank persistence rates ranged from 1 to 51% among maternal families. Percentage late emergence and percentage seed-bank persistence were inversely related to maternal-family mean seed weight in 2006, but not in 2005. These results suggest that the inverse relationship between seed size and seed longevity occurs among individuals of a population, but is affected by the environment.

While red rice (Oryza sativa L.) can remain dormant and viable for many years when fully imbibed, the environmental factors that stimulate germination or induce secondary dormancy in the field have not been characterized. In this study, the interactions between the extent of dry-afterripening and germination temperature have been evaluated as possible factors. Red rice dispersal units (florets) were afterripened for 0–10 weeks at 30°C and incubated in water at 1, 5, 15, 20, 25, 30 and 35°C for 2 weeks; then, all the ungerminated florets were transferred to 30°C for two additional weeks. Germination at the end of each of the two sequential treatments was compared to define both the effect of differing temperatures on germination (first treatment), and the effect of these temperatures on subsequent germination at the optimum temperature (30°C, second treatment). In afterripening red rice, the opening of the temperature window for germination begins at 25–35°C. Fully dormant florets acquired the ability to germinate ≥ 90% at 30°C after 4 weeks of dry-afterripening. However, imbibing florets for 2 weeks at 15°C followed by 2 weeks at 30°C, yielded suboptimal germination and induced a degree of secondary dormancy, dependent upon the extent of previous dry-afterripening. Cold stratification (1°C) had a consistent promotive effect on the subsequent germination, particularly when preceded by 1–2 weeks of dry-afterripening at 30°C. To monitor the effects of germination temperature, median afterripening time was utilized as a relative dormancy index, and changes in this index have been interpreted as an overlapping of germination and the temperature-induced changes in the dormancy status. Field weather data suggested that low-temperature stratification may be a germination trigger in the field, even in southern Louisiana, and this merits further investigation in studies of soil-buried seeds.

Little is known about the seed ecology of annual holoparasites, such as Cuscuta (dodders), and how germination is timed to occur when seedlings can attach to a host. Seeds of Cuscuta epithymum, which is a rare and often threatened species in dry heaths of north-western Europe, were water-impermeable (physically dormant) at maturity in late summer. An 8-week period at 5°C, followed by incubation at 23, 15/6 or 30/20°C, resulted in 15–30% germination. Thus, in nature, only part of the seed population exposed to low winter temperatures and a subsequent warm spring potentially becomes water-permeable and can germinate in spring. When scarified seeds were cold-stratified at 5°C for 8 weeks and then incubated at 23°C, essentially all the viable seeds (c. 65%) germinated. It is concluded that seeds have a combination of physical (PY) and physiological (PD) dormancy (the first to be reported in the Convolvulaceae), which is interpreted as a double safety mechanism preventing germination at unfavourable times or places. After PY and PD were broken, seeds did not require light or fluctuating temperatures for germination. Some loss of PD (afterripening) can occur before PY is broken. These data indicate that a portion of the seed crop remains physically dormant in spring and potentially forms a persistent seed bank, a strategy that eliminates the risk of a total reproductive failure in a particular bad year.

Mammalian herbivores can play a role in the endozoochorous dispersal of Prosopis seeds in the arid zones of Argentina, and the introduction of exotic mammals can change relevant parameters of the plant's reproductive ecology. Our specific goals were to quantify the seeds of Prosopis flexuosa, P. chilensis and P. torquata contained in the faeces of native [mara (Dolichotis patagonum), guanaco (Lama guanicoe)] and exotic [donkey (Equus asinus) and hare (Lepus europaeus)] mammals, and to determine the mortality, germination percentage and germination speed of seeds borne in faeces, compared with those collected from trees. In 2006, seeds were collected directly from trees or removed from mammal faeces. Seeds were counted and classified as apparently healthy or damaged. P. torquata and P. flexuosa seeds were found in the dung of guanaco, hare and mara, whereas only P. flexuosa seeds appeared in donkey faeces. P. chilensis seeds were only found in guanaco faeces. There was a notable relative abundance of seeds contained in small herbivore faeces in comparison to the large herbivores. The passage through the digestive tract of animals modified seed germination capacity and speed, with great variability between animal species. Guanacos had greater effects than donkeys on mortality, germination percentage and germination speed. Differences between the effects of both smaller-sized herbivores on seeds were much smaller.

To understand germination timing in an ecological context, the response to environmental events that affect seed dormancy is central, and has to be combined with knowledge of germination responses to different circumstances. In this study, seed dormancy, germination and emergence phenology of six annual co-occurring weedy Asteraceae species were investigated. Three pre-treatments (warm and cold stratification, and dry storage) were tested as possible dormancy-affecting environmental events. Seeds were also sown outdoors. Species-specific differences were revealed in analyses. To facilitate general descriptions of dormancy patterns and germination preferences separately, condensed responses to the different possible dormancy-affecting treatments and relative germination in different environments were plotted, giving species-specific patterns. Most species exhibited decreased dormancy to two or three pre-treatments. Dormancy was most effectively reduced by cold stratification for three species (Guizotia scabra, Parthenium hysterophorus, Verbesina encelioides), by warm stratification for two (Bidens pilosa, Galinsoga parviflora) and by dry storage for one (Tagetes minuta). All species germinated more when provided with light than in continuous darkness. Temperature levels most suitable for germination varied from low (15/5–20/10°C) for V. encelioides to high (25/15–30/20°C) for B. pilosa. It is concluded that, even though the species have different dormancy patterns and germination preferences that suggest different possible distribution ranges, they achieve similar emergence timing in the field in environments with a pronounced dry period after dispersal and small annual temperature fluctuations.

Torilis japonica (Apiaceae) has a widespread distribution, extending from western Europe to eastern Asia. In Europe, it usually behaves as a spring-germinating biennial species. Ripe seeds of T. japonica have an underdeveloped embryo and can persist in the soil for several years. The aim of this research was to reveal the mechanisms regulating the seasonal emergence pattern of seedlings. Experiments in a natural environment were performed to study phenology of seedling emergence and embryo growth. Seasonal changes in the dormancy status of T. japonica seeds were examined by regularly exhuming buried seeds and incubating them in controlled conditions. The action of temperature and light in regulating dormancy, embryo growth and germination was studied in the laboratory. Results showed that seeds of T. japonica have non-deep, simple morphophysiological dormancy (MPD), whereby physiological dormancy is broken by moist chilling (5°C). Once MPD was broken, embryo growth and subsequent germination started in spring, when appropriate temperature and light conditions were present. Seeds buried at a depth where light could not reach them showed cyclic changes in their dormancy status; embryo growth in these seeds could not be initiated because of the lack of a light stimulus. As far as we know, this is the first extensive study of seasonal dormancy cycles in a spring-germinating species of the Apiaceae. T. japonica occurs in a temperate climate with cool winters and warm, moist summers. In this climate, spring is often the most favourable season for seedling establishment.

Although various aspects of the biology of Anemone nemorosa have been examined, few studies present data on seed germination, and even then information tends to be rather contradictory. A. nemorosa L. is a spring-flowering, woodland geophyte, widely distributed across much of Europe. Germination phenology, including embryo development and radicle and shoot emergence, were investigated in one mountain and three lowland populations from northern Italy. Immediately after harvest, seeds were either sown on agar in the laboratory under simulated seasonal temperatures, or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of dispersal, grew under summer conditions in the laboratory and in the wild. However, seeds did not germinate under continuous summer conditions. Radicle emergence in the field was first recorded at the beginning of autumn, when soil temperatures had dropped to c. 15°C in the case of the three lowland populations, and to c. 10°C at the mountain site. Shoot emergence was delayed under natural conditions until late autumn/early winter, when soil temperatures had dropped to c. 10°C in the lowlands and c. 6°C at the mountain site. In the laboratory, a period of cold stratification was required for shoot emergence, and this requirement was more pronounced in the mountain population. Seeds of the mountain population completed embryo development, radicle emergence and shoot emergence at cooler temperatures compared with the lowland populations. These results suggest that germination in A. nemorosa is highly adapted and finely tuned to local climate. We conclude that seeds of A. nemorosa display deep, simple epicotyl, morphophysiogical dormancy, and this is the first report of such dormancy for the genus Anemone. However, the continuous development and growth of embryos from the time of natural dispersal, and the lack of evidence of developmental arrest under natural conditions, suggests that radicles are non-dormant.

The seed-bank dynamics of Ambrosia artemisiifolia (Asteraceae), an annual invasive plant introduced from North America to Europe, were studied in nine French populations developing in field crops, set-asides or wastelands. The vertical distribution of seeds was studied in two different depth sections (0–5 cm and 5–20 cm), and the spatial horizontal pattern of distribution was analysed for two selected field-crop and set-aside populations. The proportions of dormant, non-dormant and dead seeds, as well as the changes in seed-bank dormancy over time, were evaluated. Natural seedling recruitment and its variation under different disturbance treatments in competitive set-asides were also studied. From 536 ± 194 to 4477 ± 717 seeds m− 2 were found in the living seed bank (0–20 cm). The majority of seeds in field crops was found in the lower soil layer, whereas the opposite pattern was observed in set-asides and wastelands. Dormant seed proportions were low (0–18%) before natural germination, but then regularly increased. The seed bank of A. artemisiifolia was spatially aggregated irrespective of the extent of soil disturbance. On average, 23 ± 12 to 292 ± 62 seedlings m− 2 were recorded, with densities lower in set-asides than in field crops and wastelands. Seedling densities were not correlated to upper seed densities except for two field crops. Soil disturbance and the removal of vegetation had positive effects on seedling recruitment in set-asides. Seed-bank dynamics appear to be crucial in the invasive success of A. artemisiifolia, and this knowledge will provide insights for the management of the species.

Convolvulaceae is the only family in the asterid clade with species that produce physically dormant seeds, and most studies on germination in this family have focused on scarified seeds. However, no study has been done on the taxonomic/evolutionary pattern of seed dormancy in Convolvulaceae. We determined the moisture content of non-treated seeds and water uptake and germination percentages for non-treated and manually scarified seeds of 46 species in 11 of the 12 tribes in this family. Germination was tested over a range of temperatures in light/dark and in the dark. The effect of drying and storage at low temperatures was tested on seeds of Erycibe henryi and Maripa panamensis, the only species with high initial moisture content. Non-treated fresh seeds of Bonamia menziesii, M. panamensis and E. henryi imbibed water, whereas those of the other 43 species did not. Manually scarified seeds of all these 43 species took up large amounts of water. Therefore, seeds of 43 of the 46 species are physically dormant, and three are non-dormant. Seeds of all 46 species germinated after imbibition, except those of Cuscuta europaea, which are reported to have combinational dormancy. M. panamensis and E. henryi seeds are recalcitrant and those of the other 44 species orthodox. In Convolvulaceae, basal tribes or tribes derived from basal tribes contain species with non-dormant recalcitrant, physically dormant orthodox and combinationally dormant orthodox seeds. Physical dormancy of seeds in this family possibly evolved from a non-dormant recalcitrant seed-producing ancestor closely related to Erycibeae.

The soluble selenium (Se) compounds selenic acid, selenious acid, selenium dioxide, selenium tetrachloride, selenomethionine, selenourea, sodium selenate and sodium selenite broke the dormancy of scarified seeds of Townsville stylo (Stylosanthes humilis HBK). Given the chemical diversity of all these molecules, it could be deduced that Se may act as a dormancy-breaking agent of Townsville stylo seeds. Se-stimulated seeds produced great amounts of both ethylene and 1-aminocyclopropane-1-carboxylic acid, which correlated with the process of germination. As specific inhibitors of ethylene biosynthesis and action largely depressed this Se-stimulated germination, it was concluded that Se broke dormancy by triggering ethylene production by the seeds.

Seed salinity tolerance and dormancy play important roles in germination behaviour. The effects of NaCl concentration and different dormancy-breaking treatments on germination were determined for six species growing on the coasts of the Baltic Sea or the Gulf of Riga: Juncus balticus, Triglochin maritima, Triglochin palustre, Anthyllis maritima, Linaria vulgaris and Linaria loeselii. Germination percentages were significantly reduced at NaCl concentrations >100 mM. Germination of J. balticus, T. maritima and T. palustre, but not that of A. maritima and L. vulgaris, recovered after seeds were rinsed with distilled water. Seeds of J. balticus were non-dormant; those of A. maritima had physical dormancy; and those of T. palustre, T. maritima, L. loeselii and L. vulgaris had non-deep to intermediate physiological dormancy, which was broken by cold stratification or gibberellic acid. The seeds of plants growing in habitats periodically exposed to sea water (coastal meadows) were characterized by greater salinity tolerance than seeds of plants growing in habitats less exposed to sea water (dunes).