'Sub-imbibed' storage is not an option for extending longevity of recalcitrant seeds of the tropical species, Trichilia dregeana Sond.

Recalcitrant seeds of Trichilia dregeana were stored at 16 or 25 degreesC, either at the water content at which they were shed or partially dried. Although having been exposed to a short period (approx. 6 h) at temperatures up to 30 degreesC prior to storage, seeds at the original water content maintained viability for several weeks at 16 degreesC. However, storage of undried seeds at 25 degreesC was deleterious within 8 d, indicating a chemical basis for degeneration of hydrated recalcitrant seeds. Seeds that had been mildly dehydrated to the relatively high axis level of 1.68 g H(2)O g(-1) dry mass, while maintaining full germinability immediately after drying, exhibited only 4% viability after 8 d in storage at 16 degreesC and had completely lost viability after the same storage period at 25 degreesC. Ultrastructural features characterizing hydrated seeds included indications of enhanced activity associated with initial exposure to the elevated temperature as well as some signs of stress. However, over an effective 15 d storage period at 16 degreesC, ultrastructural features showed the cells to have retained little damage and to have been in an enhanced state of activity commensurate with ongoing development towards germination. After a longer storage period, however, signs of damage, including indirect evidence for disarray of the cytoskeleton in some axis cells, became apparent in line with the declining seed viability. Immediately following dehydration from an average axis water content of 1.97 to 1.68 H(2)O g g(-1) (the sub-imbibed condition), some ultrastructural abnormalities were apparent, but the seeds remained 100% germinable. However, within the 8 d storage period in this sub-imbibed condition, a spectrum of severe ultrastructural degeneration, including indirect evidence of the collapse of the nucleoskeleton and extensive cell lysis, accompanied viability decline of the seeds to 4%.