Artemisia ordosica, A. arenaria and A. sphaerocephala are semi-shrubs inhabiting desert sand dunes in China and often used to rehabilitate desertified areas. Improvement of dune rehabilitation success by sowing requires better understanding of the processes involved in the control of seed germination and seedling emergence in these species. Thus, (1) effects of temperature, light and osmotica (polyethylene glycol-6000) on seed germination, and (2) effects of seed burial depth in sand and irrigation regime on seedling emergence, were studied under controlled conditions. Seeds of the three species required light for germination, and the light fluence needed for germination was dependent on temperature. Seedling emergence of the three species was maximal (70–94%) for seeds sown at a depth of 2.5 mm, and decreased with increasing seed burial depth when the pots were initially and subsequently treated with 16 mm and 3 mm irrigation at 1-d intervals. However, when the pots were initially and subsequently treated with 8 mm and 3 mm irrigation at 2-d intervals, seedling emergence was almost completely suppressed due to water deficiency in sand. It is suggested that the probability of seed germination and seedling emergence of the three species in the field is very limited, because the light requirement restricts seed germination to shallow sand layers where water is lost rapidly due to evaporation. Temperature appeared to have secondary effects on seed germination, by modifying the light sensitivity of seeds.

Germination and survival of water-impermeable seeds of 11 species of Geraniaceae and Malvaceae were monitored during dry storage and during burial in soil for up to 2.5 years. During dry storage, seeds of annual Geraniaceae became permeable and also lost their physiological dormancy. However, during burial in natural conditions, most seeds remained impermeable and viable, with no seasonal change in germination capacity. Germination in only one species (Geranium robertianum) was enhanced by daily alternating temperatures when seeds were exhumed in spring. Drying of exhumed seeds broke physical dormancy. Seeds of the perennial Geranium pratense gradually became permeable in a prolonged germination test of 31 weeks. Most seeds of Malva remained impermeable during dry storage. Buried seeds gradually germinated in situ, and exhumed seeds had a low germination capacity in all seasons. We concluded that dormancy of hard seeds in natural conditions may be broken by drying during summer, by specific temperature regimes or by gradual softening of the seed coat, ensuring the spread of germination over many seasons.

The osmotin gene was introduced into tea [Camellia sinensis (L.) O. Kuntze] somatic embryos at the globular stage of development via microprojectile bombardment, to determine the effects of this stress-tolerance-related gene on the accumulation of storage reserves and acquisition of desiccation tolerance during embryo maturation. Changes in total soluble sugars, starch and proteins in response to osmotin were estimated in the stably transformed embryos, using standard biochemical and histochemical methods, after the globular embryos had matured to the heart stage of development. These changes also were compared with two types of controls, comprising (1) untransformed embryos and (2) embryos that were bombarded without osmotin DNA. The control embryos showed poor reserve accumulation and negligible germination but, in contrast, the embryos bombarded with the osmotin gene showed a several-fold increase in storage reserves, normal maturation and 57–63% germination. When these transformed embryos were desiccated to 15.5% moisture content, only 40% germinated, although a further increase in the accumulation of storage reserves occurred. In contrast, the control embryos became necrotic and failed to germinate. This study demonstrates the use of somatic embryogenesis as a tool for understanding seed recalcitrance in tea, and suggests that transformation with stress-tolerance genes can overcome the developmental problems associated with recalcitrant seeds.

In the Chihuahuan Desert, there are many cacti species considered to be at risk due to illegal extraction, land-use change and overgrazing. To reduce their illegal extraction, ex situ plant propagation has been suggested. However, the literature regarding seed germination biology of these species is scarce. We investigated the effect of light on germination percentages and germination rate (t50) in seeds of 28 cactus species from the Chihuahuan Desert. Seeds were incubated at a 14-h daily photoperiod (light) and in continuous darkness at 25°C for 30 d, after which seeds failing to germinate in darkness were transferred to light for 30 d. Only 11 of the species had non-dormant seeds, germinating ≥70% in the light; thus an evaluation of the effect of light versus darkness on germination was confined to them. All species were positively photoblastic, and all of them had seeds weighing <1 mg. Ten species did not germinate in darkness, and one species had only 7% germination. From these 11 species, 8 did not germinate to a significantly higher percentage when the same set of seeds was transferred from dark to light, suggesting that darkness had triggered secondary dormancy (skotodormancy). To our knowledge, these results are the first to show that darkness triggers secondary dormancy in cacti. Implications of having a light requirement for germination and having small seeds to accumulate a persistent soil seed bank are discussed. These results contribute to understanding the germination biology of cactus species at risk, and could enhance the propagation of large numbers of cultivated individuals outside their habitats, promoting ex situ conservation.

The embryo length/seed length (E/S) ratio of the early diverging eudicot Trochodendron aralioides is 0.34. Embryos in fresh seeds were 0.36±0.01 mm long, and they increased in length by about 250% (in 20 d) before radicle emergence (germination) occurred, demonstrating that the embryo is underdeveloped at seed maturity. Seeds germinated to 95–100% at 20/10, 25/15 and 30/15°C in light in ≤4 weeks, without any pretreatment, but no seeds germinated in darkness. Thus, seeds of T. aralioides have morphological dormancy (MD), which is considered to be the primitive condition in seed plants, and MD probably has existed in the genus Trochodendron since its origin in the early Tertiary.

Soil cores were collected at different times between the seed germination and dispersal seasons of Eupatorium adenophorum from 19 sites at five stations with different kinds of vegetation in Yunnan, south-western China. Mother plants of E. adenophorum were absent from eight of the sites, and their frequency was low at nine other sites. However, persistent soil seed banks were present at all 19 sites. Seed density in the 0–10 cm soil layer varied from 47 to 13,806 seeds m−2, and averaged 2199 seeds m−2. Fifty-seven percent of the seeds of E. adenophorum were in the 0–2 cm soil layer, 24% in the 2–5 cm layer and 19% in the 5–10 cm layer. The percentage of cores from which seedlings emerged ranged from 33–100% across all sites. Seed density and seedling emergence percentages varied significantly among the five stations, and both were positively correlated with abundance of mother plants.

Few data are available and little is known about spatial variation in post-dispersal seed removal at different levels throughout the geographic range of a plant species. Here, we compare post-dispersal seed removal by rodents within and among sites in two distinct regions, the south-eastern Spanish Mediterranean highlands and the Swiss Jura. Seed removal was assessed experimentally for four fleshy-fruited species (Berberis vulgaris, Crataegus monogyna, Rosa spp. and Taxus baccata) in heterogeneous sites with distinct microhabitats. A factorial general linear model (GLM) analysis was used to evaluate the relative influence of species-specific seed traits on removal at three spatial levels (microhabitat, site and region). In both highland ecosystems, live trapping revealed that rodents were the main seed removers: Apodemus sylvaticus was observed in both regions, whereas A. flavicollis and Clethrionomys glareolus occurred only at the Swiss sites. There was a significant difference in seed removal between regions, and the preferences of the rodents varied among plant species and microhabitats. Variation in rodent presence explained some differences in seed removal between regions and among microhabitats. Finally, the effect of rodent presence on seed removal differs due to both regional and microhabitat effects.

The ripening rice (Oryza sativa L.) caryopsis contains several maternal and embryonic tissues that transport assimilates along the partitioning pathway. Experimental access to transport steps in the pathway is limited by the separability of the tissues. Hence, the extent to which tissues can be mechanically and enzymatically separated was assessed. The caryopsis coat was isolated during mid-ripening, dissected and microscopically characterized. In centripetal order, the pericarp (epidermis, parenchyma-cell layer, cross-cell layer, tube-cell layer), inner integument, nucellar epidermis, aleurone layer and subaleurone layer adhered to each other. There was mechanical separation at the tube-cell layer, but not at the maternal/embryonic interface. Aleurone- and subaleurone-layer cells exposed on the inner surface of isolated caryopsis coats were macerated with Pectolyase Y-23 and manually sheared, which freed the endosperm and exposed the nucellar epidermis. Yield of endosperm cells increased linearly with the number of coats and reached a maximum after 1 h. The proportion of cells that were viable was approximately 10%. Subaleurone-layer cells contributed less than 25% to the yield. These results suggest that pectin polymers are necessary for adherence between the nucellar epidermis and the aleurone layer, and that enzymatic maceration is useful for separating the tissues at the maternal/embryonic interface.

We studied dormancy and germination requirements of seeds of Acacia aroma, A. caven and A. furcatispina from a semi-arid region of central Argentina. Imbibition experiments were performed to determine the rate of water uptake in seeds. To determine optimal temperature for germination, seeds were incubated at three temperature regimes (15/5, 25/15 and 35/20°C) with a 12/12 h daily photoperiod or in total darkness. Additionally, differences in dormancy and germination in seed colour morphs of A. aroma were studied. Seeds of A. aroma and A. caven had impermeable coats, while those of A. furcatispina did not. Seeds of the three species showed the same pattern of germination. Germination percentages were significantly lower at 15/5°C than at 25/15 or 35/20°C. The germination temperature pattern found for these species is probably related to the summer seasonal nature of rainfall in the study area. In A. aroma, seeds of the two colour morphs showed a similar pattern of dormancy and germination.

The Adansonia (baobab) genus comprises seven species in Africa, six of which are endemic to Madagascar. Depending on the species, baobabs develop in widely varying ecosystems, including arid zones and savannahs, as well as dry and wet forests. Seeds from all species exhibited orthodox behaviour, tolerating dehydration to a moisture content of around 5%. There was no physical dormancy in the two species belonging to the Brevitubae section, A. grandidieri and A. suarezensis. Their seeds germinated without any prior scarification. The five other species, belonging to Adansonia and Longitubae section, have seeds with water-impermeable coats. In the case of A. digitata and A. za, the proportion of water-impermeable seeds was around two-thirds, whereas with A. rubrostipa, A. madagascariensis and A. perrieri, the proportion was >90%. Treatments allowing for the removal of physical dormancy needed to be markedly more severe with A. madagascariensis than with the other species. None the less, it seems impossible to link these characteristics and the interspecific differences to a strategy for adaptation by these species to their environment.

The intact germination unit [seed+endocarp, (‘seed’)] of the two species of the Australian endemic genus Stylobasium (Surianaceae, Fabales) is water impermeable. Thus, the seed does not imbibe water or germinate until the integrity of the endocarp, which contains an outer layer of palisade cells, is disrupted. In this study, intact seeds of S. australe and of S. spathulatum, incubated on a moist substrate (for up to 2 years), did not imbibe water, whereas those that were mechanically scarified (both species), or dipped in boiling water for 30 s (S. spathulatum), imbibed and germinated. Thus, seeds of Stylobasium species have physical dormancy (PY). This is the first report of PY in Surianaceae, making it only the sixteenth family of angiosperms (no gymnosperms) in which this class of seed dormancy has been identified.