The increasing desiccation sensitivity of recalcitrant Avicennia marina seeds with storage time

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Abstract
To test the hypothesis that desiccation sensitivity increases with storage time, recalcitrant seeds of Avicennia marina (Forssk.) Vierh. were dehydrated by soaking in polyethylene glycol solutions after inreasing periods of storage. Germination characteristics and the ultrastructure of root primorida were assessed before and after dehydration. Short‐term storage enhanced the apparent rate of germination, consistent with the hypothesis that these seeds commence germination in storage. Root primordia of stored seeds initially showed enhanced subcellular activity, including cell division and vacuolation. Increased storage time resulted in the onset and progression of deleterious changes.Newly shed seeds and seeds stored up to the stage of cell division were comparatively resistant to desiccation. As storage time increased, subsequent dehydration caused increasing subcellular damange and consequent reduction in the rates of germination relative to non‐dehydrated controls. Ultrastructural results suggest that after the initiation of cell division of seeds in storage, there is a requirement for additional water for the germination process to continue. A model for the behaviour of recalcitrant seeds is proposed.