Lipidomics of orchid seeds: from development to storage

Orchid seeds primarily contain lipid reserves, yet details of their deposition, in quantity and quality, remain unknown. Deposition begins as carbohydrates, which are eventually converted into fatty acids during seed development. This research aimed to dissect the pattern of lipid deposition in seeds of Dactylorhiza fuchsii and Disa uniflora, from pollination to seed storage, including at five stages of seed maturation, germination capacity and relationships among fatty acids (FAs). The capsules were harvested, cleaned and measured. Extracted seeds were analysed using differential scanning calorimetry (DSC), moisture content determinations, in vitro germination tests in three different media and seed viability. A portion of the seeds was dried to analyse lipid content and types via Gas Chromatography-Mass Spectrometry (GC-MS). While Dact. fuchsii seeds showed a high percentage of dry matter at the end of maturation, Disa uniflora had a lower one. Lipid accumulation profiles differed. The proportions of saturated and unsaturated FA varied, with Disa uniflora having more saturated FA than Dact. fuchsii. Seeds began to germinate before the midpoint of capsule maturation, and germination increased with maturation time in both species, with Disa uniflora seeds reaching full germination at capsule dehiscence. Conversely, Dact. fuchsii seeds did not germinate because the seed carapace may hinder germination. Nevertheless, at capsule maturity, seeds from both species were highly viable based on the tetrazolium test. Mature seeds of both species were desiccation-tolerant (4.5% RH) and could be stored dry at 5 °C for 3 months without loss of viability, suggesting the possibility of long-term seed banking for conservation.