Desert plants are exposed to water shortage and often salinity, instantly after dormancy withdrawal. We studied the effects of aridity and salinity on germination and initial growth of Bassiaindica, B. iranica and B. prostrata. We hypothesized that: (1) all species would exhibit adaptations to water shortage immediately after germination, including rapid root growth and high seedling-survival rates; and (2) obligate halophytes benefit from positive effects of salinity on germination success and desiccation tolerance. After we germinated seeds in water or NaCl solutions, desiccated and rehydrated them, we found that all three species showed rapid germination and root elongation, as well as good germination success. However, salinity had a negative effect on the germination success of all three, with only B. indica germinating in 3% NaCl. Salinity had a positive effect on desiccation tolerance of B. indica seedlings, but had no significant effect on either B. prostrata or B. iranica. Thus the presence of salinity immediately after germination can protect halophyte seedlings from desiccation. To the best of our knowledge, survival of seedlings after periods of desiccation and rewetting with solutions of up to 3% NaCl has never been reported. Studying salinity tolerance in halophytes is important in a world exposed to expanding desertification.

Niche theory predicts that when two species exhibit major niche overlap, one will eventually be eliminated through competitive exclusion. Thus, some degree of niche specialization is required to facilitate coexistence. We examined whether two important seed bank pathogens on the invasive winter annual grass Bromus tectorum (cheatgrass, downy brome) exhibit niche specialization. These pathogens utilize seed resources in complementary ways. Pyrenophora semeniperda is specialized to attack dormant seeds. It penetrates directly through the seed coverings. Hyphae ramify first through the endosperm and then throughout the seed. Seed death results as the embryo is consumed. In contrast, the Fusarium seed rot pathogen (Fusarium sp.) is specialized to attack non-dormant seeds in the early stages of germination. It cannot penetrate seed coverings directly. Instead, it responds to a cue emanating from the radicle end with directional hyphal growth and subsequent penetration at the point of radicle emergence, causing seed death. Non-dormant seeds usually escape P. semeniperda through germination even if infected because it develops more slowly than Fusarium. When water stress slows non-dormant seed germination, both P. semeniperda and Fusarium can attack and cause seed mortality more effectively. The Fusarium seed rot pathogen can sometimes reach epidemic levels and may result in B. tectorum stand failure (‘die-off’). Stands usually re-establish from the persistent seed bank, but if P. semeniperda has also reached high levels and eliminated the seed bank, a die-off can persist indefinitely.

Osmotic priming reduces the longevity of Vigna radiata (mung bean) seeds during subsequent dry storage. The present study has investigated the relationship between volumetric changes, modified water sorption properties and the decrease in seed longevity after priming. Volumetric analysis of control embryos revealed two major dehydration-related volumetric contractions in the biopolymer matrix, reflecting structural reorganization in biopolymer matrix during drying. These contractions occurred at hydration from 0.29 to 0.23 g g–1 dw and from 0.18 to 0.11 g g–1 dw, respectively. Volumetric contractions were reduced significantly after priming and also occurred at higher water contents (i.e. 0.48–0.32 g g–1 dw and 0.21–0.11 g g–1 dw). Consequently, at the same water content, primed seed embryos had higher specific biopolymer volume and lower specific density than control embryos. Water sorption study showed that priming did not change the monolayer hydration value, but altered the properties of multilayer water sorption in seed axes. The analysis of water clustering function suggested that priming enhanced the water–water association in seed axes, but not in cotyledon tissues. Solid-state 1H-NMR (nuclear magnetic resonance) investigation confirmed that priming did not cause a significant change of water dynamic properties in cotyledon tissues at water contents below 0.20 g g–1 dw. The relevance of volumetric modifications of the biopolymer matrix and changes in water clustering function to the reduced seed longevity after priming is discussed. It is proposed that priming-induced increases in surface reactivity may enhance deteriorative chemical reactions in re-dried seed tissues.

Seeds of some eastern Australian Grevillea species show the characteristics of non-deep physiological dormancy, which is broken by exposure to heat shock and/or smoke. The current study tested whether the restrictive effect of the seed coat on germination was localized to specific regions, whether the fire cues affected the growth potential of the embryo, the mechanical strength of the seed coat itself, and the anatomy of fracturing of the seed coat. Removal of the micropylar seed coat allowed germination, while retaining it in place restricted germination. The growth potential of the embryo was increased by exposure to heat shock or to smoke, and increased the most if exposed to both cues. Estimation of the minimum force required by embryos to germinate from intact seeds suggested that this force was reduced for seeds treated with fire cues. The fire cues did not affect the resistance of the seed coat to compressive force when tested after 24 h of imbibition. Fracturing of the seed coat occurred between cell walls, except for the palisade layer, where fracturing occurred across palisade and sclerenchyma cells. While the micropylar end of the seed coat imposes dormancy, most likely by mechanical constraint, heat shock and smoke overcome dormancy by increasing the embryo's growth potential and possibly weakening the seed coat, either directly or via the embryo.

To persist (without immigration) in habitats with unpredictable environmental conditions, annuals must produce seeds each year or have a seed bank. Thus, we predicted that compared to perennials, annuals have a wider germination temperature range (GTR, the difference in temperature between the week with the highest and the week with the lowest germination during the natural germination season). We determined the GTR via germination phenology data for 350 herbaceous species in 59 families from the eastern USA: summer annuals (SA), 63; winter annuals (WA), 83; monocarpic perennials (MP), 28; and polycarpic perennials (PP), 176. There was no significant phylogenetic signal for the GTR. The width of the GTR during the first spring germination season was 9.6, 8.7 and 8.8°C for MP, PP and SA, respectively, and during the first autumn germination season 12.8, 11.8 and 12.4°C for MP, PP and WA, respectively. Annuals did not have a wider GTR than perennials in either the spring or the autumn germination season. Our data suggest that selection for early germination in either spring or autumn has resulted in only small differences in the GTR. We predict that global warming will have little or no effect on reshaping the germination phenology of herbaceous species of temperate eastern North America.

A population-based modelling approach was used to predict the occurrence of germination in Solanum sarrachoides (SOLSA) for different treatments. Seeds collected in Toledo (Spain) were exposed to constant temperatures, to temperatures alternating between 10 and 30°C and to gibberellins (GAs; 0, 50, 100, 150 and 1000 ppm) during a 24-h imbibition period. The following parameters were measured: base temperature (Tb), mean thermal time (θT (50)) and the standard deviation of thermal time (σθT ). The SOLSA seeds only germinated at constant temperatures when the highest GA concentration was applied. The thermal model suggests that the induction and loss of physiological dormancy following seed dispersal is achieved when temperatures vary and when a mean thermal time of 66 growing degree-days (d°C) and a Tb value of 16°C are achieved when no GA treatment was added. The concentration of GA applied under conditions of alternating temperatures has an additive effect, reducing θT (50) up to threefold, from basal level (66 d°C) to 19.40 d°C, when the 1000 ppm GA treatment was applied. In this last case, the germination was accelerated by reducing Tb to 14°C. A 5–10°C change in temperature and a range of average temperatures of 20–27.5°C promoted the germination of SOLSA seeds to the greatest extent in the absence of GA. However, these conditions are not frequently encountered in the irrigated areas of the studied region; this finding could explain the limited ability of SOLSA to expand its range within this area.

Fatty acid (FA) levels and profiles are vital for soybean oil quality, while cytokinins (CKs) and abscisic acid (ABA) are potent regulators of plant growth and development. Previous research suggested associations between FA biosynthesis and hormonal signalling networks; however, hormonal regulation of FA accumulation during soybean (Glycine max) seed maturation has never been measured. We analysed hormone and FA profiles obtained from HPLC-(ESI)-MS/MS and GC-FID screening during soybean seed maturation. A multilayered data processing approach, involving heat-maps, principal component analysis (PCA), correlation and multiregression models, suggested a strong relationship between hormone metabolism and FA/oil accumulation during seed maturation. Most strikingly, positive correlations were found between the levels of CK ribosides [transZeatin riboside (tZR), N6-isopentenyladenosine (iPR)] at the early stages of SM (R5-R6) and C18:0, C18:2 and oil content at the R8 stage. Moreover, multiple regression models revealed functional linkages between several CK derivatives and FA and oil content in mature seeds. To further test the significance of hormone regulation in FA metabolism, plants of two soybean accessions with contrasting hormone and FA profiles were sprayed with exogenous ABA and transZeatin (tZ) during the seed-filling period (R5-R6). Depending on the hormone type and concentration, these treatments distinctly modified biosynthesis of all tested FAs, except for C18:0. Most remarkably, tZ (50 nM) promoted production of C16:0, C18:1, C18:2, C18:3, and oil accumulation in maturing seeds. Overall, the results indicate impactful roles for ABA and CKs in FA accumulation during SM and represent a further step towards understanding FA biosynthesis, and potential improvements of soybean oil profiles.

Priming has proved to enhance seed germination, but most of the research dealing with this topic has been carried out with cultivated species. The potential applications that this process has on wild species, which can be useful for restoration, are usually overlooked. This study analyses the germination response after natural priming and hydropriming of Penstemon roseus and Castilleja tenuiflora, two perennial herbs growing in a protected area known as ‘Parque Ecológico de la Ciudad de México’. Photoblastism was evaluated for both species. Seeds were exposed to a hydration/dehydration cycle and then placed in germination chambers to determine responses to hydropriming. To identify the effects of natural priming, seeds were buried in natural conditions and then recovered every two months and placed in germination chambers. Germination percentages and rates were then quantified. Both species proved to have permeable seed coats. Penstemon roseus seeds are positive photoblastic whereas C. tenuiflora seeds are indifferent to light. Priming methods increased C. tenuiflora germination rates, but they did not affect germination capacity. For P. roseus, priming methods did not improve germination rates, and germination capacity of recovered seeds decreased after the rainy season, suggesting that P. roseus forms a short-term, transient, seed bank. The germination strategies of these two species allow them to occupy suitable microsites for germination and establishment. These responses can be helpful in developing restoration programmes based on the accelerated establishment of native and characteristic successional species.

Seed longevity is dependent on seed traits and storage conditions. This study evaluated the seed longevity and physical dormancy (PY)-break of two species of Dimorphandra endemic to Brazilian biodiversity hotspots. Longevity was tested in situ, by burying seeds in their natural habitats (12 months), and ex situ, by storage in a cold chamber (5°C; 24 months). Seeds were taken at regular intervals to assess germinability at 30°C (12 h photoperiod) using intact and scarified seeds. Intact seeds (freshly collected, and after 12 months storage) were analysed using scanning electron microscopy. The germinability of freshly collected seeds of both species reached approximately 10% for intact seeds and >85% for scarified seeds. Cold storage maintained seed viability in both species, and broke dormancy for 35% of D. wilsonii seeds. After 12 months, only 55% (for D. exaltata) and 41% (for D. wilsonii) of the buried seeds were recovered; more than 90% of which remained viable in both species. Seeds gradually overcame PY during burial, with a higher germination increase for D. wilsonii (71%) than D. exaltata (32%). Dimorphandra exaltata seeds did not show clear structural changes after cold storage although D. wilsonii seeds evidently experience an increase in the depth of fracture lines. Burial promoted deep seed coat changes in both species, more intense in D. wilsonii, indicating that temperature and humidity variations throughout the year are among the main factors releasing Dimorphandra seeds from PY. The seeds of both studied species overcame PY during burial and are able to form small persistent soil seed banks.

Impermeability of the testa hinders efficient penetration of some small chemicals, such as transcriptional inhibitors, through the endosperm and the embryo during seed experiments. In Arabidopsis seeds, 5-bromo-4-chloro-3-indolyl β-d-glucuronic acid, a substrate for β-glucuronidase, did not permeate through the endosperm and embryo efficiently at the stages before testa rupture. The Arabidopsis testa also limited efficient entry of methoxyfenozide, a chemical ligand that was used for inducible gene expression experiments, into seeds. While the detection of a reporter gene at the early imbibitional stages could be replaced by reverse transcription-polymerase chain reaction (RT-PCR), the interference of entry of the chemical ligand into seeds by the testa was still problematic to gene induction experiments. To develop an efficient inducible expression system for gene function analysis in seeds, an inducible expression system with nitrate, which is a testa-permeable ligand, was examined. The vector containing the 2.1-kb upstream sequence of NITRITE REDUCTASE 1 was able to cause expression of a test gene (long non-coding RNA) in imbibed seeds at the stage before testa rupture in a nitrate-dependent manner. This system can be used not only for characterization of genes associated with seed dormancy and germination in basic research, but also for the development of germination recovery or enhancement technologies for agricultural applications.

We hypothesized that Strychnos nux-vomica and Strychnos potatorum in seasonal tropical ecosystems have dormant desiccation-tolerant seeds, while those of Strychnos benthamii growing in aseasonal wet habitats have non-dormant desiccation-sensitive seeds. Germination, imbibition, the effect of gibberellic acid on germination and changes in the embryo to seed length ratio (E:S) during incubation were determined for the three species. Seed storage behaviour was identified with the hundred seed test. Time taken for epicotyl emergence was recorded. Radicle emergence of S. nux-vomica, S. potatorum and S. benthamii at 25°C under light/dark conditions (12/12 h) was completed within 76, 49 and 11 d, respectively. S. nux-vomica and S. potatorum seeds incubated on GA3 germinated to a higher percentage than non-treated seeds. E:S of S. nux-vomica, S. potatorum and S. benthamii had increased by 38.2, 34.5 and 25.5%, respectively, at radicle emergence. Shoot emergence of S. nux-vomica, S. potatorum and S. benthamii was observed after 76, 74 and 45 d from radicle emergence, respectively. Thus, it can be concluded that the seeds of all three species have epicotyl morphophysiological dormancy. Hundred seed tests revealed that S. nux-vomica and S. potatorum seeds were desiccation-tolerant, while those of S. benthamii were desiccation-sensitive. Our study showed that species from seasonal habitats (S. nux-vomica and S. potatorum) have desiccation-tolerant morphophysiologically dormant seeds, while those from an aseasonal habitat (S. benthamii) have desiccation-sensitive morphophysiologically dormant seeds, revealing that their dormancy and desiccation tolerance behaviour are adaptations to their environment.

Genetic and biochemical studies have greatly advanced our understanding of the biology of seeds in recent years. Another area of study, which could accelerate contemporary seed biology research, is phylogenomics that integrates the wealth of genome sequence data with evolutionary biology. The recent phylogenomic study of the DELAY OF GERMINATION1 family genes exemplifies how the molecular evolution of seed genes can be traced back through early diverging plants and what implications can be obtained from the analysis of seed gene diversification at ancient times. The identification of possible ancestors of seed genes in non-seed plants could illuminate the ancient roots of the molecular mechanisms driving seed maturation programmes. It is possible that the origins of molecular mechanisms associated with the induction of seed storage proteins and desiccation tolerance proteins date back to the time of, or even prior to, early diverging land plants. Abscisic acid-dependent growth arrest or dormancy mechanisms might date back to red algae, one of the oldest algal groups. Thus, understanding algal cell biology will also be an integral part of future seed biology research. Unravelling key events associated with the evolution of seed- and non-seed plants will not only advance basic research but could also contribute to applied aspects of seed science, potentially leading to technology development for agriculture.

Although the level of seed desiccation sensitivity (LSDS) may have an impact on plant species conservation, information is available for <10% of tropical angiosperms. A study was conducted to assess the LSDS of 28 tropical montane species in Sri Lanka. Seeds were extracted from freshly collected fruits. Initial weight was recorded, and thousand seed weight (TSW) was calculated. Seed moisture content (MC) was determined. LSDS was determined using seed desiccation experiments and predicted using the TSW–MC criterion. Seed storage behaviour was predicted using LSDS and storage data and using a model based on phylogenetic affiliation. The relationship between LSDS and seed dormancy, life form and forest strata was evaluated. Fresh seeds of only 12 species germinated to >80%. Although seeds of the other species had >80% viability, only 0–70% germinated due to dormancy. Seeds of five species had MC <15%, indicating desiccation tolerance (DT). Seeds of 12 species lost viability after desiccation, indicating desiccation sensitivity (DS). Seeds of Ardisia missionis, Psychotria gartneri and Psychotria nigra remained viable after desiccation, showing DT. Seeds of 17 species were DS and those of 11 species DT. The TSW of four species was >500 g. Thus, seeds of other species were predicted to be DT by the TSW–MC criterion. A relationship was identified between LSDS and the forest strata of the species. More canopy species produced DS than DT seeds. Since seeds of most of the studied species were DS, these species may be threatened due to prolonged droughts predicted for the region due to climate change.

Little information is available on seed dormancy of members of the Zingiberales and especially the Zingiberaceae. Our aim was to investigate the dormancy breaking and germination requirements of Alpinia galanga in vitro with a minimum number of seeds, using the move-along experiment. The mass of imbibed seeds increased by 17.5% in 1 d, showing that seeds were water permeable. The best germination in the move-along experiment (86.7%) was obtained when seeds were exposed to the sequence of temperature regimes that began with winter (20/10°C), and seeds began to germinate after 6 weeks at this temperature regime. Seeds dry stored for 4 months and then incubated at the sequence of temperature regimes that began with summer (30/20°C) started germinating in the sixth week at this temperature regime and had germinated to 93.3% after 18 weeks. Seeds kept dry for 4 months and then treated with 50 mg l−1 gibberellic acid (GA3) began to germinate at 30/20°C after 2 weeks. Control seeds incubated continuously at 20/10, 25/15 or 30/20°C germinated to 80.6, 77.8 and 60.0%, respectively. When incubated at 15, 20, 25 or 30°C, the ideal temperature for embryo growth was 20°C. Since GA3 and dry storage can break non-deep physiological dormancy and embryos grew during warm stratification, seeds of A. galanga have non-deep simple morphophysiological dormancy (MPD). This is the first report of non-deep simple MPD in the Zingiberaceae.

Serotiny is a strategy in which the retention of mature seeds in parent structures allows plants to cope with environmental variability like heat, drought or fire. Although this phenomenon might be common in Cactaceae, and particularly in Melocactus, it has generally been scarcely addressed. The main goal of our work is to investigate if there are seeds hidden in the cephalium of Melocactus matanzanus and if there are, determine whether or not these seeds maintain their viability. We also discuss some advantages the cephalium may offer as diaspore after the death of individuals. Cephalia collected from dead individuals were divided into four slices and their seeds counted; we also assessed the viability and photoblastic response of the seeds by using growth chambers at 25/30°C, and by a cut test on the seeds that did not germinate. Our results showed retention of viable seeds of different ages in all slices of the cephalium. Seeds were photoblastic positive with germination between 11–22% and viability above 50% in the portion of the lots that did not germinate.

Wheat (Triticum aestivum L) seeds contain a proteinaceous α-amylase inhibitor. We estimated the amount of the inhibitor that can bind to α-amylase rather than the total amount of the inhibitor, using an ELISA method. During 48 h of imbibition, the amount of the inhibitor did not change, while α-amylase activity increased rapidly. These results suggest that α-amylase synthesized de novo does not bind to the inhibitor. To examine further the interaction between α-amylase and its inhibitor, we localized immunohistochemically both α-amylase and the inhibitor in germinating seeds. In the embryo, we observed α-amylase only in the scutellar epithelial cells at 24 h after the start of imbibition, and later in the scutellar parenchyma cells. The inhibitor, on the other hand, was present between the scutellar parenchyma cells of the embryo at 0 h and 24 h after the start of imbibition, and disappeared later. α-amylase is separated from the inhibitor in the embryo. In the endosperm, we detected α-amylase in the aleurone cells at 24 h after the start of imbibition and later in the starchy endosperm. The inhibitor was present in the aleurone cells and starchy endosperm of the dry seed. During imbibition, the inhibitor in the starchy endosperm disappeared from the area to which α-amylase was secreted. It appears that α-amylase in the starchy endosperm also does not interact with the inhibitor. The aleurone cells are the only place that α-amylase can come into contact with the inhibitor. But, early secretion of α-amylase from the aleurone cells after imbibition started, and rapid disappearance of the inhibitor in the aleurone cells suggest that the α-amylase inhibitor does not work as an effective inhibitor of the endogenous α-amylase synthesized following germination.

Submerging Phaseolus vulgaris cv. Top Crop seed in air-saturated water for 16 h markedly depresses subsequent germination. This is termed soaking injury. The postulate by Norton (1986) that soak-injured seeds merely run out of available energy was investigated. Soaking in air-saturated water reduced the total respiration (VT; in terms of O2 uptake) of excised axes and cotyledons resulting in lower ATP levels. The contribution of both the mitochondrial cytochrome respiratory pathway (VCYT) and the alternative respiratory pathway (VALT) to the total respiration (VT) was significantly lower in these axes. However, the adenylate energy charge (AEC) values for both axes and cotyledons excised from soak-injured seeds did not drop below 0.6, the threshold value indicating death of plant material. Differences between the ultrastructure of mitochondria in the radicle tips of axes from unsoaked and water-soaked seeds were observed. However, the capacity to operate the Krebs cycle was similar in all axes and soak-injured seeds were still capable of germinating when the testas were removed or the seeds dried. This means that axes contained a sufficient amount of carbohydrates and potential energy to germinate after soaking. Moreover, soak-injured seeds produced ethanol at a rate which was five times higher than that of unsoaked control seeds, both during the soaking and post-soaking periods. Together with the low rate of oxygen consumption by soak-injured seeds during the same soaking and incubation time, it appears that soak-injured seeds lack the potential to switch from an anaerobic to an aerobic respiration pattern causing low ATP levels in these axes. It is speculated that the latter seems to be the result of limited pyruvate supply, probably due to accelerated and prolonged fermentation or futile combustion through other pathways or both.

To maximize seed longevity, seeds should be harvested at optimal maturity, that is, when seeds have acquired maximum physiological quality before deterioration begins. The aim of this study was to map the variation in temporal patterns of lentil (Lens culinaris Medik.) seed quality development when grown across four regeneration environments, which differ in the level of temperature and humidity control throughout the growing season, at the Australian Grains Genebank. Seeds of two lentil accessions (76080 and 76072) were harvested at different stages throughout development, commencing at 21 d after 50% anthesis until a maximum of 130 d. At each harvest, physiological quality traits, including germinability (fresh and dried seeds) and seed longevity, were determined, as well as seed dry weight and moisture content. Seeds of both accessions, and in all environments, started to accumulate physiological quality early on in development but did not reach their maximum until 3–54 d after mass maturity. The temporal patterns of desiccation tolerance and storage longevity were highly influenced by the environmental conditions during the maturation drying phase, affecting both ‘when’ maximum quality was attained and for how long it was maintained, thereafter. Seeds did not show a typical developmental response, rather variation was observed in seed quality development both between and within accessions grown in the different environments. The poorest storage longevity was seen when seeds of both accessions were grown in the cooler, temperature-controlled glasshouse, and the maximum longevity was observed in the warmer, semi-protected environments of the green and the big igloo for accessions 76080 and 76072, respectively.