The micropylar region of endosperm (ME) is a physical barrier to radicle emergence in seeds of many different species, including tomato (Solanum lycopersicum) and Arabidopsis thaliana. ME is thought to be weakened through cell wall-modifying proteins, and this is supported by transcriptome data showing enrichment of cell wall-associated genes in ME. Gibberellin and ethylene have been suggested to be involved in induction of these genes in ME. However, mechanisms underlying this critical event for germination still remain elusive. In addition to hormonal regulation of ME weakening, recent data from high-throughput analyses suggested that it might be important for the radicle tip to ‘touch’ ME (or mechanosensing), in terms of ME-specific gene induction. This emerging hypothesis can be integrated with previous hypotheses about hormonal regulation of ME-specific gene expression in seeds.

Seed longevity is influenced by many factors, a widely discussed one of which is the seed lipid content and fatty acid composition. Here, linear and non-linear regressions based on machine learning were applied to analyse germinability and seed composition of a set of 42 oilseed rape (Brassica napus L.) accessions grown under the same single environment and at the same time following a period of up to 31 years storage at 7°C. Mean viability was halved after 27.0 years of storage, but this figure concealed a major influence of genotype. There was also wide variation with respect to fatty acid composition, particularly with respect to oleic, α-linolenic, eicosenoic and erucic acid. Linear regression (rL) revealed significant correlation coefficients between normal seedling appearance and the content of α-linolenic acid (+0.52) and total oil (+0.59). Multivariate regression using artificial neural networks including a radial basis function (RBF), a multilayer perceptron (MLP) and a partial least square (PLS) recognized underlying structures and revealed high significant correlation coefficients (rM) for oil content (+0.87), eicosenoic acid (+0.75), stearic acid (+0.73) and lignoceric acid (+0.97). Oil content or a combination of oleic, α-linolenic, arachidic, eicosenoic and eicosadienoic acids and glucosinolates resulted in highest model fitting parameters R2 of 0.90 and 0.88, respectively. In addition, the glucosinolate content, predominantly in the Brassicaceae family and ranging from 4.6 to 79.5 µM, was negatively correlated with viability (rL = ‒0.43). Summarizing, oil content, some fatty acids and glucosinolates contribute to variations in average half-life (15.2 to 50.7 years) of oilseed rape seeds. In contrast to linear regression, multivariate regression using artificial neural networks revealed high associations for combinations of parameters including underestimated minor fatty acids such as arachidic, stearic and eicosadienoic acids. This indicates that genetic and seed composition factors contribute to seed longevity. In addition, multivariate regressions might be a successful approach to predict seed viability based on fatty acids and seed oil content.

Seed banks are often crucial for the survival of plant species, especially short-lived ones. Nevertheless, empirical studies about the fate of seeds under natural conditions are scarce, particularly for parasitic plants. Therefore, fresh seeds of the holoparasitic Cuscuta epithymum were buried in the field under natural conditions in Belgium or kept at room temperature for up to 31 months, and germination was tested periodically by incubating seeds in light at 23°C. Buried C. epithymum seeds had cyclic changes in their germinability, while those stored dry at room temperature never germinated without scarification. Buried seeds exhibited a seasonal cycle of physiological dormancy, the first to be reported for a species with combinational (i.e. physical+physiological) dormancy. The physiological dormancy of the embryo was broken during winter ( ≤ 5°C) but induced during exposure to late spring temperatures (>10°C). Therefore, germination of C. epithymum seeds is fine tuned to seasonal temperature changes. Each year only a portion of the viable seeds could germinate. The portion of seeds buried in the soil that remained available for delayed germination, i.e. in the seed bank, decreased rather quickly, with only 8.5% of them being viable after 31 months of burial; all seeds stored in the laboratory remained viable. Nonetheless, we concluded that some C. epithymum seeds are capable of surviving for several years in the soil. These data indicate that the parasite is well adapted to survive in a dynamic heathland landscape where conditions for survival change constantly, but it is still sensitive to local extinction.

The objective of this study was to evaluate the effect of day length after flowering on pollen tube elongation, embryo formation and seed development. The quinoa varieties used in this study were Amarilla de Marangani (valley type) and NL-6 (sea-level type). After sowing, the quinoa plants were cultivated in growth cabinets. From sowing to flowering, plants were exposed to a 15 h day length regime. After flowering, the plants were grown under either a 15 h or 11 h day length regime. The elongation of the pollen tube and the formation of the early embryo were not inhibited in either Amarilla de Marangani or NL-6 under the 11 or 15 h day length regimes. Although growth of the embryo in NL-6 was not inhibited by the 15 h day length regime after flowering, the same was not observed in the case for Amarilla de Marangani. In Amarilla de Marangani, seed diameter at 8 and 14 days after flowering under the 11 h day length regime was larger than that of seeds grown under the 15 h day length regime. Thus, the decrease in the number of seeds in Amarilla de Marangani grown under the 15 h day length regime may be caused by the suspension of embryo growth after fertilization.

Germination ecology was investigated in a natural population of Xyris longiscapa, a perennial herbaceous species endemic to the Brazilian campo rupestre. Seeds were collected over four consecutive years (2014 to 2017) to evaluate germination responses to a range of temperatures (from 15 to 30°C). The light requirement was evaluated in seeds collected in 2014. Seeds collected in 2014 were also buried in soil in the natural habitat of the species to evaluate changes in germinability at different temperatures over the time. Seeds showed an absolute light requirement for germination. Seed germination was affected by temperature, collection year and the interaction between these two factors. Seeds collected in 2014 showed a narrower temperature range for germination (15–20°C), compared with the seeds collected in 2015, 2016 and 2017 that germinated in a temperature range of 15–25°C. Buried seeds remained viable in soil for at least 14 months and exhibited seasonal dormancy cycling. Secondary dormancy was induced during the rainy season and alleviated during the dry season, following a conditional dormancy/dormancy cycle. The degree of primary dormancy appeared to be influenced by the environmental conditions experienced by seeds during maturation. Primary dormancy (when present), seed persistence in soil and seasonal dormancy cycles are strategies of X. longiscapa to enhance regeneration success in the harsh environment of the Brazilian campo rupestre.

Seed dormancy is the temporary inability of an imbibed seed to germinate under otherwise favourable conditions. It is an important trait for seed persistence in many higher plants. Dormant dehulled red rice caryopses can have a strong dormancy: the studied population shows an almost complete dormancy; that is, these caryopses do not germinate (usually germination is <1–2%) when incubated in water for the time usually adopted for germination tests (i.e. 2 weeks). However, after several months of incubation in water, dormant red rice caryopses start germinating in an anomalous manner. Most notably, the piercing of the caryopsis coat is very slow, sometimes arrested, until the coat completely breaks down and embryo growth is resumed. There is, therefore, a time lag between the initial rupture of the caryopsis coat and the start of seedling growth. It is argued that embryo growth can be triggered by the failure of the caryopsis coat even if seed dormancy has not been previously relieved, and thus germination is started and dormancy is forcefully interrupted. Accordingly, the time course of the anomalous germination shows a Gompertz distribution of times to failure. It is concluded that: (1) if the seed rests with the coat ruptured without further growth, it is still dormant; if so, therefore, (2) the breaking of the coat is not necessarily a marker of germination in this context.

The processes involved in rice (Oryza sativa L.) panicle ripening vary with time and topological grain position. Methods to describe the functioning and connectivity of the grains on a panicle could aid the analysis of these processes. Hence, we addressed the difficulty of encoding and representing panicle topology. Array-based decomposition and computational methods were developed to encode and analyse panicle topology and grain traits. The technique, applied to the analysis of dry matter accumulation, clearly represented the basipetal succession of asynchronous grain ripening on a panicle. These methods should be useful for the spatial and temporal analysis of a number of panicle processes and attributes, including molecular ones, involved with ripening.

Hydration-dehydration seed pretreatments are well-known to improve germination rate, germination and vigour. However, contradictory results have been reported concerning the effect of a pretreatment on longevity. The present paper shows that the effect of a seed pretreatment on longevity is largely dependent on the quality of the seed at the time of pretreatment. Pretreating wheat seeds of high quality increased the rate of viability loss during subsequent storage. On the other hand, pretreating wheat seeds of relatively low quality decreased the rate of seed deterioration during subsequent storage. In the light of these findings, hitherto contradictory results in the literature could be explained.

For physiologically dormant (PD) species in fire-prone environments, dormancy can be both complex due to the interaction between fire and seasonal cues, and extremely deep due to long intervals between recruitment events. Due to this complexity, there are knowledge gaps particularly surrounding the dormancy depth and cues of long-lived perennial PD species. This can be problematic for both in situ and ex situ species management. We used germination experiments that tested seasonal temperature, smoke, dark and heat for 18 PD shrub species distributed across temperate fire-prone Australia and assessed how germination was correlated with environmental factors associated with their home environments. We found extremely high levels of dormancy, with only eight species germinating above 10% and three species producing no germination at all. Seven of these eight species had quite specific seasonal temperature requirements and/or very strong responses to smoke cues. The maximum germination for each species was positively correlated with the mean temperature of the source population but negatively correlated with rainfall seasonality and driest months. The strong dependence on a smoke cue for some of the study species, along with examples from other studies, provides evidence that an obligate smoke response could be a fire-adapted germination cue. Germination response correlated with rainfall season of the source populations is a pattern which has often been assumed but little comparative data across sites with different rainfall seasonality exists. Further investigation of a broader range of species from different rainfall season environments would help to elucidate this knowledge gap.

Seed germination, the first and critical step of the plant's life cycle, is affected by salt stress. However, the underlying mechanism of salt tolerance during early seed germination remains elusive. Here, a comparative RNA-seq analysis was performed using early germinating seeds either under normal conditions or in 100 and 150 mM sodium chloride. A total of 575 genes were up-regulated and 913 genes were down-regulated in the presence of 100 mM NaCl. Under the 150 mM NaCl treatment 1921 genes were up-regulated and 3501 genes were down-regulated. A total of 379 or 863 genes were up-regulated or down-regulated in both 100 and 150mM NaCl. These co-regulated genes were further analysed by GO enrichment. Genes in the categories abscisic acid signaling and synthesis and nutrient reservoir activity were significantly enriched in the up-regulated genes. Transcription factors responsive to gibberellin and auxin were significantly down-regulated by salinity stress. Genes related to anti-oxidant activity were significantly enriched in the down-regulated gene clusters by NaCl treatment. Our results suggest that salt stress inhibits seed germination by activating ABA synthesis and signalling, and depressing GA and auxin signalling, while preserving nutrition and down-regulated anti-oxidant activity. Our study provides more insight into the molecular mechanism of salt tolerance during early seed germination.

Changes in germination ability and longevity were monitored during seed development in three japonica rice cultivars and one indica rice cultivar sown on three different dates, 14 October 1993, 24 November 1993 and 5 January 1994 at Los Baños, Philippines. Germinability of the seeds varied among cultivars in the early stages of development, but it was generally similar across sowing dates. The estimates of potential longevity (determined by storage at 40°C and 15% moisture and quantified by the values of the seed lot constant K1 of the viability equation) differed among cultivars and sowing dates. While the maximum potential longevity attained across different sowing dates was similar in the japonica cultivars Ju ku and Chianan 8, it was significantly higher in the first sowing than in the second or third sowings in cv. Akihikari. In the indica cultivar IR 58, maximum potential longevity attained in the second and third sowings was significantly greater than that in the first sowing. The mean potential longevity, averaged over cultivars and sowing dates, was marginally higher in the first sowing (K1=3.81) than in the second (3.65) and third (3.63); and averaged over cultivars and harvest times it was greatest at 34.8 days after flowering (DAF) in the first sowing, 31.8 DAF in the second and 28.3 DAF in the third. These results suggest that sowing in mid-October to allow seed ripening to coincide with the cooler and drier segment of the Los Baños dry season, and harvesting 35 DAF can improve the potential longevity of some japonica cultivars.

Does seed dormancy allow disturbance-oriented forest herbs such as Ageratina altissima to persist in heterogeneous natural communities? To document seed longevity and dormancy state, Ageratina seeds were buried in nylon mesh bags in second-growth forest stands in south-eastern Ohio, USA. Bags were recovered at 2-month intervals, and seeds were tested for viability and germinability in the lab. Live seed numbers declined rapidly, with seed banks exhausted in an estimated 33–37 months. Seeds showed a strong dormancy polymorphism, with 71–84% of live seeds germinable between March and July, the season of natural seedling emergence. At other dates, most seeds appeared to be in a state of induced dormancy, allowing little (0–21%) germination. The slope aspect of the burial site, an important factor controlling above-ground vegetation, had no effect on seed longevity or dormancy condition. Dormancy in Ageratina appears to be adapted to allow opportunistic germination in late spring–early summer, but to prevent germination in less benign periods. Seed longevity is shorter than the natural frequency of gaps in mesophytic forest. We conclude that a long-term dispersal/dormancy trade-off is probably an oversimplification of the spatial ecology of this species. The primary function of dormancy appears to be short-term tracking of seasonal variation.

Secondary seed dormancy in cucumber (Cucumis sativus L.) cv. Poinsett 76 could be broken with ethanol. Breakage of dormancy was accompanied by significant changes in the composition of membrane proteins in various seed parts. Compared to the intracellular membranes, a change in the protein composition of plasma membranes from the embryonic axis and cotyledons was evident early in the time-course of ethanol-induced germination of dormant seeds. While few alterations in the membrane protein composition in response to ethanol treatment occurred both in dormant and nondormant seeds, a number of changes occurred exclusively in ethanol-treated dormant seeds. Notably, a 14 kD protein in the plasma membrane from the embryonic axis and a 35 kD protein in the microsomal membranes from the perisperm-endosperm envelope disappeared in the ethanol-treated dormant seeds, but not in the ethanol-treated nondormant seeds. Also marked decrease in the content of a 23 kD protein in the plasma membrane from the cotyledons was observed in ethanol-treated dormant seeds only. It is suggested that the particular changes in cellular membrane proteins, which occurred in ethanol-treated dormant seeds much before the first visible indication of germination, might be related to dormancy breaking rather than to the germination process.

The interaction between ethylene production and seed germination of sugar beet (Beta vulgaris L.) was studied. For intact fruits, deoperculated fruits and true seeds, ethylene was only produced after the start of radicle emergence. Removal of the operculum or the whole pericarp, likely allowing better water uptake and gas exchange by the true seed, actually increased the time span between the start of radicle emergence and the beginning of ethylene production compared to intact fruits. ACC (1-aminocyclopropane-1-carboxylic acid), AOA (aminooxyacetic acid), AIB (2-amino isobutyric acid) and STS (silver thiosulphate) in the imbibition medium did not influence the germination pattern. Based on these findings, the function of ethylene during the germination of sugar beet is uncertain.

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.

Some physiological characteristics of ACC-Nmalonyltransferase (ACC-N-MTase) have been studied in the seeds of chick-pea (Cicer arietinum L.). This enzymatic activity was detectable during all periods of zygotic embryogenesis; however, the highest values were found in the dry seed. In dry seeds, the enzymatic activity was greater in the embryonic axis than in the cotyledons. During the onset of germination, activity increased more strongly in the cotyledons than in the embryonic axis, reaching its highest values in the storage organs coinciding with radicle emergence (18 to 24 h). Removal of the cotyledons strongly diminished enzymatic activity in the embryonic axis. Low concentrations of ethrel (50 µM) stimulated the axis ACC-N-MTase. The highest specific activity was found in the apical meristem of the embryonic axis, declining over the length of the organ. The role of ACC-N-MTase activity in the germinative process is discussed, together with the regulatory effect of ethylene on this ACCconjugating enzyme.

Seed reserves play vital roles in seed germination and seedling growth and their variation may be related to various environment factors, plant traits and phylogenetic history. Here, the evolutionary correlation associated with seed mass and altitude and carbon (C), nitrogen (N) and phosphorus (P) allocation of seeds among 253 alpine herbaceous plants was tested. In this study, phylogeny had strong limitations on nutrient allocation of seeds across species, and species from younger phylogenetic groups tended to have higher N and P contents, which might be considered as the evolutionary selection of seed plants. Higher seed N and P content would help seedlings to gain more survival chance and stronger competitive capacity, and their progeny would be more likely to be preserved. When phylogeny was considered, altitude only had a significant positive effect on P content, but the negative effects on seed mass were all expressed. The independent effects of altitude and seed mass suggest that the nutrient allocation of seeds might be affected by both environment and plant traits. In addition, altitude and seed mass displayed partial overlapping effects on nutrient allocation of seeds. The negative effects of seed mass were affected slightly by altitude, whereas altitude only had a significant positive effect on P content when seed mass was controlled. Above all, seed P content showed obvious and general correlations with seed mass, altitude and age of clade, which indicated that higher seed P content might be an adaptive selection of species associated with growth and survival of progeny.

The loss of percentage germination and vigour of non-sprouted and sprouted seeds of winter wheat was determined during storage for 80 days at 11 different combinations of moisture content and temperature. Before storage the initial percentage germination and vigour were reduced according to the level of sprouting. During storage the percentage germination and vigour decreased. The rate of germination loss increased with increasing seed moisture content and/or increasing temperature. The species-specific constants KE, CW, CH and CQ of the viability equation were not different for non-sprouted and sprouted seeds. Likewise, the relation between the percentage of normal and abnormal seedlings was independent of sprouting. The rate of vigour loss was also independent of the storage conditions and of sprouting.

As a tribute to A.C. Martin's classic work on embryos in seeds, we have attempted to gain a better understanding of the peripheral embryo, which puzzled Martin. The peripheral embryo is strongly curved and in contact with the inner surface of the seed coat, and Martin placed it at the base of his family tree of seed phylogeny and called it a ‘phylogenetic orphan’. We evaluated ovule/seed development, kind of embryo and occurrence of perisperm in families with and without a peripheral embryo. All families with a peripheral embryo occur in the Caryophyllales. Seeds with a peripheral embryo have a low cotyledon width:radicle width ratio that coincides with Martin's (full-sized) linear embryo. The peripheral embryo develops in campylotropous and/or amphitropous ovules and is pushed to the side of the seed as the perisperm develops. Linear-full embryos and perisperm are widely distributed across extant angiosperms but are rarely found together, except in core Caryophyllales. The non-core Caryophyllales with endosperm and various kinds of embryos, including the linear-full, diverged before the core Caryophyllales. Thus, the ancestral linear-full embryo appears to have been retained when the core lineage developed campylotropous and/or amphitropous ovules and perisperm. Seeds with a peripheral embryo merit a position on Martin's family tree; however, the position should be a side branch (‘orphan’) slightly above (more advanced than) his linear embryo and not at the base. We conclude that Martin had great insight into the relationships between the kinds of embryos and rightly questioned the position of the peripheral embryo.

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.