The production of hydrophilic mucilages by the seed coat or pericarp, which are released upon seed hydration, is a commonly found adaptation in angiosperms, known as myxodiaspory. These are composed primarily of pectins and hemicelluloses that undergo substantive swelling upon hydration. Synthesized in the Golgi apparatus and secreted to an apoplastic space via secretory vesicles, mucilages can also contain cellulose microfibrils or cellulosic fibres that are synthesized at the plasma membrane in association with microtubules. Investigation of mucilage production in, and differentiation of, the mucilage secretory cells of the genetic model plant Arabidopsis thaliana has identified a number of regulatory genes and enzymes involved in pectin synthesis and secretion, in muro pectin modification and secondary cell wall synthesis. Studies of the role of mucilages in both a number of species and in Arabidopsis mutants affected in its production suggest that they have multiple ecological roles. These include facilitation of seed hydration, mediation of germination under waterlogged conditions, prevention of seed dispersal or predation by adherence to soil, and promotion of seed dispersal by attachment to animals. The precise role of mucilages appears to be dependent on species and their environmental context.

Seeds have long been a model system for studying the intricacies of phytochrome-mediated light perception and signalling. However, very little is known about how they perceive blue and green light. Cryptochromes and phototropins, the major blue-light receptors in plants, are increasingly well-studied in vegetative tissues, but their role in light perception in seeds largely remains a mystery. Green light elicits a number of responses in plants that cannot be explained by the action of any of the known photoreceptors, and some seeds are apparently also capable of perceiving green light. Here, the responses of seeds to blue and green light are collated from a thorough examination of the literature and considered from the perspective of the potential photoreceptor(s) mediating them. Knowledge of how seeds perceive wavelengths that are suboptimal for phytochrome activation could help to improve germination and seedling establishment for both crop and native species.

We investigated seed dormancy among species of Melastomataceae from Neotropical montane vegetation of Brazil. Four out of 50 studied species had dormant seeds: Miconia corallina (Miconieae), Tibouchina cardinalis (Melastomeae), Comolia sertularia (Melastomeae) and Chaetostoma armatum (Microlicieae). For these four species, germinability of seeds collected in different years was always < 10% and the percentages of embryoless seeds and non-viable embryos were both insufficient to explain low or null germinability. This is the first unequivocal report of seed dormancy in tropical Melastomataceae. The production of seeds with permeable seed coats and fully developed, differentiated embryos indicates the occurrence of physiological dormancy. The reconstructed phylogenetic tree of the 50 species suggests that physiological dormancy evolved multiple times during the evolutionary history of Melastomataceae in this vegetation. Physiological dormancy evolved in species and populations associated with xeric microhabitats, where seeds are dispersed in unfavourable conditions for establishment. Therefore, drought-induced mortality may have been a strong selective pressure favouring the evolution of physiological dormancy in Melastomataceae. We argue that dormancy may have been independently selected in other lineages of Cerrado plants colonizing xeric microhabitats and dispersing seeds at the end of the rainy season. The contributions of our data to the understanding of seed dormancy in tropical montane vegetation are discussed.

The influence of light and temperature on germination behaviour and the longevity of seeds were evaluated in four taxa of the genus Arthrocereus (Cactaceae). Germination experiments were conducted at six constant temperatures with a 12-h photoperiod and in continuous darkness. For in situ storage tests, the seeds were buried in the soil where the species naturally occur, and germination experiments were performed for 14 months. Seeds were also stored dry at room temperature in the laboratory for 12 months. The results indicated that, in spite of the variations between the four taxa studied, there is a consistent pattern in their germination behaviour. The seeds are small, with an absolute requirement of light for germination. In the presence of light, we obtained high germinability at temperatures between 20 and 30°C and low germination percentages at 10, 15 and 35°C. This behaviour may represent an adaptive mechanism during seasons when environmental conditions in open rocky fields are not favourable for seedling survival. In general, germination was relatively slow, which would favour establishment during the rainy season. Dry storage did not significantly alter seed germination behaviour, and buried seeds, likewise, remained viable and retained high germination percentages. We can therefore infer that the seeds of the species studied here are able to form persistent soil seed-banks. All studied species are threatened with extinction, so their ability to form soil seed-banks, together with the possibility of ex situ seed preservation, will possibly give support for future conservation efforts.

The most common way to test seed quality is to use a simple and reliable but time- and space-consuming germination test. In this paper we present a fast and simple method to analyse cabbage seed deterioration by measuring ethanol production from partially imbibed seeds. The method uses a modified breath analyser and is simple compared to gas chromatographic or enzymatic procedures. A modified method using elevated temperatures (40°C instead of 20°C) shortened the assay time and improved its sensitivity. The analysis showed an inverse correlation between ethanol production and seed quality (e.g. the final percentages or speed of germination and the number of normal seedlings). The increase in ethanol production was observed when cabbage seeds were deteriorated by storage under ambient conditions or hot water treatments, both of which reduced the number of normal seedlings. Premature seeds produced more ethanol upon imbibition than mature seeds. Ethanol production occurred simultaneously with oxygen consumption, indicating that lack of oxygen is not the major trigger for ethanol production.