The rate of oxygen consumption by cabbage seeds increased on imbibition and there was a further sharp increase on germination. This was delayed in artificially aged seeds of low vigour. The increases in oxygen consumption reflect the increased oxidation of carbohydrates via respiratory pathways. The activities of key regulatory enzymes of glycolysis and the oxidative pentose phosphate pathway were measured in aged and unaged seed lots of cabbage. Differences in the activities of glucose 6-phosphate dehydrogenase and pyrophosphate:fructose 6-phosphate 1-phosphotransferase were correlated with the rate of germination (T50) in seed lots with large differences in seed vigour induced experimentally by artificial aging. However, the activities of these enzymes could not be used to distinguish between untreated seed lots which had smaller vigour differences apparent only under stress. The enzymes are presumably not controlling and determining seed vigour, but merely reflecting actual seed performance under the current conditions.

Norway maple (Acer platanoides L.) seeds were harvested at different stages of seed development and maturation in 1989–91. As maturation drying progressed, the seed populations showed increasing desiccation tolerance: at 67–69% moisture content, no seeds survived desiccation below 10% moisture content; maturation drying to 55–57% moisture content (values corresponding with the end of the seed-filling phase) improved desiccation tolerance, but nevertheless most seeds were unable to withstand desiccation to 5–7% moisture content; further maturation drying to 27–28% moisture content enabled the seeds to survive considerable desiccation, no loss in viability occurring in seeds dried to 3% moisture content. This considerable improvement in desiccation tolerance after the end of the seed-filling phase was correlated (P<0.05) with the progress of maturation drying and may be associated with the increase in the potential longevity of seeds of other species that occurs during seed development subsequent to seed filling.

Both the California chaparral species, Emmenanthe penduliflora Benth. (Hydrophyllaceae), and a tobacco native to the Great Basin Desert of south-western Utah, Nicotiana attenuata Torr. ex Wats. (Solanaceae), germinate in response to component(s) of wood smoke. Nitrogen oxides (NO and NO2), in amounts produced by a fire, have been proposed to be germination signals for E. penduliflora. We examined the germination response of dormant seeds of E. penduliflora and N. attenuata to aqueous solutions of smoke adjusted to different pHs, and two NO donors [sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP)]. The smoke solutions, at pH 4 or 5, induced the maximum germination response. Aqueous solutions of SNP and SNAP, releasing NOx as high as 42 μM, had no effect on germination. Additionally, NO2– could not be detected in aqueous smoke extracts derived from combusted cellulose or wood. Therefore, unidentified cellulose combustion factors, rather than NOx, are likely to be the ecologically relevant germination signals.

The dispersal unit of many species of Brassicaceae is an indehiscent fruit, but relatively few studies have tested the effect of the pericarp on seed germination in this family. Our aim was to determine the effect of the pericarp on seed dormancy in six species of Brassicaceae native to the cold desert of north-west China. Intact dispersal units and isolated seeds of Chorispora sibirica, Euclidium syriacum, Goldbachia laevigata, Spirorrhynchus sabulosus, Sterigmostemum fuhaiense and Tauscheria lasiocarpa were stored dry at ambient laboratory conditions for 0–12 months and tested for germination in light and in dark at 5/2, 15/2 and 30/15°C. The amount of water absorbed by fruits and by seeds within the fruits was determined. For four species, intact fruits, isolated seeds and isolated seeds plus the removed pericarps were used to test for the mechanical versus possible chemical role of the pericarp in seed dormancy. Fresh isolated seeds, which have a fully developed embryo, germinated to lower percentages and rates than afterripened seeds. Thus, seeds have non-deep physiological dormancy. The pericarp significantly reduced germination, but inhibition was not due to lack of water uptake by seeds or to chemical inhibitors. Afterripened seeds of the six species germinated to 0–50% inside the fruits. We conclude that the pericarp plays a dominant role in seed dormancy of the six study species, and it does so by mechanically restricting embryo growth. Thus, the pericarp has the potential to spread germination over an extended period of time.

Seed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimal T and/or reduced ψ are inversely proportional to the amounts by which T exceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimal T and ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even at T or ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentum Mill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin = 7.05°C) and water potential (ψmin = −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb = 11°C; ψb = −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination when T or ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimal T and ψ at which metabolic progress toward radicle emergence is possible.

Drying reduces seed moisture content, which improves subsequent seed survival periods. Diverse maximum temperatures have been recommended to limit or avoid damage to seeds, but some high-temperature drying regimes may improve subsequent seed quality. Seeds from 20 different accessions of five rice (Oryza sativa L.) variety groups (aromatic, Aus, Indica, temperate Japonica, tropical Japonica) were harvested over several seasons at different stages of maturation and either dried throughout at 15°C/15% relative humidity (RH) or for different initial periods (continuous or intermittent) in different drying regimes at 45°C before final equilibrium drying at 15°C/15% RH. Subsequent seed longevity in hermetic storage at 45°C with 10.9% moisture content was determined. In no case did initial drying at 45°C provide poorer longevity than drying at 15°C/15% RH throughout. There was a split-line relation, which did not differ amongst investigations, between longevity after initial drying at 45°C relative to that at 15°C/15% RH throughout and harvest moisture content, with a break point at 16.5% (a seed moisture status of about –14 MPa). Below 16.5%, relative longevity did not differ with harvest moisture content with little or no advantage to longevity from drying at 45°C. Above 16.5%, relative longevity showed a positive relation with harvest moisture content, with substantial benefit from drying at 45°C to subsequent longevity of seeds harvested whilst still moist. Hence, there are temporal (immediately ex planta cf. subsequent air-dried storage) and water status discontinuities (above cf. below 16.5%) in the effect of temperature on subsequent air-dried seed longevity.

This study demonstrates that Anthemis chrysantha, a ‘Critically Endangered’ annual plant, produces two morphs of achenes: white and dark achenes, which differ in size, mass, anatomy and germination behaviour. Fresh white achenes germinated at all temperatures assayed from 10 to 25°C in both continuous darkness and 12-h photoperiod, ranging between 24% at 25°C in darkness and 89% at 12/20°C in light, whereas fresh dark achenes did not germinate under any temperature or light conditions. To identify differences in dormancy type between the two morphs, germination of dry-stored achenes, and achenes stratified at 5 or 25°C for 2 months were tested in both darkness and light at 5, 15 and 12/20°C for dry-stored and warm-stratified (25°C) achenes; and at 15, 25 and 12/20°C for cold-stratified (5°C) achenes. Of the white achenes, 90% germinated during the cold stratification period. In general, dry storage and warm stratification did not increase germination compared to fresh achenes. However, dark achenes did not germinate under any conditions. Dark achene dormancy was only broken by mechanical scarification or by excising the embryo (germination reached 71%). An anatomical study showed that the mesocarp of dark achenes had no intercellular spaces and was much thicker and stronger than that of white achenes, making the entry of water difficult, and also preventing germination by mechanical restriction. This study demonstrated that dormancy in the dark achenes is likely caused by the thickness of their pericarp, physically impeding germination and hampering imbibition of water.

Chitinase is often produced in higher plants as a general defence response after wounding or pathogenic attack. Since germinating seeds are exposed to soil pathogens, the activity and expression of chitinase in muskmelon (Cucumis melo L.) seeds was investigated. One acidic and three basic chitinase isoforms were detected, beginning 40 d after anthesis in developing and fully mature seeds. Both acidic and basic chitinase isoforms were found in endosperm tissue during imbibition and after radicle emergence. Basic chitinase isoforms, but not acidic isoforms, were detected in the embryonic axes of imbibed seeds and in seeds before germination, indicating that chitinases are developmentally regulated in specific seed tissues. Two complete cDNAs, Cmchi1 and Cmchi2, were cloned from germinated muskmelon seeds and are predicted to encode chitinases that show 95% identity to a class III chitinase from cucumber (Cucumis sativus L.) and 61% identity to a class II chitinase from soybean (Glycine max L.), respectively. Southern blotting indicated that Cmchi2 was present only once in the muskmelon genome, while Cmchi1 may be present in one or two copies. Cmchi1 and Cmchi2 mRNAs were only detected in radicles of germinating seeds and in roots of mature plants, so additional genes other than Cmchi1 and Cmchi2 must be responsible for the chitinase activity in developing seeds. Salicylic acid and benzothiadiazole stimulated the expression of Cmchi1, but not Cmchi2, after radicle emergence. A putative role for chitinase in muskmelon seeds is defence against fungal pathogens.

The literature suggests that the establishment of seed yield potential in cool-season perennial grasses is based on developmental processes that take place before floral induction. The relationship between vegetative plant development to flowering and seed yield can be influenced by numerous factors, such as genotype, stand age, post-harvest regrowth environment, pests, management practices and juvenility. The objectives of our investigations and survey of literature were to identify characteristics of vegetative plant development present before floral induction (autumn regrowth period) that were related to flowering (yield potential) and seed yield (utilization of seed yield potential). The number of fertile tillers present at anthesis is a function of the number and developmental state (or biological age) of vegetative tillers present prior to floral induction. The number and size of vegetative tillers before induction was correlated with flowering and seed yield in young stands of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.) (r = 0.93 and 0.95 for first-year stands of orchardgrass and tall fescue, respectively), but older stands did not exhibit this relationship. The basal diameter of vegetative tillers in autumn was related to flowering and seed yield in young stands of Kentucky bluegrass (Poa pratensis L.) and creeping red fescue (F. rubra L) As stands aged, basal diameter was not a primary indicator of subsequent flowering and seed yield. Tiller height at the end of the regrowth period was consistently related to flowering and seed yield in Kentucky bluegrass(r = −0.81, P < 0.01) and creeping red fescue (r = −0.87, P < 0.01), regardless of stand age. Increasing the rhizome:root ratio caused reduction of flowering in creeping red fescue. Vegetative characteristics were not related to flowering and seed production in perennial ryegrass (Lolium perenne L.) and dryland bentgrass (Agrostis castellana Boiss. and Reut.). Green leaf number was a poor indicator of flowering and seed yield potential in all species tested. Ethylene production during autumn vegetative development has been implicated as a potential cause of reduced flowering in creeping red fescue. As much as 92% of the seed yield potential in several cool-season perennial grasses is set before the onset of conditions favouring vernalization of the crop. An increased understanding of developmental gateways in the formation of flowering and seed yield potential may be key to enhancing the economic and environmental sustainability of seed production enterprises.

The changes in water status of germinating and non-viable soybean (Glycine max L. Merr.) seeds were characterized by nuclear magnetic resonance (NMR) spectroscopy. There were distinct changes in water status between viable and non-viable soybean seeds. In dry seeds, there were only two components, bound and bulk water, as revealed by component analysis of NMR (T2) data. On the contrary, a three-component water proton system (bound, bulk and free water) was observed in both germinating and non-viable soybeans during Phase I of hydration. The bulk water component of non-viable seeds disappeared completely during the lag phase (Phase II) of hydration, resulting in a two-component water proton system. In contrast, the three-component water proton system in Phase II was observed in the germinating seeds. Rapid hydration (Phase III), following Phase II, was observed in germinating soybean seeds only. Due to reorganization of water protons, there was a concomitant increase in bulk and free water, but a decrease in bound water. The physical state of water in these seeds (analysed by NMR spectroscopy) and the measurements of tissue leachate conductivity suggest that non-viable soybean seeds were more affected by the disorganized cell structure in the seed membrane system. The present study also provides evidence that physical reorganization of water is essential in germinating soybean seeds during hydration.

Dormant barley grains cannot germinate at 30°C and this inability to germinate is imposed mostly by the glumellae which have been suggested to limit oxygen supply to the embryo. Hypoxia imposed either artificially or by the glumellae to embryos from dormant grains, increases embryo sensitivity to abscisic acid (ABA) and promotes the accumulation of ABA during the first hours after imbibition. Expression of candidate genes involved in ABA synthesis (HvNCED), catabolism (HvABA8OH1) and signalling (HvABI5, HvVP1 and HvPKABA) was analysed in embryos isolated from dormant whole or de-hulled grains incubated in air or in hypoxia (5% oxygen). The presence of the glumellae enhanced the expression of genes involved in ABA metabolism and signalling with respect to that observed in de-hulled grains incubated in air. These results suggest that at least part of the observed physiological responses to the presence of the glumellae are regulated at the level of gene expression. However, hypoxia imposed on dormant de-hulled grains did not mimic the presence of the glumellae in terms of expression of candidate genes. Hypoxia mimics the presence of the glumellae in terms of dormancy maintenance and ABA accumulation and sensitivity, but its effects appear to operate through different mechanisms.

Two possible sources of resistance to pre-harvest sprouting were evaluated in quinoa. They showed dormancy at harvest and significant variations in dormancy level in response to environmental conditions experienced during seed development. The aims of this work were to evaluate the importance of seed coats in the regulation of dormancy in this species, to investigate possible mechanisms of action and to assess association of seed coat properties with changes in dormancy level caused by the environment. Accessions Chadmo and 2-Want were grown under field conditions on different sowing dates during 2 years. Seed coats were manipulated and seed germination was evaluated at different temperatures. Seed coat perforation before incubation led to faster dormancy loss in both accessions. This effect decreased with delayed sowing date, and seeds expressed a level of dormancy not imposed by coats. This suggests the presence of embryo dormancy in the genus Chenopodium. Seeds of the accession 2-Want had a significantly thinner seed coat at later sowing dates, associated with a decreasing coat-imposed dormancy, but this pattern was not detected in Chadmo. The seed coat acts as a barrier to the release of endogenous abscisic acid (ABA) in quinoa, suggested by the increase in germination and a higher amount of ABA leached from perforated seeds. ABA is able to leach from seeds with an intact seed coat, suggesting that differences in seed coat thickness may allow the leakage of different amounts of ABA. This mechanism may contribute to the observed differences in dormancy level, either between sowing dates or between accessions.

In order to examine the occurrence of a glassy state in the cytoplasm of maize embryos as a function of water content, isolated embryos were examined using spin-probe electron spin resonance. The glass transition temperature was determined at various degrees of hydration (h) in the range 0.05–0.25 g H2O g−1 dry sample weight. The obtained phase diagram indicates that, at standard storage temperature (−5°C), the cytoplasm of embryos drier than 0.15 g H2O g−1 is in a glassy state.

Whether and how seed mass and shape are related to seed persistence in soil is a controversial topic in plant ecology. There is little information on this relationship in sandy habitats. We tested whether or not this pattern is retained among 141 species within a range of growth forms, from a wide range of families, in the Horqin sandy land of northern China, which belongs to the inland sand ecosystem. We collected information on seed mass, shape and persistence of these species in this region from published articles. Seed mass and shape were found to be significantly and negatively correlated to persistence in the soil in the Chinese flora, in the same way as in most other floras examined, but not in the same way as the Israeli coastal sand dune flora. The value of seed mass and shape as good predictors of persistence in the soil could be applied to the Horqin sandy land. Although many factors affect the relationship between seed mass, shape and persistence, ease of burial appears to be the main potential interpretation in the Horqin sandy land.

Seed germination is vital for persistence of many plant species, and is linked to local environmental conditions. Small increases in temperature during this critical life history transition may threaten species by altering germination timing and success. Such changes in turn may influence population dynamics, community composition and the geographic distributions of species. In this investigation, a bi-directional temperature gradient plate was used to profile thermal constraints for germination in 26 common, threatened and geographically restricted Eucalyptus species (Myrtaceae) from southern Western Australia. These observed data were used to populate models to predict optimum germination responses (mean time to germination, germination timing and success) under current (1950–2000 averages) and future (2070 high greenhouse gas emission climate scenario) mean monthly minimum and maximum temperatures. Many species demonstrated wide physiological tolerance for high germination temperatures and an ability to germinate outside current and forecast future autumn–winter wet season temperatures, suggesting that climatic distribution is a poor proxy for thermal tolerance for Eucalyptus seed germination. Germination for some species is predicted to decline under forecast conditions, but the majority will maintain or improve germination particularly during the cooler winter months of the year. Although thermal tolerance may benefit persistence of many Eucalyptus species in southern Western Australia as warming becomes more severe, large rainfall declines are also forecast which may prove more detrimental to plant survival. Nonetheless, this framework has the potential to identify seed resilience to heat stress in an early life history phase and hence species vulnerability to one characteristic of forecast environmental change.

It is normally assumed that Lavandula stoechas subsp. pedunculata (Miller) Samp. ex Rozeira (Labiatae) is dispersed by autochory in spite of the clear pioneer nature of the species. This paper examines the efficiency of autochorous dispersal (seed rain) and the possibility that the species is also dispersed endozoochorally by sheep. Seed rain was measured using pitfall traps and adhesive strips in summer 1999. The viable seed content in sheep dung was measured by greenhouse germination of dung collected monthly in the summers of 1998 and 1999. Two experimental tests were also conducted to ascertain whether dung-borne seeds could be established under field conditions and to evaluate the effect of added dung in the establishment of seeds taken from plants. The recorded seed rain was 2544 seeds m-2 inside the Lavandula patches, with an aggregated distribution. Autochory around the mother plant fitted a negative exponential distribution, with 90.5% concentrated in a 0–30 cm radius and a maximum distance of 1 m. Viable Lavandula seeds were found in 73% of the examined dung samples, with an average of 5.5 seeds per sample (6 g) and a high inter- and intra-annual variation. This high seed content, together with the daily sheep movements over several kilometres, make the species highly dispersible, possibly explaining its clear pioneer nature. Moreover, available data suggest that seeds in sheep dung can germinate and establish under natural conditions, and that dung addition has a positive effect on species establishment.

Ageing causes a delay in the onset of DNA replication in seeds. Aerated hydration for 8 h, a treatment to invigorate seeds, resulted in a reduction of about 12 h in the time difference in the onset of DNA synthesis between unaged and aged embryos of brassica seed. This effect is consistent with a recovery process occurring during aerated hydration of the seed involving the repair of accumulated DNA damage. The occurrence of hydroxyurea-resistant 3H-thymidine incorporation in aged Brussels sprouts embryos during the period 16–32 h from the start of hydration supports this interpretation.

The mechanisms and regulation of storage lipid formation in seeds are reviewed. Seed storage lipids are ultimately derived from simple carbon compounds, such as sucrose, which are imported into seeds from source tissues, such as leaves or pods. The partitioning of this important carbon towards storage lipid, carbohydrate or protein is regulated by a complex interaction between genetically-determined endogenous factors and external environmental influences. Storage lipids are synthesized from fatty acids, derived from acetyl-CoA, and glycerol 3-phosphate. Fatty acid biosynthesis and probably acetyl-CoA formation, occurs within the plastids to produce oleoyl-CoA. Further elaboration of oleoyl-CoA to produce polyunsaturates, hydroxylates or very long chain acyl-CoAs occurs on the endoplasmic reticulum, as does the esterification of acyl-CoAs to glycerol-3-phosphate to produce the final triacylglycerol storage oil. The temporal and hormonal regulation of storage lipid accumulation in seeds is discussed.

Soybean (Glycine max (L.) Merr.) seeds with elevated or reduced percentages of palmitate and elevated percentages of stearate were compared with seeds of typical composition in tests for germination, seedling growth rate and leachate conductivity. In general, seeds with altered compositions did well in these physiological tests, but their vigour tended to be negatively correlated with the percentages of stearate and palmitate in various lipid classes.