Although seed dormancy of temperate legumes is well understood, less is known about it in species that grow in subalpine/alpine areas. This study investigated dormancy and germination of four Vicia species from the Tibetan Plateau. Fresh seeds of V. sativa were permeable to water, whereas those of V. angustifolia, V. amoena and V. unijuga had physical dormancy (PY). One year of dry storage increased the proportion of impermeable seeds in V. angustifolia, but showed no effect on seed coat permeability in V. amoena or V. unijuga. Seeds of all four species also had non-deep physiological dormancy (PD), which was especially apparent in the two annuals at a high germination temperature (20°C). After 1 year of storage, PD had been lost. The hydrotime model showed that fresh seeds obtained a significantly higher median water potential [Ψb(50)] than stored seeds, implying that PD prevents germination in winter for seeds dispersed without PY when water availability is limited. After 6 months on the soil surface in the field, a high proportion of permeable seeds remained ungerminated, further suggesting that PD plays a key role in preventing germination after dispersal. Addition of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis, evened-out the differences in germination between fresh and stored seeds, which points to the key role of ABA biosynthesis in maintaining dormancy. Further, fresh seeds were more sensitive to exogenous ABA than stored seeds, indicating that storage decreased embryo sensitivity to ABA. On the other hand, the gibberellic acid GA3 increased germination rate, which implies that embryo sensitivity to GA is also involved in seed dormancy regulation. This study showed that PY, PD or their combination (PY+PD) plays a key role in timing germination after dispersal, and that different intensities of dormancy occur among these four Vicia species from the Tibetan Plateau.

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.

Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is an important technology to analyse gene expression levels during plant development or in response to different treatments. An important requirement to measure gene expression levels accurately is a properly validated set of reference genes. In this context, we analysed the potential use of 17 candidate reference genes across a diverse set of samples, including several tissues, different stages and environmental conditions, encompassing seed germination and seedling growth in Ricinus communis L. These genes were tested by RT-qPCR and ranked according to the stability of their expression using two different approaches: GeNorm and NormFinder. GeNorm and Normfinder indicated that ACT, POB and PP2AA1 comprise the optimal combination for normalization of gene expression data in inter-tissue (heterogeneous sample panel) studies. We also describe the optimal combination of reference genes for a subset of root, endosperm and cotyledon samples. In general, the most stable genes suggested by GeNorm are very consistent with those indicated by NormFinder, which highlights the strength of the selection of reference genes in our study. We also validated the selected reference genes by normalizing the expression levels of three target genes involved in energy metabolism with the reference genes suggested by GeNorm and NormFinder. The approach used in this study to identify stably expressed genes, and thus potential reference genes, was applied successfully for R. communis and it provides important guidelines for RT-qPCR studies in seeds and seedlings for other species (especially in those cases where extensive microarray data are not available).

Ecological (climatic and geographic) variation in early life-history transitions is a vital determinant of the adaptive evolution of timing of seed germination. This study aimed to investigate the correlation between timing of seed germination and environmental conditions during seed development. We examined seed germination timing of 15 coniferous seed lots of lodgepole pine, ‘interior’ spruce and western hemlock collected from natural stands in British Columbia (BC), Canada, under manipulated [stratification, thermo-priming (15 or 20°C) and their combinations] and non-manipulated (control) conditions. Timing of seed germination showed strong and positive correlation with the temperature-based environmental condition during seed development. This pattern persisted across species and seed lots within species, substantiating the historic importance of environmental conditions during seed development and maturation to life-history traits. Moreover, the strategy of phenotypic plasticity affecting timing of seed germination was observed across the applied germination treatments. These results provide insight into the germination niche as affected by global warming, indicating that conifers' seed dormancy in BC (north of 54°N) tends to increase and the changes associated with early spring warm-up are expected to accelerate seedling emergence, as shortened winters would have a minimal effect on dormancy decay.

Chromosome integrity and DNA polymerase activity are negatively affected by improper storage of maize seeds. We have extended our studies on the effect of improper storage on DNA metabolism by analysing the effect of hot–dry and hot–humid conditions on DNA ligase activity. An assay to measure ligase activity was established by using linearized plasmid DNA as substrate and protein extracts from maize axes. Optimal conditions were established for the in vitro assay. Enzyme activity was importantly reduced under both storage conditions. Activity recovered 6–9 h after imbibition. A model for loss of viability and vigour due to damage of DNA metabolism is proposed.

Dormant weed seeds were germinated at constant and alternating temperatures using five chemicals. Germination of Chenopodium album when expressed in normal equivalent deviates, increased linearly with the logarithm of chemical dose up to an optimal concentration. Ethephon (2-chloroethyl phosphonic acid) and sodium azide slightly stimulated germination of C. album seeds at 20°C while potassium nitrate, thiourea and azide each interacted positively with alternating temperatures (5°/25°C). Relief of Avena fatua dormancy by azide exhibited a positive interaction with cool constant temperatures (3–10°C), and chemicals had smaller or no effects at higher and alternating temperatures. No chemical mixture, including that of nitrate, thlourea, ethephon, azide and hydrogen peroxide, promoted more germination than azide on its own in A. fatua or nitrate together with ethephon in C. album. In C. album, this result arose largely because nitrate and azide antagonized each other in the presence of ethephon. Peroxide and thiourea together relieved this antagonism so that the fourth order interaction was positive. The negative interaction of nitrate, azide and ethephon in C. album was avoided in a sequential treatment with nitrate plus ethephon for seven days followed by sodium azide. Relief of dormancy by nitrate and ethephon was optimized at 67 mM nitrate with 1.4 mM ethephon for C. album at 20°C and 20 mM nitrate with 1.4 mM ethephon for A. fatua at 15°C. None of the chemicals used in this investigation stimulated the germination of Rumex crispus seeds. The results are discussed with respect to chemical control of soil seed banks.

Fritillaria tubiformis subsp. moggridgei (Liliaceae) is a rare, endemic species that inhabits open mountains and alpine grasslands of the Ligurian Alps. At the time of seed dispersal, the underdeveloped embryos were 27% the length of the seed. Here we report the results of laboratory experiments carried out to determine the temperature preferences for embryo growth and radicle emergence. Embryo growth commenced immediately after sowing at 4°C. Once the embryo had grown the length of the seed, the radicle emerged. The time required for embryo growth and radicle emergence was longer when seeds were placed through a seasonal sequence of temperatures, commencing with late summer (10/20°C), compared with seeds immediately placed at a temperature to simulate winter conditions (4°C). Prematurely transferring seeds from winter to spring temperatures (5/10°C) also slowed the progress of germination. Radicle emergence did not occur at 10 or − 5°C and less than 20% germination occurred in seeds placed at constant 0°C. Addition of gibberellic acid (GA3) did not promote embryo growth of seeds placed at 20°C. Overall, the temperature preferences for embryo growth and subsequent radicle emergence are such that, in situ, seed germination may occur during the winter under snow cover or at the end of winter to coincide with snow melt and warming temperatures.

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

Experiments on the facultative winter annuals Carduus acanthoides and Anagallis arvensis were performed: (i) to determine thermal conditions that induce or release dormancy, (ii) to investigate to what extent changes in dormancy level resulting from those thermal conditions explain the seasonal pattern of emergence of these species, and (iii) to estimate required thermal time and base temperature for the germination of non-dormant seeds. Carduus acanthoides required high temperatures followed by decreasing temperatures for dormancy release; however, low winter temperatures did not induce secondary dormancy as expected for a winter annual. To the contrary, low temperatures stimulated dormancy release in the long term. In A. arvensis, dormancy relief was enhanced by dry storage at 25°C, and the response to low temperature was different depending on moisture conditions. Prolonged exposure to moist-chilling increased the dormancy level of the population, while dry storage at 4°C relieved dormancy. For both species, changes in the thermal range permissive for germination as a result of dormancy modifications explained to a large extent the timing of the emergence periods observed in the field. In neither species did base temperature for germination change with the dormancy level of the population. Thermal time required forgermination of C. acanthoides varied with dormancy, while for A. arvensis seeds it was constant.

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

The performance of cucumber (Cucumis sativus L.) seeds in relation to ovary and ovule position was monitored during seed production. Seeds from three (first, seventh and tenth nodes) fruit positions and three (stylar, intermediate and peduncular) ovule positions were harvested serially during development and characterized with physiological and cellular markers. Seed moisture contents declined to 30%approx. 35 d after pollination (DAP) and remained constant thereafter. At 42 DAP the maximum dry weight was acquired in seeds except those from peduncular segments, whose dry weight accumulation lagged behind. The onset of germinability and desiccation tolerance occurred before the attainment of maximum dry weight, whereas seed performance, as shown by laboratory germination and greenhouse emergence, was largely improved after the completion of seed development. Cell cycle activities (DNA per nucleus and β-tubulin content) ceased by 28 DAP, whereas the degradation of seed chlorophyll continued during the entire maturation period. Seeds from the top fruit and from the peduncular fruit segments were delayed in reaching maximum quality compared with seeds from other positions, and this was correlated with a slower decline of chlorophyll fluorescence.

Soil samples were collected from the original land surface beneath an experimental earthwork, constructed in 1963 at Morden Bog, Dorset, England, and excavated in 1996. Large numbers of seeds of Calluna vulgaris, Erica cinerea and E. tetralix germinated from the samples, but other species present in the original flora, including Ulex minor and several grasses, were absent. The results confirm the previously-documented longevity of Calluna and E. tetralix, and for the first time demonstrate similar longevity in E. cinerea.

Systemic uptake of organic compounds from roots to leaves follows a Gaussian distribution in relation to the lipophilicity, as measured by the log Kow. Quantification of compound uptake with different lipophilicities, and applied as a seed treatment that diffuses through the seed coat into the embryo during imbibition, has not been reported. The aim of this investigation was to quantify the uptake of non-ionic compounds into seeds of soybean and corn. A series of fluorescent piperonyl amides were synthesized and a novel combinatorial pharmacodynamic technique was developed that provided a range of compounds from log Kow 0.02 to 5.7. Seeds were treated with a mixture of amides, imbibed and compounds chemically extracted and quantified by high-performance liquid chromatography using a fluorescence detector. The maximum uptake efficiency of the applied amide mixture from whole soybean and corn seeds was 67% at log Kow 2.9, and 43% at log Kow 3.4, respectively. The critical partition coefficient for uptake for both species was <4.2 log Kow. Seeds were dissected and separated as soybean embryo and testa, and corn internal tissues (embryo + endosperm) or seed covering layers (pericarp + testa), and >75% of the amides were found in the soybean embryo or corn internal tissues compared with the covering layers at log Kow <4.2. The distribution of amides showed that the corn seed covering layer had similar hydrophilic/lipophilic properties as internal tissues, while soybean tissues had different hydrophilic/lipophilic properties. Collectively, the Gaussian uptake pattern for systemic uptake into plants was not found for either seed species.

Malva parviflora L. (Malvaceae) is rapidly becoming a serious weed of Australian farming systems. An understanding of the variability of its seed behaviour is required to enable the development of integrated weed management strategies. Mature M. parviflora seeds were collected from four diverse locations in the Mediterranean-type climatic agricultural region of Western Australia. All of the seeds exhibited physical dormancy at collection; manual scarification or a period of fluctuating summer temperatures (50/20°C or natural) were required to release dormancy. When scarified and germinated soon (1 month) after collection, the majority of seeds were able to germinate over a wide range of temperatures (5–37°C) and had no light requirement. Germination was slower for seeds stored for 2 months than seeds stored for 2 years, suggesting the presence of shallow physiological dormancy. Seed populations from regions with similar annual rainfall exhibited similar dormancy release patterns; seeds from areas of low rainfall (337–344 mm) were more responsive to fluctuating temperatures, releasing physical dormancy earlier than those from areas of high rainfall (436–444 mm). After 36 months, maximum seedling emergence from soil in the field was 60%, with buried seeds producing 13–34% greater emergence than seeds on the surface. Scanning electron microscopy of the seed coat revealed structural differences in the chalazal region of permeable and impermeable seeds, suggesting the importance of this region in physical dormancy breakdown of M. parviflora seeds. The influence of rainfall during plant growth in determining dormancy release, and hence, germination and emergence timing, must be considered when developing management strategies for M. parviflora.

The phenomenon of dormancy extends beyond the boundaries of the plant kingdom. While plant biologists typically associate dormancy-breaking treatments only with seeds, buds or tubers, these chemicals and environmental stimuli have much broader activity as general terminators of developmental arrest in other, non-plant species. The activation of growth by these treatments is associated with signal transduction processes, metabolic upregulation and changes in gene expression, in addition to other events that may or may not be species specific. The study of both the classic and current developmental arrest literature beyond the boundaries of plant biology may be helpful in generating useful ideas and analogies for meaningful experimental progress towards understanding seed dormancy.

Quercus robur L. fruits are desiccation sensitive and shed from the plant at high moisture content (c. 48%). Water relations measurements were taken at intervals during the germination of prematurely-harvested immature fruits and naturally-shed mature fruits. In fruits from both harvests the pericarp and seed coat delayed germination by providing physical barriers to emergence of the radicle and by restricting the rate of imbibition. Although immature fruits could germinate in the absence of water they germinated more rapidly in the presence of an external water supply. The fully-mature fruit required a supply of external water, but germination was more rapid than in immature fruits. Substantial physiological changes, resulting in the accumulation of solutes, and increased axis size and extensibility occurred before splitting of the pericarp and subsequent germination of immature fruits. Such changes did not occur in fully-mature fruits, but fruits, from both harvests imbibed water and splitting of the pericarp appeared to result from increased embryo size and tissue pressure. Splitting was minimal prior to germination in immature fruits without an external water supply. It is suggested that the resulting reduction in Ψp when the pericarp splits was greater in the axis than in the cotyledons because of its greater capacity for expansion. This would create a Ψw gradient driving water flow to the axis from the cotyledons allowing continued radicle growth for germination.

Three questions are considered in the context of the possible effects of seed-associated mycoflora, typified by Fusarium moniliforme, during hydrated storage of recalcitrant propagules of the tropical species, Avicennia marina. These pertain to storage lifespan, whether seed susceptibility to fungal attack changes and the possibility of discriminating ultrastructurally between inherent deteriorative changes and those that are fungallyinduced. The data indicate unequivocally that if fungal activity is curtailed, then the hydrated storage lifespan of A. marina seeds can be considerably extended. When inoculated immediately with F. moniliforme, newly harvested seeds were extremely susceptible to the adverse effects of the fungus, while seeds that had been wet-stored for 4 d showed a considerably heightened resilience to the effects of the fungus when inoculated at that stage. The enhanced resilience, although declining, persisted in seeds stored hydrated for up to 10 d prior to inoculation, being lost after 12 d. After 14 d of hydrated storage, seeds became more susceptible to the effects of the fungus than those in the newly harvested condition. The resilience of seeds that had been stored in the short-term was associated with ultrastructural changes indicative of enhanced metabolic activity associated with the onset of germination. However, with the sustained stress imposed by wet-storage conditions, the seeds became increasingly badly affected by the fungus. While it was not possible to discriminate with certainty among deteriorative subcellular events ascribable to inherent deterioration or the effects of the fungus, it is concluded that a comparison of the timing of the onset of degeneration may well be diagnostic of its cause.

Smoke-water (SW), karrikinolide (KAR1) and vermicompost leachate (VCL) have been reported to possess gibberellic acid-like activity. The effects of these plant growth-promoting substances (PGPSs) on biochemical changes occurring during seed germination of Phaseolus vulgaris were assessed. Seeds were incubated/germinated under dark conditions in water (control) or with different concentrations of SW, KAR1, VCL and gibberellic acid (GA3) for 7 d. The maximum seedling fresh weight (1.863 g) was recorded for the SW (1:750 v/v) treatment. The longest seedling axes (9.9 cm) and the highest number of adventitious roots (16.3) were recorded for VCL-treated seedlings (1:10 and 1:5 v/v, respectively). Analysis of two important hydrolytic enzymes, acid phosphatase and alpha-amylase, showed maximum activity [1856 nkat mg− 1 and 3.225 mg min− 1(g FW)− 1, respectively] in the seeds incubated with 10− 8M KAR1. In all the treated seedlings, proline content was significantly reduced [43.67 μg (g FW)− 1; VCL (1:20 v/v)] in comparison to the control [87 μg (g FW)− 1] but there was an increase in amino acids with some concentrations of PGPSs. The tested PGPSs significantly influenced various biochemical parameters that play a significant role in seed germination and plant growth. This study indicates that PGPSs may act via stress-relieving biochemical pathways during seed germination.

The genus Aegilops belongs to the secondary gene pool of wheat and has great importance for wheat cultivar improvement. As a genus with only annual species, regeneration from seeds in Aegilops is crucial. In several species in Aegilops, spikes produce different seed morphs, both in size and germination patterns. However, little is known about the ecology of seed germination, nor about the seed longevity in this genus. Here we investigated the germination phenology of Ae. neglecta under laboratory and field conditions and assessed longevity of different seed morphs of five additional Aegilops species using controlled ageing tests. Large seeds were short-lived and germinated faster than small seeds in most of the species. Field experiments with Ae. neglecta showed that large seeds of the dimorphic pair germinated 3 months after dispersal in contrast to 14 months for smaller seeds. Differences in longevity were detected not only in dimorphic seed pairs, but also among seeds from different positions on the spike. Our results indicate that different longevities in seed morphs of Aegilops may reflect a different soil seed bank persistence, with smaller seeds able to maintain a higher viability after dispersal than larger ones, thereby spreading seedling emergence over two years. Differences of seed germination and longevities between seed morphs in Aegilops may have important implications for ex situ seed conservation and reinforce the hypothesis of a bet-hedging strategy in the germination ecology of this genus.

Seeds of Carduus acanthoides, Cynara cardunculus, Cirsium vulgare, Brassica campestris, and Sisymbrium altissimum were incubated at a range of decreasing osmotic potentials (Ψo) under fluctuating temperatures or the median temperature of the fluctuation cycle. Fluctuating temperatures promoted total seed germination in water and at reduced osmotic potential. Total germination was reduced as the Ψo decreased. However, this trend was smallest under fluctuating temperatures, signalling a higher tolerance of seeds to reduced osmotic potential. Effects of osmoticum and temperature were modelled with the hydrotime model. The parameters estimated from the model, the hydrotime constant (θH), the mean base water potential Ψb(50) and its standard deviation (σΨb) gave good descriptions of germination time courses. For all species, incubation under fluctuating temperatures shifted Ψb(50) values downwards without modifying their distribution substantially. This accounted for the greater tolerance of germination to reduced Ψo under fluctuating temperatures. To confirm that these effects were mediated by temperature fluctuations per se, the behaviour of C. acanthoides and C. cardunculus incubated at the minimum, the mean and the maximum temperature of the fluctuation cycle was also analysed. Constant maximum and minimum temperatures of the cycle did not stimulate germination, nor did they shift Ψb(50) towards more negative values. The hydrotime model provides a physiologically based quantitative description for germination promotion due to fluctuating temperature.