Swartzia langsdorffii seeds have recalcitrant characteristics. Nonetheless, dispersal begins in the month with the lowest precipitation in the studied region, which could lead to seed death by desiccation. Therefore, the objectives of this study were: (1) to characterize the physiological behaviour of S. langsdorffii seeds related to their desiccation sensitivity/tolerance; and (2) to assess the morphophysiological characteristics that enable the seeds to remain viable after dispersal. Fruits and seeds were subjected to biometric evaluation and the anatomical and ultrastructural features of the seeds were determined. Field assessments were performed to determine the capacity of the seeds to maintain viability and to verify the relation between seed viability, diaspore water content and environmental variables. Seeds of this species were found to be recalcitrant and showed pores distributed throughout the seed coat, and contained a large number of stomata in the hypocotyl–radicle axis epidermis. Moreover, phenolic compounds were found throughout the radicle region. Seeds remained viable in the soil for up to 7 months after dispersal without a significant decrease in water content, despite the low precipitation and soil water content. Radicle protrusion began 5 months after dispersal and coincided with partial fruit decomposition at the beginning of the rainy season. Thus, the possible microclimate created by the pericarp, with the moisture content of the aril and the soil, the presence of the structures in the axis, such as the pores and stomata, the chemical composition and the morphology of S. langsdorffii seeds could favour maintenance of their viability until the beginning of the rainy season.

This review examines the presence of free and bound PAs during the life cycle of seeds. Although data are still rather scarce, PAs, present, but with an unknown function during embryogenesis, are accumulated in relatively high quantities in mature dry seeds of some species. PA concentration can be altered by the process of stratification, and PAs are synthesized in growing organs after germination, but it is also possible that the reserve organs synthesize and export some types of PA to the axis. This metabolism and sink-source relationship depend on the germination conditions and on the greater or lesser presence of enzymes related to synthesis (ADC, ODC, LDC and AdoMetDC) and degradation (DAO and PAO) of free PAs. The biochemical mechanism binding the PAs to a series of compounds of low and high molecular weight is currently unknown in seeds. The present study also considers intra- and intercellular compartmentation of free and bound PAs in growing axes and the physiological implications of the ethylene-production pathway in relation to seed behaviour.

As a consequence of previous lack of success in cryostoring axes excised from newly shed seeds of Trichilia dregeana, the effects of the mode of axis excision on seedling production were investigated. Although vigorous root production occurred, no shoots were produced when the cotyledons were severed as closely as possible to the axis surface (explant-type 0). In contrast, shoot production was increasingly facilitated when small to larger segments of cotyledonary tissue were left attached to the axes (explant-types 1, 2 and 4), which did not compromise axis drying rate. However, root growth of explant-types 1, 2 and 4 was negatively affected, probably by leakage into the medium of an inhibitory or toxic substance(s) from the cut surfaces of the cotyledonary tissue. Microscopical examination revealed that the cotyledons were sessile, and their insertions were contiguous with the shoot apex in axes from newly shed seeds, leading to the suggestion that failure of shoot production by type 0 explants in vitro was the direct consequence of the proximity of the wound sites to the apical meristem. When seeds were stored hydrated for 6 months, the shoot apex had elongated, positioning the apical meristem some distance from the top of the cotyledonary insertions. In contrast to axes excised as type 0 explants from newly shed seeds, the equivalent explants from the stored seeds rapidly formed shoots and leaves in vitro. This indicates that the developmental status of axes, when excised, dictates failure or success in their further development in vitro, and that this aspect needs to be resolved before any further manipulations for cryostorage are attempted.

A recombinant protein (approximately 38 kDa by SDS/PAGE), induced by expression in Escherichia coli of a cDNA encoding a 1-aminocyclopropane-1-carboxylate oxidase (ACO) isolated from embryonic axes of Cicer arietinum, was recognized by an antibody raised against an apple ACO. A monoclonal antibody, obtained from recombinant ACO of chick-peas, was used for immunolocalization experiments in the embryonic axes of chick-pea seeds. The results indicate that most of the ACO was present in the apoplast of the cell wall. No evidence of this protein in the vacuole was detected. During germination of C. arietinum seeds, the production of ethylene was induced in the embryonic axis; its highest value was reached when radicle emergence occurred. At this moment there was an accumulation of 1-aminocyclopropane-1-carboxylate (ACC), transcription of ACO mRNA, as well as maximal ACO activity. In the post-germinative period the activity of the last step of ethylene biosynthesis decreased. This decrease was eliminated by indole-3-acetic acid (IAA), which caused significant transcription of ACO mRNA. It is suggested that gene expression of ACO may be induced by auxins and spermine (Spm) and inhibited by abscisic acid (ABA).