Seeds of neem (Azadirachta indica A. Juss.), a multipurpose tropical tree, have limited desiccation tolerance. Whether their intermediate storage behaviour might be caused by an elevated percentage of 4C nuclei in the embryo at maturity was investigated. Morphological development of neem seeds was monitored on selected trees in Ouagadougou, Burkina Faso. Developing seeds were tested for germinability, and cell cycle events were determined by using flow cytometry and analysing the level of β-tubulin. Germination could occur after 8 weeks of seed development, but normal seedlings resulted only after 10 weeks or more. The change in fruit colour from green to yellow began after approximately 12 weeks of seed development. Immature, 4-week-old embryos about 2 mm in length had 15% of cells in the G2 phase and 60% in the G1 phase of the cell cycle, as indicated by 4C and 2C nuclear DNA levels, respectively. During maturation, the proportion of G2 cells declined to 3% at full maturity and slightly further after drying, and the proportion of G1 cells increased to approximately 90%. A strong β-tubulin signal was observed in tips of young embryonic radicles and cotyledons, but a weak or non-detectable signal was found in 9-week-old ones and in those from green-mature and yellow fruits. Because DNA replication and β-tubulin level were almost negligible at seed maturity, as in orthodox tomato seeds, it is suggested that these factors are not involved in the intermediate storage behaviour of neem seeds.

To colonize newly disturbed areas, weedy species must disperse their seeds in space and/or in time. Cirsium vulgare has poor dispersal in space, but can form a persistent seed bank. Fresh seeds are capable of germinating in either light/dark or constant dark conditions under favourable diurnal temperatures of 25°C: 10°C. Despite this lack of dormancy, a large proportion of seeds do not germinate in the autumn after dispersal. Variation in germination requirements according to seed colour was also examined. Fresh seeds were placed under one of two overwintering treatments at 5°C, alternating light/dark or constant darkness. Some seeds of all colours: white, light, intermediate, dark and black germinated under these conditions. Six months later, ungerminated seeds subjected to the light/dark treatment did not require light for germination when placed under optimal temperatures. However, most seeds that had overwintered in constant darkness required light for germination. In the field, this induced dormancy would prevent seeds from germinating if buried or located in deep shade. Such seeds have the potential of forming a persistent seed bank. The proportion of dormant seeds did not appear to be associated with seed colour. Seeds incubated at 10°C following overwintering under light/dark conditions germinated to a higher percentage than seeds overwintered in darkness, regardless of the light conditions for germination. The results of this study help to explain the contradiction between delayed germination in the field and the lack of seed dormancy.

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.

Soil samples were collected from the original land surface beneath an experimental earthwork, constructed in 1963 at Morden Bog, Dorset, England, and excavated in 1996. Large numbers of seeds of Calluna vulgaris, Erica cinerea and E. tetralix germinated from the samples, but other species present in the original flora, including Ulex minor and several grasses, were absent. The results confirm the previously-documented longevity of Calluna and E. tetralix, and for the first time demonstrate similar longevity in E. cinerea.

Mangosteen (Garcinia mangostana L.), rambai (Baccaurea motleyana Muell.- Arg.) and jelentik (Baccaurea polyneura Hook. f.) are tropical fruit species believed to have recalcitrant seeds. The seeds showed no dormancy; they germinated easily. At harvest, the mean moisture contents (fresh weight basis) were 53.54, 51.20 and 44.90% for G. mangostana, B. motleyana and B. polyneura, respectively. G. mangostana seeds lost viability when their moisture content fell to about 24% while B. motleyana seeds lost viability below 35.5% moisture content. However, for B. polyneura, the seeds could be dried to low moisture content with high survival. The viability was still high when the moisture content was reduced to 13.46%. At this moisture content, the percentage germination was 91.76% and it was found that the seeds survived cyopreservation with 8.3% viability. For B. motleyana axes, the loss of viability occurred when their moisture content fell to about 36% (15% viability with predominantly callus formation) while for B. polyneura axes, viability was reduced to 33-67% when the moisture was 27–30%. At various moisture contents, the seeds of the fruit species studied were exposed for 48 h to 7°C and −4°C. G. mangostana seeds did not survive either temperature. Baccaurea seeds survived 7°C but failed to survive −4°C. No axes from B. motleyana seeds at various moisture contents survived cryopreservation. However, some viability (20–30%) was observed in B. polyneura axes cryopreserved at a moisture content of about 27%. At this moisture content no normal growth was obtained; callus formation was observed. It appears that the seeds vary in the degree of desiccation sensitivity. They also vary in size. Seeds of G. mangostana are larger than Baccaurea seeds and thus, more sensitive to desiccation. Seed and embryonic axis structure may also play a role in desiccation sensitivity.

The flatulence-producing soluble oligosaccharides are an important component of lupin seeds and were assayed to establish the pattern of their accumulation in relation to germinability during seed development and maturation. Maturing yellow lupin cv. Juno seeds were harvested at 5-day intervals from 15 to 45 days after flowering (DAF). Seed fresh mass increased to a maximum at 35 DAF followed by a decrease when axis and cotyledon tissues changed colour from green to yellow. Maximum seed fresh mass corresponded to the maximum seed size. Seed dry mass continuously increased until 40 DAF. About 75% of mature seed dry mass was in cotyledons, 22% in testa, and 3% in axis. Maximum seed germinability occurred at 45 DAF after maximum seed dry mass and desiccation. Maturing yellow lupin seeds were desiccation tolerant. Mature dry seeds contained 10.9% oligosaccharides and 1.5% sucrose. During seed growth stachyose accumulation preceded accumulation of raffinose and verbascose. The highest rate of oligosaccharide accumulation appeared during seed desiccation and correlated with the acquisition of the ability to germinate. The sucrose:oligosaccharide ratio continuously decreased reaching 0.13 in mature seeds. Accumulation of oligosaccharides in maturing yellow lupin seeds is associated with seed germinability and seed desiccation tolerance.

Recruitment-related traits (development and dispersal of seeds, emergence, leaf dynamics, growth and survival of seedlings) were studied in Japanese elm (Ulmus davidiana var. japonica) in relation to disturbance at the soil level (bare soil, litter and control) or the canopy level (forest edge (FE), small gaps (SG) and forest understorey (FU)), or both, in a riverside forest from 1990 to 1993. Seed germination was also tested in the laboratory. Litter accumulation severely inhibited seedling emergence. Seedling emergence from a single seed rain occurred in summer immediately after seed dissemination and in the following spring. In summer, seedling emergence was higher in FE than in FU. In the following spring more seedlings emerged in FU than in FE and SG, resulting in non-significant differences in the percentage emergence among the three sites in bare soil. Darkness or far-red light induced seed dormancy, but after chilling they started to germinate again under white or red light conditions. These results explained emergence phenology under changing light conditions in the field. In FU, the spring emerging cohort grew and survived better than the summer emerging one. In FE the reverse was true. Japanese elm avoids unfavourable periods by escaping either in time (dormancy) or in space (dispersal). Such traits compensate for late and compressed seed dissemination, and improve seedling growth and survival not only when disturbance occurs at both canopy and soil level (bare soil in FE) but also only at soil level (bare soil in FU), which may occur more frequently in riverside forests.

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.