Endosperm tissue that nourishes the embryo during seed development, upon maturity, nourishes the global population with special reference to cereal crops like maize, wheat and rice. In about 70% of the angiosperms, endosperm genome content is ‘3n’ with 2:1 (maternal:paternal) contribution, as a result of the second fertilization event. However, angiosperms evolution also documents diversity in endosperm genome content from ‘2n’ to ‘15n’, in scale with the corresponding maternal genome dosage variability (‘1n’ to ‘14n’), whereas paternal contribution is invariable. In apomicts, due to lack of fertilization, or pseudogamy (fertilization of the central cell for endosperm formation), endosperm genome dosage (m:p) has been reported to range between 1:1 and 8:3. Exceptionally, the central cell with one unreduced nucleus and fused with a reduced sperm cell, with 2:1 normal genome dosage, has been reported in Panicum. Altered genome dosage levels are reportedly correlative with eccentricities among maternal and paternal contribution to seed resource allocation. Besides endosperm ploidy variability between species of angiosperms, the present review gives an overview of the ploidy variability in endosperm cells within a seed, up to ‘690n’. In addition to genome-scale variability in the endosperm, some taxa of angiosperms exhibit chlorophyllous endosperms and some chlorophyllous embryos. Also, endosperm cell number during seed development is reported to have a strong association with grain weight at maturity. Genes underlying these traits of variability are unknown, and the present review underscores the variability and highlights the potential of the single-cell sequencing techniques towards understanding the genetic mechanisms associated with these variable traits.

The endosperm is the storage tissue of seeds and is an important source of nutrients for humans and animals. In the previous work, the gene expression was characterized at 3 and 24 h after pollination (AP). The results suggested that eATP would act as a signalling molecule at the beginning of endosperm development and that sucrose metabolism could be related to EBN insensitivity. In addition, differentially expressed transcripts derived fragments (DETDFs) were related to the failure of fusion of the polar nuclei and the accumulation of storage products in seeds of Arabidopsis thaliana. The objective of the present study was to identify genes related to endosperm development in apomictic and sexual ovaries of Paspalum notatum 48 h AP, a stage at which development is prior to post-zygotic collapse. The cDNA-AFLP analysis was carried out to analyse different crosses and DETDFs categorized according to their function. The main cellular functions at 48 h AP were metabolism and signal transduction. Fourteen out of 39 DETDFs with relevant functional information were found in crosses for which normal endosperm development was expected. Three DETDFs were found in crosses where viable and unviable seeds were predicted and presented similarity with a casein kinase II (CK2), an enzyme that governs the accumulation of storage proteins in seeds of A. thaliana and Zea mays. The results obtained at 3, 24 and 48 h AP suggest that CK2 is involved in early endosperm development in P. notatum.

Seed conservation of banana crop wild relatives (Musa L. spp.) is limited because of lack of knowledge about their germination ecology. Musa acuminata Colla, the most important banana crop wild relative, is distributed in tropical and subtropical Asian and Pacific rainforests and colonizes disturbed sites. The role of temperature in stimulating/inhibiting germination to detect disturbance when canopy gaps are formed is not well known. We assessed seed germination thermal requirements of three subspecies of M. acuminata using nine seed accessions which had been stored in the Millennium Seed Bank. Diurnally alternating temperature cycles were almost completely essential for germination compared with constant temperatures. Germination was optimal when the upper temperature of a diurnal cycle was at 35°C; the lower temperature of the cycle was less important. Subspecies occurrence coordinates were used to extract climate temperature data which were then compared against the temperature requirements for germination from our experiment results. Maximum temperatures of the warmest month across subspecies ranges were close to but below optimal germination temperatures, as were diurnal ranges, suggesting soil-warming at the micro-climate level following gap creation is important for M. acuminata seed germination. Additionally, pre-treatment for 3 months at 60% relative humidity at constant 25°C improved germination from 14 ± 10 (mean, standard deviation) to 41 ± 29% suggesting a period in the soil seed bank under the canopy may increase sensitivity to alternating temperature cycles. Overall viability was low (49 ± 28%), and considerable variance was caused by the different accessions. Germination remained somewhat inconsistent.

The timing of the germination of seeds is highly responsive to inputs from the environment. Temperature plays a key role in the control of germination, with low temperatures acting to stimulate this developmental transition in many species. In Arabidopsis, extensive gene expression changes have been reported at the whole seed level in response to cold, while much less is known about their spatial distribution across the diverse cell types of the embryo. In this study we examined the spatiotemporal patterns of promoter activity and protein abundance for key gibberellic acid (GA) and abscisic acid (ABA) factors which regulate the decision to germinate both during a time course of germination and in response to cold. Low temperature stimulated the spatial relocalization of these factors to the vasculature. The response of these seeds to dormancy-breaking stratification treatments therefore stimulates the distribution of both positive (GA) and negatively acting (ABA) components to this same cell type. This altered spatial pattern persisted following the transfer of seeds to 22°C, as well as after their rehydration, indicating that this alteration is persistent. These observations suggest that the vasculature plays a role in the low temperature-mediated stimulation of germination in this species, while novel cell types are recruited to promote germination in response to stratification.

Seeds are increasingly being stored in seed banks for ex situ conservation, food security, and restoration reserves. Although it is hypothesized that seeds of many species can survive the dry, freezer conditions (−20°C) of seed banks for many years, shelf life is unknown for many species. In particular, changes to dormancy and germination requirements following freezer storage have not yet been studied extensively. To improve our understanding of how seed dormancy and germination respond to seed banking conditions, we evaluated seed of six restoration-priority species in the southwestern United States, which is a region of increasing restoration need. Germination tendencies of seeds that were and were not exposed to a −20°C treatment for 4–6 months were evaluated under 22 cold-moist stratification and incubation treatments to broadly assess changes to dormancy and germination requirements and speed. Direct or indirect (via interactions with stratification and/or incubation treatments) differences in dormancy breaking and germination were observed in seeds for four of the six species studied. Specifically, storage temperature accounted for differences in the final germination proportion, germination during stratification, and/or rate of germination in five of the six species. Notably, seeds of the one species that exhibit a combination of physiological and physical dormancy showed significant differences in all germination measures. However, while significant differences were found between seeds exposed to short-term seed bank storage and those that were not, these differences were small and may not be biologically meaningful, indicating that seed banking these species should not change how they are used for restoration or reintroduction purposes.

The effects of cold atmospheric plasma (CAP) of dielectric barrier discharges on the wettability, imbibition and germination of Leucaena leucocephala were investigated. It was established that CAP treatment markedly hydrophilized the seed coat, especially at longer treatment times. From the profile of the imbibition curve and visual observation, it was possible to verify that there are two resistance barriers to water penetration: integument surface and region of the macrosclereid cell wall (light line). Although the plasma interacts only in the integument, increasing the density of hydrophilic sites increases the capacity of water absorption, producing enough driving force to overcome the second resistance barrier. The existence of these two barriers changes the three-phase pattern generally observed during seed germination. Despite an increase in imbibition, the plasma treatment conditions used in this work, were not enough to overcome completely the dormancy barrier.

Germination experiments are becoming increasingly complex and they are now routinely involving several experimental factors. Recently, a two-step approach utilizing meta-analysis methodology has been proposed for the estimation of hierarchical models suitable for describing data from such complex experiments. Step 1 involves fitting models to data from each sub-experiment, whereas Step 2 involves combination estimates from all model fits obtained in Step 1. However, one shortcoming of this approach was that visualization of resulting fitted germination curves was difficult. Here, we describe in detail an improved two-step analysis that allows visualization of cumulated data together with fitted curves and confidence bands. Also, we demonstrate in detail, through two examples, how to carry out the statistical analysis in practice.

The influence of temperature and water availability on seed germination can vary across the geographic range of species with a large distribution. Betula pendula is a widely spread European tree that has differentiated into two narrowly distributed taxa, endemic to Mediterranean mountains: Betula aetnensis in Sicily and B. fontqueri in Spain and Morocco. We tested the hypothesis that the regeneration niche, expressed by temperature and water potential thresholds, varies across these species and is influenced by the local climate. Seeds were collected from six populations of B. pendula, one of B. fontqueri and two of B. aetnensis. Germination tests were conducted between 5 and 30°C. The thermal thresholds were calculated before and after cold stratification. The osmotic potential tested ranged from 0 to −1.5 MPa. Time to reach 30 and 50% of germination was calculated by fitting non-linear models. Germination was promoted by high temperatures, but the response to stratification was heterogeneous. Tb and Ψb differed between and within species. Tb ranged between 2.22 and 8.94°C for unstratified seeds. Mediterranean species had higher drought tolerance, while B. pendula showed contrasting responses to low water potential. Ψb reached a minimum value of −1.15 MPa in B. fontqueri. High temperatures influenced the Tb of unstratified seeds negatively, while, after stratification, the Tb increased with precipitation in the driest month. The heterogeneity observed could reflect higher genetic variability in marginal populations of silver birch. Knowledge of their germination ecology may be useful to mitigate future impacts of climate change on core populations of B. pendula.

Cultivated northern wild rice (NWR; Zizania palustris L.) has been bred and studied since the 1950s. One challenge facing researchers is the lack of storage options, due to the seed's unorthodox behaviour. This study evaluated varying storage temperature and moisture conditions for the maintenance of seed viability and dormancy breaking in Minnesota-grown NWR. First, seeds were placed in non-submerged, freezing storage (NSFS) for 12–26 weeks, then in submerged, cold storage (SCS) for 2 weeks. The addition of SCS increased germination (%G) relative to NSFS alone (<0.1% NSFS, 15% NSFS and SCS), indicating that NSFS does not kill seeds but also does not break seed dormancy. Next, the required length of SCS was evaluated by placing seeds in NSFS for 12 weeks and then in SCS for 2–14 weeks. A longer SCS period increased %G from 3 to 79%, at 2 and 14 weeks of SCS, respectively. Lastly, seeds were placed in NSFS, followed by SCS, at varying intervals over a 29-week period. Across lines, germination increased from 20 to 76% between 4 and 7 weeks of SCS, respectively, then plateaued. The results of this study indicate that NSFS could be used to store NWR seeds, but at least 7 weeks in SCS is required to overcome dormancy. Additionally, while NSFS did not break seed dormancy, physiological changes related to stratification processes were occurring in non-submerged, freezing conditions. Results also suggest that the genotypic variation in NWR could be utilized for selection to improve germination and storage viability.

Quercus species are ecologically and economically important components of deciduous forests of the eastern United States. However, knowledge pertinent to a thorough understanding of acorn germination dynamics for these species is lacking. The objectives of this research were to determine dormancy break and germination requirements for acorns of two eastern United States bottomland species, Quercus nigra and Quercus phellos (Section Lobatae), and to present results within ecological and phylogenetic contexts. Three replicates of 50 acorns of each species received 0 (control), 6, 12 or 18 weeks of cold stratification, followed by incubation in alternating temperature regimes of 15/6, 20/10, 25/15 and 30/20°C. Eighteen weeks of cold stratification were not sufficient for dormancy break in Q. nigra acorns. Cumulative germination percentages at 4 weeks of incubation were ≥77%, but only in incubation temperatures of 25/15 and 30/20°C. Dormancy break in Q. phellos acorns was achieved with 18 weeks of cold stratification, and cumulative germination percentages were ≥87% at 4 weeks of incubation in all test temperature regimes. Gibberellic acid solutions were not an effective substitute for cold stratification in either species. Phylogenetically, Q. nigra and Q. phellos are closely related species and, ecologically, both grow in the same habitat. Acorns of both species possess deep physiological dormancy (PD), but dormancy break and germination requirements differ in acorns of these two Quercus species.

In wetlands, dormancy may be a key functional trait enabling seeds to avoid underwater germination, which could be lethal for seedling establishment. Our objectives were to find out (i) if shallow dormant (i.e. conditionally dormant) Echinochloa crus-galli seeds from an anaerobic germination resistant accession can break dormancy under hypoxic submergence and (ii) if underwater germination can be restored in scarified, non-dormant seeds. Shallow dormant E. crus-galli seeds perceived diurnally alternating temperatures (AT) and red light (R) pulses (i.e. dormancy-breaking cues) under hypoxic submergence; however, an inhibitory far-red light pulse given at the end of the 4-d inundation period demonstrated that most of the seeds (85%) were unable to break dormancy. Scarified E. crus-galli seeds, which did not express dormancy under drained conditions, were unable to germinate under hypoxic submergence, despite being exposed to dormancy-breaking cues (AT + R). Lastly, the temporal window for germination sensitivity to the inhibitory action of hypoxia, once dormancy-breaking signals have been applied, is progressively lost and bounded to approximately 18 h for half of the seed lot. These results highlight the importance of dormancy as a trait enabling E. crus-galli seeds to avoid underwater germination, a risky scenario for seedling emergence and establishment in this facultative hydrophyte.

Seed longevity is a complex process of key ecological and agronomic importance. DNA damage is a significant factor affecting seed ageing. Likewise, epigenetic changes can control gene expression and, therefore, seed response to ageing. The aim of the present work was to investigate the effect of ageing on nucleic acid stability and to identify reliable molecular markers that might help to monitor epigenetic changes within plant genetic resources during conservation. DNA profiles, evaluated by RAPD (random amplified polymorphic DNA), and methylation patterns, obtained by MSAP (methylation-sensitive amplification polymorphism), were compared in non-aged and aged Mentha aquatica seeds and plants produced by them. Germination decreased to 50% by storing seeds at 35°C and 12% wc for 28 days. RAPD profiles were 99% similar in these aged seeds compared to non-aged seeds. However, seedlings produced from the aged seeds showed a 13% dissimilarity compared to seedlings produced from the non-aged seeds. About 8% difference in the MSAP epigenetic profile was detected in seeds after storage and 16% difference was detected in the seedlings produced from them. This indicates that stress from high temperature and humidity during storage induced changes on the methylation state of seeds, and that changes were also detectable in the regenerated plants. Our results suggest that DNA integrity was compromised in seeds during ageing, and on seedlings produced by aged seeds. Genotype screening techniques such as RAPD and MSAP have the potential as markers of nucleic acid stability during seed ageing.

Information about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, including Begonia guishanensis and Paraisometrum mileense, two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15°C as well as moist chilling (MC) at 15/5°C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40–65% of B. guishanensis and 5% of P. mileense seeds were dormant at maturity. DAR at 25/15 and 15/5°C as well as MC and WD cycles at 15/5°C alleviated dormancy for B. guishanensis but not P. mileense, and WD cycles at 25/15°C induced a deeper conditional dormancy for both species. Seeds of B. guishanensis exhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO3 mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures for B. guishanensis. The field experiment indicated that seeds of B. guishanensis may be able to form a persistent soil seed bank, while almost all seeds of P. mileense germinate at the beginning of the wet season in the field.

Mudflats are exposed for short periods after flood water drawdown. They support fast-growing annual herbs with a ruderal strategy. To optimize their recruitment success, seeds of mudflat species germinate better under fluctuating temperatures, full illumination and aerobic environments that indicate the presence of optimal (non-flooded) conditions for plant growth and development. Here, we hypothesize that prior exposure of mudflat seeds to hypoxic (flooded) environment interferes with the germination process and results in more vigorous germination once aerobic conditions are regained. To test this hypothesis, seeds of five mudflat species were incubated in both aerobic and hypoxic environments at four (14/6, 22/14, 22/22 and 30/22°C) temperature regimes, reflecting different (seasonal) conditions when drawdowns may occur. All species responded positively to four temperature regimes; however, moderate 22/14 and 22/22°C temperatures were optimum for high percentages and rates (speed) of seed germination. Since seeds of four species germinated exclusively under aerobic conditions, they were moved from hypoxic to aerobic conditions. Prior exposure of seeds to hypoxic environment facilitated high percentages, rates and synchronization of germination of Limosella aquatica, Peplis portula and Samolus valerandi seeds compared to incubation under strict aerobic conditions. However, prior exposure to hypoxic environment induced secondary dormancy in non-dormant seeds of Hypericum humifusum but broke dormancy in Lythrum hyssopifolia seeds that otherwise required cold stratification to overcome physiological dormancy. All species that have a narrow ecological niche (strictly occurring in mudflat habitats) showed positive responses to prior exposure to hypoxic environments. In contrast, H. humifusum that has a wide ecological niche (from mudflats to moist sandy grasslands) showed a negative response. We conclude that the hypoxic environment may strongly affect seed germination behaviour once the aerobic environment is regained. The most striking effect is the acceleration of the germination process and, therefore, life cycle supporting the survival in an ephemeral habitat.

UK trees require increased conservation efforts due to sparse and fragmented populations. Ex situ conservation, including seed banking, can be used to better manage these issues. We conducted accelerated ageing tests on seeds of 22 UK native woody species, in order to assess their likely longevity and optimize their conservation in a seed bank. Germination at four ageing time points was determined to construct survival curves, and it was concluded that multiple samples within a species showed comparable responses for most species tested, except for Fraxinus excelsior. Of all species studied, one could be classified as very short-lived, four as short-lived and 17 as medium, with none exceeding the medium category. The most important finding of this manuscript is that although some taxonomic trends were observed, the results indicate the need for caution when making broad conclusions on potential seed storage life at a species, genus or family level. Longevity predictions were compared to actual performance of older collections held in long-term storage at the Millennium Seed Bank, Kew. Although most collections remain high in viability in storage after more than 20 years, for short-lived species at least, there is some indication that accelerated ageing predicts longevity in seed bank conditions. For species with reduced potential longevity, such as Fagus sylvatica and Ulmus glabra, additional storage options are recommended for long-term gene banking.

Fire and grazing are large-scale disturbances that shape the structure and function of open habitats. In temperate grasslands of southern South America, fire is used as a management tool to control tussock grasses and improve forage quality. In this study, we examined if fire and two of its components (heat and smoke) affect germination from the soil seed bank of a temperate grassland in Uruguay. Soil samples were extracted from a recently burned site and from an adjacent area that had not been burned for at least 4 years. The latter was subjected to four treatments: (1) heat shock, (2) smoke, (3) heat shock and smoke and (4) control. The samples were placed in a germination chamber and germination was recorded for 140 days. Field burn was the treatment that differed most from the control. This treatment produced a significant increase in density and richness of germinants and the germination peak preceded those of the remaining treatments. The three treatments involving fire-related cues did not affect the seedling richness and density, but the germination of some individual species was enhanced by some of them, mainly those in which the seeds were smoked. Our results show that fire and its components stimulate the germination of some species of the Río de la Plata grasslands, contrary to what had been observed previously in the region. We also suggest that, unlike Mediterranean-type systems, other fire cues, alone or in combination with heat and smoke, may promote germination after a fire event.