Recalcitrant seeds are not only desiccation-sensitive, but also metabolically active. In contrast, orthodox seeds, owing to their dry state, are metabolically quiescent. Lowering the water content to a level that would preclude germination but facilitate vital metabolism has been suggested as a way to extend the life-span of recalcitrant seeds in hydrated storage. However, Daniel CÃÂ´me and FranÃÂ§oise Corbineau of the UniversitÃÂ© Pierre et Marie Curie in Paris, and we, have independently shown that this practice of partial dehydration curtails the seeds' storage life-span.
Current work by graduate students DÃÂ©on Erdey and Sharon Eggers in our laboratory suggests that slight dehydration stimulates the onset of germinative metabolism, thereby shortening the window of time before additional water is required by the seeds. To optimize storage life-span, just the opposite needs to happen: The onset and progression of germinative metabolism need to be delayed.
Recalcitrant seeds are so-named for a reason.
Storage at lowered temperatures might seem an obvious answer, because metabolic rate is slowed in the cold, but many species of tropical and subtropical origin are sensitive to chilling. And even when all the conditions for short- or medium-term hydrated storage have been optimized, most species of recalcitrant seeds face a further limiting factor--fungal infections.
Seed-associated fungi are ubiquitous and pose a prodigious problem: They use seed tissues as their source of nutrition. As a result, the seeds rapidly weaken and die. With graduate student Claudia Calistru and others, we showed that if the seed's fungal load can be reduced or eliminated, then seed storage life-span can be doubled or even quadrupled, depending on the species. Although promising, even this advance is not enough for useful long-term storage of highly recalcitrant seeds.
We also have been pursuing another strategy for halting germinative metabolism in order to increase storage times:...