Pea landraces may hold genetic variation that can be exploitable in breeding/selecting new cultivars. In a small-seeded pea landrace, four phenotypes were distinguished according to testa (green, non-spotted and green, spotted) and hilum colour (white, black). The four phenotypes were tested for two growing seasons in the field for pod (seeds/pod) and seed traits (1000-seed weight, toughness, total phenols and tannins, testa colour, protein and carbon concentration, C/N ratio, bruchid infection). Significant differences were found for testa colour parameters, phenolic, tannin and carbon concentration and bruchid tolerance. The larger-seeded, spotted peas had darker testa and more phenols, while white-hilumed peas had lighter testa and more tannins. The spotted, black-hilumed phenotype, with the highest carbon concentration and C/N ratio was the most tolerant to bruchids. However, grouping the phenotypes, neither spotted nor black-hilumed ones showed to be more tolerant compared with their counterparts. Concluding, our results showed that phenotyping variation in seeds of a pea landrace revealed variation in seed traits, which could be exploitable. Since testa and hilum colour were associated with specific seed traits, they could, alone or in combination, be used as biomarkers of seed quality traits in pea. Testing of larger number of phenotypes is needed to solidify our findings.

Seed germination implies an expansion process restarting the growth of the embryonic axis (Ax) and which is completed by radicle emergence through the seed covering layers. In developing soybean seeds, abscisic acid in Ax (ABAa) mainly inhibits Ax growth. Additionally, the expression of the EXP1 gene at the elongation zone (EZ) was found to be involved in the promotion of mature soybean Ax growth, which increased during water incubation and which was repressed by exogenous ABA. This work aimed to evaluate (1) the ABAa and EXP1 levels at the EZ and (2) the role of the seed coat (SC) in developing soybean seed germination. Whole seeds (Se), embryos (Em) and Ax at 25–45 d after anthesis (DAA) germinated in vitro, and germination performance increased with DAA. ABAa decreased in planta from 25 DAA until its critical non-inhibitory threshold (ABAc) at around physiological maturity (45 DAA). At earlier ages, the ABAc was reached during the in vitro incubation. Concomitantly, EXP1 transcripts accumulated with age into the pool of long-lived mRNAs and were up-regulated during incubation. Additionally, isolated Ax germinated faster, took up more water and increased its water potential more rapidly during incubation than Ax in Se. Also, a lower osmotic gradient was required to germinate at 45 DAA, when ABAa was no longer inhibitory. Simultaneously, the pressure to protrude SC through the micropylar area increased from 25 to 45 DAA. These results support the role of ABAa and EXP1 in controlling Ax growth and the SC in delaying radicle protrusion.

Seeds of Papilionoideae (Leguminosae) species lose water after dispersal, increasing the proportion of water-impermeable seeds (physical dormancy, PY). However, changes in testa structure during this process remain unknown. The present study investigated how variation in relative humidity (RH) during the post-dispersion period affects the proportion of seeds of Erythrina speciosa with PY. Seeds from two populations were stored in drier (40% RH) and wetter (80% RH) environments and periodically subjected to physiological analysis (seed water content, imbibition and germination) and structural analysis of the testa (light and scanning electron microscopy). Drier storage resulted in seed dehydration, increasing the proportion of water-impermeable seeds and closure of cracks in the mucilaginous stratum. In contrast, wetter storage led to an increase in seed water content, a decrease in the proportion of seeds with PY, and the formation of cracks. As a result of variation in environmental humidity, we conclude that changes occur in the mucilaginous stratum of seeds, altering water loss and, consequently, the proportion of seeds with PY. Environments with low humidity cause a decrease in seed water content, the closing of cracks in the mucilaginous stratum, and, consequently, an increase in the proportion of water-impermeable seeds. On the other hand, a high RH environment increases the seed water content and the formation of superficial cracks, through which water enters during imbibition, causing a decrease in the proportion of seeds with PY.

In higher plants, the seed precursor (ovule primordia) is composed of three parts: funiculus, nucellus and chalaza, generating the latter one (II) or two (OI and II) protective maternal integuments (seed coat, SC). The appearance of a viable seed requires the coordinate growth and development of the preceding three compartments. Integuments are essentials for seed life as they nourish, protect and facilitate seed dispersion. Endosperm and integument growth and development are tightly coupled. Gymnosperm and angiosperm ovules are commonly unitegmic and bitegmic, respectively. Unusually, ategmy and threetegmy (OI, II and aril) also exist. The expression of the INO, ATS and ETT genes, involved in integument development, seems to have demonstrated that the fusion of OI and II leads to the appearance of unitegmy in higher plants. Likewise, INO expression also manifests the conservation of OI during evolution. The molecular control of SC development is constituted by a signalling network with still a multitude of gaps. The fertilization-independent development of the ovule is repressed by the FERTILIZATION INDEPENDENT SEED (FIS), a Polycomb-Repressive-Complex-2 (PRC2). Both endosperm and SC development are tightly linked to PRC2 function. As in many other developmental processes, auxin plays an essential role during ovule and SC development. Auxin transport from the endosperm to the integuments is regulated by AGL62 (AGAMOUS-LIKE 62), the encoding gene of which is specifically expressed in the endosperm to suppress its cellularization. In the absence of AGL62 (i.e. agl62 mutants), auxin remains trapped in the endosperm and the SC fails to develop (i.e. seed abortion). This update shows that auxin biosynthesis, transport and signalling play a predominant role and seem to be absolutely required in the pathway(s) that lead to SC formation, most likely not as a unique hormonal component.

Physical dormancy (PY) occurs in at least 18 angiosperm plant families and is caused by water-impermeable palisade cells in seed (or fruit) coats. Breaking of PY involves disruption or dislodgement of water-gap structures causing the seeds/fruits to become water permeable (non-dormant). The water-gap region is a morphologically distinct area of the seed or fruit coat that forms a water-gap complex. The location, anatomy, morphology and origin of water-gaps can differ between and even within families and genera. Water-gap structures sense environmental conditions that allow seeds with PY to become permeable just prior to the commencement of conditions favourable for germination and plant establishment. There are three basic water-gap morpho-anatomies characterized by the way the water-gap opens: Type-I, Type-II and Type-III. In Type-I water-gaps, specific kinds of cells pull apart to form a surface opening, while in Type-II a portion of the surface structure is pulled away from adjacent cells, opening the water-gap. Type-III is the least common type and has a circular, plug-like structure that is dislodged, whereby water entry occurs. In addition, water-gap complexes are either simple or compound, depending on whether only a single primary water-gap structure is involved in dormancy release or an additional secondary water-gap structure opens, permitting water entry.

Seed heteromorphism is the formation of different seed morphs from the same individual. Two seed morphs have been preliminarily observed in Leptocereus scopulophilus. One morph shows an apparent natural scarification of its coat. Herein we describe the seeds, taking into account shape, coat integrity, surface, dimensions, mass and the position of germination cracks. We defined two seed morphs using the integrity of the spermoderma: fragmented seed coats (FSC) and complete seed coats (CSC). We also evaluated minimum germination time, germination rate and germinability. The seed morphs did not differ significantly in traits; however, regular striations along the cuticle of the periclinal walls were more visible in the FSC compared with the CSC. Both seed morphs displayed anticlinal cell boundaries in the border region that are channelled and straight in the dorsal-ventral region but difficult to define in the lateral region. We found four morphological variations in different positions where the radicle or cotyledons emerge and variations in cuticle thickness in different regions of the seed that could determine the formation of cracks during germination. All germination variants occurred in both seed morphs, albeit in different proportions. Germination was higher and faster for the FSC compared with the CSC. These germination differences could be related to a thinner cuticle in the FSC and the punctual release of its spermoderma, which facilitates a quick imbibition of the embryo and the breaking of the seed coat. Our results indicate that differences in germination parameters between the two seed morphs relate to differences in the percentage of dormant seeds, which favour the temporal expansion of germination and reduce competition between siblings. To propagate the species for conservation purposes, we recommend using FSC, while CSC may be used to establish a seed collection ex situ.

The anatomy of the husk (lemma and palea) and caryopsis coat (pericarp, seed coat or testa, and nucellar epidermis) of a typical mature wild oat (Avena fatua L.) caryopsis was investigated using both scanning electron microscopy and light microscopy. Both the lemma and palea consist of very thick-walled, lignified cells. In section, the lemma appears almost twice as thick as the palea. The pericarp is comprised of only one or two layers of relatively thin-walled cells and is closely appressed to the underlying seed coat over most of the grain. Both the outer seed-coat cuticle and the inner cuticle are present over almost the entire caryopsis and are continuous with the pigment strand that occurs deep in the crease region of the grain. The only discontinuities in the seed coat are at the basal end of the grain near the embryo. In the dorsal region of the caryopsis, the outer cuticle is approximately 3.5 μm in thickness, whereas the inner cuticle is less than 1 μm in thickness. Where the two pass over the embryo they are much thinner, with the inner cuticle becoming almost indistinguishable in places. The remains of the nucellar epidermis are tightly amalgamated to the seed coat and outer tangential walls of the underlying aleurone cells, which are clearly distinguishable by their large size and characteristic appearance.

Sicyos deppei G. Don (Cucurbitaceae) is an annual weed that disperses dormant seeds. The influence of scarification and light on their germination was studied in the laboratory. Scarified seeds collected in 1987, 6, 7, 8, and 9 mo postharvest, gave high germination both in white light (89 to 100%) and darkness (64 to 96%), in comparison with nonscarified seeds which germinated 7 to 20% in both conditions. Scarified seeds collected in 1989, 3 mo postharvest, germinated higher (52 to 69%) than nonscarified seeds (0 to 5%). Exposure to light did not break dormancy of nonscarified seeds. The reversal of dormancy by scarification describes them as hard seeds. Scarified seeds, 3 mo postharvest, were light indifferent, germinating even in the usually inhibitory condition of far-red light. However, a low proportion of scarified seeds, 6 and 7 mo postharvest, presented a positive photoblastic response and germinated 23 and 36%, respectively.

The effects of acid scarification, prechilling, summer irrigation, and root extract stimulant from faba bean plants grown during different seasons on crenate broomrape seed dormancy and germination were determined. Immersion of 6- to 12-mo old seed in 0.5 to 5 N H2SO4 solution from 1 to 20 min increased germination by 20%. Similarly, seed pretreatment at temperatures between −4 and 6 C increased germination, regardless of the pretreatment duration. Results suggest that the hard seed coat is an important dormancy mechanism in newly formed crenate broomrape seeds. Summer irrigation did not substantially change the germination capacity of crenate broomrape seeds. The germination stimulant activity of the root extract from faba bean plants grown during different seasons varied considerably, decreasing in this order: autumn > winter > spring > summer. This suggests an ecological adaptation of crenate broomrape to its main host crop.

Velvetleaf is a troublesome annual weed in many cropping systems of the United States and Canada. Differences in the growing environment of parent plants can influence the number, structure, germinability, and viability of seeds produced. Thus, the effects across a range of competitive environments and corn planting dates on velvetleaf seed production, germination, and seed coat weight were examined under field conditions. Seed production of velvetleaf increased with increasing biomass. Total velvetleaf reproductive output was reduced in competition with corn compared with monoculture stands. Corn planting date had no effect on the dormancy status of seeds, but increased competition from corn resulted in up to a 30% decrease in the proportion of seeds that were dormant. Seed and seed coat weights also decreased for plants of velvetleaf grown in competition with corn compared with those grown in monoculture. These findings suggest that velvetleaf plants growing in relatively noncompetitive environments, such as along field edges or in field areas with poor crop stands, are likely not only to produce a greater number of seeds but also a greater proportion of seeds that are dormant. This alteration in the dormancy status of velvetleaf seeds in the absence or presence of a crop provides unique opportunities for effective long-term management of the soil seedbank in this species, especially for velvetleaf individuals bordering fields or growing in fallow areas that might require more stringent control because of increased seed dormancy.

Effective weed seedbank management requires mechanistic understanding of ecological determinants of seed persistence in the soil seedbank. Chemical and physical defense of common lambsquarters, field pennycress, giant foxtail, kochia, velvetleaf, and yellow foxtail seeds were quantified in relation to short- and long-term seedbank persistence. Seed content of ortho-dihydroxyphenols (o-DHP), a class of putative seed defense compounds, varied more than threefold between the least protected species (common lambsquarters, 9.2 µg g seed−1) and the most protected species (kochia, 34.1 µg g seed−1). Seed o-DHP was inversely related (r = −0.77, P < 0.001) to seed half-life in the soil and to short-term seed persistence in burial assays (r = −0.82, P < 0.05). The relative importance of chemical seed protection in comparison to physical seed protection, as represented by the ratio of seed o-DHP concentration to seed coat thickness, decreased linearly with increasing short-term seed persistence (r = −0.96, P < 0.01) and nonlinearly with increasing long-term seed persistence in the soil seedbank (y = 0.16 + 0.21/(0.0432 + x), R2 = 0.99, P < 0.001). Mechanical damage to the seed coat, via piercing, slicing, or grinding treatments, increased short-term mortality during burial for all six species. Mortality of pierced seeds was negatively associated (r = −0.35, P < 0.05) with seed phenol concentration and positively associated with seed half-life (r = 0.42, P < 0.01) and seed coat thickness (r = 0.36, P < 0.05). Seed phenolics, as a class, supported the results for o-DHPs. Overall, these findings suggest a potential weakness, with respect to seedbank management, in the way weed seed defenses are constructed. Weed species with transient seedbanks appear to invest more in chemical defense than those species with highly persistent seedbanks. As a result, seeds in the latter category are relatively more dependent upon physical seed protection for persistence in the soil seedbank, and more vulnerable to management tactics that reduce the physical integrity of the weed seed coat.

Anatomical and morphological seed traits are of great ecological importance and are a main subject of, for example, seed bank or endozoochory studies. However, we observed a lack of information about the relationship between seed anatomy and seed morphology and its ecological implications. To fill this gap, we linked the anatomical features of diaspore coverings to morphological characteristics of free seeds and one-seeded fruits. We predicted that: (1) the thickness and anatomical complexity of seed coat and pericarp are related to diaspore size and shape; and (2) the presence or absence of the pericarp may influence seed-coat thickness and anatomy. In our study we investigated diaspores of 39 central-eastern European herbaceous species and recorded the thickness and anatomical complexity of their seed coverings, and we determined diaspore mass and shape. Our results indicate that diaspore mass is positively related to covering thickness, lignification degree and anatomical complexity. This might be the case because bigger diaspores tend to remain on the soil surface and are more exposed to predation risk and environmental threat than smaller diaspores. Furthermore, more round-shaped diaspores had disproportionately thicker and more lignified coverings than long or flat ones, probably because round-shaped diaspores much more frequently form seed banks and therefore persist for a long time in the soil. We also found that free seeds as diaspores have a thicker and more lignified seed coat than seeds enclosed in fruits. In one-seeded fruits, the pericarp ‘takes the protective role’, it is thick, and the seed coat is poorly developed.

Fruits of Melastomataceae constitute a key resource for Neotropical frugivores. However, the mechanisms determining gut-passage effects on seed germination are poorly known. Here, we determine how bird gut-passage affects seed germination in three species of Miconieae by running germination experiments, examining changes in seed coat structure and determining germination inhibition by fruit extracts. Mature fruits of Clidemia urceolata, Leandra aurea and Miconia rubiginosa were sampled in south-eastern Brazil and seeds were submitted to treatments evaluating gut-passage effects and different concentrations of fruit extracts. Light and scanning electron microscopy were used to compare seed coat structure and thickness of control and gut-passed seeds. We found minor effects of gut passage on seed germination. However, changes in seed coat structure of gut-passed seeds of L. aurea may have been related to a decrease in germination. Our data also support the idea that germination inhibitors in fruit pulp may contribute to the inhibition effect. Our study corroborates the idea that changes in the seed coat following gut passage modulate the complex fruit–frugivore interactions, especially between plants and generalist dispersers, and that seed cleaning is a key factor determining seedling establishment in Neotropical Melastomataceae.

The seed coat of soybean (Glycine max (L.) Merrill) must protect the seed but allow water intake. Overprotection, causing impermeability, is assumed to be due to the presence of an impermeable layer in the seed coat, although validation of this assumption has relied on imbibition testing, which tends to be influenced by microfractures in the seed coat. Recent micromorphological analyses using laser-assisted topography microscopy revealed links to the surface roughness (SR) of the seed coat. To verify genetic links between hardseededness and SR, we analysed quantitative trait loci (QTLs) governing SR formation using 148 recombinant inbred lines (RILs) with a genetic linkage map covering 2663.6 cM of all 20 linkage groups of soybean, with 355 DNA markers and 5 phenotype markers. Five QTLs were detected, including previously identified hardseededness QTLs for ratio of seeds absorbing water, namely RAS1 and RAS2, which accounted for 20% of the phenotypic variance, and one near a locus inhibiting seed coat colour (I). These results indicate that the impermeability of soybean seed is genetically related to the reduction of SR.

Two possible sources of resistance to pre-harvest sprouting were evaluated in quinoa. They showed dormancy at harvest and significant variations in dormancy level in response to environmental conditions experienced during seed development. The aims of this work were to evaluate the importance of seed coats in the regulation of dormancy in this species, to investigate possible mechanisms of action and to assess association of seed coat properties with changes in dormancy level caused by the environment. Accessions Chadmo and 2-Want were grown under field conditions on different sowing dates during 2 years. Seed coats were manipulated and seed germination was evaluated at different temperatures. Seed coat perforation before incubation led to faster dormancy loss in both accessions. This effect decreased with delayed sowing date, and seeds expressed a level of dormancy not imposed by coats. This suggests the presence of embryo dormancy in the genus Chenopodium. Seeds of the accession 2-Want had a significantly thinner seed coat at later sowing dates, associated with a decreasing coat-imposed dormancy, but this pattern was not detected in Chadmo. The seed coat acts as a barrier to the release of endogenous abscisic acid (ABA) in quinoa, suggested by the increase in germination and a higher amount of ABA leached from perforated seeds. ABA is able to leach from seeds with an intact seed coat, suggesting that differences in seed coat thickness may allow the leakage of different amounts of ABA. This mechanism may contribute to the observed differences in dormancy level, either between sowing dates or between accessions.

Soybean seeds are prone to flooding injury just after planting if they are exposed to excess moisture. We investigated the flooding tolerance of soybean seeds to clarify the relationship between flooding injury and imbibition, to identify factors that could provide fundamental information for the breeding of flooding-tolerant cultivars. Seven cultivars were used for this study. The seeds were geminated in a paper towel after a flooding treatment and then evaluated for survival. The imbibition of submerged seeds (passive imbibition) was evaluated as the seed fresh weight change during the flooding process. The imbibition of seeds with capillary effect (capillary imbibition) was measured by the bottom water supply method. Furthermore, the conductivity of the seed coat and seed osmolarity were measured. After 3 h of flooding, significant differences in survival were detected among cultivars. In addition, the passive imbibition during 10–30 min of flooding, and the capillary imbibition during 0–10 min of flooding were caused by significant differences in the imbibition rate among cultivars. Although neither imbibition showed a significant correlation with the survival directly, the ratio between the passive and the capillary imbibition rate was significantly correlated with survival. Factors affecting imbibition included the hydraulic conductivity of the seed coat and seed osmolarity, which were significantly correlated with the passive and the capillary imbibition rate, respectively. Thus, the balance between the capillary and passive imbibition behaviour of seeds, affected by the hydraulic conductivity of the seed coat and seed osmolarity, was closely correlated with the occurrence of flooding injury in soybean seeds.

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 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.

Models that quantify the effects of cropping systems on weed dynamics are useful tools for testing innovative cropping systems. In these models, seed mortality in the soil is a key parameter to account for the cumulated effect of cropping systems over time via the soil seed-bank. Since seed mortality is difficult to measure, our objective was to develop a method to estimate it from easily accessible information. Seeds of 13 weed species were buried 30 cm deep in fields and were recovered regularly for 2 years to measure their viability. Seed mass, dimensions, shape, and protein and lipid contents as well as coat thickness were measured. To estimate seed mortality of species not included in the study, we searched for relationships between mortality rates and seed traits. Seed viability mainly decreased during the second year of burial, with mortality rates ranging from 0.01 to 0.63 seeds·seeds− 1·year− 1, depending on the species. Seed mortality decreased with increasing seed coat thickness. No correlation was found with other measured traits or with seed persistence data in the literature. These results were confirmed when the effects of phylogenetic relatedness with phylogenetically independent contrasts were included. The thickness of the seed coat, which varied between 17 and 231 μm over the range of species studied, can protect the seed from external attacks in the soil and slow down seed decay. This trait can be easily measured via X-ray images and could be used to estimate the seed mortality rate for a wider range of species.

Openings are present on the inside surface of the endosperm cell wall adjacent to the developing cotyledon. The objective of this study was to determine if the openings were present during seed growth, maturation and imbibition by observing the inside surface of the endosperm with low temperature scanning electron microscopy. The openings were found to be present throughout seed development, maturation and imbibition. The openings were not formed by attachment to the cotyledon surface. However, the inner surface of the endosperm was occasionally attached to the surface of the embryo. At seed maturity, outgrowths on the cotyledon cell wall surface were embedded in the cell wall of the inside surface of the endosperm. These structures were also observed in the imbibing seed. These points of contact between the endosperm and embryo of soybean seeds may align the embryo, endosperm and seed coat during growth, desiccation and imbibition.