Since experimentation with plants began in space, a wide range of information has been gained regarding how this unique environment affects the biology of seeds. Seed biology experiments in this milieu have addressed aspects of seed storage, seed germination and metabolism, seedling orientation and seed production by flowering plants. Construction of hardware that provides a suitable growth environment in microgravity has been especially challenging because of the consequences posed by microgravity for fluid and gas distribution around the plant. Fluid shifting causes seed hydration kinetics to occur at a faster rate in microgravity than in 1 g; however, it also induces hypoxic metabolism during the seed germination process. In the absence of a detectable gravitational force, seedling roots grow according to their embryonic orientation and then initiate random walk movements. Light and oxygen gradients are the primary stimuli that orient root growth in this environment. For seed development to occur in spaceflight, well-ventilated growth chambers are necessary to support the carbohydrate supply needs of the developing embryos, and to provide the necessary humidity gradient for anthers to successfully dehisce and release pollen. The dry weight of seeds formed in space is lower than that in ground controls, and seed storage reserves are altered. Seed storage phenomena in spaceflight depend on whether or not oxygen and moisture are present – if not, viability exceeds that of seeds stored under comparable conditions on the ground. Because of the key role to be played by seeds in future advanced life support scenarios in space, more research is needed on the implications of this unique environment for seed biology.

In the West, lotus (Nelumbo nucifera Gaertn.) is relatively little known. However, for more than 3000 years, lotus plants have been cultivated as a crop in Far-East Asia, where they are used for food, medicine and play a significant role in religious and cultural activities. Holder of the world’s record for long-term seed viability (1300 years) is a lotus fruit (China Antique) from Xipaozi, Liaoning Province, China. Five offspring of this variety, from 200–500-year-old fruits (14C dates) collected at Xipaozi, have recently been germinated, and are the first such seedlings to be raised from directly dated fruits. The fruits at Xipaozi, preserved in a dry ancient lakebed, have been exposed to low-dose γ-radiation for hundreds of years (having an accumulated soil irradiation of 0.1–1.0 Gy). Offspring from these old fruits show abnormalities that resemble those in various modern seedlings irradiated at much higher doses. Although these lotus offspring are phenotypically abnormal, the viability of old seeds was evidently not affected by accumulated doses of up to 3 Gy. Growth characteristics of first- and second-year lotus offspring of these fruits, products of the longest-term radiobiological experiment on record, are summarized here (rapid early growth, phenotypic abnormalities, lack of vigour, poor rhizome development and low photosynthetic activity during second-year growth). Aspects of their chromosomal organization, phenotype and physiology (rapid recovery from stress, heat-stable proteins, protein-repair enzyme) are discussed. Important unsolved problems are suggested to elicit interest among members of the seed science community to the study of old fruits recently collected at Xipaozi, with particular emphasis on aspects of ageing and repair.

The breaking of dormancy in seeds can be elicited by many factors, including temperature and short exposure to low molecular weight amphipathic molecules such as primary alcohols, monocarboxylic acids and anaesthetics. Their action has been suggested to be mediated through effecting changes to membranes. Paradoxically, though, these molecules can inhibit the germination of some non-dormant seeds. Here, we review the structure–activity relationships between amphipathic molecules and dormancy breaking and, based on the known responses of membranes to them and to temperature changes, offer an alternative interpretation of the data and a new hypothesis to explain their action. We suggest that amphipathic molecules break dormancy by partitioning into the membrane, thereby increasing and optimizing phospholipid headgroup spacing. This, in turn, facilitates the binding and activation of a peripheral membrane protein component of a signal transduction pathway that is essential for the completion of germination. In cases where amphipathic molecules inhibit germination, it is predicted that they cause the optimal headgroup spacing to be exceeded, thus preventing subsequent association of the membrane with the peripheral protein component. The hypothesis is extended to explain membrane changes that can lead to dormancy breaking during dry after-ripening.

Specific chitinases accumulate in seeds of many species as part of their normal developmental programme. Some chitinases can also be induced in developing and germinating seeds in response to microbial attack. All known seed isoforms belong to classes I, II, IV and VII, which are encoded by Chia genes, as well as to the more divergent class III encoded by Chib genes. The study of seed-specific chitinases has contributed significantly to current knowledge of this ubiquitous protein family, including antifungal properties, structure, specificity and catalytic mechanism. Indeed, the first plant chitinase for which a three-dimensional structure was solved had been isolated from barley seeds. Moreover, the finding that a chitinase could rescue a somatic embryo mutant was the first evidence of a non-defensive function. Several lines of evidence have substantiated the biotechnological potential of chitinases to counter plant fungal disease. The recent identification of several seed and fruit chitinases as major panallergens should be taken into account when selecting the genes to be introduced into food crops.

To develop an effective protocol for observation of dry pea embryonic axes (Pisum sativum L. cv. Alaska), several fixation methods were compared for ease of infiltration and sectioning and for quality of sections. These methods included osmium vapour fixation, freeze-substitution followed by an aqueous wash, and freeze-substitution using anhydrous methanol. Axes fixed with osmium vapour were brittle and difficult to section. Cells fixed using vapour from an aqueous OsO4 solution had cell walls separated from plasma membranes, while cells fixed using osmium crystals exhibited folded walls tightly appressed to plasma membranes. Axes fixed using freeze-substitution followed by an aqueous wash sectioned easily, but appeared plasmolysed, with cell walls completely separated from plasma membranes. Even a brief (10 min) rinse in 90% acetone led to separation of the walls from the membranes. Tissues infiltrated with anhydrous methanol and Spurr’s resin were difficult to section, but showed extensive folding of the cell walls, with plasma membranes appressed to the walls. Additional modifications to the infiltration protocol led to improved sectioning. The highest-quality sections were obtained using freeze-substitution with anhydrous methanol as a solvent, followed by infiltration using methanol and Spurr’s resin, with the catalyst (dimethylaminoethanol) omitted from the infiltration protocol until the final step. Through comparison of several protocols recommended in the literature for the preparation of dry tissues, it is apparent that the presence of water, even in the vapour phase, at any step can cause swelling of the cell walls and the artefactual separation of the walls from the fixed protoplast.

A method, electrical impedance spectroscopy (EIS), is introduced to study seed viability non-destructively. Snap bean (Phaseolus vulgaris L.) seeds were studied by EIS to determine the most sensitive EIS parameter(s) and the optimal range of moisture content (MC) for separation of viable and non-viable seeds. Hydrated seeds exhibited two impedance arcs in the complex plane at the frequency range from 60 Hz to 8 MHz, and impedance spectra of viable and non-viable seeds differed. The hydrated seeds were best-modelled by an equivalent electrical circuit with two distributed circuit elements in series with a resistor (Voigt model). Moisture content and seed viability had strong effects on the EIS parameters. The most sensitive EIS parameters for detecting the differences between viable and non-viable seeds were the capacitance log(C2), the resistance R2, the resistance ratio R2/R1 and the apex ratio, which all represent specific features of the impedance spectrum. The highest differentiation in the EIS parameters between the viable and non-viable seeds occurred in partially imbibed seeds between MC of 40 and 45% (fresh weight basis).

With the sequencing of the Arabidopsis thaliana genome, the field of plant biology has made a quantum leap. The sequence information available to the community has greatly facilitated the identification of genes responsible for mutant phenotypes and the large-scale analysis of gene expression in Arabidopsis. High-throughput laboratory tools for DNA sequencing (genomics), mutant analysis (functional genomics), mRNA quantification (transcriptomics) and protein analysis (proteomics) are being used to scrutinize this model plant. For seed physiologists, the challenge lies in translating this information into physiological processes in seeds from other plant species. Combining more traditional seed biology with the new high-throughput molecular tools should yield breakthroughs in seed science.

Phytochrome-induced softening of the micropylar endosperm of Datura ferox seeds is followed by radicle protrusion and preceded by a significant increase in the extractable activity of β-mannanase and β-mannosidase (6 and 3 times over the far-red light controls, respectively) and a decrease in the mannan content of the micropylar endosperm cell walls. This relationship between phytochrome-induced germination, endosperm softening and mannan degradation was studied in Datura ferox seeds subjected to a range of water potentials during the presence of Pfr. Low water potential inhibited the decrease in mannose-rich cell-wall insoluble polysaccharides, the increase in activity of β-mannosidase and endosperm softening. A good correlation was found between activity of β-mannosidase measured at 45 h after exposure to a red light pulse and germination counted 24 h later when, with different external water potentials, germination varied between 0 and 90%. In contrast, no inhibitory effect of low water potential on in vitro β-mannanase activity was detected. We suggest that the in vivo action of β-mannanase might be limited by accumulation of manno-oligosaccharides caused by inhibition of β-mannosidase. These data are consistent with the concept of a link between mannan mobilization and endosperm softening. Part of the effect of low water potential on Pfr-induced germination may be mediated by inhibition of β-mannosidase activity, with consequences for mannan hydrolysis and endosperm softening.

The seed storage behaviour of Fagus sylvatica and F. crenata was investigated. A large fraction of seeds of both species survived desiccation to about 3% moisture content (MC) (in equilibrium with 10% relative humidity at 20°C). Nevertheless, viability was reduced significantly and progressively by desiccation from 14% to 3% MC. In addition, during subsequent hermetic storage at constant temperatures of 20 to –20°C in F. sylvaticaand 10 to –20°C in F. crenata seeds, viability was lost more rapidly with reduction in MC below about 7.6–11.5% (40–71%relative humidity at 20°C). Thus, Fagus sylvatica and F. crenataexhibited intermediate seed storage behaviour. Survival at –20°C with 7.8–11.5% (F. sylvatica) and 7.6% MC (F. crenata) was comparatively good, with 64–84% of seeds remaining able to germinate normally after 2 years of hermetic storage, although this was neither appreciably better nor worse than at 0–10°C. Optimum seed storage environments, within the range investigated, were provided by combining temperatures of –10 to –20°C with 7.8–11.5% (F. sylvatica) or 7.6–9.5%(F. crenata) MC.

The distribution of ATP in tomato seeds was visualized by monitoring the luminescence of frozen sections on top of a gel containing all the components of the luciferase reaction, but excluding ATP. ATP was imaged in germinating tomato seeds at intervals of 3, 6, 17, 24 and 48 h and in seeds with primary or secondary dormancy. ATP was present mainly in the embryo and concentrated in the radicle tip towards the completion of germination. In contrast to germinating seeds, ATP was distributed more evenly in dormant seeds. For germination, the ratio of ATP concentration in the radicle tip versus cotyledons was decisive, rather than the absolute concentration.

The histological and biochemical characteristics of cacao (Theobroma cacao) endosperm were determined at different stages of seed development. At various stages, the endosperm was analysed for minerals, organic acids, carbohydrates, free amino acids, abscisic acid (ABA), indole-3-acetic acid (IAA) and cytokinins. Cacao endosperm was coenocytic and became progressively cellularized from the micropylar zone. From stage I to IIz, the endosperm started to degenerate all around the embryo. Among the minerals detected, potassium and sulphate were the most abundant. Ammonium was the major source of mineral nitrogen, and glutamine was the most abundant free amino acid. Total nitrogen concentration was quite low. No sulphur-containing amino acids could be detected. Malate was present at all endosperm stages and was the most abundant organic acid. The sugars in cacao endosperm were mainly reducing sugars: glucose and fructose. ABA was only detected from stage IIz. IAA and three cytokinins [zeatin, zeatin-riboside and isopentenyl adenosine (iPA)] were present at all stages of development. Cacao endosperm resembled the endosperm of other species in (1) the abundance of organic acids and phosphate; and (2) a unique combination of sugars. However, three features seemed to be specific to cacao: (1) nitrogen was supplied mainly in the form of ammonium and amino acids, whereas, in other species, amino acids represent the predominant form; (2) there was a relatively small amount of nitrogen, and (3) a high concentration of sulphate and the absence of sulphur amino acids.

Seed development of tea was studied to identify the maturity index and the optimal time of seed collection. After harvest, the moisture content (28–30%fresh weight basis) of mature seeds, which germinated 100%, declined progressively (19% moisture content) after shedding, with a decrease in seed germination and viability. However, this viability loss could be prevented to some extent by storing seeds within intact fruits. The maximum rate of seed dry matter accumulation coincided with the accumulation of starch in the embryos and seeds at stage 8, the embryo maturation phase. Although the embryo abscisic acid (ABA) content was highest at stage 8, free ABA declined in the tea embryos throughout the remainder of the seed maturation cycle.

Germination and seedling growth of soybean (Glycine max L.) cv. Williams were examined on paper towels pre-moistened with a range of saline solutions (germination: 0–500 mMolal NaCl; seedling growth: 0–330 mMolal NaCl). The Na+, K+ and Ca2+ concentrations in the embryonic axis immediately before germination and in the seedling 3.5 d after germination were measured. Germination decreased at NaCl concentrations of 330 mMolal (81% germination) and above. At 420 mMolal NaCl, only 40% of seeds germinated, and at 500 mMolal NaCl there was no germination. Seedling growth rate decreased drastically with increasing salinity. At 220 mMolal NaCl, seedling growth rate had declined to 5% of the control, whereas at 330 mMolal NaCl seedling growth was almost zero 3–4 d after germination. Thus, soybean seeds were more tolerant of salinity in the germination than in the seedling phase. The results suggest that the greater tolerance of salinity during the germination phase might, in part, be the result of a lower sensitivity to high tissue Na+ concentrations. Germination (40%) was possible at a tissue Na+ concentration in the embryonic axis of 9.3 mg g FW-1, whereas seedling growth was completely inhibited at a tissue Na+ concentration of 6.1 mg g FW-1. Germination at higher tissue Na+ concentrations was associated with higher K+ and Ca2+ concentrations in the embryo axis, compared with growing seedlings, suggesting that these ions may protect the seeds in the pre-germination phase against salinity.

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.

The native tobacco, Nicotiana attenuata, synchronizes its germination with the immediate post-fire environment with a combination of germination stimulants found in wood smoke and inhibitors from the unburned litter of the dominant vegetation. The inhibitors override the stimulants and prevent seeds from germinating maladaptively in unburned habitats adjacent to burns. To understand the physiological basis of this environmental control of germination, we tested several previously isolated signals, phytohormones and their respective biosynthesis inhibitors. The germination inhibitors methyl jasmonate (MeJA, a constituent of sagebrush litter), bornane-2,5-dione (BD, a constituent of juniper litter extract, JLE) and JLE did not alter abscisic acid (ABA) content of imbibed seeds. Treatment with the ABA biosynthesis inhibitor, fluridone, inhibited the dormancy-inducing effects of BD, JLE and MeJA, but surprisingly did not affect endogenous ABA levels in treated seeds. However, ABA leached from litter of the species, which dominate the plant community before fires, plays an important role in germination control. We conclude that N. attenuata seeds, which can lie dormant in the soil for 150 years between fires, time their germination with the post-fire environment by responding to smoke, ABA and four terpenes (BD, 1,8-cineole, β-thujaplicin and camphor) leaching from the litter of the dominant vegetation.

The lipid concentration (LC) of the embryo–endosperm fraction was determined for the seeds of 60 species in 22 families from an Australian tropical lowland rainforest. It was negatively related to the mass of the embryo–endosperm across all species, but the relationship was not significant at P < 0.05. LC was significantly and positively correlated with N concentration when all species were considered, but not within the families represented by the most species (Lauraceae, 13; Sapindaceae, 9; Proteaceae, 6). LC was significantly and markedly higher in more heavily defended seeds (medians: 27 and 6.9%); there is evidence for the view that seeds rich in either lipid or nitrogen are markedly defended. Lipid concentration was also markedly higher, on average, in seeds taken by the scatter-hoarding Uromys caudimaculatus (white-tailed rat) than in seeds of comparable size not taken by Uromys, but not known to be protected by any toxin or irritant (medians: 35 and 3.7%, respectively). However, LC was not notably high in one major group of seeds taken by Uromys – the largest-seeded species of Beilschmiedia and Endiandra (Lauraceae). The comparisons mostly involved different phyletic lines, and were not consistently supported by contrasts within phyletic lines.

Nitrogenous compounds, such as potassium nitrate, potentiate germination of different species of light-requiring seeds. Using light-induced Arabidopsis thaliana seed germination as a model system, our data suggested that only phytochrome A (phyA)-specific induced germination was affected after the exogenous application of nitrates, different nitric oxide (NO)-donors (such as organic nitrates) or sodium nitroprusside. The stimulative effect was very pronounced. Treated seed samples reached maximal germination after very short periods of red-light irradiation. To a far lesser extent, these substances affected phytochrome B (phyB)-specific induced germination. In phyB-specific induced germination, potassium nitrate was most effective, but germination percentages never exceeded 50%. The least effective was sodium nitroprusside, which practically did not affect phyB-specific induced germination. These results were confirmed using corresponding phytochrome mutants.

A domestic dog was used in two experiments to elucidate the role of epizoochorous seed dispersal of forest plants. First, the dog was walked through forest vegetation at different times of year and its coat analysed for seeds retained within it. The seed content of the coat was compared to seed frequencies in the vegetation. Secondly, seeds of 11 plant species were placed in different positions on the dog, and their persistence in the coat analysed with respect to distance subsequently travelled. The experiments demonstrate that seeds with morphological adaptations to seed dispersal and small seeds of tall species can be caught effectively by a dog’s coat. The morphologically adapted seeds can be dispersed over large distances as long as the dog moves steadily along a road. The same is true for species with small and smooth seeds if they are deposited on the back of the dog, but not if they are placed on its side. Comparisons of these results with the distribution of forest species in a fragmented landscape, indicated that tall species with small seeds and species with morphological adaptations for epizoochorous dispersal are good at colonizing new forest habitats.

The aim of this study was to investigate whether there was a relationship between growth of sunflower seedlings at 15°C in the dark and activities of enzymes involved in scavenging of reactive oxygen species (ROS), especially superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR), or in production of free radicals, namely lipoxygenase (LOX). Untreated control seeds were compared with seeds exposed to accelerated ageing (5 d at 45°C and 100% relative humidity), osmopriming (7 d at 15°C with a polyethylene glycol (PEG) solution at –2 MPa) and accelerated ageing followed by priming. Accelerated ageing decreased seed germinability and slowed down hypocotyl growth, whereas priming resulted in an increase in germination rate and enhanced seedling development. Osmopriming of aged seeds almost completely restored the initial rate of germination and seedling growth. The activity of all the enzymes studied increased during seed germination and seedling development, except that of SOD. Seed imbibition or radicle protrusion were related mainly with an increase in CAT activity and, to a lesser extent, in GR activity. Increase of LOX activity was clearly associated with the onset of hypocotyl elongation. However, in all cases, malondialdehyde measurements did not reveal intense lipid peroxidation. Priming induced a marked stimulation of CAT and GR during seed imbibition or very early during seedling development, as compared to the control seedlings and particularly to the seedlings generated by aged seeds. Hydrogen peroxide (H2O2) contents of seeds and seedlings were closely correlated to the activities of CAT and GR and to the kinetics of seedling development. The results obtained establish a clear relationship between sunflower seed vigour and ROS scavenging.