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Background and Aims Orchid seeds are reputed to be short lived in dry, cold storage conditions, potentially limiting the use of conventional seed banks for long-term ex situ conservation. This work explores whether Cattleya seeds are long lived or not during conventional storage (predried to ~12 % relative humidity, then stored at −18 °C). Methods We explored the possible interaction of factors influencing seed lifespan in eight species of the genus Cattleya using physiological (germination and vigour), biochemical (gas chromatography), biophysical (differential scanning calorimetry) and morphometric methods. Seeds were desiccated to ~3 % moisture content and stored at −18 °C for more than a decade, and seed quality was measured via three in vitro germination techniques. Tetrazolium staining was also used to monitor seed viability during storage. The morphometric and germination data were subjected to ANOVA and cluster analysis, and seed lifespan was subjected to probit analysis. Key Results Seeds of all Cattleya species were found to be desiccation tolerant, with predicted storage lifespans (P 50y) of ~30 years for six species and much longer for two species. Cluster analysis showed that the three species with the longest-lived seeds had smaller (9–11 %) airspaces around the embryo. The post-storage germination method impacted the quality assessment; seeds equilibrated at room temperature for 24 h or in 10 % sucrose solution had improved germination, particularly for the seeds with the smallest embryos. Chromatography revealed that the seeds of all eight species were rich in linoleic acid, and differential scanning calorimetry identified a peak that might be auxiliary to selecting long-lived seeds. Conclusions These findings show that not all orchids produce seeds that are short lived, and our trait analyses might help to strengthen prediction of seed longevity in diverse orchid species. [ABSTRACT FROM AUTHOR]

Seed storage underpins global agriculture and the seed trade and revealing the mechanisms of seed aging is essential for enhancing seed longevity management. Safflower is a multipurpose oil crop, rich in unsaturated fatty acids that are at high risk of peroxidation as a contributory factor to seed aging. However, the molecular mechanisms responsible for safflower seed viability loss are not yet elucidated. We used controlled deterioration (CDT) conditions of 60% relative humidity and 50 °C to reduce germination in freshly harvested safflower seeds and analyzed aged seeds using biochemical and molecular techniques. While seed malondialdehyde (MDA) and fatty acid content increased significantly during CDT, catalase activity and soluble sugar content decreased. KEGG analysis of gene function and qPCR validation indicated that aging severely impaired several key functional and biosynthetic pathways including glycolysis, fatty acid metabolism, antioxidant activity, and DNA replication and repair. Furthermore, exogenous sucrose and diethyl aminoethyl hexanoate (DA-6) treatment partially promoted germination in aged seeds, further demonstrating the vital role of impaired sugar and fatty acid metabolism during the aging and recovery processes. We concluded that energy metabolism and genetic integrity are impaired during aging, which contributes to the loss of seed vigor. Such energy metabolic pathways as glycolysis, fatty acid degradation, and the tricarboxylic acid cycle (TCA) are impaired, especially fatty acids produced by the hydrolysis of triacylglycerols during aging, as they are not efficiently converted to sucrose via the glyoxylate cycle to provide energy supply for safflower seed germination and seedling growth. At the same time, the reduced capacity for nucleotide synthesis capacity and the deterioration of DNA repair ability further aggravate the damage to DNA, reducing seed vitality. [ABSTRACT FROM AUTHOR]

Introduction: Tilia miqueliana is an endemic species whose population is declining. The permeability barrier and mechanical constraint of the pericarp (seed coat) are important causes of its seed dormancy. Although there has been considerable research on this subject, questions remain regarding how the permeability barrier and mechanical constraint of the seed coat are eliminated during dormancy release and how water enters the seed. Therefore, protecting the species by improving its germination/dormancy breaking in the laboratory is urgent. Methods: In this study, the changes in the cellular structure, mechanical properties, and components of the Tilia miqueliana seed coat after an H2SO4-gibberellic acid (GA3) treatment were analyzed during dormancy release. Various analyses (e.g., magnetic resonance imaging, scanning electron microscopy, and paraffin section detection) revealed the water gap and water channel. Results: The H2SO4 treatment eliminated the blockage at the micropyle and hilum of the seeds. Water entered the seeds through the water gap (micropyle) rather than through the hilum or seed coat, after which it dispersed along the radicle, hypocotyl, and cotyledon to the endosperm. During the cold stratification period, the cellular structure was damaged and an increasing number of holes appeared on the inner and outer surfaces of the seed coat. Vickers hardness tests showed that GA3 decreased the seed coat hardness. Additionally, the seed coat lignin and total phenol contents continuously decreased during the cold stratification period. Notably, the Liquid chromatography-mass spectrometry (LC-MS) analysis of the seed coat detected polyethylene glycol (osmoregulator), which may have destabilized the water potential balance inside and outside the seed and increased the water content to levels required for germination, ultimately accelerating seed dormancy release. Discussion: This sophisticated and multi-level study reveals how H2SO4 and GA3 eliminate the permeability barrier and mechanical constraints of the seed coat during dormancy release of Tilia miqueliana seeds. This will be beneficial to artificially assist the natural regeneration and population expansion of Tilia miqueliana. [ABSTRACT FROM AUTHOR]

Introduction: Cryo treatment of dry seeds is known to attenuate the structure of fruit and seed coats, but little is known about the microstructural impacts of such treatment. The seeds of Tilia miqueliana are dispersed within a hard pericarp, the manual removal (hulling) of which is time-consuming and inefficient. Rapid hulling technology is urgently needed for sustainable production and convenience of edible nuts. Methods: We explored the mechanistic basis of liquid nitrogen (N)-treatment weakening of the pericarp of T. miqueliana fruits using a range of microscopical, biophysical and chemical approaches. Results: Liquid N treatment (40 s) resulted in lower pericarp contents of cellulose and hemicellulose, and increased amounts of lignin. Profound changes in cell structure and mechanical properties included the emergence of large holes and gaps between the mesocarp and endocarp cells. Also, the toughness of the pericarp decreased, whilst the hardness and brittleness increased, thereby changing the fracture type from ductile to brittle. Liquid N treatment of dry fruits followed by tapping with a hammer, reduced the number of damaged seeds three-fold and pericarp peeling time four-fold compared with manual hulling, whilst seed viability was not negatively affected. Discussion: Comparable findings for the efficient and economical removal of hard covering structures from dispersal units of five more species from three other families following liquid N treatment indicates the potential application of our findings to large-scale production of seeds and seedlings for breeding, forestry and conservation/restoration purposes. Furthermore, it introduces a novel concept for postharvest treatment and pre-treatment of deep processing in nuts. [ABSTRACT FROM AUTHOR]

Persistence in the soil is a function of seed physiology, particularly non-germination and inherent lifespan. However, for seeds with mechanical dormancy, non-germination is also a function of the composition and activity of the soil microbiota. We attempted to screen out microorganisms in the soil that can specifically and rapidly decompose the hard fruit pericarps of Tilia miqueliana Maxim., a unique native tree species in China. Using the classical replica plating method, more than 100 different culturable microorganisms that could rapidly erode the pericarp were collected from the surface of pericarps under different culture conditions. At the same time, we successfully extended the concept of metagenomics and applied it to the identification of mixed artificial cultures. The decomposition process of the pericarps in soil was also simulated artificially. The physical and chemical data suggested a potential mechanism of microbial scarification and cracking in pericarp, whilst the embryos inside the eroded fruits retained good viability. Our discoveries could pave the way for the removal of physical and mechanical obstacles that prevent hard coat seeds from germinating. We anticipate that the use of this technology will improve the germination of other hard coat seeds. More research is needed to investigate the impacts on other seeds. The findings of this research can inform the design of experiments on the seed ecology of persistence. [ABSTRACT FROM AUTHOR]

A substantially rich diversity of the world's recorded useful plants (UPs) is captured within the Millennium Seed Bank collection hosted by the Royal Botanic Gardens, Kew, at Wakehurst, UK with 13,598 species (34%) belonging to 3696 genera and 325 families. This constitutes just over half of the total accessions and one third of the species and covers all 9 continents, 8 realms, 14 biomes, 34 biodiversity hotspots and 175 countries. The most common beneficial use category within the captured diversity is medicinal, then species with environmental, material, and human food value. About 86% of conserved UP species have a 'Least Concern' conservation status but 8% are identified as globally threatened. The advantages of mutual, continued, and long-term partnership (e.g., Mexico) are showcased when conserving plants important for local communities and addressing conservation challenges beyond seed banking. However, the geographic coverage suffers from a lack of partnerships with some parts of the world. Also, a low number of accessions contributed from many countries means that insufficient native range is yet to be captured for many species. This is particularly the case for restricted or narrow distribution species from families or genera with a high incidence of recalcitrant or short-lived seeds. Future planning must tailor better to cover the spatial distribution patterns for individual species, thereby improving the number of accessions and geographical coverage for those captured. Moreover, seed biology research should characterise desiccation tolerance and develop complementary, novel conservation methods, such as cryopreservation, to strengthen conservation options for UP species. [ABSTRACT FROM AUTHOR]

Intra-specific variation in seed storage behaviour observed in several species has been related to different maternal environments. However, the particular environmental conditions and molecular processes involved in intra-specific variation of desiccation tolerance remain unclear. We chose Citrus sinensis 'bingtangcheng' for the present study due to its known variability in desiccation tolerance amongst seed lots. Six seed lots of mature fruits were harvested across China and systematically compared for drying sensitivity. Annual sunshine hours and average temperature from December to May showed positive correlations with the level of seed survival of dehydration. Transcriptional analysis indicated significant variation in gene expression between relatively desiccation-tolerant (DT) and -sensitive (DS) seed lots after harvest. The major genes involved in late seed maturation, such as heat shock proteins, showed higher expression in the DT seed lot. Following the imposition of drying, 80% of stress-responsive genes in the DS seed lot changed to the stable levels seen in the DT seed lot prior to and post-desiccation. However, the changes in expression of stress-responsive genes in DS seeds did not improve their tolerance to desiccation. Thus, higher desiccation tolerance of Citrus sinensis 'bingtangcheng' seeds is modulated by the maternal environment (e.g., higher annual sunshine hours and seasonal temperature) during seed development and involves stable expression levels of stress-responsive genes. [ABSTRACT FROM AUTHOR]

The lifespan or longevity of a seed is the time period over which it can remain viable. Seed longevity is a complex trait and varies greatly between species and even seed lots of the same species. Our scientific understanding of seed longevity has advanced from anecdotal 'Thumb Rules,' to empirically based models, biophysical explanations for why those models sometimes work or fail, and to the profound realisation that seeds are the model of the underexplored realm of biology when water is so limited that the cytoplasm solidifies. The environmental variables of moisture and temperature are essential factors that define survival or death, as well as the timescale to measure lifespan. There is an increasing understanding of how these factors induce cytoplasmic solidification and affect glassy properties. Cytoplasmic solidification slows down, but does not stop, the chemical reactions involved in ageing. Continued degradation of proteins, lipids and nucleic acids damage cell constituents and reduce the seed's metabolic capacity, eventually impairing the ability to germinate. This review captures the evolution of knowledge on seed longevity over the past five decades in relation to seed ageing mechanisms, technology development, including tools to predict seed storage behaviour and non-invasive techniques for seed longevity assessment. It is concluded that seed storage biology is a complex science covering seed physiology, biophysics, biochemistry and multi-omic technologies, and simultaneous knowledge advancement in these areas is necessary to improve seed storage efficacy for crops and wild species biodiversity conservation. [ABSTRACT FROM AUTHOR]

Despite the importance of secondary dormancy for plant life cycle timing and survival, there is insufficient knowledge about the (epigenetic) regulation of this trait at the molecular level. Our aim was to determine the role of (epi)genetic processes in the regulation of secondary seed dormancy using natural genotypes of the widely distributed Capsella bursa-pastoris. Seeds of nine ecotypes were exposed to control conditions or histone deacetylase inhibitors [trichostatin A (TSA), valproic acid] during imbibition to study the effects of hyper-acetylation on secondary seed dormancy induction and germination. Valproic acid increased secondary dormancy and both compounds caused a delay of t50 for germination (radicle emergence) but not of t50 for testa rupture, demonstrating that they reduced speed of germination. Transcriptome analysis of one accession exposed to valproic acid versus water showed mixed regulation of ABA, negative regulation of GAs, BRs and auxins, as well as up-regulation of SNL genes, which might explain the observed delay in germination and increase in secondary dormancy. In addition, two accessions differing in secondary dormancy depth (deep vs non-deep) were studied using RNA-seq to reveal the potential regulatory processes underlying this trait. Phytohormone synthesis or signalling was generally up-regulated for ABA (e.g. NCED6 , NCED2 , ABCG40 , ABI3) and down-regulated for GAs (GA20ox1 , GA20ox2 , bHLH93), ethylene (ACO1 , ERF4-LIKE, ERF105 , ERF109-LIKE), BRs (BIA1 , CYP708A2-LIKE , probable WRKY46 , BAK1 , BEN1 , BES1 , BRI1) and auxin (GH3.3 , GH3.6 , ABCB19 , TGG4 , AUX1 , PIN6 , WAT1). Epigenetic candidates for variation in secondary dormancy depth include SNL genes, histone deacetylases and associated genes (HDA14 , HDA6-LIKE , HDA-LIKE , ING2 , JMJ30), as well as sequences linked to histone acetyltransferases (bZIP11 , ARID1A-LIKE), or to gene silencing through histone methylation (SUVH7 , SUVH9 , CLF). Together, these results show that phytohormones and epigenetic regulation play an important role in controlling differences in secondary dormancy depth between accessions. [ABSTRACT FROM AUTHOR]

Germplasm conservation strongly depends on the desiccation tolerance (DT) of seeds. Xerophytic seeds have strong desiccation resistance, which makes them excellent models to study DT. Although some experimental strategies have been applied previously, most methods are difficult to apply to xerophytic seeds. In this review, we attempted to synthesize current strategies for the study of seed DT and provide an in-depth look at Caragana korshinskii as an example. First, we analyze congenital advantages of xerophytes in the study of seed DT. Second, we summarize several strategies used to study DT and illustrate a suitable strategy for xerophytic species. Then, based on our previous studies work with C. korshinskii, a feasible technical strategy for DT re-establishment is provided and we provide illustrate some special molecular mechanisms seen in xerophytic seeds. Finally, several steps to unveil the DT mechanism of xerophytic seeds are suggested, and three scientific questions that the field should consider are listed. We hope to optimize and utilize this strategy for more xerophytic species to more systematically decipher the physiological and molecular processes of seed DT and provide more candidate genes for molecular breeding. [ABSTRACT FROM AUTHOR]

During seed aging, there is a critical node (CN) where the population viability drops sharply. Exploring the specific locations of the CN in different species of plants is crucial for understanding the biological storage properties of seeds and refining seed life span management. Safflower, a bulk oil crop that relies on seeds for propagation, has a short seed life. However, at present, its biological characteristics during storage are not clear, especially the changes in metabolic capability and cell structures. Such knowledge is needed to improve the management of safflower seed life span and effective preservation in gene banks. Here, the seed survival curve of oilseed safflower under the controlled deterioration conditions of 60% relative humidity and 50°C was detected. The seed population showed an inverted S shape for the fall in germination. In the first 12 days of aging, germination remained above 86%. Prior to the CN at approximately day 10 (C10), when viability was in the “plateau” interval, seed vigor reduced at the same imbibition time point. Further analysis of the changes in sugar concentration found that the sucrose content decreased slowly with aging and the content of raffinose and two monosaccharides decreased abruptly at C10. Differentially metabolized lipids, namely lysophospholipids [lyso-phosphatidylcholine (LPC) and lyso-phosphatidylethanolamines (LPE)] and PMeOH, increased at day 3 of aging (C3). Fatty acid content increased by C6, and the content of phospholipids [phosphatidylcholines (PC), phosphatidylethanolamines (PE), and phosphatidylinositols (PI) and glycolipids [digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulphoquinovosyl diglycerides (SQDG)] decreased significantly from C10. In addition, the activities of raffinose hydrolase alpha-galactosidase and the glyoxylate key enzyme isocitrate lyase decreased with seed aging. Confocal microscopy and transmission electron microscopy revealed shrinkage of the seed plasma membrane at C10 and the later fragmentation. Seedling phenotypic indicators and 2,3,5-triphenyltetrazolium chloride activity assays also verified that there were significant changes in seeds quality at the CN. In summary, the time point C10 is a CN during seed population aging. Before the CN, sugar and lipid metabolism, especially fatty acid metabolism into sugar, can make up for the energy consumed by aging. After this point, the seeds were irreversibly damaged, and their viability was greatly and rapidly reduced as the cell structure became increasingly destroyed. [ABSTRACT FROM AUTHOR]

Generally, orchids produce dust-like seeds in which endosperm reduction and embryo undifferentiation represent a derived state shared with species in about 11 other plant families. Orchid seeds are proposed to have a special kind of morphological or morphophysiological dormancy. We test this proposition, overcoming several design limitations of earlier studies, specifically that the in vitro germination method for orchid seeds uses pro-oxidants for disinfection and incorporates nitrate in the medium; both 'treatments' might contribute to dormancy breaking, potentially confounding judgement on the depth and nature of the dormant state. Seeds of the tropical orchid Dendrobium cruentum Rchb. f., were sown both in vitro , on a nutrient medium, and ex vitro , on plain agar omitting prior disinfection with sodium hypochlorite. Seeds previously stored and fresh seeds were incubated under combinations of vitro conditions, light treatments, constant or alternating temperatures and nitrate concentration. Seeds of D. cruentum are very small but have a large embryo that occupies most of the seed. Over a range of constant temperature seeds germinated to the spherical protocorm stage just as well ex vitro as in vitro. Neither light nor nitrate were prerequisites for ex vitro germination. The ability of D. cruentum seed to germinate in the absence of environmental or chemical stimuli suggests that mature seed can be non-dormant. Our results support the proposition that neither all DUST seed fit a dormancy class nor all orchids produce morphological or morphophysiological seeds. Finally, embryo/seed volume determinations in orchids may prove as valuable in studies on the evolution and ecology of germination and dormancy as embryo:seed ratios in other angiosperm species. [ABSTRACT FROM AUTHOR]

In small seeds, light often promotes germination and longer-term exposure to darkness reduces light sensitivity. In cacti inhabiting harsh environments, a rapid response to light exposure is potentially advantageous for seedling establishment. We exposed dark-imbibed seeds of the cactus Cereus repandus to doses of red (RED) light and far-red (FR) light. The seeds exhibited positive photoblastism to RED light. Although the initial levels of germination varied between seed lots, the sensitivity to increasing the RED dose did not. As little as 5 min per day for 4 d was sufficient to saturate the light requirement for germination. The effects of RED light were reversed by FR exposure as long as the interval between RED and FR did not extend to 2 d, by which time the seeds had 'committed' to germinate. Dark incubation for 1–2 weeks prior to RED exposure reduced light sensitivity in two seed lots, such that RED only promoted around 20% germination. Phytochrome is assumed to mediate the reversibility of the RED:FR response. High sensitivity to light spectral quality suggests that seeds of C. repandus are able to germinate quickly in high-quality microsites, but seed burial or shading may commit the seeds to form a soil seed bank. The light characteristics of the germination trait in this species are typical of many small seeded species of the drylands. [ABSTRACT FROM AUTHOR]

Background and Aims European ancient woodlands are subject to land use change, and the distribution of herbaceous understorey species may be threatened because of their poor ability to colonize isolated forest patches. The regeneration niche can determine the species assembly of a community, and seed germination traits may be important descriptors of this niche. Methods We analysed ecological records for 208 herbaceous species regarded as indicators of ancient woodlands in Europe and, where possible, collated data on seed germination traits, reviewed plant regeneration strategies and measured seed internal morphology traits. The relationship between plant regeneration strategies and ecological requirements was explored for 57 species using ordination and classification analysis. Key Results Three regeneration strategies were identified. Species growing in closed-canopy areas tend to have morphological seed dormancy, often requiring darkness and low temperatures for germination, and their shoots emerge in early spring, thus avoiding the competition for light from canopy species. These species are separated into two groups: autumn and late winter germinators. The third strategy is defined by open-forest plants with a preference for gaps, forest edges and riparian forests. They tend to have physiological seed dormancy and germinate in light and at higher temperatures, so their seedlings emerge in spring or summer. Conclusion Seed germination traits are fundamental to which species are good or poor colonizers of the temperate forest understorey and could provide a finer explanation than adult plant traits of species distribution patterns. Seed dormancy type, temperature stratification and light requirements for seed germination are important drivers of forest floor colonization patterns and should be taken in account when planning successful ecological recovery of temperate woodland understories. [ABSTRACT FROM AUTHOR]

Despite the importance of dormancy and dormancy cycling for plants' fitness and life cycle phenology, a comprehensive characterization of the global and cellular epigenetic patterns across space and time in different seed dormancy states is lacking. Using Capsella bursa-pastoris (L.) Medik. (shepherd's purse) seeds with primary and secondary dormancy, we investigated the dynamics of global genomic DNA methylation and explored the spatio-temporal distribution of 5-methylcytosine (5-mC) and histone H4 acetylated (H4Ac) epigenetic marks. Seeds were imbibed at 30 °C in a light regime to maintain primary dormancy, or in darkness to induce secondary dormancy. An ELISA-based method was used to quantify DNA methylation, in relation to total genomic cytosines. Immunolocalization of 5-mC and H4Ac within whole seeds (i.e., including testa) was assessed with reference to embryo anatomy. Global DNA methylation levels were highest in prolonged (14 days) imbibed primary dormant seeds, with more 5-mC marked nuclei present only in specific parts of the seed (e.g., SAM and cotyledons). In secondary dormant seeds, global methylation levels and 5-mC signal where higher at 3 and 7 days than 1 or 14 days. With respect to acetylation, seeds had fewer H4Ac marked nuclei (e.g., SAM) in deeper dormant states, for both types of dormancy. However, the RAM still showed signal after 14 days of imbibition under dormancy-inducing conditions, suggesting a central role for the radicle/RAM in the response to perceived ambient changes and the adjustment of the seed dormancy state. Thus, we show that seed dormancy involves extensive cellular remodeling of DNA methylation and H4 acetylation. [ABSTRACT FROM AUTHOR]

B I Seed Germination and Stress i (Theme 5) b expounded how environmental thresholds for germination and the germination niche relates to species' resilience. This is further elucidated by Santos et al. (pp. 157-165) for dormancy-breaking and germination in two palm species, I Mauritia flexuosa i and I Attalea speciosa i , which vary in their seed desiccation tolerance, and show distinct germination responses to a range of temperatures. In her talk on 'Seed ecology of Australian native seeds - germination thresholds and stress tolerance', examples were presented from the Australian alpine regions where the future climate is predicted to be warmer and drier, and coastal regions where warmer and drier conditions will combine with salt stress due to an increased frequency of extreme sea-level events. B I Seed Memory i (Theme 1) b explored how the maternal environment during development influences seed quality traits such as germination, vigour and longevity, and the biochemical and molecular signalling networks that control seed responses. [Extracted from the article]

Volatile profiling using non-invasive gas chromatography–mass spectrometry provides insight into the specific processes occurring during seed ageing. Production of alcohols, aldehydes and ketones, derived from processes such as alcoholic fermentation, lipid peroxidation and Maillard reactions, are known to be dependent on storage temperature and relative humidity, but little is known about the potential modulating role of the gaseous environment, which also affects seed lifespan, on volatile production. Seeds of Lolium perenne (Poaceae), Agrostemma githago (Caryophyllaceae) and Pisum sativum (Fabaceae) were aged under normal atmospheric oxygen conditions and in sealed vials containing either oxygen absorbers, oxygen absorbers and silica gel (equilibrated at 60% RH), or silica gel alone. Seeds of A. githago that were aged in the absence of oxygen maintained higher viability and produced fewer volatiles than seeds aged in air. In addition, seeds of A. githago and L. perenne aged in the presence of silica gel were longer lived than those aged without silica, with no effect on seed moisture content or oxygen concentration in the storage containers, but with silica gel acting as a volatile trap. These results indicate that the use of inexpensive oxygen absorbers and silica gel could improve seed longevity in storage for some species and suggests a potential, and previously unidentified, role for silica gel in ultra-dry storage. [ABSTRACT FROM AUTHOR]

Ex situ conservation of orchid seeds requires the application of modern biotechnology to determine seed quality and to optimise in vitro regeneration. The nutrient requirements for germination and seedling growth in vitro can be species-specific and influenced by life history traits and habitats. Therefore, this study aimed to explore in vitro seed germination and subsequent seedling development of selected tropical and temperate epiphytic and terrestrial orchids on different growth media. Seeds of three epiphytic orchids [Dendrobium strebloceras (tropical), D. lineale (tropical) and D. cunninghamii (temperate)] were sown on four different media supplemented with 2% sucrose: (1) Murashige and Skoog (MS); (2) Vacin and Went (VW); (3) Norstog; and (4) water agar. In addition, D. strebloceras seed were sown on the media above supplemented with 3% sucrose and half-strength MS supplemented with either 2% or 3% sucrose. Seed germination of three temperate terrestrial orchids (Gastrodia cunninghamii, Pterostylis banksii and Thelymitra nervosa) was assessed on media (1–4) but with VW replaced by terrestrial orchid medium-BM1. Whilst all epiphytic orchids germinated on all media tested, the best seedling development for the two tropical species was on full or half-strength MS media. The temperate epiphyte D. cunninghamii germinated best on Norstog medium but did not develop further. Norstog and BM1 media supported germination and seedling development better in P. banksii and T. nervosa. This study concludes that temperate terrestrial P. banksii and T. nervosa need more excating media (Norstog and BM1 media) for seed germination and subsequent seedling development compared to tropical epiphytic species D. strebloceras and D. lineale. Optimising these nutrient requirements in vitro will underpin successful ex situ conservation of orchid species. Key message: Seeds of tropical epiphytic orchids, D. strebloceras and D.linelae require a less stringent nutrient medium for in vitro germination and seedling development compared to temperate terrestrial orchids P. banksii and T. nervosa. Understanding the differences in nutrient requirements for germination and subsequent seedling development underpins successful ex situ conservation of orchids. [ABSTRACT FROM AUTHOR]

Summary: Seed size shapes plant evolution and ecosystems, and may be driven by plant size and architecture, dispersers, habitat and insularity. How these factors influence the evolution of giant seeds is unclear, as are the rate of evolution and the biogeographical consequences of giant seeds.We generated DNA and seed size data for the palm tribe Borasseae (Arecaceae) and its relatives, which show a wide diversity in seed size and include the double coconut (Lodoicea maldivica), the largest seed in the world. We inferred their phylogeny, dispersal history and rates of change in seed size, and evaluated the possible influence of plant size, inflorescence branching, habitat and insularity on these changes.Large seeds were involved in 10 oceanic dispersals. Following theoretical predictions, we found that: taller plants with fewer‐branched inflorescences produced larger seeds; seed size tended to evolve faster on islands (except Madagascar); and seeds of shade‐loving Borasseae tended to be larger.Plant size and inflorescence branching may constrain seed size in Borasseae and their relatives. The possible roles of insularity, habitat and dispersers are difficult to disentangle. Evolutionary contingencies better explain the gigantism of the double coconut than unusually high rates of seed size increase. [ABSTRACT FROM AUTHOR]

In alpine ecosystems, imbibed seeds are often exposed to temperatures as low as −35 °C, challenging their survival in the soil. Here, we show that seeds have mechanisms to survive cold climate prevalent in alpine ecosystems and have identified three such mechanisms from existing literature, including two forms of freezing avoidance (the presence of water impermeable seed coats, and the supercooling of seed tissues) and one form of freezing tolerance (by extracellular-freezing). Experimentally-derived published data on the lowest temperature recorded at which 50% of a seed sample survived (i.e., lethal temperature; LT50) was used to generate a dataset of 24 species across low altitude, boreal and alpine environments. We assumed that the ability of seeds to maintain viability at very low temperatures would increase in species associated with higher altitudes conferring a competitive advantage that would be lost under projected climate change. However, our results reveal to underpin that seeds from boreal species survive relatively better at lower temperatures than those of alpine species. Paradoxically, a warming climate could lead to alpine seed death due to extremes of cold at the soil surface resulting from snow cover loss, whilst the declining snow cover may facilitate boreal forest colonization above the current treeline. [ABSTRACT FROM AUTHOR]

Orchid pollinia have the potential to make a valuable contribution to current techniques of germplasm storage and assisted reproduction, yet information regarding their preservation and their ability to remain viable over time is currently limited. Dactylorhiza fuchsii and Disa uniflora were used as models for investigating potential techniques for storing orchid pollinia. Initially, freshly harvested pollinia of Dact. fuchsii were incubated at 25 °C and 100% RH (relative humidity) for up to 7 days and germinated in vitro. For pollinia from both species, moisture sorption isotherms were constructed and thermal fingerprints generated using differential scanning calorimetry (DSC). Pollinia were stored at three temperatures (5, − 18 and − 196 °C) after equilibration at four different RHs (5, 33, 50 and 75%) and germinated. The isotherms and DSC results varied between species. Compared with D. uniflora, pollinia of Dact. fuchsii consistently equilibrated at higher moisture content (MC) for each RH, had less detectable lipids by DSC and had shorter lifespans, remaining viable after 3–4 months only at − 20 and − 196 °C and at low RH (5 and 33%). Both species' pollinia stored well at − 20 °C and − 196 °C, although there was some evidence of a small loss of viability under cryopreservation. In conclusion, pollen of these two species can be stored successfully for at least 3–4 months, and to maximize the pre-storage quality, it is recommended that fresh pollen is collected from flowers just prior to anthesis. [ABSTRACT FROM AUTHOR]

Native trees from the Caribbean were tested for seed desiccation responses, by adapting the "100-seed test" protocol. Ninety-seven seed lots of 91 species were collected in the Dominican Republic and tested for germination immediately after collecting, and after drying and moist storage. Seed desiccation sensitivity was assessed as a continuous variable (Viability Loss Index; VLI), based on seed germination values before and after drying. The results were compared with predictions of seed desiccation responses based on seed lot traits (initial moisture content and thousand-seed weight) and with those of published predictive models based on plant and seed traits. VLI could be calculated for seed lots of 40 species. 80% of these seed lots showed consistent results among experiments and predictive models. Issues on the set up of the experiments were discussed, as well as the species for which experimental results and predictions led to contrasting results. Overall, the "100-seed test" confirmed to be an effective tool for assessing seed desiccation responses of a diverse under-investigated woody flora, guiding the seed conservation of trees and their use in reforestation programmes. In addition, by providing new data, it might improve the performance of available predictive models. [ABSTRACT FROM AUTHOR]

Because the conditions used for seed ageing studies are often conducive to changes in seed lot dormancy status, taking a neural network approach might be particularly valuable in helping to disentangle signalling pathways and to unravel cause-effect relationships between the time of death during storage and deteriorative reactions leading to seed ageing (Zinsmeister et al., 2020). But not all facilities have access to advanced technologies to enable seed quality assessment or the maintenance of seed quality through the control of seed moisture. Because more traditional seed testing methods are time-consuming and require highly skilled seed analysts, techniques that promise faster, efficient and non-destructive seed testing are under development and are in great demand by the seed sector. More traditional methods of determining seed quality remain important for many species, such as seed weight, seed width, seed thickness and seed coat colour among accessions of Bambara groundnut; seed weight showed a positive relation with germination percentage in 50 accessions (Temitope Mary Jones, Nigeria). [Extracted from the article]

Desiccation-tolerant (DT) plant germplasm (i.e. seeds, pollen and spores) survive drying to low moisture contents, when cytoplasm solidifies, forming a glass, and chemical reactions are slowed. DT germplasm may survive for long periods in this state, though inter-specific and intra-specific variation occurs and is not currently explained. Such variability has consequences for agriculture, forestry and biodiversity conservation. Longevity was previously considered in the context of morphological features, cellular constituents or habitat characteristics. We suggest, however, that a biophysical perspective, which considers the molecular organization – or structure – within dried cytoplasm, can provide a more integrated understanding of the fundamental mechanisms that control ageing rates, hence the variation of longevity among species and cell types. Based on biochemical composition and physical–chemical properties of dried materials, we explore three types of the interplay between structural conformations of dried cytoplasm and ageing: (1) cells that lack chlorophyll and contain few storage lipids may exhibit long shelf life, with ageing probably occurring through slow autoxidative processes within the glassy matrix as it relaxes; (2) cells with active chlorophyll may die quickly, possibly because they are prone to oxidative stress promoted by the photosynthetic pigments in the absence of metabolic water and (3) cells that lack chloroplasts but contain high storage lipids may die quickly during storage at −20°C, possibly because lipids crystallize and destabilize the glassy matrix. Understanding the complex variation in structural conformation in space and time may help to design strategies that increase longevity in germplasm with generally poor shelf life. [ABSTRACT FROM AUTHOR]

We argue that the need for a quality seed supply chain is a major bottleneck for the restoration of Chile's native ecosystems, thus supplementing the list of bottlenecks proposed by Bannister et al. in 2018. Specifically, there is a need for defining seed transfer zones, developing standards and capacities for properly collecting and storing seeds, reducing information gaps on seed physiology and longevity, and implementing an efficient seed supply chain with certification of seed origin and quality. Without such capacities, countries are unlikely to meet their restoration commitments. Although we focus on bottlenecks in Chile, the issues we raise are relevant to other countries and thus the global agenda for ecological restoration. [ABSTRACT FROM AUTHOR]

Drylands are predicted to become more arid and saline due to increasing global temperature and drought. Although species from the Caatinga, a Brazilian tropical dry forest, are tolerant to these conditions, the capacity for germination to withstand extreme soil temperature and water deficit associated with climate change remains to be quantified. We aimed to evaluate how germination will be affected under future climate change scenarios of limited water and increased temperature. Seeds of three species were germinated at different temperatures and osmotic potentials. Thermal time and hydrotime model parameters were established and thresholds for germination calculated. Germination performance in 2055 was predicted, by combining temperature and osmotic/salt stress thresholds, considering soil temperature and moisture following rainfall events. The most pessimistic climate scenario predicts an increase of 3.9 °C in soil temperature and 30% decrease in rainfall. Under this scenario, soil temperature is never lower than the minimum and seldomly higher than maximum temperature thresholds for germination. As long as the soil moisture (0.139 cm3 cm3) requirements are met, germination can be achieved in 1 day. According to the base water potential and soil characteristics, the minimum weekly rainfall for germination is estimated to be 17.5 mm. Currently, the required minimum rainfall occurs in 14 weeks of the year but will be reduced to 4 weeks by 2055. This may not be sufficient for seedling recruitment of some species in the natural environment. Thus, in future climate scenarios, rainfall rather than temperature will be extremely limiting for seed germination. [ABSTRACT FROM AUTHOR]

Summary: Much is known about the inter‐specific distribution of life span in a wide diversity of vertebrates and in adult plants, but not for seeds, yet the functional trait seed life span underpins global agriculture, plant species conservation and seed persistence in the soil. We sourced data for five storage conditions (soil seed bank; high temperature – high humidity accelerated ageing; temperate, cooler, open storage; cool, dry, refrigerator; and cold, dry, freezer); and analysed the distribution of orthodox seed life span amongst crop and wild species. In all cases, whether for maximum known in situ life span in the soil seed bank (417 species), or for half‐lives (P50s) ex situ (732 species), the distribution is right‐skewed. The finding that seeds of > 50% of species are likely to have life spans ≤ 20% of the longest recorded under the same conditions has implications for future research on the evolution of seed traits and gene bank collections management. [ABSTRACT FROM AUTHOR]

To elucidate biochemical mechanisms leading to seed deterioration, we studied 23 wheat genotypes after exposure to seed bank storage for 6–16 years compared to controlled deterioration (CD) at 45 °C and 14 (CD14) and 18% (CD18) moisture content (MC) for up to 32 days. Under two seed bank storage conditions, seed viability was maintained in cold storage (CS) at 0 °C and 9% seed MC, but significantly decreased in ambient storage (AS) at 20 °C and 9% MC. Under AS and CS, organic free radicals, most likely semiquinones, accumulated, detected by electron paramagnetic resonance, while the antioxidant glutathione (GSH) was partly lost and partly converted to glutathione disulphide (GSSG), detected by HPLC. Under AS the glutathione half-cell reduction potential (EGSSG/2GSH) shifted towards more oxidising conditions, from −186 to −141 mV. In seeds exposed to CD14 or CD18, no accumulation of organic free radicals was observed, GSH and seed viability declined within 32 and 7 days, respectively, GSSG hardly changed (CD14) or decreased (CD18) and EGSSG/2GSH shifted to −116 mV. The pH of extracts prepared from seeds subjected to CS, AS and CD14 decreased with viability, and remained high under CD18. Across all treatments, EGSSG/2GSH correlated significantly with seed viability (r = 0.8, p<.001). Data are discussed with a view that the cytoplasm is in a glassy state in CS and AS, but during the CD treatments, underwent transition to a liquid state. We suggest that enzymes can be active during CD but not under the seed bank conditions tested. However, upon CD, enzyme-based repair processes were apparently outweighed by deteriorative reactions. We conclude that seed ageing by CD and under seed bank conditions are accompanied by different biochemical reactions. [ABSTRACT FROM AUTHOR]

Plant persistence and migration in face of climate change depends on successful reproduction by seed, a central aspect of plant life that drives population dynamics, community assembly and species distributions. Plant reproduction by seed is a chain of physiological processes, the rates of which are a function of temperature, and can be modelled using thermal time models. Importantly, while seed reproduction responds to its instantaneous thermal environment, there is also evidence of phenotypic plasticity in response to the thermal history experienced by the plant's recent ancestors, by the reproducing plant since seedling establishment, and by its seeds both before and after their release. This phenotypic plasticity enables a thermal memory of plant reproduction, which allows individuals to acclimatise to their surroundings. This review synthesises current knowledge on the thermal memory of plant reproduction by seed, and highlights its importance for modelling approaches based on physiological thermal time. We performed a comprehensive search in the Web of Science and analysed 533 relevant articles, of which 81 provided material for a meta‐analysis of thermal memory in reproductive functional traits based on the effect size Zr. The articles encompassed the topics of seed development, seed yield (mass and number), seed dormancy (physiological, morphological and physical), germination, and seedling establishment. The results of the meta‐analysis provide evidence for a thermal memory of seed yield, physiological dormancy and germination. Seed mass and physiological dormancy appear to be the central hubs of this memory. We argue for integrating thermal memory into a predictive framework based on physiological time modelling. This will provide a quantitative assessment of plant reproduction, a complex system that integrates past and present thermal inputs to achieve successful reproduction in changing environments. The effects of a warming environment on plant reproduction cannot be reduced to a qualitative interpretation of absolute positives and negatives. Rather, these effects need to be understood in terms of changing rates and thresholds for the physiological process that underlie reproduction by seed. [ABSTRACT FROM AUTHOR]

Each taxon is characterized by a temperature range over which seed germination is possible and this may vary in space and time in relation to climate and ecological conditions. We used thermal modelling to test the hypothesis that thermal thresholds for seed germination can predict germination timing of Mediterranean species along an altitudinal and environmental gradient. Seeds of 18 species were collected in Sardinia from sea level to 1810 m above sea level, and germination tests were carried out at a range of constant (5 to 25°C) and alternating (25/10°C) temperatures. Different dormancy-breaking treatments [gibberellic acid (GA3), cold (C) and warm (W) stratifications and dry after ripening (DAR)] were applied. The annual pattern of soil temperatures was recorded using 24 data-loggers buried close to the study species. The logged soil temperatures distinguished 'Mediterranean lowland' from 'Mediterranean mountain' species. Although germination was >50% in untreated seeds of most species, GA3 had a positive effect in all species. C either inhibited or had a neutral effect on germination, W did not enhanced seed germination, while DAR had a positive effect only in species from coastal environments. The thermal time constant (S) for 50% germination ranged from 22 to 357°Cd (degree days) above base temperatures (T b) of –9 to 9°C, depending on species and treatments. Mediterranean lowland species had lower T b values compared with upland species. This study revealed significant differences in germination thresholds of Mediterranean lowland and mountain species in relation to T b and S that probably have an impact on germination timing in the field and niche competitiveness. [ABSTRACT FROM AUTHOR]

This study explores the temperature dependency of the aging rate in dry cells over a broad temperature range encompassing the fluid to solid transition (Tg) and well below. Spores from diverse species of eight families of ferns were stored at temperatures ranging from +45°C to approximately –176°C (vapor phase above liquid nitrogen), and viability was monitored periodically for up to 4,300 d (∼12 years). Accompanying measurements using differential scanning calorimetry (DSC) provide insights into structural changes that occur, such as Tg between +45 and –20°C (depending on moisture), and triacylglycerol (TAG) crystallization between –5 and –35°C (depending on species). We detected aging even at cryogenic temperatures, which we consider analogous to unscheduled degradation of pharmaceuticals stored well below Tg caused by a shift in the nature of molecular motions that dominate chemical reactivity. We occasionally observed faster aging of spores stored at –18°C (conventional freezer) compared with 5°C (refrigerator), and linked this with mobility and crystallization within TAGs, which probably influences molecular motion of dried cytoplasm in a narrow temperature range. Temperature dependency of longevity was remarkably similar among diverse fern spores, despite widely disparate aging rates; this provides a powerful tool to predict deterioration of germplasm preserved in the solid state. Future work will increase our understanding of molecular organization and composition contributing to differences in longevity. [ABSTRACT FROM AUTHOR]

With the need to meet ambitious restoration targets, an improved native seed sector for the production of herbaceous species with a practical and supportive policy framework is recognized. We evaluated the current “ready‐made” policy frameworks in Europe regarding the native seed supply of herbaceous species and found them to be, generally, unsatisfactory for both producers and users. Initially, such policies were designed for fodder seed and relate to distinctness, uniformity, and stability, traits that do not reflect the genetic heterogeneity of native species required for ecological restoration. Until recently, more suitable certification standards were designed to multiply fodder seed for preservation of the natural environment; however, due to the disparateness of the seed market in Europe, this policy is rarely practical and fails to encompass all herbaceous native species often resulting in unregulated seed sales. We recommend a new or adapted native seed policy constructed through a participatory or bottom‐up approach and supported through the formation of widely based trade associations. Such a policy could stimulate the native seed trade with concomitant impacts on the speed of improving ecosystem services. [ABSTRACT FROM AUTHOR]

Functional plant traits are used in ecology to explain population dynamics in time and space. However, because the germination niche is an essential stage in alpine plant life cycles and is under strong environmental pressure, we hypothesised that inter-specific variability in germination traits might contribute to alpine plant distributions. Germination traits of seven closely related species from calcareous and siliceous habitats were characterised in the laboratory, including base, optimum and ceiling temperatures (Tb, To, Tc, respectively), base water-potential (Ψb) and the pH range of the germination phenotype. Species’ vegetative traits (specific leaf area, leaf area and leaf dry matter content) were obtained from the TRY-database. Traits and habitat similarities and dissimilarities were assessed. Species were plotted in a multivariate space using two separate principal component analyses: one each for germination and vegetative traits. Species from calcareous habitats showed significantly higher Tb, lower Ψb and lower capacity to germinate under acidic pH than species from siliceous habitats. Moreover, high To and Tc, a narrow temperature range for germination at dispersal, and vegetative traits values were similar across both habitats. Whilst plant traits seem to have adapted to the shared environmental conditions of the two alpine habitats, some germination traits were affected by the habitat differences. In conclusion, species occurrence in two habitats (calcareous, siliceous) appears to be limited by some germination constraints and provide greater differentiation of species habitat preference than that defined by vegetative traits. [ABSTRACT FROM AUTHOR]

Abstract: Globally, annual expenditure on ecological restoration of degraded areas for habitat improvement and biodiversity conservation is approximately $18bn. Seed farming of native plant species is crucial to meet restoration goals, but may be stymied by the disconnection of academic research in seed science and the lack of effective policies that regulate native seed production/supply. To illustrate this problem, we identified 1,122 plant species important for European grasslands of conservation concern and found that only 32% have both fundamental seed germination data available and can be purchased as seed. The “restoration species pool,” or set of species available in practice, acts as a significant biodiversity selection filter for species use in restoration projects. For improvement, we propose: (1) substantial expansion of research and development on native seed quality, viability, and production; (2) open‐source knowledge transfer between sectors; and (3) creation of supportive policy intended to stimulate demand for biodiverse seed. [ABSTRACT FROM AUTHOR]

High sensitivity of seeds to water loss is a widespread phenomenon in the world's plant species. The molecular basis of this trait is poorly understood but thought to be associated with critical changes in membrane function. We profiled membrane lipids of seeds in eight species with varying levels of desiccation tolerance and found a close association between reducing seed viability and increasing phosphatidic acid (PA). We applied hydration-dehydration cycles to Arabidopsis seeds, which are normally desiccation tolerant, to mimic the onset of desiccation sensitivity with progression towards germination and examined the role of phospholipase D (PLD) in desiccation stress-induced production of PA. We found that PLDα1 became more abundant and migrated from the cytosol to the membrane during desiccation, whereas PLDδ did not change, and that all desiccation-induced PA was derived from PLDα1 hydrolysis. When PLDα1 was suppressed, the germination level after each hydration-dehydration cycle improved significantly. We further demonstrated that PLDα1-mediated PA formation modulates desiccation sensitivity as applying its inhibitor improved seed desiccation tolerance and its suppression in protoplasts enhanced survival under dehydration. The insights provided by comparative lipidomics enable us to propose a new membrane-based model for seed desiccation stress and survival. [ABSTRACT FROM AUTHOR]

Understanding the key aspects of plant regeneration from seeds is crucial in assessing species assembly to their habitats. However, the regenerative traits of seed dormancy and germination are underrepresented in this context. In the alpine zone, the large species and microhabitat diversity provide an ideal context to assess habitat-related regenerative strategies. To this end, seeds of 53 species growing in alpine siliceous and calcareous habitats (6230 and 6170 of EU Directive 92/43, respectively) were exposed to different temperature treatments under controlled laboratory conditions. Germination strategies in each habitat were identified by clustering with k-means. Then, phylogenetic least squares correlations (PGLS) were fitted to assess germination and dormancy differences between species' main habitat (calcareous and siliceous), microhabitat (grasslands, heaths, rocky, and species with no specific microhabitats), and chorology (arctic-alpine and continental). Calcareous and siliceous grasslands significantly differ in their germination behaviour with a slow, mostly overwinter germination and high germination under all conditions, respectively. Species with high overwinter germination occurs mostly in heaths and have an arctic-alpine distribution. Meanwhile, species with low or high germinability in general inhabit in grasslands or have no specific microhabitat (they belong to generalist), respectively. Alpine species use different germination strategies depending on habitat provenance, species' main microhabitat, and chorotype. Such differences may reflect adaptations to local environmental conditions and highlight the functional role of germination and dormancy in community ecology. [ABSTRACT FROM AUTHOR]

Recruitment from seeds is among the most vulnerable stage for plants as global temperatures change. While germination is the means by which the vast majority of the world's flora regenerate naturally, a framework for accurately predicting which species are at greatest risk of germination failure during environmental perturbation is lacking. Taking a physiological approach, we assess how one family, the Cactaceae, may respond to global temperature change based on the thermal buffering capacity of the germination phenotype. We selected 55 cactus species from the Americas, all geo-referenced seed collections, reflecting the broad environmental envelope of the family across 70° of latitude and 3700 m of altitude. We then generated empirical data of the thermal germination response from which we estimated the minimum ( Tb), optimum ( To) and ceiling ( Tc) temperature for germination and the thermal time (θ50) for each species based on the linearity of germination rate with temperature. Species with the highest Tb and lowest Tc germinated fastest, and the interspecific sensitivity of the germination rate to temperature, as assessed through θ50, varied tenfold. A left-skewed asymmetry in the germination rate with temperature was relatively common but the unimodal pattern typical of crop species failed for nearly half of the species due to insensitivity to temperature change at To. For 32 fully characterized species, seed thermal parameters correlated strongly with the mean temperature of the wettest quarter of the seed collection sites. By projecting the mean temperature of the wettest quarter under two climate change scenarios, we predict under the least conservative scenario (+3.7°C) that 25% of cactus species will have reduced germination performance, whilst the remainder will have an efficiency gain, by the end of the 21st century. [ABSTRACT FROM AUTHOR]

In close agreement with visible germination, orthodox seeds lose desiccation tolerance (DT). This trait can be regained under osmotic stress, but the mechanisms are poorly understood. In this study, germinating seeds of Caragana korshinskii Kom. were investigated, focusing on the potential modulating roles of reactive oxygen species (ROS) in the re-establishment of DT. Germinating seeds with 2 mm long radicles can be rendered tolerant to desiccation by incubation in a polyethylene glycol (PEG) solution (-1.7 MPa). Upon PEG incubation, ROS accumulation was detected in the radicles tip by nitroblue tetrazolium chloride staining and further confirmed by confocal microscopy. The PEGinduced re-establishment of DT was repressed when ROS scavengers were added to the PEG solution. Moreover, ROS act downstream of abscisic acid (ABA) to modulate PEG-mediated re-establishment of DT and serve as a new inducer to re-establish DT. Transcriptomic analysis revealed that re-establishment of DT by ROS involves the up-regulation of key genes in the phenylpropanoid-flavonoid pathway, and total flavonoid content and key enzyme activity increased after ROS treatment. Furthermore, DT was repressed by an inhibitor of phenylalanine ammonia lyase. Our data suggest that ROS play a key role in the re-establishment of DT by regulating stress-related genes and the phenylpropanoid-flavonoid pathway. [ABSTRACT FROM AUTHOR]

Eugenia stipitata occurs along rivers in Western Amazonia and produces berry-type fruits with economic potential. Its large recalcitrant (i.e. desiccation-intolerant) seeds have been proposed as a model to study seed stress response, as no apparent differentiation between the embryonic axis and the fused cotyledons are visible. Here, the longevity of submerged seeds was analysed with a view to understanding adaptive mechanisms to seasonal flooding. Submerged seeds began germinating after 2 months. After 1 year, 87 and 96% total germination was reached when seeds were submerged under a water column of 6 cm (where seedlings could emerge from under the water) and 26 cm (where seedlings could not reach the water surface), respectively. Seedling morphology was altered underwater, with short internodes and rudimentary leaf blades, and when submersion was terminated, seedlings transplanted to nursery conditions recovered a normal phenotype. Furthermore, when seedlings were detached from the seeds, the ‘resown’ seeds produced a second, normal seedling within 9 months. Concentrations of the antioxidant glutathione, which was measured as a stress marker, increased with submersion time in water. Seeds that had developed roots and shoots underwater had higher concentrations of glutathione disulphide than non-germinated seeds, suggesting that the flooding stress was more intense for seedlings than seeds, although more oxidizing cellular redox environments are also consistent with the conditions required for differentiation. Submergence underwater is recommended for storage of the recalcitrant seeds of E. stipitata for up to 1 year. [ABSTRACT FROM AUTHOR]

Carica papaya (papaya) seed germinate readily fresh from the fruit, but desiccation induces a dormant state. Dormancy can be released by exposure of the hydrated seed to a pulse of elevated temperature, typical of that encountered in its tropical habitat. Carica papaya is one of only a few species known to germinate in response to heat shock (HS) and we know little of the mechanisms that control germination in tropical ecosystems. Here we investigate the mechanisms that mediate HS-induced stimulation of germination in pre-dried and re-imbibed papaya seed. Exogenous gibberellic acid (GA3 ≥250 μM) overcame the requirement for HS to initiate germination. However, HS did not sensitise seeds to GA3, indicative that it may act independently of GA biosynthesis. Seed coat removal also overcame desiccationimposed dormancy, indicative that resistance to radicle emergence is coat-imposed. Morphological and biomechanical studies identified that neither desiccation nor HS alter the physical structure or the mechanical strength of the seed coat. However, cycloheximide prevented both seed coat weakening and germination, implicating a requirement for de novo protein synthesis in both processes. The germination antagonist abscisic acid prevented radicle emergence but had no effect on papaya seed coat weakening. Desiccation therefore appears to reduce embryo growth potential, which is reversed by HS, without physically altering the mechanical properties of the seed coat. The ability to germinate in response to a HS may confer a competitive advantage to C. papaya, an opportunistic pioneer species, through detection of canopy removal in tropical forests. [ABSTRACT FROM AUTHOR]

Aims The physiological responses during dormancy removal and multi-phasic germination were investigated in seeds of Paeonia corsica (Paeoniaceae). Methods Seeds of P. corsica were incubated in the light at a range of temperatures (10-25 and 25/10°C), without any pre-treatment, after W (3 months at 25°C), C (3 months at 5°C) and W + C (3 months at 25°C followed by 3 months at 5°C) stratification, and a GA3 treatment (250 mg·l-1 in the germination substrate). Embryo growth, time from testa to endosperm rupture and radicle emergence were assessed as separate phases. Epicotyl-plumule emergence was evaluated incubating the germinated seeds at 15°C for 2 weeks, at 5 and 25°C for 2 months on agar water before transplanting to the soil substrate at 10, 15 and 20°C and at 15°C for 2 months on the surface agar water with GA3. Important Findings Embryo growth, testa rupture, endosperm rupture (radicle emergence) and growth of the epicotyl were identified as four sequential steps in seeds of P. corsica. Gibberellic acid alone and warm stratification followed by 15°C promoted embryo growth and subsequent seed germination. Cold stratification induced secondary dormancy, even when applied after warm stratification. After radicle emergence, epicotyl-plumule emergence was delayed for ca. 3 months. Mean time of epicotyl-plumule emergence was positively affected by cold stratification (2 months at 5°C) and GA3. P. corsica seeds exhibited differential temperature sensitivity for the four sequential steps in the removal of dormancy and germination processes that resulted in the precise and optimal timing of seedling emergence. [ABSTRACT FROM AUTHOR]

In the context of climate change, food security and long-term human space missions, it is important to understand which species produce seeds that can tolerate extreme environmental conditions. Here we consider dry seed survival of extreme conditions encountered in both natural and artificially controlled environments. Considerable overlap exists between the two: for example, ultra-dry and anoxic conditions can be artificially imposed during seed storage and also occur naturally in the vacuum of space environments. Aside from ultra-drying and anoxia, dry seeds of many species may experience extremely high temperatures due to heat from wildfires or when exposed to solar heat in biomes such as deserts. In addition, seeds can be irradiated by UV-A and UV-B at the surface of the Earth and by the shorter wavelengths of UV-C in outer space. We focus on the effects of these extreme environmental conditions on dry seed lifespan and germination. Although it is clear that seeds from particular plant species and families can tolerate exposures to ultra-drying, high temperatures (at least 32 families) or UV radiation with minimal consequences for subsequent germination ability, further research is needed to elucidate many of the mechanisms underlying extreme tolerance of these environmental conditions found on Earth or in space. [ABSTRACT FROM AUTHOR]

Orchid seeds are among the smallest seeds in nature and they are naturally rich in fatty acids. However, the fatty acid composition of orchid seeds has not been investigated because the sample masses utilized for widely used methods for fatty acid profiling would generally require prohibitively large numbers (i.e. 10,000s) of seeds. The present work aimed to develop a method for fatty acid analysis using gas chromatography–mass spectrometry on small quantities (mg) of seeds. The method was developed using the seeds of two species, Dactylorhiza fuchsii, a temperate terrestrial, and Grammatophyllum speciosum, a tropical epiphyte. A range of sample masses was tested to determine the minimum mass required to achieve reliable fatty acid composition data. A direct transesterification method was used, which did not require extraction of fatty acids from seeds prior to analysis, and the effects of seed processing (crushed versus intact seeds) and incubation time in toluene on fatty acid yield were tested. Stable fatty acid profiles were obtained using as little as 10 mg of seeds. Neither crushing the seeds nor extending the toluene incubation step had much effect on the fatty acid yield. The simple direct transesterification method presented will enable the fatty acid composition of orchid seeds, and possibly other small seeds, to be determined reliably for studies into seed development, storage and germination. [ABSTRACT FROM AUTHOR]

Background and Aims Environmental temperature regulates plant regeneration via seed in several superimposed ways, and this complex regulation will be disrupted by climate change. The role of diurnally alternating temperatures (ΔT) in terminating dormancy will be a major factor in this disruption, as its effects on seed germination are immediate. Methods The effect of ΔT on seed germination was modelled using two populations of the wetland sedge Carex diandra, one from a montane site and one from a subalpine site. A cardinal-temperature model was fitted to germination results obtained from a thermal gradient plate, and the model was used to simulate changes in germination under two possible future climate scenarios (RCP2·6 and RCP8·5, for representative concentration pathways) as defined by the Intergovernmental Panel on Climate Change. Key Results Scenario RCP2·6 projected moderate increases in average temperatures and ΔT, whereas RCP8·5 projected greater warming and higher ΔT. Increasing ΔT decreased the base temperature for seed germination and the thermal time required for germination. The effect of higher ΔT together with the higher temperatures increased germination under both climate scenarios. Conclusions Carex diandra germination is highly responsive to potential changes in ΔT, and thus this study highlights the role of ΔT in seed responses to climate change. Comprehensive cardinal-temperature models, encompassing the different effects of temperature on seed germination, are needed to understand how climate change will affect plant regeneration. [ABSTRACT FROM AUTHOR]

Previous studies have shown that controlled deterioration treatment ( CDT) induces programmed cell death in elm ( Ulmus pumila L.) seeds, which undergo certain fundamental processes that are comparable to apoptosis in animals. In this study, the essential characteristics of mitochondrial physiology in elm seeds during CDT were identified by cellular ultrastructural analysis, whole-body optical imaging, Western blotting and semi-quantitative RT- PCR. The alteration in mitochondrial morphology was an early event during CDT, as indicated by progressive dynamic mitochondrial changes and rupture of the mitochondrial outer membrane; loss of mitochondrial transmembrane potential (Δψm) ensued, and mitochondrial ATP levels decreased. The mitochondrial permeability transition pore inhibitor cyclosporine A effectively suppressed these changes during ageing. The in situ localization of production of reactive oxygen species (ROS), and evaluation of the expression of voltage-dependent anion-selective channel and cyclophilin D indicated that the levels of mitochondrial permeability transition pore components were positively correlated with ROS production, leading to an imbalance of the cellular redox potential and ultimately to programmed cell death. Pre-incubation with ascorbic acid slowed loss of mitochondrial Δψm, and decreased the effect of CDT on seed viability. However, there were no significant changes in multiple antioxidant elements or chaperones in the mitochondria during early stages of ageing. Our results indicate that CDT induces dynamic changes in mitochondrial physiology via increased ROS production, ultimately resulting in an irreversible loss of seed viability. [ABSTRACT FROM AUTHOR]

Background and Aims Pollinator-limited seed-set in some terrestrial orchids is compensated for by the presence of long-lived flowers. This study tests the hypothesis that pollen from these insect-pollinated orchids should be desiccation tolerant and relatively long lived using four closely related UK terrestrial species; Anacamptis morio, Dactylorhiza fuchsii, D. maculata and Orchis mascula. Methods Pollen from the four species was harvested from inflorescences and germinated in vitro, both immediately and also after drying to simulate interflower transit. Their tolerance to desiccation and short-term survival was additionally assessed after 3 d equilibration at a range of relative humidities (RHs), and related to constructed sorption isotherms (RH vs. moisture content, MC). Ageing of D. fuchsii pollen was further tested over 2 months against temperature and RH, and the resultant survival curves were subjected to probit analysis, and the distribution of pollen death in time (σ) was determined. The viability and siring ability, following artificial pollinations, were determined in D. fuchsii pollen following storage for 6 years at –20 °C. Key Results The pollen from all four species exhibited systematic increases in germinability and desiccation tolerance as anthesis approached, and pollen from open flowers generally retained high germinability. Short-term storage revealed sensitivity to low RH, whilst optimum survival occurred at comparable RHs in all species. Similarly, estimated pollen life spans (σ) at differing temperatures were longest under the dry conditions. Despite a reduction in germination and seeds per capsule, long-term storage of D. fuchsii pollen did not impact on subsequent seed germination in vitro. Conclusions Substantial pollen desiccation tolerance and life span of the four entomophilous orchids reflects a resilient survival strategy in response to unpredictable pollinator visitation, and presents an alternative approach to germplasm conservation. [ABSTRACT FROM AUTHOR]

Heterogeneity in morphology, physiology and cellular chemistry of plant tissues can compromise successful cryoprotection and cryopreservation. Cryoprotection is a function of exposure time × temperature × permeability for the chosen protectant and diffusion pathway length, as determined by specimen geometry, to provide sufficient dehydration whilst avoiding excessive chemical toxicity. We have developed an innovative method of vacuum infiltration vitrification (VIV) at 381 mm (15 in) Hg (50 kPa) that ensures the rapid (5 min), uniform permeation of Plant Vitrification Solution 2 (PVS2) cryoprotectant into plant embryos and their successful cryopreservation, as judged by regrowth in vitro. This method was validated on zygotic embryos/embryonic axes of three species (Carica papaya, Passiflora edulis and Laurus nobilis) up to 1.6 mg dry mass and 5.6 mm in length, with varying physiology (desiccation tolerances) and 80°C variation in lipid thermal profiles, i.e., visco-elasticity properties, as determined by differential scanning calorimetry. Comparisons between the melting features of cryoprotected embryos and embryo regrowth indicated an optimal internal PVS2 concentration of about 60% of full strength. The physiological vigour of surviving embryos was directly related to the proportion of survivors. Compared with conventional vitrification, VIV-cryopreservation offered a ∼ 10-fold reduction in PVS2 exposure times, higher embryo viability and regrowth and greater effectiveness at two pre-treatment temperatures (0°C and 25°C). VIV-cryopreservation may form the basis of a generic, high throughput technology for the ex situ conservation of plant genetic resources, aiding food security and protection of species from diverse habitats and at risk of extinction. [ABSTRACT FROM AUTHOR]