The factual evidence for aquaporins, the constituents of water channels in cell membranes and operation of water channels is reviewed in developing, maturing and germinating seeds.

Many studies have compared diaspore dispersal ability and degree of dormancy in the two diaspores of dimorphic plant species. A primary goal of these studies was to determine if germination and dispersal characteristics of the two morphs fit within a high risk–low risk (bet-hedging) life-history strategy, i.e. high dispersal/low dormancy in one morph versus low dispersal/high dormancy in the other one. In a survey of 26 papers on 28 diaspore dimorphic species, we found that in 12 of the studies, which were published between 1978 and 2008, seeds were stored, and thus possibly afterripened, before they were tested for germination. The 14 papers that tested fresh seeds were published between 1963 and 2010. Failure to test fresh seeds likely resulted in misinterpretation of the diaspore dispersal/dormancy strategy in some of the species investigated. We conclude that it is imperative that fresh seeds be tested for germination in order to be certain that the correct relationship between dispersal and dormancy is elucidated, and thus that the correct interpretation is made concerning life-history strategy and bet-hedging, in dimorphic species.

From previously published studies we have learned that very fast-germinating species have some characteristics in common with cryptoviviparous species: (1) little or no endosperm/perisperm; (2) embryos fully developed and chlorophyllous at seed maturity; and (3) very fast germination, independent of temperature. Thus, we propose that these very fast-germinating seeds are ‘cryptoviviparous-like′.

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.

Can seed characters be used for predicting the presence of a persistent seed bank in the field? We address this question using ten cultivars of the crop Brassica napus, ten feral B. napus accessions originating from seeds collected in the field and nine accessions of the closely related ruderal species Brassica rapa. When buried for a year in the field, seeds of the wild B. rapa displayed, as expected, much higher survival fractions than those of domesticated B. napus at two different locations in The Netherlands. Compared to B. napus, B. rapa produces relatively small seeds with high levels of aliphatic glucosinolates and a thick seed coat. However, within each species none of these characters correlated with seed survival in the soil. At low temperatures, B. rapa seeds had lower and more variable germination fractions than those of B. napus; a small fraction (4.6%) of the B. rapa seeds showed primary dormancy. Rather surprisingly, B. napus displayed genetic differences in germination at low temperature, and germination fractions at 5°C correlated negatively with seed survival in the soil. Our comparisons between and within the two species suggest that foregoing germination at low temperatures is an important character for developing a persistent seed bank. We discuss our results in light of environmental risk assessment of genetically modified B. napus.

During seed germination, metabolism is reactivated, DNA is repaired and cell division is restarted in the meristems. The mechanisms that co-ordinate cell growth and division in maize embryonic axes during germination are not well understood. However, the presence of a factor similar to IGF (insulin-like growth factor) that accelerates germination has been reported. In the present work, the regulation of the cell-cycle restart by bovine insulin [which has been demonstrated to produce similar effects as insulin-like growth factor of maize (ZmIGF) in maize seeds] was studied in germinating embryonic axes. Our results showed that bovine insulin differentially stimulates growth, S6K phosphorylation, S6rp transcript accumulation on the polysomal fraction, as well as de novo DNA synthesis in the radicles and the coleoptiles of the embryonic axis. A stronger and earlier effect was observed in radicles compared to coleoptiles; therefore, the effect of insulin on the cell cycle of the root meristem was studied by flow cytometry. The G1–S transition was stimulated and cell proliferation was induced. Furthermore, it was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) that bovine insulin increased E2F and PCNA (proliferating cell nuclear antigen) transcription after 15 h of germination and PCNA de novo synthesis at 15 h of germination. These results show that bovine insulin preferentially stimulates growth in the radicles of germinating embryonic axes and suggest that its effect on the G1–S transition and the activation of cell proliferation is mediated by the induction of E2F and PCNA transcription.

The wheat transcription factor TaABF1 physically interacts with the protein kinase PKABA1 and mediates both abscisic acid (ABA)-induced and ABA-suppressed gene expression. In bombarded aleurone cells of imbibing grains, the effect of TaABF1 in down-regulating the gibberellin (GA)-induced Amy32b promoter was stronger in the presence of exogenous ABA. As these grains contained low levels of endogenous ABA, the effect of TaABF1 may also be mediated by ABA-induced activation even in the absence of exogenous ABA. Levels of TaABF1 protein decreased slightly during imbibition of afterripened grains. However, TaABF1 levels (especially in aleurone layers) were not substantially affected by exogenous ABA or GA, indicating that changes in TaABF1 protein level are not an important part of regulating its role in hormone signalling. We found that TaABF1 was phosphorylated in vivo in aleurone cells, suggesting a role for post-translational modification in regulating TaABF1 activity. Induction of Amy32b by overexpression of the transcription factor GAMyb could not be prevented by TaABF1, indicating that TaABF1 acts upstream of GAMyb transcription in the signalling pathway. Supporting this view, knockdown of TaABF1 by RNA interference resulted in increased expression from the GAMyb promoter. These results are consistent with a model in which TaABF1 is constitutively present in aleurone cells, while its ability to down-regulate GAMyb is regulated in response to ABA.

Although pear species (Pyrus spp.) are widely cultivated as an important fruit tree in the world, the regulatory mechanism of their seed dormancy is still unclear. In this research, the role of endocarp, seed coat and embryo in sand pear (Pyrus pyrifolia) seed dormancy was analysed by detecting the endogenous abscisic acid (ABA) and analysing germination experiments with different treatments. The results suggest that a combination of testa and embryo impose sand pear seed dormancy. The high concentration of endogenous ABA in the embryo effectively inhibited seed germination. The high concentration of ABA in the endocarp, as well as in the testa, suggests that dissipation and/or degradation of endogenous ABA in imbibed embryos were suppressed to maintain ABA-inhibited germination. The ABA and gibberellic acid (GA) key signalling genes, including ABI3–5, GAI, RGA and RGL2, were cloned and their expression was analysed in ABA-treated embryos and embryos of imbibed nutlets, imbibed true seeds (endocarp removed) and GA-treated true seeds. The results revealed regulation by ABA of the expression of ABA and GA signalling factors controlling the dormancy release of sand pear imbibed seeds.

Physical seed dormancy is a common attribute among plants, and a wide range of dormancy-release mechanisms have been described, but their ecological significance is rarely tested through comparative study. This study tests whether dormancy-release responses to wet heat in four legume species with physical dormancy are correlated with habitat: two wetland species (Mimosa pigra and Parkinsonia aculeata, both dispersed primarily by water) and two terrestrial species (Acacia nilotica and Prosopis pallida, both dispersed primarily through vertebrate herbivores). Dormancy release was compared at three moisture levels (80% relative humidity, saturated and submerged) at constant (20–45°C) and diurnally fluctuating (20/40°C) temperatures for 14 d. Seed viability was tested by germinating at 25°C. The functional relationship between temperature and dormancy release after 14 d differed between species: submerged seeds of the two wetland species showed a quadratic response, with low rates of imbibition below 20–25°C and complete imbibition at around 40°C; P. pallida seeds showed a linear positive relationship, whereas there was no temperature response for A. nilotica seeds below 45°C. Surprisingly, dormancy release after 14 d was relatively insensitive to moisture levels, although rate of dormancy release was generally slower under drier conditions. Dormancy release was not influenced by fluctuating temperatures. Seed viability was largely unaffected by temperature or moisture regime, although it did differ with species and was lower for non-dormant seeds. Our results suggest that a functional dormancy-release response to wet heat provides important fitness benefits for wetland species, but not for species dispersed through vertebrate herbivores, for which it may be maladaptive.

Alfalfa (Medicago sativa L.) yield is severely compromised by soil salinity, especially at the level of seedling establishment. This question was addressed by proteomics to decipher whether specific changes in protein accumulation correlate with germination performance of alfalfa seeds submitted to a salinity stress as obtained by imbibing seeds in the presence of NaCl. This study used alfalfa seeds submitted to an osmopriming invigoration treatment that proved very efficient in counteracting the negative effect of salinity stress on germination performance. Comparative proteomic analyses disclosed 94 proteins commonly characterizing the response of both the untreated control and osmoprimed seeds to the experimental salinity stress. Remarkably, many of them, representing 84 proteins, showed contrasting accumulation patterns when comparing the untreated control and osmoprimed seeds submitted to the same salt stress. Thus numerous changes observed in the proteome of the untreated control seeds imbibed in the presence of salt, and presumably accounting for the loss in seed vigour associated with salinity stress, can be substantially reversed in osmoprimed seeds undergoing this stress. These data therefore provide a biochemical understanding of the increase in seed vigour generally observed with primed seeds.

Medicago truncatula, soybean (Glycine max), Arabidopsis thaliana and rice (Oryza sativa) all belong to the core angiosperm group of plants. Seed-specific genes are important for seed formation and development in these angiosperms. The identification of genes specifically expressed in angiosperm seeds and the comparison of the expression patterns of homologous genes among different angiosperm species can provide novel insights into the functions of genes that control seed development and the evolution of angiosperms. We downloaded the sequences and expression data from the relevant databases, and the seed-specific expression of genes was identified with cut-offs of a gene expression level ratio ≥ 5 and a Z-score ≥ 6. The genes were analysed using local BLAST software with an E-value ≤ 1.0E − 505. A total of 605, 581, 778 and 722 genes showed specific expression in the seeds of Medicago, soybean, Arabidopsis and rice, respectively. Additionally, we compared the expression patterns of seed-specific genes from each species with their homologues in the other three species, and found that the degree of variation in the expression patterns of homologous genes was low among closely related species but higher among more distantly related ones. The discrepancy between the homologous gene expression patterns may be caused by the different characteristics of the cis-elements in the promoter regions of the homologous genes.

Sucrose, raffinose and stachyose accumulate as stored soluble carbohydrates in embryos during soybean [Glycine max L. (Merrill)] seed development and maturation. Raffinose and stachyose in soybean feed products are not digested by humans, chickens or pigs, resulting in flatulence and reduced nutritional value. Soybean lines selected for low raffinose and low stachyose (LRS) or low raffinose, low stachyose and low phytin (LRSP1, LRSP2) concentrations in mature seeds were compared to a CHECK line with normal raffinose, stachyose and phytin. To determine whether increasing the supply of free cyclitols to immature embryos of these lines results in increased accumulation of galactosyl cyclitols, isolated immature embryos free of maternal tissues were fed solutions containing either d-chiro-inositol, myo-inositol or d-pinitol, or a control solution without cyclitols, for 24 h. Embryos were precociously matured by slow drying for 14 d with daily transfers to stepwise lower relative humidities. Soluble carbohydrates were extracted from axis and cotyledon tissues of mature, dry embryos and analysed by high-resolution gas chromatography. Axis and cotyledons from LRS, LRSP1 and LRSP2 embryos had low concentrations of stachyose compared to CHECK embryos after feeding a control solution without cyclitols. Feeding d-chiro-inositol to isolated embryos increased fagopyritol B1 accumulation in embryos of all lines. Feeding myo-inositol increased stachyose accumulation in LRSP1 and LRSP2 cotyledons. Feeding d-pinitol increased free d-pinitol in cotyledons of all lines but increased galactopinitol A and galactopinitol B only in LRS cotyledons. Supplying additional d-chiro-inositol to immature embryos can enhance accumulation of fagopyritol B1 in mature embryos of low-raffinose and low-stachyose or low-raffinose, low-stachyose and low-phytin soybeans.

Soil tillage operations stimulate germination of buried seeds in cultivated lands, allowing them to perceive light as a germination-promoting factor. The time of burial and the effect of changing environmental factors affect the physiological state of the seeds, which may lead to an extreme light-sensitivity and very low fluence response (VLFR) through phytochrome A. This paper describes the influence of the progressive process of dormancy breakage, which is accompanied by the acquisition of extreme light-sensitivity, on processes associated with endosperm weakening and embryo growth potential in the VLFR-mediated promotion of Datura ferox seed germination. Our results show that endosperm weakening is mainly limited by β-mannosidase enzyme activity after far-red light stimulation, which is highly dependent on the dormancy level of the seeds. In addition, stimulation of the embryo growth potential by far-red irradiation did not require an extreme light-sensitivity to very low fluence of photons to reach its maximum response, and it was not completely correlated with expansin gene expression in the embryo. Our work indicates that responses of endosperm weakening and embryo growth potential to far-red irradiation, dependent on dormancy level, have different requirements for stimulation by the signalling network initiated by phytochrome A during the course of the very low fluence response in Datura ferox seeds.

Both phenotypic and genetic variation can affect the establishment success of exotic species. Using the weed Senecio vernalis Waldst. & Kit. with a continuous westward expansion of the native geographic range, we asked to what degree seed traits and germination patterns differ among different habitat disturbance types in the introduced region. We hypothesized that seed traits and germination pattern differ between different disturbance types, with lighter seeds and enhanced germination speed in highly disturbed habitats. Since S. vernalis colonizes successfully various disturbed habitats, we expected to find a high phenotypic genetic variation. Individuals from 19 populations were sampled from one region in Eastern Germany to study seed trait variation and germination success by means of a germination experiment and to assess genetic patterns using amplified fragment length polymorphism (AFLP) markers. Contrary to our expectation, habitat disturbance types did not differ in seed traits, germination characteristics or genetic variation. Instead, we found highest phenotypic and genetic variation within populations. Maximum percentage of germination was positively affected by seed mass. In addition, there was a weak but significant association between AFLP band patterns and population size and seed width, indicating that some variation in seed traits has a genetic component. In conclusion, the absence of a population differentiation at this geographic scale makes it unlikely that adaptation to different disturbance regimes is involved. Instead, a high variation in seed traits, overall high germination and genetic variation within populations under a wide range of habitat disturbance conditions seems to enable the offspring to colonize various habitat disturbance types.

Low soil water potential limits or prevents germination and emergence of rainfed winter wheat (Triticum aestivum L.). This phenomenon is particularly pronounced in the winter wheat–summer fallow region of the US Inland Pacific Northwest, where wheat is routinely sown deep to reach moisture with 12–15 cm of soil covering the seed. Wide differences in seedling emergence among winter wheat cultivars have been reported, but few previous experiments have examined germination differences among cultivars as a function of water potential. The objective of our laboratory study was to quantify seed germination of five commonly sown winter wheat cultivars (Moro, Xerpha, Eltan, Buchanan and Finley) at seven water potentials, ranging from 0 to − 1.5 MPa. Germination was measured as a function of time for a period of 30 d. At higher water potentials (0 to − 0.5 MPa), all cultivars had germination of more than 90%. At the lowest water potentials ( − 1.0 to − 1.25 MPa), however, Moro consistently exceeded the other cultivars for speed and extent of germination, with total germination of 74% at − 1.0 MPa and 43% at − 1.25 MPa. Since its release in 1966, Moro has been sown by farmers when seed-zone water conditions are marginal. Scientists have long known that coleoptile length is an important factor controlling winter wheat seedling emergence from deep sowing depths. In addition to having a long coleoptile, our data suggest that Moro's known excellent emergence ability from deep sowing depths in dry soils can also be attributed to the ability to germinate at lower water potentials than other cultivars.

Gene flow between agricultural crops and related wild plant populations can produce hybrids which differ significantly from their wild counterparts in many life history traits, including seed traits. Seeds from wild annuals often possess significant dormancy, while cultivated varieties have been selected to germinate immediately under favourable conditions. Consequently, the dormancy characteristics of crop–wild hybrids could influence their survival, seed-bank dynamics and, ultimately, the extent to which crop genes persist in wild populations. Dormancy characteristics can be influenced by both maternal effects, as well as the genetics of a seed's embryo, which are the result of contributions from both parents. Here we focus on how maternal effects and embryo genetics affect seed dormancy in crop–wild hybrid sunflowers (Helianthus annuus). Using three laboratory experiments, we quantified the germination and dormancy of 15 crop–wild hybrid sunflower cross types, while also identifying achene characteristics that may influence the differential germination observed. We found that increased frequencies of crop alleles and the maternal effects imparted by hybridization can reduce dormancy, though the effect of increased frequencies of crop alleles was more pronounced in wild- and F1-produced than in the crop-produced achenes. The more open pericarp of the crop-produced achenes and the shorter relative distance that their radicles had to travel to germinate may explain some of the observed maternal effects. Finally, we generated hypotheses about how these results could affect survival and crop gene introgression in the field.

Helianthinins are storage proteins present in Helianthus annuus seeds, belonging to the 11S globulin family. Here we describe that a fraction of the helianthinins is phosphorylated. This conclusion is supported by different criteria, including identification by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry of major protein bands revealed with a specific dye for phosphoproteins, anti-phosphoserine antibody and binding to a phosphoprotein affinity matrix. Moreover, we show that the phosphorylation status of helianthinins changes following germination.

The present study was conducted to evaluate the contribution of nitric oxide (NO) to the priming effects on seed germination, seedling vigour and low-temperature tolerance of two tomato cultivars (Solanum lycopersicum, cv. Cherry and Falcato) under four different constant temperatures (10, 15, 20 and 25°C). Treatments included priming in a polyethylene glycol 6000 (PEG 6000) solution (osmopriming) or presoaking in sodium nitroprusside (SNP) solution, a donor of NO, for 24 h at 25°C. Suboptimal temperatures reduced seed germination and subsequent seedling growth, as well as amylase activity, in both cultivars, but Falcato was more sensitive to low temperature than Cherry. Both osmopriming and SNP treatments enhanced germination capacity, germination index, seedling root and shoot length, α- and β-amylase activities and sugar content under suboptimal temperatures, especially in Falcato. We observed similarities between the modes of action of the two priming treatments. Both treatments increased seed NO content, whereas their positive effects on germination and subsequent seedling growth under low-temperature stress was reversed by the addition of methylene blue (MB), a scavenger of NO. This is the first report that suggests that positive effects of priming are most likely mediated through NO signalling.

This paper examines the dispersal–germination strategy of seeds of 66 native tree species from a seasonal evergreen monsoon rainforest on Hainan Island, China, and assesses correlations among seed germination and phylogeny, dispersal mode and dispersal season. Seeds of 15, 7, 25 and 19 species were dispersed during the warm dry (March–May), rainy (June–September), late rainy (October–November) and cool dry (December–February) seasons, respectively. Berries (16 species), drupes (14 species) and capsules (12 species) were common and represented about 64% of the species. Zoochory was the most common dispersal mode (69.7%) followed by anemochory (16.7%) and autochory (13.6%). More than 65% of species had dormant seeds. Based on germination speed and synchrony, six patterns were recognized: rapid and synchronous germination (13 species), intermediate and synchronous germination (3 species), intermediate and intermediately synchronous germination (24 species), intermediate and asynchronous germination (2 species), slow and intermediately synchronous germination (5 species), and slow and asynchronous germination (19 species). One-way ANOVAs revealed that the variance in germination percentages among species was largely dependent upon phylogeny. The mean and median length of germination (MLG) were largely dependent upon phylogeny, dispersal mode and dispersal season. Anemochorous seeds germinated faster than autochorous and zoochorous seeds. Seeds dispersed in the late dry or early rainy season (March–May) tended to germinate quickly, whereas those dispersed towards the end of the rainy season and into the cool dry season are likely to have a much longer length of dormancy. Correlation analyses indicated that larger seeds germinated faster and had higher germination percentages.