Seeds of the narrow-endemic Solidago shortii and of the geographically-widespread S. altissima and S. nemoralis collected and buried in 1992 and 1993 were incubated in light and in darkness at 15/6°, 20/10°, 25/15°, 30/15° or 35/20°C following various periods of burial in soil in a non-temperature-controlled glasshouse. At maturity in November, seeds of the three species germinated to 0–1% in light at 15/6°C and to 10–77% at 20/10°, 25/15°, 30/15° and 35/20°C. Seeds exhumed each April from 1993 to 1996 and incubated in light at 15/6° and 20/10°C germinated to ≥83% and ≥90%, respectively, whereas those exhumed each September of 1993–96 germinated to ≤2%and ≤40%, respectively. At 25/15°, 30/15° and 35/20°C in light, seeds of S. altissima and S. shortii germinated to ≥52% and those of S. nemoralis to ≥19/, regardless of when they were exhumed. Timson's index, which integrates percentages, rates and times for onset of germination, was higher at all temperature regimes for seeds exhumed in April 1995 than for those exhumed in September 1995. Freshly-matured seeds of the three species germinated to 0–11% in darkness. Furthermore, regardless of when they were exhumed, seeds of S. altissima and S. nemoralis incubated in darkness germinated mostly to only 0–9% over the range of temperature regimes. In contrast, ≤88% and ≤6% of the seeds of S. shortii exhumed and incubated in darkness each April and September of 1993–96, respectively, germinated, ≤1% of them germinating while buried in soil. Thus, although buried seeds of all three species exhibited an annual conditional dormancy/non-dormancy cycle, only those of S. shortii exhibited cyclic changes in their germination response in darkness.

Cotyledon length in onion (Allium cepa, cv. White Lisbon) was linearly related to time from radicle emergence until the formation of the cotyledon hook, but thereafter increased exponentially with time. Within each phase the rate of cotyledon elongation was linearly related to temperature, and these relations were similar among seeds from several percentiles of the germinating populations of three contrasting seed lots. The mean base temperature was 1.4°C. These thermal time relations closely predicted the elongation of cotyledons of seedlings from cohorts of early- and lategerminators from a further lot of this cultivar at two suboptimal temperatures. Eleven cohorts of seedlings from seeds of differing quality were transplanted to the field on both the same date and at the same time from visible germination. The plants were harvested 59 days later. No effect of seed quality on mean plant weight, mean bulb diameter, or interplant variation in bulb diameter was detected. It is concluded that the rate of pre- and post-emergence seedling growth in onion is independent of environmentally induced differences in seed quality (seed vigour). Thus, any effect of this factor on plant size or crop yield, at a given density, is solely a function of time to germinate.

Invasive alien plants often occur in monospecific stands with high density in the invaded range. Production of bioactive secondary metabolites in such stands could have allelopathic effects on germination of native species. We tested this component of the novel weapon hypothesis for Heracleum mantegazzianum, a prominent invader in Europe, using seeds of 11 native herbs exposed to soil or soil extracts from invaded stands, moist seeds or seed extracts of H. mantegazzianum. There was no effect of the various treatments on germination of most species, while germination was reduced in Urtica dioica on invaded soil, in Poa trivialis with H. mantegazzianum seed extract, and negative effects of the essential oil bergapten were found in three species. In P. trivialis the results of the seed extract were not supported by the experiment with added seeds of the invasive plant. Thus, there is limited evidence for allelopathic effects of the invasive H. mantegazzianum on germination of co-occurring native herbs.

The broad aim of this work was to study intraspecific variation of seed germination in Phillyrea angustifolia L. (Oleaceae), a species with a hard (water-permeable) endocarp. Germination of seeds from six different wild populations was correlated with traits related either to seed morphology or to environmental parameters. Germination of naked seeds (seeds without endocarp) at the optimum germination conditions was similar among populations and individuals, but great differences could be detected regarding the germination of seeds with endocarp both at inter- and intra-populational levels. Differences among populations could be related to climatic parameters and to morphometric variables of seeds with endocarp. A higher germination was associated with populations growing in habitats with more severe summer (higher temperature, lower precipitation and a longer drought period) and producing elongated seeds (lower Feret ratio and roundness). Moreover, seeds from eight different individuals within a population were tested independently, and great differences regarding the germination of seeds with endocarp could be detected among individuals. Our results suggest that the morphological variation found in P. angustifolia endocarp is both under strong maternal genetic control as well as influenced by environmental factors, as indicated by the high variability among individuals within one population and the significant correlation between climate variables and seed germination among populations. Finally, it is emphasized that standardization of plant propagation protocols should take into account the degree of intraspecific variation of Mediterranean species.

We isolated two cDNAs of phosphoenolpyruvate carboxylase (PEPC) from developing rice seeds, Osppc1 and Osppc3. The deduced amino acid sequences of both cDNAs share several conserved motifs with other non-photosynthetic PEPCases, and these common motifs are known to be functionally important to their regulatory properties. The deduced protein sequence of Osppc1 was clustered into a monocotyledonous plant-specific clade, and Osppc3 was clustered into a gramineous plant-specific clade in the phylogenetic tree of plant PEPCases. The mRNA accumulations of Osppc1 and Osppc3 were found in developing rice seeds throughout the grain-filling stages, although their expression patterns differed: Osppc1 was strongly expressed at 7 d after flowering, and Osppc3 was strongly expressed at 4 d after flowering. The kinetic properties of the Osppc1 recombinant protein were quite similar to those of maize root-type PEPCase, except that the sensitivity for malate at pH 7.3 was weaker. Mining rice microarray data, we observed that Osppc1 was co-expressed with aspartate aminotransferase and alanine aminotransferase, which are involved in seed nitrogen metabolism. Moreover, reannotation of the co-expressed genes revealed that Osppc1, the two aminotransferases and the enolase were mapped on to the consecutive reaction from 2-phosphoglycerate to glutamate and pyruvate in the cytosol. These results imply that Osppc1 functions cooperatively with the two aminotransferases in the synthesis of amino acids that are used for storage protein synthesis in developing rice seeds.

Seeds of the iconic Australian baobab Adansonia gregorii display physical dormancy (PY) and germinate readily once they become water permeable, a trait found in most other species in this genus. Highest germination (100%) was observed when seeds were placed in concentrated sulphuric acid (H2SO4) for 24 h, although exposure to H2SO4 for 6–12 h also resulted in >85% germination. Exposure to boiling water for 1–5 min was far less effective in promoting germination (0–23%), although a high number of seeds were water permeable (67–99%) following boiling water treatment. However, the majority of these water-permeable seeds appeared to have been injured by boiling water exposure. Germination at warmer temperatures (30 or 35°C) was found to be optimal (81–83% germination) and proceeded rapidly, with maximum germination occurring after incubation for only 8 d. In comparison, germination at 15–25°C resulted in 3–67% germination over a longer time frame (up to 20 d). While seeds of A. gregorii display PY they are unusually sensitive to dipping in boiling water and are therefore atypical when compared to most other Adansonia species.

Methanol accumulates in maturing seeds, correlating with preharvest deterioration. Since the source of methanol may be from pectin de-methylation, methanol, cell wall uronic acid, pectin methyl esterification, pectinesterase (PE; EC 3.1.1.11) activity, and neutral sugar composition and partitioning of cell wall polysaccharides were determined during soybean (Glycine max [L.] Merrill) seed development, maturation, and desiccation in planta. Axis cell wall polysaccharides were more easily solubilized, richer in uronic acid, rhamnose, and xylose, and less rich in galactose than cotyledon cell wall polysaccharides. Methanol accumulated to 9.7 μg per two cotyledons and 0.5 μg per axis; total methanol decreased to 3 μg per two cotyledons during loss of green color. Total uronic acid increased from 0.12 to 0.27 mg per axis and 0.9 to 4 mg per cotyledon between 24 and 50 days after flowering (DAF). After loss of green color, pectin methyl esterification in axes increased from 7 to 24 mole% between 50 and 60 DAF but decreased to 14 mole%by 62 DAF in latter stages of seed desiccation. In cotyledons, methyl esterification ranged from 25 to 40 mole% and was 31 mole% after desiccation. PE activity increased 100 fold in axes, including a 30-fold increase in activity after loss of green color at 46 DAF. Cotyledon PE activity was 40-fold higher than in axes at 24 DAF, declined 75% by 56 DAF, and then increased 5 fold during desiccation. Pectin methyl de-esterification by PE is sufficient to be the sole source for methanol accumulation in seed tissues during development and maturation.

The relationships among water content, relative humidity and temperature were documented in both seeds and excised embryos of Coffea spp. using water sorption isotherms. Isotherms were constructed at 5, 15 and 25°C and calculated for lower temperatures. There were no apparent differences in sorption characteristics among whole seeds of several cultivars of C. arabica and among different species of Coffea. Excised embryos of genetically diverse Coffea germplasm also exhibited similar sorption characteristics, though there were substantial differences observed between embryos and whole seeds. The shape of isotherms of coffee seed tissues was intermediate to the reverse sigmoidal shape observed for orthodox seeds and the monotonic shape observed for desiccation intolerant plant tissues. The heats of sorption calculated for RH ≤ 25% for whole seeds of Coffea spp. were similar to orthodox seeds. In contrast, the heats of sorption calculated in the same RH range for excised embryos were intermediate between those of orthodox and recalcitrant embryos. Our observations are consistent with earlier observations that desiccation sensitivity or poor longevity is linked with low levels of water sorption at relative humidities less than 25%. An explanation for this remains elusive.

The fate of cells in the endosperm of developing wheat kernels was investigated under normal conditions and upon premature slow drying on the cut ear. To follow the changes in membrane integrity and cellular ultrastructure, an electron spin resonance (ESR) spin probe technique and low temperature scanning electron microscopy (LTSEM) were used. ESR data indicated that during development, the relative amount of cells with intact membranes decreased and became almost zero at the stage of mass maturity, i.e. several days before the onset of maturation drying. This suggests that the death of starchy endosperm cells is a developmental phenomenon rather than one induced by water loss. Even at 8 days after anthesis (daa), early in the differentiation phase, a considerable proportion of endosperm cells had already lost plasma membrane integrity. Comparison of ESR data with LTSEM micrographs revealed that the loss of plasma membrane integrity occurred early in the starch accumulation process, from which it was concluded that the programmes of starch accumulation and developmental death are simultaneously switched on. When the differentiation into starchy endosperm was arrested by premature slow drying of kernels on the cut ear, meristematic cells (aleurone initials) acquired desiccation tolerance as assessed by the combination of the spin probe technique and LTSEM. In contrast, fast drying caused immediate death of these cells. Thus, meristematic endosperm cells have the competence to acquire desiccation tolerance. This occurs upon premature slow drying or during normal differentiation into aleurone cells, but is lost when the cells differentiate into starchy endosperm.

The fruit plus accessory parts, and thus not only the fruit or seed, is the diaspore in some species of flowering plants. Atriplex centralasiatica, a summer annual salt-secreting cold-desert halophyte of central Asia that produces flat and humped diaspores, is such a species. The dispersal/germination units of this diaspore-heteromorphic species are fruits enclosed in persistent ‘bracteoles’. Germination of black and brown fruits (i.e. ‘bracteoles’ removed) of this species has been studied in some detail previously, but little attention has been given to the germination biology of the intact diaspores. The aim of this study was to compare the germination biology of the intact diaspores of A. centralasiatica, and their fates in the field during 12 months on the soil surface and buried at 5-cm depth. Fresh flat diaspores germinated to 42.7–51.3% in light (12-h photoperiod) and to 16.0–59.3% in constant dark, over a temperature range of 15–20/30°C, while no freshly matured humped diaspores did so under any temperature/light regime. Neither gibberellin (GA3) nor potassium nitrate (KNO3) had an effect on germination of either diaspore. Both diaspores readily imbibed water, and removal of ‘bracteoles’ released most of the dormancy. Thus, the ‘bracteoles’ are primarily responsible for diaspore dormancy in A. centralasiatica. Humped diaspores persisted for a longer period in the soil than flat ones. The germination requirements of intact natural dispersal/germination units of A. centralasiatica differ from those previously reported for fruits of this species.

Although the underdeveloped embryo, and thus morphological (MD) or morphophysiological (MPD) seed dormancy, is basal in angiosperms, it also occurs in advanced groups. A synthesis of the literature, combining phylogeny and the kind of seed dormancy in the highly evolutionarily advanced order Dipsacales, shows that MPD (or MD) occurs throughout all clades except the most advanced one, Valerina. Seeds of taxa in the Valerina clade have fully developed embryos and physiological dormancy (PD) or are non-dormant (ND); thus, PD and ND are derived conditions in Dipsacales. Assuming that types of seed dormancy have not changed since the Early Tertiary, the fossil record suggests that MPD (or MD) was present in extant genera of Dipsacales by the Palaeocene, but PD (or ND) not until the Miocene. Molecular dating indicates that the ages of dipsacalean lineages with MPD and PD are older than those indicated by the fossil evidence.

Determining the phylogenetic and biogeographic distribution of physical dormancy remains a major challenge in germination ecology. Here, our goal was to describe a novel water-impermeable seed coat mechanism causing physical dormancy (PY) in the seeds of Chaetostoma armatum (Melastomataceae). Although seed coat permeability tests indicated a significant increase in seed weight after soaking in distilled water, anatomical and dye-tracking analyses showed that both water and dyes penetrated the seed coat but not the embryo, which remained in a dry state. The water and dye penetrated the lumen of the exotestal cells, which have a thin outer periclinal face and thickened secondary walls with U-shaped phenolic compounds. Because of this structure, water and dye do not penetrate the inner periclinal face of the exotestal cells, indicating PY. Puncturing the seeds increased germination more than tenfold compared to that of the control, but GA3 did not increase germination further. A significant fraction of the seeds did not germinate after puncturing, indicating that embryos are also physiologically dormant (PD). This paper constitutes the first report of the water-impermeable seed coat in the Myrtales and the first report of physiophysical (PD+PY) dormancy in a shrub from a tropical montane area.

Experiments were performed to determine if RAPD profiles developed using total DNA isolated from soybean seed could be affected by the physiological state or the quality of the seed. RAPD profiles were developed using template DNA isolated from a single seed lot of soybean (Glycine max L. cv. Kirby). High quality seeds were used to produce four populations varying in either quality or physiological state: untreated control seed ambient temperature and humidity storage for 12 months, accelerated aging at 41°C and 100% relative humidity for 48 h, and controlled hydration (seed priming). One hundred and eighty-eight primers were used to create separate RAPD profiles from total DNA isolated from each set of seed and from soybean leaf tissue. Sixteen polymorphisms from 14 primers were identified as a result of seed treatments. Six primers showed nine polymorphisms in RAPD profiles of ambient-stored seed DNA, while four and two primers produced polymorphisms in reactions using accelerated aged or primed-seed template DNA, respectively. Two primers showed a polymorphic fragment in vegetative DNA not observed in any of the seed DNA samples. Ten of the observed polymorphisms were due to the appearance of a DNA fragment in response to a specific seed treatment while six were the result of the treatment-induced loss of a DNA fragment. The six polymorphisms resulting from the loss of a major fragment were all due to ambient-temperature seed storage. Results were reproducibly obtained from multiple DNA isolations using three separate DNA isolation procedures involving either multiple seed or a single seed as the template source. Therefore, genetically identical seed can consistently display RAPD polymorphisms as a response to the environmental exposure.

Utilization of lipid and protein storage reserves was examined during germination and early growth of somatic and excised seed embryos in vitro, and seed of interior spruce. High germination frequencies were recorded for somatic and excised seed embryos, and elongation of radicles and hypocotyls observed for both embryo types. Although elongation of the embryo types differed (i.e. somatic ≤ excised seed < seed), fresh weight gain was similar. Utilization of triglycerides in somatic embryos was more rapid than in excised seed and seed embryos, thus it appeared to be under embryo infuence. By contrast, depletion of storage proteins appeared to be influenced by the megagametophyte, with hydrolysis in somatic and excised seed embryos preceding that of the seed embryo by 2 days. Differential utilization of the storage reserves was temporally associated with differences in growth patterns of somatic and seed embryos. The evidence presented indicates that the in vitro germination medium does not entirely supplant the role of the megagametophyte during germination and early growth. The relevance of these results to artificial seed technology is discussed.

This paper examines the composition and density of soil seed banks under a mature seasonal rain forest (>150 years old), three secondary forests (4 yr Trema orientalis forest, 9 yr Macaranga denticulata forest and 25 yr Mallotus paniculatus forest) and in a slash-and-burn field of Xishuangbanna, southwest China. Seeds in the secondary forests germinated most rapidly in the first week, while the seeds of the seasonal rain forest and the slash-and-burn field soils germinated slowly over the first 6 weeks and peaked in the seventh and eighth weeks. Seed densities were 4585–65,665 seeds m−2 for forest sites and 1130 seeds m−2 for the slash-and-burn field in the top 10 cm of the soils. The seed density decreased with soil depth in the forest sites and tended to decline during succession. Herbs accounted for the largest proportion of seeds at all five sites. The importance of woody species, however, increased as forests became older. Slash and burn eliminated a large number of seeds in the upper soil and, consequently, reversed the vertical distribution of seeds in the soil and had a negative impact on family, genus and species richness of the soil seed bank as well.

This paper describes the dispersal–germination characteristics of seeds of 77 native tree species in a seasonal monsoon forest in Uttaranchal state, northern India. Results indicate that 50% of the species dispersed in the hot, dry summer months, 18% during the rainy season, 23% during the cold season and the remainder in late spring. Germination tests on fresh and laboratory-stored seeds revealed a relationship between morphological features of the fruit and both germination percentage and mean germination time (MGT). Highest mean germination (50%) was for dry-dehiscent fruits with winged wind-dispersed seeds, followed by dry-dehiscent fruits with non-winged seeds (38%) and seeds of dry-indehiscent fruits (37%). Lowest germination (29%) was for seeds from fleshy or pulpy fruits. MGT followed the reverse course. Germination data for seeds stored dry in the laboratory during one seeding cycle indicated six patterns of seed germination: (1) average germination percentage of fresh seeds lower than that of stored seeds, indicating an after-ripening requirement; (2) initial high germination percentage followed by low values, indicating a steep to moderate decline in viability following harvest; (3) no germination after 1 or 2 months of seed storage, due to complete loss of viability, indicating short seed longevity; (4) fresh seed germination in some species equalled the average germination value of stored seeds, indicating constant germination for one whole seeding cycle; (5) germination of both fresh and stored seeds remained consistently low throughout the season, indicating a requirement for some kind of pre-treatment or having poor quality of seeds; (6) initial high germination followed by decline and again increase, showing a seasonal rhythm of germination.

Seed mass distribution in grassland communities of slopes of contrasting aspect was analysed in dolomite regions of the Pannonian Basin. Species frequencies were obtained for four pairs of data sets, which originated from corresponding south- and north-facing dolomite grasslands, thus forming four independent case studies. The data sets comprised 5–15 sample plots and 51–114 (average 85) species. The species were classified using an eight-class system reflecting their mean seed mass (MSM) records (class 1 being the lowest, MSM ≤ 0.2 mg; class 8 being the highest, MSM > 50 mg). Seed mass class distributions derived from slopes of contrasting aspect showed strong significant differences in chi-square tests for trend for all the four case studies. Small-seeded species (classes 1 and 2) showed a positive balance for the south-facing slopes, whereas large-seeded species (classes 5, 6, 7 and 8) were more frequent on north-facing slopes. Species with intermediate seed mass (classes 3 and 4) were not distinctive between the slopes. These results represent strong evidence of increased seed mass in the vegetation of north-facing grasslands, when compared to their south-facing counterparts. Among the phenomena potentially responsible for the new findings, we discuss the roles of microclimatic effects (especially drought stress and light regime), grass litter, interspecific competition and seed predation.

Recent concern about gene flow from transgenic plants to weedy species has attracted much research on the fitness of their hybrids. However, no studies have been reported on the very early effects of the seed size of hybrids compared with parental plants for germination, seedling establishment and plant growth. We produced hybrids between male sterile Brassica napus L. (oilseed rape) and five weedy relatives, including Brassica juncea (L.) Czern, B. nigra (L.) Koch, B. rapa L., Hirschfeldia incana (L.) Lagrèze-Fossat and Raphanus raphanistrum L. The hybrid seeds formed between B. napus and B. rapa varied in size, while all the hybrid seeds formed with the other species were small. In a direct-seeded field experiment, small seeds of both parents and hybrids had a lower frequency of emergence and a lower seedling survival rate than large seeds, and resulted in later flowering with less biomass. However, no difference was recorded in a transplant experiment, indicating that growth in the juvenile period was sensitive to the small seed class in field conditions only. The optimum environmental conditions in the greenhouse probably homogenized the developmental differences observed at the early stage, and thus reduced the variation during subsequent growth in the field. This point has not been, but should be, considered in risk assessment of transgenic plants. The lower seedling establishment of small-seeded hybrids could hamper further gene flow.

In nature, fruit and seed production in many plants have been shown to be pollen limited. Pollen limitation is demonstrated when open-pollinated plants that are hand-supplemented (Ps) with outcross pollen produce more fruits and/or seeds than open-pollinated controls that are not hand-pollinated (Po). There are three categories of results in such studies: Ps > Po, Ps = Po and Ps < Po, in which case pollen limitation indices are positive, zero and negative, respectively. In an index widely used to calculate pollen limitation, 1 – (Po/Ps), the bounds for Ps ≥ Po are 0 to + 1, whereas the bounds for Ps < Po are 0 to –∞. The first aim of this review was to show how the pollen limitation index can be modified so that the bounds of Ps < Po are 0 and –1, whereupon the index gives equal weight to the best performer (Ps or Po) and worst performer (Ps or Po). In addition to seed quantity, pollen supplementation can affect seed quality, including germinability. Thus, our second aim was to summarize the results of studies that have also tested the effect of pollen limitation on seed germination. In short, the 30 case studies in 15 families, 16 genera and 18 species that we identified show that seed germination percentage increased, was not affected or decreased by pollen supplementation in 12, 11 and seven cases, respectively. The effect of pollen limitation on seed germination, which can be quite large, has not been considered in developing population growth models to determine the effect of pollen limitation on λ.

This study was undertaken to test the hypotheses that germinative metabolism of recalcitrant seeds in storage induces a requirement for additional water, which may result in the development of mild water stress, and that a reduction of the rate of this germinative metabolism will increase the storage lifespan of recalcitrant seeds. Studies were undertaken on seeds of Avicennia marina (Forssk.) Vierh. and concentrated on root primordia as these constitute the tissue that undergoes most change during storage. Encapsulating seeds from which the pericarp had been removed (naked seeds) in an alginate gel increased storage lifespan fourfold compared with naked seeds. Measures of metabolic rate such as time to first germination in storage and rate of protein synthesis did not indicate differences between alginate-coated and naked seeds, although ultrastructural observations indicated that both germinative and deteriorative processes were occurring more slowly in the alginate-coated seeds. Measures of water content and water and turgor potentials did not reveal signs of a mild water stress in either treatment. However, the number of seeds visibly contaminated with fungi and the rapidity with which this contamination became apparent were much reduced in alginate-coated seeds. It is suggested that fungal contamination constitutes a major cause of deterioration in stored, hydrated seeds of A. marina (and possibly other recalcitrant seed species) and the main effect of the alginate coating was to reduce the incidence of fungal contamination.