The production of hydrophilic mucilages by the seed coat or pericarp, which are released upon seed hydration, is a commonly found adaptation in angiosperms, known as myxodiaspory. These are composed primarily of pectins and hemicelluloses that undergo substantive swelling upon hydration. Synthesized in the Golgi apparatus and secreted to an apoplastic space via secretory vesicles, mucilages can also contain cellulose microfibrils or cellulosic fibres that are synthesized at the plasma membrane in association with microtubules. Investigation of mucilage production in, and differentiation of, the mucilage secretory cells of the genetic model plant Arabidopsis thaliana has identified a number of regulatory genes and enzymes involved in pectin synthesis and secretion, in muro pectin modification and secondary cell wall synthesis. Studies of the role of mucilages in both a number of species and in Arabidopsis mutants affected in its production suggest that they have multiple ecological roles. These include facilitation of seed hydration, mediation of germination under waterlogged conditions, prevention of seed dispersal or predation by adherence to soil, and promotion of seed dispersal by attachment to animals. The precise role of mucilages appears to be dependent on species and their environmental context.

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.

Conifers are evolutionarily more ancient than their angiosperm counterparts, and thus some adaptive mechanisms and features influenced by epigenetic mechanisms appear more highly displayed in these woody gymnosperms. Conifers such as Norway spruce have very long generation times and long life spans, as well as large genome sizes. This seemingly excessive amount of genomic DNA without apparent duplications could be a rich source of sites for epigenetic regulation and modifications. In Norway spruce, an important adaptive mechanism has been identified, called epigenetic memory. This affects the growth cycle of these trees living in environments with mild summers and cold winters, allowing them to adapt rapidly to new and/or changing environments. The temperature during post-meiotic megagametogenesis and seed maturation epigenetically shifts the growth cycle programme of the embryos. This results in significant and long-lasting phenotypic change in the progeny, such as advance or delay of vital phenological processes of high adaptive value, like bud break and bud set. This phenomenon is not only of important evolutionary significance but has clear practical implications for forest seed production and conservation of forest genetic resources. The underlying molecular mechanism that causes the ‘memory’ in long-lived woody species is currently under investigation. Here we summarize the information related to epigenetic memory regulation in gymnosperms, with special emphasis on conifers. The molecular mechanism behind this is still unknown but transcriptional changes are clearly involved. Epigenetic regulation may be realized through several mechanisms, including DNA methylation, histone modification, chromatin remodelling, small non-coding RNAs and transposable element regulation, of which non-coding RNAs might be one of the most important determinants.

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.

A common understanding of the control of germination through dormancy is essential for effective communication between seed scientists whether they are ecologists, physiologists or molecular biologists. Vleeshouwers et al. (1995) realized that barriers between disciplines limited progress and through insightful conclusions in their paper ‘Redefining seed dormancy: an attempt to integrate physiology and ecology’, they did much to overcome these barriers at that time. However, times move on, understanding develops, and now there is a case for ‘Redefining seed dormancy as an integration of physiology, ecology and molecular biology’. Finch-Savage and Leubner-Metzger (2006) had this in mind when they extended and re-interpreted the definition of dormancy proposed by Vleeshouwers et al. (1995), by considering dormancy as a having a number of layers that must be removed, with the final layer of dormancy being synonymous with the stimulation/induction of germination.

A group of flowering plant species is known to germinate in less than 24 h from imbibition, but this phenomenon is often overlooked in the current literature. Here, I review this topic by searching the literature published since 1967 and listing the 28 most detailed cases found. Of these, 20 are species of Amaranthaceae (all formerly treated as Chenopodiaceae); 15 of these are from the subfamily Salsoloideae, which is characterized by the possession of spiral embryos. The non-chenopods listed are small numbers of species from the families Acanthaceae, Cruciferae, Gramineae (one species) and Salicaceae (Populus and Salix). Seeds of the Salsoloideae contain fully differentiated embryos. On imbibition, the embryo cells elongate and the spiral embryo uncoils and ruptures the thin seed coat. This can occur in as little as 10 min. Nearly all of the families showing very fast germination have small to very small seeds and little or no endosperm. Most species have soft, thin seed coats that imbibe water readily. All are from high-stress habitats, either arid or saline or from active floodplains, where they can rapidly exploit temporarily favourable conditions for germination. They exhibit one of two contrasting germination behaviours, either having seeds which all germinate within a very short time of wetting or having seed persistence whereby small amounts of rain cause germination of small fractions of seed from a long-living soil seed bank. Serious confusion in the literature in the use of the term ‘opportunistic’ is pointed out and clarified.

Seeds have long been a model system for studying the intricacies of phytochrome-mediated light perception and signalling. However, very little is known about how they perceive blue and green light. Cryptochromes and phototropins, the major blue-light receptors in plants, are increasingly well-studied in vegetative tissues, but their role in light perception in seeds largely remains a mystery. Green light elicits a number of responses in plants that cannot be explained by the action of any of the known photoreceptors, and some seeds are apparently also capable of perceiving green light. Here, the responses of seeds to blue and green light are collated from a thorough examination of the literature and considered from the perspective of the potential photoreceptor(s) mediating them. Knowledge of how seeds perceive wavelengths that are suboptimal for phytochrome activation could help to improve germination and seedling establishment for both crop and native species.

Seed germination experiments are conducted in a wide variety of biological disciplines. Numerous methods of analysing the resulting data have been proposed, most of which fall into three classes: intuition-based germination indexes, classical non-linear regression analysis and time-to-event analysis (also known as survival analysis, failure-time analysis and reliability analysis). This paper briefly reviews all three of these classes, and argues that time-to-event analysis has important advantages over the other methods but has been underutilized to date. It also reviews in detail the types of time-to-event analysis that are most useful in analysing seed germination data with standard statistical software. These include non-parametric methods (life-table and Kaplan–Meier estimators, and various methods for comparing two or more groups of seeds) and semi-parametric methods (Cox proportional hazards model, which permits inclusion of categorical and quantitative covariates, and fixed and random effects). Each method is illustrated by applying it to a set of real germination data. Sample code for conducting these analyses with two standard statistical programs is also provided in the supplementary material available online (at http://journals.cambridge.org/). The methods of time-to-event analysis reviewed here can be applied to many other types of biological data, such as seedling emergence times, flowering times, development times for eggs or embryos, and organism lifetimes.

Emerging economies (Brazil, Russia, India, China and other countries) are expected to play a major role in the global economy during the 21st century. Some of these countries have exceptional soil and climate characteristics that determine evident advantages for food production. These features, combined with a rapid adoption of technologies generated by industrialized economies (i.e. transgenic crops and others), have been instrumental to fast expansion of agricultural production in recent years. For such reasons, some of these economies are strongly based on production of food commodities (agriculture represents 18.3, 12.6, 9.4 and 8.1% of the gross domestic product of India, China, Argentina and Brazil, respectively) and have a great share in global food production. Despite the mentioned characteristics that make agricultural activity so efficient in these countries, generation of new technologies in order to guarantee the systems' sustainability and add value to agricultural production (by means of, for example, royalties or technologies generated with local criteria) relies on research carried out in areas such as crop science, biotechnology, ecology, plant breeding and, of course, seed science. However, the amount of local research carried out in these countries appears not to be in agreement with the importance that agricultural production has in their economies. For example, Argentina produces 16.20% of the soybean produced in the world but only 2% of the scientific literature related to this crop in its many aspects. This imbalance between the weight that agricultural production has on these economies and generation of knowledge in the related disciplines, threatens the sustainability of these economic models and, therefore, of global food production. Seed science, then, is called on to play a major role in these emerging economies, through the different approaches (i.e. ecological, physiological, agronomical and molecular) that the discipline has to offer. Here we provide four examples in which seed science (through any of the four approaches mentioned above): (1) has identified subtle but crucial components of newly adopted production systems; (2) has proposed means for their adjustment in order to secure the sustainability of those systems; and (3) might help to add value to agricultural production through the development of new germplasm displaying specific features (e.g. timing of dormancy release adjusted to industrial necessities).

During the maturation of dicotyledonous seeds, organic carbon, nitrogen and sulphur are stored in protein storage vacuoles (PSVs) as storage globulins. Several studies point to the coexistence of storage proteins with proteases responsible for their degradation inside PSVs. Different mechanisms have been proposed to explain why there is no proteolysis during this period. Protein aggregation to form large supramolecular structures resistant to proteolytic attack could be the reason. However, during germination, and particularly following its completion, the globulin aggregates must undergo disintegration to allow protease attack for protein reserve mobilization. Based on the well-described concentration-dependent ability of Ca2+ and Mg2+ to promote in vitro aggregation and disaggregation of globulins, we explored a possible role for these alkaline earth cations in globulin packaging and mobilization. Ca2+ and Mg2+ measurements in purified PSVs [6.37 μmol and 43.9 μmol g− 1 dry weight (DW) of cotyledons, respectively] showed the presence of these two alkaline earth cations within this compartment. To our knowledge, this is the first time that Ca2+ and Mg2+ have been quantified in purified PSVs from Lupinus albus seeds. Considering the importance of these two alkaline earth cations inside PSVs, which represent 14.6% and 60.7% of the total seed Mg2+and Ca2+, respectively, globulin aggregation and disaggregation profiles were assayed using experimental conditions closer to those that are physiologically present (proportion of Ca2+ and Mg2+, and acidic pH). Based on: (1) the high in vivo abundance of Ca2+ and Mg2+ inside PSVs; and (2) globulin aggregation and disaggregation profiles, together with structural and physiological evidence already reported in the literature, an important physiological role for Ca2+ and Mg2+ in globulin packaging and mobilization inside PSVs is suggested.

Seed researchers, like anybody else working with materials containing genes, have to deal with a variety of rules. Their ‘freedom to operate’ does not only depend on intellectual property rights but also on various rights arising from biodiversity policies and possibly traditional knowledge. The most relevant are, however, patents on both materials and biotechnologies. It is in this field that recent developments indicate that the pendulum of ever-increasing levels of rights has started to swing back a little. This is due to recent court cases both in the USA and Europe, and emerging political debates in various countries. After describing the general policy arena involving national sovereign rights, private rights and ‘group-rights’ we focus on recent trends in the patent system. Seed scientists hardly even had to deal with such rights in the past, but in the 21st century they need to be aware of their implications.

Physical dormancy refers to seeds that are water impermeable. Within the Fabaceae, the structure associated with the breaking of dormancy is usually the lens. This study verified the role of the lens in physical dormancy of seeds of Schizolobium parahyba, a gap species of Fabaceae from the Atlantic Forest of Brazil. The lens in S. parahyba seeds appeared as a subtle depression near the hilum and opposite the micropyle. After treatment of the seeds with hot water, the lens detached from the coat. Blocking water from contacting the lens inhibited water absorption in hot-water-treated seeds. High constant (30°C) and alternating (20/30°C) temperatures promoted the breaking of physical dormancy and germination in non-scarified seeds. Maximum percentage of germination occurred earlier for seeds incubated at 20/30°C than for those incubated at 30°C. Seeds with a blocked lens did not germinate at alternating or high temperatures. This study suggests that alternating temperatures are probably the cause of physical dormancy break of seeds of S. parahyba in gaps in the forest.

Assessments of seed storage physiology among Arecaceae (palm) species are often inconclusive because seeds exhibit diverse responses to low temperature and moisture conditions. Interrelationships between dry matter accumulation, cell structure and water relations during seed development of the endangered Hawaiian endemic palm, Pritchardia remota, suggest that damage from drying results from mechanical strain. Endosperm and fruits accumulate dry mass through most of the 400 d gestation period, but embryos reached maximum dry mass about 250 d post-anthesis (DPA). Mostly sucrose and some triacylglycerols accumulated in the cytoplasm and vacuoles of embryo cells, and organelles in mature embryo cells de-differentiated. Water content and water potential decreased as embryos matured and embryos contained about 0.45 g H2O (g dry mass)− 1 ( − 26 MPa) at shedding. Mature embryos survived drying to 0.16 g g− 1 ( − 49 MPa), but further drying was lethal. A model of allowable cell shrinkage is consistent with the substantial, but incomplete, desiccation tolerance acquired in P. remota embryos, and provides a new framework to explain variation in critical water contents as embryos develop. We suggest that desiccation tolerance, which distinguishes recalcitrant and orthodox physiologies among seeds, can be quantified by mechanical strain when embryo cells shrink during drying.

We investigated seed dormancy among species of Melastomataceae from Neotropical montane vegetation of Brazil. Four out of 50 studied species had dormant seeds: Miconia corallina (Miconieae), Tibouchina cardinalis (Melastomeae), Comolia sertularia (Melastomeae) and Chaetostoma armatum (Microlicieae). For these four species, germinability of seeds collected in different years was always < 10% and the percentages of embryoless seeds and non-viable embryos were both insufficient to explain low or null germinability. This is the first unequivocal report of seed dormancy in tropical Melastomataceae. The production of seeds with permeable seed coats and fully developed, differentiated embryos indicates the occurrence of physiological dormancy. The reconstructed phylogenetic tree of the 50 species suggests that physiological dormancy evolved multiple times during the evolutionary history of Melastomataceae in this vegetation. Physiological dormancy evolved in species and populations associated with xeric microhabitats, where seeds are dispersed in unfavourable conditions for establishment. Therefore, drought-induced mortality may have been a strong selective pressure favouring the evolution of physiological dormancy in Melastomataceae. We argue that dormancy may have been independently selected in other lineages of Cerrado plants colonizing xeric microhabitats and dispersing seeds at the end of the rainy season. The contributions of our data to the understanding of seed dormancy in tropical montane vegetation are discussed.

This study analysed the anatomical structure of the seed coats, identified the location of water uptake and evaluated the effects of alternating temperatures and heat treatment on the breaking of physical dormancy of two species of Fabaceae (Caesalpinioideae), Cassia leptophylla and Senna macranthera, from the Atlantic forest of Brazil. The seed coats of both species consisted of a cuticle (extra-hilar region) or remaining funicle region (hilar region), subcuticular layer, palisade layer with lignin, osteosclereids, sclerified parenchyma and white cells. The palisade layer was formed by elongated macrosclereids with a light line of callose. In thermally scarified seeds of C. leptophylla, water entered through the micropylar canal, and in S. macranthera the water entered through the lens. Alternating temperatures that ranged from 15 to 30°C did not break physical dormancy of either species; however, exposure to 50°C broke seed hardcoatedness, allowing the entrance of water in both species.

The influence of light and temperature on germination behaviour and the longevity of seeds were evaluated in four taxa of the genus Arthrocereus (Cactaceae). Germination experiments were conducted at six constant temperatures with a 12-h photoperiod and in continuous darkness. For in situ storage tests, the seeds were buried in the soil where the species naturally occur, and germination experiments were performed for 14 months. Seeds were also stored dry at room temperature in the laboratory for 12 months. The results indicated that, in spite of the variations between the four taxa studied, there is a consistent pattern in their germination behaviour. The seeds are small, with an absolute requirement of light for germination. In the presence of light, we obtained high germinability at temperatures between 20 and 30°C and low germination percentages at 10, 15 and 35°C. This behaviour may represent an adaptive mechanism during seasons when environmental conditions in open rocky fields are not favourable for seedling survival. In general, germination was relatively slow, which would favour establishment during the rainy season. Dry storage did not significantly alter seed germination behaviour, and buried seeds, likewise, remained viable and retained high germination percentages. We can therefore infer that the seeds of the species studied here are able to form persistent soil seed-banks. All studied species are threatened with extinction, so their ability to form soil seed-banks, together with the possibility of ex situ seed preservation, will possibly give support for future conservation efforts.

The seed consists of three distinct regions, the zygotic embryo and endosperm and the maternal seed coat. Development of the seed requires co-ordinated growth and differentiation within each of these regions. Although the major events that occur during seed development have been studied extensively at the anatomical, physiological and molecular level, a comprehensive understanding of gene activity in each seed region has been lacking. DNA microarrays and extensive sequencing of cDNA libraries permit genome-wide analyses of mRNA populations of biological samples. We review recent studies of genome-wide gene activity that illustrate approaches used to provide new insights into the processes that occur during seed development.

The myxocarpic diaspores of Artemisia taxa are characterized by the presence of mucilage cells in the achene coat, which differ between taxa and subgenera in shape and arrangement, and the ability to form a mucilage envelope after hydration. A detailed analysis of 38 taxa revealed three main achene behaviours related to achene coat structure and the modes of water retention after hydration. The most common achene coat possessed mucilage cells which formed a mucilage envelope after hydration; normally developed mucilage cells were able to produce mucilage after wetting. In taxa where the mucilage cells were not present in the achene coat, water was gathered under a loosely adhered achene coat or in the spaces between the covering trichomes. Myxocarpic diaspores were mostly observed in taxa occurring in dry habitats, whereas taxa devoid of the ability to produce mucilage grew predominately in mesotropic habitats. The ability to form a mucilage envelope was also related to the ploidy level. The shape and arrangement of the mucilage cells in the achene coat may differ between taxa and subgenera. In Tridentatae, the mucilage cells were dispersed in groups, forming a characteristic pattern. The role of myxocarpy in the dispersal and distribution of the Artemisia taxa is discussed.

Tephroseris longifolia subsp. moravica (Asteraceae) is an endangered narrow endemic taxon recently recorded from nine sites in Slovakia and the Czech Republic. We provide the first consistent information on its reproductive biology – mating system, seed output, germination, seedling emergence and survival. Based on results from isolation, hybridization and emasculation experiments on different subspecies, T. longifolia s.l. should be treated as an allogamous taxon without apomictic reproduction. Five populations of T. l. moravica were studied in detail for seed output and germination characteristics. The output of well-developed seeds per flowering shoot was estimated to be 592 (1125 seeds per flowering plant). A granivorous butterfly, Phycitodes albatella (family Pyralidae), was identified as a pest, reducing seed output by 18–28%. Germination (reaching 30–62% after dry storage for 4 months) rapidly decreased with storage in room conditions. Deep freeze storage increased germination, although not significantly. Seeds obtained from natural populations had higher germination percentages and germinated faster than seeds from cultivated plants. Seedling emergence in situ was very low (0.9–2.06% of the sown seeds) without significant differences among sites.