Impacts of drought and elevated temperature on the seeds of malting barley.

High seed quality is key to agricultural production, which is increasingly affected by climate change. We studied the effects of drought and elevated temperature during seed production on key seed quality traits of two genotypes of malting barley (Hordeum sativum L.). Plants of a "Hana-type" landrace (B1) were taller, flowered earlier and produced heavier, larger and more vigorous seeds that resisted ageing longer compared to a semi-dwarf breeding line (B2). Accordingly, a NAC domain-containing transcription factor (TF) associated with rapid response to environmental stimuli, and the TF ABI5, a key regulator of seed dormancy and vigour, were more abundant in B1 seeds. Drought significantly reduced seed yield in both genotypes, and elevated temperature reduced seed size. Genotype B2 showed partial thermodormancy that was alleviated by drought and elevated temperature. Metabolite profiling revealed clear differences between the embryos of B1 and B2. Drought, but not elevated temperature, affected the metabolism of amino acids, organic acids, osmolytes and nitrogen assimilation, in the seeds of both genotypes. Our study may support future breeding efforts to produce new lodging and drought resistant malting barleys without trade-offs that can occur in semi-dwarf varieties such as lower stress resistance and higher dormancy.

Does oxygen affect ageing mechanisms of Pinus densiflora seeds? A matter of cytoplasmic physical state.

During desiccation, the cytoplasm of orthodox seeds solidifies into an intracellular glass with highly restricted diffusion and molecular mobility. Temperature and water content govern seed ageing rates, while oxygen (O2) can promote deteriorative reactions. However, whether the cytoplasmic physical state affects involvement of O2 in seed ageing remains unresolved. We aged Pinus densiflora seeds by controlled deterioration (CD) at 45 °C and distinct relative humidity (RH), resulting in cells with a glassy (11% and 30% RH) or fluid (60% and 80% RH) cytoplasm. Hypoxic conditions (0.4% O2) during CD delayed seed deterioration, lipid peroxidation, and decline of antioxidants (glutathione, α-tocopherol, and γ-tocopherol), but only when the cytoplasm was glassy. In contrast, when the cytoplasm was fluid, seeds deteriorated at the same rate regardless of O2 availability, while being associated with limited lipid peroxidation, detoxification of lipid peroxide products, substantial loss of glutathione, and resumption of glutathione synthesis. Changes in metabolite profiles provided evidence of other O2-independent enzymatic reactions in a fluid cytoplasm, including aldo-keto reductase and glutamate decarboxylase activities. Biochemical profiles of seeds stored under seed bank conditions resembled those obtained after CD regimes that maintained a glassy cytoplasm. Overall, O2 contributed more to seed ageing when the cytoplasm was glassy, rather than fluid.

Rainfall, not soil temperature, will limit the seed germination of dry forest species with climate change.

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.

Wheat seed ageing viewed through the cellular redox environment and changes in pH.

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.

Thermal buffering capacity of the germination phenotype across the environmental envelope of the Cactaceae.

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.

Metabolic and physiological adjustment of Suaeda maritima to combined salinity and hypoxia.

Background and Aims: Suaeda maritima is a halophyte commonly found on coastal wetlands in the intertidal zone. Due to its habitat S. maritima has evolved tolerance to high salt concentrations and hypoxic conditions in the soil caused by periodic flooding. In the present work, the adaptive mechanisms of S. maritima to salinity combined with hypoxia were investigated on a physiological and metabolic level. Methods: To compare the adaptive mechanisms to deficient, optimal and stressful salt concentrations, S. maritima plants were grown in a hydroponic culture under low, medium and high salt concentrations. Additionally, hypoxic conditions were applied to investigate the impact of hypoxia combined with different salt concentrations. A non-targeted metabolic approach was used to clarify the biochemical pathways underlying the metabolic and physiological adaptation mechanisms of S. maritima . Key Results: Roots exposed to hypoxic conditions showed an increased level of tricarboxylic acid (TCA)-cycle intermediates such as succinate, malate and citrate. During hypoxia, the concentration of free amino acids increased in shoots and roots. Osmoprotectants such as proline and glycine betaine increased in concentrations as the external salinity was increased under hypoxic conditions. Conclusions: The combination of high salinity and hypoxia caused an ionic imbalance and an increase of metabolites associated with osmotic stress and photorespiration, indicating a severe physiological and metabolic response under these conditions. Disturbed proline degradation in the roots induced an enhanced proline accumulation under hypoxia. The enhanced alanine fermentation combined with a partial flux of the TCA cycle might contribute to the tolerance of S. maritima to hypoxic conditions.

Dry seeds and environmental extremes: consequences for seed lifespan and germination.

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.

Simulating the germination response to diurnally alternating temperatures under climate change scenarios: comparative studies on Carex diandra seeds.

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.

Genome-wide association mapping and biochemical markers reveal that seed ageing and longevity are intricately affected by genetic background and developmental and environmental conditions in barley.

Globally, over 7.4 million accessions of crop seeds are stored in gene banks, and conservation of genotypic variation is pivotal for breeding. We combined genetic and biochemical approaches to obtain a broad overview of factors that influence seed storability and ageing in barley (Hordeum vulgare). Seeds from a germplasm collection of 175 genotypes from four continents grown in field plots with different nutrient supply were subjected to two artificial ageing regimes. Genome-wide association mapping revealed 107 marker trait associations, and hence, genotypic effects on seed ageing. Abiotic and biotic stresses were found to affect seed longevity. To address aspects of abiotic, including oxidative, stress, two major antioxidant groups were analysed. No correlation was found between seed deterioration and the lipid-soluble tocochromanols, nor with oil, starch and protein contents. Conversely, the water-soluble glutathione and related thiols were converted to disulphides, indicating a strong shift towards more oxidizing intracellular conditions, in seeds subjected to long-term dry storage at two temperatures or to two artificial ageing treatments. The data suggest that intracellular pH and (bio)chemical processes leading to seed deterioration were influenced by the type of ageing or storage. Moreover, seed response to ageing or storage treatment appears to be significantly influenced by both maternal environment and genetic background.

Salicornia as a crop plant in temperate regions: selection of genetically characterized ecotypes and optimization of their cultivation conditions.

Rising sea levels and salinization of groundwater due to global climate change result in fast-dwindling sources of freshwater. Therefore, it is important to find alternatives to grow food crops and vegetables. Halophytes are naturally evolved salt-tolerant plants that are adapted to grow in environments that inhibit the growth of most glycophytic crop plants substantially. Members of the Salicornioideae are promising candidates for saline agriculture due to their high tolerance to salinity. Our aim was to develop genetically characterized lines of Salicornia and Sarcocornia for further breeding and to determine optimal cultivation conditions. To obtain a large and diverse genetic pool, seeds were collected from different countries and ecological conditions. The external transcribed spacer (ETS) sequence of 62 Salicornia and Sarcocornia accessions was analysed: ETS sequence data showed a clear distinction between the two genera and between different Salicornia taxa. However, in some cases the ETS was not sufficiently variable to resolve morphologically distinct species. For the determination of optimal cultivation conditions, experiments on germination, seedling establishment and growth to a harvestable size were performed using different accessions of Salicornia spp. Experiments revealed that the percentage germination was greatest at lower salinities and with temperatures of 20/10 °C (day/night). Salicornia spp. produced more harvestable biomass in hydroponic culture than in sand culture, but the nutrient concentration requires optimization as hydroponically grown plants showed symptoms of stress. Salicornia ramosissima produced more harvestable biomass than Salicornia dolichostachya in artificial sea water containing 257 mM NaCl. Based on preliminary tests on ease of cultivation, gain in biomass, morphology and taste, S. dolichostachya was investigated in more detail, and the optimal salinity for seedling establishment was found to be 100 mM. Harvesting of S. dolichostachya twice in a growing season was successful, but the interval between the harvests needs to be optimized to maximize biomass production.

Manipulating the antioxidant capacity of halophytes to increase their cultural and economic value through saline cultivation.

Halophytes, salt-tolerant plants, are a source of valuable secondary metabolites with potential economic value. The steady-state pools of many stress-related metabolites are already enhanced in halophytes when compared with glycophytes, but growth under conditions away from the optimum can induce stress and consequently result in changes to secondary metabolites such as antioxidants. However, direct evidence for increasing the concentration of valuable secondary metabolites as a consequence of altering the salinity of the growing environment still remains equivocal. To address this, we analysed a range of metabolites with antioxidant capacity (including total phenols, flavonoids, ascorbate, reduced/oxidized glutathione and reactive oxygen species scavenging enzymes) in seedlings and plants from different families (Amaranthaceae, Brassicaceae, Plantaginaceae and Rhizophoraceae) and habitats grown under different salt concentrations. We show that it is possible to manipulate the antioxidant capacity of plants and seedlings by altering the saline growing environment, the length of time under saline cultivation and the developmental stage. Among the species studied, the halophytes Tripolium pannonicum, Plantago coronopus, Lepidium latifolium and Salicornia europaea demonstrated the most potential as functional foods or nutraceuticals.

Back to the future with the AGP-Ca2+ flux capacitor.

BACKGROUND: Arabinogalactan proteins (AGPs) are ubiquitous in green plants. AGPs comprise a widely varied group of hydroxyproline (Hyp)-rich cell surface glycoproteins (HRGPs). However, the more narrowly defined classical AGPs massively predominate and cover the plasma membrane. Extensive glycosylation by pendant polysaccharides O-linked to numerous Hyp residues like beads of a necklace creates a unique ionic compartment essential to a wide range of physiological processes including germination, cell extension and fertilization. The vital clue to a precise molecular function remained elusive until the recent isolation of small Hyp-arabinogalactan polysaccharide subunits; their structural elucidation by nuclear magentic resonance imaging, molecular simulations and direct experiment identified a 15-residue consensus subunit as a ß-1,3-linked galactose trisaccharide with two short branched sidechains each with a single glucuronic acid residue that binds Ca(2+) when paired with its adjacent sidechain. SCOPE: AGPs bind Ca(2+) (Kd ∼ 6 µm) at the plasma membrane (PM) at pH ∼5·5 but release it when auxin-dependent PM H(+)-ATPase generates a low periplasmic pH that dissociates AGP-Ca(2+) carboxylates (pka ∼3); the consequential large increase in free Ca(2+) drives entry into the cytosol via Ca(2+) channels that may be voltage gated. AGPs are thus arguably the primary source of cytosolic oscillatory Ca(2+) waves. This differs markedly from animals, in which cytosolic Ca(2+) originates mostly from internal stores such as the sarcoplasmic reticulum. In contrast, we propose that external dynamic Ca(2+) storage by a periplasmic AGP capacitor co-ordinates plant growth, typically involving exocytosis of AGPs and recycled Ca(2+), hence an AGP-Ca(2+) oscillator. CONCLUSIONS: The novel concept of dynamic Ca(2+) recycling by an AGP-Ca(2+) oscillator solves the long-standing problem of a molecular-level function for classical AGPs and thus integrates three fields: AGPs, Ca(2+) signalling and auxin. This accounts for the involvement of AGPs in plant morphogenesis, including tropic and nastic movements.

Increasing temperatures can improve seedling establishment in arid-adapted savanna trees.

Plant species are shifting their ranges in response to global climate change, thus intensifying the need to predict such changes accurately. As the environmental requirements controlling plant distribution act differently at each developmental stage, there is a need to acquire a demographic-specific understanding of the factors which determine these distributions. Here we investigated the germination niche of two common savanna species Acacia nigrescens and Colophospermum mopane, with the aims to disentangle the direct and indirect effects of temperature on seed germination and establishment and to explore the impact of higher temperatures on the establishment success of savanna trees. Under laboratory conditions, we used thermal gradient plates to determine the thermal germination niche of both species, and a water stress experiment was conducted on C. mopane to account for water-temperature interactions. Using these data we parameterised a soil-moisture model to determine germination and establishment success under field conditions at current and future temperatures (+4 °C). Based on this model, higher future temperatures will not limit germination directly, but they will reduce the number of germination events by reducing the time window of suitable available soil water. Conversely, warmer conditions will accelerate the rate of radicle extension and increase the frequency of seedling establishment events. An additional advantage of higher temperatures is that fewer seeds will germinate, resulting in slower seed bank depletion when successful seedling establishment events do occur.

A central role for thiols in plant tolerance to abiotic stress.

Abiotic stress poses major problems to agriculture and increasing efforts are being made to understand plant stress response and tolerance mechanisms and to develop new tools that underpin successful agriculture. However, the molecular mechanisms of plant stress tolerance are not fully understood, and the data available is incomplete and sometimes contradictory. Here, we review the significance of protein and non-protein thiol compounds in relation to plant tolerance of abiotic stress. First, the roles of the amino acids cysteine and methionine, are discussed, followed by an extensive discussion of the low-molecular-weight tripeptide, thiol glutathione, which plays a central part in plant stress response and oxidative signalling and of glutathione-related enzymes, including those involved in the biosynthesis of non-protein thiol compounds. Special attention is given to the glutathione redox state, to phytochelatins and to the role of glutathione in the regulation of the cell cycle. The protein thiol section focuses on glutaredoxins and thioredoxins, proteins with oxidoreductase activity, which are involved in protein glutathionylation. The review concludes with a brief overview of and future perspectives for the involvement of plant thiols in abiotic stress tolerance.

Salt stress, signalling and redox control in seeds.

Abiotic stresses, including salt stress, can impair electron transport chains, thereby increasing the production of reactive oxygen species (ROS). An excess of ROS can damage macromolecular and cellular structure, but ROS are also key components of signalling networks, through which they regulate developmental processes. Surprisingly little is known about the effects of salt stress upon seeds given their pivotal role in plant reproduction and dispersal. This review provides information on tolerance mechanisms and redox control in relation to seed metabolism and performance. First, the effects of salt stress throughout the seed life cycle are discussed, comprising salt effects on the mother plant and its implications on seed development, salt uptake upon seed imbibition and effects on seed germination. Then, responses to elevated salt concentrations are discussed according to a recently proposed triphasic seed stress model comprising the phases alarm, resistance and exhaustion. Implications of redox control in seeds on the physiological, biochemical and molecular level are considered and the review concludes with a perspective on future research in relation to salt stress and seed biology.

Redox state of low-molecular-weight thiols and disulphides during somatic embryogenesis of salt-treated suspension cultures of Dactylis glomerata L.

The tripeptide antioxidant γ-L-glutamyl-L-cysteinyl-glycine, or glutathione (GSH), serves a central role in ROS scavenging and oxidative signalling. Here, GSH, glutathione disulphide (GSSG), and other low-molecular-weight (LMW) thiols and their corresponding disulphides were studied in embryogenic suspension cultures of Dactylis glomerata L. subjected to moderate (0.085 M NaCl) or severe (0.17 M NaCl) salt stress. Total glutathione (GSH + GSSG) concentrations and redox state were associated with growth and development in control cultures and in moderately salt-stressed cultures and were affected by severe salt stress. The redox state of the cystine (CySS)/2 cysteine (Cys) redox couple was also affected by developmental stage and salt stress. The glutathione half-cell reduction potential (E(GSSG/2 GSH)) increased with the duration of culturing and peaked when somatic embryos were formed, as did the half-cell reduction potential of the CySS/2 Cys redox couple (E(CySS/2 Cys)). The most noticeable relationship between cellular redox state and developmental state was found when all LMW thiols and disulphides present were mathematically combined into a 'thiol-disulphide redox environment' (E(thiol-disulphide)), whereby reducing conditions accompanied proliferation, resulting in the formation of pro-embryogenic masses (PEMs), and oxidizing conditions accompanied differentiation, resulting in the formation of somatic embryos. The comparatively high contribution of E(CySS/2 Cys) to E(thiol-disulphide) in cultures exposed to severe salt stress suggests that Cys and CySS may be important intracellular redox regulators with a potential role in stress signalling.

Post desiccation germination of mature seeds of tea (Camellia sinensis L.) can be enhanced by pro-oxidant treatment, but partial desiccation tolerance does not ensure survival at -20°C.

The maximal potential desiccation tolerance (MPDT) of tea (Camellia sinensis) seeds has been a matter of debate for decades. Here we assessed the ability of tea seeds from three sites in China to germinate after desiccation. Desiccation tolerance was greatest in Kunming, followed by Puer and Lincang, with Kunming seeds tolerating drying to 8% moisture content (MC), or ∼0.5 water activity (a(w)). Such tolerance was observed in Lincang seeds only when hydrogen peroxide (H2O2) at 0.5 or 1M was applied to seeds, indicating a stimulatory role for H2O2 in post-desiccation germination. Puer seeds exhibited MPDT of 16% MC (∼0.7 a(w)). Therefore, seeds from all three sites were not recalcitrant. The length of the dry season after dispersal and the high ratio of seed coat to seed mass (>0.3) support the observation of non-recalcitrant behaviour. The seeds were not immature, as the lipid signal in embryonic axes mirrored that of the cotyledons (30% oil). Even after high survival [>60% total germination (TG)] on drying to 10-13% MC, no Kunming seeds tolerated 1 month storage at -20 °C coinciding with lipid transitional changes at this temperature. The results indicate that tea seeds from China are neither recalcitrant nor storable at -20 °C.

What is stress? Concepts, definitions and applications in seed science.

'Stresses' that impact upon seeds can affect plant reproduction and productivity, and, hence, agriculture and biodiversity. In the absence of a clear definition of plant stress, we relate concepts from physics, medicine and psychology to stresses that are specific to seeds. Potential 'eustresses' that enhance function and 'distresses' that have harmful effects are considered in relation to the seed life cycle. Taking a triphasic biomedical stress concept published in 1936, the 'General Adaptation Syndrome', to the molecular level, the 'alarm' response is defined by post-translational modifications and stress signalling through cross-talk between reactive oxygen and nitrogen species, and seed hormones, that result in modifications to the transcriptome. Protection, repair, acclimation and adaptation are viewed as the 'building blocks' of the 'resistance' response, which, in seeds, are the basis for their longevity over centuries. When protection and repair mechanisms eventually fail, depending on dose and time of exposure to stress, cell death and, ultimately, seed death are the result, corresponding to 'exhaustion'. This proposed seed stress concept may have wider applicability to plants in general.

Quantification of seed oil from species with varying oil content using supercritical fluid extraction.

INTRODUCTION: The quantity and composition of seed oil affects seed viability and storability and hence the value of a species as a resource for nutrition and plant conservation. Supercritical fluid extraction with carbon dioxide (SFE-CO2) offers a rapid, environmentally friendly alternative to traditional solvent extraction. OBJECTIVE: To develop a method using SFE-CO2 to quantify the seed oil content in a broad range of species with high to low oil contents. METHODOLOGY: Seed oil was extracted using SFE-CO2 from four crop species representing high, medium and low oil content: Helianthus annuus, Asteraceae, with ca. 55% oil; Brassica napus, Brassicaceae, with ca. 50% oil; Glycine max, Fabaceae, with ca. 20% oil; and Pisum sativum, Fabaceae, with ca. 2% oil. Extraction pressures of 5000, 6000 and 7500 psi and temperatures of 40, 60 and 80 degrees C were examined and a second step using 15% ethanol as a modifier included. Oil yields were compared with that achieved from Smalley Butt extraction. The optimised SFE-CO2 method was validated on six species from taxonomically distant families and with varying oil contents: Swietenia humilis (Meliaceae), Stenocereus thurberi (Cactaceae), Sinapis alba (Brassicaceae), Robinia pseudoacacia (Fabaceae), Poa pratensis (Poaceae) and Trachycarpus fortunei (Arecaceae). RESULTS: The two-step extraction at 6000 psi and 80 degrees C produced oil yields equivalent to or higher than Smalley Butt extraction for all species, including challenging species from the Brassicaceae family. CONCLUSION: SFE-CO2 enables the rapid analysis of seed oils across a broad range of seed oil contents.